Development of hollow fiber membrane systems for nitrogen generation from combustion exhaust gas: Part I. Effects of module configurations

This study deals with nitrogen separation from carbon dioxide using hollow fiber membranes, having the ultimate objective of developing a hollow fiber membrane system for nitrogen generation from combustion exhaust gas. The membranes used were integrally asymmetric hollow fibers that were preferentially permeable to carbon dioxide, thereby resulting in a nitrogen enriched residue stream and a CO2 enriched permeate stream. A laboratory scale hollow fiber membrane module containing 45 hollow fibers of 105 cm long was used in the study to identify the best module configuration and flow arrangement. It was shown that, among all the module configurations studied, the best separation of CO2 and N2 was obtained if the feed gas flowed inside the hollow fibers and the feed gas and permeate flows were countercurrent. With a feed pressure of 300 psig (2.07 MPa gauge) and the permeate at atmospheric pressure, this bore side feed countercurrent flow configuration yielded a nitrogen productivity of 4.8 sccm per fiber at a nitrogen purity of 98.5% and a recovery of 81% when a simulated dry combustion gas containing 18.3% CO2 (balance N2) was used as the feed. This configuration was selected for use in the subsequent development of a full scale membrane module that comprised several hundred thousand fibers.