Date of Graduation

1977

Document Type

Dissertation/Thesis

Abstract

The development of an efficient underground coal gasification process may become an important step in achieving energy selfsufficiency. To realize the benefits of the underground coal gasification process, an electromagnetic monitoring system must be developed to convey information about the status of the gasification process. To aid in the design of the monitoring system an electromagnetic model of the underground coal gasification process is formulated, which will prove beneficial in the saving of time and cost in the research and development stages of the system. Two types of electromagnetic systems are investigated analytically and proposed for the monitoring of the underground gasification process. The first type, called the reflection monitoring system, consists of a transmitter and receiver placed on the same side of the gasified coal section. The model of this system is developed in steps using the geometrical optics (GO) technique. The GO method of formulation is linked strongly to the classical and well established Sommerfeld model technique. The GO method is found to be accurate at low frequencies, where it is not normally considered valid, and becomes more accurate at the higher frequencies used for the monitoring system. A swept frequency monitoring scheme is demonstrated for the reflection type system, showing considerable sensitivity in the detection of the burn front of the gasified section. The sensitivity of the 164 reflection system, in locating the gasified section's burn front slanted at 45°, is reduced considerably. In general, the most sensitive system is produced when the receiver is placed in the far field of an infinitesimal vertical dipole transmitter. The second type, called the transmission monitoring system, consists of a transmitter and receiver placed on opposite sides of the gasified coal section. This system is modeled using the transmission equation of geometrical optics developed here. The formulation of this equation involves the interesting theoretical analysis of a plane wave incident on a boundary between two lossy media. The swept frequency response of the model, for the transmission monitoring system, is used to investigate a monitoring scheme for the measurement of the overall width of the gasified section. The swept frequency transmission monitoring system is not as sensitive to changes in the overall length of the gasified section as is the reflection system to changes in the leading edge of the burn.

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