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Biomass Gasification Gas, refers to the combustible gas produced in a gasifier by means of thermochemical and redox reactions under high temperature and limited oxygen or gasification agent conditions with biomass as raw material. Common biomass materials such as agricultural & forestry waste, municipal refuse and other be collected, crushed, and pressed into blocks to produce gasification gas at high temperatures in a gasifier.
The biomass gasification gas includes woody gasification gas formed by gasification of wood chips, shrubs, sawdust, cotton stalks, etc., fruit shell gas, straw gas, rice husk gas, municipal refuse gas, and the like of these.
Biomass gasification technology is suitable for conversion of wood processing waste and hard raw materials such as rice husk and cotton stalk. Compared with the adaptability of raw material of anaerobic fermentation technology, it can be found that there are obvious differences between biomass gasification technology and anaerobic fermentation technology in the adaptability of raw materials. The biomass which is not suitable for anaerobic fermentation treatment is just suitable for the fuel of gasification equipment.
Gasifier is the main equipment of biomass gasification reaction. According to the operation mode of gasifier, it can be divided into three types: Fixed bed, Fluidized bed and Rotating packed bed. At present, the main gasifiers used in biomass gasification process are fixed bed gasifier and fluidized bed gasifier. Gasifiers are widely used for gasification, heating and power generation of various agricultural and forestry waste, straw, rice husks, peat, coal powder and municipal solid waste. The heat value of a single system is 5 - 20 MJ, and the power generation capacity is 100 kW-2 MW. Gasifier well solved the environmental problem.
The biomass pyrolysis or gasification produces crude gas, which needs to undergo purification treatment such as dust removal, coke removal, desulfurization, and component adjustment before use to obtain high-quality synthesis gas. Can be used as an ideal fuel for power generation. The different methods or reaction conditions (raw materials, temperature, gasification medium, etc.) of biomass gasification result in significant differences in product composition and application directions.
Fluidized bed gasification system
Fixed Bed Gasification system
Biomass gasification needs to be carried out with limited oxygen or gasification agents (such as air, oxygen, water vapor, CO₂, etc.), relying on partial oxidation-reduction reactions to generate H₂ and CO. Its calorific value is significantly affected by the type of gasification agent and process conditions:
1. Using circulating fluidized bed gasification technology, the gas calorific value can exceed 5.0 MJ/m³, and the gasification efficiency can reach over 78%. In fluidized bed gasification process, The content of gasification components: CO: 12.57%, H₂: 14.0%, CH₄: 6.0%, N₂: 62.22% (Dry gas mole fraction).
2. When using air as a gasifying agent, the resulting gas is a low calorific value gas, with a calorific value generally between 4.2 - 7.56 MJ/m³ (i.e. 4200 - 7560 kJ/m³). The content of gasification components: CO: 15% - 20%, H₂: 10% - 18%, CH₄: 1% - 3%, N₂: more than 50% (dilution effect leads to lower calorific value, about 5 MJ/m³).
3. If high-efficiency gasifying agents such as oxygen or water vapor are used, it can generate gas with a medium calorific value (10.92-18.9 MJ/m³)，among which components of oxygen gasification: CO: 25% - 30%, H₂: 20% - 25%, CH₄: 5% - 8%, CO₂: 5% - 10%, N₂ almost non-existent, calorific value 13 - 16 MJ/m³. The components of steam gasification: H₂: 20% - 26%, CO: 28% - 42%, CH₄: 10% - 20%, with a calorific value of up to 17 - 21 MJ/m³, close to urban gas.
This gas can also be treated through processes such as purification, dust removal, tar removal, reforming, and water-gas reaction to obtain a gas mainly composed of CO and H₂, known as biosyntgas.
Gas requirement of Biomass Gas：
● Calorific value ≥ 4.0 MJ/Nm³; Gas temperature ≤ 40 ℃.
● Gas pressure 2.5～10 kPa; Pressure change rate ≤ 1 kPa/min.
● Hydrogen content (H₂ Volume) ≤ 50%; Oxygen content (O₂ Volume) ≤ 1%.
● Moisture content ≤ 40 g/Nm³, no free water.
● Impurity content ≤ 30 mg/Nm³; Impurity size ≤ 5 μm.
● Tar content ≤ 50 mg/Nm³.
● H₂S ≤ 50 mg/Nm³; Total sulfur content ≤ 100 mg/Nm³.
● NH₃ ≤ 20 mg/Nm³; Cl content ≤ 50 mg/Nm³.
