某电厂锅炉选择性催化还原脱硝装置数值模拟研究

Numerical simulation of selective catalytic reduction denitrification device for coal-fired boiler

随着燃煤机组大气污染物排放要求的提高,脱硝性能诊断与流场优化成为近年来的热点和难点问题,通过数值模拟方法对燃煤锅炉选择性催化还原(SCR)脱硝装置内的流动进行分析是对SCR装置性能进行诊断和优化的有效手段。针对上述问题,对某600MW亚临界燃煤锅炉SCR装置在不同负荷下的流场进行了计算分析,在计算中采用二方程k-ε模型模拟湍流,利用多孔介质模型实现催化剂床层的模拟。利用催化剂前和脱硝出口处的烟气流速测量结果以及催化剂实际磨损情况对计算结果进行了校核,计算结果与实际情况吻合良好,催化剂前截面烟气Y方向速度计算值和试验值的最大相对偏差小于7.7%(设计值要求<10%),表明所采用的数值模拟方法以及采用多孔介质模型计算催化剂层作用能够有效地评估SCR装置内的复杂流场。不同负荷的流场计算结果表明,该SCR装置总体流动情况良好,流场稳定性、阻力特性等均能满足设计要求,但尾部导流板对烟气的导流作用较差。根据计算结果提出了导流板优化方案,导流板改造前试验测量区域流速相对标准偏差为0.262,改造后相对标准偏差降低至0.142,改造后SCR反应器前截面流场均匀性得到有效改善,100%负荷时脱硝系统阻力降低6%,按年利用小时5000h计算,年经济效益10万元。所述流场优化方案对同类工程实践有一定的参考价值。

With the increasingly strict requirements for the emission of air pollutants from coal-fired power plants,performance diagnosis and flowfield optimization for denitrification devices have become hot and difficult issues in recent years.Numerical simulation methods which simulate and analyze the flow in the selective catalytic reduction(SCR)denitrification device of coal-fired boilers can be effective means for diagnosing and optimizing its performance.In view of the above-mentioned problems,this paper calculates and analyzes the flow field of a 600MW subcritical coal-fired boiler SCR device under different loads.In the calculation,the two-equation k-εmodel is used to simulate turbulence,and the porous media model is used to simulate the catalyst bed.The calculation results are validated by the measurement results of flue gas flow rate in front of the catalyst and at the outlet of the SCR device,as well as the actual wear condition of the catalyst.The calculation results are in good agreement with the actual situation,and the maximum relative deviation between the calculated value and the experimental value of the velocity of the flue gas in the front section of the catalyst in the Y direction is less than 7.7%,indicating that the numerical simulation method used in this paper and the use of porous media model to calculate the catalyst layer can effectively simulate the complex flowfield inside the SCR device.The detailed analysis of the calculation results of the flow field under different loads shows that the overall flow condition of the SCR device is well,and the flow field stability and resistance characteristics can meet the design requirements.However,the tail deflector has a poor effect on the flow of flue gas.An optimization plan for the deflector is proposed according to the calculation results,and the uniformity of the flow field in the front section of the SCR reactor is effectively improved after the equipment modification.The relative standard deviation of the flow velocity in the test measurement area before the reformation of the deflector was 0.262,and the relative standard deviation was reduced to 0.142 after the reformation.The uniformity of the flow field in the front section of the SCR reactor is effectively improved,and the resistance of the denitration system is reduced by 6%at 100%load(design value<10%).The annual economic benefit is RMB100000,based on annual utilization hours of 5000h.As described in the flow field optimization scheme,the using methods and process contribute some reference value to the similar engineering practice.