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Massive heat in the exhaust air of cryogenic air separation purification system is wasted in conventional systems. Its intermittent and dynamic characteristics are major constraints to achieve heat recovery. Cascaded latent thermal energy storage (LTES) is considered as a promising solution, but actual application is rarely reported. This paper initially investigates a two-stage LTES tank which is incorporated with a pilot plant of cryogenic air separation purification system, and a test under a real operation condition is performed. The tank contains five heat storage units in high-temperature stage and five units in low-temperature stage, which are loaded with commercial paraffin of melting temperatures 70 °C and 48 °C, respectively. Moreover, heat pipes combined with vertical fins are assembled to increase the heat transfer rate. Results show that 51369.5 kJ heat is saved in a charging-discharging cycle by introducing LTES tank to air separation system. 64.7% of waste heat in the exhaust air could be recovered based on waste heat criterion of 40 °C. Also worth noting that payback period of LTES tank is 2.3 years, and 25784.3 kg CO2 emission is reduced per year. The LTES demonstrates good performance when compared with other reported LTES for industrial application.

The latent thermal energy storage (LTES) system, which uses phase change materials (PCMs), has received a great deal of attention as an effective means of storing thermal energy. However, because of the low thermal conductivity of most PCMs, there is still an urgent need to develop efficient heat transfer enhancement techniques. In this study, a novel combination of heat pipe-fins-copper foam (HP-Fin-CF) has been proposed, and its performance was evaluated via comparisons to the performances of HP-Fin and HP-CF combinations. The effective heat capacity method and thermal resistance network are used in numerical modeling. The results indicate that the HP-Fin combination has better melting performance, whereas the HP-CF combination leads to better solidification. Compared with the basic HP configuration, the total time for melting and solidification can be reduced by 82.70%, 89.03%, and 93.34% for the HP-Fin, HP-CF, and HP-Fin-CF combinations, respectively. The evolution of melting rates suggests that natural convection accelerates the melting of the PCM with the HP-Fin and HP-Fin-CF combinations, but may extend the complete melting time of the PCM in the HP-CF combination under some specific conditions. Also, the exergy analysis was performed to study the thermodynamic properties of the three combinations.