Operating Strategy of Chemical Looping Systems with Varied Reducer and Combustor Pressures

In chemical looping technology when applied to gasification, reforming, and chemical syntheses, the operating pressure is an important factor that dictates the reactant conversion and product formation economics of the technology for the processes. Common consideration of the operating pressure for the chemical looping system that includes reducer/fuel reactor and combustor/air reactor operation is based on the condition in which the reducer and the combustor are operated under similar pressures. This study considers another operating condition, characterizing the Fan chemical looping system, where the reducer and the combustor are operated under different pressures while solids are continuously or discontinuously circulating through the loop system. As an example, the chemical looping natural gas conversion to syngas with the eventual production of liquid fuels is given in this study. This example illustrates the thermodynamic limits and their associated compression duty with chemical looping syngas production at pressures between 1 and 30 atm, with a goal of obtaining syngas suitable for cobalt based Fischer–Tropsch synthesis at 30 atm. The adaptation of thermodynamic operating conditions to maximize syngas yield and balance between the syngas compression and the air compression are discussed in this study over a range of operating pressures and temperatures. Further, a novel operating strategy characterized by differential operating pressures between the fuel reactor and the air reactor in a continuous solid flow system is presented. Such a strategy allows the fuel reactor to operate at elevated pressures, closer to the syngas requirements of downstream units, while the air reactor operates near the ambient pressure conditions. This strategy has broad implications for other process system applications such as reaction–regeneration and adsorption–desorption processes where pressure variations are a key part of the optimum operation considerations. Considering the cost of the key components of the system including the reactors, valves, and compressors, such a strategy is shown to reduce the capital cost for the chemical looping system by 29% compared to equal pressure chemical looping reforming.