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Abstract
Driven by the requirement of portable power for people in remote locations, a solar powered micro-reactor for methanol reforming is proposed and analysed in this thesis. The proposed reactor utilises concentrated solar thermal energy for methanol reforming to produce hydrogen that can be used to generate electricity in a proton exchange membrane fuel cell (PEMFC).
As this chemical reaction is an endothermic process and can only occur when temperatures are higher than 220oC, a CPC-based solar thermal collector and vacuum insulation is used to concentrate solar energy and maintain the required temperature. The designed collector consists of a small, flat, double-sided selective-surface receiver in a vacuum package. The vacuum pressure is kept below 10-2Pa to eliminate convective heat loss from the receiver when in operation. In this thesis, a micro CPC was designed following a typical CPC design method, but with specific design requirements for portable methanol reforming. Both optical and thermal models of the proposed CPC were developed to analyse the performance of the collector theoretically. The optical analysis shows that the optical performance of the proposed CPC critically depends on the properties of the reflectivity of the CPC mirror and the absorptance of the selective surface on the receiver. Aiming for a total optical efficiency above 70%, several materials (e.g. polished surfaces and 3M reflective films) were analysed and tested, with the final optical efficiency reaching 74% in ray-tracing analysis. Using the optical modelling results (for short wavelengths), a thermal model at long wavelengths was also established. These models were then, validated through the experimental work. Using the geometry found from the ray-tracing analysis, a prototype of the proposed CPC was manufactured and tested in a vacuum. The results show agreement between the thermal model and the experimental data. A stagnation temperature of 327oC was achieved, which proves that the design can operate at temperatures suitable for methanol reforming. Using the same heating conditions, an electrically-heated reformer with insulation was made for a hydrogen production test. The results show that with a comparable heat flux with solar flux of 900W/m2, a methanol conversion rate of 23% was obtained in the preliminary testing. Overall, this thesis proves the feasibility of using a small, portable solar thermal collector for hydrogen production through methanol reforming. This is the first time that a portable concentrated solar thermal collector is proposed for such an application, and due to the demand for off-grid electricity supply, the proposed solar-powered reformer may have a potential to be used in fuel cells for commercialisation in future work.