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Numerical simulation of boiler primary air flow through a throttle orifice

classification No.: o242.1:tk223.2 document identification code: a

Article No.: 1001-2060 (2000) 02 - numerical simulation of a boiler primary air flow through a throttle origin platepan Weiguo Shen Feng Zheng Puyan, et al

（Shanghai Electric Power Institute）Abstract：A numerical simulation was conducted of the air and pulverized-coal multi-phase flow pattern after an adjustable throttle orifice-plate was installed in the pulverized-coal horizontal feed-pipe of a boiler combustion system. It has been found through the above-mentioned simulation that an effective numerical simulation method consists in the following：a gas-phase turbulent flow model is first described by the use of a K- ε Dual equation model and with t he help of simple algorithm the gas phase speed field can be calculated Then, a FSRT model and Lagrange method are employed to calculate the particle field characteristics.

key words: gas solid multiple phase flow, numerical simulation ▲ 1 Introduction

gas solid multiphase flow widely exists in energy, chemical industry, metallurgy and other industries. The mixture of pulverized coal and air in the primary air duct of utility boilers is a typical gas-solid multiphase flow, and its research has important theoretical significance and engineering application value

in the research process of gas-solid multiphase flow, in the early stage, it mainly relied on experimental means [1, 2]. Then with the continuous development of computer technology and computing technology, multiphase flow entered a new field, and numerical simulation began to replace experiments. Various computational models continued to emerge, followed by turbulent viscosity model, pseudo fluid model and K- ε Two equation model. In addition, for the flow near the pipe wall, there is K with low Re number successively- ε Double equation model, wall function method and Q proposed by Gibson m m and Dafa ′ alla a [3] et al- ζ Model, and they have respectively carried out numerical simulation of different flow conditions, and achieved satisfactory results. Although the flow models are diverse, they can be divided into four models theoretically, namely, no slip model, small slip model, slip diffusion model and particle swarm orbital model. Among them, non slip model, small slip model and slip diffusion model treat particles as continuous media, which generally use two fluid model to complete different experimental calculations; The particle trajectory model is generally solved by the particle source method (PSCI method) proposed by Crowe [4], which investigates the motion of the fluid phase in the Euler coordinate system and the motion of the particle swarm in the Lagrange coordinate system

although the two fluid model and the convergent development channel model of the rail driven aluminum base high-end metal material base are widely used and have many good results, they can not well reflect the actual situation, especially problems such as different turbulent diffusion effects under different particle sizes. For this reason, some scholars proposed FSRT model on the basis of PSIC method, and calculated the gas-solid two-phase jet problem with this model, and the result is closer to the actual working condition [5]. In this paper, the corresponding mathematical model will be used to study the flow of gas powder mixture through the primary air duct with different orifice openings by numerical simulation. 2. The basic method of numerical simulation of gas-solid multiphase flow

now the simple algorithm in the pressure correction method is generally used to solve the Navier Stokes equations, that is, in single-phase flow, the continuity equation is used to correct the pressure, so as to obtain the corrected value of velocity and new flow field distribution; Then for gas-solid multiphase flow, using the previously calculated velocity distribution, the corresponding multiphase fluid flow model and the particle wall collision rebound model, the motion characteristics of the particle field are calculated by using the L ------- the agrange method of Dr. Sun Jingyao, School of electrical engineering, Beijing University of chemical technology, and the coupling calculation of the gas-phase field and the solid-phase field is carried out

this paper adopts the turbulence model K, which is widely used in engineering- ε For the two equation model, the partial differential equations closed in the rectangular coordinate system can be written in the following general form: (1) where, Γ， See reference [6] for the significance of s items

the fluctuating spectrum random particle trajectory model considering the turbulent diffusion of particle groups is used to simulate the gas-solid two-phase flow, and the empirical relationship of collision rebound recovery ratio (beacher Tabakoff, 1982) obtained by Taba koff et al. From a large number of experiments is used to simulate the collision between pulverized coal particles and the wall: (2) (3) where α 1 and α 2 is the collision angle and rebound angle respectively; VP1 and VP2 are particle collisions, respectively

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