Study of ammonia adsorption/desorption characteristics of CaCl2 - Expanded natural graphite composite for thermal energy storage

In this work, the composite adsorbent bed of CaCl2 + Expanded Natural Graphite (80:20) is tested for heat and mass transfer behavior of ammonia adsorption/desorption for thermal energy storage application. 500 g of CaCl2 + ENG was used in the reactor and the variations of average temperature in the reactor and mass of ammonia adsorbed/desorbed with time are studied at different operating conditions. Adsorption rates were measured at ammonia supply pressure of 10 and 12 bar and adsorption temperatures of 80, 85 and 90 degrees C. Adsorption at these operating conditions was then followed by desorption rate measurement at 75 degrees C and 80 degrees C, where desorption takes place at ambient pressure. It was observed that adsorption is fastest when it was done at 80 degrees C and supply pressure of 12 bar and desorption was fastest when it was done at 80 degrees C with preceding adsorption at 80 degrees C at 12 bar. Average temperature of adsorbent dropped down to about 52 degrees C under these operating conditions. Based on amount of ammonia adsorbed/desorbed by CaCl2 + ENG, values of theoretical maximum energy storage density and the amount of heat that can be recovered at different adsorption temperatures and supply pressures were evaluated.