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What is biogas?

Introduction: What is biogas exactly?

Biogas is produced by anaerobic digestion (AD) or fermentation of organic matter, including organic fractions of household and industry waste, manure, sewage sludge, energy crops, biodegradable waste in landfills or any other biodegradable feedstock, under anaerobic conditions. In industrialized countries, biogas is produced during anaerobic digestion (AD) of organic substrates in large scale biogas digesters. Biogas is also produced during anaerobic degradation in landfills and is then referred to as landfill gas.

What is biogas?

Anaerobic digester

The biogas mainly contains methane and carbon dioxide, but also small amounts of other gases and trace elements such as hydrogen sulphide, ammonia, siloxanes, oxygen, mercaptans, etc. The gas is usually saturated with water. Biogas valorisation typically occurs in gas turbines or combustion engines coupled to an alternator. A typical power capacity would be 1MW / 500 Nm³/h biogas. Depending on the end use, the source of raw material and the local legal environmental requirements, different biogas treatment steps are necessary.

 

What is biogas: composition

During anaerobic digestion, organic material is broken down in several steps by different types of micro-organisms. The end-products are a gas containing mainly methane and carbon dioxide, referred to as biogas; and a slurry or solid fraction consisting of what is left of the digested substrate, referred to as digestate. The biogas composition and the yield of biogas will depend on the substrate composition used during the anaerobic digestion.

Components

Household waste

Wastewater treatment plants sludge

Agricultural waste

 
CH4 % vol

50-60

60-75

60-75

 
CO2 % vol

30-40

20-30

20-30

 
H2O % vol

6 (at 40 °C)

6 (at 40 °C)

6 (at 40 °C)

 
N2 % vol

0-5

0-1

0-1

 
O2 % vol

<1

< 0,5

< 0,5

 
H2S, Siloxanes, Aromatics,H2, etc.

Balance

Table1 Biogas composition

 

Complete biogas solutions by DESOTEC activated carbon

To increase the quality of the raw biogas, the gas is usually purified of unwanted substances such as hydrogen sulphide, oxygen, nitrogen, water and particulates. The main reason for doing this is to prevent corrosion and mechanical wear of the equipment in which the biogas is used. DESOTEC activated carbon is the leader in the purification of biogas in the agriculture and food industry, landfills and municipal sewage treatment stations.The purification of biogas consists of the removal of hydrogen sulphide and siloxanes compounds from the filtered medium.

Looking for a complete solution for biogas treatment? Be sure to contact us!