Charge-Discharge Characteristics of an Adsorbed Natural Gas Storage System under Ambient Conditions

The performance of an adsorbed natural gas (ANG) storage system with natural convection heat transfer between the ANG bed and the ambient air is studied. Results are obtained for the bed without and with external fins on ambient air side. A one dimensional transient conduction model with suitable kinetic equation is formulated to simulate the performance of the bed filled with a homogeneous mixture of activated carbon and graphite. The model duly considers non-ideal behaviour of natural gas, variable specific heat of the adsorbed phase and heat of adsorption. Results are obtained for the case of constant pressure charging and constant flow discharging. The performance of the ANG bed is evaluated in terms of delivery capacity and discharge time. Results are obtained at an ambient temperature of 308 K and 35 bar for a charging time of 3.34 min. It is found that under this condition, the bed temperature increases by 70 and 45K and the storage capacity reduces by 75 and 60% without and with external fins, respectively. During discharge also, due to insufficient heat supply the bed temperature drops to very a low value thereby increasing the amount of adsorbate retained at the end of discharge process. This study clearly shows the need for improving the heat transfer rate from or to the ANG bed for higher delivery capacity.