660MW超超临界燃煤机组脱硫废水雾化蒸发零排系统运行对锅炉热效率的影响

Effects on the boiler′s thermal efficiency of running a zero-discharge desulfurization wastewater atomization evaporation system for 660 MW ultra-supercritical coal-fired unit

脱硫废水是燃煤电厂在生产运行中产生的污染物,为了保护生态环境,需对其进行净化处理。热烟气蒸干技术因系统稳定、效率高被广泛用于脱硫废水处理,部分电厂采用旋转雾化蒸发技术实现脱硫废水零排放。为评估该蒸干系统对锅炉热效率以及空气预热器性能的影响,以660 MW超超临界燃煤机组为研究对象开展现场实验,在400 MW蒸干系统投运和退出工况、660 MW蒸干系统投运工况下测量锅炉排烟温度以及烟气成分,对入炉煤、飞灰、炉渣、脱硫废水进行化验分析。通过反平衡热效率计算方法得到各工况的热效率,并根据冷端综合温度与空预器性能修正计算结果评价各工况下空预器性能。结果表明,400 MW负荷下,退出蒸干系统时热效率为95.11%,投运蒸干系统时热效率为95.08%,系统投运降低了0.03%的锅炉热效率;400 MW负荷下系统处理废水流量为4.72 m^(3)/h,660 MW负荷下系统处理废水流量为6.93 m^(3)/h,高负荷下投运系统可以抽取更少的烟气来处理更多脱硫废水,投运系统更为有利;系统投运后灰渣的含碳量发生变化,这表明蒸干系统运行会对锅炉燃烧产生影响;系统投运期间空预器冷端综合温度较低,运行时需要注意空预器压差,避免发生空预器堵塞危害机组安全运行。

Desulfurization wastewater is a pollutant that coal-fired power plants produce during production and operation.To save the natural environment,this wastewater must be cleaned and treated.Because of its stable system and high efficiency,hot flue gas evaporation technology is extensively used for desulfurization wastewater treatment.Some power plants also utilize rotary atomization evaporation technology to achieve zero discharge of desulfurization wastewater.To assess how this evaporation system affects the boiler′s thermal efficiency and the air preheater′s performance,a 660 MW ultra-supercritical coal-fired unit was used in a field experiment,at 400 MW(system out and into operation)and 660 MW(system operation),boiler flue gas temperature and composition were monitored,and laboratory tests were used to assess the incoming coal,fly ash,slag,and desulfurization wastewater.The thermal efficiency of each working condition was obtained by the counter balance calculation method,and the air preheater performance was evaluated under each working condition according to the results of the calculation of the combined cold end temperature and air preheater performance correction.The results show that under 400 MW,the thermal efficiency is 95.11%when the evaporation system is out of operation,95.08%when the evaporation system is in operation,and the boiler thermal efficiency is reduced by 0.03%after system operation.The system could evaporate 4.72 m^(3)/h wastewater of under 400 MW after operation,and 6.93 m^(3)/h under 660 MW.The system can extract less flue gas to treat more desulfurization wastewater under the high load,it is more favorable to put the system into operation.The carbon content of the ash slag has changed after the system is put into operation,which indicates that the system operation will have an impact on boiler combustion.While the system is in operation,the combined temperature of the cold end of the air preheater is lower,and it is necessary to pay attention to the air preheater differential pressure during the operation,to avoid the occurrence of air preheater blockage that will jeopardize the safe operation of the unit.