C4+ liquid recovery from natural gas by temperature swing adsorption followed by liquefaction of heavy extracted product

Abstract

Recovery of natural gas liquid (NGL) was investigated by temperature swing adsorption (TSA) process. The process was designed with four columns of H-type silica gel adsorbent, working in a cyclic adsorption–desorption operation of natural gas at high pressure. The NG feed composition contained 89 % methane, 1.6% C4+ (butane and pentane), and other impurities such as CO2, with feed inlet weight hourly space velocity of 5.7 kgfeed/hr.kg,ads, at 85 bar pressure and 30 °C temperature. The cyclic operation was designed with three steps consisting of adsorption at high pressure, heating by purging with the hot NG at 270 °C and 25 % purge/feed ratio, followed by cooling with clean NG product from adsorption step, at the same pressure. Thereafter the regenerated heavy product from the heating step was liquified to gather C4+ product. Modeling and simulation of this process were carried out to simulate and optimize the operating conditions with the aim of maximizing recovery of the C4+ liquid product and minimizing outlet NG dew point. The required model parameters were evaluated by the experimental studies at the static and dynamic conditions and fitting to the proper isotherm and kinetic models, respectively. As the results of the process optimization, the fraction of C5 in the light NG product was reduced from 0.7 % to 0.1 % and the fraction of C4 was decreased from 0.9 % to 0.4 %. By this process the light NG product dew point was reduced from −9.5 to −58 °C and the molar fraction of C4+ in the liquid product was reached to 43.5 %, whereas it was only 1.6 % in the initial natural gas.