Study on Thermal Effects of Natural Gas Adsorption and Desorption in Activated Carbon

In this paper the temperature changes, during adsorption and desorption dynamics of natural gas in activated carbons to quantify their effects on the performance of an Adsorbed Natural Gas System (ANG), are studied. Commercial Norit RB3 activated carbon is used as the adsorbent, which is packed into a 0.47 L volume steel cell. Isothermal storage tests were performed to obtain the corresponding adsorption isotherm of activated carbon at room temperature in the pressure range from atmospheric to 500 psig. It was observed that the amount of gas adsorbed in the coal packed bed plus the compressed gas in the outer porosity is greater than the amount of gas stored in the empty cell at 500 psig.

      Dynamic adsorption tests were conducted at the latter pressure using three different load gas rates toward the cell. The results confirm that the increase in temperature during the dynamic adsorption capacity decreases system storage. It was found that the isothermal volumetric storage capacity of carbon Norit RB3 is 80.4 V/V at a storage pressure of 500 psig and that this capacity drops to 16% due to exothermic effect arising from the heat of adsorption. The dynamic desorption is affected mainly by the decrease in temperature accompanied by the drastic drop in pressure during delivery of gas. The delivery capacity was found to be 56.8 V/V. At this stage, the bed undergoes cooling from room temperature (30°C) to -1.7°C.