Dissertation > Industrial Technology > Energy and Power Engineering > Thermal engineering, heat > Thermal Engineering Theory > Heat Transfer

Kinetic Theory of Rough Spheres and Numerical Simulation of Fluiidzed Bed Gasifier

Author HaoZhenHua
Tutor LuHuiLin
School Harbin Institute of Technology
Course Thermal Power Engineering
Keywords Coarse particle kinetic Coal Gasification Dense gas-solid flow Particle rotation Numerical Simulation
Type PhD thesis
Year 2011
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The gas-solid two-phase flow phenomena are widespread in the field of chemical, electric power, metallurgy, food, pharmaceutical and other Solid Flow in-depth understanding and mastering the inner mechanism and the law has an important practical significance. With the continuous development of computer technology and computational methods, numerical simulation has become one of the main methods of gas-solid flow studies. However, due to the complexity of the gas-solid system, there is still much to improve and enhance the theoretical models of gas-solid two-phase flow simulation. Solid Flow, the particles having different surface roughness, the coarse particles in the collision and turbulence will be generated under the action of the rotary motion. The experimental and theoretical simulation results show that the the particles rotation will affect the trajectory of the particles, the concentration distribution, as well as a variety of other macro-and microscopic parameters. Unfortunately, the current the particles kinetic theory is based on smooth particle assumed from the theoretical derivation process only consider the translational motion of the particles, the rotational motion of the particles is not considering. Based on this, there is a need to develop coarse particle kinetic and applied to the gas-solid two-phase flow simulation. Departure from the basic principles of particle kinetic the coarse particles kinetic model. The traditional particle kinetic theory using only pseudo-particle translational temperature to describe the strength of the particle fluctuation, this article introduces the concept of particle proposed total temperature, particle quasi-total temperature comprehensive characterization of particle translational motion and particle rotational motion fluctuation intensity. The combined transport theory to consider the quality of the particle phase rotation of particles, momentum, and the proposed total Wen Shouheng equation. Take the Chapman-Enskog approximation linear solution method for solving the corresponding force has both translational and rotational movement of the particles, the heat flux and energy dissipation parameters on particle velocity distribution function. And on this basis, the particle phase pressure, the particle phase shear viscosity and particle phase dissipative such constitutive equation, calculation model and boundary conditions. Rough particle kinetic model of gas-solid two-phase flow characteristics in the numerical simulation bubbling bed. Yuu and Taghipour size and condition of the experimental structure numerical simulation, the simulation results show that using coarse particle kinetic model when the bubble diameter and bed expansion were increased. Simulated bed particle speed and fluctuating velocity distribution with Yuu measured results coincide. Bed particle concentration distribution, velocity distribution, and the size of the bed expansion is close to Taghipour measured results. By changing the cut to the elastic coefficient of restitution, analysis and comparison of the different tangential restitution coefficient of particle intend total temperature, shear viscosity, bulk viscosity, particle pressure and thermal conductivity with particle concentration variation. Rough particle kinetic model, numerical simulation to enhance the gas-solid two-phase flow characteristics within the tube. The simulation results show that the riser of particle concentration the distribution under concentrated along the bed axial dilute, along dilute side wall, the middle of the bed radial concentrated distribution. Within the riser at the same time can be clearly observed the formation of particle clusters, sports and disappear. At high mass flow rate, the simulation obtained when the concentration of particles radially, when experimental measurements of the average mass flow rate of particles radially as well as the distribution of the bed pressure drop and Knowlton such good agreement. When in a low mass flow rate, the simulated consistent with the measured results of the particle phase concentration, velocity and mass flow rate distribution and Miller et. , As compared with conventional particles kinetic roughness the particle dynamic mathematical model consider the energy loss caused by the rotational movement, and other reasons, increasing the concentration of particles at the wall, while the lower concentration in the central region, along the radial direction of the particle velocity becomes smaller. Analysis of the different cut at the same time enhance the macroscopic parameters such as concentration and speed changes in the tube, as well as particles contemplated changes in the total temperature, shear viscosity dissipation microscopic parameters to the elastic coefficient of restitution, the results show that different tangential restitution coefficient simulation parameters distribution trend. Considering particle rotation coarse particle kinetic - gasification reaction solid flow - the reaction calculation model, numerical simulation fluidized bed gasification reaction and central jet fluidized bed flow - the reaction process. The simulation results with experimental measurements of others coincide. Simulation results show that relative to the combustion reaction to generate large volume of carbon dioxide, carbon monoxide and hydrogen and other combustible gases at very low concentrations in the bottom of the fluidized bed reactor, the gas-solid isobutyl. Accompanied by implantation layer increases the oxygen is depleted, the reduction reaction began to dominate, and the volume concentration of carbon dioxide is gradually decreased, the volume of a gas such as carbon monoxide and hydrogen concentration increases. The results show that the bottom of the uniform inlet of fluidized bed reactor bed is such that the temperature rise due to the combustion reaction. In the upper portion of the bed although the reduction reaction absorbs heat, but the vigorous stirring effect due to the bubbles in the bed, so that the fluidized bed upper temperature more uniform. Central jet fluidized bed, the central jet region to form a local high temperature region, the temperature of the side wall area is relatively low, and the uneven distribution of the temperature within the bed can help the oxidation - reduction process of the coal particles in the bed.

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