Study On Dynamic Modeling On Bed Temperature Of Coal Slime Co-combustion Circulating Fluidized Bed

Slime is a waste produced by deep processing of coal.It has the characteristics of small particle size,high moisture content and et al.It is difficult to store or transport,which accumulate in the outdoors can cause environmental pollution.The circulating fluidized bed boiler has a unique advantage in terms of fuel adaptability and pollutant discharge.Therefore,the coal slime co-combustion circulating fluidized bed technology provides an effective way to reduce the cost of power generation and the environmental pollution.The internal combustion process of circulating fluidized bed boiler is complicated,and the object of combustion control system has the characteristics of multivariable,strong coupling and large delay.As one of the most important parameters of the combustion control system,bed temperature is supposed to maintain within 850?900?.When the bed temperature is too high,the desulfurization efficiency will be decreased and the bed material will coke,on the contrary,the combustion efficiency will be reduced.In the coal slime co-combustion CFB boiler,burning slime will reduce the boiler bed temperature,even leads to boiler fire-off.Therefore,it is of great significance to predict the bed temperature in real time for guaranteeing the safety and stability of the unit.In this paper,a 300MW circulating fluidized bed unit in Linhuan is taken as the research object.The research contents are as follows:(1)Based on the previous research on the combustion,flow and heat transfer process in the circulating fluidized bed boiler combustion system,the bed temperature mechanism model was established.By analyzing the physical and combustion characteristics of slime,the structure and characteristics of the circulating fluidized bed boiler combustion system,the furnace is divided into dense phase and dilute phase area.Through analyzing the dominant process,which includes dynamic material balance,dynamic residual carbon balance,oxygen balance and dynamic energy balance,a dynamic model with input of coal feed,slime,primary air,secondary air and the opening of external bed valve.Based on Linhuan 300MW circulating fluidized bed unit field operation data,this paper used MATLAB for simulation verification.The results show that the model is consistent with the actual field data,and the accuracy of the model is verified.(2)In order to study the influence of different modeling methods on the accuracy of the model,in this paper,the least squares support vector machine(LSSVM)algorithm was used to establish the dynamic model of bed temperature of coal slurry circulating fluidized bed.Firstly,the basic principle of least squares algorithm is introduced,and the least squares support vector machine(LSSVM)dynamic modeling method is proposed,which takes into account the delay characteristics of each input variable and output variable to improve the accuracy of the model.Through the theoretical analysis,the input variables and the delay order of each variable are selected.Finally,the dynamic model of bed temperature is established with input of coal feed,slime,primary air,secondary air and the opening of external bed valve.The simulation results show that the result is consistent with the actual data.(3)Compared with the LSSVM dynamic model,the mechanism model is low accuracy.But the two models can correctly reflect the trend of bed temperature,it provides references for the research of coal-slime co-combustion circulating fluidized bed combustion system.