operational guidelines plönninge biogas plant

Operational guidelines for Plönninge

biogas plant

Release History

Version 1.0, June 2011

Any question about this document should be addressed to:

Bioprocess Control Sweden AB

Scheelevägen 22

SE-223 63 Lund

Sweden

Tel: +46 (0)46 163950

Fax: +46 (0)46 163959

E-mail: [email protected]

Web: www.bioprocesscontrol.com

mailto:[email protected]

http://www.bioprocesscontrol.com/

Table of Contents

1 INTRODUCTION ............................................................................................................ 1

1.1 Description of the plant ............................................................................................... 1

2 DESCRIPTION OF THE OPERATIONAL UNITS .................................................... 3

2.1 Operational units for solid and liquid materials .......................................................... 5

2.1.1 Manure tanks 1 & 2 .............................................................................................. 6

2.1.2 Mixing tank .......................................................................................................... 7

2.1.3 Buffer tank .......................................................................................................... 15

2.1.4 Digester .............................................................................................................. 17

2.1.5 Digestate storage containers 1 & 2 ..................................................................... 19

2.2 Operational units for storage, purification, analysis and distribution of biogas ........ 21

2.2.1 Raw gas storage .................................................................................................. 21

2.2.2 Gas room ............................................................................................................ 23

2.2.3 Upgrading unit .................................................................................................... 25

2.2.4 High pressure gas storage ................................................................................... 26

2.2.5 Filling station ...................................................................................................... 27

2.2.6 Stirling engine .................................................................................................... 28

2.2.7 Gas burner .......................................................................................................... 29

2.2.8 Torch .................................................................................................................. 30

2.3 Control room .............................................................................................................. 31

2.3.1 Control cabinet ................................................................................................... 33

2.3.2 Work station ....................................................................................................... 34

2.4 Heating/cooling system ............................................................................................. 35

3 CONTROL PANEL ....................................................................................................... 36

3.1 Start menu .................................................................................................................. 37

3.2 Process overview (Huvud) ......................................................................................... 38

3.2.1 Mixing tank menu (Blandningstank) .................................................................. 39

3.2.2 Manure tank 1 (Pumpbrunn 2) ........................................................................... 41

3.2.3 Manure tank 2 (Pumpbrunn 3) ........................................................................... 43

3.2.4 Buffer tank menu (Bufferttank) .......................................................................... 45

3.2.5 Digester menu (Rötkammare) ............................................................................ 48

Digester settings menu ..................................................................................................... 49

3.2.6 Digestate storage unit (Efterrötkammare) .......................................................... 52

3.2.7 Gas measuring menu (Gasmätning) ................................................................... 55

3.2.8 Gas consumption menu (Gasanvändning) .......................................................... 58

3.3 Data logger (Logging) ............................................................................................... 60

3.3.1 Logger 1 ............................................................................................................. 61

3.3.2 Logger 2 ............................................................................................................. 62

3.3.3 Logger 3 ............................................................................................................. 63

3.4 Energy measuring (Energimätningar) ....................................................................... 64

3.4.1 Alarm list (Larm) ............................................................................................... 65

4 ANALYSIS AND MONITORING ............................................................................... 66

4.1 Determination of feedstock characteristics ................................................................ 66

4.1.1 pH ....................................................................................................................... 66

4.1.2 Moisture content ................................................................................................. 67

4.1.3 Total (TS) and volatile solids (VS) .................................................................... 68

4.1.4 Biochemical methane potential (BMP) test ....................................................... 69

4.2 Monitoring of process parameters in anaerobic digestion process ............................ 70

4.2.1 Temperature ....................................................................................................... 71

4.2.2 pH ....................................................................................................................... 71

4.2.3 Alkalinity ............................................................................................................ 71

4.2.4 Nutrients and toxins ........................................................................................... 72

4.2.5 Biogas flow and composition ............................................................................. 73

4.2.6 Volatile fatty acids (VFA) and dissolved hydrogen (DH) ................................. 74

4.3 Sampling and analysis ............................................................................................... 74

4.3.1 Sampling points .................................................................................................. 74

4.3.2 Analysis of liquid samples ................................................................................. 80

4.4 Analysis of gaseous samples ..................................................................................... 89

4.5 Online monitoring and data logging .......................................................................... 93

5 EVALUATION OF THE OPERATION AND PROCESS PERFORMANCES ...... 94

5.1 Process operation ....................................................................................................... 94

5.1.1 Organic loading rate (OLR) ............................................................................... 94

5.1.2 Hydraulic retention time (HRT) ......................................................................... 94

5.2 Process performances ................................................................................................ 95

5.2.1 Gas normalization .............................................................................................. 95

5.2.2 Gas productivity ................................................................................................. 95

5.2.3 Gas yield ............................................................................................................. 96

5.2.4 VS reduction ....................................................................................................... 96

5.3 Process stability ......................................................................................................... 97

6 DOCUMENTATION ..................................................................................................... 99

6.1 Navigation ............................................................................................................... 100

6.2 Sorting of raw data (Rådatasortering) ..................................................................... 101

6.3 Raw data (Rådata) ................................................................................................... 102

6.4 “Manual” data (Manuell data) ................................................................................. 103

6.5 Daily data (Dagsvärden) .......................................................................................... 105

6.6 Weekly data (Veckovärden) .................................................................................... 107

6.7 Monthly data (Månadsvärden) ................................................................................. 109

6.8 Printable document (Utskriftsformulär) .................................................................. 112

6.9 How to insert data from the data logger .................................................................. 113

6.9.1 Download data from Datalogger ...................................................................... 113

6.9.2 Insert data into Process_data.xlsm ................................................................... 116

7 METHODOLOGY FOR PROCESS IMPROVEMENTS ....................................... 120

7.1 Meetings .................................................................................................................. 121

8 OPERATIONAL ROUTINES .................................................................................... 122

8.1 Daily operational routines ....................................................................................... 122

8.2 Weekly operational routines .................................................................................... 133

9 PROCESS EVALUATION ......................................................................................... 136

9.1 Weekly evaluation ................................................................................................... 136

9.1.1 Saving the data for weekly evaluation ............................................................. 138

9.2 Monthly evaluation .................................................................................................. 142

9.3 Yearly evaluation ..................................................................................................... 143

1

1 INTRODUCTION

The Plönninge biogas plant serves as a demonstration and research site and was built to

promote small scale biogas production. It is situated at Plönninge Agricultural High School

and is operated in collaboration with Region of Halland.

Region of Halland has, together with Bioenergicentrum Halland, an ambition to promote

regional development related to renewable energy sources. The focus is on agricultural

enterprises and most of the work is carried out by Plönninge Agricultural High School. To

ensure that this facility can serve as a demonstration plant for future farm-based biogas plants

in the region and around the world, it is important that the plant can be run as efficiently as

possible and that the produced biogas can be fully utilized.

The purpose of this document is to serve as a support and a guide for operators at the

Plönninge biogas plant.

1.1 Description of the plant

General

The biogas plant in Plönninge is a small farm scale plant that has been in operation since

2004. It was constructed by Läckeby Water AB with the original objective of decomposing

remnant silage and cow manure from farms and other available waste products in the area.

The volume of the digester is 300 m3 with an expected gas production of 250-300 Nm

3/day.

The average retention time of the digester is around 30 days, depending on the availability of

manure.

Operation

Manure from around 80 cows is collected in a manure tank, which is then pumped into a

larger mixing tank. Furthermore, this is mixed, in the same tank, with more solid substrates

(e.g. silage or potatoes). Iron chloride (FeCl3) is also added to reduce the amount of hydrogen

suphide (H2S) in the produced biogas, by precipitation of FeS from sulphur-containing

compounds. The mixed material is then pumped further into a buffer tank where it spends

around one day before it is fed into the digester. The digester is top mixed with two sets of

impellers and it is kept at an average temperature of 37 ºC. As the material is fed into the

digester, digested slurry or digestate is removed into two serial connected storage units, where

it is stored for around half a year before it is used as a fertilizer to cultivate crops at the farm.

The produced gas is consumed in three different ways using the following systems: i) in a gas

burner for producing heat; ii) in a Stirling engine for producing electricity and heat; and iii) in

an upgrading unit for producing biomethane as a vehicle fuel.

2

Originally, only the gas burner was installed at the plant but, in order to promote the

production of higher value products, the Stirling engine and the biogas upgrading unit were

installed in 2008; the Stirling engine started operations in 2011.

3

2 DESCRIPTION OF THE OPERATIONAL UNITS

The most important operational units at the Plönninge biogas plant are presented in this

section. They have been divided into four categories:

1) Operational units for liquid and solid materials

2) Operational units for gas flows

3) Operational units in the control room

4) Heating / cooling system

An overview picture of the Plönninge biogas site, where some of the larger operational units

have been marked, can be seen in Figure 2-1.

Figure 2-1 Satellite photo (Google maps) of Plönnige biogas site.

A simplified process drawing of Plönninge biogas plant can be seen in Figure 2-2.

4

PS

LC

FI

LC

LC

LC

LS

TC

LC

TC

Pi FI

GFL1

DigesterRK1, 300 m3

Digestate storage 1ERK1, 1600 m3

FI Flow indicator

LC Level control

PS Tryckutlösare

LS Level switch

TC Temperature control

PI Pressure indicator

LC

Manure storageLT1, 1200 m3

TITI

Gas alarmTorch

Condensation trapSF1

Condensed water

Raw gas storage

GL1,

Iron chloride

Buffer tankBT1, 12 m3

Mixing tankPB1, 50 m3

Manure tank 1PB2, 12 m3

Manure tank 2PB3, 50 m3

PotatoesFruit &

Vegetables

Horse manure

Silage

Manual loading

Gas burnerGP1, 60 kW

FI

GF1

Condensation trapSF2

Condensed water

Digestate storage 2ERK2, 1500 m3

LC

P1

P2

P3

P4

P6

Stirling engineSM1, 8kW (36 kW)

Electric production

Water scrubberWS1

High pressure gas storage

Gas pump

X-ripper

P7

Figure 2-2 Simplified process drawing of the Plönnige biogas plant.

5

2.1 Operational units for solid and liquid materials

In this section all the operational units that handle the liquid and solid material in the

Plönninge biogas plant are listed and described. A summary of their properties can be seen in

Table 2-1.

Table 2-1 Summary of operational units handling liquid and solid material.

Abbreviati

on

Volume

(m3)

Mixing Heating Sensors Connections

in

Connections

out

Manure

tank 1

PB2 12

Recirculation No Level Stable (cow) PB1

Manure

tank 2

PB3 50

Recirculation No Level Stable (calf) LT1

Mixing tank PB1 50 Submersible

mixer,

recirculation

No Level PB2, Manual

loading

BT1

Buffer tank BT1 12 Recirculation No Level PB1 RK1, ERK1

Digester RK1 300 Mixer Yes Level, level

switch,

temperature (2)

BT1 ERK1

Digestate

storage 1

ERK1 1600 Submersible

mixer (2)

No Level RK1 ERK2

Digestate

storage 2

ERK2 1500 Mobile mixer No No ERK1 -

Manure

storage

LT1 1200 Mobile mixer No No PB2, PB3,

RK1

-

In total, there are eight operational units handling the solid and liquid material in Plönninge.

6

2.1.1 Manure tanks 1 & 2

Figure 2-3 Photos of manure tank 1.

A Housing covering the manure tank

B Tap for manure sampling

C Container used for loading the 1.7 m3 pilot plant (described in a separated document)

with manure

D Pipe for recirculation

E Motor for recirculation pump

F Manure tank (lid)

Role

The role of the manure tanks is to collect and store manure from the cow stables.

Dimensions

The manure from the cow stable is collected in two tanks (PB2 and PB3) that are situated

below ground. Both tanks have a rectangular shape with PB2 having a volume of 12 m3 and

PB3 having a volume of 50 m3.

Mixing

The tanks are mixed by recirculation of the content. The same pump is used for both

recirculating and removing content. This is controlled by an actuator that regulates a 3 way

valve.

Connections

Manure tank 1 (PB2) is connected to the main cow stable on the incoming side and the mixing

tank on the outgoing side.

7

Manure tank 2 (PB3) is connected to the calf stable on the incoming side and the manure

storage tank (LT1) on the outgoing side. The content can also be pumped to the buffer tank

(BT1) by manually regulating several valves.

Sensors

Both manure tanks have level sensors to monitor the occupancy of the tank and to make sure

that no flooding will occur or the pumps will go dry.

Regulation/Automation

The outgoing pump is regulated by the level in the manure tank and in the mixing tank. A

maximum and minimum level is specified by the user in the control panel. The minimum

level is important in order to avoid that the pump goes dry and the maximum level is

important in order to avoid flooding of the tank. If the level reaches the minimum level the

outgoing pump will be inactivated, whereas if it reaches the maximum level the outgoing

pump will be activated in order to reach an acceptable level in the mixing tank.

Operation

At the moment, only manure tank 1 (PB1) is in operation. The manure is pumped from the

manure tank into the mixing tank.

2.1.2 Mixing tank

Figure 2-4 Photo of mixing tank.

8

A Waste containers for fruit and vegetables

B Feeder band connecting the funnel and the mixing tank

C Loading funnel for waste

D Disintegration unit with cutting knifes

E Mechanical lid for covering mixing tank

F Mixing tank

G Container for FeCl3 solution

Role

The role of the mixing tank is to mix the solid substrates with the manure.

Dimensions

The mixing tank is situated below ground and has a cylindrical shape with a total volume of

50 m3. The tank is covered with a lid to minimize the odors and keep away the rain water.

Mixing

The mixing is carried out with a submersible mixer and recirculation of the content. As for the

manure tank, the same pump is used for recirculating and pumping away the content,

controlled with an actuator that regulates a T-valve. The submersible mixer is manually

operated using an on/off button placed next to the control panel.

Figure 2-5 Photo of the buttons for controlling the submersible mixer.

9

Connections

The mixing tank is connected to the manure tank 1 (PB2) on the incoming side and the buffer

tank on the outgoing side.

Sensors

The mixing tank has a level sensor to monitor the occupancy of the tank and to make sure that

it will not flood or that the pump goes dry.


The outgoing pump is regulated by the level of the mixing tank and the buffer tank. A

maximum and minimum level is specified by the user in the control panel. The minimum

level is important in order to avoid that the pump goes dry and the maximum level is

important in order to avoid flooding of the tank. If the level reaches the minimum level the

outgoing pump becomes inactive, whereas if it reaches the maximum level the outgoing pump

will be activated in order to reach an acceptable level in the buffer tank.

Operation

In the mixing tank, the manure from manure tank 1 is mixed with all the solid substrates. The

substrates are manually added with the help of a front loader, or a lift system for certain

containers. When the lift system is used, the substrate is also passed through a disintegration

unit equipped with knives for reducing the size of the solid material.

To load substrate through the front loader, the cover has to be opened from an open/close

panel located next to the tank.

Miscellaneous

In the mixing tank, FeCl3 solution is added manually from a container placed next to the tank.

X-ripper (to be installed)

Figure 2-6 Pictures of the X-ripper (Vogelsang).

10

Role

The role of the X-ripper is to reduce the particle size of the added solid substrate. Its robust

design, using the proven double-shaft system, allows for economical shredding of large

amounts of solids in liquid media.

Connections

The X-ripper is connected to the mixing tank.

