Physical and Numerical Modeling Results for Controlling Groundwater Contaminants Following Shutdown of Underground Coal Gasification Processes

摘要

Groundwater contamination has resulted from some of in-situ gasification field tests, and concern over groundwater contamination may hamper commercialization. When UCG recovery operations are terminated, energy remains stored as heat in the adjacent masses of rock and coal ash, and this energy is transferred into the coal seam. Coal continues to pyrolyze as a result of the transferred energy; the products of this coal pyrolysis are a source of groundwater contamination resulting from UCG. A laboratory simulator was developed, and six simulations of UCG postburn coal pyrolysis have been completed. The simulations show that the products of coal pyrolysis are the source of most contaminants associated with UCG operations. Injection of water directly into the UCG cavity can limit postburn coal pyrolysis and reduce the production of contaminants by cooling the masses of rubble and coal ash in the cavity. Water flow through the coal towards the cavity also limits postburn pyrolysis and subsequent contaminant generation; however, steam produced in the heated portions of the coal limits the rate of water flow. Simulation results indicate that UCG field tests should be operated so that the flow of pyrolysis liquids and gases into the formation is prevented and that the natural influx of water into the cavity is allowed. This can be accomplished by minimizing gas leakage to the formation during gasification, venting the cavity after the gasification process is complete, and maintaining low postburn cavity pressures. 11 refs., 17 figs., 17 tabs. (ERA citation 12:040325)