High pressure multi-component vapor-liquid equilibrium data and model predictions for the LNG industry

Accurate simulations of scrub columns in liquefied natural gas (LNG) plants are challenging, requiring frequent solution of the non-linear equations governing vapor-liquid equilibrium (VLE), material, and energy balances for multi-component mixtures. Reliable fluid property predictions at high pressures and low temperatures are thus crucial; however, no high-quality multi-component VLE data at conditions relevant to the LNG scrub column are available to test commonly-used equations of state (EOS). Here we report VLE measurements at pressures to 9 MPa and temperatures from (203 to 273) K for mixtures containing CH4, C2H6, C3H8, iC4H10, nC4H10 and/or N2. Far from the mixture's critical point, the GERG-2008 EOS predictions were more accurate than the Peng-Robinson EOS predictions. Above 7 MPa both EOS under-predicted the liquid phase's methane content and over-predicted its butane content by 10-50 times the experimental uncertainty. Rowland et al.'s recent revision of the GERG model reduced the maximum deviations by (17-35)%. Further optimizations should improve the constituent binary departure functions and hence improve the description of multicomponent VLE data, particularly at conditions relevant to LNG production.