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Concept
Oxy-fuel combustion process
Summary
Oxy-fuel combustion is the process of burning a fuel using pure oxygen, or a mixture of oxygen and recirculated flue gas, instead of air. Since the nitrogen component of air is not heated, fuel consumption is reduced, and higher flame temperatures are possible. Historically, the primary use of oxy-fuel combustion has been in welding and cutting of metals, especially steel, since oxy-fuel allows for higher flame temperatures than can be achieved with an air-fuel flame. It has also received a lot of attention in recent decades as a potential carbon capture and storage technology.
There is currently research being done in firing fossil fuel power plants with an oxygen-enriched gas mix instead of air. Almost all of the nitrogen is removed from input air, yielding a stream that is approximately 95% oxygen. Firing with pure oxygen would result in too high a flame temperature, so the mixture is diluted by mixing with recycled flue gas, or staged combustion. The recycled flue gas can also be used to carry fuel into the boiler and ensure adequate convective heat transfer to all boiler areas. Oxy-fuel combustion produces approximately 75% less flue gas than air fueled combustion and produces exhaust consisting primarily of CO2 and H2O (see figure).
The justification for using oxy-fuel is to produce a CO2 rich flue gas ready for sequestration. Oxy-fuel combustion has significant advantages over traditional air-fired plants. Among these are:
The mass and volume of the flue gas are reduced by approximately 75%.
Because the flue gas volume is reduced, less heat is lost in the flue gas.
The size of the flue gas treatment equipment can be reduced by 75%.
The flue gas is primarily CO2, suitable for sequestration.
The concentration of pollutants in the flue gas is higher, making separation easier.
Most of the flue gases are condensable; this makes compression separation possible.
Heat of condensation can be captured and reused rather than lost in the flue gas.
Because nitrogen from air is absent, nitrogen oxide production is greatly reduced.
Official source
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