Services to sugar millsO&M training for sugar mills professionals

Session : Boilers

Trainer: Frans Baltussen

Date: July 2017

O&M of bagasse based High Pressure Boiler

O&MO&M of bagasse based High Pressure Boilerof bagasse based High Pressure BoilerThe course will help to understand:

1. The fuel consumption/efficiency of boiler and power output of power plant

1.1 Boiler efficiency

1.2 The power output

2. Reliability

2.1 Boiler

2.2 Fuel /firing System

2.3 The fly ash arrestor and ash removing systems

2.4 The fans and dampers

2.5 The controls

2.6 The sootblowing system

2.7 The feed water system

2.8 The water and steam side conditioning/ chemistry

2.9 The piping systems and valves

2.10 The refractory and insulation systems

2.11 Preservation during standstill

3. Safeties in system for protection persons and equipment

What are main objectives:

• Ensure a high Reliability of the plant

• Ensure a high Efficiency of the plant in order to minimize the fuel consumption and to maximize the power output

• Ensure the safety of the plant at highest level so that persons can work safely and equipment will be not damaged in case of upsets.

You need to understand the basics of the plant.

Bagasse needs to be fired efficiently

The power and steam needs to be generated during season and off season in the most efficient way.

1.1: Boiler efficiency

Boiler efficiency is : heat absorbed by the water steam system/heat input

Heat absorbed by water steam system is in KW : (mst * hst – mw * hw)

mst = mass of steam at outlet in kg/shst= enthalpy of steam at outlet in KJ/kgmw= mass of water at economizer inlet in kg/shw= enthalpy of water at economizer inlet in kJ/kg

1. The fuel consumption/ efficiency of boiler and power output of power plant

Heat input is: mf * heating value of fuel + m air * (Tair –Treference air).

mf = mass of fuel supplied into boiler

Question is how to measure the fuel amount.

Is possible with fuel cells in conveyor

However a very complicated system which requires maintenance and spares and is costly

Therefore the efficiency is mostly determined in an indirect way

Into silo chutes boiler

Conveyor with fuel cells

Conveyor with fuel cells

Surplus bagasse to storage yard

heating value of fuel is in KJ/kg

2 types of heating value are considered:

* on higher heating value (HHV) also called gross heating value (GCV)

* on lower heating value (LHV) also called nett heating value (NCV)

The difference between the 2 is the latent heat

Tube with cold

water

Flue gasses with water vapourand dewpoint of 50 C

Flue gasses with no water vapour at 50 C

Water heated up from 10 to 30 C by condensation of water vapour on tube

Heat for condensing and evaporating the vapour is called latent heat

Basis is bagasse with 52% moisture

Common used in

Heating value based on 52% moisture

efficiency Moisture content in Flue gasses

In KJ/kg In kcal/kg % % weight % volume

HHV/GCV USA 9178 2192 8817.5 26.7

LHV/NCV Europe 7295 1742 70

Comparison between the 2 heating values

Both can be used.

Condensation of flue gasses we will avoid in bagasse fired boilers as we have some Sulphur in it and a lot of ash.

Causing: corrosion and fouling.

Therefore mostly efficiency on basis of lower heating value is used. The latent heat is not seen as a loss.

Heating value bagasse versus moisture content

It is , however, not said that water content is not important.

How less water in bagasse how more we save in fuel consumption

This is related to the bagasse with lower moisture content at inlet boiler

This is related to the bagasse with 52% moisture content from mill

Efficiency calculation in indirect way/ as per indirect method

Boiler

Q fuel

Q stack

Q rad and conv

Q Blow down

Q nett

Q air

Q ash including unburned

M fuel * LHV

M fuel * m (air stoich) * 1,35 * cpm * T air

M steam* ( hst – hw)

.%/100 *Q nett

0,1/100 * mst * h’2/100 * Q fuel

M fuel * (m flue gas * cpm * T flue gas + LHV of CO * m flue gas * CO vol%/100)

Only unknown is M fuel

10

Heat balance boiler

Is very smallAmount.

Efficiency = 100% - losses%Losses can be determined on basis of each kg of fuel supplied. Fuel flow is not needed

What information is required to calculate the losses

Data required unit Measuring device

Oxygen content Vol % wet or dry portable

CO content Vol% wet or dry portable

Stack temperature C portable

Air temperature at outlet steam air preheater

C portable

Water content in bagasse Wt% Lab of sugar mill

Ultimate analysis and heating values bagasse

Wt% and KJ/kg Lab outside

Ash content from boiler and its heating value

Kg and KJ/kg Lab outside

Ash content from cyclones and its heating value

Kg and KJ/kg Lab outside

What is needed to measure the performance of boiler

The ash collection should be done properly. Take several samples over a longer period and mix those very well and then take the sample for the lab.

The stack losses

The measuring of oxygen content and temperature should be taken at the right spot in order to have average value.

The best location for the oxygen measurement is in case of one ID fan at 2 m from outlet of ID fan. In case of 2 ID fans the average of 2 outlets

For the stack temperature we need to measure the flue gas temperature at outlet of last heating surfaces of boiler.

The ID fan will increase the flue gasses with 2 to 5 C and the long ducting and i.e. electrostatic filter will cool down the flue gasses.

Flue gasses do not mix easilyEspecially over the width of boiler

At outlet of cyclone more proper mixedHowever still not over the width.Require a temperature measurement over the complete width to determine the average temperature.

In case of no cyclone we need a grid measurment

Flue tubes of flue gas air preheater heavy corrodedAnd many tubes with leakages

Take care for tube leakages in flue gas air preheater

Cold air

Flue gas outlet

Condensation of vapour in flue gasses on tubes what result in corrosion

To ID fan

Install at boiler outlet a proper oxygen analyzer suitable:• for high humidity in flue gasses• For dusty flue gasses ( puffing system)

Important is regular calibration of analyzer

Also check each shift the flue gas emissions with portable analyzer.• At boiler outlet • And at ID fan outlet

O2 vol% dry

CO2 vol% dry

CO vol% dry

Portable Analyzer

Take always a longer probe of approx 1 m length of InconelDeep into flue gas flowSuitable for also furnace measurement at different spots

Excess air

percentage

Note: By measuring also the CO2 content it is possible to check if the analyzer is working properly

Bagasse in sugar mills

Water content wt% 46 till 52 ( some times 54)

Fibre content wt% 43 -52

Soluble solids wt% 2-6

Average density Kg/m3 150 loose

400 bailed

Proximate Analysis On Dry Basis(% of Dry Basis)

Ash wt% 2,5

Volatile wt% 85,5

Fixed carbon wt% 12

Higher heating value (HHV or GCV)Is including the latent heat

KJ/kg 9178 on basis of 52% water

Lower heating value (LHV or NCV)

KJ/kg 7295 on basis of 52% water

Ultimate Analysis On Dry Basis(% of Dry Basis)

C wt% 47,82

H wt% 5,85

N wt% 0,14

S wt% 0,3

Ash wt% 3,23

O (by diff) wt% 42,66

Cl wt% 0

For accurate data the fuel should be analyzed in the laboratory.

