Autothermal Operation Strategies of Chemical Looping Processes for Hydrogen Generation: Process Simulation, Parametric Studies, and Exergy Analysis

Chemical looping is an advanced material and energy conversion technology that can achieve both high-level process intensification and efficiency. To analyze chemical looping processes, it is essential to include process conditions that are realistic and comparable to those that are expected in industrial systems. Relevant variations in these conditions as occurred in bench versus industrial-scale systems include isothermal versus adiabatic operation of the reactors and local versus global process heat integration. Naturally, the types of reactors employed dictate how the reactor operation is to be conducted from the heat integration viewpoint in the overall process arrangement. As an example, in industrial applications, a fluidized bed reactor is operated near uniform temperature conditions. A fixed bed or a moving bed reactor, on the other hand, is typically operated adiabatically, and thus under the autothermal operation, the nonisothermal condition prevails, leading to different strategies for process simulations and heat integration requirements. This study presents the chemical looping process simulation based on a moving bed reactor used as a reducer for two H-2 generation process configurations under autothermal operating conditions. The two process configurations are represented by the two-reactor (reducer-combustor followed by the water-gas shift reaction) and the three-reactor (reducer-oxidizer-combustor with water splitting for H-2 generation in the oxidizer) chemical looping systems with each configuration producing H-2 in a different operating scheme. The simulation results are compared with the conventional steam methane reforming (SMR) system as a baseline case to underscore the attractiveness of the chemical looping configurations. Specifically, for each configuration, the parametric study under the adiabatic conditions is used to optimize the operating conditions that can satisfy the heat balance requirements and can achieve a maximum H-2 yield. The exergy analysis indicates that the two-reactor chemical looping and three-reactor chemical looping systems can achieve, respectively, a 4.0 and 11.4% increase in relative percentage in the overall process exergy efficiency over the conventional steam methane reforming system.