With the increasing shortage of fossil fuels and the pollution problems caused by their use, people pay more and more attention to the development and utilization of biomass energy. This paper introduces the characteristics of biomass fuels, compression molding, gasification and continuous carbonization Technology and other energy-saving technologies. Advocate to seek for a new model of biomass resource system suitable for the characteristics of the region, popularize and improve the rural fuel structure and improve the quality of life of farmers.
introduction
Biomass energy refers to the energy sourced from biomass such as wood, straw and animal excrement. Unlike fossil fuels, they come from newly surviving organisms that can be directly burned for energy or biomass fuels. Because of its recyclability, it is considered to be an important source of future energy and chemical fuels, accounting for about two-thirds of all renewable energy in the world. China is a big agricultural country with very rich biomass resources. Only the biomass fuel produced in rural areas can be converted into 217 × 108t standard coal per year, accounting for about 40% of the total energy consumption in rural areas. However, the proportion of biomass energy used in China's commercial energy structure is very small. It is mainly used as primary energy in rural areas, most of which is directly burned or discarded as fuel, has low utilization level, causes serious waste and pollutes the environment, Development, systematic and reasonable application of biomass energy is of great significance to improving the energy utilization environment in rural areas of our country and increasing the high-grade utilization of biomass energy.
1 Biomass fuel characteristics
1) Low carbon content, the maximum carbon content of biomass fuels will not exceed 50%, equivalent to the carbon content of lignite. In particular, the content of fixed carbon is obviously less than that of coal, so the fuel has a short combustion time and a relatively low energy density.
2) Volatile and more, the majority of carbon in the fuel and hydrogen into the lower molecular weight hydrocarbons, met the volatile easily decomposed volatile matter contained in the volatile energy accounted for more than half of all its energy, if the combustion is not Fully produce black smoke pollutes the environment.
3) More oxygen content makes the biomass flammable and does not require too much oxygen supply.
4) The density of biomass fuel is small, it is relatively easy to burn out, and the residual carbon in ash is small, but the transportation of fuel is unfavorable.
Similar to the combustion of coal, the combustion process of biomass fuels can be divided into four stages: preheating, drying, volatile precipitation and coke combustion. Thermal decomposition starts at 250 ° C, and volatilization at 325 ° C can precipitate nearly 80%. Volatile precipitation time is very short, if the lack of ventilation, volatiles may not be completely ruled out, will produce black smoke or even thick yellow smoke. Volatile combustion, the fuel remaining loose coke, air movement will be part of the carbon particles wrapped in the flue, the formation of black floc, so if the ventilation is too strong will reduce the combustion efficiency. Fixed carbon burning by the air more difficult to penetrate the impact of ash, carbon residue easily left.
2 biomass compression molding
Biomass fuels have the problem of excessive volatilization during direct combustion, difficulty in controlling air supply, and the like.
These problems are not easily solved in the general stove, villagers also use poor control. In order to improve this kind of problem, it will be scattered and light in shape, difficult to store and transport, and the inconvenient biomass fuel is compressed and used after being shaped to increase the calorific value of the fuel and improve the combustion performance. This technology is called biomass compression molding technology. In the 1980s, this technology was greatly expanded.
As shown above for the biomass compression molding process flow chart. In rural areas, straw, rice husk and other biomass resources are abundant. During the collection process, soil entrainment is reduced as much as possible to prevent slagging during combustion. Conditions permit the use of mechanized collection. Crushing is the basic treatment of the material before compression molding, only small size materials such as rice husk can be removed only by large foreign objects. For large size agricultural and forestry waste such as straw, the crushing operation is usually performed twice or more Crushed, generally first sliced ​​into small pieces and then crushed with a hammer mill.
The raw material is crushed to have a dehydration process, commonly used equipment rotary drum dryer and vertical air dryer, the best humidity control at 10% -15%, moisture content reached the molding requirements of the range of transport to the next process.
In order to increase productivity, the propeller "feed" before the loose material preload, and then pushed to the front of the molding. Multi-use pre-spiral propeller, hydraulic thrusters, but also hand pre-pressure, the production scale can be selected according to the production. Compression in the "mold" is the key raw material forming, it was before the small cone after the material into the main thrust, friction and the mold to the heart of the reaction force of three kinds of force, the mold is divided into internal and external mold Die, the same model, the model can be changed, the angle generally start debugging from 3 °.
On the one hand, the heating in the compression molding process can soften the lignin contained in the raw material and play a role of bonding; on the other hand, the raw material itself can be softened and easily compressed. Or adding a binder, for example adding 10% -20% of coal powder or carbon powder can increase the heat value of the briquette, and adding a binder can increase the binding force for molding. Prototypes are made within a section of the sleeve after the biomass has been formed and have an inner diameter slightly larger than the smallest part diameter of the compression molding in order to relieve part of the stress on the formed material and to retain the shape as the temperature decreases. Finally, cutting, packaging and transportation to the user. Biomass compression molding fuel can be widely used in various types of home heating, hot water boiler, hot stove and small power generation equipment, is a good alternative to coal.
3 biomass thermal chemical conversion
With the progress of mankind and the development of society, people demand more and more energy. The quality is getting higher and higher. The utilization of biomass energy also changes the traditional direct combustion mode. First, it is converted into high-grade energy , Then use it again. The most recent development of new technologies in conversion technology are mainly gasification technology and carbonization technology.
3.1 gasification technology
Biomass gasification is a technique of thermochemical conversion of biomass, which heats the raw materials under incomplete combustion conditions, cleaves the higher molecular weight organic hydrocarbon chains into CO, H2, CH4 Combustible gas, in the conversion process to add gasification agent. Straw, rice husk, firewood and other agricultural waste gasification use of high calorific value. It is estimated that direct combustion can only use 20% of its calorific value, which not only caused a tremendous waste of resources, but also incineration of the smoke caused serious pollution to the atmosphere; if it is placed in the gasifier combustion, then The utilization of calorific value can be raised to more than 80%. The uniform control of the supply of air by the machinery can make the combustion be full and the soot discharge is small and the residual ashes are few (less than 7%), which is higher than that of the general farm direct combustion calorific value Utilization rate can be increased by more than 60%.
The basic principle of the gasifier is that the hot steam and the oxygen react with the material, the reaction temperature is from several hundred degrees to nearly thousand degrees and the pressure is from 1 to 30 atmospheres. At the beginning of the process, the volatiles were released leaving charcoal, which reacted with the hot steam oxygen and eventually produced the "producer gas" containing mainly carbon monoxide and hydrogen with small amounts of methane, hydrocarbons and Coalesced tar, and of course carbon dioxide and water. Next, clean the gas and separate it for use. If this process uses air, then the gas also contains nitrogen, the final value of the low heat value of the gas 3-5MJ / m3. If you use pure oxygen calorific value will be increased. It is recommended to use compressed biomass fuels to increase the calorific value of the gas.
3.2 biomass distillation gas
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