Operation

The solid material is loaded into the receiving funnel and shredded by the X-ripper before

falling into the mixing tank. More detail description needs to be added once the X-ripper is

installed on the site.

Supplier

Company: Vogelsang Sverige AB

Adress: Duvesjön 450

SE – 442 92 Romelanda

Contact

person

Klas-Göran Brevik

Tel: +46 (0) 31 7512 70 0


mailto:[email protected]

11

Old macerator

Figure 2-7 Photo of old macerator.

Role

The role of the old macerator is also to reduce the particle size of the added solid substrate.

Connections

The old macerator is connected to the mixing tank.


The old macerator is controlled manually from a control panel located next to the unit.

Operation

The solid material is loaded into the receiving funnel where it is ground down and fed into the

mixing tank.

12

Substrate handling units

Figure 2-8 Photos of substrate handling units.

A Bunker silos

B Lifting device for 200 L barrels

C 200 L barrels

D 140 L waste containers

E Loading of glucose from a 200 L barrel

Many different types of substrates are added to the mixing tank. The substrates are either

added directly to the mixing tank with a front loader, or via the old macerator unit or the X-

ripper. Examples of how several substrates are processed and handled can be seen in Table

2-2.

13

Table 2-2 Example of several processed substrates.

Storage Pretreatment Front loader Maximum

storage time

Silage Bunker silo No Yes Several months

Potatoes 140 L waste

container, bunker

silo

X-ripper, old

macerator

Yes/No (with old

macerator)

1 month

Fruit and Vegetables 140 L waste

container

Old macerator No 1 week

Jam 200 L barrel No Yes 1 month

Glucose 200 L barrel Heated (winter) Yes Several months

Horse manure Bunker silo No Yes Several months

FeCl3 solution container

Biogas from anaerobic digestion of animal waste (i.e. manure) typically contains 500 to 3000

ppm of H2S, depending on the composition of solid substrates. Removal of H2S is needed to

reduce air pollution, protecting at the same time the power generation equipment, and

increasing the safety of the operations.

Figure 2-9 Photo of FeCl3 solution container.

Role

The role of the FeCl3 solution is to reduce the levels of H2S in the produced gas. The iron

precipitates out the sulfur and prevents the production of H2S in the digester.

14

Connections

The FeCl3 solution container is connected to the mixing tank.


The FeCl3 solution container is operated with a manually switched tap.

Operation

Every day, a certain amount of FeCl3 solution is added into the mixing tank by the operator.

The addition of the solution is regulated by opening and closing a tap.

Front loader

Figure 2-10 Photo of the front loader.

Role

The role of the front loader is to transport some of the solid material from its storage unit and

to load it into the mixing tank.

Operation

The front loader is shared by the whole farm and should only be operated by personnel with

proper training. It has a few different lifting devices for different types of material. A device

formed like a scoop is normally used to handle loose material, like silage and horse manure,

while a specially designed device with attachment points is used to handle liquid or semisolid

materials in barrels, such as jam and glucose.

Miscellaneous

The lifting device for loading loose material has weighting cells for controlling the loaded

amount of material.

Since the front loader is shared by the whole farm, it is important to be handled with care.

15

2.1.3 Buffer tank

Figure 2-11 Photo of the buffer tank.

A Buffer tank

B Motor for pump

C Actuator for T-valve

D T-valve

E Recirculation pipe

F Pipe to digester

Role

The role of the buffer tank is to provide an additional place for the substrate to mix and be

further disintegrated before pumped into the digester.

Dimensions

The buffer tank is situated below the ground and has a rectangular shape with a total volume

of 12 m3. The tank is covered with a lid to minimize the odors and keep away the rain water.

Mixing

The buffer tank is mixed by recirculation of the content. The same pump is used for

recirculating and pumping away the content. This is controlled by an actuator that regulates a

valve in a T-connection.

16

Connections

The buffer tank is connected to the mixing tank (PB1) on the incoming side and the digester

(RK1) on the outgoing side.

Sensors

The buffer tank has a level sensor to monitor the occupancy of the tank and to make sure that

no flooding will occur or that the pump will go dry.


The outgoing pump is controlled from the control panel where the user can regulate the

frequency of pumping and the amount of material pumped in during each cycle. A maximum

and minimum level can also be provided by the user. If the level reaches the minimum level

the outgoing pump will become inactive, whereas if it reaches the maximum level the

outgoing pump will be activated.

A flow alarm is activated if the level does not decline as much as it should when the outgoing

pump is turned on.

17

2.1.4 Digester

Figure 2-12 Photos of the digester and digestate pump.

A Ladder for climbing to digester roof

B Biogas outlet pipe

C Top cover and motor for mixer

D Digester

E Manhole cover

F Digestate feeding pump

Role

In the digester, the anaerobic degradation of the organic material in to biogas is taking place.

Dimensions

The digester has a cylindrical shape with a total volume of 300 m3.

Mixing

The content of the digester is mixed by a top mixer with impellers at two different levels. The

speed of the mixer can be controlled.

At the top of the mixer there are two specially designed rotor blades which prevent formation

of floating hard layers inside the digester. More detail description needs to be added once

rotor blades are installed on the site.

18

Connections

The digester is connected to the buffer tank on the incoming side and digestate storage 1 on

the outgoing side. There is also an outgoing biogas pipe from the top of the digester.

Sensors

The digester has three sensors

Bottom temperature sensor

Top temperature sensor

Level sensor


The operation of the digester is controlled mainly in three ways:

1) The level in the digester is maintained by controlling the pump for the outgoing

sludge. The sought level is entered in the control panel and is maintained by activating

or deactivating the outgoing pump.

2) The temperature in the digester is maintained by controlling a shunt valve that

regulates the flow of heating water. A PID controller regulates the shunt valve based

on the difference between the setpoint temperature and the actual temperature. The

setpoint temperature, along with the P (Proportional), I (Integral) and D (derivative)

constants can be entered in the control panel.

3) The top mixer is controlled by an on/off timer as well as a direction setting in the

control panel.

Operation

Normally, feeding from the buffer tank is set to give a retention time in the digester of around

30 days. The temperature is normally set to be around 37 ºC and the slurry volume is

normally set to be around 270 m3 (i.e. the height of the slurry level is about 760 cm).

Miscellaneous

The digester has a manhole cover at the bottom, where it is possible to enter in the digester

when it is empty. There is also a smaller manhole cover on the top. There is a ladder on the

side of the digester, allowing the possibility to climb onto the digester roof.

Supplier

Company: Svenska Neuero

Adress: Sätuna Storegården

521 98 Broddetorp

Contact

person

Stefan Persson

Tel: 046-249630


19

2.1.5 Digestate storage containers 1 & 2

Figure 2-13 Photos of digestate storage container 1 (upper) and digestate storage container 2 (bottom).

A Cover of digestate storage 1

B Digestate storage container 1

C Digestate storage container 2

Role

In the digestate storage container 1 & 2, the digestate is stored when coming from the digester

until used as a fertilizer.

Dimensions

Digestate storage container 1 has a total volume of 1600 m3 and digestate storage container 2

a total volume of 1500 m3.

Mixing

Digestate storage container 1 has two submersible mixers that are regulated via the control

panel. Digestate storage container 2 has no mixing.

20

Connections

The digestate storage container 1 is connected to the digester on the incoming side and the

digestate storage container 2 on the outgoing side. The digestate storage container 1 can also

be connected to the manure storage tank and the buffer tank.

The digestate storage container 2 is connected to the digestate storage container 1 on the

incoming side. The digestate storage container 2 is emptied by pumping its content into the

fertilizer tanks.

Sensors

There is a level sensor in the digester storage container 1.


The digestate storage container 1 is filled with digestate from the digester using a pump. The

content of the digestate storage unit 1 is then flown by gravity force into the digestate storage

container 2.

Operation

The digestate storage container 1 is filled first when the digestate is pumped out from the

digester.

Miscellaneous

No gas from any of the digester storage units is collected. The digester storage container 1 has

an open cover only for preventing the rain water and digester storage container 2 has no cover

at all. The digester storage container 2 is mainly emptied during spring and fall, when the

fertilizer is needed for cultivating crops.

21

2.2 Operational units for storage, purification, analysis and distribution of biogas

2.2.1 Raw gas storage

Figure 2-14 Photos of raw gas storage.

A Raw gas storage container

B Gas pipe from pilot plant

C Valve for connection to pilot plant

D Water block

Role

The role of the raw gas storage unit is to store the produced raw gas in order to maintain a

stable flow to the gas utilization units (upgrading, burner and Stirling engine).

Connections

The raw gas storage unit is connected to the gas system of the plant. The pressure in the raw

gas storage unit and the gas fan in the gas room determine if the gas flows out from the

storage unit or not.

22

Sensors

The raw gas storage unit has two sensors:

A Level sensor (%), which can measure how full the storage unit is.

A Pressure sensor (mbar), which measures the pressure in the raw gas storage unit.

Operation

The gas storage unit is filled as the biogas produced from the reactor. The emptying is

dependent on the gas level in the storage unit as well as the status of the gas utilization units.

Normally, the upgrading unit is prioritized and activated when the level in the gas

storage is above 60 % and deactivated at a level below 20 %.

The Stirling engine is normally activated when the upgrading unit cannot take any

more gas (i.e. high pressure storage is full) and is also normally activated at levels

above 60 % and deactivated at a level below 20 %.

The gas burner is the third in line and is normally activated when the level of the gas

storage is above 80 % and deactivated at a level below 20%.

The torch is ignited if the pressure in the gas storage gets too high.

Miscellaneous

The raw gas storage has a water block controlling the release in the atmosphere of the excess

gas (i.e. when the pressure in the storage unit exceeds 13-14 mbar).

23

2.2.2 Gas room

Figure 2-15 Photos of gas room.

24

A Gas filter

B Incoming gas pipe

C Outgoing gas pipe to upgrading unit

D Outlet for gas sampling

E Condensation trap

F Outgoing gas pipe to Stirling engine

G Flow meter for measuring the flow to gas burner

H Flow meter for measuring total gas flow

I Gas fan

J Outgoing gas pipe for torch

K Outgoing gas pipe for gas burner

Role

The gas room is the core of the gas system at the biogas site and contains most of the sensors,

valves and fans. The unit for removing condensation is also located in the gas room, where

the gas sampling also takes place.

Connections

The gas room is connected to the gas storage/digester on the incoming side and the upgrading,

Stirling engine, gas burner and torch on the outgoing side.

Sensors

Four sensors are placed in the gas room:

two pressure sensors

two flow meters

Miscellaneous

The gas room contains a gas filter to make sure no particles are coming into any of the gas

utilization units.

25

2.2.3 Upgrading unit

Figure 2-16 Photo of upgrading unit (water scrubber).

A Upgrading unit

B Scrubber column

C Gas compressor

Role

The role of the upgrading unit is to upgrade the biogas to biomethane by removing the carbon

dioxide (CO2). The technique used is water scrubbing, i.e. dissolving the carbon dioxide into

water at high pressure.

Capacity

The upgrading unit can handle raw gas flows up to 18 m3/hour.

Connections

The upgrading unit is connected to the raw gas storage unit on the incoming side and the high

pressure storage on the outgoing side.


The upgrading unit is activated when the sought level in the raw gas storage is obtained and

the high pressure storage is not full (below 170 bar). This is carried out by opening a valve

and activating the fan in the gas room.

Supplier

Company: Biorega AB

Adress: L Rya

SE - 314 92, Långaryd

Homepage: www.biorega.se

Contact person: Peter Karlsson

Tel: +46 (0)371 430 11

Email: [email protected]

26

2.2.4 High pressure gas storage

Figure 2-17 Photo of high pressure gas storage unit.

A High pressure gas storage for biomethane

B Pressure sensor

Role

The role of the high pressure gas storage unit is to store the upgraded biomethane at a high

pressure (230 bar) so it can be filled into vehicles using the standard gas filling system.

Connections

The high pressure gas storage unit is connected to the upgrading unit on the incoming side

and the gas pump on the outgoing side.

Sensors

A pressure sensor is used.

Operation

The high pressure storage unit is filled up when the upgrading unit is active. It is emptied

when the gas pump from the filling station is used.

27

2.2.5 Filling station

Figure 2-18 Photo of the filling station.

A Filling pump

B Payment system for gas filling

Role

The filling station allows the filling of the upgraded biomethane in corresponding vehicles.

Connections

The filling station is connected to the high pressure gas storage unit on the incoming side.

Sensors

The filling station has a flow meter that measures the amount of gas that is filled into a car.

Operation

A valve on the filling device opening connects the high pressure storage unit to the gas tank in

the car. The pressure difference between the two systems makes the gas flow from the high

pressure storage unit into the car reservoir until an equal pressure is achieved.

28

2.2.6 Stirling engine

Figure 2-19 Photo of the Stirling engine.

Role

The role of the Stirling engine is to produce electricity by utilizing the compression and

expansion of gas given from the heat produced from the combustion of biogas.

Capacity

The production capacity of the Stirling engine is 8 kW electricity, whereas the total capacity

(including heat) is 36 kW.

Connections

The Stirling engine is connected to the raw gas storage unit on the incoming side. The heating

system is lead through the Stirling engine, where it absorbs some of the produced heat. Before

the heating water reaches stirling engine, it is lead through a cooler (see heating/cooling

system below) to make sure the incoming water is at a low enough temperature. The leftover

products from the combustion are released into the atmosphere through a chimney.

29


The Stirling engine is activated when the sought level in the raw gas storage is obtained and

the prioritized gas utilization units (upgrading unit) cannot consume more gas. This is carried

out by opening a valve and activating the fan in the gas room.

2.2.7 Gas burner

Figure 2-20 Photo of the gas burner.

Role

The role of the gas burners is to combust the incoming biogas and produce heat in the heating

system.

Capacity

According to the specification, the capacity of the gas burner is supposed to be 60 kW.

However, normally a lower capacity, close to 50 kW, is obtained.

Connections

The gas burner is connected to the raw gas storage unit on the incoming side. The heating

system is lead through the gas burner were it absorbs the produced heat. The leftover products

from the combustion are released into the atmosphere through a chimney in the roof.

30

Sensors

The gas burner is equipped with temperature sensors.


The gas burner is activated when the sought level in the raw gas storage is obtained and the

prioritized gas utilization units cannot consume more gas. This is carried out by opening a

valve and activating the fan in the gas room.

2.2.8 Torch

Figure 2-21 Photo of the torch.

A Torch for excess biogas

Role

The role of the torch is to burn of any excess gas the other gas utilization units cannot

consume. This is carried out to avoid the release of the gas into the atmosphere.

Capacity

The torch is designed to handle gas flows up to 10 m3/h.

Connections

The torch is connected to the raw gas storage on the incoming side. The leftover products

from the combustion are released into the atmosphere.

31


The torch is activated when the pressure in the raw gas storage exceeds a certain limit. This is

carried out by opening a valve and activating the fan in the gas room. The pressure that

activates the torch is specified in the control panel.

2.3 Control room

32

Figure 2-22 Photos of the control room.

