Optimised design and operating strategies for latent heat-thermal energy storage for steam generation
Date
2026
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Abstract
The characteristic high energy density within a narrow temperature interval makes latent heat-thermal energy storage (LH-TES) systems a promising technology in the field of carbon-neutral process-steam generation. State-of-the-art LH-TES systems are based on the tube-and-shell heat exchanger design with the storage material, the so-called phase change material (PCM), in the shell and the heat transfer fluid (HTF) flowing in the tubes. The challenge in storage operation lies in the low thermal conductivities of potential PCMs, which result in a characteristic transient power profile that strongly depends on the state of charge of the storage system. To meet the specific requirements of an application, suitable operating strategies are needed in which the heat transfer characteristics of the storage are combined with appropriate control of the steam flow. So far, the focus in the development of LH-TES for process-steam supply was on the heat transfer processes within the storage. This thesis provides a comprehensive experimental, analytical and numerical analysis of the interaction between the LH-TES and the processes in the steam flow. On this basis, it proposes an extended design method for the thermo-economic optimisation of steam-driven LH-TES systems by also considering partial-load operation. Analytical studies show the effects of the HTF mass flow rate and the transient thermal resistances on the storage power. A numerical storage model is used to determine strategies for controlled storage operation. These proposed strategies are assessed on a finned single-tube PCM steam generator test rig with PlusICE® A133 as the storage material, precise control of the HTF parameters and detailed monitoring of the storage tank. The results of the experiments under full and partial load with water/steam between 1.4 bar and 6.7 bar and mass flow rates between 1.26 kg/h and 4.30 kg/h at inlet temperatures between 20 °C and 200 °C demonstrate the feasibility of these operating strategies and show that pressure and mass flow rate on the fluid side can be used effectively to shape the power profile of LH-TES. Furthermore, the numerical storage design model is validated with experimental charging results in the operating range under consideration. Finally, this work shows that for applications where sufficiently powerful fins are not available or economically not feasible to provide stable steam pressures, temperatures and mass flow rates, partial-load strategies with reduced mass flow rates can be used to provide process-steam at increased material efficiency. It is a first step towards a more integrated approach to the development of LH-TES systems and complements the existing approach of heat transfer enhancement on the storage side in LH-TES under full-load operation.