Abstract
The adsorptive separation system of water vapor from natural gas using a multi-layer adsorber was studied. Commercial silica gel and two sizes of 4A molecular sieve were packed in layers in the adsorber. The mathematical model used for predicting the water breakthrough profile was investigated and developed. The experiments were carried out under different humidity levels of the natural gas feed: 7%RH, 30%RH and 50%RH, and different contact times: 17 seconds and 34 seconds, aiming to compare with the theoretical breakthrough curves obtained from the mathematical model. From the sensitivity analysis of parametrical effects on the theoretical breakthrough curves in order to investigate the existing mathematical model, the interstitial velocity (v) and the effective bed voidage (ε) were more sensitive to the theoretical breakthrough curves than the effective axial dispersion coefficient (DL,eff). To develop the existing mathematical model, the parameters and the equilibrium adsorption isotherm constructed for each adsorbent were employed specifically in the model. Since the water concentration in the natural gas feed is very low, the decrease in the interstitial velocity due to the water adsorption can be neglected. Therefore, the assumption of constant fluid velocity was applied in the mathematical model. From the sensitivity analysis, in order to achieve the best agreement between the experimental and theoretical breakthrough patterns, the overall mass transfer coefficient of approximately 8.5x10-5 s-1 was suggested in the model for all experimental cases. The modified mathematical model for predicting the breakthrough profiles of water adsorption provided an excellent correspondence with the experimental breakthrough curves under various experimental conditions. The differences of the experimental and theoretical breakthrough times were only about 3% to 5%.
