Research On Fuel-steam Pressure System Model And Control Strategy Of Supercritical Power Plant

At present,energy and environmental problems become increasingly prominent,the supercritical units are increasingly becoming the developmental trend of thermal power plant due to the characteristics of high efficiency and low energy consumption.The combustion control system of the supercritical units is an important part of the whole control system.At present,most coal-fired power plants have wide sources of coal and large calorific value deviation,which seriously affect the control of the combustion system.The control level further affects the safety and economy of the whole unit.Therefore,it is necessary to study a kind of coal self-adaptive control strategy which is suitable for supercritical units,to improve the safety and economy of unit operation and to optimize the control system of supercritical units.Based on the idea of combined forecasting model,a forecasting model of coal feed rate is designed.The optimal weight of current coal coefficient affected by the last hour is calculated by the reciprocal of variance method,and the prediction of the current coal coefficient and the amount of coal feed rate are realized.The forecasting model is verified by using the prediction model of 660 MW unit #4 boiler.The results show that the real coal feed rate can be 97.0%.The main steam pressure is an important parameter to characterize the relationship between the supply and demand of the furnace energy of the supercritical units.The main influencing factor is the fuel quantity.At present,most of thermal power plant fuel coal is miscellaneous and calorific value fluctuates,resulting in frequent fluctuations in the main steam pressure,seriously affecting the safe operation of the unit.Based on the feed-forward control system of fuel quantity,a second-order active disturbance rejection controller is designed.In the feedback control system of fuel quantity,closed-loop feedback control is replaced by active disturbance rejection control instead of traditional PID.The coal thermal value spontaneous disturbance is estimated and compensated in real time in the dynamic process by extended state observer,to further improve the accuracy of coal feed rate and to prevent the frequent fluctuations in the main steam pressure caused by fluctuations in the calorific value of coal.The dynamic mathematical model of the supercritical once-through boiler is divided into three pressure nodes by means of pressure nodes.The mass conservation and energy conservation equations arelisted for each pressure node.Then the equations are simplified and dimensionless.Finally,The fuel-steam system model of the supercritical units can be obtained.The model parameters of 100% THA,75% THA and 50% THA for the supercritical units fuel-steam system are modeled and calculated by using a 660 MW supercritical units design data.The simulation results show that compared with the traditional PID control,the active disturbance rejection control has stronger anti-interference ability and better robustness,and better control of the main steam pressure quality.By comparing the traditional PID controller and the active disturbance rejection controller,it is known that the active disturbance rejection control scheming with the elimination of the disturbance effect has a promising control scheme.