World Energy Outlook 2007

scheduled to operate in the first half of 2009. However, relatively low
operating temperatures mean CFBCs may not be practicable for ultrasupercritical
plants, which operate at steam temperatures much higher
than 550°C.
Integrated gasification combined-cycle: IGCC combines coal gasification with
a combined-cycle power plant. Coal is gasified under pressure with air or
oxygen to produce fuel gas which, after cleaning, is burned in a gas turbine
to produce power. Exhaust gas from the gas turbine passes through a heatrecovery
steam generator or boiler to raise steam for a steam turbine which
generates extra power. Only four successful IGCC plants have so far been
built: two in Europe and two in the United States. At high temperatures,
efficiency can be as high as 41%, or even higher with the latest gas-turbine
models. For IGCC to establish itself in the market, further development to
bring down costs and improve operational flexibility is necessary. A number
of plants are being built in China and Japan, and several others are being
considered elsewhere. IGCC has inherent advantages for emission control,
as gas clean-up takes place before combustion of the fuel gas, using relatively
small equipment, and solid waste is in the form of a vitrified slag. If CCS
becomes an established mitigation measure, then CO 2
capture from an
IGCC plant is technically easier than post-combustion capture from a
conventional steam plant.
Other technologies: A number of other technologies and hybrid systems are
at the research and development stage, notably in the United States and
Japan. Integrated gasification-fuel cell combined cycle involves combining
a fuel cell and the combined cycle component of IGCC to generate power.
Efficiency could reach 60%.
While clean coal technologies have made significant progress in the last
decade or so, there are still considerable challenges in exploiting the
remaining potential, particularly for low-grade coals. For high-moisture
coals, a cheaper and more efficient drying system is needed together with a
reliable system for feeding these coals into a pressurised gasifier. For highash
coals, the main challenge is to overcome fouling problems in
gasification and combustion. For all types of coals, gas clean-up at higher
temperature is needed to obtain higher efficiency in IGCC units.
Considerable research to address these problems is under way. For emerging
technologies – especially CCS – the main challenge is to lower costs and
demonstrate reliable operation. The addition of CCS equipment increases
significantly the capital cost of capacity for all coal technologies, not least
because thermal efficiency is lower (Figure 5.18).
222 World Energy Outlook 2007 - GLOBAL ENERGY PROSPECTS: IMPACT OF DEVELOPMENTS IN CHINA & INDIA