Hydrogen is an increasingly attractive low-carbon energy carrier for a variety of stationary and mobile applications. Currently, the vast majority of hydrogen in the United States is produced via the energy intensive steam reforming of natural gas. The cost and carbon emissions associated with hydrogen production can be reduced by improving the efficiency of this process. Thus, this thesis investigates the potential of differential temperature water-gas shift (WGS) microreactors to intensify the steam reforming process.
First, a COMSOL Multiphysics model of the WGS reaction is developed and compared against experimental values from the literature to validate its performance. The model is then used to evaluate improvements in the performance of the WGS reaction when operating under an optimal temperature profile when compared to the performance of a baseline model of the standard high temperature shift and low temperature shift (HTS/LTS) reactor configuration most frequently deployed in industry over a range of operating conditions. The results of this modeling effort are used to inform the design of a microreactor prototype that can be additively manufactured using a selective laser melting (SLM) process. The thermal-hydraulic performance of this prototype is experimentally verified to further validate the modeling results. Finally, a simplified version of the developed differential temperature WGS microreactor model is implemented into a flow sheet of the overall steam reforming process and its economic benefits are evaluated through a rigorous optimization process.
The study results suggest that the implementation of a differential temperature WGS reactor operating under optimal temperature conditions significantly reduces both the required reactor volume to achieve a specific CO conversion level and the hydrogen production cost associated with the overall steam reforming process. The results also suggest that the developed prototype's performance is accurately predicted (within a maximum error of 20%) by the modeling results and that SLM processes can potentially be leveraged for the design and manufacture of WGS microreactors, though there are still a number of obstacles with these processes that must be overcome first.
Funding Statement (additional comments about funding)
I acknowledge portions of this work were funded through the RAPID Institute under the U.S. Department of Energy contract (DE-EE0007888-10-4) and through the High Impact Opportunity Project program under the Oregon Innovation Council.