Technoeconomic analysis of oxygen-nitrogen separation for oxygen enrichment using membranes

Abstract

Enriched oxygen is a valuable commodity and has a range of applications including coal-gasification and uses in the chemical industry. Enriched oxygen can be obtained from air using different processes, such as cryogenic distillation, pressure swing adsorption, membrane-based air separation, etc. Air can be separated into component gases using membranes that do not require any regenerative steps and the products can be directly used or discharged. To understand the economics of polymer membrane-based oxygen enrichment, Idaho National Laboratory (INL) has developed a spreadsheet based technoeconomic analysis model that considered numerous parameters including selectivity and permeability of the membranes, performance conditions such as number of stages, module material, electricity cost, membrane cost, financing, etc. INL calculated the cost of production of product gas (containing an enriched O2 content) in US$/kg gas product at different oxygen purities and compared that with cryogenic distillation and pressure swing adsorption processes. This analysis helped to determine the membrane module scale performance targets in terms of permeability and selectivity of membrane modules to be economical for use in a small modular coal-fired gasification plant (10–25 tons/day). INL determined that a double staged membrane process with the selectivity of 5.5 and permeance of 1000 GPU has a cost of gas production of US$0.05/kg for 90% pure oxygen. This production cost is lower than pressure swing adsorption and competitive with cryogenic distillation, which only meets its cost targets at a much larger scale. Similarly, a three staged membrane process with the selectivity of 3.1 and permeance of 1000 GPU has the cost of production of US$0.071/kg for 90% pure oxygen.