A Pipe and valve controlling the substrate entering the digester

B Pipe and valve controlling the substrate leaving the digester

C Moisture analyzer

D Gas composition analyzer

E Digestate sampling hose

F Digestate pump

G Stirling engine

H Shunt valve regulating the heating of the digester

I Control panel

J Gas burner

K Control cabinet

L Computers and printer

M Work station

The control room is the place where the operation of the biogas plant is controlled via the

control panel. This is also the location of the Stirling engine, gas burner, large parts of the

heating/cooling system, as well as for simple substrate analysis. The control room also

contains a work station with a computer, where all data can be entered and accessed. In the

control room a number of tools (e.g., moisture analyzer, pH meter, portable gas analyzer) are

also available.

33

2.3.1 Control cabinet

Figure 2-23 Photos of the control cabinet.

A Control cabinet

B Control panel

The control cabinet is the place for the electronic communication interface. Here all the

operational units are centrally controlled. A short description of some of the units in the

control cabinet is presented below.

PLC

The PLC (Programmable Logical Controller) is a local computer that controls all processes in

the plant. It receives incoming signals from sensors and sends out outgoing signals to control

pumps, valves, etc.

Relays

The relays determine if certain processes or units are active or not (e.g. motors, valves, etc).

This is performed with the help of electromagnets that open or close certain high voltage

electrical circuits using low voltage or low current circuits.

34

Digester top mixer frequency converter

It regulates the speed of the top mixer in the digester by regulating the frequency of its power

input. It operates within a 0-60 Hz interval.

2.3.2 Work station

Figure 2-24 Photo of the work station.

The work station is the place where all information regarding the process is gathered and

processed. The process data from the datalogger in the control panel can also be downloaded

onto a computer at the work station.

35

2.4 Heating/cooling system

Figure 2-25 Photo of the heating/cooling system.

A Shunt valve

B WM1

C Cooler

The heating/cooling system at the site is connected to the same system that Plönninge

Agricultural High School also uses. This makes it possible to easily utilize the extra heat

produced from the gas burner. A measuring device (WM1) measures the heat energy

produced and consumed by the plant by monitoring the incoming and outgoing heating water.

The only operational unit that is heated by the heating/cooling system is the digester. This

process is controlled by a shunt valve (A) that acts on signal from a PID controller in the PLC.

The heat energy that is consumed in the digester is monitored by the device WM1 (B).

The heating/cooling system is also used to cool the upgrading unit and the Stirling engine. To

make sure the Stirling engine can operate properly, a cooler (C) is connected to the

heating/cooling system just ahead of the engine. This is necessary since the Stirling engine

requires cold incoming water to be able to handle the excess heat produced in the

compression/expansion process.

36

3 CONTROL PANEL

Figure 3-1 Photo of control cabinet with control panel.

Many parts of the process can be monitored and controlled from the control panel. A touch

screen is used to navigate between the different menus. It is developed by Apptronic in 2004

and has been continuously updated over the years.

The control panel can be found on one of the control cabinet doors in the control room (Figure

3-1).

37

In this section all the menus in the control panel are described. The menus are presented with

a screenshot together with a table of all of their functionalities.

3.1 Start menu

Figure 3-2 Screenshot of start menu.

From the start menu (Figure 3-2) you can navigate between the four different main menus

(process overview, energy measuring, alarm list and system). A list of the functionalities in

the start menu can be seen in Table 3-1.

Table 3-1 Functionalities of the start menu.

Name Action Information displayed

A Översikt Go to process overview menu

B Energimätning Go to energy measuring menu

C Larm Go to alarm list

D System Go to system menu

38

3.2 Process overview (Huvud)

Figure 3-3 Screenshot of process overview (översikt) menu.

From the process overview menu (Figure 3-3) the different menus available in the control

panel including the operational panels, alarm list, data logger and energy measuring can be

accessed. In Table 3-2 a list of all functionalities in the process overview can be seen.

Table 3-2 Functionalities of process overview menu.


A Blandningstank Go to mixing tank menu Mixing tank pump on (green) or off (white)

B Pumpbrunn 2 Go to manure tank 1 menu Manure tank 1 pump on (green) or off (white)

C Prumpbrunn3 Go to manure tank 2 menu Manure tank 2 pump on (green) or off (white)

D Bufferttank Go to buffer tank menu Buffer tank pump on (green) or off (white)

E Rötkammare Go to digester menu

F Efterrötkammare Go to digestate storage menu

G Gasmätning Go to gas measuring menu Raw gas storage pressure (mbar)

H Gasanvändning Go to gas utilization menu

I Huvud Go to start menu

J Larm Go to alarm list

K Energimätning Go to energy measuring menu

L Loggning Go to data logger

Separate information displayed

1 “pump symbol” Pump to digestate storage on (green) or off (white)

2 Producerad energi Produced energy for the current day (kWh)

3 Förbrukad energi Consumed energy for the current day (kWh)

39

3.2.1 Mixing tank menu (Blandningstank)

Figure 3-4 Screenshot of the mixing tank menu.

From the Mixing tank (Figure 3-4) menu, the operation of the mixing tank can be controlled.

You can choose to have it in automatic mode (the pumping and mixing are automatically

controlled) or manual mode. A list of the functionalities in the mixing tank menu can be seen

in Table 3-3.

Table 3-3 Functionalities of mixing tank menu.


A Inställningar Mixing tank settings menu

B Driftsläge Change between automatic and manual operation of the pump

If pump operation is in automatic or manual mode

C Ventil AV1 Change between circulation and feeding

mode for the pump If pump direction is in circulation or feeding

mode

D Pump P1 Turn pump on or off in manual mode If pump is on (0) or off (1)

E Översikt Process overview menu

F Larm Alarm list

G Energimätning Energy measuring menu

H GP 1 Buffer tank menu

I PB2 Manure tank 1 menu


1 “Level indicator” Liquid level in mixing tank as well as lower and upper boundaries

2 Nivå i PB1 Liquid level and corresponding volume in mixing tank

3 “Valve symbol”

AV1

If pump direction is in circulation or feeding mode

4 “Pump symbol” P1 If pump is on or off

40

Mixing tank settings menu

Figure 3-5 Screenshot of the mixing tank settings menu.

Functionalities

From the mixing tank settings menu, instructions on how the mixing tank should be operated

can be set. Parameters such as circulation time for each feeding of material as well as the

upper and lower level boundary of the mixing tank can be controlled. A list of the

functionalities in the mixing tank menu can be seen in Table 3-4.

Table 3-4 Functionalities of mixing tank settings menu.


A Cirkulationstid Set time for circulation ahead of

feeding

Current time for circulation ahead of feeding

B Övre nivå i tank Upper boundary for liquid level Current upper boundary for liquid level

C Undre nivå i tank Lower boundary for liquid level Current lower boundary for liquid level

D Tillbaka Go back to the Mixing tank menu

41

3.2.2 Manure tank 1 (Pumpbrunn 2)

Figure 3-6 Screenshot of manure tank 1 menu.

Functionalities

From the manure tank 1 menu (Figure 3-6) the operation of the manure tank 1 can be

controlled. It can be operated in automatic mode (the pumping and mixing is automatically

controlled) or manual mode. A list of the functionalities in the manure tank menu can be seen

in Table 3-5.

Table 3-5 Functionalities of manure tank 1 menu.


A Inställningar Manure tank 1 settings menu

B Driftsläge Change between automatic and

manual operation of the pump

If pump operation is in automatic or manual

mode

C Ventil AV2/3 Change between circulation and

feeding mode for the pump

If pump direction is in circulation or feeding

mode

D Pump P2 Turn pump on or off in manual

mode

If pump is on (0) or off (1)


F Larm Alarm list


H PB1 Mixing tank menu



1 “Level indicator” Liquid level in manure tank 1 as well as lower and upper boundaries

2 Nivå i PB2 Liquid level and corresponding volume in manure tank 1

3 “Valve symbol”

AV2

If pump direction is in circulation or feeding mode


42

Manure tank 1 settings menu

Figure 3-7 Screenshot of manure tank 1 settings menu.

Functionalities

From the manure tank 1 settings (Figure 3-7) menu, the instructions on how the manure tank 1

should be operated can be set. Parameters such as circulation time before each feeding of

material as well as the upper and lower level boundary of the manure tank 1 can be controlled.

A list of the functionalities in the manure tank 1 menu can be seen in Table 3-6.

Table 3-6 Functionalities of manure tank settings menu.


A Cirkulationstid Set time for circulation (mixing)

before feeding

Current time for circulation (mixing) before

feeding



D Tillbaka Manure tank 1 menu

43

3.2.3 Manure tank 2 (Pumpbrunn 3)


Functionalities

From the manure tank 2 menu (Figure 3-8), the operation of the manure tank 2 can be

controlled. It can be operated in automatic mode (the pumping and mixing is automatically

controlled) or manual mode. A list of the functionalities in the manure tank 2 menu can be

seen in Table 3-7. Table 3-7 Functionalities of manure tank 2 menu.


A Inställningar Manure tank 2 settings menu




mode

C Ventil AV5 Change between circulation and



mode



F Larm Alarm list


H PB1 Mixing tank menu



1 “Level indicator” Liquid level in manure tank 2 as well as lower and upper boundaries

2 Nivå i PB3 Liquid level and corresponding volume in manure tank 2

3 “Valve symbol” AV5 If pump direction is in circulation or feeding mode


44

Manure tank 2 settings menu

Figure 3-9 Screenshot of the manure tank 2 settings menu.

Functionalities

From the manure tank 2 settings (Figure 3-9) menu, the instructions on how the manure tank 2

should be operated can be set. Among the parameters which can be set are the circulation time

for each feeding of material as well as the upper and lower level boundary of the manure tank

2. The functionalities presented in the manure tank 2 settings menu are listed in Table 3-8.

Table 3-8 Functionalities of the manure tank 2 settings menu.



feeding




D Tillbaka Manure tank 2 menu

45

3.2.4 Buffer tank menu (Bufferttank)

Figure 3-10 Screenshot of the buffer tank menu.

Functionalities

From the buffer tank menu (Figure 3-10), the operation of the buffer tank can be controlled.

The operation can be set in automatic mode (the pumping and mixing is automatically

controlled) or manual mode. A list of the functionalities in the buffer tank menu can be seen

in Table 3-9.

Table 3-9 Functionalities of the buffer tank menu.


A Inställningar Buffer tank settings menu




mode




mode


E Flödesmätning Go to Flödesmätning menu

F Översikt Process overview menu

G Larm Alarm list

H Energimätning Energy measuring menu


J RK1 Digester menu


1 “Level indicator” Liquid level in buffer tank as well as lower and upper boundaries

2 Nivå i PB3 Liquid level and corresponding volume in buffer tank

3 “Valve symbol” AV11 If pump direction is in circulation or feeding mode


46

Buffer tank settings menu

Figure 3-11 Screenshot of the buffer tank settings menu.

Functionalities

From the buffer tank settings (Figure 3-11) menu, the instructions on how the buffer tank

should be operated can be set. The circulation time for each feeding of material as well as the

upper and lower level boundary of the buffer tank can be set here. The feeding to the digester

as well as setting from which operational unit the buffer tank is filled. A list of the

functionalities listed in the buffer tank settings menu can be seen in Table 3-8.

Table 3-10 Functionalities of the buffer tank settings menu.



feeding




D Beskickningsintervall Set how often the digester is fed Current setting for how often the digester is fed

(min)

E Beskickningsmängd Set how much is fed each time Current setting for how much is each time (m3)

F Nivåhållningsfunktion Set which tank that should feed to the

buffer tank

Current order of tanks that should pump to the he

buffer tank

G Nivåhöjning Set additional margin of height for

liquid filling when the lower boundary

level is reached

Current additional margin of height for liquid

filling when the lower boundary level is reached

H Tillbaka Buffer tank menu

47

Buffer tank flow measuring menu

Figure 3-12 Screenshot of the buffer tank flow measuring menu.

Functionalities

From the buffer tank flow measuring menu (Figure 3-12), the feeding of the digester can be

followed. A list of the functionalities listed in the buffer tank flow measuring menu can be

seen in Table 3-11.

Table 3-11 Functionalities buffer tank flow measuring menu.


A Tillbaka Back to buffer tank menu


1 Momentant flöde Current flow rate to digester

2 Beskickad mängd Volume counter for each individual feeding cycle

3 Dygnsmängd Volume fed to digester current day (starts at 00:00)

4 Total mängd Total amount fed to digester since flow meter was installed

48

3.2.5 Digester menu (Rötkammare)

Figure 3-13 Screenshot of the digester menu.

Functionalities

From the digester menu (Figure 3-13) the operation of the digester can be controlled. The

operation can be set to automatic mode (the pumping to the digestate storage is automatically

controlled) or manual mode. Changing the settings for the temperature control and the mixer

can also be performed in this menu. A list of the functionalities in the digester menu is

presented in Table 3-12.

Table 3-12 Functionalities of the digester menu.


A Inställningar Digester settings menu




mode




mode

D Pump P4 Turn pump on or off in manual

mode

If pump is on (0) or off (1)

E Temp I RK1 Digester temperature control

menu

Current temperature in digester

F “Mixer symbol” OM5 Mixer settings menu If mixer is on or off

G Översikt Process overview menu

H Larm Alarm list

I Energimätning Energy measuring menu

49

J BT1 Buffer tank storage

K ERK1 Digestate storage menu


1 “Level indicator” Liquid level in digester as well as lower and upper boundaries

2 Nivå i RK1 Liquid level and corresponding volume in digester

3 “Pump symbol” P6 If digestate pump is on or off

Digester settings menu

Figure 3-14 Screenshot of the digester settings menu.

Functionalities

From the digester settings (Figure 3-14) menu, the instructions on how the digester should be

operated can be set. The setpoint for the digester temperature and the lower level boundary

can be specified in this menu. A list of the functionalities in the digester settings menu can be

seen in Table 3-12.

Table 3-13 Functionalities of the digester settings menu.


A Undre nivå I tank Set lower boundary for liquid level Current lower boundary for liquid level (cm)

B Temp. börvärde Set temperature setpoint Current upper boundary for liquid level (ºC)

H Tillbaka Digester menu

50

Digester temperature menu

Figure 3-15 Screenshot of the digester temperature menu.

Functionalities

From the digester temperature menu (Figure 3-15), the set point for the digester temperature

can be set and the latest temperature trends can be followed. A list of the functionalities in the

digester temperature control menu can be seen in Table 3-14.

Table 3-14 Functionalities of the digester temperature control menu.


A Börvärde Set the digestate temperature setpoint Current digester temperature setpoint (°C)

B REGULATOR Go to digester temperature control menu

C Tillbaka Back to digester menu


1 Temp TC50 Current temperature in from lower sensor in digester

2 Temp TC51 Current temperature in upper sensor in digester

3 “Graph” Temperature trends for the upper and lower sensor for the last 4 days

51

3.2.5.1.1 Digester temperature control menu

Figure 3-16 Screenshot of the digester temperature control menu.

Functionalities

In the digester temperature control menu (Figure 3-16), the control parameters for the PID

controller that regulates the digester temperature can be modified. A list of the functionalities

in the digester temperature control menu can be seen in Table 3-15.

Table 3-15 Functionalities of the digester temperature control menu.


A K-värde Set the K constant (proportional coefficient) Current value for K constant

B I-värde Set the I constant (integral coefficient) Current value for I constant

C D-värde Set the D constant (derivative coefficient) Current value for D constant

D Samplingsperiod Set the sampling frequency (0=continuous) Current sampling frequency

E Min. Set the minimum controller output Current minimum output

F Max. Set the maximum controller output Current maximum output


1 Utstyrt värde Current controller output (signal to shunt valve)

2 Är Current digester temperature

3 Bör Digester temperature setpoint

4 Ut Current controller output (signal to shunt valve)

52

3.2.6 Digestate storage unit (Efterrötkammare)

Figure 3-17 Screenshot of the digestate storage unit menu.