By combustion calculation the following can be calculated for bagasse:• heating values,• Air requirement ,• flue gas flow, • Compositions• Heat content• Adiabatic flame temperature

Bagasse composition

Bagasse in sugar mills

At stoichiometric combustion with air of 72% relative humidity the values are as follows:• Air quantity: 2,11 Nm3/kg / 2,70 kg/kg• Flue gas flow: 3,05 Nm3/kg / 3,68 kg/kg• O2 : 0 vol% • CO2 : 13,63 vol% • SO2 : 0,03 vol%• N2 : 52,74 vol%• Ar : 0,62 vol%• H2O : 32,98 vol%• Adiabatic firing temperature: 1465 C

The bagasse can be fired with an excess air of 1,35.Means 35% more air is supplied then required for stoichiometric combustion.

What are the O2 and CO2 contents?

• Air quantity: 1,35 * 2,11 =2,85 Nm3/kg

• Flue gas flow: 3,05 + 0,35*2,11 = 3,79 Nm3/kg

• O2 : (0,35*2,11*0,2047/3,79 ) * 100% = 3,99 vol%

• CO2 : {(0,35*2,11*0,0003) + (0,1363*3,05)}/3,79 *100%= 10,98 vol%

• H2O : {(0,35*2,11*0,0223) + (0,3298*3,05)}/3,79 *100%= 26,98 vol%

• Adiabatic firing temperature is 1264 C

• The CO content will be approx. 350 mg/Nm3• The efficiency losses due to CO is approx. 0,175 %

For combustion air of 72% relative humidity the composition is as follows:• O2 : 20,47 vol% • CO2 : 0,03 vol% • N2 : 76,37 vol%• Ar : 0,9 vol%• H2O : 2,23 vol%

Air and flue gas flows from bagasse firingBasis 52% water in bagasse

Flue gas composition versus bagasse moistureFlue gas composition versus bagasse moisture

At lower water content in bagassethe cpm value will drop.At 45% water approx 0.6% less

CO content during capacity test and the impact on efficiency:Based on operating data running at 141 tph HP steam

Oxygen content in flue gas: vol% wet

Measured CO content in flue gas: ppm

Eff. LossDue to CO%

Improved eff due to less excess air (ref from 5 vol% oxygen) %

Overall improved eff. Due to less excess air.%

Additional power consumptionfansKW

T stack

3,5 (n=1,3) Estimate 600

0,3 (estimate)

1,4 1,1 -190 156

4(n=1,35)

Approx 350 0,175 0,9 0,725 -141 158

5(n=1,45)

Approx 152 0,075Reference point

164

6 (n=1,59) Approx 50 0,025 -1,4 -1,375 +140 171

Impact excess air and CO on boiler efficiency

Max allowable CO = 800 ppmv

The Higher CO content indicate mostly higher unburned content in fly ash

In existing boilers seen ash samples of fly ash with 22% carbon in ash with LHV value of 1861 KJ/kg. This is seen with CO contents of approx. 300 till 1000 ppmv.

However also seen 59% carbon and LHV value of 4800 kcal/kg. The CO contents are then 6000 to far above 10000 ppmv

When ash is 2.5 % on dry basis then the losses due to unburned ash are:

• 1.6% on basis of 22% carbon• 6.9 % on basis of 59% carbon

The water content in bagasse should be maximum 52%. At higher content the firing get more poor what increases the unburned.

Unburned in ash

Convection and radiation losses

Difficult to measure.

Measure the casing temperature in C and surfaces in m2 and ambient temperature.

Temperatures are for each surface different . Calculate average.

Determine the heat transfer coef. In w/m2 C.Mostly there is some wind . Also due to natural draft. Take 14 W/m2C

Losses in KW= (14/1000 * surface area) * (temperature difference casing and ambient)

Calculate the total convection and radiation heat and total fuel input.

Can be taken also from the ABMA standard radiation loss chart (PTC 4.1) which is based on the average wall temperature measured by the staff

Or from DIN 1942 standard

Graphic as per DIN 1942Also ASME has a graphic

24

Important for measuring the performance

Not important are steam pressure and steam temperature

Important is the steam capacity. At lower capacity the efficiency will slightly increase .

100% MCR: 87 % 70% MCR: 87.9%60% MCR: 86.9%

The feed water temperature is important. How lower how lower the flue gas temperature when eco installed at boiler outlet.In case of flue gas air preheater at boiler outlet then air temperature is important.

Before testing first 4 hr stabilization period on constant load

Then test run at constant load for 4 hrsNo sootblowing during test.Blow down is closed. Cleaning of fuel bed during test is permittedReadings at 15 min intervalsFlows at each 5 minute intervalsAll instruments should be calibrated , certificates to be present

There have been hardly any studies available on bagasse based biomass decomposition.

There is some know how available which makes it possible to make some assumption.

Bagasse is one of the easiest decomposable lingo cellulose species.

Anarobic digestion is the bacterial fermentation of organice material like bagasse in oxygen free condition.

It produces a gas composed of methane (CH4) and carbon dioxide (CO2). Called biogas Optimum temperature for this process is 38 C.

Biomass decomposition

Bagasse decomposition

Approx. 4,6 % reduction in LCV value per month

The heating value can drop fast during storage. See below graph

Be aware that during off season much more fuel will be required.

Other Biomass available in Pakistan

1. Bagasse2. Sugar cane Trash3. Corncobs4. Rice husks5. Cotton Stalks6. Wheat straw7. Wheat rice

All those fuels have common:•High Volatile content•Nett Heating value on basis of ash and water free all approx the same (17,8 till 19 MJ/kg)

NOTE:• The composition can vary per season and per area.• It is necessary to send fuel to lab for analysis• The fuels can be fired on different stoker types and in fluidized bed system.

Fuels are different in:• moisture content•Ash content• Alkali content in ash• Sulfur• Chloride• density

28

The ash characteristics of fuels are important.

Specially important are:• the alkali metals (Ca, Na, K) are important.• silica

Further the sulfur and Chlorine content in the fuel is an important factor

Those contents needs to be verified in the lab before deciding the best combustion and boiler system.

Later in the session concerning boiler fouling we will discuss this in more detail

Chlorine, sulfur and ash characteristics

29

Characteristics of biomass

30

8.4

30

811

52

15 15

5.710

1511

1513

7

13 12

2529

4.4

11.7

2

18

2.5

8

18.516

7.0

0.0

10.0

20.0

30.0

40.0

50.0

60.0

Moisture Content % LHV(MJ/Kg) Ash

Effect on fuel handlingfor solid fuels

31

2,3091,302

2,5991,526

2,9541,615 2,098

20,336

23,780

0

5,000

10,000

15,000

20,000

25,000

LHV(MJ/M³)

Elements in biomass & coal potentially

leading to corrosion and deposits.

32

0.600.2

0.02 0.1 0.030.3 0.2

7.1

0.80.50 0.4

0.2 0.1 0.01

0.70.5

1.47 1.47

0.730.32 0.18

2.442.22

0.12 0.09

0.00

1.00

2.00

3.00

4.00

5.00

6.00

7.00

8.00

Sulphur (S)%

Chlorine (Cl)%

K+Na%

Dewpoint of flue gasses with biomass firing

Dewpoint of water vapour in flue gasses:

Water content in flue gas is based on 52% moisture in bagasse and excess air of 35%: 29 vol%Means partial pressure of H2O is approx. 0,29 bara which result in dewpoint of approx. 66 C

Dewpoint of SO2/SO3 vapour in flue gasses:

Sulfur content in bagasse is approx. 0,3% on dry weight basis

There will be a certain conversion of SO2 into SO3 (approx. 2%) which will condense at certain temperature as H2SO4 on the tubes.

