types of biogas plant
TRANSCRIPT
Gas produced by the anaerobic digestion or fermentation of organic
matter under anaerobic conditions.
Biogas = CH4 + CO2 + H2S + N2 + H2 etc
Typical biogas composition:
Methane, CH4 : 55-70% Carbon dioxide, CO2 : 25-40% Nitrogen, N2 : 0-2 %
Hydrogen Sulphide, H2S : 0-3 % Hydrogen, H2 : 0-2 %
Oxygen, O2 : 0-2 % • pH-value : 6.5 to 7.5• Due Point : < - 80° C
What is biogas?
Why should we go for biogas?
• Disposal and treatment of biological waste - a major challenge for the waste industry.
• Anaerobic fermentation - a superior alternative to composting.
• Limited domestic reserves and uncertain foreign supply of hydrocarbons.
• Provides clean combustible gas and high quality organic fertilizer for sustaining soil-fertility and also for Pisciculture.
• It has a typical calorific value of 21.48 MJ/m3 or 4,800 kcal/m3.
• Recognized renewable energy source • Potential reduction of green house gas emissions.
Methanogenesis
Complex Organic Carbon
Monomers & Oligomers
Organic Acids
Acetate – H2 / CO2
CH4 + CO2
Hydrolysis
Acidogenesis
Acetogenesis
Anaerobic Digestion
COMPLEXORGANICMATTER
SIMPLEORGANICS
ACETATEH2 / CO2
METHANE and CARBON DIOXIDE
LOW ODOR EFFLUENT
LIQUEFACTIONPHASE
GASIFICATIONPHASE
ACIDOGENS METHANOGENS
Electrical and/or thermal energy
Biofertilizer
Organic wastes
Anaerobic digestion
Biogas
Solar energy
Biomethane production
Animal husbandry
Crop harvesting
Industrial processing
Human consumption
Photosynthesis
H2OCO2
Biogas Cycle
Energycrops
Natural gas pipeline
Cleaning &Upgrading
Energy crops
CO2
Factors affecting Biogas generation
1. pH concentration
2. Temperature
3. Total solid content of the feed material
4. Loading rate
5. Seeding
6. Uniform feeding
7. Diameter to depth ratio
8. Carbon to nitrogen ratio
9. Nutrients
10. Mixing or stirring or agitation of the digester
11. Retention time or rate of feeding
12. Type of feed stocks
13. Toxicity due end product
14. Pressure
15. Acid accumulation inside the digester.
Biogas potential in India
• The annual estimated biogas generation potential based on available cattle dung is about 17,340 million m3.
Biogas plants in India
• Potential -12 million family type biogas plants • Achieved - 4.12 million family type biogas plants -
34% of the potential. • Functionality of the biogas plants is about 95.80%• Domestic biogas plants can supply few hours of
electricity for domestic needs .i.e. More beneficial in rural areas.
• Electricity can simply be produced by using Biogas generators of few kW capacity.
*APITCO Survey
Experimentally introduced in the 1930's.
First research on Sewage Purification Station at Dadar in Bombay, undertaken by S.V. Desai and N.V. Joshi of the Soil Chemistry Division, Indian Agriculture Research Institute, New Delhi.
The early plants were very expensive, not cost effective, and not producing enough gas.
Some of the early models were also prone to burst, so the technology was not viable for dissemination.
In 1956, Jashu Bhai J Patel developed a design of floating drum biogas plant popularly known as Gobar Gas plant.
In 1961, Khadi and Village Industry Commission (KVIC) promoted Jashbhai Patel's design, which was later known
as KVIC model. Planning Research and Action Division (PRAD) based in
Uttar Pradesh developed the 'Janata' fixed-dome plant - a
modified chinese design. Janata system is about 30% cheaper than a KVIC model.
1984 - Action for Food Production (AFPRO), New Delhi developed Deenbandhu model (an improved version of Janata model).
30 percent cheaper than Janata Model and 45 percent cheaper than KVIC model.
Presently, designs and models are galore in market.
