Coal-Direct Chemical Looping Gasification for Hydrogen Production: Reactor Modeling and Process Simulation

A novel process scheme for hydrogen production from coal with in situ CO2 capture, known as the coal-direct chemical looping (CDCL) gasification process, is discussed in this article. The CDCL process utilizes an iron oxide based oxygen carrier as a chemical looping medium to indirectly gasify coal into separate streams of H-2 and CO2. ASPEN Plus reactor simulation models based on both thermodynamic equilibrium limitations and kinetic limitations are developed to analyze individual CDCL reactors. Process simulations are subsequently performed to estimate the performance of the CDCL process under various mass and energy management schemes. Reactor modeling results indicate that a moving bed reducer can effectively convert coal while reducing the oxygen carrier. The reduced oxygen carrier can in turn be oxidized by steam to produce hydrogen in a moving bed oxidizer. The fates of pollutants as well as the effects of various process operating parameters such as carbon and iron oxide conversions are also evaluated. Process simulation indicates that, even under a set of conservative assumptions, the CDCL process has the potential to convert coal to hydrogen at a thermal efficiency of nearly 78% (HHV) while capturing >90% CO2, which is 30% higher, on a relative basis, than conventional hydrogen generation processes.