Abstract

Underground coal gasification has been tested in many countries but reached industrial scale application only in Russia. In this process, partial oxidation of coal provides the energy required for gasification and a low-Btu fuel gas is produced. The potential of UCG to recover energy from coal resources is outlined for the Canadian situation.

Design and operation of a UCG field test carried out at Forestburg, Alberta, in 1976 are discussed. The test yielded a fuel gas with calorific value ranging up to about 150 Btu/ft.2. The coal deposit tested contains sub-bituminous cool in a 12 foot seam under 60 feet of overburden.

Introduction

Most of Canada's reserves of sub-bituminous coal are located in Alberta and studies currently underway have defined extensive reserves of deep (> 400 feet deep) coal. The possibility of utilizing this energy resource without requiring under ground mining is the incentive which has led to the interest in underground coal gasification (UCG) technology.

This interest was shown by the positive response of a number of government and private companies and organizations to a UCG field test proposed by the Alberta Research Council (ARC) in early 1975. Over the balance of that year, more detailed plans for the test were drawn up and a site chosen – at the Vesta Mine of Manalta Cool Ltd. near Forestburg, Alberta (see Fig. 1). The test took place during the summer of 1976 with the stated objectives:

  • to better evaluate and understand current technological methods in underground coal gasification;

  • to demonstrate the feasibility of those technological methods in a Canadian context;

  • to demonstrate that gas with a low Btu content (a heating value of 100 – 200 Btu's/SCF) can be produced on a sustained basis; and

  • to make a preliminary and basic assessment of the factors pertaining to the environment that may be affected by an underground coal gasification test.

Energy Recovery Considerations

Several different methods of calculating efficiency have been used for underground coal gasification. These relate usually to the product heating value generated per unit of in-situ heating value or the energy recovered per unit of process energy input. A third form of recovery efficiency is the proportion of the total energy in a cool deposit which is recovered for use on the surface through UCG. The latter efficiency is difficult to determine but is certainly the most significant for resource utilization.

The object of underground coal gasification is to convert coal in-situ into gaseous fuel which can be transported to the surface for use. Chemically this requires reaction of the carbon in cool with water to generate carbon monoxide and hydrogen.

Chemical equation (Available in full paper)

As this reaction is endothermic, additional heat is supplied by burning some of the coal.

Chemical equation (Available in full paper)

Looking at the energy recovery potential of this system, 0.46 moles C must be oxidized to generate the heat to vaporize a mole of water and read it with one mole of carbon by the carbon-steam reaction.

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