Performances and control aspects of steam storage systems with PCM: Key learnings from a pilot-scale prototype

Abstract

Medium and High temperature steam is used as Heat Transfer Fluid in a wide range of industrial processes. Steam storage is required when steam production or consumption is variable in time, like in solar thermal facilities or batch industrial processes. In introduction, this paper gives an extensive review of the PCM storage prototypes that were operated worldwide for steam applications between 120 and 400 °C. At CEA Grenoble, a PCM steam storage prototype was operated during >300 days during three tests campaigns from 2013 to 2019. 78 charge–discharge cycles were performed with the same PCM volume under a wide range of operating conditions. This paper aims at reporting some significant experimental results obtained from this prototype. Thermal performance indicators (storage capacity, utilization rate, storage efficiency, and exergy efficiency) are evaluated in detail for the first time for a pilot scale PCM steam storage. For a complete charging-discharging cycle at sliding pressure, constant mass flow, and from homogeneous temperatures in initial conditions, utilization rate is estimated at 81.9%, storage efficiency at 79.3%, and storage exergy efficiency at 76.2%. From 2013 to 2019, thermal testing of the storage prototype showed very repeatable results: in this paper, the authors demonstrate that heat transfers were not altered between 2013 and 2019. Beyond most commonly used operating modes for PCM steam storage (fixed pressure and sliding pressure), advanced control strategies are proposed. Two examples of advanced controls are described in this paper, showing an insight of the valuable services that a PCM storage system can provide to an industrial steam user (power cycle, industrial steam network,…).