Classification of biogas plant
Biogas plants may be classified in several ways:
• Continous, semi-continuous and batch types (as per the process)
• The dome and the drum type• Depend on shape of the digester (Horizontal or Vertical)• Depend on loading rate• Depend on HRT• Depend on construction material • Depend on feed material
Biogas Digesters
Biogas Digesters
Conventional Biogas Plants
High Rate Digesters
For Insoluble wastes
(also called as High-strength wastes)
For Soluble wastes
(also called as low-strength wastes)
Conventional biogas plants in India
1. Fixed dome type
2. Floating drum type
3. Bag type• Deenbandhu model with brick masonry
• Deenbandhu ferrocement model
• Pre-fabricated RCC fixed-dome
• Janta biogas plant
KVIC floating metal drum type
KVIC type plant with ferrocement digester and fibre
glass reinforced plastic gas holder
Pragati modelFlexi Model
Characteristics of floating drum type
Consists of a deep well, and a floating drum (usually made of mild steel).
Drum rises as gas collects. Constant gas pressure due to the drum weight.
(The pressure is equivalent to the weight of gasholder over unit area)
Inlet is higher than the outlet tank, creating hydrostatic pressure which helps slurry to move through the system.
Maxing gas pressure attained - 8-10 cm water column.
Characteristics of fixed dome type
Invented in China in 1930’s. Underground brick masonry compartment
(fermentation chamber) with a dome on the top for gas at the storage.
Fermentation chamber and gas holder are combined as one unit.
Movement and weight of digested the slurry decides the gas pressure.
Variable gas pressure (0-90 cm water column) Less expensive and requires less maintenance than
floating drum type.
Components of biogas plant
Inlet pipe: The slurry is moved into the digester through the inlet pipe/tank.
Mixing tank: The feed material like dung is gathered in the mixing tank. Using sufficient water, the material is thoroughly mixed till a homogeneous slurry is formed.
Digester: Inside the digester, the slurry is fermented. Biogas is produced through bacterial action.
Gas holder or gas storage dome: The biogas thus formed gets collected in the gas holder. It holds the gas till the time it is transported for consumption.
Outlet pipe: The slurry is discharged into the outlet tank. This is done through the outlet pipe or the opening in the digester.
Gas Pipeline: The gas pipeline carries the gas to the utilization point like a stove or lamp
Fixed dome type biogas plant
( Janta biogas plant)
Deenbandhu biogas plant
Approved by GOI in 1986. Design consists of two spheres of different
diameters, joined at their bases. Sphere shaped design - reduce the surface area of
biogas plant - reduce cost. The curvature in the bottom of the digester - nullify
the earth pressure. Structural strength of spherical structure is more than
a rectangular structure.
Deenbandhu biogas plant
Mixing tank
Gas outlet pipe
Plinth level
Outlet tank cover
Displacement Chamber
Outlet Tank
Slurry Discharge
Hole
DigesterOutlet gate
Gas storage Area
Inlet Pipe
Foundation
Initial slurry level
Method of Emptying Deenbandhu
Stage IStage II
Open Gate Valve
G.L
First step
Second step
P.L
Second step
First step
Open Gate Valve
P.L
Contd..
Stage IIIStage IV
First step
Second step
Open Gate Valve Open Gate Valve
P.L P.L
First step
Second step
KVIC Vs Deenbandhu Sr. No KVIC type Deenbandhu model
1. This is floating gas holder type This is fixed dome type masonry structure
2. It is made above the ground level
It is under ground masonry structure
3. Space above ground is used for
fitting of movable drum
The space above ground can
be used other beneficial
purpose
4. Initial investment is low. Initial investment is high.
5. It requires some cost of
maintenance to maintain the
steel structure.
No. cost of maintenance
6. Effect of low temperature during
winter is more.
Effect of low temperature is less
Contd..Sr.No
KVIC type Deenbandhu model
7 Gas is always produced at
constant pressure.
Gas pressure is variable.
8 Required less excavation Required more excavation
comparatively.
9 Any skilled mason can construct
the plant.
It requires specially trained
mason to construct the plant
10 Well suitable for plain as well as for hilly areas where temperature variation goes to very low level.
Suitable for plain area
11 Suitable for Rocky area also. It is not suitable for Rocky and
hard soil area.
Biogas Plant models available in India
Sr.no Biogas
Plants with movable gas holder
Fixed dome type
Digester and gas holder separate
Flexible bag plant
1 KVIC Design Sichuan Model Sulabh Model Neoprene Bag Model
2. IARI Design Shanghai Model Bardoli Model Swasrik Biogas Plant
3. PRAI design (Two Chambers)
Janata (Brick Masonry)
PAU Model Red Mud Plastic Model
4. Kamdhanu (baked clay) model
Bhagya Laxmi Sangli Model
Contd…
Sr.