The dewpoint as per formula of Ganapathy is as follows:• For 0,14% S in bagasse on wt%: 139 C• For 0,07% S in bagasse on wt%: 133 C• For 0,04% S in bagasse on wt%: 129 C• For 0,01% S in bagasse on wt%: 116 C

The flue gas temperature should not drop to low due to condensation of vapour on heating surfaces

DEWPOINT

This means there is a potential of corrosion of tubes at cold end due to condensation of sulfuric gasses.

This is also observed in the flue gas air preheaters of the 25 bara boilers.

The dewpoint for bagasse firing is normally approx 90 C.

Means metal temperature should not drop below 90 C

a. When economizer at boiler outlet metal temperature is approx same as water temperature

b. When flue gas air preheater metal temperature is higher then air inlet temperature

Air 13 m/sAt 27 C

Flue gas 8,7 m/sAt 152 C

ao = 65 W/m2K

ai = 44 W/m2K

Metal temperature is 110 C

Heat transfer coef at innerside

Heat transfer coef at outerside

A perfect expansion process as in a steam turbine is with a constant entropy. See line A – B in

This is a isentropic process (ideal)However this is not possible as all kind of losses will occur like leakages between wheels and friction losses.

h1= friction losses in diffusor, heat into steamh2= friction losses in wheels, heat into steamh3= friction losses at outlet, heat into steamH4= losses through seals of wheels

The isotropic efficiency is the hT = 100 * (hA – hF) / (hA – hB) %

The power supplied to the shaft is m * (hA – hF) KWm= mass of steam per kg

The power at generator terminal is minus the losses in gearbox and generator. This approx. 5%

h1h2h3h4

A

B

CD

EF

H in KJ /kg

S in KJ /kgK

The Entropy:

35

The isotropic efficiency of steam turbine

enthalpy

entropy

1.2 the power output:

Extraction point in sugar mill at 2,5 baraSteam temperature should be slightly superheated 5 C. Other wise the heating surface in evaporators are not working properly.

110 bara 540 C 64 bara ,

480 C

25 bara , 350 C

Isotropic efficiencies different pressure levels:

At 110 bara:Isotropic eff= (3464 – 2350)/(3464 – 2090) * 100%= 80,2%Power per kg/s of steam: 1114 KW

At 62 bara:Isotropic eff= (3370 – 2360)/(3370 – 2150) * 100%= 82,7%Power per kg/s of steam: 1020 KW

36

550 C

500 C

50 C

400 C

350 C

300 C

250 C

200 C

150 C

100 C

450 C

103 bara 535 C: h=3461 KJ/kg82 bara 515 C: h=3434 KJ/kg62 bara 480 C: h=3370 KJ/kg

2.6 bara 129 C; h= 2720

65

0 K

J/kg

64 KJ/kg9.8 % more

27 KJ/kg3.8 % more

Dry steam towards the 1st effect at

62

bar

a 4

80

C8

2 b

ara

51

5 C

10

3 b

ara

53

5 C

Mollier diagram

Difference in heat available for power generation

Steam condition at inlet existing steam turbines

22

bar

a 3

50

C

entropy

enthalpy

110 bara 540 C 64 bara ,

480 C

25 bara , 350 C

Isotropic Efficiency existing steam turbine with 66% is lower then the 80 to 83% for the HP steam turbine.Means high losses

Why the existing steam turbine in sugar mill for driving the shredder and crushing rollers are

replaced by electric drives??

The flows of 15 to 30% are too high for extracting from High pressure steam turbine. Will reduce the isotropic efficiency.

The steam temperature is too high at extraction point which requires de-superheating. This results in less steam over HP steam turbine.

38

System with one boiler and one

condensing /extraction steam turbine

Process steam2,2 bara, 135 C

E

Condensate return85% at 98 CDemi water

E

Advantage Disadvantage

It is a simple Condensing wheel has low efficiency during season

Having low investment

When one main equipment trip then sugar mill will

shut down

39

Process steam2,2 bara, 135 C

E

Condensate return85% at 98 C

Demi water

E

E

System with two parallel systems each 50% capacity and consisting each of one

boiler and one condensing/extraction steam turbine

Advantage Disadvantage

High redundancy in case same quality will be taken

for equipment as of ‘option. a’Condensing wheel has low efficiency during season

When one unit trips then other unit can run at 50%

load

High investment costs because of additional boiler

and steam turbine.

40

Process steam2,2 bara, 135 C

E

Condensate return85% at 98 CDemi water

E

E

Advantage Disadvantage

In case back pressure trips then

condensing/extraction steam turbine can run and

plant has an output of 70% load

2nd steam turbine which result in higher investment

cost

High efficiency during season and off season High storage of bagasse

The size of boiler and steam turbine can be 10%

smaller

System with one boiler and one back pressure steam turbine for

season operation and one condensing steam turbine for season

and off season

41

Process steam2,2 bara, 135 C

E

Condensate return85% at 98 CDemi water

E

E E

System with two parallel systems each 50% capacity and consisting each of one

boiler and one back pressure steam turbine for operation during season, and one

condensing/extraction steam turbine for off season

Advantage Disadvantage

In case back pressure steam turbine trips the plant

can run still at 100% capacity.

3rd steam turbine and 2nd boiler which result in

higher investment cost.

High efficiency during season and off season High storage of bagasse

In case one boiler trips the plant can run still at 50%

capacity

42

More process steam required in relation to electric power result in higher plant efficiency

seasonOff-season

Minimum steam flow over condensing wheel into condensor

High losses in condensor

What is efficiency during season and off season

43

Boiler

Process steam2,2 bara, 135 C

E

Condensate return85% at 98 C

Demi water

E

FG

eco stack

Steam air preheater

air

To water storage

For additional steam air pre heaters

System with one boiler and one condensing

/extraction steam turbine and air steam

preheater

Prevents corrosion in flue gas air preheater and generate more power over full season for fixed bagasse amount

Approx. 5 % more power

44

The HP co-generation plant with steam air preheaters 66 bara

More steam over steam turbine and extracted to heat up the air.

No increased losses in condenser while more energy generated

2,5 barg

9 barg

Extraction pressure control

45

The HP co-generation plant with steam air preheaters 86 and 110 bara

Flue gas air preheater eliminated

46

Extraction pressure control

Extraction pressure control

The HP co-generation plant with BFW preheaters for 66 and 110 bara

More steam over steam turbine and extracted to heat up the air.No increased losses in condenser while more energy generated

Boiler

Process steam2,2 bara, 135 C

E

Condensate return85% at 98 C

Demi water

E

FG

eco stack

air

BFW preheaters

Take care for corrosion at cold end

47

Take care during operation for following parameter;

parameter target consequences

Water content in bagasse Keep as low as possible High water content more unburnedLower efficiency and higher fuel consumption

Oxygen content Keep it at 3.5 vol % wet More oxygen lower eff and lower fuel consumptionMore oxygen less CO and less unburnedToo high then check flue tubes. Leakages. Tune the air control

CO content Keep it below 800. Prefer 300 ppmv Too high CO means high unburned and high fuel consumptionCheck the firing.

Flue gas temperature Keep as low as possible Higher eff and lower fuel consumptionToo high then sootblowing.

