THE KINETIC STUDTY OF BIOGAS PRODUCTION

Biogas
 Biogas typically refers to a gas produced by the biological breakdown of organic matter in the absence of oxygen. Organic waste such as dead plant and animal material, animal dung, and kitchen waste can be converted into a gaseous fuel called biogas. Biogas originates from biogenic material and is a type of biofuel. Biogas is produced by the anaerobic digestion or fermentation of biodegradable materials such as biomass, manure, sewage, municipal waste, green waste, plant material, and crops.  Biogas comprises primarily methane (CH4) and carbon dioxide (CO)and may have small amounts of hydrogen sulphide (H2S), moisture and siloxanes.The gases methane, hydrogen, and carbon monoxide (CO) can be combusted or oxidized with oxygen. This energy release allows biogas to be used as a fuel. Biogas can be used as a fuel in any country for any heating purpose, such as cooking. It can also be used in anaerobic
digesters where it is typically used in a gas engine to convert the energy in the gas into electricity and heat.  Biogas can be compressed, much like natural gas, and used to power motor vehicles. In the UK, for example, biogas is estimated to have the potential to replace around 17% of vehicle fuel. Biogas is a renewable fuel, so it qualifies for renewable energy subsidies in some parts of the world. Biogas can also be cleaned and upgraded to natural gas standards when it becomes
biomethane. 

OBJECTIVE:

• To arrive proper proportion of the feed materials through kinetic study
• To analyse the gas production for various proportions.

 ANAEROBIC DIGESTION

1.1.Anaerobic digestion definition

Anaerobic digestion is a biological process making it possible to degrade organic matter by producing biogas which is a renewable energy source and a sludge used as fertilizer.

The production of biogas is carried out in the environment in a natural way (e.g. gas of marshes - vegetable and animal matter decomposition where the formation of bubbles at water surface can be observed).

In the absence of oxygen (anaerobic digestion), the organic matter is degraded partially by the combined action of several types of micro-organisms. A succession of biological reactions (see diagram) led to the formation of biogas and sludge.
The bacteria which carry out these reactions exist in natural state in the liquid manure and the anaerobic ecosystems; it is not necessary to add more, they develop naturally in a medium without oxygen.

1.2.Anaerobic Digestion Diagram

1.3.Hydrolysis  

The organic macromolecules break up into simpler elements - solid waste thus is liquefied and hydrolyzed in small soluble molecules (e.g. the cellulose is transformed into soluble sugars such as glucose or cellobiose.

1.4.Acidogenesis

This process transforms these simple molecules into acids of weak molecular weight such as lactic acid and volatile fatty-acids from 2 to 5 carbon atoms. In parallel are produced low-weight molecular alcohol, such as bicarbonate ethanol and molecular hydrogen.

1.5.Acetogenesis 

The products resulting from fermentation require an additional transformation before being able to produce methane. It is here that intervene the acetogenes reducing bacteria and the sulfato-reducing bacteria, producing hydrogen sulphide (H2S)

1.6.Methanogenesis

The ultimate phase during which two types of methanogenes bacteria take over: the first ones (acetogenes) reduce methane acetate, CH4 and bicarbonate. The second ones, reduce methane bicarbonate.

1.7.Advantages of anaerobic digestion

Anaerobic digestion involves a considerable reduction in the organic load, thanks of the biological reactions, and the polluting load of the digested sludge. It is thus, a complete depollution. A correctly controlled anaerobic digestion leads to very high rates of purification.

It also has other advantages:

Economic advantages:

Ø  Additional income 

Ø  Autonomy in heat in a context of increase in the cost of fossil energies

Ø  Diversification of outlets for crops

Ø  Reduction of manure purchase thanks to valorisation of digested sludge

Agronomic advantages

Ø  Transformation of the liquid manure and the manure into a fertilizer, more easily assimilated by the plants, with reduction in the odours and the disease-causing agents

Ø  Organic waste processing for competitive prices

Ø  Insect ellimination at the storage pit 

Ø  Odours supression

Environmental advantages

Ø  Biogas resulting by anaerobic digestion is a source of renewable energy because it replaces fossil energy

Ø  Reduction of pollution due to nitrogen stripping (please refer to the  “Sludge” heading)

Ø  Sustainable management of organic waste

1.2.1BIOGAS COMPOSITION

Biogas is characterized based on its chemical composition and the physical haracteristics which result from it. It is primarily a mixture of methane (CH4) and inert carbonic gas (CO2). However the name “biogas” gathers a large variety of gases resulting from specific treatment processes, starting from various organic waste - industries, animal or domestic origin waste etc

1.2.2Chemical composition

Different sources of production lead to different specific compositions. The presence of H2S, of CO2 and water make biogas very corrosive and require the use of adapted materials. The composition of a gas issued from a digester depends on the substrate, of its organic matter load, and the feeding rate of the digester

Components	Household waste	Wastewater treatment plants sludge	Agricultural wastes	Waste of agrifood industry
CH4 % vol	50-60	60-75	60-75	68
CO2 % vol	38-34	33-19	33-19	26
N2 % vol	5-0	1-0	1-0	-
O2  % vol	1-0	< 0,5	< 0,5	-
H2O % vol	6 (à 40 ° C)	6 (à 40 ° C)	6 (à 40 ° C)	6 (à 40 ° C)
Total % vol	100	100	100	100
H2S mg/m3	100 – 900	1000 - 4000	3000 – 10 000	400
NH3 mg/m3	-	-	50 - 100	-
Aromatic mg/m3	0 – 200	-	-	-
Organochlorinated  or organofluorated  mg/m3	100-800	-	-

1.2.3. Physical characteristics

According to its composition, biogas presents characteristics interesting to compare with natural gas and propane. Biogas is a gas appreciably lighter than air, it produces twice as less calories by combustion with equal volume of natural gas.

Types of gas	Biogas 1 Household waste	Biogas 2 Agrifood industry	Natural gas
Composition	60% CH4 33% CO2 1% N2 0% O2 6%                   H2O	68% CH4 26% CO2 1% N2 0% O2 5 %                           H2O	97,0% CH4 2,2% C2 0,3% C3 0,1% C4+ 0,4%                               N2
PCS kWh/m3	6,6	7,5	11,3
PCI kWh/m3	6,0	6,8	10,3
Density	0,93	0,85	0,57
Mass (kg/m3)	1,21	1,11	0,73
Indiex of Wobbe	6,9	8,1	14,9

BIOGAS MEASUREMENT TO TAKE MINI DIGESTER

digester model
 

BIOGAS MEASUREMENT FOR ROOM TEMPERATURE 

 

mini digester

MY PROJECT METHODLOGY

• Identification of feed stocks,
• Feeding the digester,
• Measurement of gas- Gas analyses or water displacement method,
• Feeding with various proportions, varying organic loading rate and varying hydraulic retention  time,
• Gas measurement,
• Identification of optimum proportion through above analysis.
  
  FEEDING PROCEDURE 
  • The ratio cow dung feeding:- 1:1
  • Per day 250 gms cow dung, 250ml water
  • The staring of cow dung feeding- 07/02/2012
  • The cow dung feeding for 5 days