Functionalities

From the digestate storage unit menu (Figure 3-17), the operation of the digestate storage unit

1 and the manually control of the mixers in the digestate storage unit 1 can be controlled. A

list of the functionalities listed in the digestate storage unit menu can be seen in Table 3-16.

Table 3-16 Functionalities of the digestate storage unit menu.


A Inställningar Digestate storage unit 1 settings

menu

B ERK1 till LT1 Pumping from digestate storage

unit to manure storage unit menu

C Omrörare OM60/61 Set digestate storage unit 1 mixers

on or off

If mixers is on (0) or off (1)

D Översikt Process overview menu

E Larm Alarm list

F Energimätning Energy measuring menu

G RK1 Digester menu

H GAS M Gas measuring menu


1 “Level indicator” Liquid level in digestate storage 1

2 Nivå i ERK1 Liquid level and corresponding volume in digestate storage 1

3 “Mixer symbol” OM60 If mixer OM60 is on or off

4 “Mixer symbol” OM61 If mixer OM61 is on or off

53

Settings menu of the digester storage unit

Figure 3-18 Screenshot of the digestate storage unit settings menu.

Functionalities

From the settings menu of the digestate storage unit (Figure 3-18), the instructions for the

operation of the digestate storage unit can be controlled by setting an upper level boundary.

When the upper level is reached, an alarm is activated. A list of the functionalities in the

digestate storage unit 1 settings menu can be seen in Table 3-17.

Table 3-17 Functionalities of the digestate storage settings menu.


A Övre nivå I tank Set upper boundary for liquid level Current upper boundary for liquid level (cm)

B Tillbaka Back to digestate storage menu

54

Pumping from digestate storage unit to manure storage unit (ERK1 till LT1)

Figure 3-19 Screenshot of pumping from digestate storage to manure storage menu.

Functionalities

From the settings menu of the digestate storage settings (Figure 3-19) menu, the instructions

on how to pump from the digestate storage unit to manure tank unit 1 are specified. Setting

pumping duration and time for starting and stopping the pump can also be performed in this

menu. A list of the functionalities in the menu for pumping from digestate storage unit to

manure storage unit can be seen in Table 3-18.

Table 3-18 Functionalities of the menu for pumping from digestate storage unit to manure storage unit.


A Pumpning ska pågå i Set duration time for pumping Current set duration time for pumping

B Starta Start and stop pumping If the pump can be started or stopped

C Tillbaka Back to digestate storage menu


1 Förlupen tid How long time the pump has been active since started

55

3.2.7 Gas measuring menu (Gasmätning)

Figure 3-20 Screenshot of the gas measuring menu.

Functionalities

From the gas measuring menu (Figure 3-20), the current gas flows, raw gas storage pressure

as well as operation of the torch can be followed. A list of the functionalities in the gas

measuring menu can be seen in Table 3-19.

Table 3-19 Functionalities of the gas measuring menu.


A GM1 Go to gas flow meter menu Current flow rate in flow meter 1

B GM3 Go to gas flow meter menu Current flow rate in flow meter 2 (gas

burner)

C Inställningar Go to gas measuring settings

menu

D Översikt Process overview menu

E Larm Alarm list

F Energimätning Energy measuring menu

G ERK1 Digestate storage menu

H GAS Gas utilization menu


1 PC1 Current pressure in raw gas storage

2 GFA1 If torch is on (green) or off (white) and current days online time of torch

3 GF1 If gas pump in on (green) or off(white)

56

Gas measuring settings menu

Figure 3-21 Screenshot of the gas measuring settings menu.

Functionalities

From the gas measuring settings menu (Figure 3-21), the raw gas storage pressure limit for

activating the torch can be set. A list of the functionalities in the gas measuring settings menu

can be seen in Table 3-20.

Table 3-20 Functionalities of the gas measuring settings menu.


A Tändning av gasfackla Set minimum raw gas storage

pressure for activation of torch

Current minimum raw gas storage

pressure for activation of torch (mbar)

B Tillbaka Go to back to gas measuring

menu

57

Gas flow meters menu

Figure 3-22 Screenshot of the gas flow meters menu.

Functionalities

From the gas flow meters menu (Figure 3-22), the process parameters of the two gas flow

meters in the system can be followed. A list of the functionalities in the gas flow meters menu

can be seen in Table 3-21.

Table 3-21 Functionalities of the gas flow meters menu.


A Tillbaka Back to gas measuring meter


1 Momentat (GM1) Current value for gas flow meter (total gas flow) (m3/h)

2 Dygnsvärde (GM1) Gas produced the current day (total gas flow) (m3/d)

3 Totalt (GM1) Total gas production of the plant (total gas flow) m3

4 Momentat (GM3) Current value for gas flow meter (gas burner) (m3/h)

5 Dygnsvärde (GM3) Gas produced the current day (gas burner) (m3/d)

6 Totalt (GM3) Total gas production of the plant (gas burner) (m3)

58

3.2.8 Gas consumption menu (Gasanvändning)

Figure 3-23 Screenshot of the gas consumption menu.

Functionalities

From the gas consumption menu (Figure 3-23), the gas consumption units can be monitored.

The status of several gas alarm systems can also be followed in this menu. A list of the

functionalities in the gas consumption menu can be seen in Table 3-22.

Table 3-22 Functionalities of gas consumption menu.


A Inställningar Go to gas utilization settings menu

B Översikt Process overview menu

C Larm Alarm list

D Energimätning Energy measuring menu

E GAS M Gas measuring menu

F PB1 Mixer tank menu


1 GASLAGER Level in raw gas layer (%)

2 GASVARNARE Level of gas alarm (not functioning)

3 GASPANNA If gas burner is on (green) or off (white) and on time the current day so far

4 STIRLING If stirling engine is on (green) or off (white) and on time the current day so far

5 FORDONSGAS If upgrading unit is on (green) or off (white) and on time the current day so far

59

Gas consumption settings menu

Figure 3-24 Screenshot of the gas consumption settings menu.

Functionalities

From the gas consumption settings menu (Figure 3-24), the settings controlling the levels for

the upgrading unit, Stirling engine and the gas burner can be set. This is carried out by

specifying a filling level of the raw gas storage unit at which the gas consumption should be

activated, as well as a corresponding level when it should be deactivated. A list of the

functionalities in the gas consumption settings menu can be seen in Table 3-23.

Table 3-23 Functionalities of gas flow meter menu.


A Start (Fordonsgasanl.) Set raw gas storage level to activate

upgrading unit

Current raw gas storage level to activate

upgrading unit

B Stopp (Fordonsgasanl.) Set raw gas storage level to deactivate

upgrading unit

Current raw gas storage level to

deactivate upgrading unit

C Start (Sterlingmotor Set raw gas storage level to activate

Stirling unit


Stirling unit

D Stopp (Sterlingmotor Set raw gas storage level to deactivate

Stirling unit


deactivate Stirling unit

E Max (Gaspanna) Set the maximum raw gas storage level

for the gas burner

Current the maximum raw gas storage

level for the gas burner

F Start (Gaspanna) Set raw gas storage level to activate gas

burner unit


gas burner unit

G Stopp (Gaspanna Set raw gas storage level to deactivate gas

burner unit


deactivate gas burner unit

H Gaslarm Set gas alarm level to give gas alarm Current gas alarm level to give gas alarm

I Tillbaka Back to gas utilization menu

60

3.3 Data logger (Logging)

Figure 3-25 Screenshot of the data logger menu.

Functionalities

From the data logger menu (Figure 3-25) the three different loggers in the control panel can

be accessed. A list of the functionalities in the data logger menu can be seen in Table 3-24.

Table 3-24 Functionalities of data logger menu.


A Loggning 1 Go to Logger 1 menu

B Loggning 2 Go to Logger 2 menu

C Loggning 3 Go to Logger 3 menu

D Läs av nu View the latest collected data points

E Nollställ Erase the loggers

F Huvud Back to start menu

G Översikt Go to process overview menu

H Larm Go to alarm list

61

3.3.1 Logger 1

Figure 3-26 Screenshot of the Logger 1 menu.

Functionalities

From the logger 1 menu (Figure 3-26), the parameters stored in the logger can be seen and

their trends for the four last days can be monitored. A list of the functionalities in the logger 1

menu can be seen in Table 3-25.

Table 3-25 Functionalities of logger 1 menu.


A Tillbaka Back to data logger menu

B Loggning 2 Go to logger 2 menu

C Loggning 3 Go to logger 3 menu


1 LOGGER 1 Parameters stored in logger 1

2 “Graph” Four day trend lines for parameters stored in logger 1

62

3.3.2 Logger 2

Figure 3-27 Screenshot of the Logger 2 menu.

Functionalities


their trends for the four last days can be monitored. A list of the functionalities in the logger 2


Table 3-26 Functionalities of logger 2 menu.








63

3.3.3 Logger 3

Figure 3-28 Screenshot of Logger 3 menu.

Functionalities


their trends for the four last days be monitored. A list of the functionalities in the logger 3


Table 3-27 Functionalities of the logger 3 menu.








64

3.4 Energy measuring (Energimätningar)

Figure 3-29 Screenshot of the energy measuring menu.

Functionalities

From the energy measuring menu (Figure 3-29), the amount of energy that has been

consumed and produced can be monitored. A list of the functionalities in the energy

measuring menu can be seen in Table 3-28.

Table 3-28 Functionalities of energy measuring menu.


A Huvud Back to start menu

B Översikt Got to process overview menu

C Larm Go to alarm list


1 Totalvärden Readings of totally produced (blue) and consumed (red) energy

2 Dygnsvärden Readings of produced (blue) and consumed (red) energy for the current day

3 “Graph” Trend lines of the produced (blue) and consumed (red) energy

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3.4.1 Alarm list (Larm)

Figure 3-30 Screenshot of the alarm list.

Functionalities

From the gas alarm list (Figure 3-30) the gas consumption units can be monitored. The status

of several gas alarm systems can also be followed in this menu. A list of the functionalities in

the gas consumption menu can be seen in Table 3-29.

Table 3-29 Functionalities of alarm list.


A ESC Go back to previous menu

B “ Arrow up” Go up in list

C “Checkmark” Acknowledge alarm

D “Magnifying glass” Zoom in

E “Wristwatch” Display the time for the alarms

F “Arrow down” Go down in list


1 “Alarm list” Current alarms in list and if they are active (red) or acknowledged (grey)

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4 ANALYSIS AND MONITORING

There is an increasing need to analyze the liquid or solid raw materials before their use as

feedstock (substrates) in anaerobic digestion processes and also to monitor suitable process

parameters which can give early indications of imbalances in the microbial system and early

warnings of external disturbances.

4.1 Determination of feedstock characteristics

Biogas can be produced from a broad range of substrates that are suitable for anaerobic

digestion, e.g. manure, residual sludge, energy crops, municipal solid waste and industrial

waste. Operation of a pilot and/or full-scale anaerobic digester working on a single substrate

or in a co-digestion mode requires analysis of each substrate. The substrate should be

characterised with regard to pH, moisture content, total (TS) and volatile solids (VS) and also

to its potential to produce bio-methane.

4.1.1 pH

pH is a measure of the acidity/alkalinity of a solution. A neutral solution (H2O) has a pH of 7.

Alkaline or basic solutions have a pH higher than 7 and acidic solutions less than 7. pH is

defined as negative decimal logarithm of the hydrogen concentration in a solution; a low pH

indicates a high concentration of hydrogen ions [H+], while a high pH indicates a low

concentration.

pH = − log[H+] (1)

pH can be measured experimentally using a pH sensor, which consists of an ion-selective

electrode covered with a glass membrane and a reference electrode (e.g. calomel or silver

chloride electrode).The pH sensor measure a potential difference between the ion-selective

and the reference electrodes, and this potential difference is dependent of hydrogen

concentration according to the Nernst equation:

E = E0 +RT

nFln[H+] (2)

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Figure 4-1 Photo and schematic representation of a pH sensor.

The pH value of the substrate influences the growth of microorganisms; most methanogens

and acetogens grow best near neutral pH conditions, whereas acidogens prefer to live in weak

acidic conditions.

4.1.2 Moisture content

Moisture content (MC) is the quantity of water contained in a sample. The gravimetric

method is a widely used method for determination of trace amounts of water in a sample. This

can be done by drying a known amount of sample in an oven.

The moisture analyzer is based on the principle of thermogravimetric analysis: the sample is

weighted both before and after drying (using a 400 W halogen lamp as a heating source); the

water content is calculated as the ratio between the difference in amounts of the sample before

(mWet) and after drying (mDried) and the initial amount of sample, and the moisture content is

usually expressed as weight %.

𝑀𝐶 % =𝑚𝑊𝑒𝑡 −𝑚𝐷𝑟𝑖𝑒𝑑

𝑚𝑊𝑒𝑡× 100 (3)

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Figure 4-2 Photo of the moisture analyzer used for the determination of the total solids of a target sample.

The total content of solids is a measure of the amount of material remaining after all the water

has been evaporated.

𝑇𝑆 % =𝑚𝐷𝑟𝑖𝑒𝑑

𝑚𝑊𝑒𝑡× 100 = 100 − 𝑀𝐶 (%) (4)

4.1.3 Total (TS) and volatile solids (VS)

The dry matter, i.e. all inorganic and organic compounds, is often expressed as TS and can be

measured according to a standard protocol. For a given biomass sample, it is necessary to heat

the sample up to 105 °C in order to remove all water content.

VS is represented by the organic compounds in the sample. After finishing the TS

measurement, heating the sample up to 550 °C for two hours should be continued for burning

up the organic matter. The weight difference between the sample after heating at 105 and 550

°C reflects the VS content of the biomass.

The next three steps are usually followed to determine the TS and VS of a target sample:

1). Preparation

a) Heat a dish to 550 °C for 1 h.

b) Place the dish in a desiccator for cooling.

2). TS determination

a) Weigh the dish and record this value.

b) Add 2-3 ml of a representative sample into the dish.

c) Place the dish with the sample in an oven preheated to 105 °C and allow the volatiles

to evaporate for 20 h.

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Figure 4-3 The main steps performed for TS determination.

3). VS determination

a) Take the dish out of the oven and allow it to cool to room temperature in a desiccator.

b) Weigh the dish and record the value.

c) Transfer this dish into a furnace pre-heated to 550 °C (ignition).

d) After 2 h, take the dish out of the furnace and cool it to RT in a desiccator.

e) Weigh the dish and record the value.

Figure 4-4 The main steps performed for VS determination.

TS is calculated as the ratio between the amount of dried sample (mDried) and the initial

amount of wet sample (mWet), whereas VS is calculated as the ratio between the difference in

the amount of sample after drying and burning (mBurned) and the initial amount of sample.

𝑇𝑆 % =𝑚𝐷𝑟𝑖𝑒𝑑

𝑚𝑊𝑒𝑡× 100 (5)

𝑉𝑆 % =𝑚𝐷𝑟𝑖𝑒 𝑑−𝑚𝐵𝑢𝑟𝑛𝑒𝑑

𝑚𝐷𝑟𝑖𝑒𝑑× 100 (6)

4.1.4 Biochemical methane potential (BMP) test

A laboratory-scale procedure in which substrates are characterized and then evaluated using

the biochemical methane potential (BMP) analysis is usually carried out in the first step. This

test provides a preliminary indication of the biodegradability of a substrate and of its potential

to produce methane via anaerobic digestion.

