Kinetics and reactor modeling for CaO sorption-enhanced high-temperature water–gas shift (SE–WGS) reaction for hydrogen production

Abstract

Hydrogen, an important energy carrier of the future, produces no pollution and has a high content of energy. It is formed as a direct product of the water–gas shift (WGS) reaction, which occurs in various processes for the production of hydrogen, ammonia, methanol and different hydrocarbons, and is also a side reaction during the steam reforming of hydrocarbons and Fisher–Tropsch synthesis. Since it is an equilibrium reaction, it may be intensified by the selective removal of the products, which can lead to higher yields and energy savings. In this study, carbon dioxide was removed through chemisorption on CaO particles. In the first part, the WGS reaction kinetics were obtained on an industrial iron-chromium catalyst in a packed-bed reactor. In the second part, the CO2 chemisorption kinetics on CaO sorbent particles were examined, simultaneously with the WGS reaction. A modified dynamic shrinking-core model was used to describe the carbonation reaction, which accounted for the non-ideal core shrinkage. With the introduction of a sorbent conversion-dependent effective diffusion coefficient, the model perfectly reproduced the obtained experimental results. Valuable insight into the sorption-enhanced process was obtained with the full concentration profiles of the species involved (CO, H2O, CO2, H2) in time and space, as well as the conversion of the sorbent particles, also in the radial dimension. The developed model was used to simulate a cyclic sorption-enhanced water–gas shift operation in a revolver-type manner which allows for continuous sorbent regeneration and a much higher-than-equilibrium hydrogen production for various operational parameters. The significance of the model lies in the precise replication of the experimental results and its applicability to the vast area of the newly-emerged industrial sorption-enhanced technologies.