Mass Transfer Changes Induced in Coal Blocks During Thermal Processing

摘要

In-situ processing of coals allows energy extraction from underground seams without usual societal and environmental costs of coal technology. Current concepts involve hot-gas underground processing to effect a partial oxidation of the coal, i.e., underground gasification. Modeling these processes requires comprehension of mass transfer mechanisms that drive the thermal transport processes within coal blocks. Mass transfer is initially limited by the relatively low permeability of the naturally occurring material. Pore geometries in coal suggest that mass transfer channels are near 50 nm. These pores are typically filled by absorbed moisture; moisture removal changes permeability by 10 exp 2 . exp 5 . Once moisture is removed, other absorbed gases, CH sub 4 , CO sub 2 , etc., flush from the interior volume. These combined gases, during the drying steps, control preliminary heat transfer. Modeling studies suggest that heat transfer mechanisms switch from conduction to convection as permeability is changed from 0.01 md to 5 md, those variations in mass transfer resistance formed during coal drying. Results that predict heat transfer rates in blocks of subbituminous coals during the initial drying stages of in-situ processing are described. (ERA citation 03:042119)