Production of SNG by free-fall dilute-phase hydrogasification of coal

Hydrogasification of coal has been under investigation at PERC since the mid-1950's. Initial experiments led to the development of the vertical free-fall, dilute-phase reactor with large diameter so that coal particles were dispersed to reduce contact while in the plastic temperature range. Very rapid particle heating in the dilute-phase by mixing with concurrently fed hot hydrogen controlled agglomeration and eliminated the need for oxidative coal pretreatment. In the dilute-phase hydrogasification process, coal which has been washed, pulverized and dried is fed directly to the reactor without a requirement of oxidative pretreatment. Pretreatment, to destroy the coal's agglomerating property, may consume 9% of the volatile matter and 13% of the weight. A further advantage of hydrogasification is in the minimum use of the methanation reaction. This reaction is highly exothermic, but the heat cannot be used directly in the gasifier because the temperature must be limited to 450/sup 0/C for protection of catalysts. In the DPH process, typically 65-75% of total methane product may be produced directly in the reactor. Dilute-phase hydrogasification has been demonstrated in successful, continuous, long duration experiments. Carbon conversion necessary for balanced plant operation with lignite has been demonstrated at hydrogen/coal ratios producing a high-Btu SNG withmore » no residual hydrogen separation requirement. High carbon selectivity to gas phase products has been demonstrated with no benzene and only trace oil formation. Parametric testing has established effects of throughput upon carbon conversion and product distribution. Steady operation was achieved at a throughput of over 800 lb/ft/sup 2/hr. Reproductility of test results has been demonstrated by duplicated test operation.« less