Coal Demethanation Principles And Field Experience

Abstract

Abstract INTRODUCTION A program was initiated by Noval Technologies Ltd., a subsidiary of NOVA, An Alberta Corporation, in 1976 to develop coal demethanation technology and demonstrate its econonic viability. Theoretical studies and field experiments were started in Alberta in 1977 and are continuing. In 1979, in conjunction with Petro-Canada, Naval started a test program in Nova Scotia that is to lead to commercial development. This report is a brief coverage of the theoretical background, and the results of field experience, not only of the Naval project, but also of other major demethanation projects. The relations between basic physical parameters of the coal and their impact on the demethanation process are discussed, as are the results of the field experience using vertical boreholes and the effect of the various stimulation methods used, indicating the advantages and drawbacks of each. After over five years of experience, Noval feels that coal demethanation techniques are sufficiently advanced to make a commercial project feasible. INTRODUCTION Methane has been known to exist in association with coal beds for many years. It has been known under many names, such as firedamp, methane, coal gas, etc. Traditionally, the methane in the coal was only considered when the coal was being mined and then only as a hazard. Recently, mostly as a result of the energy shortage, methane in coal has been given attention as a potential energy source. Its use as a fuel is not entirely new or innovative because, mostly in Europe, collieries have used the gas for many years. However, its use in North America in large quantities is new. Two different methods are known for extracting methane from coal. One is an underground system operating within a mine, normally referred to simply as methane drainage. It was first applied about 50 years ago in Europe. The second takes place on the ground surface and is often referred to as Virgin Coal Demethanation (VCD). The extraction technology was started in the USA approximately 12 years ago. Both methods achieve the same goal, nevertheless they go about it in entirely different ways. The major aim of the methane drainage method has traditionally been to achieve an immediate impact on the mine ventilation system by decreasing the methane concentration in the mining operations. The use of methane as a potential energy source is only a secondary concern, even though many collieries end up utilizing it. VCD, which is independent of mining operations, also reduces the methane content of the coal and makes for safer mining operations. However, being independent of a mine, it can and has been used to obtain methane for use as a fuel, irrespective of whether or not the coal will be mined. This paper will briefly discuss the principles and field experience of VCD in general and relate it to Noval's experience. The terms ?gas? and ?methane? are used interchangeably in this paper, because gas from coal is almost 100% methane. In some cases, traces of other gases are present, such as CO2, Hz, N2 and 02, but these usually constitute less than 2%.