Effects of Turbulent Mixing and Controlling Mechanisms in an Entrained Flow Coal Gasifier

Abstract

There is a large range of time and length scales of turbulent fluctuations in an entrained flow coal gasifier. To figure out the turbulent effects on coal gasification processes and the controlling mechanisms of different regions in an entrained flow coal gasifier, the characteristic time and length scales for all major processes are estimated. On the basis of the comparison between the length/time scales of turbulent mixing in all ranges and the characteristic time of homo- and heterogeneous reactions, turbulent effects on reactions and coal gasification processes in different regions in an entrained coal gasifier are studied. In the flame region, there is a strong coupling effect between macro-scale turbulent fluctuation and heterogeneous reactions. The combustion of the volatile is strongly affected by the fluctuation of micro-scale Kolmogorov scales because the diffusion boundary layer of the particles is destroyed by this kind of fluctuation. In the nonflame region, the heterogeneous char gasification reactions are not affected by turbulent fluctuations; however, the coupling effect between turbulent mixing and gas-phase reactions should not be omitted.