Temperature Control Strategy Of Boiler Main Steam Based On DCS Control System

In recent years,China's economy has developed rapidly.Therefore,in order to adapt to the pace of economic development,people's demand for electricity is also increasing.Although new generation methods such as nuclear power,wind power and solar power have developed rapidly in China,thermal power generation still occupies a dominant position.By the end of 2019,thermal power generation still accounts for more than 70%.However,thermal power is inseparable from the role of the boiler.In the normal operation of the boiler,the superheated steam temperature at the outlet of the high-temperature superheater,that is,the main steam temperature,is an important parameter in the operation of the boiler.Its level directly affects the stability,economy and environmental protection of the boiler operation.Therefore,in order to prevent the main steam temperature of the boiler from being too high and maintain it near the set temperature value,this paper combines a DCS control system commonly used in boiler operation to study a strategy for controlling the main steam temperature.This paper is based on the thermal process and heat transfer theory of the boiler main steam system.First,the structure of the boiler main steam system and the basic control method of the main steam temperature are studied.Moreover,this paper analyzes the static characteristics of the main steam temperature from the perspective of the temperature rise characteristics of the convection superheater and the radiant superheater in the boiler hearth.It also analyzes the dynamic characteristics of the main steam temperature from three factors: steam flow change,flue gas heat,and desuperheated water flow and introduces control characteristics of the main steam temperature and the dual-loop control system.Secondly,the structure and function of the PID control system applied to the main steam temperature control are deeply researched and analyzed.A cascade PID control system with feedforward and feedback is proposed,and it is modeled andsimulated in one dimension by using Simulink.The step signal is used as the initial signal in the simulation,and the interference signal is added during the simulation.The analysis of the simulation results shows that the control system with feedforward and feedback has good control characteristics.Subsequently,the main steam system of the boiler is analyzed,and the thermal calculation model of the main steam system is established by using MATLAB software.The calculation model is divided into five calculation modules: fuel combustion calculation,furnace thermal calculation,partition screen superheater calculation,high temperature superheater calculation,and temperature reduction water calculation.This model can calculate the total air volume,total coal volume,primary and secondary desuperheating water,and other parameters of the boiler,and these parameters can be displayed in the written GUI panel for easy input and calculation.Then,the nominal setpoints of the three typical loads of the boiler(50%,75%,100%)are compared with the module calculation results,and the error is within the range allowed by the model calculation,thereby verifying the accuracy of the calculation model.Finally,the MATLAB calculation model is used to calculate the relationship between the main steam flow rate and the temperature of the desuperheated water in the spray desuperheater,and it is applied to the main steam temperature feedforward-feedback control loop in the boiler DCS system.At the same time,the corresponding SAMA diagram is constructed and tested,and the test results show that after applying this system,the fluctuation of the main steam temperature is small and stable,and it has a good control effect.Through the above work,a complete main steam temperature control strategy based on the DCS control system is finally formed.