NoBiogas Plants with movable gas holder
Fixed dome type Digester and gas holder separate
5. ASTRA Model Kalinga (RCC) CV Krishna Model(FRP Fixed Dome)
6. JWALA Model ASTRA (Chinese type)
7. Ganesh Model GAIC/ATRC (RCC segment) Model
8. Khira model AFPRO (Horizontal RCC pipe ) model
9. FRP Model Deen Bandhu Model
10 Ferrocement Digester Model,
SERC Model, SPRERI Model.
Bharat Model
Flexible Balloon Digester
Originated in Taiwan, China, in the 1960s. Rectify - problems experienced with brick and metal
digesters. Material - Neoprene coated nylon
- PVC- RMP – Red mud plastic (produced from the
residue from aluminum refineries) The membrane digester is extremely light Can be installed easily by excavating a shallow trench,
slightly deeper than the radius of the digester. Simple construction, prefabricated, digester cost is low.
Flexible balloon biogas plant
What is meant by High rate digesters?
1. Refer to bioreactors in which the SRT (time for sludge biomass solids to pass through system) is separated from the HRT (time for liquid to pass through system).
2. Slow growing anaerobes can be maintained in the reactor at high concentrations, enabling high volumetric conversion rates.
3. Widely used for wastewater treatment
4. Retaining sludge in the reactor is immobilization onto support material (microorganisms sticking to surfaces, eg. filter material in the "anaerobic filter") or self-aggregation into pellets (microorganisms sticking to each other, eg. sludge granules).
Contd…
Anaerobic fixed-film (sludge blankets) systems hold the bacteria in the digester for relatively long periods and provide for long SRTs and short HRTs.
The bacteria grow as fixed films of dendritic or “stringlike” masses on the supportive media or as clumps of solids within the openings or voids of the supportive media (such as gravel, plastic, and rock).
The openings make up approximately 50% or more of the media.
Soluble organic compounds are absorbed (diffuse into) by the bacteria, whereas insoluble organic compounds are adsorbed (attach) to the surface of the bacteria.
The flow of wastewater through fixed-film systems may be from the bottom to the top (upflow) or from the top to the bottom (downflow).
Types of High rate digesters (Fixed-film)
Baffled reactor Expanded bed Expanded granular sludge bed (EGSB) Continuous stirred tank reactor (CSTR) Fluidized-bed reactor Fully packed upflow Hybrid flow Rotating biological contactor Thin-film bioreactor Upflow anaerobic sludge blanket (UASB)
What are sludge granules?
At the core of UASB and EGSB technology.
A sludge granule is an aggregate of microorganisms forming during wastewater treatment due to constant upflow hydraulic regime.
The flow conditions creates a selective environment in which only those microorganisms, capable of attaching to each other, survive and proliferate.
Eventually the aggregates form into dense compact biofilms referred to as "granules“.
Due to their large particle size (generally ranging from 0.5 to 2 mm in diameter) , the granules resist washout from the reactor, permitting high hydraulic loads.
Contd..
Biofilms are compact allowing for high concentrations of active microorganisms i.e. high organic space loadings.
One gram of granular sludge organic matter (dry weight) can catalyze the conversion of 0.5 to 1 g of COD per day to methane.
i.e. on a daily basis granular sludge can process its own body weight of wastewater substrate.
Anaerobic sludge granules from a UASB reactor treating
effluent
Granular Sludge
Granular sludge (1-3 mm)
The spaghetti theory of granulation
disperse methanogens
Floccule formation via entanglement
Pellet formation ("spaghetti balls")
Mature granules, with attachment of other
anaerobic microorganisms onto
the pellet.
Inside a granule
Top applications of high rate anaerobic reactor systems
Breweries and beverage industry
Distilleries and fermentation industry
Food Industry
Pulp and paper.
Other Applications of high rate digesters
Sulfate reduction for the removal and recovery of heavy metals and sulfur
Denitrification for the removal of nitrates Bioremediation for the breakdown of toxic priority
pollutants to harmless products
USABUpflow anaerobic sludge blanket
• Developed by Dr. Gatze Lettinga & colleagues in1970's at the Wageningen University (The Netherlands).
