Exergy Analysis of Cold Recovery in a Cryogenic Packed Bed System

Cold recovery and storage in a packed bed is suggested during the regasification of LNG and liquefied air; the latter is found in a cryogenic energy storage system. The efficiency of cold recovery depends on the pressure, temperature, thermophysical properties of the packing material and the fluid, fluid flow rate, bed geometry and bed dimension. These factors dictate the irreversibilities accompanying the heat leakage from the surroundings, heat transfer between the flowing cryogen and the packing material and pressure drop along the flow direction. These irreversibilities lead to exergy losses in the packed bed. As a result, the exergy efficiency of the charging operation is lowered. The present work focuses on the effect of inlet temperature on the thermodynamic performance of cryogenic packed bed during charging. Losses due to irreversibilities are quantified and exergy efficiency of charging operation is evaluated. It was seen that the axial conduction within the bed resulted in temperature drop at the outlet, thereby reducing the exergy efficiency of the charging operation. The exergy efficiency of the charging operation increased with inlet temperatures.