Key Factors Affecting the Economics of Oxygen Enriched Air Production Via Membranes

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c & 40 t-------+-------+--------1 >­)( o ~ 30 t---.....;;;:::::..-~ - CO') c B 4ii 20 t-------+-------+-----~ iii o U 01 ~as 10 ~-----~-----~-----~ CD Q. o A/G Technology Membranes Vacuum Mode of Operation o ~----------~ __________ ~ __________ ~ 3 5 10 E8325°C c:::J50°C Figure 7. Plant Capacity, Tons/day Pure Available Oxygen Projected Operating Costs for Production of 35% OEA. 20 A/G Technology hollow fiber membrane OEA systems producing 35% oxygen are about $24/ton pure available oxygen at a 25 C operating tempera­ture and less than $22/ton pure available oxygen at 50 C. Although the economic data presented covers the range of system capacities below 20 tons/day pure available oxygen, their is no intrinsic limitation on the capacity of a membrane OEA generation system. In fact, the A/G Technology Corporation hollow fiber membrane systems des­cribed in this paper will further benefit in terms of lower energy consumption per unit output and more favorable operating and capital costs as the OEA process is scaled-up. SUMMARY AND CONCLUSIONS The fuel savings and productivity improve­ments achievable with OEA combustion have been well documented, however, industry has not converted to this technology due to the high costs of conventional on-site oxygen generation equipment and delivered LOX. Membrane air separation sys­tems are now available which offer economical OEA production in the range most suitable for combustion applications: 35% to 40% oxygen. In assessing the economics of the membrane process, several key factors must be considered. First, the intrinsic properties of the membranes must be capable of generating 35% to 40% oxygen. This level of oxygen requires membranes with oxygen to nitrogen selectivity values of at least 3. Secondly, for economical operation in the energy­efficient vacuum mode of operation, membr~ie eff~ctive per2"eability should exceed 1 x 10 cm (STP)/cm sec cm-Hg. At lower effective permeability values, the membrane area require­ment may be excessive, adversely affecting system capital costs. To minimize capital costs, low permeability membranes are often operated in the pressurized 184 mode of operation. While this mode of operation may be suitable in some instances (e.g., inter­mittent operation or very small systems), the nearly 3-fold increase in energy requirements versus the vacuum mode generally make pressurized operation economically prohibitive in terms of operating costs. Overall improvements in OEA generation economics are achievable by either of two means. First, if 35% OEA is required, the system can be operated at a feed air temperature above ambient (I.e., 50 C). Secondly, single stage production of 40% OEA is economically attractive versus 35% oxygen generation. With current membrane technology, it would be difficult to achieve this 40% concentration at operation above about 25 C. It is of note, however, that increased temperature operation or higher OEA concentration levels, do impose a small penalty in energy requirements. For all operating mode and OEA concentration levels, economic benefits are achieved from in­creased scale of operation due to hardware cost reductions per unit capacity and to improved blow­er and vacuum pump efficiency ratings. 1. 2. 3. 4. 5. 6. 7. 8. 9. REFERENCES Pohl, J. H., et. al., "Technology Research Needed in Industrial Combustion Processes", Energy & Environmental Research Corp., prepared for EG&G Idaho, Inc., (Contract C84-130349-GHL-44-84), 1984. Salton, Lo, "Oxygen - A Way to Lower Energy Consumption and Increased Capacity", Presented at the First Finnish Flame Days, Tampere, May, 1982. Midland Ross Corporation, Surf ace Combustion Division, Engineering Manual. Ward, W. J., "Immobilized Liquid Membranes", Chapter In Recent Developments in Separation Science, Volume 1, N. Li, editor, CRC Press Raton, FL, 1979. Fluid Systems Division of UOP, Inc. Product Literature presented in Reference (10). Power calculated from, Dow Chemical USA Product Literature, "Membrane Air Separation System, Enriched Oxygen from Compressed Air" Form No. 174-484-86. Gollan, A., and KIeper, M. H., "Membrane­Based Air Separations" presented at the AIChE National Convention, Seattle, WA, August, 1985. Gollan, A., and KIeper, M. H., "Research into an Asym metric Membrane Hollow Fiber Device for Oxygen Enriched Air Production, Phase 1 Final Report", for Department of Energy Contract DE-AC07- 831D12429, September, 1984. Gollan, A., and KIeper, M. H., "Research into an Asymmetric Membrane Hollow Fiber Device for Oxygen Enriched Air Production, Phase 2 Final Report", for Department of Energy Contract DE-AC07- 831D12429, January, 1986 (to be published).