(236g) Scale up Analysis of Inductively Heated Metamaterial Reactors

The electrification of heavy industry is critical in the broader effort to decarbonize chemical manufacturing, and the scaling of electrified thermochemical reactors is particularly crucial to meeting industrial demands. Methods such as resistive and microwave heating reactors face considerable scaling challenges in construction feasibility, heating volume, and efficiency, limiting their large-scale deployment for many applications. Induction heating, on the other hand, is an established concept in the metallurgy industry, and industrial induction furnaces are technologically mature and operate at megawatt power levels. For chemical reaction processes, induction heating is further distinguished by its potential for volumetric heating, safe operation, and ease of implementation.

In this work, we explore the potential for scaling up inductively heated reactor systems using a combination of analytical modeling, numerical simulations, and experiments. We will show that heating efficiency, defined as the conversion of external electricity to energy consumed by the chemical reaction process, increases towards values over 90% as the reactor scales up, and that heating efficiency is fundamentally limited by AC-DC electrical power conversion efficiency. This study builds on previous work where we demonstrated a high-efficiency induction-heating reactor termed a metamaterial reactor. Our prototype reactor has a 1.5-inch diameter and utilizes an open-cell SiSiC foam baffle that simultaneously serves as a heating susceptor and catalyst support. Proper tailoring of SiSiC foam's effective electrical conductivity and induction frequency led to reactor conditions supporting uniform radial temperature distributions and a heating efficiency 87%, and we showed that the reactor could be used to perform the reverse water-gas shift (RWGS) reaction across a temperature range of 500 – 650 °C with ideal plug flow behavior.

To analytically deduce efficiency scaling trends with metamaterial reactors, we develop a model that investigates power consumption within the reactor system, as decomposed by useful contributions (i.e., heating of the inlet gas stream and reaction enthalpy) and parasitic contributions (i.e., energy loss via thermal conduction, induction coil heating, and energy dissipation in the amplifier). In our model, we consider the scaling of each linear dimension of the reactor (i.e., diameter and height) by a factor 𝛽, and we adjust gas flow rates to keep mass flow per reactor volume constant. Utilizing our experimental data and analytical expressions to evaluate each component, we establish that these factors scale differently with 𝛽—gas heating, reaction enthalpy, and amplifier loss are proportional to 𝛽³, coil loss is proportional to 𝛽², and thermal conduction loss is proportional to 𝛽. As a result, when projecting these effects for larger reactors, our model anticipates an enhanced overall energy efficiency surpassing 90% when reactor radius approaching 0.25 m, and that the cap in total efficiency is set by the efficiency of the power amplifier.

Numerically, we construct a multiphysics model (implemented in COMSOL Multiphysics) to further investigate the temperature distribution and power consumption characteristics of our reactors. These models combine and couple electromagnetic, heat-transfer, and computational fluid dynamics simulations. Our simulation is first constructed and refined to fit our experimental results and analytical modeling. The model is then extended to scaled up reactor systems to investigate how the heating and temperature profiles evolve as the reactor scales up. The simulations reveal that our inductively heated reactors are capable of sustaining a uniform radial temperature profile and enhanced efficiency as it scales, due to its ability to support volumetric heating capabilities. We also analyze wall-heated reactors and find that they support radial temperature gradients that become increasingly non-uniform as the reactor is scaled up.

To complement these theoretical findings, we experimentally construct reactors with diameters of 1.5 inches and 3 inches and perform the RWGS reaction within each reactor. In this scale up effort, the effective conductivity (σ) of the SiSiC baffle is adjusted such that the penetration depth of the magnetic field into the reactor (skin depth, δ = √(1/πσfμ₀)) scales with the reactor radius. Through an energy consumption analysis and the experimental characterization of temperature profiles within the reactors, we show that the heating efficiency of the reactors increase with reactor diameter in a manner that agrees well with analytic and numerical modeling.