Effect of gas composition in Chemical-Looping Combustion with copper-based oxygen carriers: Fate of sulphur

Chemical-Looping Combustion (CLC) is an emerging technology for CO2 capture because separation of this gas from the other flue gas components is inherent to the process and thus no energy is expended for the separation. Natural or refinery gas can be used as gaseous fuels and they may contain different amounts of sulphur compounds, such as H2S and COS. This paper presents the combustion results obtained with a Cu-based oxygen carrier using mixtures of CH4 and H2S as fuel. The influence of H2S concentration on the gas product distribution and combustion efficiency, sulphur splitting between the fuel reactor (FR) and the air reactor (AR), oxygen carrier deactivation and material agglomeration was investigated in a continuous CLC plant (500 W-th). The oxygen carrier to fuel ratio, phi, was the main operating parameter affecting the CLC system. Complete fuel combustion were reached at 1073 K working at phi values >= 1.5. The presence of H2S did not produce a decrease in the combustion efficiency even when working with a fuel containing 1300 vppm H2S. At these conditions, the great majority of the sulphur fed into the system was released in the gas outlet of the FR as SO2, affecting to the quality of the CO2 produced. Formation of copper sulphide. Cu2S, and the subsequent reactivity loss was only detected working at low values of phi <= 1.5, although this fact did not produce any agglomeration problem in the fluidized beds. In addition, the oxygen carrier was fully regenerated in a H2S-free environment. It can be concluded that Cu-based oxygen carriers are adequate materials to be used in a CLC process using fuels containing H2S although quality of the CO2 produced is affected. (C) 2010 Elsevier Ltd. All rights reserved.