Investigation of Agglomeration and Defluidization during Spouted-Bed Gasification of High-Sodium, High-Sulfur South Australian Lignite

The mechanisms of agglomeration and defluidization during the fluid-bed gasification of an Australian low-rank coal are investigated. Experiments were conducted in a 77 mm inner diameter spouted-bed gasifier with a high-sodium, high-sulfur coal from the Lochiel deposit in South Australia. The effect of the bed temperature, air/fuel ratio, and superficial velocity on the stable operation of the spouted bed over a 4 h period was investigated. The results of this study indicate that stable bed operation is governed by a "high-temperature defluidization limit", suggesting that defluidization can be delayed or avoided by operating the bed with high superficial velocity and/or low bed temperatures. In experiments that resulted in agglomeration and in some experiments that did not, the average particle size within the bed material had increased, which was mainly attributed to coating of mineral particles. These coated particles were observed to be more prevalent in runs that led to defluidization of the bed. Particle growth also coincided with the increased inorganic content of the bed compared to stable runs. Agglomeration and defluidization may hence be avoided or delayed by operating the bed below about 850 degrees C, increasing the superficial velocity of gas within the bed, or maintaining the ash content of the bed below approximately 80%, where possible.