The conventional BMP assay involves incubating a substrate inoculated with anaerobic

bacteria for a period of 30 to 60 days, commonly at 37 ºC, and monitoring the biogas

production and its composition throughout the test. Most such tests require a relatively high

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workload for manual sampling of the produced gas at different time points, followed by

analysis, data recording and processing.

The Automatic Methane Potential Test System (AMPTS) II follows the same analysing

principles as conventional biochemical methane potential tests, which make the results fully

comparable with common methods. However, in an AMPTS, the sampling, analysis and

recording are fully integrated and automated, the bio-methane production being recorded

continuously 24 h per day, 7 days per week with minimal workload. The system is able to

analyse substrates with or without pre-treatment in order to allow biogas producers to

determine the methane production potential and degradation profile of any substrate,

providing the optimum co-digestion possibilities, retention times and plant utilisation.

Figure 4-5 Photo of AMPTS and a screenshot with the graph page.

The AMPTS provides the following advantages over conventional BMP tests: (i) automated

analytical procedure, reducing workload and time, (ii) on-line and real-time data logging of

total biogas or bio-methane production and flow rate, (iii) user friendly interface for real-time

data display and analysis overview, (iv) high quality data allowing extracting process kinetic

information, (v) easy and low maintenance, (vi) cost effectiveness, (vii) possibility of

multiplexing, allowing simultaneous evaluation of co-digestion and substrate pre-treatment.

4.2 Monitoring of process parameters in anaerobic digestion process

Anaerobic digesters require monitoring of critical parameters (e.g. temperature, pH and

buffering capacity, the concentration of nutrients and inhibitors, gas composition) in order to

obtain an optimal production efficiency and biogas yield. However, due to the expensive

and/or time-consuming character of most analysis methods for anaerobic digestion, industrial

digesters are usually not extensively monitored and only few parameters may be continuously

measured, such as pH and gas flow. Therefore the loading rate of a digester has to be kept

relatively low for safety reasons.

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4.2.1 Temperature

Anaerobic treatment is normally carried out within two distinct temperature ranges: i)

thermophilic range, where the optimal temperature is about 55 ºC, and ii) mesophilic range,

where the optimal digestion occurs at about 37 ºC.

The advantages of thermophilic digestion over the mesophilic one include a high CH4

production rate and the support of a higher organic load. However, thermophilic digestion

appears unstable in comparison to degradation under mesophilic conditions due to

denaturation of enzymes at high temperature.

Besides the two temperature ranges mentioned before, methanogenesis is also possible at

temperatures below 20 ºC, under psycrophilic conditions, but occurs at lower rates. At this

low temperature, the enzymatic hydrolysis of organic matter rich in carbohydrates is also

slow. In conclusion, the mesophilic conditions are the most used for the anaerobic digestion

of organic materials.

4.2.2 pH

For the successful operation and control of the anaerobic fermentation it is essential to

measure the reactor pH since a change in pH is a good indicator of process stress for the

systems with low buffer capacity or alkalinity.

The pH of the reactor should be maintained close to neutrality in anaerobic processes

(between 6.8 and 7.4) to ensure stable operation. Each of the microbial groups involved in the

process has a specific pH region for optimal growth. For the acidogens the optimal pH is

around 6, whereas for the acetogens and methanogens the optimal pH is around 7. For

example, process overloaded results in excessive production of fatty acids and this will be

reflected in decreased pH if the buffering capacity of the fermentation liquid is low.

4.2.3 Alkalinity

Another important parameter in anaerobic digestion systems is alkalinity, which is a measure

of the capacity of a sample to resist a change in pH. For maintaining a neutral pH and a stable

operation of the reactor, the fermentation mixture should provide enough buffering capacity to

neutralize any possible volatile fatty acids (VFA). Carbonic acid (bicarbonate form),

dihydrogen phosphate, hydrogen sulphide and ammonia are the compounds that provide a

significant buffering capacity around pH 7.

Even if alkalinity represents the total concentration of bases in solution, it is expressed as ppm

or mg/L CaCO3. Alkalinity is determined by a titration method using a buret/digital titrator

and a pH meter. Titration is the addition of small quantities of the reagent (H2SO4 or HCl) to

the sample until the sample reaches a certain pH known as an endpoint (pH of 4.3).

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Figure 4-6 Photo of the digital titrator used for the determination of alkalinity.

Alkalinity (AK, expressed as mg CaCO3/L) is calculated as a function of the volume (Vacid)

and normality of standard acid (Nacid) which is used for titration.

CaCO3 (sample) + 2H+

(acid) → Ca2+

+ H2CO3

𝐴𝐾 = 𝑉𝑎𝑐𝑖𝑑 × 𝑁𝑎𝑐𝑖𝑑 ×50000

𝑚𝐿 𝑠𝑎𝑚𝑝𝑙𝑒 (7)

At pH 4.3, more than 99% of the bicarbonate system is converted to carbonic acid. If VFA are

present, more than 80% of the total VFA will be measured and this leads to overestimation of

the total alkalinity. Therefore a new end point is proposed, titration of a sample to a pH of

5.75. At this pH 80% of the bicarbonate will be converted to H2CO3 and VFA will have less

contribution on the alkalinity giving a better measure of the buffering capacity. For a stable

operation it is recommended to have partial alkalinity of 1200 mg CaCO3/L.

4.2.4 Nutrients and toxins

Efficient biodegradation requires that nutrients, such as N, P, and trace elements are available

in sufficient amounts. The most important nutrients are nitrogen and phosphorus and it has

been suggested as a rule of thumb, that COD:N:P ratio should be kept at a minimum of

250:5:1. The anaerobic digestion of a substrate with high nitrogen content (e.g. manure or a

feedstock with high protein content) will release ammonium and this will lead to ammonia

inhibition. Therefore, co-digestion of manure with carbohydrate rich-organic wastes will

improve the C/N ratio and will lead to a more efficient digestion. It has also been reported that

supplementation of trace elements, such as Ni and Co, stimulates anaerobic processes.

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Besides compounds which stimulate anaerobic digestion process, there are toxic compounds

which can inhibit the degradation. Methanogens are commonly considered to be the most

sensitive to toxicity, although all microorganisms involved in digestion can be affected.

The toxicity of NH3, H2S and VFA is pH dependent since only the non-ionized forms exhibit

microbial toxicity. Ammonia is toxic at a pH higher than 7. At pH 8, 10% is in free ammonia

which is more toxic than ammonium ion (90%). In general, free ammonia levels should be

kept below 80 ppm to avoid toxic effect. H2S and VFA (acetate, propionate, butyrate) are

toxic at pH below 7. As the pH decreases, the concentration of the undissociated form of the

acid increases relative to the ionized form. Digester failure occurs when the concentration of

the undissociated VFA (expressed as acetic acid) reach a level of 30 ppm. Volatile acid

accumulation has been used, therefore, as an indicator of system imbalance.

Heavy metal ions exhibit toxicity for the microorganisms by inactivating the sulphydryl

groups (thiolic groups) of their enzymes in forming mercaptides.

Methanogenic bacteria are very sensitive to O2. In an anaerobic digester, any O2 present in the

digester will be rapidly consumed by hydrolysing and acidogenic bacteria.

4.2.5 Biogas flow and composition

Monitoring of the biogas production rate and composition is common at pilot and full-scale

anaerobic digester facilities. Inhibition of methanogenesis would cause a decrease in gas

production and overloading would result in increased gas production at the beginning,

followed by a decrease when VFA have accumulated. The proportion of CH4 to CO2 in biogas

depends on the substrate. However, temperature, pH and pressure can also alter the gas

composition slightly. Typical gas composition for carbohydrate feeds are 55% CH4 and 45%

CO2, while for fats the gas can contain as much as 75% CH4.

Figure 4-7 Photos of the gas sampling port and the gas sensor.

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Even though measuring parameters such as biogas production and composition is common at

biogas plants, they have been shown not to be sensitive enough for process monitoring and

control. Due to limitations in mass transfer between liquid and gas phases, the gas-phase

concentration does not always reflect the actual concentration in the liquid.

4.2.6 Volatile fatty acids (VFA) and dissolved hydrogen (DH)

Propionate, butyrate and valerate are intermediate compounds from the acidogenic step and

can be converted further into CH4 and CO2 through the acetogenesis step. Accumulation of

these acids results in a decreased pH, leading to an increased amount of protonated VFA

which causes inhibition of degradation of the feedstock. Since accumulation of these

compounds reflects an imbalance between the microbial groups involved in the degradation,

monitoring of these intermediates is therefore a method of tracking the status of the process.

The concentration of dissolved hydrogen has also been shown to be a key factor in the

fermenter since its concentration affects thermodynamics and the degradation pathway of the

anaerobic process. Hydrogen works as both an intermediate and electron carrier in the

degradation process. High hydrogen concentrations can inhibit volatile acid degradation,

resulting in VFA accumulation. Thus, hydrogen accumulation can be suggested as an early

stage indicator of process imbalance and toxic inhibition.

Figure 4-8 Photo of a hydrogen sensor.

Selection of parameters for process monitoring and control depends on the reactor

configuration, the characteristics of the feedstock, and available sensors, as well as the

implemented control strategy, and may not be generally applicable. However, it is quite

common that several parameters are monitored at the same time, as they can provide

complementary information about process dynamics.

4.3 Sampling and analysis

4.3.1 Sampling points

At the Plönninge biogas site, the liquid samples can be collected mainly from four places (i.e.

manure tank, mixer tank, buffer tank and digester) whereas the gas sampling is carried out

from the condensation trap in the gas room.

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Sampling from the manure tank

For sampling from the manure tank a sampling stick and a bucket are required; a description

of the operational steps to be followed is presented below.

Figure 4-9 Photo of the sampling port from the manure tank.

1) In the control panel, access the manure tank menu and do the following tasks:

Figure 4-10 Screenshots of manure tank 2 menu with instructions on how to turn on the mixing.

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a) Make sure the level is high enough for using the pump. The level should be above 50

cm.

b) Turn the pump on manual mode.

c) Turn the pump on recirculation mode.

d) Start the pump and run it for at least five minutes.

2) Remove the cover of the manure tank.

3) Take a sample using the sampling stick. Immerse the stick a bit below the upper liquid

level and mix in order to get a more representative sample.

4) Empty the content of the sample stick in the bucket.

5) Place the cover back on the manure tank.

6) Take the bucket with the sample back into the control room for analysis.

7) In the control panel, perform the following steps:

a) Turn off the pump.

b) Turn the pump on automatic mode again.

Sampling from the mixing tank

For taking a sample from the mixing tank, a sampling stick and a bucket are required.

1) In the control panel, access the mixing tank menu and do the follwing tasks (same as for

manure tank):

a) Make sure the level is high enough for using the pump. The level should be above the

lower boundary.

b) Turn the pump on to manual mode.

c) Turn the pump on to recirculation mode.


2) Turn on the submersible mixer.

3) Remove the cover of the mixing tank.

4) Take a sample using the sampling stick. Immerse the stick a bit below the liquid level and

mix in order to get a more representative sample.


6) Put the cover back on the mixing tank.


8) Turn off the submersible mixer.



77


Sampling from the buffer tank

For taking a sample from the buffer tank, a sampling stick and a bucket is required.

1) In the control panel, access the buffer tank menu and do the follwing tasks (same as for

manure tank):

a) Make sure the level is high enough for using the pump. The level should be above the

lower mark.

b) Turn the pump on to manual mode.

c) Turn the pump on to recirculation mode.


2) Remove the cover of the buffer tank.

3) Take a sample using the sampling stick. Immerse the stick a bit below the liquid level and

mix in order to get a more representative sample.

Figure 4-11 Photo of the sampling stick immersed in the buffer tank.


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Figure 4-12 Photo of the sampling stick emptied in the bucket.

5) Put the cover back on the buffer tank.





Sampling from the digester

For taking a sample from the digester, a bucket is required.

1) Make sure the valve of the digestate hose (situated behind the control room) is closed (the

tap is in the opposite direction to the hose).

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Figure 4-13 Photo of the valve of the digestate hose in “closed” position.

2) Go back inside and open (in the same direction as the hose) the valve and hold it open for

three seconds.

Figure 4-14 Photo of the pump from the control room.

3) Go outside, carefully open the valve (the tap should be in same direction as the hose) while

holding the hose outlet firmly into the collecting bucket. The digestate will now flow into the

bucket.

Figure 4-15 Photo of the valve of the digestate hose in “open” position and the bucket full with

a sample collected from the digester.

4) When no more digestate is flowing from the hose outlet, close the valve again.

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Figure 4-16 Photo of the valve of the digestate hose in “closed” position.

Sampling from the condensation trap (in the gas room)

For taking and analyzing a gas sample from the condensation trap, an MSA Altair 5IR sensor

is required.

Figure 4-17 Photo of the MSA Altair sensor for measuring CH4 and H2S concentrations in a gas sample.

4.3.2 Analysis of liquid samples

The only tests currently performed for raw materials, at the Plönninge biogas plant, are the

measurement of moisture content (which is indirectly a measure of the total solids) and the

pH. These measurements are performed using a moisture analyser (Kern MLB_N, version

2.1, Germany) and a pH sensor (Impo electronic, type 1510, Denmark), respectively.

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Figure 4-18 Photo of Kern MLB_N moisture analyser situated in the control room.

Determination of moisture content

1) Turn on the analyzer by pressing the On/Off button until digits appears on the display.

2) The analyser needs a pre-heating process before measurement. For that, place a sample tray

on the tray support and press the Start/Stop key to initiate the heating.

Figure 4-19 Photo of the moisture analyzer when the “Start” key is pressed for initiating the heating.

3) When the temperature of the analyser reaches equilibrium, a downward arrow is displayed

on the top right corner. Open the lid and place a sample tray previously kept at room

temperature in the tray support.

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Figure 4-20 Photo of the sample tray placed on the tray support of the moisture analyzer.

83

4) Press the Tare button and wait the value on the display to stabilize.

Figure 4-21 Photo of the “Tare” key from the moisture analyzer.

5) When a downward arrow appears on the top right corner of the display, the sample may be

placed in the sample tray. Make sure that the sample is properly mixed before sampling. Use a

proper sample quantity, e.g. 5-10 g.

84

Figure 4-22 Photo of the previously mixed sample added to the sample try of the moisture analyser.

6) When the display shows a stable value, close the heating cover to start the analysis. A

blinking bright light should appear inside the moisture analyser.

Figure 4-23 Photo of the sample before staring the moisture analyser.

7) When the change of moisture content per minute (drying rate) is below 0.1%, the

measurement is completed. Open the heating cover and remove the sample using the tray

handle. Turn off the analyzer by pressing the On/Off button.

8) Calculate the TS value by subtracting the displayed value of moisture content from 100.

85

Figure 4-24 Screenshot of the Excel file process_data.xlsm.

8) Enter the aquired TS value for the sample in the excel file process_data.xlsm.

86

Determination of pH

Figure 4-25 Photo of the pH sensor situated in the control room.

