Preparation and performance of energy storage materials and application for recovery of industrial waste heat

Sammanfattning: Due to the rapid increase of energy consumption and the environmental concerns on climate change caused by the fossil fuel combustion, it becomes a big issue on how to use alternative renewable energy resources to replace fossil fuel and to improve energy utilization efficiency. In Sweden, there are plenty of detached buildings without connection with district heating (DH) network, which use oil to supply the hot water for space heating and tap water. One way is to extend the district heating network for supply the heat for the detached houses. However, this will need increased costs for the district heat pipeline which might not be economically variable for the area with less density of population. Another alternative is to apply so called mobilized thermal energy storage (M-TES) to transport heat from, e.g. industrial waste heat, to the end-users of the detached houses. This will enable to keep the detached houses in the same state as a distributed heat system while replacing the fossil fuels for heating demand. The mechanism of energy storage and release is on the basis of transition of phase change materials (PCMs), which can solve the problem in time and spatial mismatch between the energy supply and consumption. Polyethylene glycol (PEG) as a type of organic PCMs is studied in this licentiate thesis due to its large heat capacity and multi-melting temperatures. As a representative of organic PCMs, PEG also has some disadvantages, like encapsulation needed for preventing leakage and low thermal conductivity. To resolve those, a type of so-called form-stable energy storage materials is prepared by blending PEG with silica gel. Modified aluminium nitride (AlN) powder is then added to enhance the thermal conductivity of materials. Meanwhile, another form-stable energy storage material is prepared by mixing the melted PEG into expanded graphite (EG). The results show that two types of composite materials can keep the form stable during the transition, and AlN powder can enhance the thermal conductivities of energy storage materials. Based on the knowledge of energy storage technology, M-TES system is designed and combined with the existing heat system in Eskilstuna. The feasibility study of M-TES is carried out through the data collected from CHP plant and end-user in this licentiate thesis. The results show that there are economic and environmental benefits by using M-TES system to supply heat for detached houses.