Economics of electricity and SNG from in situ coal gasification

Conceptual process designs and cost estimates are presented for two potential applications of underground coal gasification: a 900 MW(e) combined-cycle electric generating plant fueled by low-Btu gas; and a substitute natural gas (SNG) plant producing 155 MMscfd of 954 Btu/scf gas. Designs were based on experimental data obtained at the Laramie Energy Research Center on subbituminous coal using the linked vertical well in situ gasification process. Respective capital investments were estimated to be $395 and $351 million in first-quarter 1977 dollars. Product prices were calculated as a function of the debt/equity ratio, the annual earning rates on debt and equity, the cost of coal, and plant factor (onstream efficiency). Using a debt/equity ratio of 70/30, an interest rate on debt of 9%, an after-tax earning rate on equity of 15%, and a coal feed cost of $5/ton, product prices were 24 mills/kWh for electricity at 70% plant factor and $2.89/10/sup 6/ Btu for SNG at 90% plant factor. Calculated overall thermal efficiencies for the two facilities were 24 and 38% respectively, based on in-place coal.