In spite of its established role in reliably providing high-throughput, high-purity oxygen for gasification, cryogenic distillation-based air separation is costly and energy-intensive to operate, accounting for up to 15% of the total gasification plant capital cost, and consuming a major portion of in-plant power use. Moreover, any outages of the air separation unit (ASU) can disrupt the entire gasification plant process. Other oxygen supply technologies, such as pressure swing adsorption (PSA) and polymeric membranes are available, but at present commercially available offerings are limited in applicability to much smaller scales or cannot provide oxygen at a high enough purity (>95%) for gasification.
Since the cryogenic oxygen production patent issued to Carl Von Linde in 1903, the technology has been refined in engineering configuration and optimized in terms of efficiency to reduce costs to the greatest possible extent. Presently, the thermodynamic efficiency of state-of-the-art cryogenic air separation plants approaches theoretical limits as near as is practicable and is quite cost-effective at its large scale. However, cost effectiveness decreases at smaller scales and modular implementation is not practicable. Accordingly, there is great incentive to develop a new approach or technology for oxygen separation that meets or exceeds cryogenic incremental cost at these smaller scales.
Accordingly, DOE/NETL recognized a need and an opportunity, and has been exploring alternative options for producing modular, low-cost oxygen via innovative air separation technologies. In 2018, four projects were awarded to other National Laboratories for oxygen production in the 1-5 MWe energy system size, targeting competitive efficiency and cost to conventional cryogenic-based air separation. These projects are highly innovative, involving varied approaches including membranes made of unconventional materials like carbon molecular sieves or of mixed matrix composition in efficient hollow fiber format, high temperature ceramic membranes leveraging SOFC stack technology, and even a unique magnetocaloric, solid-state refrigerant-based method of air liquefaction.
The current DOE/NETL portfolio in Air Separation technology includes these and other important oxygen separation technology development projects.