A numerical study was conducted to investigate effects of flow distribution of WSF(Well-Stirred Flow)/PF(Plug Flow) region in a pulverized coal reactor on the combustion efficiency at coal gasification process. The computation model was based on gas phase eulerian balance equations of momentum, mass, and energy. The solid phase is described by lagrangian equations of motion. The code was formulated with κ-ε model for turbulence flow, Monte Carlo method for radiation heat transfer, and eddy dissipation model for turbulent gas phase reaction rate. One-step two reaction model was employed for the devolatilization process of a Kideco coal. By comparing the computations with the experiments, the usefulness and application of the numerical code were evaluated. In case that the multi-species over three species were evolved during the devolatilization and Q factor, indicating the ratio of actual volatile yield to the proximate volatiles contents, was defined as 1.2, the optimal results were obtained. The computations agreed well with the experiments, but the flame front was closer to the burner than the measured one.
The flow distribution of stirred part and plug flow part in a reactor is a function of the swirl number. The maximum combustion efficiency was found around S=1.2, having minimum stirred part. However, the combustion efficiency depends upon not only the flow distribution but also the particle residence time through hot reaction zone. Particularly, it was important for the weak swirl without internal recirculation zone and long liftoff height of the flame, since many particles moved to the low temperature region near the wall.
Effect of the radiative heat transfer on the flow field was comparatively small. The ratio of wall heat loss to the total enthalpy was dominant only in the wall temperature distribution. The steam had a detrimental effect on gasification process. The decrease in primary jet velocity and initial turbulent intensity increased the liftoff height of the flame.
The experiments in two reactors, which had the different heating mechanism, were performed to offer the data for the validation of computations. For reactor A losing large heat through transparent quartz wall, pulverized coal particles were ignited by secondary air of 1050K and visualized. Reactor B, insulated with castable reflactory to minimize the heat loss through the wall, was conducted to measure the gas temperature and concentrations within the reactor. The heating rate for the flame liftoff was of the order of $10^4$ to $10^5$K/s and for coal flame at least over $10^4K$/s. The heating mechanism of convection and radiation had little impact on extinction limits.