(221d) Dynamic Simulation of Reforming and Regeneration Processes for Fixed-Bed Adsorption-Enhanced Natural Gas Reformer

In this paper, mathematical models are presented for all processes involved in absorption-enhanced-reforming (AER) of natural gas. The dynamic model includes mass balance, energy balance for both gas phase and solid beds, and heat and mass transfer between gas and solid. Empirical correlations are used to describe SMR, shift, CO2 adsorption and CaCO3 calcination kinetics. The model has been successful in predicting the reforming, regeneration and cooling processes. Detailed model results will be presented in the paper.

Conventional Steam Methane Reforming (SMR) is the most common hydrogen production technology. Because the SMR reaction is highly endothermic, conventional SMR requires high temperatures and robust heat exchangers to increase the methane conversion to an acceptable level. This results in high capital and operating costs.

It has been proposed that AER can significantly improve steam reforming process. The CO2 absorption drives the steam reforming and water-gas-shift equilibrium to achieve higher CH4 conversion at lower temperatures. Instead of conventional multi-step SMR process (including reforming and water gas shift reactors), AER needs only a single-step to achieve high H2 purity (about 95% compared to about 75% for conventional SMR). Hence, it is anticipated that this technology can be used for numerous hydrogen production applications such as fuel cell power plants, internal combustion engines, refinery and other industrial applications.

In AER process, CO2 adsorption is exothermic and provides the heat for endothermic steam reforming reaction. The combined reforming and CO2 adsorption is nearly adiabatic, which can lead to a very simple reactor design. After reforming, the CO2 adsorbents have to be regenerated to be used for next reforming cycle. Also, as an intermediate step, the CO2 adsorbent bed needs to be cooled to an optimum temperature for efficient CO2 adsorption during reforming. Therefore, the AER process involves cycles of reforming, regeneration and an intermediate cooling step. Since AER process is inherently dynamic, dynamic simulation is necessary for optimizing the reforming, regeneration and cooling steps.

Acknowledgement: This project which is partially funded by DOE under contract DE-FC36- 03GO13102 is acknowledged.