Potentials in the power-heat-refrigeration coupling of hydrogen plants

Regardless of the location of hydrogen production or hydrogen utilisation, the efficient utilisation of the converted energy has top priority. In the production of green hydrogen by means of electrolysis or utilisation in hydrogen CHP units based on fuel cells or hydrogen combustion engines in plants developed and implemented by IAV, the possible use of waste heat is consistently taken into account. In this way, economic efficiency is increased through an intelligent combination of different technologies, in that the primary energy requirement for heating and cooling is partly or completely covered by the existing energy flows.

Once the customer- and site-specific electricity, heating and cooling requirements are known, IAV uses this as a starting point to develop a concept for providing all the energy flows required. Various technologies come into question here, both for hydrogen production and for energy recovery. If, for example, low-temperature electrolysis or fuel cell systems are used, the resulting waste heat (between 30 and 70°C) is brought to the temperature level required for heating buildings or providing hot water by means of heat pumps. High-temperature heat pumps also enable heat recovery for more demanding applications such as district heating networks.

When using high-temperature PEM fuel cells or hydrogen combustion engines, on the other hand, the temperature level of the waste heat is usually well above 100°C and thus so high that a heat pump can be dispensed with. If direct heat utilisation is not the focus, thermally driven steam processes – for example in organic Rankine or Kalina plants – can also become interesting for large-scale plants in order to increase the electrical efficiency.

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If, on the other hand, solid oxide electrolysis systems (SOEC) or fuel cells (SOFC) are used, they offer the possibility of using the resulting waste heat (> 650 °C) directly in many industrial processes. For example, these systems can be advantageously combined with liquid organic hydrogen carriers (LOHCs). If this is not desired, a gas turbine can alternatively extract the residual enthalpy from the exhaust gas flow in order to achieve an increase in efficiency in this way.

Both solid oxide fuel cells and, in principle, internal combustion engines benefit from fuel variability. This enables the use of hydrogen-natural gas mixtures and thus the gradual switch from natural gas to hydrogen with increasing availability of hydrogen and decreasing hydrogen prices, which makes cogeneration plants, which are often expensive to invest in, “H2-ready” and future-proof.

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«Depending on the customer's requirements, IAV thus combines the various technologies to create an efficient and environmentally friendly overall system.»

Dr.-Ing. Ingmar Hartung — Team Manager Hydrogen Infrastructure & Electrolysis at IAV

If cooling is required in addition to electricity production (such as in data centres, in specially air-conditioned production facilities or in deep-freeze logistics), the waste heat can be used to provide cooling by means of absorption chillers, thus significantly reducing the electricity requirement for cooling. In this constellation, the absorption chillers replace or supplement conventional compression chillers to provide the required cooling capacity – often with the aid of cold accumulators.

Depending on the customer’s requirements, IAV combines the various technologies to create an efficient and environmentally friendly overall system. Our concrete practical experience with the various types of plant guarantees quality and our number of competent employees with a very broad range of experience sets us apart from the classic, small engineering firms.

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