Numerical analysis of fuel reforming systems for efficient hydrogen production

Abstract

This thesis includes the extensive simulation results for heat and mass transfer phenomena in the reforming systems such as steam reforming and autothermal reforming systems. In order to investigate the multidisciplinary phenomena in the reactors, a numerical code has been successively developed. The reforming process occurs over the catalytic surface, and therefore Langmuir-Hinshelwood model is adopted to model the surface catalytic reactions. In addition, reforming takes process in the solid phase, which can be modeled as porous media. The developed code also has been validated with various experimental data as well as other typical numerical simulations. In order to understand the relationship between operating conditions such as oxygen to carbon ratio, steam to carbon ratio, gas hourly space velocity, gas inlet temperature, and the reformer wall temperature. various numerical investigations are carried out. For the steam reforming, higher gas hourly space velocity results lower hydrogen production due to heat transfer limitation from the reformer wall. To enhance the heat transfer, the spatial and temporal lags are newly introduced, respectively. In the spatial lag, mixed packing is proved to be economically efficient in view of catalyst usage with inert and active catalysts repeatedly. Additionally, the transient behavior of the steam reforming characteristics is effectively used to get high hydrogen yield during the same operating time compared with continuous gas mixture feeding. However, these methods are only advantageous in the higher gas flow rate region. Also, the gas hourly space velocity is reevaluated by aspect ratio of the reformer. In order to design the reformer effectively, appropriate aspect ratio is determined under the same heat flux environment. Autothermal reforming is also investigated as various operating conditions such as oxygen to carbon ratio, steam to carbon ratio, gas hourly space velocity, and the thermal boundary condit...