Air inlet temperature Keep it sufficient high to avoid to low metal temperature

Too low then fouling and corrosion. Metal temp measurement.Increase air inlet temperature by feeding more steam to steam air preheater

Carbon in ash Keep low. Max 20% High energy losses. High fuel consumption.Check the firing

High surface temperature casing and cladding

Keep surface temperature approx 20 to 25 C maximum ablve ambient temperature

High energy losses. High fuel consumptionImprove the insulation

parameter target consequences

Too low flue gas pressure Approx same as in clean condition In case to high then high fouling. Steam temperature too low, stack temperature too high . High power consumption. ID fan could be running at max speed. No control anymore.

Overpressure in furnace Should be 5 to 10 mbar underpressure

ID fan could be at max speed due to leakages and/or high pressure drop due to fouling.

Steam temperature too low

Should be at setpoint In case too low then steam turbine performance too low and possible trip. Put control on manual and try to increase it.Also perform additional sootblowing

Steam temperature too high

Should be at setpoint In case too high then overheating in superheater tubes, piping and steam turbine. Put control on manual and bring it down.

2. Reliability

The operator should understand the basics of design

The equipment should be kept in good and optimal condition

The operator should check during operation the proper working of the equipment

The operator should understand the controls and be able to fine tune if necessary.

Do avoid any manual control

During outage the equipment should be thoroughly checked and cleaned, greased, etc.

Make check lists of each equipment

Make record sheets of inspections including findings

Make directly clear objective reporting of incidents and collect all data and damaged material parts.

9621247 1345 1451

18381531 1406 1255

328 613 690 759

25 BARA, 350 C 66 BARA, 490 C 86 BARA, 520 C 110 BARA, 540 C

HEAT LOAD HEATING SURFACES AT DIFFERENT PRESSURES

eco evap sup

51

2 types of boilers:

• Self supporting• suspended

Both with single or bi-drum possible

2.1 Boiler

HP bagasse fired boiler 140 tph 65,7 barg 485 C, single drum and self supporting

Economiser 3

evaporator

HP superheatersingle-drum

Flue gas Air preheater plus steam air preheater

cyclones

Economiser 1

Economiser 2

In HP cogeneration system are nowadays 2 designs used in sugar mills:• suspended• self supporting

To ID fan and stack 150 till 160 C

Desuperheating station

furnace

Dumping grate

Bagasse spreader

Over firing air

22

50

0

Boiler type

52

For 86 and 110 bara

Alternatives in self supporting boilers

Bi drum supported on downcommer

Bi drum supported on downcommer

Boiler type - suspended

HP bagasse fired boiler 140 tph 65,7 barg 485 C, bi-drum drum and suspended

Bi-drumHP superheaters

Economiser

Flue gas Air preheater

cyclones

furnace

Dumping grate

54

In case of 110 bara moduleAnd single drum

Also for 86 bara

Expansions

Top suspendedExpansion from top downwards

Bottom supportedExpansion from bottom upwards

Boiler should not be restricted in expansions

Put indicator on the different point of expansions and check regularly.

100 mm downwards

Steam drum suspension

Al weight taken by hangers. Inspect those regularly for cracks, malfunctioning, deformation

Distance needed for flexibility hanger to take the expansion differences

The hanger in the top of steelstructure

Rotation should be made possible

Example of expansions in bottom supported boiler

Linear expansion coefficient of CS steel: 1,2 mm/m per 100 C.

Saturation temperature:• 70 bara = 286 C• 80 bara = 295 C• 90 bara = 303 C• 100 bara = 311 C• 110 bara = 318 C• 115 bara = 321 C

Expansions for 150 tph , 110 bara and 540 C

10 m

12

m

25

m

1,2 * 321/100 * 25= 96 mm

1,2 * 321/100 * 10= 39 mm

46 mm60 mm

39 mm

The sliding forces from bottom supported parts

High sliding forces

W

F l

F f

F f = F l = m * W

Friction factors: m• Steel to steel and dry clean surface: 0,5 till 0,8• Steel to steel and grease lubricated: 0,16• Steel to stainless steel: 0,5• steel to Teflon: 0,05 to 0,2• Teflon to Teflon: 0,04

Galling in case for carbon steel on carbon steel .Is adhesion of 2 sliding materials.Take at least stainless steel plus carbon steel of lubricate the surfaces

Support on concrete structure

Support in concrete structure

Concrete floor

Keep height lowApprox 200 mmTo avoid cracking of concrete

Hole for installing beam piece under plate in concrete

Beam piece for transferring the sliding force deeper into concrete structure

Anchors to take keep the support into position and taking the moments

High sliding forces

Wrong !!!!

The guidance for sliding

guidance

2 mm free gap

Height 2 mm more then plate

Take sufficient space for expansions

Install 2 mm plate under the support plate and weld to plate

Prepare hole and weld SS sheet to base plate

Buckstays

cold hot

Wall expand

Take care for high expansion differences. Check if those are free expanding

buckstay

Heating surfaces

Check the fouling.

Check if sootblower reaches all areas

Slagging on superheater tubesSuperheaters needs sootblowing with retractable sootblowers to have more penetration

Suspended to headers

Check the supports

Check the seals of tubes through walls

Check supports

Ensure that superheater coils have sufficient space for expansions

Check expansions headers of superheaters

Is refractory or insulation still in position

Check supports

66

Check the sootblower supports

Check foulingImpulse of sootblowing steam can be too less

Check if sootblower steam is not damaging tubes.

Could be due to condensate formation in sootblower lines

Flue tubes of flue gas air preheater heavy corrodedAnd many tubes with leakages

Check the tubes of flue gas air preheaterFor corrosion

seal

ex

tube

Tube sheet

Check the seals near tube sheet

Measurement furnace pressure Tube in Top with this shape of opening

Ensure that it is always open.

No blockage of ash

Clean also during operation

Steam drum with vertical cyclone separator

Steam drum outlet

scrubbers

cyclone

baffles

cyclone

Downcommerinlet

Feed water pipes

scrubbers

NOTE:Minimum size of steam drum with cyclone is 1450 mm ID diameter when installed at both sides

The number of cyclone required is depending on its design. Normally cyclone capacity is for each:• 66 bara :approx. 5,6 tph• 110 bara :approx. 7,7 tph

Vortex breaker

69

Check the steam drum internals Clean the chevron plates

Check if baffles are in place. undamaged

Check the fouling in steam

Check the small nozzles of level instruments and clean

Check cyclones on wear and tear

For high steam purity

100

100

55% of radius

LLTrip

Recheck water levels

demister

Baffles and demister

demister

D

Vst hor

Clean and check demister

Close all gaps.No bypass of steam

Demister

Spreader stokers

• Fuels to be uniform thrown / spread over then grate area

• Fines ignite and burn in suspension

• The coarser particles fall on the grate and burn on a thin fast burning bed.

• The fuel and air needs to be uniformly distributed over the bed

• A part of the air (overfiring air) is injected above the grate into the furnace to mix the unburned gasses and particle with air

• The furnace is made large enough to ensure complete combustion before entering the convection part.

