Process designs and economic evaluations for the linked vertical well in situ coal gasification process

Conceptual process designs and cost estimates are presented for three facilities illustrating the following potential applications of underground coal gasification: (1) a 900-MW(e) combined-cycle electric generating plant fueled by low-Btu gas, (2) a substitute natural gas (SNG) plant producing 155 MMscfd of 954 Btu/scf gas, and (3) a synthesis gas (syngas) plant producing 388 MMscfd of gas suitable for further chemical conversion. Designs were based on experimental data and mathematical models from the Laramie Energy Research Center on the linked vertical well (LVW) in situ coal gasification process. In-place coal consumption for the three facilities is 18,073, 22,951, and 22,951 tons/day, respectively, based on a subbituminous Wyoming coal. Respective capital investments were estimated to be $395, $351, and $312 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%, a coal feed cost of $5/ton, and aplant factor of 90%, product prices were 19 mills/kWh for electricity, $2.89/10/sup 6/ Btu for SNG, and $2.48/10/sup 6/ Btumore » for syngas. Calculated overall thermal efficiencies for the three facilities were 24, 38, and 40%, respectively, based on in-place coal.« less