Effect of Fuel Gas Composition in Chemical-Looping Combustion with Ni-Based Oxygen Carriers. 2. Fate of Light Hydrocarbons

Chemical-looping combustion (CLC) has been suggested among the best alternatives to reduce the economic Cost Of CO(2) capture using fuel gas because CO(2) is inherently separated in the process. Natural gas or refinery gas can be used as gaseous fuels, and they may contain different amounts of light hydrocarbons (LHC). The purpose of this work was to investigate the effect of the presence of light hydrocarbons (C(2)H(6) and C(3)H(8)) in the feeding gas of a CLC system using a nickel-based oxygen carrier prepared by impregnation on alumina. The reactivity of the oxygen carrier with light hydrocarbons and the combustion efficiency of the process were analyzed in a batch fluidized bed (FB) and a continuous CLC plant. The experiments in the batch FB showed that light hydrocarbons can be fully converted in a CLC process at temperatures above 1173 K. The influence of the fuel reactor temperature (1073-1153 K), solid circulation flow rate (7-14 kg/h), and gas composition was studied in a continuous CLC plant (500 W,h). Neither unburnt hydrocarbons nor carbon formation were detected at any experimental condition. Moreover, there were no agglomeration problems in any case. High energy efficiencies, close to the thermodynamic limit using Ni-based materials, were reached when the oxygen carrier-to-fuel ratio was higher than 3 and the fuel reactor temperature was 1153 K. According to the results found in this work, it was concluded that no special measures should be taken in a CLC process with respect to the presence of LHC in the fuel gas, e.g. refinery gas or crude natural gas.