Effect of Support on the Behavior of Cu-Based Oxygen Carriers during Long-Term CLC Operation at Temperatures above 1073 K

Abstract

Chemical-Looping Combustion (CLC) is a combustion technology with CO 2 capture that is characterized by its low energy penalties because the CO 2 separation is inherent to the process. The CLC concept is based on the transfer of oxygen from the combustion air to fuel by means of an oxygen carrier (OC) in the form of a metal oxide. The OC circulates between two interconnected reactors, the fuel (FR) and the air reactor (AR). To scale up the CLC process for industrial application OC materials suitable to work at high temperatures are needed. Cu-based OCs had been proved to fulfill the requirements for an OC material, although operating temperatures lower than 1073 K were recommended due to its likely agglomeration problems. In this work, several Cu-based OCs have been developed by impregnation on different supports. The supports were prepared by thermal or chemical modifications of commercial γAl 2 O 3 with the aim to reduce the interaction with the metal oxide. The behavior of the OCs was studied in a CLC continuous unit of 500 W th during long-term tests using methane as fuel gas and high operation temperatures (1173 K in the FR and 1223 K in the AR). The effect of the high FR and AR temperatures on the process performance was evaluated taking into account important aspects such as combustion efficiency, resistance to attrition, fluidization behavior (no presence of agglomeration), and maintenance of the oxygen transport capacity and reactivity. Agglomeration or deactivation of the particles was never detected with either of the oxygen carriers used. At these high temperatures, stable operation for more than 67 h was feasible only using an oxygen carrier with γAl 2 O 3 modified with NiO addition as support. This is the first time that a Cu-based OC, prepared by a commercial manufacturing method, and used at 1173 K in the FR and 1223 K in the AR has exhibited such good properties: high reactivity together with high mechanical durability and absence of agglomeration. This result opens new possibilities for the application of Cu-based materials in industrial-scale CLC processes.