洁净煤技术

2019, v.25;No.124(06) 158-164

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1000 MW机组低温省煤器及烟道流场模拟优化研究
Simulation and optimization study of low temperature economizer and flue flow field of 1 000 MW unit

邓晓川;胡龙彬;李斌;方芳;
DENG Xiaochuan;HU Longbin;LI Bin;FANG Fang;Beijing Guodian Futong Science and Technology Development Co.,Ltd.;

摘要(Abstract):

由于双进气烟道结构复杂,对低温省煤器内的烟气流场分布有很大影响。为了提高双进气烟道结构的低温省煤器内部气流分布均匀性,从而保证换热效率,降低设备故障率,通过计算流体力学(CFD)数值模拟技术,采用标准k-ε模型,以多孔介质模型替代结构复杂的翅片换热管的方法,对某1 000 MW燃煤机组低温省煤器及其双进气烟道内的流场分布进行数值模拟与结构优化研究。为了确保模拟结果更接近实际情况,在不同工况条件下,对低温省煤器及其烟道对应测点的烟气压力损失进行了测量和数值模拟计算,获得了可靠的模型边界参数。低温省煤器烟道结构优化前的测量值与数值模拟对应的压力损失值的偏差控制在-23~31 Pa,验证了数值模型的准确性。优化低温省煤器及其烟道的结构后,利用建立的模型进行流场模拟,根据气流均匀性评判方法(RSM法),在不同锅炉负荷对应烟道入口流速3.7、6.1、8.5、9.7、12.2 m/s工况下,分别对低温省煤器优化前后的翅片管换热区入口截面流场速度均匀性进行评价。经过多次流场数值模拟,结果显示结构优化前,烟道入口烟气流速达5.3m/s时,原结构的低温省煤器换热区入口截面的气流分布已不合格,且随着锅炉负荷增加,该截面的气流均匀性变得更差。结构优化后,随烟气流速增大,低温省煤器换热区入口截面的气流分布均匀性有所变差,但都保持在气流分布优秀的范围(σ≤10%),换热区入口截面的气流分布均匀性明显提升。数值模拟结果表明烟道弯头与直段烟道不等径、扩散弯头及导流板设置不合理是造成流场分布不均匀的主要原因。通过结构优化,将竖直烟道上下2个弯头改变为与竖直烟道等径的弯头,并合理设置导流板,使得该低温省煤器竖直烟道中气流向内侧偏移现象明显减弱,竖直烟道上弯头顶部气流流量过少,底部气流流速过快的现象也明显减弱,低温省煤器换热区入口气流均匀性明显提升。分析认为在烟道转弯处,选择与直段烟道等径的弯头,有利于提升烟道内气流分布的均匀性。烟道转弯后又需连接扩散烟道时,烟道先等径转弯一段距离后再连接扩散烟道,有利于提升烟道内气流分布的均匀性。
The complex structure of double inlet gas flue has a significant influence on gas flow field distribution in a 1 000 MW coal-firedboiler′s low temperature economizer. In order to optimize gas flow field of the low temperature economizer with double inlet gas flues andensure the heat exchange efficiency and reduce its failure rate,based on the computational fluid dynamics(CFD) numerical simulationtechnology and the standardk-εmodel,the porous medium model was used to replace the fin heat exchanger with complex structure.Theflow field distribution in the low-temperature economizer and its double inlet flue of a 1 000 MW coal-fired unit is studied by numericalsimulation and structural optimization. In order to ensure that the simulation results were closer to actual situation,the numerical simula-tion model was verified by comparing measured values with calculated values of flue gas pressure loss at the corresponding sampling pointof low temperature economizer under different working conditions,then the reliable boundary parameters of the model were obtained.Thedeviation between the measured value and the pressure loss value corresponding to the numerical simulation before the optimization of thelow-temperature economizer flue structure was controlled at-23-31 PA,which verified the accuracy of the numerical model. After optimi-zing the structure of the low-temperature economizer and its flue,the established model was used to simulate the flow field. In differentboiler load conditions corresponding to the gas flue inlet velocity of 3.7,6.1,8.5,9.7,12.2 m/s,the numerical simulations had been maderespectively before and after optimizing structure of the low temperature economizer's inlet gas flue. The evaluation results show that gasflow field distribution in low temperature economizer has been worse and worse,when the velocity of flue gas at the flue inlet is more than5.3 m/s,before optimizing structure of the low temperature economizer's inlet gas flue and with the increase of boiler load,the air flowuniformity of the section becomes worse and with the increase of boiler load,the air flow uniformity of the section becomes worse.Afterstructural optimization,with the increase of flue gas velocity,the gas flow field distribution in low temperature economizer becomes worse,but within the excellent flow field distribution range(10%) and the uniformity of air flow distribution in the entrance section of the heat ex-change area is obviously improved.The results of numerical simulation show that the main reasons for uneven distribution of flow field ineconomizer and its inlet gas flues are unequal diameter of flue elbow and straight flue,unreasonable setting of guide plate and diffusion flueelbow. After making structural optimization of the low temperature economizer such as equalizing elbow to the straight flue diameter andsetting the guide plate reasonably,the gas flow deviation inside the vertical flue of the low-temperature economizer is obviously weakened,the air flow at the top of the elbow on the vertical flue is too small,and the air flow velocity at the bottom is too fast,so the air flow uniform-ity at the inlet of the heat exchange area of the low-temperature economizer is obviously improved. The analysis shows that the elbow withthe same diameter as the straight flue is beneficial to improve the uniformity of air distribution in the flue. When it is necessary to connectthe diffusion flue after the flue turns,the flue should be connected to the diffusion flue after a certain distance of equal diameter turning,which is conducive to improving the uniformity of air distribution in the flue.

关键词(KeyWords): 低温省煤器;多孔介质;流场模拟;烟道优化
low temperature economizer;porous medium;CFD;flow field optimizing

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基金项目(Foundation): 国家重点研发计划资助项目(2016YFB0600400)

作者(Author): 邓晓川;胡龙彬;李斌;方芳;
DENG Xiaochuan;HU Longbin;LI Bin;FANG Fang;Beijing Guodian Futong Science and Technology Development Co.,Ltd.;

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