Here is one of the best explanations of integrated gasification controlled cycle (IGCC). It's from The Clean Tech Revolution(book review coming soon):
"...there is one clean-coal technology that seems to offer some future hope, with an increasing chorus of diverse interest groups calling for it: integrated gasification controlled cycle, much better known by its initials IGCC, or simply coal gasification. This process essentially breaks coal down into gaseous components, including natural gas, a cleaner-burning fossil fuel, and CO2 [carbon dioxide]. That enables the easier use of carbon sequestration, a promising but still widely developmental technique of capturing CO2 and storing it underground or underwater - that is, out of the earth's atmosphere. The technique remains expensive and unproven on a large scale..."