Survey of Energy Resources 2007
Clean Coal Technologies
An array of clean coal technologies has been, and continues to be, developed to address environmental concerns surrounding coal utilisation. Traditional pollution-control technologies have been installed worldwide to address sulphur, oxides of nitrogen and particulate-matter emissions, and retrofit programmes continue to improve power plant performance. However, more remains to be done, and greater deployment of these technologies must be encouraged. (Fig. 1-3)
As climate concerns have come to the fore, increasing the combustion efficiency of both conventional and advanced new power systems has become paramount. The development of innovative techniques such as carbon capture and storage will lead to a near-zero emissions future for coal.
New power plants worldwide are being built to perform at 'supercritical' and 'ultrasupercritical' conditions of temperature and pressure, increasing electricity generation efficiency to 40-50% and higher. China has engaged on an aggressive strategy of power generating capacity growth, with some 93 000 MW of coal-fired plant added in 2006. The first 1 000 MW supercritical plant came online in November 2006, in line with the Chinese Government's aim of phasing out small, inefficient plant.
Integrated Gasification Combined Cycle (IGCC) is another advanced technology which holds out a number of benefits for coal-fired power generation. Coal is not burnt to raise steam, as with conventional power plants, but instead reacted to form a synthesis gas of hydrogen and carbon monoxide. A gas turbine is used to generate electricity, with waste heat being used to raise steam for a secondary steam turbine. Not only are efficiencies raised in doing so - thereby reducing emissions of CO2 - but pollutant emissions are also significantly reduced, even compared to advanced conventional technologies, with 33% less NOx, 75% less SOx and almost no particulate emissions. IGCC uses 30-40% less water than a conventional plant and up to 90% of mercury emissions can be captured (at typically one-tenth of the costs for a conventional plant).
One of the main barriers to the widespread uptake of IGCC in the past has been cost. (Fig. 1-4) IGCCs have been significantly more expensive than conventional coal-fired plant - typical comparisons have suggested US$ 1 500/kW for IGCC compared with US$ 750/kW for conventional plants and US$ 1 000/kW for advanced conventional systems such as supercritical power plants. However, recent studies in the USA (IGCC Alliance) have shown that the cost of IGCC is similar to that of supercritical plant, on a cost-of-electricity (COE) basis, once the cost of SOx, NOx and mercury emission allowances are taken into account. Where a price for CO2 must also be factored in, IGCC is significantly more competitive.
IGCC provides a more cost-effective route for capturing CO2 - EPRI's CoalFleet for Tomorrow programme has found that the incremental cost penalty for removal of CO2 from IGCC syngas is considerably lower than that for its removal from the flue gas of a supercritical unit.