ESTIMATION OF RETENTION OF POLLUTANTS ON
UNBURNED COAL AFTER IN SITU GASIFICATION
Wade C. Bishop,Graduate Research Assistant
William A. Sack, Professor
Department of Civil Engineering
West Virginia University
Morgantown, West Virginia 26506
INTRODUCTION
The Department of Energy has for some time been working to develop and demonstrate
commercial technology for converting coal in place into low and medium BTU gas. In-situ
coal gasification (ISCG) carries a higher risk than processes which are entirely surface-based
in that it is harder to monitor and control. However, the potential rewards are also great
including lower capital investments, lower product selling price, increase in available coal
reserves, and less adverse environmental impact compared to mining plus surface processing.
A major problem for today's coal-associated industry is containment of the enormous
volumes of solid waste residuals formed both during coal preparation and after burning.
These residuals would remain underground during ISCG which is a major environmental
plus for the process. ISCG is certainly not without potential environmental problems.
Ground water pollution, air pollution, and ground subsidence are all areas of serious concern.
The Morgantown Energy Technology Center (METC) of the Department of Energy is
conducting an underground coal gasification (UCG) program in the Pittsburgh coal seam
near Pricetown, West Virginia. The Linked Vertical Well concept of gasification is being
used where vertical wells are drilled into the coal seam and linked by reverse combustion to
form permeable, hot char paths; gasification then occurs by forward combustion. The
Pittsburgh seam at the Pricetown location is nominally six feet thick and 885 feet below
the surface.
West Virginia University is working with METC/DOE [ 1 ] to carry out environmental
monitoring of air and water quality at the Pricetown site prior to, during, and subsequent
to ignition of the coal seam. After gasification, a void will be left in the coal seam as depicted in Figure 1. Ash remains where the coal has gasified which, in turn, is surrounded by a
char ring formed where the heat has pyrolyzed but not gasified the coal. Outside the burn
boundary is a zone contaminated by condensation of cooling gases during and after gasification. As cooling of the burn area proceeds, groundwater flow through the coal and surrounding strata will be slowly re-established. A variety of organic and inorganic materials
will be extracted from the burn zone and will migrate with the groundwater and by diffusion through the coal seam and possibly through other strata such as over-lying shales. In
order to predict transport of pollutants away from the burn area, a number of analytical
and numerical approaches are being considered [ 1]. Any approach used must estimate the
retention of pollutants in surrounding strata during their migration. Possible mechanisms
Figure 1. Plan view of post-gasification cavity and pollutant plume.
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