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Air Separation

Air Separation Example

Air Separation focuses on identification of new concepts and technologies for production of oxygen for use in gasification systems. Many gasification-based energy plants run more efficiently if the oxidant is oxygen rather air, but they rely on conventional cryogenic air separation which is expensive both in terms of capital expenditure and cost to operate. Accordingly, the technologies under development target both low cost and high levels of operational efficiency. Fields of investigation under Air Separation currently include:

  • Membranes
  • Sorbents
  • Ion Transport Membranes
  • Cryogenic-based Air Separation Systems Improvements and Modularization
  • Innovative Concepts

The historical context for development in this area was oxygen production for large integrated gasification combined cycle power plants (e.g. by scaling up high-temperature ceramic membrane-based ion transport membrane technology). This has shifted to innovative technologies that can deploy in concert with modular gasification-based systems. NETL continues to be interested in potential of development of innovative air separation technology, including hollow fiber membranes and modules, improved sorbents, various cryogenic system improvements, use of solid oxygen carriers in chemical looping to provide in situ oxygen production in gasifiers, and innovative concepts including magnetic field-based air separation.

The Gasification Systems Program plans to continue to develop air separation technologies to be utilized in advanced modular energy systems that will make substantial progress toward enabling cost-competitive, coal-based power generation with near-zero emissions. Consistent with the overall Program strategy, technological development of air separation systems will be suitably sized for integration in modular gasification systems. The Program continues a non-restrictive strategy of fostering technology advancement in any of the air separation technology areas, from cryogenic to innovative concepts, if potential for cost reduction and performance advancement exist.

Modularization of Ceramic Hollow Fiber Membrane Technology for Air Separation

Improving Energy Efficiency of Air Separation Via Hollow Fiber Sorbents
Low Cost Air Separation Process for Gasification Applications
Pilot Testing of a Modular Oxygen Production System Using O2 binding Adsorbents
Radically Engineered Modular Air Separation System Using Tailored Oxygen Sorbents
Advanced Sorbents for Modular Oxygen Production for REMS Gasifiers
Oxygen Binding Materials and Highly Efficient Modular System for Oxygen Production
Low-Cost Oxygen (LCO) for Small-Scale Modular Gasification Systems

Ion transport membranes
ITMs are nonporous ceramic membranes that are permeable only to oxygen ions and are therefore 100% selective. At temperatures of 1450-1650°F, oxygen from feed air adsorbs on the membrane and dissociates to form oxygen ions by electron transfer. The oxygen anions enter and migrate through the ceramic lattice counter-currently with electrons and are driven toward the permeate side by the oxygen partial pressure differential that can be established variously by pressurizing the feed air, establishing vacuum on the permeate side, or gas sweeping the permeate side. ITM systems afford the opportunity of integrated operation with turbines, and their operation at elevated temperatures increases efficiency/reduces parasitic energy penalty compared to conventional cryogenic oxygen production systems. Systems analyses on a variety of gasification-based processes have shown significant cost and efficiency advantages with the application of ITM membranes for oxygen production compared to conventional cryogenic technology; however, technical issues with membrane life and production yield continue to be problematic. As such, ITM oxygen production technology’s potential may be best realized in application to smaller, modular systems, and in efforts to improve membrane durability and operational integrity of air separation modules.
Design and Fabrication of Novel Mixed Ion-Electron Conducting Membranes for Oxygen Separation—Poster Presentation at the Gasification Systems and Coal & Coal-Biomass to Liquids Workshop, August 10-11, 2015

Cryogenic-based Air Separation Systems Improvements and Modularization
The cryogenic air separation unit (ASU) in a conventional IGCC plant typically accounts for 12 to 15 percent of the overall capital cost of the plant, requiring a large parasitic power load primarily to operate gas compressors.
Development of a Two-Phase Dense Fluid Expander for Advanced Cryogenic Air Separation and Low-Grade Heat Recovery

Innovative concepts

Systems Analyses
As part of the support for Air Separation key technology, systems studies are being conducted to provide unbiased comparisons of competing technologies; determine the best way to integrate process technology steps; and predict the economic and environmental impacts of successful development.


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Other key technologies within Gasification Systems include the following:


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