Experimental Investigations on Cold Recovery Efficiency of Packed-bed in Cryogenic Energy Storage System

Cryogenic Energy Storage (CES) system has large power generation capability, and comparable cost with respect to the non-cryogenic technologies (pumped-hydro, compressed air energy storage systems). This is not location specific unlike the non-cryogenic energy storage systems and also is environment friendly. High-energy requirement for liquefaction process in the CES system, however, leads to low turnaround efficiency of the system. Efforts have been made to reduce the specific work-requirement in the liquefaction process by thermal energy storage at temperature around 150 K as available during power generation stage of the system. One of the methods of storing the thermal energy at such low temperature is using packed-bed of pebbles. A few studies have been reported in the available literature indicating a reduction in storage efficiency during continuous operation of such packed-beds leading to reduction in turnaround efficiency of the CES system. In this paper, experimental findings for better insight into the packed-bed behavior are reported. An experimental setup of packed-bed thermal energy storage using rock pebbles as bed material was used for this purpose. Temperatures along the axial direction inside the bed were measured and the results were analyzed and the storage efficiencies during full-load and part-load of operations were determined.