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Removal of the CO2 between the combustion chamber and the gas turbine
The Norwegian company Sargas is developing a power plant concept where the removal of CO2 is done between the combustion chamber and the turbine at high pressure and concentration.
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The process of removing the CO2 between the combustion chamber and the gas turbine
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The Sargas pilot plant in Stockholm (Source: Marius Gjerset/ZERO) |
Sargas is developing this technology in cooperation with Siemens, and it can be used both on gas powered and coal powered plants. Sargas has already built a pilot plant in Stockholm. The Norwegian power company Hammerfest Energi is planning to implement the Sargas technology in a new 100 MW gas power plant in Hammerfest.
Compressed air is lead into a boiler where natural gas or coal is burned under high pressure. The low combustion temperature in a boiler allows for higher oxygen consumption than do turbines. While the latter needs cooling air, further diluting CO2 concentration of the flue gas, this is not the case with a boiler. Thus a much higher CO2 concentration is achieved and the boiler pressure is maintained rather than being lost in driving the turbine.
Pipes carrying water/steam inside the boiler absorbs heat and generates power in a steam turbine. The flue gas leaving the boiler has a temperature of about 850°C, considerably lower than in conventional gas power plants.
Subsequently the flue gas is cooled using a large heat exchanger. The temperature required depends on the process used for CO2 absorption. When using an amine, a process temperature of 40-50°C is necessary. The cooled flue gas is highly pressurized (about 11-12 bars) and has a high CO2 concentration (8-10 per cent), resulting in a partial pressure for the CO2 of 1-1.5 bars. This allows for other more efficient capture processes than CO2 capture posterior to the gas turbine. Equivalent figures for conventional post-combustion capture are 3-4 per cent CO2 concentration, 1 bar pressure and hence a partial pressure of 0.03-0.04.
The CO2 lean flue gas is then heated to about 800°C, using heat exchanged when cooling the exhaust from the boiler. The hot, CO2 lean flue gas then expands in a gas turbine and generates extra power before it is released into the atmosphere.
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