Numerical investigation of combustion characteristics in an oxygen transport reactor

The paper presents a numerical investigation of thermal characteristics of oxyfuel combustion in an oxygen transport reactor (OTR). The reactor is made of a combustion chamber of tubular shape and surrounded by an annular air flow compartment. The walls of the combustion chamber are made of dense, nonporous, mixed-conducting ceramic membranes that only allow oxygen permeation from the annular air compartment into the combustion chamber. A mixture of CO2 and CH4 (sweep gas) enters the reactor from one side and mixes with the oxygen permeating through the ion transport membrane. The resulting combustion products (composed of H2O and CO2) are discharged from the other side of the reactor. The modeling of the flow process is based on a numerical solution of the conservation equations of mass, momentum, energy and species in the axi-symmetric flow domain. The membrane is modeled as a selective layer in which the oxygen permeation depends on the prevailing temperatures as well as the oxygen partial pressure at both sides of the membrane. The comparison between reactive and separation-only OTR units showed that combining reaction and separation increases significantly O2 permeation rate to about 2.5 times under the assumptions given herein. Uniform axial temperature of about 1250 K is achieved in most of the reactor length with high CH4 conversion of 75% to 35% for CH4/CO2 mass ratio ranging from 0.5/0.5 to 1.0/0. Since the thermal resistance of these membranes is low, the heat of reaction is mostly transferred to the air side with a portion used to heat the O2 permeating flux. © 2013 John Wiley & Sons, Ltd.