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