Power generation by using biomass gas from rice husk, wood chips ,saw dust and crop stalks can not only save expenditure in electricity tariff in the production cost of rice mills and timber processing mills, but also can bring about benefits by means of selling surplus electric power to the power grid. As the higher conversion efficiency of the equipment, by taking rice husk as an example, every kwh power generation consumes only 1.6~1.8kg if rice husk. If using wood dust or crop stalks as fuel, the unit consumption of the fuel will be still lower. Water used for gas cleaning and cooling can be used in a circulating way after it is treated through water treatment facilities such as a sediment pond without environmental pollution and with need only some amount of making-up water. The water porn for each unit of 200kw generator covers only an area of about 50m² .The engines and generator, electrical equipment should be arranged indoor, but other equipment can be arranged outdoor. The area of building for each 200kw generator unit is approximately 40~50m². The rate of self use power for the complete set of equipment is very low-only 5~8% of the generated power. Therefore, such a project is an ideal one with significant benefits for the area where there is a lot of discarded biomass resources but is short of electric power supply or with higher electricity tariff. In general, the investment for major equipment can be recovered from power generation benefits within first tow years. The equipment can be safety and reliable operated with operational technology easy to be mastered by workers and the maintenance and repair work of the equipment are similar as for ordinary diesel generators.

2. Efficiency of purification

In normal pressure, biomass pyrolysis gasification has different production ratio of tar for different operation temperature. If carbonization temperature is 400-600, the production ratio of tar is 13%~37%, and it is 5%~15% when use fixed bed gasification furnace. When operation temperature is 800, the production ratio in fluid bed gasifying furnace is about 2.5%. Tar content in rough gas without treatment is about 1~3mg/Nm3. Gas must be condensed to remove tar before it is send to internal combustion engine. As is well know, the caloricity of tar is very high and it is about 30MJ/kg. The caloricity of tar make up of 10% of total caloricity of gas. It is good if we can crack the tar into low molecular gas and make full use of it, but this idea is not suitable to medium and small scale power station because its high investment and complex operation.

Standard of 50mg/m3 is the highest allowable norm the internal combustion engine manufacturer gives. (If adopt this standard, the maintenance work of the engine will be heavy. Inlet valve casing should be cleaned once a week and engine oil should be replaced once a month. ) The internal engine manufacturer also opposes other requirement: dust content ≤20mg/m3; H2S≤10mg/m3.

The impurity content is the total content combined with dust and tar. In fact, minim dust cant be separated from tar. In rated power, according to our practically test, the content of tar and dust is under 23mg/m3.