Tuesday, 5 March 2019

Oxy Fuel Combustion

Oxy Fuel Combustion

Oxy-fuel combustion is currently considered to be one of the major technologies for carbon dioxide (CO2) capture. This book focuses on the development of oxy-fuel combustion technologies using coal as fuel.

Oxy-fuel combustion for CO2 capture incorporates three main components: the air separation unit (ASU) that provides oxygen for combustion, the furnace and heat exchangers where combustion and heat exchange take place, and the CO2 capture and compression unit. Due to the large quantity of high purity oxygen typically required in oxy-fuel combustion, cryogenic air separation is currently the technology of choice for oxygen production.

In oxy-fuel combustion, conventional boiler technology is deployed to prepare and combust the fuel, and to transfer the combustion heat from the flue gas to a working fluid (typically steam) to generate electricity. In most implementations, a large portion of the flue gas is recycled back to the furnace to control the flame temperature and to reconstitute the flue gas volume to ensure proper heat transfer. The resulting flue gas consists mainly of CO2 and water, as nitrogen has been eliminated from the combustion medium. Flyash in the flue gas is collected in an ESP or bag house, and flue gas desulfurization is employed to reduce sulfur oxide emissions. Compared with most other combustion technologies, oxy-fuel combustion has the inherent advantage of producing low NOx emissions since oxygen is used for combustion and the re-burning mechanism via flue gas recycle. Consequently, a NOx control process is typically not required. Recycled flue gas can be drawn at several locations, for example, before or after the flue gas condenser.

Due to the high concentration of CO2 in the flue gas, no chemical solvent or physical sorbent is required to separate CO2 from the flue gas. The CO2 capture and compression unit comprises multi-stage compression and cooling processes in which the flue gas is first dried and the impurities such as oxygen, nitrogen, and argon are separated from the CO2.

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