Prior to entering cryogenic regions of an LNG plant, the CO2 concentration of natural gas needs to be < 50 ppm to avoid dry ice formation and potential blockages in the process equipment. The H2O content needs to be < 2 ppm to avoid ice formation. Two separate, consecutive and energy intensive processes are used to reach these necessary gas specifications: amine absorption (of CO2) and molecular sieve adsorption (of H2O), respectively. Some of the operating costs of these two processes may be redundant and avoidable. Certain adsorbents have an affinity for CO2 almost as strong as their affinity for H2O. Li et al. have shown that there is a synergistic effect of CO2 adsorption in the presence of H2O (i.e. CO2 sorption capacity goes up with H2O partial pressure), whilst the H2O adsorption is unaffected by the presence of CO2. The PhD student will use advanced process simulation tools incorporating this synergistic sorption effect to investigate how to reduce amine treatment operating costs by (i) allowing the CO2 content of the gas leaving the absorber to increase slightly (e.g. to 500 ppm), and (ii) relying on the molecular sieve dehydration process to also reduce the gas CO2 content to the requisite 50 ppm. Smaller amine treatment facilities would be of particular value to FLNG plants.
Synergistic CO2 & H2O Removal in FLNG Operations
