Research On Modeling And Control Strategy Of SCR Flue Gas Denitrification System In Thermal Power Plant

With the increase of the total installed capacity of coal-fired thermal power generating units and the enhancement of people's environmental awareness,the emission standards of NOx in China will be further rigorous.Selective catalytic reduction(SCR)denitration technology is widely used,because of its high denitration efficiency,little secondary pollution,and mature technology,however,part of the power plant has not reached the requirements of ultra-low emission.The mathematical model and control strategy of SCR denitration system can be used to provide technical means for the emission of nitrogen oxides in power plant,and also have some reference value for improving the control effect in the field.In this paper,the SCR flue gas denitrification system of a 600 MW thermal power unit was taken as the research object,and the process of its denitrification and the factors affecting the efficiency of denitrification were analyzed.Based on the fading memory recursive least squares(FMRLS)method and the useful information from the historical operating data of denitrification system,ammonia flow and NOx emission model of SCR denitrification system under turbine heat acceptance(THA),85% THA,75% THA and 50% THA were established by using experimental modeling method on Matlab simulation platform,and the precision of the model was verified and analyzed.The results show that compared with the RLS model,this method has the advantages of small deviation range,fast convergence speed and high fitting degree,which verifies the validity of the model.The model can approximately reflect the dynamic and static characteristics of the denitration system in a power plant,which provides a model reference for the automatic control of the ammonia injection and the efficient reduction of NOx emission.Secondly,this model is used to study the control strategy of ammonia injection in the SCR denitration process,and the gain scheduling controller of denitrification feed-forward plus cascade system is designed.Taking the load as the dispatch variable,the above four conditions were selected as the basic working condition points.Using genetic algorithm to optimize the PID parameters of the primary and secondary controllers,and the multi-node spline interpolation algorithm was used to design the PI parameter values between two conditions to complete the global gain scheduling controller.And the control effect of the controller was verified at non-basic operating conditions.Finally,the model and control strategy are introduced into the integrated process model development platform IMMS system.The algorithm is written by Fortran language,and built the SCR control model to study its operation characteristics undervariable conditions.The experimental results show that the model has good control effect,has strong stability and practicability,which verifies the feasibility of IMMS platform applied to denitrification control system of power plant.