Not Just your Granny’s Fuel
No longer just used to produce heat in the conventional sense, the possible future for coal lies in many different directions. Some of these are well established areas; others are growing in commercial importance and market entry; and others still are at the frontier of research and development activities
Often thought of as the fuel of the Industrial Revolution, today coal remains an enormously important energy source; it is the most common source of electricity world-wide. In the United States, for example, the burning of coal generates over half the electricity consumed by the nation.
Many countries are vigorously pursuing cleaner coal technologies (CCT)—technologies designed to enhance both the efficiency and the environmental acceptability of coal extraction, preparation, and use for power generation—with large financial investment being spent annually on developments in utilization techniques. These technologies have the potential to reduce emissions and waste, and increase the absolute amount of energy gained from each tonne of coal. Figure 1 graphically depicts the many opportunities for Canadian coal. It is important to look at these efforts as collaborative; adding value through the creation of synergies achieved through the operation of a broad ‘coal’ portfolio that maximizes feed interaction and product outputs.
Over the last few years, it would seem that the challenges and opportunities for cleaner coal have been focused on carbon dioxide emissions and the need to reduce these to meet climate-change agendas. However, the agenda of the coal and power industry is to address the broader, and more relevant, issue of sustainability of the coal resource. This includes the socio-economic and environmental aspects associated with the coal industry: air emissions, water management, solid waste management, thermal management, environmental mining techniques, and reclamation management.
Power Generation
An impressive array of technologies is already commercially viable for coal-fired power generation; a large number of others will become available in the near future. Figure 2 shows the potential growth in coal-to-power technology innovation and the associated reductions in carbon emissions. Perhaps the biggest challenge of this growth is changing the perception that emitting carbon has a negative value; carbon dioxide is a resource that has a market. The key to its development is ensuring that the source and sink for the carbon dioxide are married in a technical and economically viable manner. This is the intent of carbon sequestration technologies show schematically in Figure 3.
Pulverized Coal Combustion (PCC)
These technologies are currently available commercially, and have been previously demonstrated with proven reliability at a commercial scale. Worldwide, most coal-fired power plants greater than 200 MW use pulverized coal combustion technology and generate electricity in a steam turbine. These plants, when operated with Alberta sub-bituminous coal, burn the coal effectively, with almost 100 per cent carbon conversion. In a sub-critical PCC plant, typically about 35 per cent of the higher heating value of the coal is converted to electricity, with the remainder rejected as low quality heat and relinquished to cooling ponds and/or cooling towers.
Supercritical Pulverized Coal Combustion (SPCC) Supercritical plants operate with steam pressure and temperature above the critical point for steam, resulting in higher efficiency of the steam turbine. This translates to a 23 per cent reduction in the emissions of CO2 for an equivalent amount of electricity. This improvement in efficiency also reduces NOx, SOx, and particulate emissions per unit of electricity produced compared to that of a conventional sub-critical pressure PCC. Supercritical pulverized coal combustion is a proven, commercially available technology, e.g., 450MW TransAlta/EPCOR Genesee 3, commissioned in 2005.
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