热解燃烧链条炉低NO_x排放特性的数值模拟

Numerical Simulation of Low NOx Emission Characteristics in a Pyrolysis-Combustion Chain Grate Boiler

利用Fluent软件,对功率为1.4MW的新型热解燃烧链条炉的NOx排放特性进行了数值模拟,其中,煤热解产生的还原性可燃气简化为CH4,采用添加元素N的乙烯-空气混合物模拟链条炉排半焦层燃烧及其生成的NO.数值计算结果表明,在过量空气系数为1.2、再燃比为30%的燃烧条件下,热解燃烧比传统燃烧可降低NO排放14.6%.热解燃烧链条炉由于热解气的再燃作用,在炉膛中形成一局部还原区,可较有效地降低NOx排放,证明了热解燃烧技术的可行性.增大再燃比和减小炉排前段风室配风量可提高出口NO还原率,减小炉膛前拱长度和前后拱间距会使NO还原作用增强.

Computational fluid dynamics Fluent software was used to simulate NOx emission characteristics of a pyrolysis-combustion chain grate boiler with heat capacity of 1.4 MW.In the simulation,methane was adopted as reburning fuel,while the combustion of air-ethylene mixture added with N element was employed to simulate the combustion of semicoke on the chain grate and the formed NO.Numerical simulation results show that NO emissions can be effectively decreased by 14.6% in pyrolysis-combustion chain grate boiler compared with traditional chain grate boiler,at the combustion conditions of excess air coefficient of 1.2 and reburning fuel fraction of 30%.Forming a partial reduction zone in the furnace by pyrolysis gas reburning is the major contribution for the reduction of NOx,demonstrating the feasibility of pyrolysis-combustion technology.Optimization calculation further clarified that improving the NO reduction rate can be realized by increasing reburning fuel fraction and decreasing air volume in the air plenum underneath forepart of the grate.Varying the configuration of boiler furnace shows that NO reduction rate increases when decreasing the front arch length,as well as the width between front and rear arch.