What is biogas?

Biogas

When decomposing organic matter, a mixture of gasses is produced that we refer to as biogas. It is produced in the absence of oxygen and consists of methane, carbon dioxide and usually contains hydrogen sulfide. The gas may also have small amounts of moisture and siloxanes. Biogas can be used as a renewable energy source.

Feedstock

Organic matter typically is processed in an anaerobic digester, a closed system that digests raw materials such as agricultural waste, manure, organic waste, municipal waste, waste from a WWTP or waste from the food processing industry. Biogas produced at a landfill is referred to as landfill gas and can be used in the same way as biogas. In other words, a fermentation process that breaks down organic matter, turning waste into a renewable energy source.

Renewable Energy Source

Untreated biogas containing methane (CH₄), Hydrogen Sulfide (H₂S), and carbon monoxide (CO) can be combusted or oxidized with oxygen. This energy release allows biogas to be used as a fuel; it can be used for any heating purpose. Raw biogas can be used in gas engines and convert energy in the gas into electricity and heat.

Upgrading the raw biogas leads to higher efficiency of the gas. Components such as carbon dioxide and the traces of Hydrogen Sulfide and sometimes siloxanes are removed to purify the gas consisting mostly of pure CH₄, biomethane. If the biogas is upgraded to biomethane, it can be used as a replacement for its fossil counterpart natural gas. It now can be used for cooking, heating and when compressed to CNG as a vehicle fuel.

Stages of biomethane production

1. Organic matter such as agricultural waste, slurry or organic waste, is mixed into a slurry and prepared for digestion. Adding liquid to the biowaste, the feedstock, will make it easier to process into a slurry that is then fed into a digester.
2. An anearobic digester needs to be in perfect condition to function and process the slurry. Bacteria, microbes, need warm conditions, therefore the biowaste is heated to about 37 °C.
3. Biogas is produced through anaerobic digestion in large tanks. A fermentation process processing the organic matter, and takes about three weeks.
4. In the last stage, the gas that is produced during in the anearobic digester, is purified (upgraded) by removing the impurities such as carbon dioxide and hydrogen sulfide.

Biogas upgrading

Upgraded biogas is also referred to as biomethane or renewable natural gas. Both indicate the same product and are a perfect replacement for the fossil fuel natural gas. Biomethane or Renewable Natural gas can also be used as vehicle fuel. Biogas that is cleaned and upgraded, H2S and CO2 are removed, and it is compressed to 200 bar. Biomethane that is used as vehicle fuel is referred to as CNG, Compressed Natural Gas, or Bio-CNG when the original source of the gas is (organic) waste.Biogas Upgrading in your industryBiogas Ugprading references