Han Chang Cho

A numerical study on the effect of flow distribution on reactor performance

A numerical study was conducted to analyse the effect of flow distribution of stirred part and plug flow part on combustion efficiency at the coal gasification process in an entrained bed coal reactor. The model of computation was based on gas-phase Eulerian balance equations of momentum and mass. The solid phase was described by Lagrangian equations of motion. The k–ϵ model was used to calculate the turbulence flow and the eddy dissipation model was used to describe the gas-phase reaction rate. The radiation was solved using a Monte-Carlo method. A one-step two parallel reaction model was employed for the devolatilization process of a high volatile bituminous Kideco coal. The computations agreed well with the experiments, but the flame front was closer to the burner than the measured one. The flow distribution of a stirred part and a plug flow part in a reactor was a function of the magnitude of recirculation zone resulting from the swirl. The combustion efficiency was enhanced with decreasing stirred part and the maximum value was found to be around S=1·2, having the minimum stirred part. The combustion efficiency resulted from not only the flow distribution but also from the particle residence time through the hot reaction zone of the stirred part, in particular for the weak swirl without IRZ (internal recirculation zone) and the long lifted flame. Copyright

NOx Emission Characteristics in Radiant Tube Burner with Oscillating Combustion Technology

An experimental study was carried out in a small-scale furnace to investigate the performance, such as NOx emission, enhancement of heat transfer, uniformity of temperature, and etc., of oscillating combustion applied in radiant tube burner system for heat treatment furnace. A premixed type burner and a solenoid type oscillating control valve were designed and used. The fuel was used commercial LPG in this study and the fuel flow was oscillated by periodically opening and shutoff of the solenoid valve. From the tests, it was found that NOx emission, compared to no oscillation, could be reduced by 32% at 2.0 Hz. However, as oscillating frequency was increased, abatement of NOx emission was gradually reduced. At the high NOx abatement of 1.0 Hz, carbon monoxide was emitted above 10,000 ppm. Although rate of NOx abatement was low, oscillation condition of 2.5 Hz and duty ratio of 10-30% was recommended for low carbon monoxide emission. From the measurement of furnace heating time from 100 ℃ to 720 ℃, it was shown that heat transfer was increased by 11.5% at 2 Hz oscillating frequency. Temperature distribution of radiant tube surface was more uniform at 2 Hz oscillating frequency with drop of the peak temperature and rise of low temperature. From these results, it was confirmed that oscillating combustion was useful in radiant tube burner system.