Effect of Solvent Concentration on the Energy Demand of an Absorption-Based Natural Gas Sweetening Plant

Abstract

The removal of CO2 from natural gas will enhance its energy content, decrease the volume to be transported and –if coupled with storage technology- it will also contribute to the control of CO2 emissions. Amine-based chemical absorption is the most advanced CO2 capture system. Yet, high energy requirement is a major hinder to its wide deployment. Among the possible routes of improvement is the use of novel amines that can achieve the trade-off between robustness and low regeneration energy. In this paper, we have studied the use of MDEA/DEA as solvent for the capture of CO2 from natural gas. The presence of BTEX (Benzene, Toluene, Ethyl Benzene and Xylene) in the raw natural gas was taken into account. AspenHysys v9 was used to simulate the chemical absorption system. The impact of solvent composition on key process variables, the required flow rate to achieve transport specification, required reboiler duty, pumping energy, BTEX incineration energy and amine losses, were studied. The optimal operating point corresponding to the lowest energy requirement was identified and the separate contribution of each process parameter was estimated. The study showed that the optimal amine mass fraction is influenced by the presence of BTEX and that it shifts from 0.5 if BTEX are not present in the sour feed gas to 0.45 if their incineration is taken into account.