Research And Application Of Boiler Combustion System Based On Generalized Predictive Control

With the increasing demand for power supply,at present,China's thermal power plant small boiler is gradually replaced by sub-critical,supercritical or ultra-supercritical large-capacity boiler.But because that our equipment is not advanced,coupled with the technical level behind the developed countries,China's thermal power plant boiler combustion has the problems of low thermal efficiency,high coal consumption.Improving the performance indicators still exist a lot of room for development.In 2002,China put forward the reform of "plant network separation,bidding online" model,so the power plant must minimize the cost of power generation under the premise of protecting of safety of boiler operation that can participate in the competition effectively.On the other hand,China and the world have a serious energy crisis,environmental problems are becoming increasingly serious.Therefore,it is an important research topic of power plant development in China to improve the thermal efficiency of boiler combustion system,optimize combustion,reduce power generation cost,save energy and reduce pollutant discharge.It is also the research goal of many scholars at present.In this paper,a large-capacity direct current boiler of 600 MW unit in a power plant is taken as the research object.The combustion system of the boiler is analyzed and studied.The combustion process of the pulverized coal in the boiler is very complicated with the problems such as large time delay and nonlinearity.There are many factors that affect the burning process.Therefore,it is very difficult to establish the mathematical model of the boiler combustion system.In this paper,according to the three basic tasks to be completed in the boiler combustion system,the main steam pressure,the oxygen content of the flue gas and the change of the negative pressure ofthe furnace are controlled by the amount of air supply,the amount of coal and the amount of air(the speed of the draft fan)as the controlled variable,a mathematical model of multiple input and multiple output is set up as the controlled object to realize the research of the boiler combustion system.In the process of modeling,In order to prevent the neglect of some data of the original data that is smaller but characterizing the characteristics of the controlled object,the data are normalized by calculating the mathematical expectation and variance of the original data,The data is used to establish the mathematical model instead of the original data.In order to verify the accuracy of the model,another set of data input to the model,through the model output and real output comparison,proved that the model can replace the boiler combustion system as a controlled object to study.In addition,according to the characteristics of combustion hysteresis,the model is further optimized,and the time-lag term is added and processed.The identification results show that the optimized model is more accurate and has the characteristics of boiler combustion system.In this paper,the generalized predictive control algorithm is used to design the controller instead of the traditional PID controller to optimize the control of the boiler combustion system.Predictive control is generated in the industrial process control.The requirements of the controlled object model are not very high,which makes up the defects that the model is not enough accurate to lead to control effects are not accurate.At the same time,generalized predictive control rolling optimization and feedback correction features to make it a strong robustness and anti-jamming capability.The display algorithm of generalized predictive control needs to solve Diophantine with a large number of matrix inversion of the operation,which will cause large workload,long working hours.In this paper,the generalized predictive control of the implicit algorithm is selected which does not need to solve Diophantine,but the use of input and output data directly to identify the control rate parameters,reducing the amount of computation and saving time.The simulation results show that the implicit generalized predictive control algorithm has a good control effect on the boiler combustion control system,that improving the economy of the boiler combustion,maintaining the stability of the main steam pressure and maintaining the furnace negative pressure within the allowable range.