Research On The Feed Water Strategy Of Supercritical Circulating Fluidized Bed

Clean-coal power generation technology is the cross-century project guide for electricity industry in our country.Circulating fluidized bed(CFB)boiler technology is one of the most widely used clean-coal power generation technologies,which has the advantages of wide range of fuel,high desulfurization efficiency,small NOx emission,high combustion efficiency,large load regulation ratio and comprehensive utilization of ash and slag.The rapid commercial development of CFB boiler needs higher requirements in the automatic control,so it is an urgent task to development the automatic control technology.In this paper,the feed water control system of supercritical CFB boiler is researched and the main work is as follows:Firstly,according to the combustion and operation characteristics of supercritical CFB boiler,we conclude that CFB boiler has the characteristics of large inertia and delay because of its large heat storage in the furnace and the complicated combustion process of fuel.The traditional feed water control strategy of the once-through pulverized coal boiler is no longer suitable.Therefore,it is necessary to find some feedforward signals with more advanced and dynamic characteristics to instruct the water supply control.In that case,the nonlinear control models of the boiler,the steam water and the steam turbine of supercritical CFB unit are established according to the coal feeding system,the heat in furnace,the differential pressure of superheater and the dynamic process of steam turbine.Then,based on the history data of Sichuan Baima power plant 600 MW supercritical CFB unit,the static parameters and dynamic parameters and the unknown function in the model are worked out by the methods of system identification,genetic algorithm and curve fitting.And we verify the correctness of the mechanism and good generalization ability of the model.In addition,the accuracy of the advanced signals is guaranteed such as dynamic heat,intermediate point parameters and load instructions,which lays the foundation for the design work of feed water control system for supercritical CFB boilers.Finally,a double-feedforward self-balance feed water control strategy is proposed in the paper.Besides the traditional feed water control which is based on the intermediate point enthalpy feedback,the more advanced and accurate self-balance feed water instruction is added.It contains three parts:the theoretical reference value of water supply calculated by the steam water balance theory,the dynamic heat deduced from the air and coal,the load demand.After analyzing the theoretical feasibility of the self-balance feed water control strategy,we design the configuration diagram of the control system by using the EDPF NT+ engineering configuration tool developed by Guodian Zhishen Control Development Technology Co.Ltd.And it is applied to the 2×350 MW CFB supercritical unit of Jiangsu Xuzhou Huamei thermal power plant.The excellent control effect is achieved according the actual running results,providing some references for the control system design of 660 MW ultra supercritical CFB unit which will be completed in 2020.