(211c) Advanced Operating Strategies to Enhance the Performance of Chemical Looping Natural Gas Reforming Processes

Natural gas is a crucial feedstock for chemical production in modern industry, and the reforming of natural gas into syngas, a mixture of H₂ and CO, is often an essential first step to convert natural gas into chemicals. However, conventional natural gas reforming processes, mainly including steam methane reforming (SMR) and autothermal reforming (ATR), suffer greatly from efficiency losses induced by the endothermic reactions and the need for air separation, respectively. Moreover, the efficiency of these processes become even lower when they are integrated with CO₂ capture. Chemical looping reforming (CLR) is a novel process that can address these challenges faced with conventional natural gas reforming. CLR performs the reforming reaction in two separate reactors, namely a reducer (fuel reactor) and a combustor (air reactor). In the reducer, natural gas is partially oxidized by metal oxides into syngas. In the combustor, the reduced metal oxides are regenerated using air. Unlike SMR, the CLR system can operate under autothermal conditions without external fuel combustion. Unlike ATR, the CLR system does not require air separation. These advantages allow the CLR system to achieve a much higher energy efficiency and much lower capital and operating costs.

By producing the syngas and regenerating the oxygen carriers in separate reactors, the CLR process offers significant flexibilities in process design. Many advanced process design strategies can be adopted in CLR processes to further improve the product yield, the energy efficiency, and the economic benefits. This work focuses on analyzing these different strategies and quantify their benefits. The following strategies are studied in detail: (1) separating the reducer into multiple modules operated at different conditions; (2) operating the reducer and combustor at different pressures by using solid pressure changing device; and (3) recycling downstream flue gas and purge gas back to the reducer. The CLR system as well as its integration with downstream chemical production are simulated in ASPEN Plus. Material, heat, and power balances are established in the process models to achieve autothermal operation in the overall process systems, and their performance is compared with SMR and ATR. The results indicate that the CLR processes can improve the product yield by 5-15% over conventional technologies. Moreover, using the advanced operating strategies can further improve the energy efficiency of those CLR processes by ~5%, which is an additional benefit granted by the flexibility of the CLR processes.