Chemical Looping Gasification for Producing High Purity, H2-Rich Syngas in a Cocurrent Moving Bed Reducer with Coal and Methane Cofeeds

A novel design of a coal gasifier using the chemical looping concept is introduced in the present study for high purity, H-2-rich syngas generation using coal and methane as cofeeds. In this work, an iron-titanium composite metal oxide (ITCMO), capable of cracking the heavy hydrocarbons produced in coal pyrolysis as well as regulating the product syngas purity, is used as the oxygen carrier. The cocurrent moving bed avoids back-mixing of solid and gas reactants, allowing both phases to interact, reaching thermodynamic equilibrium conditions at the reactor gas outlet. This paper focuses on demonstrating the cocurrent moving bed reducer with the ITCMO oxygen carrier. A sensitivity analysis is performed to determine the optimal operating conditions for converting Powder River Basin coal using ASPEN Plus modeling. The tar-cracking capability is ascertained by the gas chromatography-mass spectrometry analysis. The bench scale moving bed reducer substantiated its capability of achieving near-full conversion of the carbon species. The cofeeding of methane can yield a high purity syngas with H-2/CO ratio of 2 or higher, which is suitable for downstream chemical synthesis. The gas and solid compositions obtained at reducer outlets match the predictions from the ASPEN Plus model. The results indicate that the extent of char gasification at the top moving bed is a critical factor for achieving a high coal conversion. The results further indicate that the sulfur in the coal is mostly converted into the gas phase emitted with the syngas product in the reducer, while the remainder is retained in the ash.