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The Biogas


Biogas composition

CH4

Biogas is characterized based on its chemical composition and the physical characteristics 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

Chemical 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 ( 40 C) 6 ( 40 C) 6 ( 40 C) 6 ( 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 - -

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




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2009 Naskeo Environnement