Improved Design And Application Of Control Scheme For Desulfurization System Of 300MW Coal Gangue Generator Unit

Under the new situation of strict national environmental protection,in the face of the requirements of ultra-low emission and energy saving transformation,the removal of SO₂ by circulating fluidized bed unit has changed from single in-furnace desulfurization to limestone-gypsum wet desulfurization.Limestone-gypsum wet flue gas desulfurization is the most widely used desulfurization method at home and abroad,and the process is relatively mature.The desulfurization process has the characteristics of fast reaction speed,high desulfurization efficiency and good comprehensive economic performance.It is widely used in domestic power plant desulfurization process.In the limestone-gypsum wet flue gas desulfurization system,the design of control system is very important.Whether the design of control strategy is reasonable and effective directly affects the safe and stable operation of the desulfurization system.Taking Shanxi Pingshuo 300MW coal gangue circulating fluidized bed generating unit as the research object,the control scheme improvement of flue gas desulfurization system is studied and designed.Firstly,by analyzing the mechanism and influencing factors of flue gas desulfurization outside the furnace,according to the present situation of the desulfurization control system of the field test unit,the automatic control strategy of flue gas desulfurization of the unit is determined.The improved control scheme of wet flue gas desulfurization system is discussed in detail.Due to the large delay of the desulfurization system and the uncertainty of the object model,the conventional PID and some advanced control strategies are not applied to the control of the desulfurization system.The improved control scheme is proposed and designed based on the above situation.Its improved control strategy is realized on the basis of optimized cascade plus feedforward compound control.The improved desulfurization control strategy is based on expert control,fuzzy control,and other control methods.This paper proposes a dynamic superposition of fast and slow speed adjustment+feedforward control strategy.By combining the improved control strategy of desulfurization system with DCS control system of coal-fired units,field debugging and operation tests were carried out.The results show that:1)Limestone slurry supply can better track the change of SO₂ concentration in the flue gas before the absorption tower,so that the SO₂concentration in the net flue gas of the exhaust absorption tower varies from 20mg/Nm³ to 30 mg/Nm³,which meets the national design standard of 35 mg/Nm³ for SO₂ emission from coal-fired units;2)The measured value of pH can better track the change of setting value;3)Before and after the reform of desulfurization control system,the average consumption of limestone slurry per ton of SO₂ emission was13.49 m³ and 10.42 m³,respectively,which reduced the consumption of limestone slurry per ton of SO₂ emission by 22.8%compared with that before the reform.Field operation shows that the whole system works well and the improvement effect is obvious.The expected goal and requirement of field modification of flue gas desulfurization control system are realized.