Oxy-fuel combustion uses pure oxygen instead of air to burn fuel, allowing for easier removal of carbon dioxide without the need to remove nitrogen. This technology can be applied to coal-fired power plants, gas turbines, and welding applications. The resulting gas is nitrogen-free and can be easily purified and stored. While still under development, oxy-fuel technology shows promise for cleaner and safer power generation.
Oxy-fuel is the combustion of fuel with pure oxygen instead of the mixture of oxygen, nitrogen and carbon dioxide in the air. When fuel is burned using pure oxygen, any carbon dioxide content can be stored without the need to remove nitrogen, which is a critical step in purifying waste products in power plants. The gases released by power plants are 75% nitrogen, which must be removed from any carbon dioxide vapor. The most promising application is in coal-fired power plants, but gas turbines, oxygen production and welding applications could also benefit.
Coal-fired power plants can be reconfigured to burn oxyfuel without changing the boiler design, although the combustion temperature is high for most boilers. The oxy-fuel combustion process produces coal with a much higher combustion temperature, but this can be controlled by mixing oxygen with steam or flue gases from other plant processes. Nitrogen is present in the boiler only at low levels and little nitrogen or nitric oxide is produced to contaminate the air.
The fumes from burning fossil fuels with oxyfuel are nitrogen-free. Carbon dioxide and water are the main components of the gas, which can be concentrated into streams of nearly pure carbon dioxide. The advantage is that the remaining gas can be compressed, dried and purified much faster and cheaper than with traditional methods before being transferred to storage.
The gas turbine cycle is improved through the use of oxy-fuel, but because gas turbine blades do not tolerate high temperatures well, the turbines require redesign to run on oxygenated fuel. The high temperature fumes coming out of a modified turbine actually make the steam cycle more efficient. Oxy-fuel welding and cutting also give welders more control over the amount of heat generated, so that the temperature of a weld zone can be kept at safe levels. The size and shape of the weld bead are more easily controlled, and the modifications required to use oxy-fuel in welding are fairly straightforward.
Full applications of oxyfuel are still under development. The technology has been tested in the United States, Canada, Europe and Japan and the less complexity and risks of the technology are attractive. Demand for clean-burning coal-fired power plants and environmentally safer power generation plants could trigger a large increase in oxygen-based power systems as technology progresses. It may also be possible to produce oxygen and separate it from the air at a lower cost than cryogenic methods.
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