Coal-Dust Explosion Study as Related to Entrained Coal-Gasification Schemes. Final Report

摘要

In summary, the preliminary model study indicates that because of the high temperature in the gasifier, the reactions during coal feed failure are injection flow rate limited, and the explosion risk is low. When the coal feed restarts, there are two types of explosion risks involved. If the reactants in the gasifier are not hot enough to insure an instantaneous ignition, a delayed spontaneous ignition or a hot spot ignition could occur. When spontaneous ignition occurs the final pressure ratio depends on the volume of the mixing zone between oxygen and fuel gas, and the initial temperature of the mixture. If a hot spot ignition occurs, the final pressure ratio depends on the ignition source, fuel gas concentration, diffusion and mixing, and particle cloud characteristics. In the case of hot spot ignition a detonation wave with overpressure ratio on the order of twenty could occur. A study of operating and design solutions indicates that the risk of initiating a detonation can be minimized by the following techniques: two-stage gasifier design, aspect ratio(1/d) of approximately one in the combustion section, mixing mechanism control, and heat transfer control. The effects of deflagration explosions can be reduced by: optimum combustion section volume, mixing control in the combustion and gasification sections, heat transfer control, and vent design. In this study, only preliminary quantitative trends of the key physical and chemical phenomena were studied. More parametric modeling studies are needed to quantify the results to assess more exactly the explosion risks, and to provide design guidelines to reduce the risks. (ERA citation 08:025317)