Numerical Investigation Of Coal Combustion Characteristics In A 660MW Supercritical CFB Boiler

In the current era of increasingly prominent environmental problems,the new clean coal combustion technology represented by CFB combustion technology deserves attention.Large and supercritical scale is an inevitable trend in the future of CFB boiler,so the development of CFB boiler is becoming more and more urgent for the research of coal combustion in the furnace.Because of the difficult reality of experimental research,it is a feasible method to study the coal combustion process in the furnace by numerical simulation.The flow,combustion and heat transfer process synthetically constitute the coal combustion process in the CFB,so a reasonable and effective mathematical model needs to be established in the study of simulation.Firstly,the control equation and the formula of particle dynamic model under the framework of Euler flow model are introduced.At the same time,the corresponding mathematical model is selected for the main chemical reaction process of the coal combustion in the furnace.The corresponding model is selected for the heat transfer process in the furnace.Pollutants like NOX and SO2 produced in the furnace also introduced about the corresponding reaction equation and rate formula,which is a good preparation for the following simulation research.Secondly,the combustion process of coal in a small CFB experimental device is simulated.The conclusion of calculation are compared with the experimental data to receive the result of the rationality and accuracy of the selected model.On the base of multiphase flow model,the burning chemical reaction models and thermal transmission models can be coupled to simulate the coal combustion process in furnace.The results show: volatile gas releases rapidly after the coal particles enter the furnace.The volatile gas concentration gets maximum at the coal inlet,then it gradually decreases with the increase of height.In the dense area of the bottom of the furnace,the gas phase temperature rises with the increase of height.The gas temperature reaches the maximum value near the second air inlet.In the dilute phase region of the upper and middle part of the furnace,the temperature goes down with the increase of height.NO begins to occur at the feed back of the furnace,reaching the maximum at the coal inlet,and the concentration in the dilute phase decreases gradually.The mole fraction of SO2 increases in dense phase with the increase of height,whose concentration reaches the maximum at the coal inlet.The SO2 concentration is relatively well-distributed in the dilute phase above the second air inlet,which increases lightly.Finally,the combustion process of coal in 660 MW supercritical CFB boiler is studied,and the Z velocity,temperature,gas types and chemical reaction in the furnace is obtained.Meanwhile,the influence of different operation parameters on the combustion characteristics of the furnace is studied.The results show: particle Z direction velocity shows a typical "ring core" flow state.With the increase of height,the gas phase temperature in the furnace increases rapidly in the dense area,and gradually decreases in the dilute area of the furnace.The main distribution of mole fraction of O2 and CO2 is that with the increase of the height,t the concentration of CO2 goes up and the concentration of O2 does contrarily.The volatile gas has a maximum concentration at the coal inlet and depletes with the reaction.The area of char combustion reaction is very large,and the reaction in dense phase area is larger than that of the dilute phase zone.The combustion mode of char is generally under the diffusion control.With different running parameters,the increase of primary air and second air speed will increase the O2 concentration and decrease the CO2 concentration at the outlet of the furnace.Concentration at outlet of O2 decreases and CO2 increases as particle size increases.