Comparison of economics of in situ coal gasification with surface processing

The Los Alamos Scientific Laboratory (LASL) concept for underground coal conversion (gasification) involves preliminary hot-gas drying and pyrolysis steps followed by gasification of the resulting char through combustion with a carbon dioxide--oxygen mixture. This staged recovery process produces both an enhanced-Btu (1300 Btu/scf) fuel gas to mix with natural gas and a clean, low-Btu gas for electricity production. Detailed engineering and economic analyses have been completed that point to the feasibility of this approach. Comparable economic analyses, all based on costs of existing Lurgi surface technology, are given for three processes with roughly similar commercial goals, i.e., the LASL concept above; Lurgi gasification of surface-mined coal, followed by gas cleanup; and a steam--oxygen underground process analogous to those processes used at Hanna and Hoe Creek, WY, followed by gas cleanup. The analyses indicate that the costs of Lurgi and of current underground coal conversion technologies are similar at the present stage of the development of in situ technology. Simple modifications of the methods of underground conversion, which are evaluated in the paper, can be expected to improve the byproduct recovery and to much reduce the capital costs of conversion--such conversion systems appear to be economically competitive with strip mining plus pollution control. The analyses emphasize the critical importance of controlling capital costs. Thus well-completion and labor charges are less important expenses than gas cleanup costs; these latter costs enforce volume minimization throughout all process steps. As corollary, expensive and power-consuming systems including oxygen-generating units and pumps are required

Kinetics of Subbituminous Coal Drying

This paper explores both the effects of stress upon water removal from subbituminous coal and the consequences of drying upon underground coal conversion. Laboratory tests studying compressive stress effects on moisture transfer in the hygroscopic region are reported. Measurements of CO/sub 2/ permeability are also reported as a function of compressive stress and fluid saturation levels. Results indicate that molecular transport phenomena are unaffected by compressive stress levels while viscous transport is markedly influenced by stress. This flow decrease results from alteration of the size of larger flow channels which are necessary to support viscous fluid transport

Long-term exposure of /sup 238/PuO/sub 2/ to an arid terrestrial environment

Two environmental simulation chambers were used to study the behavior of a /sup 238/PuO/sub 2/ heat source deposited in an arid, temperate environment. Large fragments from an impact-tested source were deposited in the first chamber, and fines from the source were placed in the second. Plutonium released into the soil, the soil drainages, and the condensates from the dehumidifiers were monitored throughout the experiment. The bulk of the released plutonium, up to 0.04% of the source, was retained in the soil. Of the remainder, larger amounts of plutonium were released to the condensates (to the air) than to the soil percolates. Release rates to the condensates and percolates increased with time for both chambers. Condensate release rates averaged 23 nCi/day for the fines chamber and 90 nCi/day for the chamber with the large fragments. Percolate release rates averaged 224 nCi/rain for the fines chamber and 170 nCi/rain for the other chamber. Spalling of particles from the surface of the plutonium oxide to the air, caused by the action of rain on the hot source fragments, seemed to be a significant release mechanism for the large source fragments but not for the fines. A simulated cleanup operation, involving removal of the source and a small amount of soil, had little effect on the continuing release of plutonium to the soil percolates and to the dehumidifier condensates, except that the condensate release rates from the chamber that had contained the large source fragments dropped to a value equal to that of the other chamber. The large source fragments remained virtually unchanged after 8.5 yr of exposure, in contrast to one previous experiment in which fragments of similar size disintegrated into fines

Long-term exposure of pressed plutonium oxide heat sources to aquatic environments

Plutonium-238 oxide fuel pellets were exposed to water for 2.5 to 6.4 yr, and the concentration of plutonium in the water was monitored. Water composition and temperature were found to be important factors in determining the rate of plutonium release into the water. Typical release rates ranged from 10 to 40 ng/m/sup 2//s in cold fresh water and from 0.3 to 11 ng/m/sup 2//s in cold sea water. Release rates in sea water varied over time and sometimes were erratic. The plutonium release per unit area did not depend on the size of the PuO/sub 2/ source. The released plutonium was in an extremely fine form, able to pass through 10,000 molecular weight cutoff filters. Apparent differences in the fuel pellet surfaces after exposure suggest that plutonium release is controlled by physical and chemical processes occurring at the solid-liquid interface. Release mechanisms and their implications are discussed