FIELD-TESTS OF MEMBRANE MODULES FOR THE SEPARATION OF CARBON-DIOXIDE FROM LOW-QUALITY NATURAL-GAS

A commercial-scale, single-stage, spiral-wound membrane system has been operated for approximately 20 months to upgrade low-quality natural gas from a well in East Texas. Throughout the test period the retentate product (''sales'' gas) met pipeline specifications. Data were obtained on two membrane modules containing two types of asymmetric cellulose acetate membranes, one ''standard'' and the other one of higher density. A summary of the field test data shows the effects of the operating variables of pressure, feed flow rate, and CO2 concentration in the feed (from 3 to 25 mole percent). Concentrations greater than 6 mole percent were obtained by adding pure CO2 to the feed gas. In addition, computer models for the separation of gases under ''perfect mixing'' and cross-flow conditions were applied to the analysis of the field data. In general, the field test data were consistent with a flow regime which was intermediate between perfect mixing and cross-flow.