330 MW亚临界CFB锅炉烟气再循环深度调峰运行性能研究

Performance research on deep peak regulation with flue gas recirculation in a 330 MW subcritical CFB boiler

为了消纳新能源上网,循环流化床(CFB)锅炉机组利用自有调峰能力强特点,参与深度调峰灵活性运行。但超低负荷运行时,受密相区流化安全约束,一次风总量无法持续下降,从而破坏了固有的一、二次风分级还原特性,导致更多的NOx生成。同时,炉膛出口温度远低于选择性非催化还原(SNCR)温度窗口,导致设置在分离器内的脱硝系统效率下降。烟气再循环技术是一种适合CFB锅炉低负荷运行的NOx控制技术,介绍了330 MW亚临界CFB锅炉机组烟气再循环改造前后的运行性能对比,结果表明,在超低负荷条件下,采用烟气再循环技术能在维持密相区流化安全的同时,显著降低一次风量,强化密相区还原氛围,同时降低密相区温度,延迟炉膛内燃烧,显著提高炉膛出口烟温,有效避免了分离器内SNCR脱硝效率的降低。并针对烟气再循环系统内的腐蚀提出了合理的运行控制策略。

To consume renewable energy,the Circulating Fluidized Bed(CFB)boiler units can play great role in the deep peak regulation and operation flexibility with its strong peak regulation capability.However,due to the safety limitation of fluidization in dense phase zone under ultra-low load operation,the total amount of primary air cannot continue to decrease,which destroys the inherent reductive characteristics of staged primary and secondary air and causes more nitrogen oxides to be formed.In the meanwhile,the furnace outlet temperature is much lower than the temperature window of selective non-catalytic reduction(SNCR),which causes efficiency drop of denitration system in the separator.Flue gas recirculation technology is a kind of low-load NO x control technology suitable for CFB boilers.In this paper,the comparison of operating performance before and after the flue gas recirculation modification in a 330 MW subcritical CFB boiler unit was introduced.The results show that under low load conditions,flue gas recirculation technology can significantly reduce the primary air volume while maintaining the safety of fluidization in the dense zone,strengthen the reducing atmosphere and reduce the temperature in the dense zone,delay the combustion in the furnace,and significantly improve the flue gas temperature at the furnace outlet,which greatly avoid the reduction of SNCR efficiency in the separator.At last,a reasonable operation control strategy was provided for the corrosion in the flue gas recirculation system.