Investigations of oxy-fuel combustion and oxygen permeation in an ITM reactor using a two-step oxy-combustion reaction kinetics model

In this work, a modified two-step oxy-combustion reaction kinetics model for methane-oxygen combustion is used to predict the oxy-combustion characteristics inside an ITM reactor. The membrane reactor has a symmetric design allowing the reduction of the number of coordinates to 2D without reducing the accuracy of the calculations. A detailed study is presented in order to understand the performance of an ITM reactor under the oxy-combustion conditions in the permeate side of the membrane using CH4 as a fuel and CO2 as sweep gas. Coefficients of the oxygen permeation equation used in this work have been calculated for a LSCF 1991 ion transport membrane by fitting of the experimental data in the literature. It was found that parameters such as the inlet gases temperature (feed and sweep), percentage of CH4 in the sweep gas mixture and the reactor geometry can have great effects on the operation of ITM reactors. In contrast, there are some other parameters that are less important such as feed and sweep gas volume flow rates and oxygen partial pressure in the feed side. The effect of reactivity is investigated through the comparison of cases that include and exclude reactivity. It was found that activation of the chemical reactions in the permeate side of the membrane results in increase in the oxygen permeation flux. This was attributed to the increase in the partial pressure driving force across the membrane surface as a result of depletion of oxygen molecules in the permeate side as a result of combustion. It was attributed to the rise of the membrane surface temperature which leads to reduction of the surface resistance of the membrane to oxygen permeation. (C) 2012 Elsevier B.V. All rights reserved.