660 MW超超临界CFB锅炉失电壁温计算及运行措施

Calculation of heating surface wall temperature and operation measures for660 MW ultra supercritical CFB boiler under electricity failure

超超临界循环流化床锅炉发生失电时,保证锅炉受热面安全至关重要。对超超临界循环流化床锅炉在失电事故后影响受热面安全性的因素进行分析,根据质量、动量、能量守恒以及金属管壁蓄热方程组成的锅炉汽水系统非稳态流动传热计算模型,开发出锅炉汽水系统动态特性计算软件,用于计算锅炉失电工况受热面工质温度及金属壁温随时间的变化规律。通过计算得到了锅炉发生失电事故后保证受热面安全措施为高压旁路阀以40%BMCR的流量进行排汽,且最短排汽临界时间为110 s,同时省煤器进口需以140 t/h的流量补水。可知该工况下水冷壁、低温过热器、中温过热器、高温过热器工质温度及管壁温度随时间先上升再下降,管壁温度最高值均低于受热面选材的允许使用温度。该措施可保证超超临界CFB锅炉在失电事故下各受热面的安全,解决了CFB锅炉发生失电事故后受热面超温问题,为电厂运行提供指导。

It is important to ensure the heating surfacesafety of ultra-supercriticalcirculating fluidized bed(CFB)boiler under electricity failure.The factors that affect the safety of heating surfaces of a supercritical circulating fluidized bed boiler after a power outage accidentwere analyzed.The transient flow heat transfer calculation model for the boiler heating surfaces was established based on the conservation of mass,momentum,energy,and the heat storage equation of the tube-wall.A program for calculating the dynamic characteristics of the boiler steam water systemwas also developed,which can calculate the variation of the working fluid temperature and tube-wall temperature with timeon the heating surface of a boiler under power loss conditions.The result shows that the high-pressure bypass valve needs to exhaust steam at a flow rate of 40%BMCR,with a minimum critical time of 110s for exhaustwhen the safety of the boilerheating surface is ensured.Meanwhile,the inlet of the economizer needs to be replenished with water at a flow rate of 140 t/h.Theworking fluid and tube-wall temperature of the water wall,low-temperature superheater,medium temperature superheater,and high-temperature superheater rise first and then decrease over timeunder this condition.The highest value of tube-wall temperature is lower than the allowable temperature for heating surface material.The measures proposed can ensure the safety of heating surfaces of the ultra-supercritical CFB boiler under electricity failure,solve the problem of overheating of the heating surface after the power loss accident of the CFB boiler,which provides guidance for the operation of the power plant.