1) Turn on the pH sensor by pressing the On button until numbers appears on the display.

Figure 4-26 Photo of the pH electrode.

87

2) Remove the protection cap of the electrode. Place the sensor in the buffer standard

solution(s) and calibrate it (single- or two-point(s) calibration).

Figure 4-27 Photo of the protection cap of the pH electrode.

3) Place the electrode in the sample. Be sure that the membrane of the electrode is well

immersed in the liquid.

Figure 4-28 Photo of a pH electrode immersed in a liquid.

88

4) Place the sensor on a solid surface and make sure the electrode remains stable and doesn’t

get completely submerged.

Figure 4-29 Photo of a pH meter registering pH of a target sample.

5) Wait for the pH value to stabilize (normally takes 2-3 minutes).

6) Remove and rinse the electrode under running water.

7) Make sure that the protection plastic cap still contains storage liquid and place it back over

the membrane of the sensor.

Figure 4-30 Screenshot of the Excel file process_data.xlsm.

8) Enter the registered pH value for the sample in the Excel file process_data.xlsm

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4.4 Analysis of gaseous samples

The analysis of the biogas samples are performed using an MSA Altair sensor.

Figure 4-31 Photo of MSA Altair sensor for measuring biogas composition.

1) Turn on the MSA Altair sensor by pushing down on the button in the middle and holding it

for a few seconds until a sound is generated and the screen lights up.

Figure 4-32 Photo of MSA Altair sensor in “On” position.

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2) Perform a pump test by blocking the tube until the screen displays “Pump test OK”.

Figure 4-33 Photo of MSA Altair sensor in its “test” stage.

3) When the calibration is finished, the “FRISKLUFT SETUP” will appear on the display and

at that moment press the right button.

Figure 4-34 Photo of the gas outlet on the condensation trap.

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4) Open the valve for the gas outlet on the codensation trap.

Figure 4-35 The connection of the gas sensor with the gas outlet on the condensation trap.

5) Connect the sample unit to the gas outlet by placing the plastic tube of the sampling unit

inside the plastic tube of the gas outlet.

Figure 4-36 Photo of the display of the gas sensor.

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6) Wait for the values on the display to stabilize (this usually takes 1-2 minutes) and then note

the values for CH4 and H2S concentration.

Figure 4-37 Photo of the gas sensor placed in its holder for charging.

7) Place the sampling unit back in its holder for charging. Make sure that the green light is on.

Figure 4-38 Screenshot of the Excel file containing the registered values for CH4 and H2S

concentrations.

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8) Enter the registred values for CH4 and H2S concentrations in the Excel file

process_data.xlsm.

4.5 Online monitoring and data logging

Several process parameters are measured online to give information about the operation of the

plant. A number of these parameters are also locally saved in the computer of the control

panel.

Totally, there are three data loggers that save and store daily the measured values of 14

parameters (Table 4-1). There is a memory limit in the data logger which causes it to

overwrite older values after a certain time (after about 2-3 months). Therefore, it is important

to download the data on a regular basis.

Table 4-1 Parameters that are logged in the data logger.

Name in control panel Name in Excel filea Description

Logger 1 1 TC50 Temp1 Temperature digester bottom

2 TC51 Temp2 Temperature digester top

3 LC5 Nivå RK Level in digester

4 LC6 Nivå ERK Level in digestate storage unit 1

5 GM1 DYGN Gasflöde Daily gas production

6 GM3 DYGN Gasflöde panna Daily gas flow in gas burner

Logger 2 1 EM1 DYGN EM1 Consumed electricity by operational

units

2 WMM1 DYGN WMM1 Consumed heat energy by digester

3 WMM2 DYGN WMM2 Produced heat from plant

4 GP1 TID DYGN Tid gaspanna Gas boiler on time

5 FI5 DYGN Beskickning Amount fed to digester

Logger 3 1 STERLING TID DYGN Tid stirling Stirling engine on time

2 FORDON TID DYGN Tid uppgradering Upgrading on time

3 FACKLA TID DYGN Tid fackla Torch on time

a) Excel file for data handling in Plönninge. More information is given in section “6. Documentation”.

The data from the logger can be downloaded as a csv (comma separated values)-file that can

be open in Excel. A guide of how this conversion is carried out is presented in chapter 6.

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5 EVALUATION OF THE OPERATION AND PROCESS PERFORMANCES

5.1 Process operation

5.1.1 Organic loading rate (OLR)

The OLR is a measurement of how much organic material is loaded into the digester each day

and is expressed as 𝑘𝑔𝑉𝑆/𝑚𝑑𝑖𝑔𝑒𝑠𝑡𝑒𝑟3 /𝑑𝑎𝑦. This parameter considers both the concentration

and the amount of the incoming substrate and is independent of the digester size, thus

representing a very good parameter for regulating the feeding of the digester and in the same

time assessing the performances of the digester.

A recommended value to start with for a mesophilic process (35-39 ºC) is normally around 2-

3 𝑘𝑔𝑉𝑆/𝑚𝑑𝑖𝑔𝑒𝑠𝑡𝑒𝑟3 /𝑑𝑎𝑦; however, the processes should also be tested at higher levels of

ORL.

The OLR can easily be calculated by dividing the concentration of the incoming substrate

(𝐶𝑉𝑆 ,𝑠𝑢𝑏𝑠𝑡𝑟𝑎𝑡𝑒 ) with the inflow (𝐹𝑖𝑛 ) to the digester (Equation 8).

𝑂𝐿𝑅 =𝐶𝑉𝑆 ,𝑠𝑢𝑏𝑠𝑡𝑟𝑎𝑡𝑒

𝐹𝑖𝑛

(8)

5.1.2 Hydraulic retention time (HRT)

The HRT is a measurement of how long time the incoming material spends in the digester on

average. A too short HRT can lead to a washing-out of the bacteria (due to the fact that more

bacteria is leaving the digester than they can reproduced) which can cause digester crashes.

As a recommendation, the HRT should be kept above 20 days to make sure there is no risk of

bacteria cells washout. A longer HRT will also lead to a longer time for the bacteria to

degrade the substrate which in turn will increase the gas yield. However this will also lower

the productivity in most cases (see section 5.2). Therefore, it is important to find a good

balance for HRT.

The HRT can easily be calculated by dividing the average volume of liquid in the digester

(𝑉𝑙𝑖𝑞 ,𝑑𝑖𝑔𝑒𝑠𝑡 𝑒𝑟 ) to the average inflow (𝐹𝑖𝑛 ) (Equation 9).

𝐻𝑅𝑇 =𝑉𝑙𝑖𝑞 ,𝑑𝑖𝑔𝑒𝑠𝑡𝑒𝑟

𝐹𝑖𝑛

(9)

Table 5-1 Process operation parameters.

Recommended value Comment

OLR >3 kg VS/m3/day Varies from process to process, changes in

OLR should be conservative

HRT 30 days Should be kept above 20 days

95

5.2 Process performances

There is a number of parameters used to evaluate the performances of a biogas plant. These

parameters are often standardized, making it possible to compare different plants with each

other and get a good understanding of what performances should be expected. The normalized

accumulated volume of gas, gas productivity and the reduction in VS are the most

representative parameters which are reviewed and evaluated in a daily, weekly and/or

monthly basis.

5.2.1 Gas normalization

Gas normalization is a way to get a standardized measurement of the gas volume or flow rate

by compensating for the effects of temperature and pressure. The pressure deviation is often

so small that it can be excluded. Since raw biogas contains small amounts of water vapor, this

effect should be also removed.

There are several standards for carrying out such compensation; below is the one accepted by

IUPAC (International Union of Pure and Applied Chemistry).

𝐹𝑏𝑖𝑜𝑔𝑎𝑠 = 𝐹𝑟𝑎𝑤 ,𝑏𝑖𝑜𝑔𝑎𝑠 ∙273.15

273.15 + 𝑇𝑏𝑖𝑜𝑔𝑎𝑠∙ 𝐾 (10)

𝐾 = 1 −10

8.19625−1730.630

𝑇𝑏𝑖𝑜𝑔𝑎𝑠 +233,426

1013

(11)

5.2.2 Gas productivity

The gas productivity is a standardized parameter to measure and compare how productive a

biogas digester is. It is a measurement that describes the amount of gas produced per reactor

volume and day with the unit 𝑁𝑚𝑔𝑎𝑠3 /𝑚𝑑𝑖𝑔𝑒𝑠𝑡𝑒𝑟

3 /𝑑𝑎𝑦 . Since the parameter considers the

volume of the digester, it may be used for comparison of performances of different biogas

plants. The parameter can be calculated from either the total volume of biogas and/or

methane. For standardization, the gas is usually normalized by compensating for the effect of

temperature, pressure and water content; the normalized values are around 9% lower than the

ones for the raw biogas.

A well performing plant has a biogas productivity (Pbiogas) of around 2-3 𝑁𝑚𝑔𝑎𝑠3 /𝑚𝑑𝑖𝑔𝑒𝑠𝑡𝑒𝑟

3 /

𝑑𝑎𝑦 and a methane productivity of 1-2 𝑁𝑚𝑔𝑎𝑠3 /𝑚𝑑𝑖𝑔𝑒𝑠𝑡𝑒𝑟

3 /𝑑𝑎𝑦 . However, these values

depend greatly of what type of substrate is used and the configuration of the plant. The gas

productivity (P) can be calculated by dividing the average normalized gas flow (F) with the

total volume of the digester (Vdigester) (Equations 12 and 13):

𝑃𝑏𝑖𝑜𝑔𝑎𝑠 =𝐹𝑏𝑖𝑜𝑔𝑎𝑠

𝑉𝑑𝑖𝑔𝑒𝑠𝑡𝑒𝑟 (12)

96

𝑃𝑚𝑒𝑡 ℎ𝑎𝑛𝑒 =𝐹𝑏𝑖𝑜𝑔𝑎𝑠 ∙ 𝑋𝑚𝑒𝑡 ℎ𝑎𝑛𝑒

𝑉𝑑𝑖𝑔𝑒𝑠𝑡𝑒𝑟

(13)

5.2.3 Gas yield

The gas yield is a standardized parameter to measure and compare how efficient a biogas

digester is. It is a measurement that describes the amount of gas produced per amount of

organic material and is expressed as 𝑁𝑚𝑔𝑎𝑠3 /𝑘𝑔𝑉𝑆 . Since the parameter considers how much

gas is produced per amount of organic material, it may be used as a comparison between

biogas plants digesting the same or similar substrates. Similarly to the gas productivity, this

parameter can be calculated with both total biogas and/or methane. For standardization, the

gas is usually normalized by compensating the effect of temperature, pressure and water

content; the normalized values are around 9% lower than the ones for the raw biogas.

A well performing plant usually has a biogas yield of 0.6-0.8 𝑁𝑚𝑔𝑎𝑠3 /𝑘𝑔𝑉𝑆 and a methane

productivity of 0.4-0.5𝑁𝑚𝑔𝑎𝑠3 /𝑚𝑑𝑖𝑔𝑒𝑠𝑡𝑒𝑟

3 /𝑑𝑎𝑦 . As mentioned above, these values depend

greatly on what type of substrate is digested. For a farm scale plant where manure and

carbohydrate rich substrates normally are digested, these values are normally somewhat

lower. A good way to find out what level to be expected is to perform a BMP analysis (see

section 4.1.4). A rule of thumb is that the process should have a similar or higher gas yield

compared to the gas potential from the BMP analysis to be considered as a well performing

process.

The gas yield can be calculated by dividing the average normalized gas flow with the organic

loading rate (OLR) (Equations 14 and 15):

𝑌𝑏𝑖𝑜𝑔𝑎𝑠 =𝐹𝑏𝑖𝑜𝑔𝑎𝑠

𝑂𝐿𝑅 (14)

𝑌𝑚𝑒𝑡 ℎ𝑎𝑛𝑒 =𝐹𝑏𝑖𝑜𝑔𝑎𝑠 ∙ 𝑋𝑚𝑒𝑡 ℎ𝑎𝑛𝑒

𝑂𝐿𝑅

(15)

5.2.4 VS reduction

The VS reduction is another measurement that indicates the efficiency of the anaerobic

process. It corresponds to the amount of the organic material that was digested during

fermentation. This is an especially interesting parameter if the focus is on waste reduction

instead of gas production.

The expected VS reductions depend greatly on the type of substrate digested.

The VS reduction can be calculated by dividing the difference between the incoming and

outgoing VS to the incoming VS (Equation 16). If the volumetric inflow and outflow can be

97

assumed to be the same (if the volume in the digester is constant) this can be calculated by the

same equation but with concentration of VS instead of the mass.

𝑉𝑆𝑟𝑒𝑑 =𝑉𝑆𝑖𝑛 − 𝑉𝑆𝑜𝑢𝑡

𝑉𝑆𝑖𝑛≈

𝐶𝑉𝑆 ,𝑖𝑛 − 𝐶𝑉𝑆 ,𝑜𝑢𝑡

𝐶𝑉𝑆 ,𝑖𝑛 (16)

Table 5-2 Process performance parameters.


Gas productivity >1 Nm3/m

3/d

Methane productivity >0.6 Nm3/m

3/d

Total gas yield >0.5 Nm3/kgVS Depends greatly on type of substrate

Methane yield >0.3 Nm3/kgVS Depends greatly on type of substrate

VS reduction >60 % Depends greatly on type of substrate

5.3 Process stability

One of the most important aspects of having a well performing process is to have a stable

process. The losses in gas production can be substantial if the process gets disturbed. Aside

from that, a constant environment usually makes the microorganisms in the digestate perform

optimally.

pH is a well-known parameter to measure the stability of the anaerobic digestion process. This

is due to the fact that many of the bacterial groups (especially the methane producing bacteria)

are sensitive to pH levels outside the optimal intervals. For a stable process, the pH value

should be stable around 7-7.5. Normally, an instable process is suffering from decreasing pH

due to production of more intermediate products (i.e. VFA) than the methane producing

bacteria can consume. When the pH becomes low enough, the methane producing bacteria

gets inhibited, leading to more accumulation of VFA.

Measuring pH is a relatively simple and cheap method, giving a rather good indication of the

process’ status. However, in order to truly know the condition of a process, the concentrations

of VFA and total alkalinity (TA) (see section 4.2) also need to be measured.

The alkalinity is a measurement of the buffer capacity and therefore gives an indication of

how much VFA the process can absorb before the pH starts to drop. Normally, the alkalinity

is rather high in processes that are fed with cow manure since the manure often is rich in basic

ions.

The procedure demands a lab with titration equipments and is therefore not performed on

routine basis. However it is recommended to perform the test on the digestate at least three to

four times per year, preferably combined with the VFA analysis. It is however more

interesting to record the ratio between VFA and total alkalinity (see, VFA/TA) than just

alkalinity, since this relationship actually determines the effect on the pH value.

98

The gas composition partly provides information on how the intermediate steps are

performing. Normally, the composition is rather constant as long as a similar substrate is fed

to the process. However, if the methane concentration starts to decrease, it is a sign that the

process is not working under optimal conditions. A lower concentration of methane often

means that there is an inhibition of a methane producing step. A normal methane

concentration for the Plönninge biogas plant is 60-65 %.

Ammonium nitrogen (N-NH4) gives an indication of how much inorganic nitrogen is present

in the process. The concentration of ammonia is in direct correlation with the concentration of

N-NH4, depending especially on pH and temperature. Ammonia can be very toxic for the

biomass at higher concentrations. The values for N-NH4 should be lower than 2-3 g/L.

