A gasifier 10 includes a first chemical process loop 12 having an exothermic oxidizer reactor 14 and an endothermic reducer reactor 16. CaS is oxidized in air in the oxidizer reactor 14 to form hot CaSO.sub.4 which is discharged to the reducer reactor 16. Hot CaSO.sub.4 and carbonaceous fuel received in the reducer reactor 16 undergo an endothermic reaction utilizing the heat content of the CaSO.sub.4, the carbonaceous fuel stripping the oxygen from the CaSO.sub.4 to form CaS and a CO rich syngas. The CaS is discharged to the oxidizer reactor 14 and the syngas is discharged to a second chemical process loop 52. The second chemical process loop 52 has a water-gas shift reactor 54 and a calciner 42. The CO of the syngas reacts with gaseous H.sub.2O in the shift reactor 54 to produce H.sub.2 and CO.sub.2. The CO.sub.2 is captured by CaO to form hot CaCO.sub.3 in an exothermic reaction. The hot CaCO.sub.3 is discharged to the calciner 42, the heat content of the CaCO.sub.3 being used to strip the CO.sub.2 from the CaO in an endothermic reaction in the calciner, with the CaO being discharged from the calciner 42 to the shift reactor 54.