直流余热锅炉蒸发段长度和位置变动特性的仿真分析

Simulation Analysis on Variation Characteristics of Evaporation Section Length and Position of Once-Through Heat Recovery Steam Generator

在直流余热锅炉变工况运行过程中蒸发段长度和位置的改变会造成锅炉管壁温度分布、工质出口参数等产生较大的波动,影响锅炉安全运行。以某立式直流余热锅炉为研究对象,建立其动态仿真模型,研究锅炉烟气流量、入口烟温、高压给水流量和给水温度分别发生阶跃扰动后蒸发段长度及相变点位置的变化规律。仿真结果表明:余热锅炉在设计工况下运行,锅炉入口烟温对锅炉蒸发段长度的影响程度最大,入口烟温阶跃升高10℃后,蒸发段迅速缩短,相变点均向锅炉管内工质入口方向移动,蒸发段长度和相变点位置恢复稳定所需时间相对较短;烟气流量阶跃升高5%后,蒸发段长度迅速缩短而后缓慢增长,沸腾点向管内工质入口方向移动距离大于蒸干点,恢复稳定所需时间较长;给水流量阶跃升高5%后,蒸发段长度迅速增长而后缓慢缩短,蒸干点向管内工质出口方向移动距离大于沸腾点,恢复稳定所需时间最长;给水温度阶跃变化20℃对蒸发段长度和相变点位置的影响很小。

In the process of variable condition operation of an once-through boiler,the change of the length and position of the evaporation section will cause great fluctuations in the boiler tube wall temperature distribution and working medium outlet parameters,which will affect the safe operation of the boiler.Taking a vertical once-through heat recovery steam generator(HRSG)as the research object,its dynamic simulation model is established to study the variation law of evaporation section length and phase transition point position after step disturbance of boiler inlet flue gas flow,inlet flue gas temperature,high-pressure feed water flow and feed water temperature respectively.The simulation results show that when the HRSG operates under the design working condition,the boiler inlet flue gas temperature has the greatest impact on the length of the boiler evaporation section,after the inlet flue gas temperature step rises by 10℃,the evaporation section shortens rapidly,the phase transition point moves towards the inlet of the working medium in the boiler tube,and the time required for the length of the evaporation section and the position of the phase transition point to restore stability is relatively short.After a 5%step rise in the flue gas flow,the length of evaporation section decreases rapidly and then increases slowly,the moving distance of the boiling point to the inlet of the working medium in the tube is greater than that of the evaporation point,and it takes a longer time to restore stability.After a 5% step rise in the feed water,the length of evaporation section increases rapidly and then decreases slowly,the moving distance of the evaporation point to the outlet of the working medium in the tube is greater than that of the boiling point,and the time required to restore stability is the longest.The step change of feed water temperature of 20℃ has little effect on the length of evaporation section and the position of phase transition point.