Patent Application
20240353174
The present invention generally relates to a method and apparatus for efficiently operating an air separation plant that produces a liquid oxygen (LOX) stream. More specifically, the present invention relates to a method and apparatus for producing LOX at two different temperatures.
Air separation plants separate atmospheric air into its primary constituents: nitrogen and oxygen, and occasionally argon, xenon and krypton. These gases are sometimes referred to as air gases.
A typical cryogenic air separation process can include the following steps: (1) filtering the air in order to remove large particulates that might damage the main air compressor; (2) compressing the pre-filtered air in the main air compressor and using interstage cooling to condense some of the water out of the compressed air; (3) passing the compressed air stream through a front-end-purification unit to remove residual water and carbon dioxide; (4) cooling the purified air in a heat exchanger by indirect heat exchange against process streams from the cryogenic distillation column; (5) expanding at least a portion of the cold air to provide refrigeration for the system; (6) introducing the cold air into the distillation column for rectification therein; (7) collecting nitrogen from the top of the column (typically as a gas) and collecting oxygen from the bottom of the column as a liquid.
During the process of liquid oxygen (LOX) production, the LOX is typically produced and stored at low pressure (1.03 to 1.4 bar (a)) and as a saturated liquid (i.e., bubble point), which is at a temperature of roughly −183° C. This is because cryogenic products (LOX, liquid nitrogen, liquid argon), cannot be stored in a subcooled state, since the system will naturally come to equilibrium conditions, thereby collapsing the pressure of the vapor space. See e.g., U.S. Pat. Nos. 3,214,926 and 4,152,130.
When customer demand requires a subcooled product (e.g., rapid LOX fueling to a rocket) then LOX is withdrawn from the saturated LOX storage (−183° C.) and subcooled to (approximately −190° C. to −206° C.) by heat transfer with an external saturated LIN stream(s).
It is desirable to have a process to reduce the external LIN refrigeration demand that is required for subcooling the LOX. Therefore, it would be advantageous to provide a method and apparatus that is operated in a more efficient manner.
The present invention is directed to a method and apparatus that satisfies at least one of these needs.
In addition to producing LOX at typical conditions at or near saturated (−183° C.), it is desirable for the ASU to also produce very subcooled LOX (e.g., less than −190° C.) product directly from the ASU.
In one embodiment, the first LOX stream (saturated, ˜−183° C.) can be cooled in parallel to a stream that is lean in nitrogen (for temperature match). At least one second LOX stream (subcooled to <−185° C.) can be cooled in parallel to a stream that is rich in nitrogen (for cold temperature match).
In certain embodiments, the method for production of at least two liquid oxygen product streams from an air separation unit is provided. The method may include the steps of:
In optional embodiments of the method:
In another embodiment, an apparatus for production of at least two liquid oxygen product streams embodiment is provided. The apparatus may include:
In optional embodiments of the apparatus:
the first subcooled temperature is in the range of −179° C. to −185° C., and wherein the second subcooled temperature is in the range of −183° C. to −193° C.;
the first oxygen product stream is cooled in parallel to at least one first auxiliary liquid stream and the second oxygen product stream is cooled in parallel to at least one second auxiliary liquid stream;
the first auxiliary liquid stream comprises an oxygen-rich liquid from a bottom section of the higher-pressure column;
the second auxiliary liquid stream comprises a nitrogen-rich liquid from an upper section of the higher-pressure column;
the auxiliary heat exchange zone and the second auxiliary heat exchange zone are combined in a common heat exchanger;
the auxiliary heat exchange zone and the second auxiliary heat exchange zone are in separate heat exchangers;
the apparatus may also include a control system configured to control the first subcooled temperature, wherein the control system comprises a controller that is configured to adjust the first subcooled temperature by varying a flow rate of a first fluid through a first bypass line, wherein the controller is further configured to adjust the second subcooled temperature by varying a flow rate of a second fluid through a second bypass line, wherein the first bypass line is in fluid communication with the first oxygen product conduit, wherein the second bypass line is in fluid communication with the second oxygen product conduit; and/or
These and other features, aspects, and advantages of the present invention will become better understood with regard to the following description, claims, and accompanying drawings. It is to be noted, however, that the drawings illustrate only several embodiments of the invention and are therefore not to be considered limiting of the invention's scope as it can admit to other equally effective embodiments.
While the invention will be described in connection with several embodiments, it will be understood that it is not intended to limit the invention to those embodiments. On the contrary, it is intended to cover all the alternatives, modifications and equivalence as may be included within the spirit and scope of the invention defined by the appended claims.
The terms “nitrogen-rich” and “oxygen-rich” will be understood by those skilled in the art to be in reference to the composition of air. As such, nitrogen-rich encompasses a fluid having a nitrogen content greater than that of air. Similarly, oxygen-rich encompasses a fluid having an oxygen content greater than that of air.
