350MW Supercritical Pressure Boiler Control Strategy Study Of Once-through CFB

CFB is recognized as the most promising technology for clean-coal burning,especially under the situation of increasing environmental pressure,there is a better development opportunity in the field of thermal power.At present,there are few Once-through CFB units in China.There are some difficulties in controlling for it's large inertia and delay.In addition,it's different from the ordinary coal-fired units,CFB can make full use of boiler heat storage and realize "boiler shutdown without stopping turbine" when MFT or BT.Based on a new project which has two CFB units in Guangdong province,this paper study control strategy for Once-through CFB of 350 MW supercritical pressure boiler.The research has accumulated experience for its development.Main content includes the following aspects:1.Based on the analysis of main conventional control loop for coal-fired unit and specific control loop for CFB in actual project.Several aspects of control strategy should be paid attention are put forward for better control effect.2.The grid assessment requirements of AGC and primary frequency modulation are studied.In addition,the problems in test and actual operation are summarized and analyzed.Based on those,We have mainly solved the problems of AGC regulation rate does not meet the grid assessment requirements,AGC target load oscillations,contribution rate is insufficient and the movement direction is not correct for primary frequency modulation,signal selection and logical processing are not reasonable to affect the reliability of the equipment.3.The characteristic of large inertia for CFB determines reducing load more difficulty in RB.This paper summarizes and analyzes the problems which are exposed during experiments.It has mainly solved the problems of the main steam overtemperature due to the improper matching of feed wate,affecting accuracy and reliability of the action due to unreasonable RB signal processing,auxiliary equipments easy to over-current trip,the interferes of relevant MCS in RB,RB reset signal is not reasonable and so on.4.The characteristic of large inertia determines realizing "boiler shutdown without stopping turbine" is one of its greatest strengths for CFB.It is not simply cancelling the traditional logic of "boiler intertripping steam turbine" but also considering the safety and stability of the unit.Taking the two accidents "boiler tripped but steam turbine not tripped" for example,this paper analyzes relevant data and curves during the test,further more,some control strategy optimization measures for adapting to this particular conditionare are put forward.Finally,it realize "boiler shutdown without stopping turbine" safety and stability and win time for repair and recovery of equipments.