Numerical Simulation On The Heating Process Of Pulverized-Coal Particles In Boilers

This paper presents a model on heating up analysis of pulverized-coal cloud heated by the smoke convection and radiation correlated in the boilers. It is aimed at the heating up analysis of pulverized-coal cloud heated by the smoke in the form of convection. The calculation methods of heat convection are different due to different pulverized-coal particle diameters. There is a large error with the calculation methods of convection to the small pulverized-coal particles if we adopt traditional methods. A new method is raised here, the coal combustion smoke is free molecule liquid or continuous liquid to the small particles. We get the calculation expression with physical parameters of pulverized-coal cloud and external heating conditions. When the Knudsen number is larger than 0.001, the gas flow is uncontinuous to the pulverized-coal particles, and the calculation of heat convection should be reconsidered. Base on the mechanism of molecule collision heat exchange, the computation method of heat convection from uncontinuous flow to the particles is obtained in this paper, and it fits the particles of different diameters. In the radiation computation, the thickness of flames is different in different volume sizes, and the equivalent blacken is different, thus, a new method of calculation fitting the furnace better is raised. The pyrolysis, the devolatilization, the heterogeneous reaction of coal char in the process are calculated by numerical simulation. Also the relationships of pulverized-coal thickness, coal particle size, the volatile yield for pulverized and coal devolatilization, heating temperature, heated time and particle temperature are investigated here. The model simulates the heating-up process in the furnace exactly, and the proportion of convection and radiation in heating source is analysed. In the computation, the result using means in this paper is more accurate to the particles less than 10 μm, and it is anastomotic with the traditional methods when the diameters of the particles increase, the proportion of heat convection is about 15% by analysis. The simulation of particle temperature of the model which reflects the mechanism of temperature changes while heating particles. Calculating method for pulverized-coal efflux micro-element's heating and firing is presented, besides the referenced data when designing the industrial coal combustor and the optimum combustion of boiler is also provided.