Now turning to
Higher-pressure column 20 is configured to separate air into oxygen-rich liquid 22 and nitrogen-rich gas 26. This oxygen-rich liquid 22 is withdrawn from a bottom section of higher-pressure column 20, subcooled in first auxiliary heat exchange zone 30, and then expanded across another JT valve, before being introduced into lower-pressure column 50 for further rectification therein.
A common condenser/vaporizer is disposed in a lower section of lower-pressure column 50, and it is configured to condense rising nitrogen-rich gas from the higher-pressure column 20 while vaporizing oxygen-rich liquid in the lower section of the lower-pressure column 50. The condensed nitrogen can be withdrawn as nitrogen-rich liquid 24 from an upper section of higher-pressure column 50, before being subcooled in second auxiliary heat exchange zone 40, and then expanded across another JT valve, before being introduced into lower-pressure column 50 for further rectification therein.
Lower-pressure column 50 is configured to further rectify the air gases, resulting in relatively pure liquid oxygen (LOX) settling in the lower section of lower-pressure column 50, while gaseous nitrogen collects at a top section of lower-pressure column 50. In the embodiment shown, lower-pressure gaseous nitrogen 54 can be withdrawn from the lower-pressure column 50, and then warmed sequentially in second auxiliary heat exchange zone, first auxiliary heat exchange zone, and main heat exchange zone.
A first LOX stream 52 can be withdrawn from lower-pressure column 50, and then vaporized in main heat exchange zone to form gaseous oxygen 53. In the embodiment shown, additional refrigeration for main heat exchange zone can be provided by withdrawing a higher-pressure gaseous nitrogen stream 26 from higher-pressure column 20, wherein it is partially warmed in main heat exchange zone 10, before being expanded in turbine 60, and then reintroduced into main heat exchange zone 10 for further warming, wherein it can be combined with lower-pressure gaseous nitrogen 54 to form warm gaseous nitrogen 55. While not shown, turbine 60 and booster air compressor 7 can share a common shaft, such that turbine 60 is configured to provide rotational power for booster air compressor 7.
A second LOX stream 56 can be withdrawn from lower-pressure column 50, wherein it is further cooled in first auxiliary heat exchange zone 30 to form a cooled LOX stream, preferably to a first subcooled temperature in the range of −179° C. to −185° C. This cooled LOX stream can then be split into a first oxygen product stream 32 and a second oxygen product stream 42, wherein the first oxygen product stream 32 is collected at the first subcooled temperature, while the second oxygen product stream 42 is further cooled in second auxiliary heat exchange zone to a second subcooled temperature in the range of 183° C. to −193° C. and collected at this second subcooled temperature. Consequently, embodiments of the present invention allow for collection of liquid oxygen at two different temperatures, all without the use of externally provided nitrogen.
In an optional embodiment shown in
While the invention has been described in conjunction with specific embodiments thereof, it is evident that many alternatives, modifications, and variations will be apparent to those skilled in the art in light of the foregoing description. Accordingly, it is intended to embrace all such alternatives, modifications, and variations as fall within the spirit and broad scope of the appended claims. The present invention may suitably comprise, consist or consist essentially of the elements disclosed and may be practiced in the absence of an element not disclosed. Furthermore, if there is language referring to order, such as first and second, it should be understood in an exemplary sense and not in a limiting sense. For example, it can be recognized by those skilled in the art that certain steps can be combined into a single step.
The singular forms “a”, “an” and “the” include plural referents, unless the context clearly dictates otherwise.
“Comprising” in a claim is an open transitional term which means the subsequently identified claim elements are a nonexclusive listing (i.e., anything else may be additionally included and remain within the scope of “comprising”). “Comprising” as used herein may be replaced by the more limited transitional terms “consisting essentially of” and “consisting of” unless otherwise indicated herein.
“Providing” in a claim is defined to mean furnishing, supplying, making available, or preparing something. The step may be performed by any actor in the absence of express language in the claim to the contrary.
Optional or optionally means that the subsequently described event or circumstances may or may not occur. The description includes instances where the event or circumstance occurs and instances where it does not occur.
Ranges may be expressed herein as from about one particular value, and/or to about another particular value. When such a range is expressed, it is to be understood that another embodiment is from the one particular value and/or to the other particular value, along with all combinations within said range.
All references identified herein are each hereby incorporated by reference into this application in their entireties, as well as for the specific information for which each is cited.
This application claims priority to U.S. Provisional Application Ser. No. 63/460,229 filed on Apr. 18, 2023, which is hereby incorporated by reference in its entirety.
| Number | Date | Country | |
|---|---|---|---|
| 63460229 | Apr 2023 | US |
