(563b) Inductively Heated Swiss Roll Metamaterial Reactor

With the need to globally scale a net zero carbon economy within the next few decades, it is essential to reduce greenhouse gas emissions from all sectors, including industrial chemical manufacturing. Electrified thermochemical reactors that are powered using intermittent renewable electricity sources, such as wind and solar, present a compelling technological route towards decarbonizing this industry while leveraging existing infrastructure. With electrification, power is delivered using electricity instead of the combustion of fossil fuels, eliminating the challenge, infrastructure, and cost involved in capturing and removing carbon emissions from combustion flue streams.

In a recent development, we proposed inductively heated metamaterial reactors, in which external electricity is converted to internal volumetric heat within a thermochemical reactor through the heating of a three-dimensional susceptor (i.e., the element that absorbs electromagnetic power). With proper multi-physics co-design of the susceptor, power electronics, and catalyst, it is possible to tailor and optimize physical properties including the coupling between the induction coil and susceptor, volumetric power delivery profile, effective thermal conductivity, and heat transfer from the susceptor to the catalyst. Notably, this can be exploited to reduce or even eliminate temperature gradients within reactors, improving catalyst utilization and system efficiency.

In a previous demonstration, we configured our metamaterial reactor to perform the reverse water gas shift (RWGS) reaction using a 38mm diameter conductive ceramic foam as a susceptor, and we showed that volumetric heating can eliminate radial thermal gradients allowing reactors to operate in ideal plug flow regimes. The reactor displays an experimental marginal efficiency of 86.6% upon increasing the GHSV from 1700 h^-1 to 8800 h^-1, indicating a scaled reactor could achieve excellent power-to-reaction efficiency.

While these concepts show promise, susceptor design for the induction process in this regime fundamentally requires tradeoffs in desired properties. In this talk, we present the “Swiss Roll” resonant metamaterial reactor, which is a conceptually new framework for realizing structured inductively heated reactors. The concept is inspired by the electromagnetic Swiss roll, which was introduced to the electromagnetics community in 1999 and has been utilized in radio frequency metamaterial applications. The Swiss roll reactor consists of a sheet of metal that is rolled into a cylinder with a dielectric spacer or air gap between consecutive layers. The structure features a large self-capacitance and inductance and therefore supports a resonant magnetic mode at a frequency specified by the roll geometry.

The Swiss roll metamaterial reactor supports several distinct features. First, when inductively heated at resonance, the Swiss roll can be uniformly and volumetrically heated, distinct from non-resonant inductively heated reactors which feature some radial nonuniformity. Second, the Swiss roll reactor can be heated with almost arbitrarily high coupling efficiencies (i.e., relative heating of the susceptor versus that of the induction coil). By limiting dielectric and sheet resistance losses in the roll to achieve a sufficiently high quality factor, we have produced systems with 99%+ coupling efficiencies. Further, since this resonance is characteristic of the geometry and not the material, these efficiencies can be achieved at any design frequency. This elimination of coil losses is distinct from the non-resonant reactor case, where coil heating represented approximately half of the observed marginal losses in prior RWGS reactor studies.

Third, this intrinsically high coupling efficiency can be achieved at Swiss roll resonance independent of coil geometry or its spatial positioning. Relaxed constraints on induction coil geometry and position allow for thicker thermal insulation to be used in the reactor system, reducing thermal conduction losses. Multiple Swiss rolls can potentially be multiplexed with different resonant frequencies from a single coil to provide heating to different regions of the reactor in a simple and programmable manner.

Finally, the Swiss roll presents numerous viable manufacturing methods for large scale reactors. Depending on external design constraints, Swiss rolls can be additively manufactured, formed from sheet metals, rolled from flexible materials with a suitable high-temperature insulator, or subtractively manufactured via laser cutting or EDM. Catalysts can be washcoated onto the metal structure or loaded on supports between the layers as needed. Such scalability presents a major advantage over many non-resonant reactor concepts, which can’t be manufactured large enough to be industrially relevant.

We demonstrate a lab scale Swiss roll reactor with a 96 mm diameter and use it to perform the RWGS reaction. We use DLMS 3D printed stainless steel to fabricate the Swiss roll, and powdered K₂CO₃/Al₂O₃ catalyst is readily added between the layers of the roll. In benchmark experiments with a similarly sized non-resonant metamaterial reactor, we show that the Swiss roll reactor operates with higher heating efficiencies due to its ability to accommodate thicker insulation and decreased coupling losses. Thermal profiling and multiphysics modeling display a high degree of radial temperature uniformity. The reactor shows near unity marginal efficiency upon process intensification, limited only by losses in the power amplifier.