Coal Gasification

History

Coal gasification is a process by which coal is converted into a fuel gas rich in hydrogen and carbon monoxide. The process was first developed in about 1780 and was widely commercialized by the early 1900s. Before natural gas became widely available in the 1940s, many North American and European cities used coal gas as a heating and lighting fuel. It was referred to variously as blue gas, producer gas, water gas, town gas or fuel gas. Often using the same low-pressure mains for distribution, natural gas replaced fuel gas in most uses by the 1950s because of its greater heating value and lack of contaminants.

The oil crises of the 1970s triggered a renewed interest in various alternative coal utilization technologies, such as coal gasification and coal liquefaction, as a means of replacing or supplementing petroleum resources such as oil and natural gas. In many parts of the world, including Canada, coal resources are so large that gaseous and liquid fuels from coal could become viable alternative fuels if conventional resources run low. However, the return of abundant and cheap oil supplies has effectively killed the near-term commercial prospects of these technologies.

Recently, coal gasification has been attracting attention as part of an integrated gasification-combined cycle (IGCC) technology. In IGCC, coal is gasified and the gasification products are purified to remove acidic compounds and particulates before entering gas turbines attached to power generators. Heat recovered from the gas turbine exhaust gas can be used to generate steam to drive additional steam turbines. Because the combustion flue gas exiting from the gas turbines is almost free of acidic species and particulates, IGCC is being considered as a front-running technology to combat acid rain. More importantly, the efficiency of IGCC-based electricity generating plant is significantly higher than a conventional thermal generating plant, which results in significantly less carbon dioxide (one of the main greenhouse gases) being emitted per tonne of coal consumed. This makes IGCC the preferred technology for countries which must reduce their greenhouse gas emissions but cannot switch to other energy sources with still lower carbon dioxide emissions.

Canadian Applications

In Canada, feasibility studies have been conducted by TransAlta and SaskPower to evaluate the gasification suitability of Highvale subbituminous (Alberta) and Shand lignite (Saskatchewan) coals, respectively. However, major decisions were postponed because of the wide availability and competitive price of natural gas, as well as a lower demand for electricity. Interest in IGCC technology has also been shown by Nova Scotia Power and the New Brunswick Electric Power Commission. Feasibility studies, conducted under the auspices of the Canadian Electricity Association, have shown that it is possible to achieve a still higher overall efficiency through more integration of units and systems. A decision to build a commercial plant has been postponed.

Research and Development

During the 1980s and early 1990s, R&D activities in coal gasification were conducted by the Canadian Coal Gasification R&D Consortium, comprising most utilities, the federal government and various provincial agencies. The projects were carried out by the Alberta Research Council at Devon, Alberta, and Natural Resources Canada/CANMET in Ottawa.