A new technology currently in the demonstration phase is the integrated gas combined-cycle or IGCC generator. While none of the basic technologies used – coal gasification and a combined-cycle gas turbine – are new. What is new is combining the two to create an integrated power plant. IGCC technology takes solid coal, converts it into synthetic gas, and then uses the gas to power a combined-cycle gas turbine.
Gasification of coal requires three key processes:
- Air separation — where ambient air is separated into oxygen and nitrogen using a cryogenic process.
- Gasification — in this process the coal is crushed and mixed with water to become a slurry. The slurry is then fed into a gasifier along with oxygen from the air separation unit. The gasifier is a high-pressure high-temperature chemical reactor. Under these conditions, the chemical bonds in the coal are severed by the extreme heat, producing steam plus a synthetic gas, called syngas. The syngas consists of hydrogen and carbon monoxide as well as other elements.
- Gas clean-up — where the syngas is cleansed to remove particulates, sulfur, and trace metals such as mercury. If desired, the syngas can be additionally treated to convert the carbon monoxide to carbon dioxide, which can be removed from the stream prior to combustion.
After these three processes, the syngas is then used in a combined-cycle gas turbine in a manner similar to that previously described for natural gas.