Dielectric Properties of Various Ranks of Coal and Numerical Modeling Under Electromagnetic Irradiation
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DIELECTRIC PROPERTIES OF VARIOUS RANKS OF COAL AND NUMERICAL MODELING UNDER ELECTROMAGNETIC IRRADIATION 2
1. Chatterjeel and M. Misra 1 Department of Electrical Engineering/Computer Science 2Department of Chemical and Metallurgical Engineering, University of Nevada, Reno, Nevada 89557
ABSTRACT
The dielectric properties of different ranks of Argonne Premium coal samples have been measured using an automated network analyzer system in the frequency range 0.3MHz to 3GHz. These measurements indicate that the inherent moisture present in the various ranks of coal has dielectric properties which are different from that of free water. The dielectric properties were also observed to increase with the moisture content as well as with the amount of oxygen present in the coal sample. A mixture model was successfully used to predict these dielectric properties. The measured dielectric properties have been incorporated into numerical calculations of the distribution of absorbed energy in coal irradiated with electromagnetic waves. The numerical technique used is the Method of Moments. Subsequently, the temperature distribution obtained in the coal is evaluated using a Finite Difference technique to solve the heat conduction equation. These calculations should prove very useful in the microwave drying of coal where it is difficult to monitor the temperature using probes. INTRODUCTION
The presence of water in fine coal is a recognized problem in the utilization, storage and transportation of coal [I]. It has been established that removal of water from coal can significantly reduce the heat loss during combustion due to the evaporation of surface and intrinsic moisture, decrease transportation costs and eliminate to some extent the corrosion and erosion problem associated with the formation of sulfuric acid condensate at the air heater. It is estimated that a 1% reduction in moisture content can increase the thermal efficiency by 0.1% and decrease transportation cost by 5-10% [1]. Recent work at the Bureau of Mines Twin Cities Research Center has demonstrated that the ultimate drying of fine coal can be accomplished by microwave heating [2]. This is because the ultimate removal of water is accomplished by selective heating of the water molecules without heating the coal particles with microwaves. It appears that microwave drying has a strong potential for commercialization provided several fundamental and technical aspects are fully understood. One of the intriguing and difficult problems in microwave heating is the determination of the exact temperature distribution in the material and hence control of temperature. In this paper, mathematical models for coal have been developed with the explicit objective of predicting the temperatures which would be attained in the sample under various conditions of exposure to electromagnetic waves. The measured dielectric properties of various ranks of coal have been incorporated into these models. EXPERIMENTAL PROCEDURE AND DISCUSSION
Five different Argonne Premium Coal samples were used
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