Dry Gasification Oxy-combustion Power Cycle

Proposed within this work is a novel coal conversion process, dubbed the "dry gasification oxy-combustion" (DGOC) power cycle. In the unique two-stage conversion process, feed coal is partially oxidized at high pressures in an oxygen-blown, fluidized-bed gasification unit, using recycled flue gas as a gasification agent (approximate to 61% CO(2) and 32% H(2)O). In addition, the reducing environment of the gasifier provides an opportunity to perform pre-combustion sulfur removal through sorbent-based capture. The second stage, oxy-combustion, also uses recycled flue gas, for temperature moderation, while providing the energy to raise steam for power generation. The process effluent is concentrated in CO(2) and at high pressures, which enables the use of ambient cooling to flush out the water from the process stream. Full condensation of the remaining CO2 in a high-purity liquid stream requires the indusion of a refrigeration cycle. The resulting stream is ready for further compression, drying and pipelining for sequestration. Analysis of a preliminary design was carried out using process simulation models developed in Aspen Plus. Results suggest that DGOC can achieve carbon capture and sequestration (CCS) goals with a 4.9% higher thermal efficiency over the estimated 29.3% for current CCS technologies based on oxy-combustion. This is due to benefits gained by shifting sulfur removal from the flue gas desulfurization (FGD) recycle loop to the gasifier, as well as recovery of CaS oxidation heat. Furthermore, recoverable latent heat is available as a result of high-pressure operation and is provided primarily from the condensation of water contained in the flue stream. Results also suggest that DGOC will remain competitive against the integrated gasification combined cycle (IGCC) process, in terms of fresh water consumption.