Biomass energy is mainly used by direct combustion, gasification, liquefaction and anaerobic fermentation. Because of its high volatile content, high carbon activity, low emission pollution and other characteristics, it is particularly suitable for combustion conversion and utilization, and is a kind of high-quality fuel. Compared with the more mature pressed molded biomass fuel, the biomass powder fuel has a great potential in the development and utilization of biomass energy due to its simple production process, low processing energy consumption and high combustion efficiency.
China started relatively late in biomass suspended combustion, and the theoretical and applied research on biomass suspended combustion is still in its infancy. Xiao Bo et al. proposed a biomass powder three-stage combustion model, based on which a special combustion furnace was designed. After the agricultural waste was broken into powder, it was directly sprayed into the combustion experimental furnace developed. The combustion characteristics of the material powder were studied. In view of common crop straw powder, the biomass suspended combustion characteristics experiment was carried out on the new biomass powder burner to study the influence of temperature distribution, fuel feed amount, ratio of primary and secondary air and particle size in the pre-combustion chamber burner on furnace temperature and flue gas emission.
Influence of fuel feed
The feed amount of powder fuel is controlled by the speed of feed screw regulated by frequency converter. The higher the rotating speed of feed screw, the more feed amount. The volatile content of biomass powder fuel is relatively high, and it is pyrolyzed out in the pre-combustion chamber. The combustion in the boiler is similar to that of gas, so the control of feed amount is very important. As the amount of powder fuel volatilization in the precombustion chamber increases, the combustion intensifies, and the temperature of the precombustion chamber rises rapidly, the high temperature in the precombustion chamber accelerates the volatilization and combustion speed of the fuel, so that the fuel is mainly burned in the precombustion chamber rather than in the furnace, thus reducing the thermal efficiency Rate.
The influence of the ratio of primary and secondary air
Secondary air can not only to supplement a wind, also can be adjusted to precombustion chamber air flow and secondary air through the guide vane cyclone into the precombustion chamber, a mixture of air and the powder fuel in precombustion indoor spiral forward, on the burning torch vents form, increase the powder out of fuel in a precombustion chamber volatile analysis, make the combustion more fully. When the ratio of primary and secondary air is large, the secondary air volume is small, the mixing of air and powder fuel in the furnace is not sufficient, and the combustion is not complete, CO Higher in content.
Influence of particle size
Fuel with small particle size can be heated rapidly, releasing volatiles earlier than fuel with large particle size. Reducing the particle size of biomass powder can effectively improve the combustion performance of biomass powder fuel, but the smaller the particle size of biomass powder is not the better. The particle size of biomass powder is too small, which easily leads to complete combustion of fuel before it enters the furnace. Excessive particle size of biomass powder delays the volatilization and combustion of fuel, making the combustion reaction move to the outlet position of furnace, leading to the discharge of volatiles and carbon particles before complete combustion, and increasing the content of volatiles and CO in the flue gas. The swirl design of the precombustion chamber increases the fuel combustion distance, which can appropriately relax the particle size requirements, on the one hand reduce the cost of grinding, on the other hand improve the safety problems in the grinding process.
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