Steam-generating heat pumps show great potential for reducing carbon emissions in the industrial sector. However, predicting their performance is challenging, as the irreversibilities of components evolve differently with temperature lift and condenser temperature. With over seventy design improvements mentioned in the literature, selecting the most effective design improvement is cumbersome. In this study, energy and exergy-based methods were compared in their ability to identify favourable design changes to a single-stage subcritical heat pump for the generation of steam from hot condensate. The introduction of a sequential compressor with an intermediate cooler, based on the results of the energy analysis reduced the heat pump’s techno-economic performance. The results of exergy-based methods lead to the addition of either an internal heat exchanger or a flash vessel by and improved in both cases technoeconomic performance. The internal heat exchanger performed best and increased the coefficient of performance from 2.3 to 2.8 and reduced operational costs by 0.8 M€ after 5 years of operation. Additionally, the initial investment decreased by 135 k€, and the total costs of operation decreased from 10.3 M€ to 8.7 M€. These findings show that exergy-based methods are the way forward in identifying effective design improvements for steam generating heat pumps.@en

Heat pumps are a promising option to decarbonize the industrial sector. However, their performance at a plant-level can be affected by other process changes. In this work, process changes that improve the heat pump's performance have been identified using Process Change Analysis (PCA), where the background pinch point is used as a reference point for appropriate placement. The effects of the process changes on the heat pump's work requirements are studies by introducing exergy to PCA to form the split exergy grand composite curve. This graph shows the work potential of the streams connected to the heat pump and therefore its work targets. The framework is demonstrated in two case studies. In a biodiesel production plant, it allowed to identify technologies that enhance heat pump performance while reducing overall heating requirements. Here, a heat pump transfers 1.9 MW with a COP of 4.2 but incurs a 40 kW penalty for transferring heat above the background process's pinch temperature. Replacing the wet water washer with a membrane separation unit avoided this penalty, while drastically reducing energy requirements from 0.9 MW to 0.3 MW. in a vinyl chloride monomer-purification process, PCA showed how the extraction of heat by the heat pump impacted the formation of the background pinch, from which an implementation strategy was derived that increased the heat pump's plant-level performance by 6.5% with respect to standard implementation.

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In view of the energy transition, it is important that engineering students are familiar with the concept of exergy and the added value of exergy analysis compared to energy analysis. Exergy analysis tells the truth about energy efficiency and exergy is directly related to sustainable development. This paper focuses on teaching exergy to students at the Delft University of Technology (TU Delft), but the contents are valuable to other engineering students as well. To encourage the teaching of exergy, the basics of exergy and exergy analysis are presented, as well as examples and ideas for teaching exergy to BSc students that are related to the topics of their BSc programme. It is recommended that the contents of this paper be discussed with many teachers of BSc programmes, especially teachers of BSc programmes that do not yet seem to include the teaching of exergy, and that attention be paid to teaching exergy to MSc students as well.@en

Steam generating heat pumps show great potential for reducing carbon emissions in the industrial sector. However, predicting their performance is challenging as the exergy destruction of e.g., compressors and expansion valves increases with the temperature lift and condenser temperature. With over seventy design improvements mentioned in the literature, selecting the most effective design improvements is crucial. In this study, energy and exergy-based methods were compared in their ability to identify design improvements for a single stage subcritical heat pump to produce steam from hot condensate. The energy-based method suggested the addition of a sequential compressor with an intermediate cooler; however, this design did not improve the heat pump's techno-economic performance. The suggestion of adding either an internal heat exchanger or a flash vessel by exergy-based methods did lead in both cases to improved techno-economic performance. The internal heat exchanger performed best and increased the coefficient of performance from 2.3 to 2.8 and reduced operational costs by 0.8 M€ after 5 years of operation. Additionally, the initial investment decreased by 135 k€, and the total costs of operation decreased from 10.3 M€ to 8.7 M€. These findings show that exergy-based methods are the way forward in identifying effective design improvements for steam generating heat pumps.

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