Proposed is a novel coal conversion process, dubbed the Dry Gasification Oxy Combustion (DGOC) Cycle, because of its unique two stage conversion process. Feed coal will be partially oxidized at very high pressures (60 bar) in an oxygen-blown gasification unit, using recycled flue gas as a gasification agent (~65% CO2, 35% H2O b/v). This is in contrast to typical gasification systems that use steam as a gasification agent. In addition, the reducing environment of the gasifier will provide an opportunity to perform in situ sulfur removal through sorbent based capture.
The second stage oxy-combustion unit will also utilize recycled flue gas; for flame temperature moderation. The oxy-combustion stage will provide energy to raise steam for power generation, while maintaining a process effluent that is very concentrated in CO2. This effluent stream, already at high pressure, will utilize ambient cooling to 1) flash out the water from the effluent stream and 2) condense remaining CO2 into a high purity liquid stream, ready for further compression and sequestration.
Analysis of a preliminary design was carried out using process simulation models developed with Aspen Plus and Matlab. Results suggest that DGOC can achieve carbon capture and sequestration (CCS) goals with only a 3.4% detriment to plant efficiency (compared to the estimated 10% for current CCS technologies). Results also suggest that DGOC will remain competitive against the IGCC process, in terms of fresh water consumption.