Abstract
Oxy-fuel combustion is one route to large scale carbon capture and storage. Fuel is combusted in oxygen rather than air, allowing pure CO2 to be captured and sequestered. Currently, the required oxygen is produced via cryogenic air separation, which imposes a significant energy penalty. Chemical looping air separation (CLAS) is an alternative process for the production of oxygen, and relies on the repeated oxidation and reduction of solid oxygen carriers (typically metal oxides). The energy efficiency is governed by the thermodynamic properties of the oxygen carrier material, and how well the CLAS process can be heat-integrated with the process consuming oxygen. In this study, key thermodynamic properties have been identified and assessed using a steady state model of a CLAS-oxy-fuel power plant. It is demonstrated that energy penalties as low as 1.5 percentage points can be obtained for a narrow range of material properties. Based on density functional theory calculations, 14 oxygen carrier systems, which are novel or have received little attention, have been identified that could potentially achieve this minimal energy penalty.
Highlights
The oxy-fuel process is a promising approach for capturing carbon dioxide from power plants fired with fossil fuels [1]
“potential oxygen carriers” shows combinations of ΔHro and Teq likely to be accessible by existing materials; this region is computed by considering the base case as shown, with the limits set by potential differences in the value of ΔSro,298 K
A model was constructed which links the thermodynamic properties of an oxygen carrier to the steady state operation of an oxy-fuel power plant to estimate the viability of oxygen carriers for chemical looping air separation
Summary
The oxy-fuel process is a promising approach for capturing carbon dioxide from power plants fired with fossil fuels [1]. One of the drawbacks of the Brin process, which looped between BaO and the peroxide BaO2, was the need to first remove the carbon dioxide present in the air, which otherwise led to the irreversible formation of BaCO3. In 2000, the idea of exploiting a chemical loop for the separation of air was reintroduced, in this case using a perovskite (LSCF) as the oxygen carrier [7,8]. Later, simpler compounds, such as CuO/Cu2O, Mn2O3/ Mn3O4 and CoO/Co3O4, were considered as oxygen carriers [9,10]. Copper oxide and other transition metal oxides do not react with the CO2 in air to form stable carbonates under process conditions
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