Design analysis of a hybrid storage concept combining Ruths steam storage and latent thermal energy storage

In industrial processes, temporal differences between steam consumption and production can be compensated by integrating Ruths steam storage. The extension of a Ruths steam storage to a hybrid storage component by means of latent heat thermal energy storage with integrated electrical heating elements or heat exchangers was developed and is discussed in this paper. The latent heat thermal energy storage is arranged at the shell surface of the Ruths steam storage, which can be divided into chambers filled with different phase change materials. The aim of this concept is to create a flexible component with a high energy density, which can store thermal energy from steam, and surplus electrical energy or waste heat both short and long term. In this study, different hybrid storage arrangements are tested and analyzed. In the presented examples, the arrangement of one phase change material with a phase change temperature near the minimum inside the Ruths steam storage stores 34% more energy than the Ruths steam storage without phase change material. For discharging, with 15% additional provided energy the best obtained result is achieved with a phase change temperature near the maximum inside the Ruths steam storage vessel. The low thermal conductivity of most phase change materials may limit the performance of the hybrid storage component. Therefore, a layer arrangement of metal and phase change material for improving the heat transfer inside the phase change material of the hybrid storage is modeled and discussed. This method for heat transfer enhancement exhibits a significant decrease in melting time, with a metal fraction of up to 20% and a ratio between the phase change material layer thickness and layer arrangement height of up to 1.5.