某600MW四角切圆燃煤锅炉在完成灵活性改造后,于高负荷运行时出现炉膛出口烟气温度偏差大以及NOx排放浓度控制难等问题。为此,运用流体计算仿真软件构建炉内燃烧、流动和传热全耦合的三维模型进行数值模拟计算,旨在确定锅炉的最佳运行参数。其中,采用Standardk-ɛ模型描述流体流动,运用双步竞争模型模拟煤中挥发分的析出过程,借助动力/扩散控制模型阐释焦炭燃烧反应,通过拉格朗日随机轨道模型考量煤粉颗粒与烟气的两相流过程,利用P1辐射模型计算炉内辐射传热,采用有限速率/涡耗散模型模拟气相燃烧,并通过后处理方式计算烟气中NOx的质量浓度。重点分析了在100%锅炉最大连续蒸发量(BMCR)工况下,过量空气系数α、一次风率β和二次风角度θ等参数对炉膛切圆燃烧和出口处NOx排放的影响。数值模拟结果表明:在锅炉实现良好切圆燃烧和低NOx排放的条件下,最优运行参数为α=1.1,β=30%和θ=0°。通过锅炉燃烧调整试验对模拟结果的准确性予以了验证,试验结果表明:在最优运行参数下,锅炉省煤器出口的NOx质量浓度降低了9.96%,排烟温度降低了2.66%,烟气温度偏差降低了2.26%,锅炉效率提高了0.28%。

After completing the flexibility retrofit of a 600 MW tangentially coal-fired boiler, several issues arose during high load operation,including large flue gas temperature deviations at the  furnace outlet and difficulties in controlling NO  emissions.  To address these challenges and deter‐ mine the optimal operating parameters of the boiler, a three-dimensional model of combustion, flow  and heat transfer in the furnace was constructe dusing the computational fluid dynamics software.  The  established model employed the standard k-ɛ model to describe fluid flow, the two-step competition  model to simulate the release of volatile matter in coal, the dynamic/diffusion control model to explain  the coke combustion reaction, the Lagrangian stochastic trajectory models to consider the two-phase  flow process of pulverized coal particles and flue gas, the P1 radiation model to calculate the radiation  heat transfer in the furnace, the finite rate/eddy dissipation model to simulate the gas phase combus‐ tion, and NO  mass concentration in flue gas was calculated based on the simulated combustion field  in a post-processing way.  The effects of excess air coefficient α, primary air rate β and secondary air  angle θ on furnace tangential combustion and NO  emission at the outlet were analyzed in the condition  of 100% BMCR.  The numerical results show that the optimal operating parameters are α=1. 1, β= 30% and θ =0° to achieve both good tangential combustion and low NO  emission.  The simulation  results were validated by a boiler combustion adjustment test.  The test results demonstrate that under  the optimal operation parameters, NO  mass concentration at the economizer outlet of the boiler is  reduced by 9. 96%, exhaust gas temperature is reduced by 2. 66%, flue gas temperature deviation is  reduced by 2. 26%, and the boiler efficiency is improved by 0. 28%.