Copper-based chemical looping air separation process: Thermodynamics, kinetic modeling, and simulation of the fluidized beds

Abstract

Chemical looping air separation is one of the potential processes for oxygen separation from air constituents using oxygen carriers with chemical looping oxygen uncoupling properties that are circulated between reduction and oxidation reactors. Copper-based oxygen carriers have been recognized as a suitable class of materials for the process due to their promising properties and low cost. In this study, copper-based material has been investigated for chemical looping air separation to identify the process parameters that affect the performance and oxygen generation. Firstly, thermodynamic analysis was performed to predict the suitable conditions for oxygen generation and oxygen carrier oxidation, and to model oxygen equilibrium partial pressure. Then, CuO (40 wt%)/ZrO2 was prepared by impregnation synthesis technique to examine the oxygen carrier kinetics using a thermogravimetric analyzer. Results showed that 1.5-dimensional Avrami-Erofeev model best fitted the reduction data with an activation energy of 230 ± 25.2 kJ/mol, whereas the oxidation data were fitted by 1.5 reaction order model with an activation energy of 211 ± 8.0 kJ/mol. The process was simulated using Aspen Plus software package, and the reactors were represented using Fluidbed units to account for both the kinetics and hydrodynamics, to identify the suitable fluidization regimes for specific operating conditions. Simulation results showed that the highest oxygen generation occurred while operating both reactors at bubbling fluidization regimes. Moreover, the temperature effects on the process performance and output were examined, and findings indicated that operating the reducer at 1000 °C and the oxidizer at 800 °C would give out the highest solids conversion and oxygen generation flowrate (23.26 ton/day) with specific energy consumption of 132.26 kWh/tonne of oxygen. However, operating the process at high temperatures would increase the energy penalty and the operating costs, and a more comprehensive technoeconomic study will be required to decide whether lower temperatures operation would be feasible.