2.2 Fuel/ firing system

Bagasse feeder should guarantee:

• Continuous flow of bagasse.

means chutes should be with angles and no sharp corners, smooth surfaces internally.

the bagasse should not get be compressed and then fall out of feeder

• No lumps at outlet. The bagasse get in silo and in feeder compressed. The lumps at outlet of feeder need to be broken by a lump breaker

high amount of fines supply into spreaders

Large lumps fall on grate

Bridge forming Above feeder

Feeders should run at same speeds to guarantee same feed over full area

Spreading of bagasse should be uniform over depth

Same speed and equalized spreading

Different speed

Equalized spreading in depth

Continuous pulsating damper in each air line to spreader for equalizing the spreading of bagasse over the fuel grade

E ETo bagasse spreaders

Pulsating damper

Existing air distribution improved air distribution

500 1000

80

0

Air ductAt hopper inlet

Take 8 mm thick plate of CS

80

0Weld at both sides to existing air duct

Duct approx. 920 * 650 mm

Approx 920

Cut hole 30 mm in plate and weld to duct

800Air distribution in hopper

Air distribution over grate in hopper should be equalized.

Dumping grate

Cast iron grate bars with venture openings for air supply installed on a horizontal bar which is supported in bearing at both side in frame

All horizontal bars connected with lever for dumping

Pneumatic or hand lever

Split in 2 sections

multiple dumping grate sections

More sections besides each other

Ash removal not continuously

Ash removal by stopping feed of fuel and air.

Disturb firing

Pressure drop in boiler during dumping.

Effect on steam temperature

Dumping grate example 1

The dumping grate has a lot of moving parts and requires a high maintenance activity

Support structure can be damaged due to fire in hopper

Air distribution is poor due to large opening and low pressure drop

Dumping grate example 2

The dumping grate has a lot of moving parts and requires a high maintenance activity

Support structure can be damaged due to fire in hopper

Air distribution is poor due to large opening and low pressure drop

Water cooled pinhole grate

The grate is water cooled so that the supported structure underneath will be protected against overheating.

The ash removal is by discontinuous by blowing steam through nozzles installed in the grate as a pin.

This system is worldwide applied for bagasse firing and used up to 220 tph steam capacity

The grate tiles supported on water cooled tubes

Example of cast iron grate section of pinhole grate as per Joh Thompson design

The cast iron grate sections protected with stainless steel plates

Cast iron parts

Example watercooled pinhole grate as per design of TES from USAinstalled in Jamaica for 113 tph steam capacity

Cast iron grate sections

Steam cleaning systemPinhole grate

Example of cleaning pinhole grate

before

after

Travelling grate

Rotation directionVery slow speed

Continuous ash removal

Re-firing of unburned particlesCashed separated from flue gasses possible

Air supply

Large travelling grate sections

Section maximum5, m width and 6,5 m depthLarger ones split in 2 sections with at each side a drive.The drive is normally hydraulic

Hydraulic drive

Need of special parts for smooth operationand to resist the wear and tear

High alloy steel shafts and sleeve bearings

Forced steel chain links, case steel hardened pins and rollers. Supports and rails also hardened

High strength steel hardened ductile iron sprockets

Special shaped Grate castings in alloy

The grate and furnace heat release

The loading of the grate and furnace are important factors for firing the biomass.

When there is high moisture we will need more time for drying the fuel before it ignites. How more fine it is how easier to dry. So the grate loading should be lower

When there is a high moisture content it is important to supply the primary under the grate as high possible.

The air distribution over the grate should be as equal as possible in order to lower the excess air as far as possible

The upwards flue gas velocity should not be too high to ensure that particles will not be blown out to fast from furnace.

The slagging and clinkering should be avoided

There are many figures mentioned as heat release for grates by supplierwhich are confusing

Recommended heat release for grates with spreader stokersbased on GCV value of fuel

Excess air in relation to moisture content of fuel

Furnace heat release

Velocity is lower and need more time for complete combustion

Velocity is approx. same as flue gas and need less time for complete combustion

Total volume of furnace should be such that residence time is minimum 3 seconds

Experience shows good burn out of 1 to 3% with a furnace heat release of 186 to 230 KW /m3 on GCV value. However, the overfiring system should then also made proper.

Overfiring system

The distribution of air and fuel including sizing is never equal.There will be CO strains and areas where to less air is available for further combustion.Further the biomass has lighter particles which will be blown out easy from furnace.

Therefore biomass firing requires always high over firing air required up to 50%

Mixingof all flue gasses

and particles with air

Overfiring system in bagasse fired boilers

Overfiring system in furnace of bagasse fired boiler

Openings in furnace walls of approx. 13 * 50 mm

Overfiring systemwith small jets at multilevel

Originally from stoker fired coal boilersPorts on front and rear wall

The small jets have not much penetration by which the mixing is not optimum.Channeling occurs

Some flow modelling of small air jets

No deep penetration

Test done by creating a cyclone effect in furnace

• installed above fuel distributors• Intended to create swirl• Could be made of larger capacity• The larger jets had higher momentum• However. Poor coverage still• Also channeling• Poor mixing• Higher excess air was required• Imbalance in gasses leaving furnace

Studied Alternative type of air jets in a cyclonic effect

Studied effect with large jets from front and rear wallResults are:

• Installed above fuel distributors • Large pipes of approx. 100 m in one layer• Outlet velocity approx. 40 to 50 m/s• Could be made of higher capacity and momentum• Interlaced or opposed jet arrangements• Good coverage is possible with interlaced• However in arrangement interference with fuel

distributors, ah re injection and furnace openings

Large jets from front and rear wall

Studied effect with large jets from side walls

The effect was also positive

However when furnace is more then 10,5 m width and 6 m deep then it is not possible to get a deep injection of air

High capacity cyclone 400 to 500 mg/Nm3

Approx. 70% fly ash captured.Not high efficient but high capacity one

2.3. The fly ash arrestor and ash removing systems

Mostly used in pakistan

Multi cyclone

Use the right swirler

Check erosion of cyclone body and swirlers

High efficiency cyclone to 200 /250 mg/Nm3

High efficiency cyclone

Alternative for low emissions of 50 mg/Nm3

High pressure drop of 15 to 20 mbar and high power consumption due to air compressor for pulse jet cleaning

Very important is to control the air pressure for cleaning the bags.

Need sufficient pressure

50 to 100 mg/Nm3

Electric static precipitator ( ESP)50 to 100 mg/Nm3.

High voltage between plates and gridsParticles are charged by the grids and migrate to the plates.Plates gets cleaned by rapper system.

Needs large areaHow lower the emission how larger the ESP

Ash removal from hoppers of grate

Manual:

• takes time to remove • air supply to grate get disturbed• Effect on steam pressure

With wet ash conveyor

• Preferred.• No disturbance of air supply to grate• Ensure always that seals are sufficient under the water level

100 mm

High wear and tear

In case of pinhole and travelling grate always wet ash conveyor required

Ash removal from hoppers heating surfaces and fly ash arrestor

From hoppers of heating surfaces only a small ash quantity. Remove manuallyRequired an ash rotary valve for continuous removal and sealing of air leakage.

Take care that the openings in valve are very small to minimize air leakage.

From hoppers of fly ash arrestor the ash discharge should be continuously.Normally wet ash system is applied. Same as from grate.Water seal is more difficult as pressure difference is 200 mWG.The ash is very light and difficult to discharge from hopper.Mostly no water seal used.

Each hopper provided with ash rotary valve and discharge in wet ash conveyor

Dry fly ash removal is also possible. The ash should be collected in bottle and blown into the silo.This system is however expensive and is costly in maintenance.

