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Packed bed and temperature sensors after filling the test storage unit.
© ZAE Bayern
High-temperature heat storage unit
14.09.2017

Exterior of the pilot storage unit with the test rig
© ZAE Bayern

Design model of the storage unit
© ZAE Bayern

Foundry utilises waste heat from the melting furnace

Together with industrial partners, researchers at ZAE Bayern are developing a cost-effective energy storage system for industrial waste heat. It shall enable discontinuously generated waste heat to be utilised for processes for which this has previously not been done for economic reasons. The implementation phase has now begun. The scientists want to put a demonstration plant into operation in the spring of 2018. It will be used to provide the waste heat from a foundry melting furnace from the metal industry as process or thermal heat.

Energy-intensive industrial plants, such as foundries or cement works, can significantly reduce their energy consumption if they recycle their waste heat as process or thermal heat. However, it is often difficult to realise economic applications, particularly with discontinuously generated waste heat above 100 °C. This is due to the high investment costs for high-temperature heat storage units with currently comparatively low energy costs for gas and electricity. Economic operation is hardly achievable if the typical system operation only allows a low number of charging and discharging cycles for the storage unit.

Together with the Heunisch foundry and the Küttner plant engineering company, the researchers at ZAE Bayern are therefore developing a system for utilising waste heat that is as cheap as possible. It consists of a heat storage unit for temperatures up to 300 °C, an absorption heater/chiller for transforming the heat to the usage temperature and a superordinate energy management system. As a demonstration system, the system shall store the waste heat from a foundry melting furnace (cupola furnace) and provide process and thermal heat during standstill periods.

The core component is a high-temperature heat storage unit. It is designed as a dual-media storage system in which a liquid heat transfer medium flows directly through a packed bed made of rock. The pressurelessly operated storage unit can be produced at a lower cost than, for example, pressurised water or thermal oil storage tanks. The suitability of different types of rocks was first of all investigated during the project. The scientists subsequently tested the storage concept in the laboratory. For this purpose they built a storage tank with a volume of around 670 litres. The test storage unit achieved discharge rates of up to 250 kW (discharge from 210 to 100 °C) with a high efficiency. This clearly exceeds the requirements in pilot operation.

In order to provide process cooling as well as thermal heat, the researchers are currently adapting an absorption heat pump to operate with thermal oil as the heat transfer medium. In addition, they have started the planning work in order to integrate the absorption heat pump into the foundry's existing energy system.

Testing the system

The first storage unit is set to be built in spring 2018. The pilot storage unit consists of standardised storage modules, each with a volume of 50 m3. These containers are double-walled for safety purposes. At the same time, the cavity is used for insulation with vacuum super-insulation. The demonstration plant will be subsequently tested under real operating conditions.
The project was funded as part of the Energy Storage research initiative. The research work and findings are continuously updated on the research initiative's website.

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Project management
ZAE Bayern - Garching

Plant construction
Küttner GmbH & Co. KG

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