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Wednesday, January 27, 2010

Laboratory Scale Bio Gas Plant





STARTING UP A BIO GAS PLANT

POST NUMBER :08   Date : 02/05/2004
BIO GAS PLANT PROCESS DESCRIPTION:

FLOW CHART: CRUSHER(less than 7mm particle size)----thermophilic Aerobic digester(Temp 55 degree C)---Mesophilic Anaerobic Digester(37 Degree C and pH at 7.5)---Manure Pit

Biotechnology process
stage one : hydrolysis by hydrolytic bactaria, conversion of extracellular molecules
stage two : thermophilic fermentation based on carbohydrates
stage three : synthesis of volatile fatty acids by acetogenic bacteria
stage four : synthesis of methane by methanogenic organisms

STARTING UP A BIO GAS PLANT:


OPERATION OF BIO GAS PLANT

FLOW CHART: CRUSHER(less than 7mm particle size)----thermophilic Aerobic digester(Temp 55 degree C  pH  5.5)---Mesophilic Anaerobic Digester(37 Degree C and pH at 7.5)---Manure Pit


Aspect
Bottlenecks
Remarks
CONTROLS
Check for Gas leaks
Check hood , pipe etc. Monthly checking of leakage by pressure system and or with soap water
Cow dung slurry
Make slurry of cow dung and fresh water in the ratio 2kg dung 15 liter water (thumb rule 10% dung of water volume). Fill up the bio digester with the slurry.
Slurry fermentation
Wait for slurry to form gas. It normally takes 3 to ten days.Gas formation can be seen by rising of floating dome or pressure gauge in fixed dome.
Start of Feeding
Start fresh feeding after formation of gas. Start with small quantity of feed material in 1:1 ratio. After 15 days, start feeding full capacity.
Complete Release of first gas produced
Gases should be released to the atmosphere at least three  times at a gap of three days each.
It may be needed to be released more till methane percentage of 60% reached .Do a sample bio gas test to know exact position of gas produced.
Technical
Improper preparation of influent solids
leading to blockage and scum formation
Proper milling and other treatment measures (pre-
soaking, adjustment of C/N ratio); removal of inert
particles: sand and stone.
Temperature fluctuations
Careful regulation of temperature through use of
incorporation of auxiliary solar heating system.
Maintenance of pH for optimal growth of
Methanogenic bacteria
C/N ratio
Appropriate choice of raw material, regulation of
C/N ratio and dilution rate.
Appropriate mixing of N-rich and N-poor
substrates with cellulosic substrates.
Dilution ratio of influent solids content
Appropriate treatment of raw materials to avoid
stratification and scum formation.
Retention time of slurry
Dependent upon dilution ratio, loading rate,
digestion temperature.
Loading rate
Dependent upon digester size, dilution ratio,
digestion temperature.
Seeding of an appropriate bacterial
Population for biogas generation
Development of specific and potent cultures.
Corrosion of gas holder
Construction from cheap materials (glass fibre,
clay, jute-fibre reinforced plastic) and/or regular
cleaning and layering with protective materials
(e.g., lubricating oil).
Pin-hole leakages (digester tank, holder,
inlet, outlet)
Establishment of "no leak" conditions, use of
external protective coating materials (PVC,
creosotes
Occurrence of CO2 reducing calorific
value of biogas
Reduction in CO2 content through passage in
lime-water
Occurrence of water condensate in gas
supply system (blockage, rusting)
Appropriate drainage system using condensate
traps
Occurrence of H2S leading to corrosion
On a village scale, H2S removed by passing over
ferric oxide or iron filings
Improper combustion
Proper air gas  mixing appliances necessary
Maintenance of gas supply at constant
pressure
Regulation of uniform distribution and use of gas;
removal of water condensate from piping systems;
appropriate choice of gas holder in terms of weight
and capacity
Residue
utilization
Risks to health and plant crops resulting
from residual accumulation of toxic materials
and encysted pathogens
Avoid use of chemical industry effluents; more
research on type, nature, and die-off rates of
persisting organisms; minimize long transportation
period of un-dried effluent
Health
Hazards to human health in transporting
night soil and other wastes (gray-water)
Linkage of latrine run-offs into biogas reactors
promotes non-manual operations and general
aesthetics
Safety
Improper handling and storage of methane
Appropriate measures necessary for plant
operation, handling, and storage of biogas through
provision of extension and servicing facilities


DO NOT USE eggshells, Onion peels or left-over bones in this system as they will affect the efficient functioning of the system
Hazards: Methane in a concentration of 6 to 15 percent with air is an explosive mixture. Since it is lighter than air, it will collect in rooftops and other enclosed areas. It is relatively odorless and detection may be difficult. Extreme caution and special safety features are necessary in the digester design and storage tank


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