Conference Agenda

The use of waste heat from electrolysis has been shown to significantly increase the efficiency of the process [1]. The most mature electrolyzer technologies are alkaline and PEM electrolyzers, which produce low-temperature waste heat below 90ºC [2]. Therefore, most studies focus on the direct use of this waste heat for low-temperature applications, such as district heating [3]. Another alternative is to upgrade the waste heat, which allows a wider range of applications also in the chemical industry, e.g., for low-pressure steam generation. This is enabled by the recent development of steam generating heat pumps [4]. However, the potential of combining low-temperature electrolysis and emerging heat pump technologies has not been sufficiently explored yet. Furthermore, if heat is to be considered as a valuable output, it is still not clear what changes could be made in the design of the electrolyzers to improve efficiency and economics.

In this work, we analyze the use of heat pumps for waste-heat upgrading from low-temperature electrolyzers using simple models. We evaluate the performance of the combined system, i.e., electrolyzer with a heat pump, under different operating conditions. In addition, we investigate the benefit of co-designing both units compared to the case of adding a heat pump to an electrolyzer designed without waste-heat utilization (i.e., a posteriori coupling). We show that designing for waste-heat utilization changes the preferred operating conditions for the electrolyzer. This new approach leads to a more compact electrolyzer design, which reduces capital costs and sacrifices efficiency, while allowing more heat as useful output. Additionally, we highlight similarities and differences between waste-heat upgrading from PEM and alkaline electrolyzers.

[1] van der Roest, E., Bol, R., Fens, T. & van Wijk, A. Utilisation of waste heat from PEM electrolysers – Unlocking local optimisation. Int J Hydrogen Energy 48, 27872–27891 (2023).

[2] Arsad, S. R. et al. Recent advancement in water electrolysis for hydrogen production: A comprehensive bibliometric analysis and technology updates. Int J Hydrogen Energy 60, 780–801 (2024).

[3] Malcher, X. & Gonzalez-Salazar, M. Strategies for decarbonizing European district heating: Evaluation of their effectiveness in Sweden, France, Germany, and Poland. Energy 306, 132457 (2024).

[4] Klute, S., Budt, M., van Beek, M. & Doetsch, C. Steam generating heat pumps – Overview, classification, economics, and basic modeling principles. Energy Convers Manag 299, 117882 (2024).

In recent years, the transition of the energy grid to hydropower, wind, and solar photovoltaics has gained significant attention. While renewable sources are at the core of energy transition and remain among the most determining factors in the process of decarbonization of economies, their output is variable, such as daily and seasonal, which may lead to fluctuations in energy supply. Advancements in electrolysis technologies, such as proton exchange membrane water electrolyzer (PEMWE) systems, are critical in addressing the challenges of integrating renewable energy sources for hydrogen production. PEMWE stands out among other technologies, including solid oxide electrolyzers and alkaline electrolyzers, due to its simplicity, reversible operation, higher current densities supported, and ability to supply highly pure hydrogen. These attributes make PEMWE a promising option for coupling with intermittent renewable energy sources, contributing to the decarbonization of various sectors (e.g., transportation, industry, and power generation).

This study aims to develop a novel systematic approach to quantify the safe operating window of a PEMWE system considering energy intermittency and varying hydrogen demand. The PEMWE model has been developed based on first principles with the polarization curve validated against a lab-scale experimental setup. The impact of key operational variables will be investigated including current density, inlet temperature, and water flow rate (utilized for both feed and system cooling). Emphasis is given to operating temperature, a safety-critical variable, as its elevation can pose significant hydrogen safety risks within both the electrolyzer cells and the storage system. Increased temperatures also have negative effects on the durability of PEMWE, accelerating the degradation processes of the membrane and catalysts and thus increasing the likelihood of reaching hazardous conditions. The impact of temperature will be quantified via a risk index considering the fault probability and consequence severity. Process operability analysis is employed to quantify the achievability of a safe and feasible region through the integration of design and control strategies in early design stages. By calculating the possible output space given a set of inputs, forward mapping offers insights into the capabilities of the system under various operating scenarios (e.g., fluctuating energy supply and demand-driven operations). Inverse mapping computations are then carried out to evaluate the viability of functioning within a certain targeted area, pinpointing the required input configurations to meet the productivity objective while maintaining process safety. By combining forward and inverse mapping, this analysis provides a comprehensive framework to optimize PEMWE systems for enhanced operational flexibility and robust performance with application to modular hydrogen production using renewable energy sources.

The electrification of chemical processes represents a promising approach to improve efficiency and utilize waste heat, while potentially introducing flexible operational frameworks exploiting period of abundant and/or cheap electricity supply. Electrolysers could be pivotal in this shift, enabling hydrogen production from renewable sources and converting CO₂ into value-added products. However, these processes present inefficiencies leading to the release of significant amounts of low-temperature heat (<100 °C) by the electrolysers, which can account from 20% up to 60-70% of the input power to the stacks (Dal Mas, 2024, Front. Energy Res.). This research tackles the challenge of utilising this waste energy by modelling a system that combines electrolysers with downstream separation processes, employing heat pumps to upgrade and use the waste heat for the separation process.

The study utilizes a steady-state model of a system that includes multiple electrolyser stacks, a balance of plant, and a product separation system composed of electrodialysis and distillation, which allows also for the recycle of unreacted water and electrolyte. The case study of choice is formic acid production via direct CO₂ electrolysis, a process which could become feasible for large-scale industrial implementation (Dal Mas, 2024, Comput. Aided Chem. Eng.). A key objective is to ensure that the energy needs of the downstream processes are, to the extent possible, satisfied by the upgraded waste heat from the electrolysers, thus optimizing the overall system efficiency and minimising the need for external heating sources.

