Biomass gasifiers convert the solid biomass (basically wood waste, agricultural residues, etc.) into a combustible gas mixture, known as producer gas. The conversion efficiency of the gasification process is in the range of 60-70%. The producer gas consists of mainly carbon monoxide, hydrogen, nitrogen gas and methane and has a lower calorific value (1,000-1,200 kcal/Nm3).
The “biomass gasification—electricity generation” system is a technology which converts any kind of biomass energy with low heat value (such as waste from agriculture and forest and organic waste) into combustible gas and then feeds this gas to generator for generation of electrical energy.
Discovery of method of biomass gasification for generation of electrical energy can solve both problems of effective use of renewal energy and environmental pollution from organic waste. That is why the technology of biomass gasification for electricity generation attracts more and more research as well as applications. Thereby, this technology is being continuously optimised.
The model of biomass gasification for electrical energy generation can be realized in Fig. 7.67.
As shown in Fig. 7.67 biomass gasification for electricity generation can be realized in three ways:
1. Fuel gas produced in a biomass gasifier enters directly into a boiler to generate steam, which then drives a steam turbine coupled to an electric generator for generation of electricity.
2. The clean gas drives a gas turbine coupled to an electric generator for generation of electricity.
3. The clean gas drives a gas engine coupled to an electric generator for generation of electricity.
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Above methods of electric energy generation correspond to large-scale, medium-scale and small-scale generation respectively.
Today, commercially successful technologies for biomass gasification for electrical energy generation using gas engines get wide application because of their small system capacity, low investment, compact structure, reliable technique, low operating cost, simple operation and maintenance and their low demand for gas quality.
Electricity Generation System Equipped with a Gas Engine:
Electricity generation system equipped with a gas engine mainly consists of a gasifier, a gas cleaner and gas engine.
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A gasifier is a system that converts solid biomass into combustible gas. Biomass is combusted by way of controlling the flow of air into the gasifier for conversion of solid state into gas state, producing a combustible gas consisting of H2, CO, CH4 and CnHm.
The gas temperature in the outlet of the gasifier is in the range of 350°C as 650°C depending on the type of gasifier. The gas contains impurities like dust and uncracked tar. For reliable operation of gas engine operation over a long period of time, it is necessary to clean the gas at temperatures below 40°C as well as to reduce the content of dust and tar below 50 mg/Nm3. After cleaning the gas is supplied to the gas engine for generation of electrical energy.
In the gas engine, the gas is mixed with air, burns and drives the main shaft to rotate at a high speed. The latter then drives the electric generator to produce electrical energy.
Through above procedure, any waste can be converted into electrical energy, thereby solving the problems of pollution from waste.