Patent Grant
7875101
None
Room temperature gas separation techniques, used to produce enhanced concentrations of specific gasses found in air, are becoming more refined and finding broader areas of application. Two methods of gas separation at ambient temperatures are membrane separation and PSA (Pressure Swing Adsorption). Typically, PSA generally separates only the nitrogen from a flow of air and produces oxygen at purity levels of 90% to 94%. The major contaminant in this oxygen-rich stream is argon, which is concentrated from its normal level of 1%, through the removal of nitrogen.
Membrane gas separation is a mature technology that has been utilized and commercialized for separating gas mixtures. Oxygen is separated from air by applying a pressure differential across an oxygen-selective material, typically a synthetic polymer. In the system described herein, the membrane is specially formulated to specifically remove some nitrogen and most of the argon from the flow. This is illustrated in
Producing oxygen gas with purities greater than 98% is not economically feasible because of a lack of highly oxygen selective membrane materials. However, the enriched oxygen stream produced by the membrane can be purified further by pressure swing adsorption to generate high purity (>98%) oxygen.
Pressure swing adsorption (PSA) units are currently used in medical, refining, chemical and gas industries to produce oxygen. For oxygen concentration, the PSA utilizes zeolite materials to capture nitrogen from a flow under elevated pressures, leaving behind an oxygen-rich gas mixture, which is fed under pressure to down stream processes for utilization. While under pressure, the adsorbent material becomes saturated with nitrogen after some interval of time. After saturation with nitrogen, the unit is depressurized to desorb the nitrogen and regenerate the zeolite bed materials. If the flow has been pretreated to remove argon, and a portion of the nitrogen, the PSA system can be reduced in size and become capable producing oxygen flows at concentrations greater than 98% purity.
PSA systems come in various designs, processing the gas flow either continuously in a flow-through design, or in a batch mode where the elevated pressure is cycled from one pressure vessel to an accompanying one. Various designs use proprietary valving and flow recycling to achieve tradeoff in plant size, oxygen purity, and power requirements.
Previous methods of producing high purity oxygen (98% purity) use a two-stage industrial PSA system. Such a system first attempts to produce as high of purity oxygen stream as possible using a large PSA section, and thereafter remove argon using carbon molecular sieve adsorbents. This two-stage process is bulky, energy demanding, and oxygen recovery efficiencies are low. In order to reduce the size and the energy demands of an ambient temperature gas separation process capable of producing 15 L/min at greater than 98% purity, we have devised a method of using highly selective permeable membrane to enrich the stream flowing to a much smaller PSA separation unit.
A portable, non-cryogenic, oxygen generation system capable of delivering oxygen gas at purities greater than 98% and flow rates of 15 L/min or more is described. The system consists of two major components. The first component is a high efficiency membrane capable of separating argon and a portion of the nitrogen content from air, yielding an oxygen-enriched permeate flow. This is then fed to the second component, a pressure swing adsorption (PSA) unit utilizing a commercially available, but specifically-formulated zeolite compound to remove the remainder of the nitrogen from the flow. The system is a unique gas separation system that can operate at ambient temperatures, for producing high purity oxygen for various applications (medical, refining, chemical production, enhanced combustion, fuel cells, etc . . . ) and represents a significant advance compared to current technologies.
The accompanying drawings, which are incorporated in and form part of the specification, illustrate various examples of the present invention and, together with the detailed description, serve to explain the principles of the invention.
Unless otherwise specified, all gas composition percentages are in mole percent, not weight percent.
In the hybrid membrane-PSA system as shown in
Two variations are envisioned for this system, one utilizing a recycle of the PSA vent gases (
In the no-recycle configuration, mass balance calculations show oxygen gas could be produced at a purity of 98.6% with a flow rate of 15 L/min. In addition, the bed size of the PSA unit 16 could be reduced by 55%, when compared to a standalone PSA unit producing a comparable flow. The efficiency of recovering oxygen from air is 36% for the no-recycle system.
For the recycle system, which recycles the vent and purge streams of the PSA (stream (8) in
Typically, the processes of the present invention are run at ambient temperature, e.g., 20-25° C. The processes are non-cryogenic.
No-Recycle Example
In this example of a ‘no-recycle’ process (corresponding to
The calculated system values were:
Table 1 summarizes the flow pressure, flow rate, and gas composition for the No-Recycle example above.
Recycle Example
In this example of a ‘Recycle’ process (corresponding to
The calculated system values were:
Table 2 summarizes the flow pressure, flow rate, and gas composition for the Recycle example above.
The particular examples discussed above are cited to illustrate particular embodiments of the invention. Other applications and embodiments of the apparatus and method of the present invention will become evident to those skilled in the art. It is to be understood that the invention is not limited in its application to the details of construction, materials used, and the arrangements of components set forth in the following description or illustrated in the drawings.
The scope of the invention is defined by the claims appended hereto.
The United States Government has rights in this invention pursuant to Department of Energy Contract No. DE-AC04-94AL85000 with Sandia Corporation.
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| Number | Date | Country | |
|---|---|---|---|
| 20100116132 A1 | May 2010 | US |