Working :
Feed passes upwards through an anaerobic sludge bed where the microorganisms in the sludge come into contact with substrates.
Sludge bed is composed of microorganisms that naturally form granules (pellets) of 0.5 to 2 mm diameter
Sludge bed have a high sedimentation velocity i.e. resist wash-out from the system even at high hydraulic loads.
Resulting anaerobic degradation process is responsible for production of biogas.
Contd..
Upward motion of released gas bubbles causes hydraulic turbulence provides reactor mixing without any mechanical parts.
At the top of the reactor, the water phase is separated from sludge solids and gas in a three-phase separator (also known the gas-liquid-solids separator).
Three-phase-separator is commonly a gas cap with a settler situated above it.
Baffles are used to deflect gas to the gas-cap opening.
UASB reactor
Process flow diagram of UASB
Expanded Granular Sludge Bed (EGSB) reactor
Variant UASB concept
Distinguishing feature - faster rate of upward-flow velocity
Increased flux permits partial expansion (fluidization) of the granular sludge bed, improving wastewater-sludge contact & enhancing segregation of small inactive suspended particle from the sludge bed.
Increased flow velocity is either accomplished by utilizing tall reactors, or by incorporating an effluent recycle (or both).
Appropriate for low strength soluble wastewaters (less than 1 to 2 g soluble COD/l) or for wastewaters that contain inert or poorly biodegradable suspended particles which should not be allowed to accumulate in the sludge bed.
Schematic diagram of EGSB reactor
EGSB
EGSB reactor
Buffer tank
Conditioning tank EGSB reactor
Sludge storage
CSTRContinuous Stirred Tank Reactor
• Also known as vat- or backmix reactor. • One or more fluid reagents are introduced into a tank reactor
equipped with an impeller while the reactor effluent is removed.
• Impeller stirs the reagents to ensure proper mixing.
• Simply dividing the volume of the tank by the average volumetric flow rate through the tank gives the residence time, or the average amount of time a discrete quantity of reagent spends inside the tank.
Contd..
• Behavior of a CSTR is often approximated or modeled by that of a Continuous Ideally Stirred-Tank Reactor (CISTR).
• Run at steady state with continuous flow of reactants and products; • Feed assumes a uniform composition throughout the reactor. • Exit stream has the same composition as in the tank.
CSTR
CSRT
Sr.No
Conventional biogas plants High rate anaerobic digesters
1. Suitable for Insoluble wastes (such as particulate and colloidal organics) Also called high-strength wastes.
Suitable for treatment of soluble wastewater. Also called low-strength wastes
2. Require lengthy digestion periods for
hydrolysis and solubilization. Wastewaters do not require hydrolysis and solubilization
3. HRT of at least 10–20 days Much faster rates of treatment are obtained. Have retention time of less than 8 hours.
4. Suspended growth systems are being used for treatment.
Fixed-film systems are being used for treatment.
5. SRT is the same as the HRT Minimal HRT to reduce digester volume and capital costs. Maximal SRT is desired to achieve process stability and minimal sludge production.
One m3 of biogas is equivalent to
0.7 m3 of natural gas,
0.7 kg of fuel oil,
0.6 kg of kerosene,
0.4 kg of benzene,
3.5 kg of firewood,
12 kg of manure
4 kWh of electric energy,
1.5 kg of coal,
0.433 kg of LPG
1.6 kg of CO2
Size of plants, requirement of cattle dung
and estimated cost
Size of plant Quantity of cattle dung
required daily
No. of cattle
heads required Estimated cost*
1 Cubic metre 25 2-3 Rs. 7000/-
2 cubic metre 50 4-6 Rs. 9000/-
3 cubic metre 75 7-9 Rs. 10,500/-
4 cubic metre 100 10-12 Rs. 12,500/-
*The cost is higher by 30 per cent and 50 per cent in hilly areas and North Eastern Region States, respectively.
MNRE
Biogas consumed for different applications
Use Specification Quantity of gas
consumed (m3 /hr)
Cooking
2" burner 0.33
4" burner 0.47
6" burner 0.64
per person per day 0.24 m3/day
Gas lighting mantle lamp of
100 Candle Power 0.13
Duel fuel engine 75-80% replacement
of diesel oil per B.H.P.
0.50
Electricity 1 kWh 0.21
