超超临界CFB锅炉外置换热器启动过程模拟分析  

Simulation and analysis on startup process of external heatexchangers in ultra-supercritical CFB boilers

作　　者：许兆峰[1] 薛亚丽[1] 李政[1] XU Zhaofeng;XUE Yali;LI Zheng(State Key Lab of Power Systems,Department of Energy and Power Engineering,Tsinghua University,Beijing 100084,China)

机构地区：[1]清华大学能源与动力工程系电力系统国家重点实验室,北京100084

出　　处：《洁净煤技术》2020年第3期23-30,共8页Clean Coal Technology

基　　金：国家重点研发计划资助项目(2016YFB0600205)。

摘　　要：通常超超临界CFB(循环流化床)锅炉均设置外置换热器来增加换热面积和换热量。为了研究CFB锅炉外置换热器的启动过程特性,为CFB宽负荷运行和灵活性调峰提供依据,在已有的CFB锅炉系统机理动态数学模型的基础上,建立了外置换热器动态模型,并以某660 MW超超临界CFB锅炉为对象,模拟分析其外置换热器的冷态启动过程和热态启动过程。冷态启动和热态启动前炉膛温度均为776℃,外置换热器温度分别为50℃和660℃。第30 min时,打开锥形阀启动外置换热器,由于冷态启动时外置换热器温度低,为避免外置换热器管道升温过快,锥形阀开度仅为5%;而热态启动时则不存在该限制,锥形阀开度可达30%。为了体现单一变量引起的变化,在冷态启动和热态启动过程中仅锥形阀开度不同,其他主动控制量中仅自动控制排渣量来保持炉膛压力稳定。在冷态启动过程中,外置换热器初始温度低于工质(中温过热蒸汽)温度,先从工质吸热;当外置换热器温度高于工质温度后开始向外放热,因此外置换热器放热量是从负值变化到正值。而热态启动过程中,外置换热器初始温度远高于工质温度,外置换热器始终向工质放热。因此,不管是冷态启动还是热态启动前,工质流量都应维持在设定值及以上,否则启动瞬间工质放热冷凝或吸热升温会导致壁温剧烈变化,出现爆管等事故。冷态启动和热态启动后达到平衡时,在CFB锅炉输入能量不变的情况下,由于外置换热器的放热量增大,炉膛内的放热量相应减小,因此炉膛温度有不同程度降低;在热态启动时锥形阀开度为30%,外置换热器循环灰流量和放热量较大,从而导致炉膛内放热量小于冷态启动,这也体现在热态启动的炉膛平衡温度小于冷态启动。冷态启动过程中外置换热器温升更高,为避免换热面壁面温升速率过高而采用5%锥形阀开度,从而导致冷态启动In general,ultra-supercritical circulating fluidized bed(CFB)boilers are equipped with external heat exchangers(EHE)to increase the heat transfer area and heat transfer.In order to study the startup process characteristics of the external heat exchanger of CFB boiler,so as to provide the basis for wide load operation and flexible peak regulation of CFB,The dynamic characteristics of startup process of EHEs of a 660 MW ultra-supercritical CFB boiler were studied,by establishing the dynamic mathematical models of CFB boiler with EHEs and simulating and analyzing the cold startup process and the hot startup process of EHEs.Before the cold startup and the hot startup,the furnace temperature is 776℃,while the temperature of EHEs is 50℃and 660℃respectively.At the 30th minute,the conical valve is opened and EHEs start to work.Due to the low temperature of EHEs in the cold startup,the conical valve is only 5%open in order to avoid overheating of the EHE pipe.Such limitation does not exist in the hot startup,and the conical valve can be open up to 30%.In order to show the change caused by one variable,only the opening degree of the conical valve is different in the cold startup process and the hot startup process,and the slag discharge quantity is automatically controlled in other active control quantities to maintain the stable furnace pressure.In the cold startup process,heat released from EHEs changes from negative value to positive value:EHEs absorb heat from the working medium(medium temperature superheated steam)first because the initial temperature of EHEs is lower than that of the working medium;when the temperature of EHEs is higher than that of the working medium,EHEs release heat to the working medium.In the hot startup process,EHEs always release heat to the working medium all the time,because the initial temperature of EHEs is much higher than that of the working medium.Therefore,the flow rate of working medium should be maintained at the set value and above before cold startup or hot startup,otherwise

关 键 词：循环流化床锅炉(CFB) 外置换热器 动态建模 启动过程 模拟 

分 类 号：TK229.6[动力工程及工程热物理—动力机械及工程]