Dissertation > Industrial Technology > Energy and Power Engineering > Steam Power Engineering > Steam boiler > Theory

Numerical Simulation of Gas-solid Two-phase Flow and NOx Reduction

Author MoGuiYuan
Tutor ZhouZuo; QiuKunZan
School Zhejiang University
Course Engineering Thermophysics
Keywords Gas-solid two-phase flow Numerical simulation Particle collision SNCR
Type Master's thesis
Year 2012
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Gas-solid two-phase flow and NOx control are two important factors in the research of boiler. Gas-solid two-phase flow is a common phenomenon in the pulverized coal conveying, it will influence the solid distribution downstream of the burner outlet and then affect the combustion efficiency. Pollutants emission control is am important issue related to the environmental protection for the high pollution industries. In this work, numerical simulation of the gas-solid two-phase flow and pollutant control are carried out.Lattice Boltzmann method (LBM) was used to calculate the particle distribution and the turbulent vortex in the flows around a circular cylinder and a turbulent jet flow. When the Reynolds number is less than50, the flow is steady and no vortex structures are formed. Unsteady vortex shedding occurs when the Reynolds number is greater than50. The symmetrical model of recirculating zones changes to asymmetrical pattern when the Reynolds number increases. As for the turbulent jet flow, the flow changes from initial symmetric mode to asymmetric mode with the development of the flow. And asymmetric pattern appears first at the position of x/d=4, where the vortex structures begin to form. The dispersion of particles at different Stokes number shows various distributions.Discrete element method (DEM) with the computational fluid dynamics (CFD) was employed to simulate the gas-solid two-phase flow jet in a fuel rich/lean burner. The particle dispersion became more uniform between the fuel-rich side and the fuel-lean side for particles with small Stokes number; while for particles at St>1, a better fuel rich/lean separating performance was achieved. A good fuel rich/lean separating performance can be obtained with the collision block height of60mm. The particle dispersion between the fuel rich side and the fuel lean side became more uniform as a result of the particle-particle interaction. The corresponding experimental results were used to validate the numerical results, and a better agreement between the simulation and experiments was achieved due to the particle-particle collision.Selective Noncatalytic Reduction (SNCR) is one of the widely used methods in removing the NOx. In this work, numerical simulation of SNCR in Circulating Fluidized Bed (CFB) was conducted. The influence of the ammonia spray jet location and the NSR on the NOx remove efficiency was investigated. The results show that the spray jet on the lower side has the best performance of NOx reduction and efficiency is57.6%. With the increase of NSR. the efficiency increases, but the NH3slip also increases. The proper NSR should be1-1.2for CFB SNCR application.

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