Researchers from the Technical University of Denmark and Haldor Topsoe, with colleagues from the Danish Technological Institute and Sintex have developed a “disruptive approach to a fundamental process” by integrating an electrically heated catalytic structure directly into a steam-methane–reforming (SMR) reactor for hydrogen production. A paper describing their approach is published in the journal Science.
Intimate contact between the electric heat source and the reaction site drives the reaction close to thermal equilibrium, increases catalyst utilization, and limits unwanted byproduct formation. The integrated design with small characteristic length scales allows compact reactor designs, potentially 100 times smaller than current reformer platforms. Electrification of SMR offers a strong platform for new reactor design, scale, and implementation opportunities. Implemented on a global scale, this could correspond to a reduction of nearly 1% of all CO2 emissions.—Wismann et al.
Heating principles. (A) Conventional fired reactor. (B) Electric resistance–heated reactor. Characteristic radial length scales and temperature profiles are shown across the heat source, reactor wall (gray), and catalyst material (green). In (B), the heat source and reactor wall are one. Illustrations are not to scale. Wismann et al.
Steam methane reforming (SMR) is the most common process used to produce hydrogen on a large industrial scale. Using very high temperatures and steam, SMR reformers convert methane into carbon dioxide and hydrogen. However, this widely used method also has a significant CO2 footprint; not only is the greenhouse gas produced as a byproduct of the reaction, fossil-fuel burning furnaces are used to supply the heat required to drive the reactions.
While SMR generates nearly 50% of the global supply of hydrogen, it’s estimated that the process accounts for nearly 3% of global CO2 emissions, and despite decades of research into improving the efficiency of the process, no lower-emission alternatives have been implemented at an industrial scale, the authors say.
We see the electrified reformer as the next logical step in the chemical industry because in this way we can transform the industry going towards greener processes, but [with] processes that are at the same time feasible so ... we don’t have to increase the production prices.—co-author Peter Mortensen
The electrically-driven version of methane reforming uses an AC current and direct electrical resistance to heat the reactors. Unlike conventional SMR, the electrified process supplies heat uniformly across the reactor. The integrated heating also allows for exceptionally compact reactor designs.
The electrification, uniform heating, and potential for exceptionally compact reactors present a disruptive approach to resolving CO2 emission issues and current constraints regarding design, operation, and process integration for hydrogen production by SMR. In addition to reducing CO2 emissions, implementation of the resistance-heated reactor into existing plants could offer alternative operation conditions, reducing the steam-to-carbon ratio, or operate at increased methane conversion, typically limited by carbon deposition and temperatures (i.e., material constraints). High methane conversion coupled with an alternative purification technology could even provide a local source of CO2 for other processes.
With less need for heat recovery, resistance-heated reforming is efficient and applicable at many different sizes, promoting delocalization designs by using the existing and well-developed infrastructure of natural gas and potentially also biogas. Low thermal mass can also lead to reformers optimized for intermittent operation, following the fluctuations in availability of excess renewable energy with possible startup times in seconds. The operating costs for an electrified reformer are directly related to the cost of electricity, natural gas, and CO2 taxes. Preliminary estimates indicate that a resistance-heated reformer would be on par with current fired reformers in regions with a high production of renewable electricity.—Wismann et al.
Sebastian T. Wismann, Jakob S. Engbæk, Søren B. Vendelbo, Flemming B. Bendixen, Winnie L. Eriksen, Kim Aasberg-Petersen, Cathrine Frandsen, Ib Chorkendorff, Peter M. Mortensen (2019) “Electrified methane reforming: A compact approach to greener industrial hydrogen production” Science Vol. 364, Issue 6442, pp. 756-759 doi: 10.1126/science.aaw8775