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Biogas refers to the combustible gas produced by organic matter through microbial fermentation under anaerobic conditions. It is a mixed combustible gas produced by the decomposition and transformation of straw, mushroom residue, livestock manure, domestic refuse, sewage sludge and other organic substances under anaerobic (in the absence of oxygen) conditions in a sealed biogas pool. The main components of biogas are methane (CH4) and carbon dioxide (CO2), which are colorless and odorless and will burn when mixed with appropriate amount of air. It is an ideal gas fuel.
Popular biogas fuels mainly include bio gas such as gas produced by straw and mushroom residue, etc.; sewage gas such as gas produced by sewage & sludge, livestock manure and food waste, etc.; and landfill gas, etc.
Although various kinds of raw lignocellulosic materials such as straw and aquatic plants can be treated by anaerobic fermentation technology from the theoretical point of view, however, from the technical and economic point of view, anaerobic fermentation technology is not suitable for treating raw materials of high lignin content, such as cotton stalk, wood processing waste and so on.
Biogas power plant
Biogas tanks
The composition of biogas is composed of CH4 (content of 50% - 70%), CO2 (content of 25% - 40%), N2 (content of 0% - 5%), H2 (content of less than 1%), O2 (content of less than 0.4%,), and H2S (content of 0.1% - 3%). Because biogas contains a small amount of H2S, it smells slightly odorous. Its characteristics are similar to natural gas. If the air contains 8.6-20.8% of CH4, explosive gas mixtures will be formed.
The calorific value of biogas is about 20.8-23.6 MJ/m³, that is when 1 m³ of CH4 is completely burned, it can produce heat equivalent to 0.7 kg of anthracite. Compared with other gases, it is a good clean fuel with better explosion resistance.
Landfill gas (LFG) refers to the combustible gas produced by the decomposition of organic matter in the garbage under the action of microorganisms after landfill. The main components of landfill gas are CH4 and CO2, and the other components are N2, O2, HN3, H2S and H2, etc., of which CH4 content is about 35-60% and CO2 20-45%. It has calorific value of about 20 MJ / Nm³, and it is a clean fuel with high utilization value.
China has the characteristics of large capacity, simple and practical technology, high organic matter content and high gas production rate for handling of municipal solid waste landfill. About 300 Nm³ landfill gas can be produced per ton of landfill gas, which can generate economic benefits by generating and contributing electricity to the grid. At the same time, the recycle heat resources are fully utilized to realize recycle generation and improve the comprehensive utilization efficiency of energy. The government actively encourages and advocates greatly landfill gas utilization to power generation for industry development.
Gas requirement of Biogas：
● Gas temperature ≤ 40 ℃. ● Gas pressure 2.5～10 kPa. ● Methane content ≥ 50%. ● Pressure change rate ≤ 1 kPa/min. ● Moisture content ≤ 40 g/Nm³, no free water. ● Sulfur content ≤ 200 mg/Nm³. ● NH3 ≤ 20 mg/Nm³.
● Impurity content ≤ 30 mg/Nm³. ● Impurity size ≤ 5 μm.
