Researches On Dry-wet State Conversion Principle And Automatic Control System Of Once-through Boiler

Under the industry background of developing new energy in China,the proportion of renewable energy power generation is increasing,and leads to large fluctuation of power grid.Thermal power generating units need to bear the role of peak shaving and load changing.Supercritical thermal power units have the characteristics of high parameters,low energy consumption and fast load change,and need to participate in the deeply variable load process,which are different from the requirement of base load operation in the past.Unlike drum boilers,supercritical once-through boilers often have problems of wet and dry state conversion in deeply low load operation.In order to track power generation instructions quickly and vary load flexibly,it is necessary to improve the stability and rapidity of dry-wet conversion process.The main work of this paper is as follows:(1)According to the characteristics of once-through boilers and their operation,this paper studies the problems of once-through boilers when they need deeply variable load,analyses the basic principles and control difficulties of conventional control methods for dry-wet conversion,and researches the control objectives and parameters changing process of onee-through boilers under different operation modes.Based on mechanism analysis,a wet dynamic model of once-through boiler is built to verify the change and correlation of working fluid flow,coal feed rate,water level of water storage vessel and enthalpy of intermediate point in the process of conversion.(2)According to the coupling relationship of parameters in the conversion process,the control scheme and the principle of automatic control are designed,including the design of enthalpy control system at intermediate point,water level control system,circulating water flow control system and switching techniques between them.(3)Engineering configuration is designed based on the principle of automatic control system.After simulation and debugging,automatic control of wet-to-dry and dry-to-wet state is completed in the field to verify the effectiveness of the automatic control system.