The temperature is an important parameter for the process to perform optimally. In a

mesophilic process, the temperature should be around 35 – 39 ºC. It is important to have

constant temperature even within this interval (in the interval of starting temperature ±0.5 ºC).

A constant temperature will allow the bacteria to perform optimally since they do not have to

adapt to temperature changes.

Table 5-3 Process stability parameters.


Temperature 37 ⁰C Should be stable, max ± 1 ºC

VFA <4 g/l Depends on degree of adaption and alkalinity

VFA/TA <0.3 >0.3 indicates possible process instability

N-NH4 <2-3 g/l High values in combination with high pH is dangerous

pH 7.2-8.5 Should be stable

Methane

concentration

60-65 % Depends much on substrate, decreasing concentration gives

indication of problem

99

6 DOCUMENTATION

In order to have a good understanding and follow up of the process operation, it is important

to keep a detailed logging of the recorded data. This will help to make a good review of

historical performance and learn lesson from the past on how the plant should be operated

better in future. For this purpose an Excel file template has been created in which all the

process data can be entered and saved for process evaluation (Table 6-1). The Excel file is

named Process_data.xlsm in this document.

Table 6-1 Different sheets in the Excel file template.

Sheet Comment Input Manual/Automatic

Rådatasortering Sort and remove duplicates in data from data

logger

Manual input

Rådata Place to paste the managed data from

“Rådatasortering”

Manual input

Manuell data Input analysis results and amounts of loaded

solid substrate

Manual input

Dagsdata Presentation of daily values from data logger Automatic

Veckodata Presentation of weekly process data Partly manual input

Månadsdata Presentation of monthly process data Automatic (VS/TS required)

Urskriftsformulär Printing form for manual data input -

Beräkningar Used for monthly data calculations -

This Excel file should be updated on daily basis with new results from the different analyses.

The data should then be reviewed on a weekly basis to get a good overview of the process

performances.

100

6.1 Navigation

To navigate among the different sheets in the Excel file template, click the name of the sheet.

Figure 6-1 Screenshot of the Excel-file, also displaying where to navigate between different sheets.

101

6.2 Sorting of raw data (Rådatasortering)

In this sheet the raw data from the data logger is first pasted (Figure 6-2). A macro function is

used automatically to remove all duplicates from the raw data and sort it based on the dates.

Figure 6-2 Screenshots of “Rådatasortering” sheet where (A) is empty and (B) is pasted and treated data.

102

6.3 Raw data (Rådata)

In this sheet the data managed in “Rådatasortering” are inserted. The data from the 3 different

loggers (i.e. loggers 1-3) are here combined.

Figure 6-3 Screenshot of “Rådata”-sheet where data from two data loggers (i.e. loggers 1-2) have been inserted.

103

6.4 “Manual” data (Manuell data)

In this sheet results from the liquid (i.e. TS, pH) and gas analysis (gas composition in %) as

well as the amounts of all manually loaded solid substrate. The results are grouped on months

(Figure 6-4) for a better overview.

Figure 6-4 Screenshot of all the “Manuell data”-sheet when the display is minimized to show only the monthly

values.

The daily values for each month (Figure 6-5) can then easily be displayed by clicking on the

corresponding ”+” sign on the left side of the sheet.

104

Figure 6-5 Screenshot of all the “Manuell data”-sheet when one month is expanded to show all daily inputs.

105

6.5 Daily data (Dagsvärden)

In this sheet the data from the data logger is displayed. The form uses the data read from

“Rådata” and recalculates it to more manageable units. The data is displayed as daily values,

then grouped into months.

An average value for each month is calculated for the various parameters (displayed in the

rows “Medel”). When possible, the parameters are also added together to give monthly sums

(displayed in the row “Total”).

Figure 6-6 Screenshot of “Dagsvärden”-sheet when the display is minimized to show only the monthly values.

The daily values for each month (Figure 6-7) can then easily be displayed by clicking on the

corresponding “+”sign on the left side of the sheet.

106

Figure 6-7 Screenshot of all the “Dagsvärden”-sheet when one month is expanded to show all daily inputs.

As mentioned above, the raw data is modified in the form to give more proper units. To avoid

using decimals the posts in the data logger are stored as larger numbers (e.g. 37 oC

corresponds to 3700 in the data logger). All the different actions performed to modify the raw

data are presented in Table 6-2.

Table 6-2 List of how the raw data is modified in “Dagsvärden”-sheet.

Parameter Action Raw data Treated data

Temp1 Divide by 100 to give ºC 3710 37.10

Temp2 Divide by 100 to give ºC 3710 37.10

Nivå RK Divide by 100 to give meter 721 7.21

Nivå ERK Divide by 100 to give meter 292 2.92

Gasflöde - - -

Gasflöde Panna - - -

EM1 - - -

WMM1 - - -

WMM2 - - -

Tid gaspanna - - -

Beskickning Divide by 10 to give m3/d 98 9.8

107

6.6 Weekly data (Veckovärden)

In this sheet the weekly data are grouped together (Figure 6-8). The user has to copy and paste

the data from “Manuell data” and “Dagsvärden” in this sheet (see the guide in section 9).

Figure 6-8 Screenshot of “Veckodata”-sheet when minimized to display only the weekly values.

The daily values for each individual week (Figure 6-9) can then easily be displayed by

clicking on the corresponding ”+”-sign on the left side of the sheet.

Figure 6-9 Screenshot of all the “Veckovärden”-sheet when one week is expanded to show all daily inputs.

108

Table 6-3. Parameters listed in the “Veckovärden”-sheet.

Parameter Unit Time period Comment

Added amounts

Total kg Day and week Sum of all substrates

Substrate 1 kg Day and week Sum







TS content

Manure tank %ww Day and week Average

Mixing tank %ww Day and week Average

Buffer tank %ww Day and week Average

Digester %ww Day and week Average

pH

Manure tank -log[H+] Day and week Average

Mixing tank -log[H+] Day and week Average

Buffer tank -log[H+] Day and week Average

Digester -log[H+] Day and week Average

Gas composition

Methane content %Vol Day and week Average

Carbon dioxide content %Vol Day and week Average

Hydrogen Sulphide ppmVol Day and week Average

Data logger

Temperature lower °C Day and week Average

Temperature upper °C Day and week Average

Level digester m Day and week Average

Level digestate storage m Day and week Average

Daily total gas production m3/d Day and week Average

Daily gas consumption burner m3/d Day and week Average

EM1 kWh/d Day and week Average

WMM1 kWh/d Day and week Average

WMM2 kWh/d Day and week Average

Daily On time gas burner min/d Day and week Average

Daily load to digester m3/d Day and week Average

Daily On time Stirling engine min/d Day and week Average

Daily On time upgrading min/d Day and week Average

Daily On time torch min/d Day and week Average

Weekly total gas production m3/week Day and week Sum

Weekly gas consumption burner m3/week Day and week Sum

EM1 kWh/week Week Sum

WMM1 kWh/week Week Sum

WMM2 kWh/week Week Sum

Weekly On time gas burner min/week Week Sum

Weekly load to digester m3/week Week Sum

Weekly On time Stirling engine min/week Week Sum

Weekly On time upgrading min/week Day and week Sum

Weekly On time torch min/week Day and week Sum

Process

parameters

VS/TS %TS Day and week Given by user

HRT days Day and week Average

OLR kgVS/m3/d Day and week Average

Total gas productivity m3/m3/d Day and week Average

Methane productivity m3/m3/d Day and week Average

VS reduction %VS Day and week Average

Total gas yield m3/kgVS Day and week Average

Methane yield m3/kgVS Day and week Average

109

6.7 Monthly data (Månadsvärden)

In this sheet all data for every month is summarized and displayed (Figure 6-10). Both the

average and total values are given.

The only input required is the average VS/TS ratio. All the other parameters are automatically

generated from the data recorded in “Rådata” and “Manuell Input” sheets.

In this sheet the average values for all parameters are given for each month and the whole

year (Medel). A monthly and a yearly total (Total) are also given for certain parameters.

Figure 6-10 Screenshot of “Månadsvärden”-sheet.

In Table 6-4 all the parameters displayed in the “Månadsvärden” sheet are listed.

110

Table 6-4 Parameters listed in the “Månadsvärden”-sheet.

Parameter Unit Time period Comment

A Added amounts

Total kg/month Month and year Sum of all

substrates

Substrate 1 kg/month Month and year Sum

Substrate 2 Kg/month Month and year Sum

Substrate 3 Kg/month Month and year Sum





B TS content

Manure tank %ww Month and year Average

Mixing tank %ww Month and year Average

Buffer tank %ww Month and year Average

Digester %ww Month and year Average

C pH

Manure tank -log[H+] Month and year Average

Mixing tank -log[H+] Month and year Average

Buffer tank -log[H+] Month and year Average

Digester -log[H+] Month and year Average

D Gas composition

Methane content %Vol Month and year Average

Carbon dioxide content %Vol Month and year Average

Hydrogen Sulphide ppmVol Month and year Average

E Data logger

Temperature lower °C Month and year Average

Temperature upper °C Month and year Average

Level digester m Month and year Average

Level digestate storage m Month and year Average

Ave daily total gas

production

m3/d Month and year Average

Ave daily gas consumption

burner

m3/d Month and year Average

EM1 kWh/d Month and year Average

WMM1 kWh/d Month and year Average

WMM2 kWh/d Month and year Average

Ave daily On time gas

burner

min/d Month and year Average

Ave daily load to digester m3/d Month and year Average

Ave daily On time Stirling

engine


Ave daily On time

upgrading


Ave daily On time torch min/d Month and year Average

F Data logger

Monthly total gas

production

m3/month Month and year Sum

Monthly gas consumption

burner

m3/month Month and year Sum

EM1 kWh/mont

h

Month and year Sum

111

WMM1 kWh/mont

h

Month and year Sum

WMM2 kWh/mont

h

Month and year Sum

Monthly On time gas

burner

min/month Month and year Sum

Monthly load to digester m3/month Month and year Sum

Monthly On time Stirling

engine


Monthly On time

upgrading


Monthly On time torch min/month Month and year Sum

G Process

parameters

VS/TS %TS Month and year Given by the user

HRT days Month and year Average

OLR kgVS/m3/d Month and year Average

Total gas productivity m3/m

3/d Month and year Average

Methane productivity m3/m

3/d Month and year Average

VS reduction %VS Month and year Average

Total gas yield m3/kgVS Month and year Average

Methane yield m3/kgVS Month and year Average

112

6.8 Printable document (Utskriftsformulär)

This sheet (Figure 6-11) is a printer friendly version of the “Manuell data”-sheet. It can be

used if the operator prefers to write down the data on paper before entering it into the Excel-

sheet.

Figure 6-11 Screenshot of “Utskriftformat”-sheet.

113

6.9 How to insert data from the data logger

The input of data from the data logger can be divided into two steps:

1. Download data from data logger.

2. Insert data into the Process_data.xlsm file.

Both these steps are presented below.

6.9.1 Download data from Datalogger

1. The data from the Datalogger need to be first downloaded from the local computer.

Use the shortcut called “Gasverk (logggiler)” located on the desktop (Figure 6-12).

Figure 6-12 Screenshot of desktop where “Gasverk (loggfiler)” shortcut is marked out.

2. A list of different files should appear (TEMP, ENERGI, LOGGER1, LOGGER2

LOGGER3) (Figure 6-13). Start to download a file by clicking on its name.

114

Figure 6-13 Screenshot of FTP catalogue with downloadable log files.

3. A window should appear where “open”, “save” or “cancel” can be selected (Figure

6-14). To download the document click on the “Spara”-button.

Figure 6-14 Screenshot of window that appears when clicking on logger1.SKV.

115

4. Use the windows explorer to choose where you want to save the log file (Figure 6-15).

Preferably a folder for log files needs to be created first. Name the file with the logger

name and date. Click “Spara” for saving the data file.

Figure 6-15 Screenshot of “save as”-window that appears when “save” is chosen.

116

6.9.2 Insert data into Process_data.xlsm

1. Open the downloaded log file (Figure 6-16).

Figure 6-16 Screenshot of log file in Excel.

2. Copy all the data and open the Process_data.xlsm and paste it in the top left cell (A1)

in the sheet “Rådatasortering” (Figure 6-17).

Figure 6-17 Screenshot of how to paste log file data in Excel.

117

3. All the data should now be pasted into the sheet. To remove the duplicates access the

“view” menu (top menu board) and click on the “Macro”-symbol on the right side. In

the scroll menu that appears choose “View Macro” (Figure 6-18).

Figure 6-18 Screenshot of how to access Macros in Excel.

4. A new window containing a list of macros should now appear (Figure 6-19). Mark the

function called “Remove Duplicates” and then click on “Run”.

Figure 6-19 Screenshot of how to run the Macro “RemoveDuplicates” in Excel.

118

5. The list without duplicates should now be displayed (Figure 6-20).

Figure 6-20 Screenshot of results after running Macro “RemoveDuplicates”.

1. To insert the data into the data handling algorithms of the Process_data.xlsm, copy all

the data besides the dates and go to the sheet called “Rådata”. There paste the data in

its correct position. Remember to paste the data at the location corresponding to the

correct date.

a. Logger1 starts with Temp 1 and should therefore be pasted there (Figure 6-21).

Figure 6-21 Screenshot of where to paste data from Logger1.

119

b. Logger 2 starts with EM1 and should therefore be pasted there (Figure 6-22).

Figure 6-22 Screenshot of where to paste data from Logger2

120

7 METHODOLOGY FOR PROCESS IMPROVEMENTS

In order to optimize the process it is important to first define a clear goal of the plant

operation, i.e. whether the purpose of plant operation is for energy production, waste handling

or combination of both. Plönninge biogas plant is defined as a demonstration plant at farm-

scale. There is a need not only to show the feasibility of producing vehicle fuel, electricity and

heat production, but also a need to use manure wastes as a part of the feedstock and to

demonstrate that the digested residues can be used as fertilizers for crops cultivation. In order

to achieve these goals, it is essential to maximize the biogas production at Plönninge biogas

plant.

Once the goal of plant operation is defined, it is important to apply a good methodology on

how to constantly improve the plant operation. There are several important aspects to be kept

in mind before defining the most suitable strategy for the operation of Plönninge biogas plant.

In general, the following aspects can give a big impact on plant operation and biogas

production:

i. Quality and quantity of the feedstock

ii. Whether there is suitable process/plant configuration and instrumentation to ensure

reasonable flexibility for plant optimization

iii. Right operational routine and follow up to ensure that plant operation can be

continuously improved

Plönninge biogas plant has a rather simple process and plant configuration based on selected

feedstock. The available instruments (i.e. sensors and actuators) can support the basic

requirement of plant operation. Although it is always possible to further improve the plant

configuration and instrumentation, it is assumed that the process optimization can be based on

the current process/plant configuration and instrumentation. The process optimization strategy

should therefore be focused on feedstock selection and right operation routine and follow up.

Feedstock

In order to achieve as high biogas production as possible, it is important to select feedstock

with high methane potential. In general, liquid cow manure has relative low methane

potential. It is therefore important to use more energetic and easy degradable feedstock,

depending of course on their availability at the Plönninge plant.

