Thursday, March 6, 2014

Utilization And Properties Of Biogas

Biogas has many energy utilisations, depending on the nature of the biogas source and the local demand. Generally, biogas can be used for heat production by direct combustion, electricity production by fuel cells or micro-turbines, CHP generation or as vehicle fuel.

Figure bellow shows end uses of biogass.




Properties of biogas


The energy content of biogas from anaerobic digestion is chemically bounded in methane. The composition and properties of biogas varies to some degree depending on feedstock types, digestion systems, temperature.

Table 1 show average composition of biogas.


Compound Chemical symbol Content [%]
Methane CH4 50-75
Carbon dioxide CO2 25-45
Water vapor H2O 2-7
Oxygen O2 <2
Nitrogen N2 <2
Ammonia NH3 <1
Hydrogen H2 <1
Hydrogen sulphide H2S <1


The biochemical composition of different feedstock types varies is determinant for their theoretical methane yield. You can see value in table 2.


Substrate Liter gas/kg TS CH4 [%] CO2 [%]
Raw protein 700 70 – 71 29 – 30
Raw fat 1200 – 1250 67 – 68 32 – 33
Carbohydrates 790 – 800 50 50


Methane yield production from common household waste in table 3.


Item Biogas yield [m^3/t]
Pasta 667
Oil and fat 600
Old bread 486
Vegetable oil 400
Kitchen waste 220
Grass 103
Waste from potatoes 68


The methane yield of the anaerobic digestion substrates depends on the content of proteins, fats, and carbohydrates. You can see values in table 4.


Feedstock Methane yield [%] Biogas yield [m^3/tFF]
Liquid cattle manure 60 25-45
Liquid pig manure 65 28
Distillers grains with solubles 61 40
Cattle manure 60 45
Ping manure 60 60
Poultry manure 60 80
Beet 53 88
Organic waste 61 100
Sweet sorghum 54 108
Forage beet 51 111
Grass silage 54 172
Corn silage 52 202


References:
Biogas Handbook, Teodorita Al Seadi, Dominik Rutz, Heinz Prassl, Michael Köttner, Tobias Finsterwalder, Silke Volk, Rainer Janssen. ISBN 978-87-992962-0-0
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