Dynamic Modeling of Charge and Discharge of Adsorbed Natural Gas storage Tank

Recently, adsorbed natural gas (ANG) has been considered as a low pressure and safe method for storage of natural gas, especially in vehicles. Nevertheless, the usage of the ANG storage system is hindered by the thermal effects due to both heat of adsorption and desorption during the charge and discharge processes and hence, an effective thermal enhancement is essential for the development of this technology. The purpose of this study is the investigation of transient thermal behavior of an ANG tank during charge and discharge cycles. There is a gas diffuser at the center of the tank to improve its temperature fluctuations by changing the flow direction from axial to radial. In this study, mass and energy equations were first derived and the resulting equation system was solved by implicit finite difference numerical method. By solving these equations, radial temperature and pressure distributions of adsorbent bed were obtained over time. Then, the effective parameters on the temperature fluctuations and efficiency of the ANG tank were studied. Numerical results show that the gas diffuser increases dynamic efficiency around 5% during the charge and discharge cycles. The results also show that the time of process, adsorbent bed thermal conductivity, convection heat transfer coefficient, tank geometry and dimensionless Biot and Fourier numbers are important factors on the efficiency enhancement. Also it was shown that high penetration resistance of the adsorbent bed may have a significant impact on the storage capacity and charge process time of the ANG tank.