COAL'S CLEAN FUTURE
Ecoal, Vol. 78, June 2012
Reducing pollutant and particle emissions and limiting the carbon footprint of coal combustion are the key challenges for coal and other fossil fuels. Although the deployment of all energy generating technologies invariably leads to some degree ofenvironmental impact, technologies improving the environmental performance of coal-fired power stations are widely available.
Significant progress has been made to date in reducing the environmental footprint of coal use. From the climate change perspective, significant reductions in greenhouse gas emissions can be achieved through improving the efficiency of power plants using coal and, in the longer term, through the deployment of carbon capture and storage (CCS) technology.
Reducing pollution from coal combustion
The release of pollutants such as oxides of sulphur (SOx) and nitrogen (NOx) and particulates, which occur during coal combustion, can be controlled and substantially reduced with the use of technologies such as electrostatic precipitators, fabric filters and wet scrubbers. These technologies have been effectively used in a number of countries to tackle the problem of pollutant emissions. In the USA, coal use has risen by 77% since 1980 while SO2 emissions have declined by 40%. Mercury emissions from coal can also be reduced through the application of these technologies or through mercury-specific technologies such as activated carbon injection. In fact, mercury emissions occurring during coal combustion can be reduced by up to 90% with the existing technologies.
Improving the carbon footprint of coal energy
Improving power plant efficiency and replacing old inefficient plants with state-of-the-art technology presents a significant GHG emissions savings potential. Improving the efficiency of the oldest and most inefficient coal-fired plants would reduce CO2 emissions from coal use by almost 25%, representing a 6% reduction in global CO2 emissions - which is more than the intended impact of all measures under the Kyoto Protocol. The deployment of high efficiency-low emissions coal technologies such as supercritical pulverised coal combustion (SC), ultra-supercritical pulverised coal combustion (USC) and integrated gasification combined cycle (IGCC) increased from 25% of new additions in 2000 to around 50% in 2011.
During this time, deployment of advanced coal technologies has rapidly accelerated in China and India. This progress came regardless of the fact that RD&D spending for advanced coal technologies remained constant over the last decade. In the longer term CCS will allow 90% reduction of CO2 emissions from coal-fired power plants, making coal a low-carbon source of energy. CCS is one of the most important technologies for mitigating climate change and its deployment can substantially decrease the overall cost of decarbonisation. The IEA estimates that the cost of addressing climate change could go up by as much as 70% if CCS was not deployed.
Alternative ways of using coal
The environmental footprint of coal can also be reduced through alternatives ways of using coal, such as through underground coal gasification (UCG) or converting coal into liquids (CTL). UCG is a method of converting coal that is still in the ground into combustible gas which can be used for industrial heating, power generation or the manufacture of hydrogen, synthetic natural gas or diesel fuel. UCG presents the opportunity to reduce greenhouse gas emissions as synthetic gas obtained from coal gasification would result in roughly 50% less CO2 emissions than direct combustion of coal. UCG technology could also have synergies with CCS as the CO2 could be stored in the coal cavity after gasification. CTL technology involves converting coal to a liquid fuel. It allows coal to be utilised as an alternative to oil which is sulphur-free, low in particulates and low in nitrogen oxides.
Liquid fuels obtained from coal can be used for transport, cooking, stationary power generation, and in the chemicals industry. In South Africa around 30% of the country's gasoline and diesel needs are produced from indigenous coal.
While CTL is more CO2 intensive than conventional oil refining, there are options for preventing or mitigating emissions. For CTL plants, CCS can be a low cost method of addressing CO2 concerns. Where co-processing of coal and biomass is undertaken, and combined with CCS, greenhouse gas emissions over the full fuel cycle may be as low as one-fifth of those from fuels provided by conventional oil. All energy generating technologies invariably lead to some degree of environmental impact. A great number of technologies which reduce the environmental and carbon footprint of coal have already been deployed in developed countries. Pollution control technologies are also present in most new coal-fired power plants built in the emerging economies, such as China. As more countries rely on coal to alleviate energy poverty and fuel economic development, it is important that international financial institutions, such as development banks, facilitate access to state-of-the-art technologies allowing the sustainable use of coal.
CCS technology can be used by industry to remove carbon dioxide from gas streams and pipe it underground for long-term storage.