两种烟气热量全温区吸收方式对三压缩sCO_(2)燃煤发电系统性能影响分析

Effect of two methods for flue gas energy extraction over the entire temperature range on the tri-compression sCO_(2) coal-fired power plant

超临界二氧化碳(supercritical CO_(2),sCO_(2))三压缩循环(tri-compression,TC)与再压缩循环(recompression cycle,RC)相比有较大的效率提升,为进一步提升燃煤sCO_(2)发电系统效率,有必要构建TC燃煤发电系统.烟气热量全温区吸收是超临界二氧化碳循环应用于燃煤热源时会面临的关键问题之一,目前主要有两种解决方法,分别为基于能量复叠利用原理构建复合循环(overlap energy utilization,OEU)和尾部烟道添加烟气冷却器(flue gas cooler,FGC).本文以三压缩+再热(tri-compression plus reheating,TC+RH)为基本循环,耦合锅炉水动力模型,基于两种烟气热量全温区吸收方法,构建了OEU和FGC两个燃煤发电系统,针对烟气中低温区余热吸收性能进行对比分析.研究发现,由于FGC系统中温区工质吸热能力不足,并且受限于尾部受热面30°C夹点温差,锅炉排烟温度高达172.6°C,锅炉效率仅为90.64%.对于OEU系统,锅炉排烟温度可降低至126.0°C,对应的锅炉效率为92.85%,满足系统性能的要求.另外,FGC系统烟气中温区和低温区的传热?损均高于OEU系统,说明OEU系统锅炉中低温区的烟气与工质能级更加匹配.

For the supercritical CO_(2) cycle(sCO_(2)),the tri-compression(TC)cycle significantly improves thermal efficiency compared to the recompression cycle(RC).Then it is necessary to construct a TC coal-fired power plant for further efficiency improvement.Flue gas energy extraction across the entire temperature range is a serious challenge for indirect sCO_(2) coal-fired power plants.A flue gas cooler(FGC)installed in the boiler tail flue and a combined cycle based on overlap energy utilization(OEU)are designed to address this issue.The basic cycle is tri-compression plus reheating(TC+RH).Two thermodynamic models of OEU and FGC are constructed in conjunction with the boiler’s thermal-hydraulic characteristics.Due to a lack of flue gas heat load cooler and a pinch temperature difference limit of 30°C,the boiler exhaust flue gas temperature(Tfg,ex)for the FGC system is as high as 172.6°C,lowering boiler efficiency to 90.64%.However,for the OEU system,Tfg,ex can be cooled to 126.0°C,which corresponds to a boiler efficiency of 92.85%.Additionally,the FGC system’s energy destruction in the moderate-and low-temperature flue gas regions is greater than that of the OEU system,indicating that the OEU system’s energy quality of flue gas and working medium in the above-flue gas region is more closely matched.