A carbonaceous fuel gasification system for a supercritical CO2 power cycle system includes a micronized char preparation system comprising a devolatilizer that receives solid carbonaceous fuel, hydrogen, oxygen, and fluidizing steam and produces micronized char, steam, hydrogen, and volatiles. An indirect gasifier includes a vessel comprising a gasification chamber that receives the micronized char, a conveying gas, and steam where the gasification chamber provides syngas, ash, and steam. A combustion chamber receives syngas and an oxidant and burns the mixture of syngas with the oxidant to provide heat for gasification and for heating incoming flows, thereby generating steam and CO2. The heat for gasification is transferred from the combustion chamber to the gasification chamber by circulating refractory sand. A syngas cooler cools the syngas and generates steam and provides to a supercritical CO2 power cycle system that performs a supercritical CO2 power cycle for generating power.