Operational routine and follow up

A higher biogas production can also be achieved by implementation of better loading regimes

with a constant pushing of the process, so the biomass throughput and energy throughput of

the plant can be increased whereas a stable operation can still be retained. Every week or

month should be seen as new test were the loading regimes is changed a little bit from the last

period and the effect of this change is continuously monitored. Depending on the

performances obtained, these changes should be considered permanent or be rejected. This

dynamics of the process parameter changes – continuous evaluation should be implemented

as a part of operational routine, so operational lesson in the past can be well recorded,

evaluated and follow up in order to improve future operation.

121

7.1 Meetings

In order to have a good follow up of the plant operation, meetings should be held on a regular

basis among operators and all personnel should be involved. In these meetings the

performance of the plant and any potential problems should be reviewed and discussed.

Objectives and aims for the plant operation should also be set, and any deviation should be

evaluated.

Such meetings should at least be held once per month.

Topics that are recommended to be discussed during these meetings include:

Performance of plant on weekly and monthly base

Any deviation from the feedstock supply in terms of both quality and quantity?

Is there any problem with the operation in terms of technical, logistic and personnel aspects?

Any progress and lesson learn since the previous meeting?

Any improvement that can be foreseen?

Was the set goals reached?

Is the economic plan reached/on schedule?

Decide on new or keep old goals.

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8 OPERATIONAL ROUTINES

These operational routines list and describe all the tasks that should be carried out on a daily

and weekly basis at the Plönninge biogas plant.

8.1 Daily operational routines

In this section operational tasks that should be carried out each day are listed and described.

Preferably, these tasks are carried out at the beginning of the working day. It is important to

build up routines where all these tasks are carried out every day.

1. Perform a quick check of the biogas plant to make sure nothing went wrong during the

night. Look especially for flooding in any of the operational units.

2. Check the control panel of the SCADA system:

i. Check the alarm list If there is any alarm indication for a particular process

unit, please check whether it is possible to make any suitable tuning and

adjustment so the process unit can go back to the normal operational mode. If

there is no alarm indication, move on to the next point (Figure 8-1).

Figure 8-1 Screenshot of alarm list.

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ii. Check the conditions of the operational units

1. Digester level and temperature. Make sure the values are within the specified

levels (e.g., the same as or close to setpoints). If the values are not within the

default range, try to identify the reason and check whether it is possible to make

any suitable tuning and adjustment so that the digester level and temperature can

come back into the operational range (Figure 8-2).

Figure 8-2 Screenshot of digester menu.

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2. Check the filling level; if this is too high or too low, try to identify the reason

and evaluate whether it is possible to make any suitable tuning and adjustment

so that the slurry level of the buffer tank level can be brought back within the

optimal range (Figure 8-3).

Figure 8-3 Screenshot of buffer tank.

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3. Check the filling level; if this is too high or too low, try to identify the reason and

evaluate whether it is possible to make any suitable tuning and adjustment so that the

slurry level of the mixing tank level can be brought back within the optimal range

(Figure 8-4).

Figure 8-4 Screenshot of mixing tank.

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4. Manure tank level. Check the filling level; if this is too high or too low, try to

identify the reason and evaluate whether it is possible to make any suitable tuning and

adjustment so that the slurry level of the manure tank level can be brought back within

the optimal range (Figure 8-5).


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i. Fill up the mixing tank by manually pumping sufficient amount of the content

from manure tank 1 as possible. Make sure that level in the mixing tank does

not get too high (Figure 8-6).

Figure 8-6 Screenshot of manure tank 1 and mixing tank menus with instruction on how to pump from manure

tank 1 to mixing tank.

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ii. Check the gas utilization. Make sure that the gas storage level is at a

reasonable level. If it is not, please check the reason and see whether it is

possible to make any suitable tuning and adjustment so that the gas storage

level is brought within the right range (Figure 8-7).

Figure 8-7 Screenshots of gas consumption and gas measuring menu.

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5. Turn on the submersible mixer (Figure 8-8).

Figure 8-8 Photo of showing how to turn on submersible mixer in mixing tank.

6. Go outside to the gas room and perform a gas composition test (Figure 8-9). Enter the

registered data in the file Process_data.xlsm in the computer.

Figure 8-9 Photos of the equipment used for the analysis of gas composition.

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7. Go outside to the mixing tank and add FeCl3 into the tank (Figure 8-10). This is

carried out by opening the tap and waiting for 5 seconds before closing the tap. Enter

the date and amount in the form placed in the mail box next to the FeCl3 container.

8.

Figure 8-10 Photos of FeCl3 solution adding.

9. Go outside to the front loader and load the X-Ripper with potatoes (the amount

decided at the operational meeting). Enter the loaded amount in the file

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Process_data.xlsm in the computer. More detail instruction needs to be added after the

installation of X-Ripper has been implemented.

10. Take a sample from the buffer tank and perform a quick-TS (using the moisture analyzer) and

a pH analysis, and enter the result in the file Process_data.xlsm in the computer (Figure 8-11).

Figure 8-11 Photos of buffer tank sampling and quick TS analysis with moisture analyser.

11. Fill up the buffer tank as much as possible by manually pumping feedstock from the

mixing tank (Figure 8-12). Make sure that the level in the buffer tank does not get too

high (e.g., not above 250 cm).

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Figure 8-12 Screenshots with instructions of how to pump from the mixing tank to the buffer tank.

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12. Turn off the submersible mixer in the mixing tank (Figure 8-13).

Figure 8-13 Photo of showing how to turn off submersible mixer in mixing tank.

8.2 Weekly operational routines

In this section operational tasks that should be carried out once or several times per week are

listed and described. Suggestions of which week days these tasks should be performed are

also given.

Monday

1. Look at the data from the previous week and decide on whether to keep the same

loading regime or make any adjustment if necessary.

2. Load the silage (if this is specified in the operational plan).

Tuesday

1. Take a slurry sample from the manure tank 1 and perform a quick TS (using the

moisture analyzer) and a pH analysis. Enter the data in the Excel file

Process_data.xlsm.

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Figure 8-14 Photo of quick TS test with moisture analyser.

3. Load any other substrate available (if this is specified in the operational plan).

Wednesday

4. Load the silage (if this is specified in the operational plan).

Thursday

1. Collect the waste containers with fruit and vegetables from the local ICA Maxi.

2. Add the fruit and vegetables to the mixing tank via the x-ripper.

Friday

1. Load the ensilage (if this is specified in the operational plan).

Task to perform before the weekend

1. Turn on the submersible mixer (from the switch located next to the control panel,

(Figure 8-8)); allow it to run for about 60 minutes in order to homogenize the

feedstock in the mixing tank.

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2. Fill up the buffer tank as much as possible. Make sure the level does not get too high.

3. Fill up the mixing tank as much as possible. Make sure the level in the manure tank

does not get to low and that the level in the mixing tank does not get to high.

4. Go outside the mixing tank and add a double dosage of iron chloride into the tank.

This is performed by opening the tap for 10 seconds. Enter the date and the amount of

iron chloride added in the form placed in the mailbox next to the iron chloride

container.

5. Add a double load of potatoes into the mixing tank via the x-ripper.

6. Do not forget turning off the submersible mixer in the mixing tank.

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9 PROCESS EVALUATION

9.1 Weekly evaluation

Evaluation of the plant performance should be carried out weekly. This should be performed

independently by the operator mainly or by a larger working group where other internal and

external process engineers might be involved. For weekly operational evaluation, the process

performance should be studied by comparing the plant performances of the latest week vs.

previous weeks. The purpose of the meeting should be to set an operational plan for the

coming week. The time for the meeting should be the same every week (preferably on

Monday morning in order to get a fresh start of the week and also maximize the number of

working days close to the operational changes).

Manipulating parameters, parameters that should be used for tuning the operation.

Response parameters, parameters that should be used to evaluate the performance of the plant

based on settings of manipulating parameters.

Other important parameters, parameters whose effect on the process should be

considered when the response from changes in operation can be observed.

The parameters that should be considered in the evaluation are listed below. The parameters

are dived into 3 different categories:

Manipulating parameters, parameters that should be used for tuning the operation.

Response parameters, parameters that should be used to evaluate the performance of

the plant based on settings of manipulating parameters.



Table 9-1 Parameters considered in process evaluation (for description of parameters, please see section 5.1).

Manipulating parameters Response parameters Other important parameters

Feeding interval Methane productivity TS concentration in buffer tank

Size of each load Methane yield pH in digester

Amount of added solid

substrate

Total gas productivity Temperature in digester

Type of solid feedstock Total gas yield H2S concentration

HRT VS reduction

OLR Methane concentration

Manipulating parameters

The parameters that should be adjusted to alter the operation are the feeding rate and added

amount of solid substrate. These parameters will then have an indirect effect on the HRT

and the OLR which are important to consider in the evaluation. Especially the HRT should

be monitored to make sure it does not get too low (e.g., above 20 days) to avoid washout of

the bacteria. OLR is a more general parameter to know how hard the process is loaded and it

can be used to compare the operation with other plants.

The focus should be placed on adding as much solid substrate as possible to maximize the

OLR and still keep a long HRT. However, with this strategy it is important to control the TS

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concentration in the buffer and mixing tank since too high values could cause problems

with the pumps.

Response parameters

The most important response parameter to consider is the methane productivity. If it has

increased compared to the previous operational period it could be considered as a positive

result. However, the reason for the increase in methane production should also be

investigated. Another important parameter to consider is the methane yield since this gives

information of how efficient the process is.

Strategy for optimizing the operation

1. Increase the load:

a. Focus on adding as much as possible of energy rich substrate that is regional

abundant and can be accessible and easier to load into the digester.

b. Make sure that the TS content in the buffer tank does not get too high (not over

10%).

c. Closely monitor and follow up the operation in order to maximize the performances

of all process units.

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9.1.1 Saving the data for weekly evaluation

1. Open the Excel data file and in the sheet “Manuell data” copy the data from each day

of the previous week (Figure 9-1).

Figure 9-1 Screenshot of “Manuell data”-sheet where the values for 1 weeks are marked.

2. Go to the sheet “Veckodata” and open the week of interest by clicking on the ”+”-sign

on the left of the week number (Figure 9-2).

Figure 9-2 Screenshot of Veckovärden”-sheet in compressed form (click “+”-signs on right side to show daily

values for a week).

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3. In the top left cell (e.g., Silage for Monday) right click and choose “Paste Special”

(“Klistra in special”) (Figure 9-3).

Figure 9-3 Screenshot of how to paste the data from “Manuell data”-sheet into “Veckovärden”-sheet using

“Paste Special”.

4. Choose “Values” in the menu that opens (Figure 9-4).

Figure 9-4 Screenshot of “Paste Special” window that appears.

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5. Now the values should be pasted into the formula; an example is presented below

(Figure 9-5):

Figure 9-5 Screenshot of “Veckovärden”-sheet where the data from “Manuell data”-sheet has been pasted.

6. Next step is to paste the data from the DataLogger. This is carried out in the same way

as the manual data. Open the sheet “Dagsvärden” and copy the values for the specified

dates (Figure 9-6).

Figure 9-6 Screenshot of “dagsvärden”-sheet where the values for 1 weeks are marked.

7. Go back to the sheet “Veckodata” and right click on top left cell after the manual

inputs (e.g., Temp1 for Monday). Choose “Paste Special” and choose values again

(Figure 9-7).

Figure 9-7 Screenshot of how to paste the data from “Dagsvärder”-sheet into “Veckovärden”-sheet using “Paste

Special”.

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8. The values should now be inserted in the form; an example is presented below (Figure

9-8).

Figure 9-8 Screenshot of “Veckovärden”-sheet where the data from “Dagsvärden”-sheet has been pasted.

9. In order to calculate the process parameters a value for VS/TS (% of VS per TS) needs

to be entered. This is inserted in the top row under the column “VS/TS” (Figure 9-9).

Figure 9-9 Screenshot of to enter VS/TS value in “Veckovärden” sheet.

10. After this, given that all other necessary data is in place, the process parameters should

automatically be calculated (Figure 9-10).

Figure 9-10 Screenshot of “Veckovärden”-sheet showing the calculated process paramteters.

11. All the data for that specific week is in place and the performances can be evaluated.

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9.2 Monthly evaluation

A review of the plant operation should be carried out on monthly basis by the operator or

process engineers. This monthly evaluation should be performed from more plant-wide and

systematic aspects and give a good overview on total mass and energy outputs, as well as

operational economic over a one-month period. The data can then be compared with historical

data from the previous months in order to set up a strategy to maintain a good operation

and/or get further improvement (if possible). It is recommended to present and discuss the

monthly evaluation during the first weekly meeting of next month.

In Manipulating parameters, parameters that should be used for tuning the operation.





The parameters that should be considered in the evaluation are listed. The parameters are

dived into 3 different categories:

Mass throughput, in this category parameters that reflect the amount of feedstock

entering and of digestate exiting the reactor, type of feedstock and their characteristics

(VS, TS, pH, BMP), feedstock load regime, etc should be summarized.

Energy throughput, parameters reflecting the totally produced biogas volume,

specific biogas production rate, utilization of biogas (heat, vehicle fuel, electricity),

electricity consumption, heat consumption, etc should be summarized.

Economical aspects, in this category parameters reflecting the operational costs

(material, electricity, manpower, logistic, equipment depreciation, etc.) and potential

income sources (electricity, vehicle fuel, heat, digestate as fertilizer) should be

summarized.

Table 9-2 Examples of parameters that should be considered in process evaluation.

Mass throughput Energy throughput Economic aspect

Feedstock volume Biogas volume Operational cost

Feedstock type Specific biogas production rate Saving from electricity generation

Solid content of feedstock Heat production Saving from heat production

Digestate volume Electricity production Potential income from vehicle fuel

OLR Biomethane production Potential income from digestate

Electricity consumption

Heat consumption

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9.3 Yearly evaluation

A yearly review of plant operation should also be carried out by operators or process

engineers. This should be very similar to monthly evaluation; however the time scale is over

12 months and should give a good overview on the total mass and energy throughputs, as well

as on operational economic parameters. The data can be compared with historical data from

the previous years in order to set up a yearly strategy to maintain a good operation and/or get

further improvement (if possible).

In Manipulating parameters, parameters that should be used for tuning the operation.





The parameters that should be considered in the evaluation are listed below. The parameters

are dived into 3 different categories:

Mass throughput, in this category parameters reflecting the amount of feedstock

entering and digestate exiting the reactor, type of feedstock used and their

characteristics (VS, TS, pH, BMP), feedstock loading regime, etc should be

summarized.

Energy throughput, parameters reflecting the total produced biogas volume, specific

biogas production rate, utilization of biogas (heat, vehicle fuel, electricity), electricity

consumption, heat consumption, etc should be summarized.

Economical aspects, in this category parameters reflecting the operational cost

(material, electricity, manpower, logistic, equipment depreciation, etc.) and potential

income sources (electricity, vehicle fuel, heat, digestate as fertilizer) should be

summarized.

Table 9-3 Examples of parameters that should be considered in process evaluation.

Mass throughput Energy throughput Economic aspect

Feedstock volume Biogas volume Operational cost

Feedstock type Specific biogas production rate Saving from electricity generation

Solid content of feedstock Heat production Saving from heat production

Digestate volume Electricity production Potential income from vehicle fuel

OLR Biomethane production Potential income from digestate

Electricity consumption

Heat consumption