Powder Technology, Vol.235, 359-367, 2013
Numerical simulations and experiments on heat transfer around a probe in the downer reactor for coal gasification
The heat transfer performance of a downer reactor has great significance for coal gasification processes due to the very short residence time of coal. In this study both experimental and numerical works were carried out to study heat transfer around a heating probe in a downer. Both experimental results and numerical results revealed that average heat transfer coefficients decreased with increasing superficial air velocity or decreasing solid mass flux, which could be attributed to decreasing solid holdup, as particle-particle convection was dominant in the heat transfer mechanism for the current cases. Numerical simulations also revealed that heat transfer may deteriorate with increasing particle size. Finally it was found that the heat transfer performance with constant temperature boundary condition around the probe was much better than that with constant heat flux boundary condition. These results may help us better understand heat transfer in downers for improving the design of downers with higher efficiencies. (C) 2012 Elsevier B.V. All rights reserved.