The new biomass hot blast stove is composed of furnace body, air duct and settling chamber (its working process is that after the biomass on fixed grate is burned once in the furnace, unburned carbon particles and combustible gases enter the secondary combustion chamber with high temperature flue gas for secondary combustion. The high temperature flue gas after combustion is dedusting through the settling chamber for drying equipment. 1.1 Clean biomass combustion technology at present, most drying biomass hot stoves in China use biomass (bark, waste wood, etc.) as fuel. Biomass generally has the characteristics of high water content, large fuel size and high ash content. In addition, the non-uniform distribution of air, incomplete combustion of fuel and low thermal efficiency of hot blast stove cause serious environmental pollution.
Practice has proved that the stoker furnace is suitable for biomass with high moisture content, large fuel size and high ash content. Therefore, when designing the grate, it is necessary to ensure the uniform distribution of fuel, and the ash layer can cover the entire grate surface. In addition, another important technology of staged combustion furnace is staged combustion. It divides the combustion area into primary combustion chamber and secondary combustion chamber, separates the gasification and oxidation stages, and avoids premature mixing of secondary air. In order to reduce the disorder and maintain the stability of the fuel layer above the grate, the air and flue gas are not fully mixed in the primary combustor. The structure of the secondary combustor and the injection mode of the secondary air should ensure the good mixing of the flue gas and the secondary air as far as possible. The more fully the flue gas is mixed with the secondary air, the smaller the excess air coefficient required for complete combustion and the higher the efficiency. At the same time, secondary air is injected at a higher speed, and the mixing effect is good. It is better to use cyclone in combustion chamber to achieve full mixing.
1.2生物质热风炉的结构和特点 生物质热风炉设计必须采用适合于生物质燃料的结构和措施。在设计中采用逆流燃烧方式,即燃烧火焰方向与进料方向相反,这种燃烧方式使热烟气流经过湿燃料表面,促进了燃料的干燥和水蒸气输送,使燃料易于着火。同时二次风以较高的速度沿着圆形炉墙切向喷入,旋风保证烟气和二次空气良好的混合,延长了未燃尽碳粒在炉膛的滞留时间。在炉膛后部设置副燃烧室,使炉膛内未燃尽碳粒和可燃气体完全燃烧,减少了高温缺氧不完全燃烧所产生的黑烟。燃烧后的高温烟气在经过沉降室来进一步捕捉烟尘,降低了烟气中的含尘量。在配风方面,由于热风炉后部配有引风机,炉膛燃烧方式为微负压燃烧,一次空气通过炉排下的炉渣室吸入,二次空气通过高压鼓风机沿两侧风管切向喷入炉膛。这样既有效地控制强风将炉排上的飞灰和未燃尽的碳粒吹走,又保证了生物质燃料完全燃烧所必须的大量空气。 由于上述技术和措施,所设计的热风炉燃烧效率明显提高,燃料的消耗量与常规热风炉相比节约10%左右,而且冒黑烟的频率明显减少,达到了洁净 燃烧的目的 。
1.2 The structure and characteristics of biomass hot blast stove The structure and measures suitable for biomass fuel must be adopted in the design of biomass hot blast stove. In the design, counter-current combustion mode is adopted, that is, the direction of combustion flame is opposite to the direction of feed. This combustion mode makes hot smoke flow through the surface of wet fuel, promotes fuel drying and water vapor transportation, and makes fuel easy to ignite. At the same time, secondary air is injected tangentially along the circular furnace wall at a higher speed. The cyclone ensures a good mixing of flue gas and secondary air, and prolongs the retention time of unburned carbon particles in the furnace. A secondary combustion chamber is installed at the rear of the furnace to make the unburned carbon particles and combustible gases completely burn in the furnace, thus reducing the black smoke produced by incomplete combustion under high temperature and anoxia. The high temperature flue gas after combustion is further captured by the settling chamber to reduce the dust content in the flue gas. In the aspect of air distribution, as the back of the hot blast stove is equipped with induced draft fan, the combustion mode of the furnace is micro-negative pressure combustion. The primary air is inhaled through the slag chamber under the grate, and the secondary air is injected tangentially into the furnace along both sides of the air duct through the high-pressure blower. In this way, not only the fly ash and unburned carbon particles on the grate are effectively controlled by strong wind, but also the large amount of air necessary for the complete combustion of biomass fuel is guaranteed. As a result of the above technology and measures, the combustion efficiency of the designed hot blast stove is obviously improved, the fuel consumption is about 10% less than that of the conventional hot blast stove, and the frequency of black smoke is obviously reduced, thus achieving the goal of clean combustion.
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