108

QH curve fan with speed control

Curve of system pressure dropagainst capacity

100% MCR

design

70 KW

Besides power savings speed control gives a more smooth control of the flow than with dampers.

When 2 * 50% are installed then dampers are installed at the inlet side of ID fans and at outlet side of FD fans.The dampers can be provided with drives for air control in case of problems with VFD.

The dampers require positioning transmitters and limit switches.Those instruments need to be checked regularly to ensure they will work correctly when needed.

Check during operation regularly the bearing temperatures and vibrations

The ID and FD fans are provided with variable speed electric drives

2.4. The fans and dampers

Take care for pressure drop and distribution in ducting

Pressure drop:Bend R=D factor 0,3Round bend with 3 sections

Factor 2 till 2,5 Factor 3

Install in bends with short radius a guide vaneFactor 0,5

Install in inlet sections vertical plates for improved distribution of flue gassesFactor 1

At stack inlet a 45 degree uplift is required . Factor 0,5

Install baffle in middle of duct to minimize turbulence between flows Dampers with 2 or more blades

Factor 0,5

1/3 Ri=500

Check the damper blades for cracks

Check the guide vanes for cracks

Keep screen at inlet venture clean during operation

venturi

To keep excess air low as possible it is measured in an air venture.Also any deviation in air flows can be easily noticed during operation

Damper installed at inlet ID fan to avoid dust collection in fan during a fan stop/trip

ducting

Stiffening required

Round duct only small stiffening inside to keep round shape

Check internal of ducting for cracks

Check if ducting can expand freely in right direction.

Expansion joints

For air ducting fabric material can be used

Take care that there is always an internal baffle at inner side installed to minimize the pressure losses

In flue gas ducting use SS bellows. Collected dust will not harm the material in case of fire

Flow direction

Weld joint to duct . No bolting

Check during outage the expansion bellows for cracks and leakagesCheck during operation the expansions

Expansion of hot ducting

The SS bellows needed mostly at each side of duct

Check during operation the expansions

114

PID’s bagasse firing system

E

E

E

E

Plate slide Plate slide

E

VSD

VSD

Fixed speed

VSD

Fixed speed

Signal load control4- 20 mA-

E

E

PI

PS

Spreader air fans

MCCAutomatic

start standby

Sight glassSight glass

Sight glassSight glass

peepholes

2 inch connections

3inch

inch

inchinch

Rotary air damper

Rotary air damper

Spreader fans

3 more

Bagasse feeding and spreading system2.5. The controls

Air system

FGAP2grate

FGAP2 overf

FGAP1grate

GFAP1overf

Right side wall

left side wall

Overfiring nozzles

2 * 5 dumping grates

5 air dampersPut air on and it will closeNormally open by spring

Raw water 1 inch

overflow

Push button for operation at each grate

E

VSD

E

VSD

StapOFA

Stapgrate

FT

FT

TT

TT

TT

TT

PT

E

VSD

o/c

o/c

E

VSDo/c

o/c

Load controlAir fuel ratio

E

Damper fan close directly

automatic when fan stops.

PT

116

PID’s Flue gas system

Dumping grate

PT

TP

TP

TP

TP

TP

TP= testpoint of 1 inch

Fly ash arrestor

PI

TT

Pressure control

PS

PS

H L

Flue gas system

E

FGAP2grate

FGAP2 overf

FGAP1grate

GFAP1overf

sup2

sup1B

sup1A

evap

2 *

eco

E 2 * E 2 *

XT

O2E

VSD

E

VSD

o/c

o/c

pT

TP

TP

TP

TP

TP

TP

TP

TP

TT

drain

Damper fan close directly

automatic when fan stops.

Trip boiler

Sootblowing system

Fly ash arrestor

FGAP2grate

FGAP2 overf

FGAP1grate

GFAP1overf

sup2

sup1B

sup1A

eco

2 *

E

E

E

E

E

eco

E

E

E

E

E

E

2 *

2 *

2 *

3 *

evap

evap

E

2 *3 *

3 *

3 *

3 * 3 *

3 *

3 *

2 inch

PT

PI

From de-superheating line at inlet superheater 2

1,5 inch

1,5 inch

1,5 inch

Blow down vessel

TT

TT

2 inch

Design pressure 25 bargDesign temp. 400 C

Design pressure 124 bargDesign temp. 450 C

Pressure control

Automatic sequence control

Signal to start/stop sootblowers

Signals from sootblowers

temperature control

118

Sup 1 BDeaerator

LT

LIC

PT

PI

LS

LG

LIC

To sample cooler ¼ inch

Dosing hydrazine½ inch

Dosing ammonia½ inch

Design pressure deaerator at 2 barg, saturated and 100% vacuum

2 inch drain

Condensate And demi water return

??inch

From LP header? inch

Into demi water tank1 inch

? inch

1/2 inch

Steam air preheater

1 inch drain

To pressure/temperature reducing station

?? inch

BFW pumps

Boiler feed water system

Capacity?

To BFW pumpsL

HTo cond pumps

E

? inch

PI

PI

?? inch? inch

Second pump

2nd

2nd

To boiler

2nd

PT

Start 2nd

pump

L

condensate

Condensate vesselDiam 1000 and 1500 mm highOn 4 m level

2 inch balancing line

?? tph LP steam from outlet steam turbine at 1,2 barg

To condensate clean tank

LT

LG

12 inch

? inch? inch

? inch

? inch

? inch

3 inch

System Steam air preheater

8 inch

? inch globe

Condensate vessel

Installed near vessel

Water level control valve

TIC

At 8 m level

Design 3 barg 150 C

Steam air preheater system for higher air temperatures like 105 C

Water system boiler

2 inch

2 inch

LS

LG

LL

LT

1 in

ch

1 in

ch

2 inch

2 inch

LS

LG

LL

LT

1 in

ch

1 in

ch

Steam drum

eco

1 in

ch

Tri phosphate dosing

??inch

FT

1 inch

From BFW pumps

FIC

LIC

1 in

ch 1 in

ch

To de-superheater

Parabolic valve for manual control

1 i

nch

1,5 inch

1,5 inch

1,5 inch

1,5 inch

Sample cooler

Trip boiler ( stop feeder and air supply)After stop air fans then stop ID fan

The ash characteristics of fuels are important.

Specially important are:• the alkali metals (Ca, Na, K) are important.• silica

Further the sulfur and Chlorine content in the fuel is an important factor

Those contents needs to be verified in the lab before deciding the best combustion and boiler system.

121

2.6. The sootblowing system

Elements in biomass potentially leading to corrosion and deposits.

122

0.600.2

0.02 0.1 0.030.3 0.2

7.1

0.80.50 0.4

0.2 0.1 0.01

0.70.5

1.47 1.47

0.730.32 0.18

2.442.22

0.12 0.09

0.00

1.00

2.00

3.00

4.00

5.00

6.00

7.00

8.00

Sulphur (S)%

Chlorine (Cl)%

K+Na%

Those elements determine the clinkering, slagging and fouling and also the erosion and corrosion potentials of the fuels.

