| China's primary energy is mainly coal.The combustion of coal produces nitrogen oxides,sulfur dioxide,particulate matter and other atmospheric pollutants,which have a serious impact on the atmospheric environment and people's production and life.The Chinese government attaches great importance to environmental protection and actively promotes the ultra-low emission transformation of coal-fired power plants.The emission of coal-fired flue gas pollutants will reach the most stringent international standards.The efficient and stable operation of the denitration system is the key to achieving the NOx emission concentration of coal-fired power plants.Due to the nonlinearity and hysteresis characteristics of the denitration system,the traditional PID control technology is difficult to maintain the stability of the NOx concentration at the outlet of the denitration system,resulting in excessive fluctuations in the concentration of NOx in the outlet.On the one hand,the phenomenon of excessive NOx concentration in the outlet is frequently caused,and on the other hand,it is guaranteed.When the export NOx concentration reaches the standard rate,it is necessary to increase the amount of ammonia sprayed,and the cost of ammonia injection in the denitration system will increase.How to solve the control problems caused by the nonlinearity and hysteresis characteristics of denitration system,reduce the fluctuation of export NOx concentration,and reduce the ammonia injection cost of denitration system is an important research direction for the operation and control of denitration system in coal-fired power plants.In this paper,the following research work is carried out around the optimization problem of denitration system:Firstly,aiming at the hysteresis characteristics of the denitration system,a correction method for the determination of the inlet NOx concentration of the denitration system based on the cyclic neural network was established.The NOx concentration measurement lag time at the inlet of the denitration system is obtained through actual data.The NOx concentration at the inlet of the denitration system is corrected and modeled,and the NOx concentration measurement at the inlet of the denitration system is predicted in advance.Reduce the error introduced by the CEMS measurement lag.The simulation results show that the NOx concentration measurement correction method of the denitration system significantly improves the NOx concentration measurement accuracy and can reduce the CEMS measurement lag error by 32.6%.Secondly,for the nonlinear characteristics of denitration system,a multi-model Predictive Control(MMPC)for denitration system was established.Multiple load sub-intervals are divided based on working conditions,and multiple predictive controllers are used to obtain a nonlinear control strategy covering full load,which improves the control stability of the denitration system under wide-scale fluctuations.At the same time,combined with the NOx concentration measurement correction method,a measurement correction-multiple model predictive control(MC-MMPC)based on the inlet NOx concentration measurement correction is proposed to further improve the control stability of the denitration system.The simulation results show that the model accuracy of the multi-model can be improved by 23.5% compared with the single model.The MMPC control strategy can reduce the standard deviation of the export NOx concentration by 18.1% compared with the PID control strategy.The SS-MMPC control strategy is compared with the PID control strategy.It can reduce the standard deviation of export NOx concentration by 34.0%.Thirdly,in order to realize the efficient and stable operation of the denitration system,the engineering application research of the denitrification system predictive control strategy was carried out on a 220t/h thermal power unit.Based on the established coal quality,denitration system equipment,denitration system operation database,etc.,obtain the dynamic matrix control strategy(DMC)suitable for denitration system,and analyze the performance of various working conditions in the actual operation process..The results show that compared with PID control,the standard deviation of outlet NOx concentration is reduced by 11.2% and the ammonia-nitrogen ratio is reduced by 2.7%.Further comparison and analysis of the steady and variable working conditions of the denitration system can be concluded.Under the DMC control,the DMC control is similar to the PID control.Under the variable working condition,the response speed of the DMC control is better than the PID control. |
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