Simulation Modeling And Dynamic Characteristic Analysis Of Double Pressure Direct Current Heat Recovery Boiler

A waste heat boiler is one of the most important pieces of equipment for recovering waste heat,which can effectively improve the comprehensive energy utilization rate and the efficiency of the gas-steam combined cycle system.Under the influence of deep peaking of gas turbines,waste heat boilers are often in variable operating conditions.At present,there are many studies on the dynamic characteristics of natural cycle waste heat boilers in variable operating conditions,but there is a lack of research on the dynamic characteristics of DC waste heat boilers.Therefore,it is important to study the dynamic characteristics of DC waste heat boilers to improve the efficiency of gas-steam combined cycle systems.In this paper,a dual-pressure DC waste heat boiler is studied,and a single-phase flow heat transfer model and a two-phase flow heat transfer model are established based on the basic conservation equation and the heat transfer equation by using the total set parameter method.Simulation algorithms for the low-pressure economizer,lowpressure evaporator,low-pressure superheater,high-pressure economizer,highpressure evaporator,and high-pressure superheater have been written in Fortran language.A simulation model of the dual-pressure DC waste heat boiler system was established by applying the engineering integrated model development platform(Gen System).The simulation model calculates that the error value between the simulation result and the design result is less than 1% under the design working condition.Based on the established waste heat boiler simulation model,single-factor step disturbance,two-factor step disturbance,and waste heat boiler start-up and shutdown simulation tests were carried out to analyze the dynamic characteristics of steam parameters and exhaust smoke temperature,the metal wall temperature of the heating surfaces at all levels and the dynamic characteristics of the medium pressure inside the tubes after the boiler shutdown.The simulation results show that1,single-factor step disturbance: flue gas temperature has the greatest influence on the high and low-pressure steam outlet temperature,the feed-water flow has the greatest influence on the high and low-pressure steam outlet pressure and high and lowpressure steam outlet flow,and flue gas flow has the greatest influence on the exhaust temperature.2,Double factor step disturbance: when the flue gas inlet temperature is reduced by 10%,the feed water flow rate is reduced by 15%,the outlet temperature of high pressure steam can be increased by 100℃,and the feed water flow rate is reduced by20%,the outlet temperature of high pressure steam can be increased by 115℃.When the flue gas flow is reduced by 10%,the feed water flow is reduced by 10% to increase the high pressure steam outlet temperature by 80℃,and when the flue gas flow is reduced by 20%,the feed water flow is reduced by 20% to increase the high pressure steam outlet temperature by 180℃.Increasing feed water flow or decreasing feed water temperature can effectively reduce the exhaust temperature and improve the thermal efficiency of waste heat boiler.3.During boiler start-up,the high-pressure steam outlet temperature rises the fastest and requires the highest thermal stress on the metal tube wall,while the dynamic response of the exhaust smoke temperature is the slowest.After the boiler shutdown,high and low-pressure superheater metal tube wall temperature change is the largest,the largest thermal stress.Each level of high and low-pressure heating surface in the tube pressure gradually decreases and the downward trend is consistent.