Ask the Experts
Coal-fired heat and power generation is the largest single source of CO2 emissions resulting from fuel combustion. But the environmental impact of the different steps in the coal supply chain, from mining to final use, can differ widely depending on the technologies and means used. The collection of technologies known as clean coal offers ways to reduce carbon emissions as well as other forms of pollution. IEA Senior Coal Analyst Carlos Fernández Alvarez explains those technologies and their potential.
What are the various clean-coal technologies?
Two-thirds of global coal is used for power generation, so the term clean-coal technology tends to focus on electricity production. In that sense, clean coal refers to high-efficiency low-emissions power generation plants. Principal examples include supercritical (SC) and ultra-supercritical (USC) plants that produce heat and pressure sufficient to drive water above the critical point where there is no difference between steam and liquid. The higher temperature and pressure involved means USC pulverised coal combustion can reach efficiency rates of 45%; traditional plants that run below the critical point produce a mix of water and steam, for a typical efficiency rate in the range of 30% to 38%. The difference cuts USC pulverised-coal plants’ CO2 emissions by as much as 30%, while also producing more electricity for the same amount of fuel.
Clean-coal technologies address other forms of pollution, too, of course: scrubbers as well as selective catalytic reduction, electrostatic precipitators and other technologies can reduce emissions of sulphur, nitrogen oxide (NOx) and particulate matters by two orders of magnitude.
While high-efficiency, low-emissions power plants cut carbon emissions significantly, by themselves they are not enough for an energy system to mitigate climate change: clean-coal technologies must include carbon capture and storage.
Are clean-coal plants cost-competitive?
SC and USC plants have been built profusely in the last decade, from Japan to the United States to Europe, so the shift from subcritical is under way. But the IEA warns that this transition is proving very slow. Insufficient or expensive finance, very cheap fuel (with no carbon price) and the need to limit risks are among the reasons subcritical plants remain common in power systems.
Cleansing equipment in general involves a trade-off between additional cost and reduced pollution. But regarding the competitiveness of SC and USC plants, their high efficiencies and hence lower operating costs can offset their higher investment costs compared with subcritical – so much so that cutting-edge coal plants in, for example, China, Japan and Korea are fully competitive with older technologies.
Are high-efficiency low-emissions plants sufficient to lower coal-fired generation’s carbon footprint?
While SC and USC plants cut carbon emissions significantly, by themselves they are not enough for an energy system to mitigate climate change: clean-coal technologies must include carbon capture and storage (CCS). CCS technology allows for the capture of around 90% of CO2 from a coal-fired plant, which must then be transported to a suitable storage site, where it is injected and monitored to ensure that it will not escape into the atmosphere. If the CO2 can be used before it is stored, even better: at the moment, enhanced oil recovery (EOR) is the most promising use of CO2.
A CO2 capture plant at the Boundary Dam coal-fired power plant in Canada entered operation in October 2014, and several others are under development. But the market for CCS is lagging a long way behind other clean-coal developments. Putting a price on CO2 emissions, incentivising low-carbon power generation and supporting exploration for suitable CO2 storage are among the necessary actions.