Analysis of flow, gas-particle radiation, and particulate deposition in radiant boilers

Abstract

Flow, heat and mass transfer processes in the radiant boilers of magnetohydynamic power plants are analyzed. Flow field in the radiant boiler is simulated by assuming a uniformly mixed zone to exist in the entrance region, followed by a developing boundary layer region. Heat transfer is presumed to occur by both turbulent convection and radiation. The radiation model includes the simultaneous contribution to heat transfer of carbon dioxide, water vapor, potassium atoms, and slag particles which are allowed to absorb as well as scatter thermal radiation. The absorption coefficients of gaseous species are determined from band correlations and experimental data. The extinction and scattering coefficients of slag particles are computed directly from Mie theory. For computing heat transfer, radiation transport equation is solved on a spectral basis. The complete flow, heat and mass transfer model is used to study the thermal characteristics of the radiant boilers. Impacts of slag-refractory interface temperature on corrosion and erosion of refractory, and of slag layer thickness on plant start-up time are discussed. By presenting the scale-up of heat transfer with refractory thickness and boiler diameter, the factors involved in designing an experimental facility for simulating base load boilers are highlighted. The temperature history computed from the heat transfer model is used in an extant chemical kinetics code to determine the practical levels to which NO/sub x/ can be decomposed in MHD radiant boilers. Calculations indicate that the EPA specified limit on NO/sub x/ levels can be met in properly designed radiant boilers operating with sub-stoichiometric products of combustion. The potential of the complete model to serve as a strong analytical tool in selecting an optimum geometry for radiant boilers is stressed by proposing an optimization procedure. (WHK)