Research And Application Of Flue Gas Desulfurization Control Strategy For Foal-fired Units

Limestone-gypsum wet desulfurization is a commonly used desulfurization process in the flue gas desulfurization system of coal-fired power plants in my country,and it has the characteristics of high desulfurization efficiency and stable operation.With the increasing national requirements for atmospheric SO₂ emission standards,thermal power plants have higher and higher control requirements for wet flue gas desulfurization systems.It is necessary to ensure that SO₂ emissions meet the national ultra-low emission requirements,and to control operating costs,therefore,put forward higher requirements for the desulfurization automatic control operation rate.However,at present,the desulfurization control strategy adopted by most domestic thermal power plants is based on cascade PID control w ith the p H value of the absorber slurry as the controlled object,which has problems such as weak anti-disturbance ability,poor control effect,and low degree of automation.The control effect under dynamic conditions of unit load lifting is often unsatis factory.This paper analyzes the characteristics of wet flue gas desulfurization control system,based on historical operating data of the unit,a composite control strategy of wet flue gas desulfurization system with outlet sulfur dioxide concentration as the controlled quantity is designed,and apply it to the desulfurization control system of the actual coal-fired unit,the feasibility of the control strategy is proved by analyzing the operation results.The main research arrangements of this paper are as follows:（1）The control method of wet flue gas desulfurization system and the current status of desulfurization technology are briefly described,the basic principle and basic operating characteristics of the WFGD system are introduced.（2）By analyzing the conventional feedforward control strategy of desulfuri zation system,it is found that simple load feedforward control is difficult to meet the demands of desulfurization control system.Aiming at this problem,a feedforward control method of flue gas desulfurization composite control strat egy is designed by using the soft measurement of flue gas flow and the real-t ime correction method of slurry replenishment.（3）Aiming at the characteristics of large delay and large inertia of wet flue gas desulfurization system,a feedback control method of desulfurization composite control strategy based on internal model control was designed with the concentration of outlet sulfur dioxide as the controlled object,and the effectiveness of the internal model control is verified based on the historical operation data of the unit.（4）After the designed desulfurization composite control strategy is configured in DCS,it is applied to the actual desulfurization system of coal-fired units.By observing the operating curves of the parameters under typical working conditions,it is found that the designed control strategy is feasible and effective.