Approximately one third of all CO2 emissions due to human activity come from fossil fuels used for generating electricity. A variety of other industrial processes such as oil refineries, fertilizer and cement plants also emit large amounts of CO2. In general, industrial GHG emissions including those from the power plants and other sources could be reduced substantially by capturing and storing CO2. Towards this end the novel application of oxy-fuel combustion to process heaters, utility boilers and gas turbines represents an emerging opportunity for cleaner fossil fuel combustion.

In oxy-fuel combustion, nearly pure oxygen (instead of air) is used for combustion resulting in a flue gas that is comprised mainly of CO2 and H2O as well as a small concentration of excess O2. This approach eliminates nitrogen from the process (except for minor air infiltration) and hence the concentration of CO2 in the flue gas can be greatly increased. As a result, only simple gas purification is required to capture CO2 in this process. A consequence of this combustion mode is that fuel burnt in pure oxygen results in a flame temperature which is excessively high. Hence, a portion of the CO2 rich flue gas is recycled back and introduced into the combustor in order to reduce the flame temperature. This recycle combustion process has the further benefit of suppressing NOx formation and providing a unique opportunity to reduce other combustion pollutants. Furthermore, flue gas recirculation reduces the volume of outgoing flue gas to approximately 1/5th that normally anticipated from air-fired combustion reducing the scale, capital and operating costs of downstream process equipment. In addition the CO2 rich stream, generated from oxy-fuel combustion, can be readily captured by a CO2 capture and compression unit (CO2CCU) without any further treatment. This practically eliminates the need for a costly separation plant. In the case of air combustion, a CO2CCU is not directly applicable due to dilute CO2 concentration in the flue gas stream unless a capture plant, such as an amine absorption process is associated with it. This is the major disadvantage for the conventional units as far as the direct CO2 capture is concerned.

In this paper we review the state of the art of oxy-fuel combustion from the perspective of such system components as burner design, CO2 capture and compression, air separation, and overall plant configuration. Furthermore, we seek to provide some insight into the future of oxy-fuel combustion with consideration on improving the cycle efficiency. Pollution control strategies of oxy-fuel systems will also be discussed. Finally, the test results of our latest oxy-fuel burner design, performed in our 0.3MWth pilot plant test facility, will be presented. This novel burner design which employs an alternate means of moderating flame temperature all but eliminates the need for recycle greatly simplifying overall design of the oxy-fuel system.

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