GeoHex excellence lies in the concept of developing materials for heat exchangers (HX) addressing both the improvements in the anti-scaling and anti-corrosion properties as well as the heat transfer performance of the HX materials, leading to smaller, more efficient and cheaper systems. These improvements will have a positive impact on the competitiveness and hence growth of the geothermal sector. This will in itself support the EU decarbonisation policy objectives and climate mitigation target.
Current problem areas that will be addressed in order to promote geothermal energy have been identified and are addressed in the GeoHex project:
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Low overall plant efficiency. In order to minimise the problem of silica scaling, the brine is usually reinjected at a higher temperature meaning that the full potential of the geothermal energy cannot be exploited.
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Corrosion and scaling issues. Direct heat exchangers (e.g. geothermal brine to district heating) and ORC HXs such as superheater, preheater and evaporator, are in direct contact with the geothermal brine, causing scaling and corrosion rates that vary depending on the thermophysical condition and chemical composition of the geofluid. These are mitigated against in a variety of ways, all of which add costs or reduce efficiency. Mitigation methods include:
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To handle aggressive geofluids, expensive titanium or corrosion resistant alloys (CRAs) are usually recommended as the heat exchanger material
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Increased cleaning is used to reduce scale build up but this increases plant downtime
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Inhibitors are used to reduce scale build up, an added cost
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Overdesign as a result of suboptimal heat transfer performance. To date limited research has been conducted to improve the heat transfer performance of the heat exchangers used in geothermal plants. If improvements could be made this would result in a reduction in the heat transfer area and therefore a reduction in the overall size of the heat exchanger, and potential capital cost savings on the units. An understanding of the transition phenomenon is required:
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For condensation, the transition from drop to film wise condensation
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For boiling, the transition from nucleate to film boiling
Phase change heat transfer is difficult to model because it is a transient and multiscale phenomenon involving dynamic motion of multiple interfaces.
GoeHex aims to develop a solution through a combination of numerical modelling and image processing algorithm to characterise the droplet/bubble dynamics mechanism of transition phenomenon occurring in phase change heat transfer along with the failure modes of induced wettability characteristics.