Electrically heated steam methane reforming

Abstract

Increasing focus on sustainability has driven a growing implementation of renewable energy in recent years, resulting in economically competitive costs of renewable electricity compared to electricity generated from fossil fuels. However, the lack of solutions for efficient storage of excess renewable energy creates a demand for technologies compatible with the intermittent nature of renewable energy production. Production of synthesis gas by steam methane reforming (SMR) is a strongly endothermic reaction, today heated by combustion of fossil fuel. Global production of syngas accounts for ca. 3% of all CO2 emissions. Electrification of the SMR process can supplant the combustion as heat source, reducing emissions by a third. This thesis describes the research into two types of electrical heating: induction and resistance heating. The work is based on experimental results at laboratory scale, elucidated by computational fluid dynamics modelling, which is further used to extrapolate to industrial relevant conditions, to gauge the potential of the respective technologies. Electrification of the SMR process provides several substantial benefits compared to current industry. In this thesis, we show that thermal gradients are practically eliminated, providing a substantial increase in catalyst effectiveness. Additionally, it is found that integrated heating enables reactors at industrial capacity two orders of magnitude smaller than current fired reformers. The lower thermal mass enables start-up within minutes, potentially compatible with the intermittent nature of renewable energy. Moreover, electrically heated SMR significantly reduce flue gas from combustion, enabling changes to current plant designs. With compact reactors and less heat recovery, electrically heated SMR is less susceptible to economy of scale, and offers a flexible and scalable platform. Induction-heated reforming by magnetic hysteresis of a ferromagnetic catalyst or susceptor for high temperature endothermic reactions presents a paradigm shift for direct heating of endothermic processes, supplying heat directly to the catalytic sites. Here, it is demonstrated how the traditional temperature profile is inverted by hysteresis heating, effectively removing all limitations of thermal conductivity within the catalytic bed. It is shown how the Curie temperature can serve as a safety limit, but at the same time limits application at industrial conditions. Adding layers of increasing Co/Ni ratio to increase the effective Curie temperature can extend the operational temperature range. It is shown how resistance-heated reforming enables improved reaction control, and supports operation at harsher conditions and higher methane conversion than conventional fired reformers. Moreover, paths for significant improvement in reactor capacity per volume is predicted by optimizing reactor dimensions and geometry, tailoring the effectiveness factor up to 75%, potentially reducing the required amount of catalyst by 2 orders of magnitude. In summary, electrically heated SMR provides a new, flexible, and competitive, platform for greener production of syngas. Electrification of SMR could reduce CO2 emissions by nearly 1% if implemented on a global scale. Flexible operation capacity, and fast transient behavior, shows promise considering compatibility with the intermittent nature of renewable energy production. Significant reduction in reactor volume and improvements in catalyst efficiency enables simplification in current industrial plants, and enables efficient operation at smaller scales. Electrification of endothermic processes is an important step towards a sustainable society.