Ash fusion temperatures

Initial deformation temperature C 1380

Sintering temperature C 1400

Hemispherical temperature C 1400

Fluid temperature C 1400

The ash starts to get sticky

First sign of softening. Change of outer surface

The form is changing too its half of heightIt did shrunk till one third of height

Ash Behaviour

123

Mechanisms of deposit build up in biomass boilers

124

Rotable sootblower

125

Check if nozzles are installed inbetween tubes

Rotable sootblower installed

126

The poppet valve

127

Set pressure in lanceInstall pressure gauge for checking the pressure in lance

The nozzle and support

128

Check the nozzles for cracks and fouling

Long retractable sootblower

129

The travelling of long retractable sootblowers

130Check the travel path of sootblower.

The long retractable sootblower installed

131

Grease theTeeth bars andKeep those clean from dust

Check limit switches of sootblower

The semi retractable sootblower installed

132

Grease theTeeth bars andKeep those clean from dust

Check limit switches of sootblower

Guidance at both sides

Especially for finned tubes required

The sootblower system

From primairysuperheater

To secondairysuperheaterPTPI

E E E

E E E

E

TT

Keep temperature 20 C above saturation temperatureOpen this valve shortly when sootblower stop and other starts

Small orifice for keeping line warm

Ensure slope of 1 degree

Always connection from below

Take care for expansion differences between line and sootblowerconnections

Valve should be fast reactingEspecially when sootblower stop

Take steam from far end of de-superheateroutlet

To blow down vessel, Install diffusor in blow down vessel at inlet to reduce wear and tear and noise

133

Sootblowing direction

Execute sootblowing at hot side in direction of flue gas flow

134

2.7. The Feed water system

Deaerator:

Deaerator has to remove the oxygen.

Check during operation its working. High oxygen content will result in corrosion.

Minimum pressure in deaerator is 0.2 barg. Ensure no lower pressure.

Check during operation if the vibrations are not too high. If so then problem have to be solved asap.

Keep the level always as high as possible to have always sufficient water buffer.

Also check the expansions

During outage check the fouling at inlet sprayer. Larger parts can block it.

Check also the trays during outage for fouling and for cracks. Also check bolts

Same for steam distribution pipe.

Clean nozzles for water level measurement during outage.

BFW pumps:

During operation check regularly for vibrations and bearing temperature

Also record the discharge pressure of BFW pump in order to have an indication of the wear and tear of internals

The minimum flow valve can leak and will lower the capacity and/or increase the power consumption.

At higher loads check by closing the minimum flow valve if the pressure at outlet pump is increasing and read from QH curve how much it is leaking

Change each week the pump in operation. Also standby pump should run

Boiler

Process steam

Condensate return85% at 98 C

Demi water

E

FG

eco stack

Air100 C

E

E115 C

155 C

200 C

115 C

150 C

Water storage

E

Washing steam

deaerator

Extraction condensing steam turbine

condensor

Chemical transport in steam cycle

Injection BFW for steam temp controlImpurities in BFW will lower purity of steam which could harm superheater and steam turbine

Mechanical carry over

Blow down

Malfunction deaeratorresults in high concentration of oxygen in system. pitting

Ingress of O2 and CO2

Silica deposits in condensing wheelsalt deposits in wheels

pH of BFW should be high enough to avoid flow accelerated corrosion in BFW line, eco, pumps and BFW heaters

Any contaminated condensate with sugar will harm the system

Preciparations of Ca and Mg saltsIn natural circulation system boiler

2.8. The conditioning of water and steam side/chemistry

Steam purity requirements

Boiler Water requirements

Boiler drum water requirements BOILER PRESSURE

66 bara 80 bar 110 bar

Boiler water Conductivity After cation Exchanger @25 °C pH 25 °C Silica Phosphate Hydrazine

SiO2 PO4 N2H4

MicrS/cm

mg/kg mg/kg mg/kg

150 9.5-10.5

<6 <6

Traces

150 9.5-10.5

<4 <6

Traces

150 9.5-10.5

<1,8 <6

Traces

max. max. max. max.

For controlling the oxygen level in the feed water hydrazine will be injected into the deaerator storage vessel.

The pH of the boiler feed water to the boiler will be controlled by injection of ammonia into the feed water line at the inlet of the deaerator,The pH value of the boiler water in the evaporator system will be controlled by injecting Natrium Tri-phosphate into the feed water line downstream the economizer.

Boiler Feed Water requirements Non-solids-containing water

Boiler Feed Water

De-Superheater spray water

Conductivity After cation Exchange @ 25 °C pH @ 25 °C Hardness Total CO2 Silica Total iron Total copper Oxygen Permangate Oil

CaCO3 CO2 SiO2 Fe Cu O2 KMnO4

Micro S/cm mg/kg mg/kg mg/kg mg/kg mg/kg mg/kg mg/kg

0.2 9

N.d. N.d. 0.02 0.02

0.003 0.02

5 0.5

0.2 9

N.d. N.d. 0.02 0.02 0.003 0.02

5 0.3

max. min. max. max. max. max. max. max.

Boiler Feed water requirements

To meet the steam purity requirements high purity water shall be fed into the system.Further the return condensate from sugar mill should also meet those requirements.

This water quality can be generated by a demineralized water treatment plant extended with a mixed bed ionization exchange.

Conditioning the water and sampling during operation

Boiler

Process steam

Condensate return

Demi water

E

FG

eco stack

Air

E

E

115 C

150 C

Water storage

E

Washing steam

deaerator

Extraction condensing steam turbine

condensor

Ammonia for pH controlFor water system min PH is 8,5For BFW pumps min pH is 9,2 when CS materials are used. Quantity based on measured conductivity upstream and at outlet deaerator and corrected on BFW flow.

Note: take always as minimum Cr impellers in BFW pumps

HydrazineIn case oxygen in outlet is too highAnd for conservation during standstill

Dosing phosphate to keep pH in natural circulation system at 9,8 and reduce the hardness, catch the salts

Continuous blow down toControl the conductivity after cation exchange at 50 micro S. Take out the deposits

Intermittent blow down lower headers to remove sludge during each shift

Sample: Continuous check on contaminations

SampleConductivitybefore cation of pH continuously

SampleConductivity after cationfilter continuously

Steam sample

sample

Sample: at outlet demi water plant is a continuous sampling

Blow off O2 and CO2

Sampling of water and steam during operation

Dosing rate of ammonia

Supplied as liquid and can be reduced to concentration of 10% in dosing vessel before dosing it into boiler.The dosing needs to be continuously and quantity depends on PH of boiler feed water and BFW flow

Morpholine is a good alternative

Hydrazine is not recommended as it can cause cancer. Only used for oxygen scavenging in case deaerator does not work properly. Then dose approx. 0,1 mg/lAnd for conservation. 25 till 100 mg/l depending on standstill period. Alternative is eliminox.

Dosing rate of phosphate

Normally 3 is taken

Max 6 ppm PO4 in boiler water

Band of pH control

Phosphate is supplied as powder and needs to be mixed with water in vessel to concentration of 5%.The dosing is discontinuously with the pH band.

Care shall be taken for proper mixing.

Put dosing pump at floor level, not on top of vessel otherwise it could block the lines.

Doing system of phosphate

M

M

FE

silencer

Steam blow off for start up of boiler

Steam from future boilers

To steam turbine 1

To steam turbine 2

To steam turbine 3To steam turbine bypass station

Steam header with condensate drip and steam trap

PT

PT

Note :The boiler needs a steam blow off facility to be able to start up the boiler and to bring the steam temperature till acceptable levels before feeding into the steam turbine

When the first boiler will be started up the steam of boiler should go as fast as possible in steam air preheater and deaerator for warming up.

