循环流化床预热燃烧过程中，预热燃料在下行燃烧室的燃烧过程至关重要。为了研究预热燃料在下行燃烧室中的流动和燃烧特性，采用计算流体力学软件Fluent，结合试验手段，对不同二次风喷口配风方式下，预热燃料在下行燃烧室的燃烧过程进行试验及数值模拟，对比了不同配风方式下，流动特性、温度特性、组分浓度分布特性以及氮氧化物排放特性的差异。结果表明，预热燃料在下行燃烧室的燃烧过程中，二次风会卷吸烟气在下行燃烧室上部产生回流，稀释反应物，在中心喷口配风时回流区域更大。不同配风方式下，下行燃烧室中的温度分布不同。环形喷口配风时下行燃烧室中的温度峰值为1 459 K，而中心喷口配风时下行燃烧室的温度峰值为1 555 K，同时环形喷口配风时下行燃烧室的高温区域较小，温度分布更加均匀。环形喷口配风时，预热燃料和二次风的混合更加充分，高温煤气和空气的反应更加强烈，有助于燃料的着火及升温。而中心喷口配风时下行燃烧室顶部的CO和H2等还原性气体浓度较高，有助于还原NOx。同时较高的温度促进了气化反应，生成更多的CO和H2，在燃尽风喷入前的区域形成还原性气氛，有助于进一步还原NOx。二次风中心喷口配风时，更多的氮氧化物被还原，尾部烟气中的NOx排放浓度为107×10-6，二次风环形喷口配风时，尾部烟气中的NOx排放浓度为121×10-6。

In the process of preheating combustion of circulating fluidized bed,the combustion process of the preheated fuel in the down-fired combustor（DFC)is very important. In order to study the flow characteristics and combustion characteristics of the preheated fuel in the DFC,the computational fluid dynamics software Fluent was used,combined with experimental methods,to test and simulate the combustion process of the preheated fuel in the DFC under different secondary air nozzles. the differences in flow characteristics,temperature characteristics,component concentration distribution characteristics and nitrogen oxide emission characteristics under different air distribution methods were compared. The results show that during the combustion process of the preheated fuel in the DFC,the secondary air can entrain the flue gas and reflow in the upper part of the down-fired combustor to dilute the reactants,and the recirculation area is larger when the air is distributed at the central nozzle. Under different air distribution modes,the temperature distribution is different. The peak temperature in the DFC is 1 459 K when the air is distributed at the annular nozzle,while the temperature peak is 1 555 K when the central nozzle is distributed. At the same time,when the air is distributed at the annular nozzle,the high temperature area is smaller and the temperature distribution is more evenly. When the air is distributed at the annular nozzle,the mixing of preheating fuel and secondary air is more sufficient,and the reaction between high temperature gas and air is more intense,which is helpful to the ignition and heating of fuel. When the air is distributed at the central nozzle,the concentration of CO and H2 at the top of the DFC is higher,which helps to reduce NOx. What′s more,a higher temperature promotes the gasification reaction,forming a reducing atmosphere,which is conducive to further reduce NOx. When the central nozzle is used for air distribution,more nitrogen oxides are reduced,the NOx emission in the tail flue gas is 107×10-6. When the annular nozzle is used for air distribution,the NOx emission is 121×10-6.

0 引言

1 预热燃烧试验

   1.1 试验系统

   1.2 试验样品

   1.3 试验工况

2 数值模拟

   2.1 模拟参数

   2.2 数值模型

   2.3 模型验证

3 结果与讨论

   3.1 二次风喷口配风方式对流场的影响

   3.2 二次风喷口对温度分布的影响

   3.3 二次风喷口对组分分布的影响

   3.4 二次风喷口配风方式对NO排放的影响

4 结论