The Numerical Simulation Of Gas-Solid Flow And Combustion In Chamber Of Four Wall Tangentially-fired Pulverized Coal Boiler

Currently China has already regarded coal as the principle energy. The burn of coal is the ecological heavy pollution sources of environmental disruption. Tangentially-fired technique is the main combustion way that widely adopted by large electricity station boiler, especially the four-wall tangentially-fired combustion as a new technique has good engineering application foreground. The research on the pulverized coal flow and combustion in the pulverized coal furnaces is one of the most significant studies of the control of pollution resulting from the coal combustion. One of the key problem on the combustion technique is to find the reasonable condition that both the coal can combust fully and the pollutant for example as the nitrogen oxide can have a low exhaust. Therefore, the main text of this paper is, firstly to construct a reasonable mathematics model for the combustion, And then to analyze the turbulence flow velocity field, the temperature field and the density field with numerical simulation method, lastly to compare the test data and to prove the rationality of the model. On the foundation of above calculation analysis the effect that extra air quantity or coal powder densities bring to the combustion and the production of nitrogen oxide.This paper is to take the test model of a 1MW pulverized coal fumaces of four wall-tangentially-fired as the research subject and analyse the temperature field and pollution density field. According to the structure characteristic of the chamber and the flow characteristic, the author uses the approach of rotating the mesh system to divide the area of burning and the approach of the block-structured grid method and the adaptive grid technology to divide the mesh and refine the grid. This method can reduce false diffusion in the numerical simulation, ease the difficulty of the mesh generation, and control the numbers of the mesh, which can save the computing time efficiently.As to the gas phase flow field, the author choose the realizable k-s model and the Reynolds stress model to make simulation and comparison. The results show that the realizable k — s model is more reasonable in the chamber simulation on the common condition for its little computation amount. The convective term adopted the QUICK scheme which is accurate enough to discrete. This paper adopted the track model of particle on simulating trajectory of the particles of the two-phase flow anddeals with the turbulent difiusion with stochastic tracking approach. The paper adopted gas burning with mixer fraction-probability density function model and radiation with P-l model.To simulate the combustion of pulverized-coal, Single kinetic rate model and two competing rate Kobayshi model are compared in the stage of volatiles combustion, Difiusion limited reaction rate model and Kinetic/Diffusion reaction rate model are compared in the stage of char combustion. The results show that the combination of Two competing rate Kobayshi model and Kinetic/Diffusion reaction rate model are suitable for calculate the combustion.The result show that increase the air excessive coefficient can decrease combustion efficiency and increase the exhaust of production of nitrogen oxide, therefore the air excessive coefficient should be controlled in some certain range.