Coal Oxyfuel Combustion: A Review

摘要

Coal is an abundant and relatively cheap fuel, but growing concerns over greenhouse gas emissions and climate change represent a formidable challenge for the coal-based utility sector. Increasing plant efficiency, as in supercritical or ultra-supercritical plants, or in IGCC plants, could reduce CO_2 emissions by a maximum of 20-25% compared to conventional PC units. For further reductions in CO_2 emissions from coal plants, CO_2 capture and storage is the only solution. CO_2 capture technologies are usually divided into three groups: 1) post-combustion capture (dilute CO_2 is scrubbed from the flue gas), 2) pre-combustion capture (typically involves gasification and CO_2 capture from syngas) and 3) oxyfuel combustion. In oxyfuel combustion oxygen coal is burned in an O_2-CO_2 environment as opposed to an O_2-N_2 environment (air) in the case of conventional combustion. If coal is burned with pure oxygen, some of the flue gas is recycled to reduce the boiler temperature. The resulting flue gas is mostly CO_2 which can be subsequently pressurized and pipelined to a storage site. This paper presents a review of the latest R&D related to oxyfuel combustion, which many consider as a viable CO_2 capture technology, despite some economical challenges associated notably with the cost of oxygen. In addition to presenting the inherent advantages and technical challenges of the oxyfuel combustion process, this paper also describes how the development of new air separation processes, based on ionic transport membranes, can affect the economics of the whole plant.