Despite years of promises and efforts, the diffusion of hydrogen as energy vector is still limited due to low efficiencies and high costs in its production, storage and transportation. One possible solution is the development of a distributed grid using small units producing hydrogen via steam methane reforming (SMR). Small-scale fuel processors are under study for micro-combined units (m-CHP), which promise to cogenerate heat and power e.g. for residential applications. This approach would leverage on existing local natural gas infrastructures to avoid unsustainable side costs and the need to store and transport hydrogen. However, today this is still technologically out of reach. In fact, due to the large negative temperature gradients inside the reactor caused by the strongly endothermic nature of the reaction chemistry, m-CHP units require high working temperatures, as well as a quite stable demand as output. The latter is impossible to have in real life since energy and heat demand is typically characterized by strong fluctuations over time.
The project INSTANT proposes to mitigate all the issues associated with the design and operation of compact SMR reactors for m-CHP units by implementing the very same concept of conductive structured catalytic reactors developed within the parent ERC AdG 2015 project INTENT (www.intent.polimi.it). Significant performance improvements were indeed observed in SMR experiments when Rh-based catalyst particles were packed inside highly conductive copper foams.
The goal of INSTANT was to scale up for the first time the innovative concept of packed foam reactor, developing and demonstrating a semi-industrial prototype of compact methane steam reformer for m-CHP fuel processors. Validation of the prototype reformer in a relevant industrial environment enables a true proof of concept (TRL 5-6), setting the stage for a rapid industrialization.
Preliminary lab-scale testing was realized at Politecnico di Milano, whereas pilot scale testing was performed at the site of an industrial sub-contractor: ICI Caldaie had previously developed a small-scale reforming unit for micro-CHP generation, able to serve the thermal and electrical demand of a 10-family housing. This system is characterized by a reactor with an internal radiant burner and an annulus filled with catalyst pellets. In INSTANT, we have loaded the annulus with copper foams to enhance the heat transfer limited performance of the reformer.
In the first stage of INSTANT, mathematical modelling was used to generate a detailed performance analysis of the new reformer. After preliminary validation of the model, running lab-scale tests of copper foams packed with Rh-catalyst particles at the PI’s Host Institution, the model was adapted to simulate the pilot-scale setup and predict the expected potential of the inserts based on copper foams.
The core of the INSTANT projects has relied on the pilot-scale experimental campaign at the ICI Caldaie site. The aim was to perform first benchmark methane steam reforming runs at practically relevant conditions with the reformer in its conventional configuration (i.e. loaded just with Rh-based catalyst particles and inert particles, Al2O3). To assess the INSTANT concept, the experiments were then replicated in the reformer loaded with Cu open-cell foams packed with the same catalyst particles.
The results of the campaign have highlighted that the reformer performances were greatly improved by the introduction of the conductive internals, as the reformer is operated with reduced thermal gradients and a more uniform temperature distribution. Performance indicators evaluated during the test sessions have successfully met the expected targets, demonstrating a 52% increment of the H2 productivity in comparative tests with the same methane feed flow rate and thermal power input (INSTANT target = +30%). At full methane conversion the hydrogen productivity was three times higher in the INSTANT configuration than in the conventional reformer, which holds promise for reducing the footprint of the CHP unit. Furthermore, the innovative reformer was operated for 108 hours without any significant issues. Also, loading and unloading of both copper foams and catalyst particles was shown to be practically feasible.
The outcomes of INSTANT pave the way for a new generation of fuel processors for micro-combined cogeneration systems.