Through this research, a novel process design integrating electrolysis and downstream separation systems with heat pumps has been developed, exploiting simulations in Aspen Plus. The project offers valuable insights into the efficient integration of electrolysers and downstream processes, emphasizing the role of heat pumps in enhancing system performance and energy utilization (based on 25 MW power input to the electrolyser, a COP of 3 was obtained through the application of vapour compression heat pumps).

In addition to steady-state analysis, the aim of the work is also to conduct dynamic simulations to understand the system's response to various disturbances, including partial shutdowns and subsequent startups of the electrolysers. This dynamic study will evaluate how such fluctuations impact separation performance and energy demand, with a particular interest in the performance of the heat pump and of the separation processes.

The CO₂-emissions of the chemical industry must be reduced significantly to meet Europe’s climate goals of zero net-emissions by 2050. A large proportion of the heat demand in process industry is still met by burning fossil fuels such as natural gas which results in significant amount of CO₂ emissions to the atmosphere. Therefore, an effort should be made to reduce the supply of process heat supplied from fossil fuels. This can be achieved by improving the efficiency of chemical processes or using alternative, low-carbon sources of heat supply. Compression heat pumps offer a possibility of providing heat with low CO₂-emissions when powered by electricity with a low CO₂-emission factor. The use of formerly unused waste heat which is lifted to a higher temperature level by the heat pump can substitute process heat provided by fossil sources.
Despite the advantages of heat pumps for providing process heat with low CO₂-emissions, heat pump integration into chemical processes is still limited by mayor challenges. Among others, these challenges include economic feasibility and a lack of experience regarding the identification of appropriate heat pump sizing. Tackling the challenge of appropriate heat pump sizing requires thorough process data analysis regarding heat supply and waste heat availability. Especially non-continuous processes with fluctuating waste heat supply and process heat demand present an additional challenge for heat pump sizing. Key evaluation criteria must be derived which support further decision-making in heat pump sizing. Usually, mathematical programming methods sometimes combined with concepts of pinch analysis are used for this task [1]. This requires a good understanding of modelling and optimization techniques on behalf of the process engineer. A more user-friendly way to quickly estimate and evaluate investment decisions could enhance the broader application of heat pumps in chemical engineering.
In this contribution, a collection of methods and criteria are presented which may be useful for quick decision-making regarding heat pump sizing. These criteria vary for different configurations of heat supply system design including e.g. combinations of heat pumps and heat storages. Moreover, the availability of waste heat and the demand of process heat play a crucial role in decision making for heat pump sizing and therefore need to be included in the derivation of sizing criteria. Using a case study, possible methods to determine heat pump integration configurations for different scenarios are derived. By integrating relevant operational constraints, the sensitivity of the different evaluation criteria is determined.

References
[1] J.V. Walden, B. Wellig, P. Stathopoulos, Heat pump integration in non-continuous industrial processes by Dynamic Pinch Analysis Targeting, Applied Energy 352 (2023) 121933. https://doi.org/10.1016/j.apenergy.2023.121933.

The goal of achieving net zero emissions by 2050 has driven industries to intensify their efforts toward implementing CO₂ reduction strategies, particularly as CO₂ quotas increase. While, hard-to-abate sectors like steel, cement, glass and lime production etc., characterized by high-temperature energy demands, are the focus of much attention, other sectors which are characterized with lower emissions and typically low to moderate temperature heat demands, also play a vital role in collective manner. The objective of this study is to analyze the overlooked potential of energy transition in these sectors, given their substantial contribution to the overall emissions reduction strategy necessary to meet long-term climate goals.

Key CO₂ reduction strategies include heat recovery, fuel substitution (e.g., electricity, hydrogen, biomass, and biogas), and CO₂ capture technologies. A superstructure optimization based methodology is developed to evaluate the various transition pathways in each sector and Blueprint (BP) models are developed which incorporate detailed mass and energy balance plus cost parameters of each sector. Afterwards, the Osmose Lua optimization framework, developed at EPFL, is utilized to solve mixed-integer linear programming (MILP) based formulation containing objective functions of total specific cost and emissions. It optimizes the superstructure of the BP model, serving as a decision-support to identify the most effective _CO2 reduction strategy tailored to each sector's specific needs.

Three industries, namely laundry, frozen vegetable processing, and syrup production, were selected as case studies due to their low-temperature heat demand, predominantly met by natural gas-fired boilers. These industries offer significant opportunities for efficiency improvements through heat recovery and the integration of heat pumps. For instance, in the frozen vegetable processing industry, the implementation of heat pumps to recover waste heat from air cooling processes can reduce specific energy consumption by up to 17%. In sectors producing liquid and solid waste, such as the food processing industry, there is further potential for bio-sourced fuel production. The syrup industry, for example, could cut its CO₂ emissions by 50% by converting solid waste into biogas, to fuel its boilers.

The viability of these technological solutions is heavily influenced by future energy scenarios, including the price of energy and CO₂ emissions. Hence, this study provides critical insights into how industrial sectors with low-T heat demand can transition toward cleaner energy sources in future scenarios, while balancing economic constraints and technological readiness. The findings underscore the importance of tailored, sector-specific strategies for achieving significant emissions reductions and meeting global climate objectives.