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1、哈尔滨工业大学工学硕士学位论文 - I - 摘 要 生物质作为一种可再生的环保能源，其利用在世界范围内正起到越来越重 要的作用。由于炉排炉适应性强，可以焚烧不同水分含量的燃料并且很少需要 对燃料进行预处理，故炉排炉在生物质直燃获取热能和动力领域内是一种颇具 竞争力的技术。 在计算流体力学（CFD）软件 PHOENICS 和 FLUENT 平台上，分别模拟 生物质炉排炉内炉排上燃烧及稀相空间的燃烧并进行耦合。计算中燃料层的燃 烧采用一维非稳态模型获取从燃料层向稀相空间逸出的气体温度、速度和各成 分浓度分布；稀相空间使用床层模型的输出作为边界条件进行稀相空间气相混 合和燃烧的 CFD 数值模拟，
2、包括飞灰颗粒在稀相空间的燃尽， 提供稀相空间中 火焰和壁面向燃料层的辐射热流密度。重复以上两个步骤直至前后两次计算之 间逸出床层的可燃气体以及燃料层表面辐射热流密度的变化控制在允许范围内 为止。 在床层模拟中添加 NO x 前驱产物生成模块，获得沿床层方向生物质燃料层 逸出气体中 NO、 HCN 等 NO x 前驱产物浓度分布， 并使用 FLUENT 自带的 NO x 后处理模块模拟了稀相空间中 NO x 前驱产物的转换， 得出结论： NO 生成的主 要区域是在炉排前半部分燃料层表面；通过空气分级技术合理布置富氧和贫氧 区域，抑制 HCN 氧化为 NO，促进其还原 NO 生成 N 2 ；可以最
3、大限度的减少 NO 排放。 在生物质炉排炉耦合数值模拟模型的基础上， 进行一 25MW 生物质水冷往 复炉排炉膛几何结构设计及配风设计，研究炉膛几何结构及配风对生物质炉排 炉燃烧特性的影响，得到了炉膛内温度、速度、烟气成分分布。数值模拟结果 表明：动量合成法设计的炉膛不适合生物质锅炉；生物质锅炉宜采用较高、较 短的后拱；后拱倾角在 40到 50之间变化时，对炉内生物质燃烧的影响不大； 后拱二次风下倾角度取 20时，下炉膛火焰中心位置适中；后拱下方回旋区域 较大，延长可燃气体和飞灰行程，形成稳定的高温燃烧区，促进飞灰和底灰残 炭的燃尽；还可以形成较大范围的贫氧区，降低 NO 排放。采用先进的燃尽
4、风 布置方式如“ 双旋流” 布置，有助于提高上部炉膛火焰充满度，均匀屏区和炉膛 出口的烟气温度；下部炉膛增设循环风有助于降低下部炉膛的温度水平，延缓 下部炉膛尤其是喉口处的结渣；改善烟气的混合，促进可燃物的燃尽。再循环 百分数在合理范围内的再循环烟气还可以降低 NO 排放。循环风通入位置对锅 炉燃烧工况有重要作用，因后拱二次风通入的地方正是水冷壁热负荷较大的区哈尔滨工业大学工学硕士学位论文 - II - 域，所以循环风布置在此处有助于降低此处的结渣，保护后拱二次风喷口。本 文还采用不同入炉燃料后对炉排炉内燃烧进行耦合模拟，得到的结论是：燃料 中灰分和水分的变化会对锅炉内燃烧工况产生影响，所设计
5、炉膛对燃料变化具 有一定的适应性。 关键词：生物质；层燃炉；数值模拟 哈尔滨工业大学工学硕士学位论文 - III - Abstract As a renewable energy sources, biomass plays an increasingly important role worldwide. Grate firing is one of the main technologies that are currently used in biomass combustion for heat and power production. Grate-fired boilers can
6、 fire a wide range of fuels of varying moisture content and show great potential in biomass combustion. Computational fluid dynamics (CFD) software platform such as PHOENICS and FLUENT are used to simulate biomass grate-firing, include modeling of biomass conversion in the fuel bed on the grate and
7、CFD modeling of mixing and combustion in the freeboard. Calculation of biomass conversion in the fuel bed on the grate are brought out by developing a 1-D bed model, providing the inlet conditions (e.g., distribution of gas species concentration, velocity, and temperature along the grate) for freebo
8、ard simulation; while the freeboard simulation returns the heat flux released from the flame and furnace walls onto the fuel layer to the bed model. The two simulations iterate again and again, until convergence criteria are reached. Module which can forecast the release of the NO xprecursors from t
9、he fuel bed is added in the bed model, obtaining the distribution of the NO xprecursors such as NO and HCN along the fuel bed, which are used as the grate inlet boundary conditions. NO xpostprocessor included in FLUENT is used for the CFD modeling of NO xformation in the freeboard. Results indicates
10、 that NO xmainly formed in the front-bottom part; the advanced air staged combustion process which forms appropriate local air-rich environment and anaerobic environment, can suppress the chemical process during which HCN is oxidized to NO, and promote the de-NO xprocess in which HCN can react with
11、NO to form N 2 . The advanced air staged combustion generates a considerable improvement in a big NO xreduction. Biomass grate-firing combined model is used to design the geometric structure and the air supply of a 25MW biomass boiler with water-cooled reciprocating stokers, obtaining the distributi
12、on of temperature, velocity and flue gas components in the furnace. Numerical simulation results show that the momentum-synthesis method is unsuitable for the geometric design of the biomass grate boiler. It is 哈尔滨工业大学工学硕士学位论文 - IV - appropriate for biomass grate boiler to use shorter and higher rea
13、r arch. The angle of the rear arch ranges from 40to 50makes little difference to the burning condition in the furnace. When the angle between the second air jets located on the rear wall in the lower furnace and horizontal level (counter clock wise) is set at 20, the center of the flame is right in
14、the middle of the furnace; recirculation zone in the rear bottom of the furnace is larger, prolongs the paths of the volatiles and fly ash, helps stable the combustion on the last section of the grate and reduces the incompletely burned char in fly ash and the bottom ash; a larger local anaerobic en
15、vironment is formed, which reduces NO xformation. Using advanced OFA air supply such as forming a double rotating flow on the horizontal cross-sections in the burnout zone, can distribute the secondary air inside the boiler more evenly and make the aerodynamic configuration more effective for reduct
16、ion of pollutant emissions. Adding flue gas recirculation in the primary combustion zone leads to a lower temperature level there, which mitigates deposit formation on furnace walls in the primary combustion zone, especially in the throat zone. Flue gas recirculation has a considerable potential to optimize the mixing and reduces the incomplete burning losses. Selective flue gas recirculation radio makes an additional reduction of
