Allam power cycle

The Allam power cycle or Allam cycle is a process for converting fossil fuels into mechanical power, while capturing the generated carbon dioxide and water. The main inventor behind the process is Rodney John Allam.

A conventional combined cycle power station burns natural gas or gasified coal with air to drive a gas turbine and then uses the hot exhaust gas to heat water and drive a steam turbine. The working fluid for the gas turbine is carbon dioxide and water vapor from the combustion, along with nitrogen from the air (partially converted into nitrogen oxide). With this system, it is possible to achieve an LHV efficiency of around 55 to 59 percent. The gases driving the gas turbine will also constitute the principal emissions from the station, unless captured by an external system, at expense of a lower total efficiency. In addition, the station requires a cooling tower or access to large amounts of water for cooling.

In contrast, the Allam cycle uses a single turbine, driven by a working fluid consisting of only water and carbon dioxide, the mass of the latter being around 97 percent of the total. This is achieved by using pure oxygen instead of air to burn the fuel. Similarly to combined-cycle plants, the intended fuel is natural gas or gasified coal. The exhaust gas is cooled in a heat exchanger, and the steam is condensed and separated from the flow, becoming a potential source of fresh water. The carbon dioxide is compressed mechanically, and a small amount, matching the amount continuously added through combustion, is captured at high pressure, ready for pipeline transmission. The rest of the carbon dioxide is reheated in the heat exchanger and recycled into the combustion unit, where it continues to form the vast majority of the working fluid.

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