Research On Predictive Control Application In Denitration System Of Thermal Power Unit

With the atmospheric pollution problem going more and more serious, and the improvement of the public’s awareness of environmental protection. The coal-fired power plants are all required to conduct flue gas denitration process before they are connected to the grid. The most widely used denitration technology in power plants is a selective catalytic reduction (SCR) technology, However the traditional PID control effect does not meet the practical demand because the control object SCR system is big inertia, pure time-delay and nonlinearity. Predictive control is an advanced computer control algorithm, especially suitable for large inertia object. Research on application of predictive control to the denitration system control not only can realize the optimal denitration control to reduce costs, but also can reduce the ammonia injection quantity to reduce secondary pollution. So the research can bring great economic benefit and social value to power plant.Based on introducing the mechanism of nitrogen oxides generated, the NOx control technologies are systematically summarized in this paper. Then the theory and system composition of SCR denitration technology are introduced in details, the key factors of denitration effect are mainly analyezed. The traditional three SCR denitration control methods are fixed mole ratio control, fixed export concentration control and composite control. The control principle, advantages and disadvantages are analyzed and compared. The composite control is mainly applied in real industrial field, the control results of the composite control based on fixed mole ratio and the another based on dynamic mole ratio are compared in MATLAB simulation, they are two kind composite control. It can be figured out that the control effect based on dynamic mole ratio is better than the other, but the regulation time is still long, the actual control effect is not good. Finally, the dynamic model control of predictive control method are applied into the spraying ammonia control of SCR denitration. Considering the export NOx concentration and spraying ammonia valve life, the simulation result indicate that the predictive control effect is better than the composite control. Although there is certain overshoot for DMC, its response speed is fast and the regulation period is short, the regulation period is less almost 200s compared with the composite control. Moreover, the ammonia injection valve opening changes slowly, and there is no changes in volatility. The SCR based on predictive control is adaptive to the change condition and interference, so it can realize a better optimal control to not only save ammonia, but also extend the life of the ammonia injection valve.