Energy recovery systems based on high temperature phase change materials

Energy recovery from the waste heat released by industrial processes represents one of the greatest opportunity to reduce the consumption of primary energy and the related emission of greenhouse gases. Nevertheless, the fluctuating and/or intermittent nature of many energy-intensive processes (e.g. electric arc furnace in steel industry) hinders the deployment of current energy recovery systems. Thus, the development of technologies able to minimize the thermal power fluctuations released by such processes is required to enable the deployment of affordable energy recovery systems. With the aim of developing such type of technology, this thesis explores the potential of latent heat storage systems based on phase change materials (PCMs) to minimize the thermal power fluctuations of high-temperature waste heat sources. In particular, three significant areas of investigation characterised by different types of thermal power fluctuations are investigated: electric arc furnace, billet reheating furnace and waste-to-energy plant. An interdisciplinary approach is adopted to face the crucial issues of developing a PCM-based technology (e.g. thermo-mechanical stresses, transient heat transfer). Chapter 1 includes the background, the motivation, the aim, the methodology and the structure of thesis. In chapter 2, a general overview on the thermal energy storage systems with a particular focus on latent heat storage systems based on PCMs is provided. Chapter 3 addresses the issues related to the energy recovery from the electric arc furnace and proposes three different configurations of a PCM-based device to increase the efficiency and the capacity factor of the downstream energy recovery system. In Chapter 4 an existing waste heat recovery system of a steel billet preheating furnace is retrofitted by adding a PCM-based device. In Chapter 5 a refractory brick technology based on PCMs is proposed for the protection of the radiant superheaters against high temperature corrosion and temperature fluctuations. At the end of each chapter a series of conclusions are reported, concerning the performed investigations and the obtained results.