method of producing syngas in an igcc system , comprising compressing and heating carbon dioxide - rich gas to produce heated compressed carbon dioxide - rich gas , mixing the heated compressed carbon dioxide - rich gas with oxygen and feedstock to form a feedstock mixture , subjecting the feedstock mixture to gasification to produce syngas , cooling the syngas in a radiant syngas cooler , contacting syngas cooled in the radiant syngas cooler with compressed carbon dioxide - rich gas to further cool the syngas , and removing an amount of carbon dioxide - rich gas from the product mixture and compressing the removed carbon dioxide - rich gas prior to mixing with oxygen and feedstock .