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