Abstract
A power plant based on chemical-looping combustion offers both a possibility of high net power efficiency and separation of the greenhouse gas CO2. This is due to the way the oxidation of the fuel takes place. Instead of oxidizing the fuel with oxygen from the combustion air, the fuel is oxidized by an oxygen carrier, i.e., an oxygen-containing compound. The oxygen carriers that have been suggested in previous studies are metal oxides like NiO, Fe2O3 and Mn3O4. The reduced oxygen carrier is in the next step reoxidized by air in a second reactor and then recirculated to the first reactor. In this way, fuel and air are never mixed and the fuel oxidation products CO2 and water leave the system undiluted by air. All that is needed to get an almost pure CO2 product is to condense the water vapour and remove the liquid water.Chemical-looping combustion (CLC) is also claimed to reduce the fuel exergy destruction in the overall reaction of combustion of the fuel. This gives a possibility to increase the net power efficiency.This paper gives an introduction to chemical-looping combustion. Results from simulations and a detailed exergy analysis of two different CLC gas turbine (GT) systems are also presented. The first system utilizes methane as a fuel and NiO as oxygen carrier. The second system utilizes a fuel gas mixture consisting mainly of CO and H2, simulating a fuel gas from for instance coal gasification. Results for this system are given for simulations with both NiO and Fe2O3 as oxygen carrier. The two systems are compared to comparable simulated systems with conventional combustion of the same fuel. The exergy analysis shows that the irreversibilities generated upon combustion of the fuel are reduced. The net power efficiency of the CLC–GT systems is similar or higher than for the corresponding GT systems with conventional combustion. The net power efficiency of CLC systems could be even further increased if the exergy remaining in the exhaust could be utilized in an efficient way.
Published Version
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