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'Heat battery' offers opportunities for the chemical industry

26 Sep 2014

The European Union's targets for reducing CO2 emissions need to be taken seriously. Heat storage in the built environment is part of the solution. And it also offers opportunities for the chemical industry, whether in the form of applying the ultimate solution in practice or helping to develop materials. Dr Joris Salari of TNO answers the most pressing questions.

The EU's aim is to be completely energy-neutral by 2050, when we should be obtaining 100% of our energy from renewable sources. But these are not always available: the highest energy demand takes place at night and in the winter, when the sun is not shining, or not shining so strongly. In the chemical industry it is not so much a question of using solar heat but of efficiently re-using the residual heat produced in the industry. It is in that context that the 'heat battery' is developed. Large industrial sites often create large quantities of residual heat that they would like to re-use for themselves or that could be used in the built environment, thus (a) improving energy efficiency on site and (b) creating value. To achieve cost-efficient, scalable materials and systems we should like to involve the industry in the development of the heat battery at an early stage.

Wouldn't a system of that kind be big?

'There are already ways of storing heat, such as heat and cold storage (TES, thermal energy storage) in the ground, but they are not yet practicable in every situation. In the built environment in particular there is not always enough room. The losses are also very high using this type of storage. That is why we are working on a compact heat battery – think of a substantial boiler, or a modular system – that can store heat without losses for a whole season and that has broad applications in the built environment and the chemical industry. We are focusing on salt hydrates that can dehydrate and hydrate reversibly, known as 'thermochemical materials' (TCMs). When you heat the salt hydrate, thus dehydrating it, you store the heat in it, as it were. In that process you generate salt and water, which you store separately. Heat is then generated by an exothermic reaction when you recombine the salt with the water.'

What problems do you need to solve?

'Salt hydrates have inherently high storage capacity and are moreover very cheap, but they are unstable compounds. During dehydration and hydration they can fuse or even disintegrate: that affects their performance and in the long run can even clog the reactor. So in particular we are investigating how to improve the stability of these materials.We anticipate that stability can be improved by means of microencapsulation, by physically enveloping the salt hydrate particles in a polymer material that is inherently stable under the conditions required. We have already demonstrated this principle, but further research is needed to arrive at a scalable solution. Once the composite material is stable it can be re-used several times in succession. We have also found that the rate of the process can be controlled.'

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