1000MW机组低温省煤器流场优化数值模拟

Numerical simulation of flow field optimization of low temperature economizer for 1000 MW power unit

山东某电厂1000MW机组自运行以来存在低温省煤器内烟气分布不均匀、换热效果差、热效率低等问题,针对上述问题采用数值模拟技术,通过导流板优化设计,对省煤器入口对冲烟道进行流场优化。采用Realizableκ-ε双方程模型来模拟烟气流动状况,对低温省煤器烟道、引风口至省煤器阶段的烟道按照比例1∶1建立模型,并进行分区域网格划分。由于模型复杂的内部结构,计算区域选用六面体结构网格划分,省煤器内换热部分按照一个计算区域,其余区域依次为入口段变截面段,换热部分中间段以及省煤器出口变截面段以及引风口至省煤器阶段的烟道等,共划分五个区域。通过数值计算,对低温省煤器入口加装导流板方案的数值模拟结果进行流场和压力场分析。结果表明:原设计的烟道设计烟气流经低温省煤器入口烟道区域,烟气发生剧烈扰动,产生大量旋流运动形成回流漩涡,省煤器区域存在大量换热死区,速度误差小于15%的速度分布占比仅为39.1%,烟气均匀性极差;加装导流板优化设计之后,烟气流旋流性下降,速度误差小于15%的速度分布占比提升至为76.28%,均流效果显著,并且省煤器入口到出口烟气压降较改造仅增加33Pa,对整体压力分布和风机负荷的影响不大,原烟气入口渐扩段两侧回流死区优于原设计。

There were some problems such as uneven distribution of flue gas,poor heat transfer effect and low heat efficiency of low temperature economizer in the operation of a power plant in Shandong Province.In order to solve the problem,the numerical simulation technology was used to optimize the flow field of the inlet flushing flue of the economizer through the optimization design of the guide plate.The Realizableκ-εtwo-equation model was used to simulate the flue gas flow.The model of the low temperature economizer flue and the flue from the air intake to the economizer was established as 1∶1 according to the proportion,and the regional grid was divided.Because of the complex internal structure of the model,the calculation region was divided by hexahedral structure grid.The heat transfer part in the economizer was divided according to one calculation region.The other regions were in turn the variable cross-section section of the entrance section.The middle section of the heat transfer part,the variable cross-section section of the economizer outlet and the flue from the air intake to the economizer stage,etc.,which were divided into five regions.Through the numerical calculation,the flow field and pressure field of the numerical simulation results were analyzed.The results showed that the original designed flue gas flows through the inlet flue area of the low temperature economizer,the flue gas was violently disturbed,a large number of swirling movements were produced to form a reflux vortex,and there were a large number of heat transfer dead zones in the economizer area.The proportion of velocity distribution with velocity error less than 15%was only 39.1%,and the flue gas uniformity was very poor.After the installation of baffle,the swirl property of flue gas decreases,the proportion of velocity distribution with velocity error less than 15%has increased to 76.28%,and the effect of flow sharing is remarkable.Compared with the retrofit,the flue gas pressure drop from economizer inlet to outlet only increases 33 Pa,which has little effect on the overall pressure distribution and fan load,and the reflux dead zone on both sides of the original flue gas inlet expansion section was better than the original design.