Abstract
Four different coals were gasified to investigate the relationship be-tween gasification efficiency and coal properties in an entrained-bed gasifier. The increase in the oxygen-coal ratio resulted in a maximum value of cold-gas efficiency (ηg). The optimum oxygen-coal ratio (λoop), corresponding to the maximum value of cold-gas efficiency (ηgmax.), was dependent on coal properties. Under actual operating conditions, ηgmax. ax could not be obtained if the ash fluid point (Tf) of the coal was comparable to the temperature coresponding to λoop. In this case, oxgen-coal ratios larger than Aoop were re-quired to obtain temperatures high enough to maintain the flow of molten slag. For coals containing relatively large amount of carbon, higher rate of oxygen were required to gasifiy all the carbon. This resulted in reduced values of η gmax. However, operation at Aoop was possible as the associated temperatures were sufficiently high to maintain slag flow. It was determined that the slag flowing temperature (Tsg) is related to ash fluid point by: Tsg=Tf +100°C.
In order better to understand the relationship between cold-gas efficiency and coal properties, the maximum cold-gas efficiency was estimated theoretically using the values of an ultimate analysis as well as the ash fluid point. The ratio of the experimental value (ηgmax) to the theoretical value (ηgmax*) was introduced as a performance index of the gasifier. The analysis of this index provided the adaptability of coal types and suggestion of increasing cold-gas efficiency in entrained-bed gasification.
