(48d) Waste-Heat Recovery from Electrolyzers: A Path to Combined Heat and Hydrogen Systems

Hydrogen produced from water electrolysis is a promising energy carrier with multiple applications, especially in the chemical industry. However, its production remains expensive and requires a significant energy input [1]. Waste-heat recovery has been shown to improve both the efficiency and cost-effectiveness of the process [2], but this aspect is not usually considered when designing electrolyzers [3]. Instead, electrolyzers are mainly designed to minimize the levelized cost of hydrogen [4], often including hydrogen compression in the design stage [5]. Subsequently, the available waste heat is sometimes utilized for other applications, thus increasing the efficiency of the process and reducing hydrogen costs. However, the most mature electrolyzer technologies operate at low-temperature levels (below 90°C), leading to a focus on the direct use of the waste heat for district heating networks [6]. Conversely, upgrading the waste heat to temperatures suitable for industrial applications (e.g., steam generation) has been less explored, despite the development of emerging high-temperature heat pumps capable of reaching up to 200°C [7]. This presents an opportunity to further leverage the use of waste heat from electrolyzers, enabling the supply of both hydrogen and heat to the industry.

In this contribution, we conduct a techno-economic assessment of waste-heat utilization from low-temperature electrolyzers to supply both hydrogen and heat to downstream processes. We compare the differences between using the waste heat directly at low-temperature levels and upgrading it using high-temperature heat pumps. Additionally, we identify the optimal hydrogen and heat supply networks, considering air-source heat pumps and electric boilers as alternative solutions to meet the heat demand. We also perform a sensitivity analysis to account for variability in investment costs, energy prices, and energy emission factors. We find that waste-heat utilization from electrolyzers enhances both energetic and exergetic efficiencies, while also reducing costs and emissions. Designing electrolyzers to simultaneously produce hydrogen and heat offers greater benefits than designing them for hydrogen production only and using their waste heat afterward. When determining optimal hydrogen and heat supply networks, using the waste heat from electrolysis is consistently preferred over other electric heating alternatives. Furthermore, when both temperature heat demands need to be met, upgrading waste heat is prioritized over direct use, provided the upgraded heat has greater economic value than the low-temperature heat. Finally, incorporating additional heat sources, like compression intercooling, can slightly increase efficiency and reduce dependance on the waste heat from the electrolyzer.

These results indicate that designing electrolyzers with waste-heat utilization in mind can offer significant benefits if the waste heat is to be utilized. Additionally, it suggests that existing electrolyzer installations can be retrofitted to co-produce steam, thereby contributing to the decarbonization of industrial heating. Future research will explore waste-heat utilization from electrolyzers at a flowsheet level, enabling comprehensive thermal management at both the stack and system levels, and allowing the optimal design of all units.

Acknowledgments

The authors gratefully acknowledge funding through Internal Funds KU Leuven (STG/22/060).

References

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