IGCC is short for 'integrated gasification combined cycle'. The name itself indicates that this is a completely different power plant technology. Here, the coal is not burned and used to generate steam within a steam turbine process as in the other two processes, but is first converted into a fuel gas. After a series of conversion and treatment steps, the fuel gas generates electricity in a combined-cycle gas turbine process.
In order to capture the CO2 in the IGCC process, the nitrogen - much as in the oxyfuel process-is first removed at the very start ofthe process chain using air separation. The coal is then gasified with pure oxygen. A raw gas emerges with the main components CO and H2. In a 'conventional' IGCC process without CO2 capture, this raw gas would be directly burned in the gas turbine after undergoing various cleaning steps, and the CO share would form CO2, which is emitted into the atmosphere. To avoid this CO2 formation, the CO must be removed before the gas turbine process, though without losing its energy content. For this purpose, two process steps are supplemented. First, the CO is converted into CO2 using water vapor. At the same time, hydrogen is produced, to which the CO' s combustion energy is transferred. The chemical equation for this CO shift reaction is (Scheme 11.4):
CO + H2O ^ w CO2 + H; Scheme 11.4 CO shift reaction.
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