Normal practice for connecting high pressure systems

2.9. The piping systems and valves

FT

Block and bleed

Understand how piping will expand.

Check the piping for its expansions. Is it as per expectations?If not then high stresses

Check the hangers of piping. Is the loading as per expectations

Desuperheater.Check the desuperheater for cracks and check the springs. and also check internally the surface of pipe for cracks

Expansions

Expansions in Headers and connecting piping in superheaters

Header is 540 C

wall is 320 C

Difference in expansion for 10 m wide wall:(1,4 * 540/100 – 1,2 * 320/100 ) * 10 = 37 mm

18,5 mm

Need enough distance to create flexibility for 18,5 mm deflection.If not enough then split header in 2 parts

Ensure header can expand in both directions

The de-superheater loop and connecting piping

10 D

20 D

Condensate trap

Heavy header cannot supported by small flexible tubes

Take care that de-superheater has enough length upstream and downstream

De-superheater type

Ensure sufficient length upstream and downstream the orifice

Orifice or venturi

30 d 7 d

D= internal diameter

HP steam flow measurement

Safety valve testing

• Steam blow off over the steam blow off valve• Increase pressure slowly to 85% of set pressure• Install the gags to not tested safety valves• Raise pressure to set pressure by closing start-up valve

slowly • Maintain in all circumstances some flow over the

steam blow off valve for superheater cooling• Record set pressure opening• Record maximum pressure raise• Open slowly steam blow off valve to lower pressure• Record the seating pressure• Lower the pressure to 85%.• Check the set pressure and closing pressure as per

design.• If not then adjust the set or blowdown pressure and

retest• Also do same for the other 2• Record the test. With pictures

Insulation Functions:• Reduce energy losses to ambient• Avoid corrosion of boiler parts due to rain water

Insulation is mostly a under estimated part of the boiler

We take in our design a low loss of heat in order to lower bagasse consumption

In existing boilers is insulation system very poor:• To thin• Several hot parts are uninsulated• Not weatherproof ( rain water)• Poor material

The losses are in existing boilers approx. 5 to 6%

While we need to meet approx 0,8 %. The surface temperature should be max 25 C above ambient

Therefore insulation needs high attention during design and installation.

Also the installation of roof at steam drum guarantees the condition

2.10 . The refractory and insulation systems

Poor insulation

What to insulate

surfaces above 50 C accessible from grade or platform during operational inspections

-personal protection.

All surfaces above 50 C and having effect on the efficiency of the system should be

provided with a proper heat insulation system.

Systems like flue gas ducting at boiler outlet or piping systems like drain or blow down

piping need only personal protection from downstream first block valves . No heat

insulation as it has no effect on the efficiency of the system

All parts in which flue gasses could condense during the normal operation should be

also insulated. Like hoppers of cyclone

Insulation wool available in Pakistan

wired mat with galvanized hexagonal wire netting

The available thickness of ceramic wool blanket in Pakistan market is 25 mm

Require for all those materials that they are free from Chlorides

Selection of type and thickness of insulation wool

• Always use the 50 and 75 mm thickness blankets.

• The 100 mm thick blanket should not be used as overlapping is preferred above 75

mm thickness .

• When more thickness required use 2 layers .

• The layers should be min 50 mm overlapped.

• The density of the insulation mat depends on the application.

Normally use 80 kg/m3 density

Above 500 C install always first a layer of ceramic wool with density of min. 120 kg

/ m3 till the surface temperature of rockwool is lowered below 500 C.

What are economic insulation thicknesses

economic insulation thickness tableRockwool isolation hard board 850

0

20

40

60

80

100

120

140

160

180

200

220

240

260

280

300

0 50 100

150

200

250

300

350

400

450

500

550

600

650

700

750

800

850

900

950

1000

diameter outside (mm)

ins

ula

tio

n t

hic

kn

es

s

50

100

150

200

250

300

350

400

450

500

550

note rockwool 850:density kg/m3 110 to 125temperature C 50 100 150 200 250 300thermal conductivity: w/mk 0,039 0,045 0,051 0,059 0,067 0,078

Piping cladding supporting

Each 1 m

Insulation thickness for walls

Operating pressure in boilerBarg

Operating temperature in boiler C

Required Insulation thickness and to be usedmm

Cladding temperature above ambient temperature C

Till 1 60 to 120 40 (50) 17

1,1 to 4 120 to 152 50 (50) 20

5 to 10 159 to 184 75 (75) 20

11 to 15 188 to 201 90 (2*50) 19

16 to 20 204 to 215 100 (2*50) 20

21 to 25 217 to 226 104 (2*50) 20.4

26 to 30 228 to 236 110 (2*50) 21,6

31 to 35 237 to 244 120 (75 +50) 19

36 to 40 246 to 252 125 (75 +50) 20

41 to 60 253 to 276 150 (75 +75) 20

61 to 80 278 to 296 175 (2* 75 +50) 20

81 to 120 297 to 325 200 (4*50) 20

Density : 80 kg/m3

Cladding systems for walls

Cladding systems for walls

Cladding systems for ducting

refractory

There is limited amount of refractory inside the boiler:

• Around the grate• for peephole • For inspection doors• for burner openings• For sealing areas

The castable needs to be suitable for 1600 C and needs to have a pH value of min 8 to protect the materials

Normally applied with manual pouring

Castable have a hydraulic binder, which hardened in the presence of moisture.Once in place castable should not dry to exposure of heat.Curing start immediately after the castable is placed.Moist condition can be mainatained by covering the castables with wet sack or by frequent sprinkling.Curing takes at least 24 hrs, preferred 72 hrsAfter the curing period, natural air drying of 2 to 3 days.

Dry out of refractory

Dry out is needed to :• Remove mechanical water added during the mixing process• Chemical water added during manufacturing

For dry out a slow ramp rate of the heat is requiredRecommended 30 to55 C.First hold point is between 100 and 200 C.This hold point is most critical for removing the mechanical waterThe next hold points is to remove the chemical water and to form the final bondWithin the refractory for maximum strength2nd hold point is at 300 till 370 C3rd hold point is at 500 till 600 CHold up time is 1 hr for each inch of castable thickness

2.11. Preservation boiler during standstill

During off season the plant will run some further in single cycle mode to burn all bagasse and to supply power into grid.

Thereafter some months a stop.

After stoppage of boiler record the fouling of all boiler parts at inner and outer side.Also record the damages noticed. Including pictures.

Thereafter clean the heating surfaces fully and remove all dirt. Avoid any pockets of dirt.Keep the boiler fully open and ensure the boiler will be vented properly so that all water can be evaporated.

The steam drum and lower headers of boiler should be all fully cleaned.Flush the boiler after cleaning several times till you are sure that it is clean.

Then let the innerside also be dried by the natural draft.

Check the boiler entirely for corrosion, erosion and damages

Check the insulation of boiler and remove wet mats and dry out the areas. Check the corrosion of parts. Repair where needed. Then reinstall when quality is oke.Ensure all cladding of insulation is rain water tight.

Check all equipment on corrosion, erosion and damages. Repair where needed.

Check the refractory for damages and replace where required.

Ensure the boiler and equipment are all clean and dry so that in months before start of season the boiler parts cannot corrode

3. Safeties in system for protection persons and equipment

Thank You for Your Kind Attention