METHOD FOR THE PRODUCTION OF AIR GASES BY THE CRYOGENIC SEPARATION OF AIR WITH VARIABLE LIQUID PRODUCTION AND POWER USAGE

Abstract

A method for the production of air gases by the cryogenic separation of air can include the steps of sending a purified and compressed air stream to a cold box under conditions effective for cryogenically separating the air stream into oxygen and nitrogen using a system of columns, wherein the purified and compressed air stream is at a feed pressure when entering the system of columns; withdrawing the oxygen at a product pressure; delivering the oxygen at a delivery pressure to an oxygen pipeline, wherein the oxygen pipeline has a pipeline pressure; and monitoring the pipeline pressure. The method can also include a controller configured to determine whether to operate in a power savings mode or a variable liquid production mode. By operating the method in a dynamic fashion, a power savings and/or additional high value cryogenic liquids can be realized in instances in which the pipeline pressure deviates from its highest value.

Claims

1. A method for the production of air gases by the cryogenic separation of air, the method comprising the steps of: a) compressing air to a pressure suitable for the cryogenic rectification of air to produce a compressed humid air stream, the compressed humid air stream having a first pressure P.sub.o; b) purifying the compressed humid air stream of water and carbon dioxide within a front end purification system to produce a dry air stream having reduced amounts of water and carbon dioxide as compared to the compressed humid air stream; c) compressing a first portion of the dry air stream in a booster compressor to form a boosted air stream, the boosted air stream having a first boosted pressure P.sub.B1; d) introducing a second portion of the dry air stream and the boosted air stream to a cold box under conditions effective to separate air to form an air gas product, wherein the air gas product is selected from the group consisting of oxygen, nitrogen, and combinations thereof; e) withdrawing the air gas product from the cold box, the air gas product having a first product pressure P.sub.P1; f) introducing the air gas product to a pipeline, wherein the pipeline is configured to transport the air gas product to a location located downstream of the pipeline, wherein the pipeline operates at a pipeline pressure P.sub.PL, wherein the air gas product is introduced to the pipeline at a first delivery pressure P.sub.D1; g) monitoring the pipeline pressure P.sub.PL within the pipeline; h) determining a mode of operation to operate using the pipeline pressure P.sub.PL of step g), wherein the mode of operation is selected from the group consisting of variable power usage, variable liquid production, and combinations thereof, wherein during periods of time in which the mode of operation is variable power usage, the method further comprises the step of: i) adjusting one or more pressure set points within the cold box based on the pipeline pressure P.sub.PL wherein during periods of time in which the mode of operation is variable liquid production, the method further comprises the step of: j) adjusting one or more pressure set points within the cold box based on the pipeline pressure P.sub.PL; and k) adjusting liquid production from the cold box based on the one or more pressure set points adjusted in step j).

2. The method as claimed in claim 1, wherein the step of determining the mode of operation further comprises providing a process controller configured to access process conditions selected from the group consisting of spot pricing data for electricity, local liquid inventories, and combinations thereof.

3. The method as claimed in claim 1, wherein the one or more pressure set points of steps i) and j) is the first product pressure P.sub.PL

4. The method as claimed in claim 1, wherein during periods of time in which the mode of operation is variable liquid production, the first boosted pressure P.sub.B1 is kept substantially constant during steps j) and k).

5. The method as claimed in claim 1, wherein during periods of time in which the mode of operation is variable power usage, the first boosted pressure P.sub.B1 is adjusted such that the difference between the first delivery pressure P.sub.D1 and the pipeline pressure P.sub.PL is below a given threshold.

6. The method as claimed in claim 5, wherein the threshold is less than 5 psi.

7. The method as claimed in claim 5, wherein the threshold is less than 3 psi.

8. The method as claimed in claim 1, wherein the cold box comprises a main heat exchanger, a system of columns having a double column composed of a lower pressure column and a higher pressure column, a condenser disposed at a bottom portion of the lower pressure column, and a liquid oxygen pump.

9. The method as claimed in claim 8, wherein the air gas product is oxygen and the pipeline is an oxygen pipeline.

10. The method as claimed in claim 9, wherein the liquid oxygen pump pressurizes liquid oxygen from the lower pressure column to the first product pressure P.sub.P1.

11. The method as claimed in claim 1, wherein the first product pressure P.sub.P1 is adjusted based upon the monitored pipeline pressure P.sub.PL.

12. The method as claimed in claim 11, wherein the first boosted pressure P.sub.B1 is adjusted based upon the first product pressure P.sub.P1.

13. The method as claimed in claim 8, wherein the air gas product is nitrogen and the pipeline is a nitrogen pipeline.

14. A method for the production of air gases by the cryogenic separation of air, the method comprising a first mode of operation and a second mode of operation, wherein during the first mode of operation and the second mode of operation, the method comprises the steps of: sending a purified and compressed air stream to a cold box under conditions effective for cryogenically separating the air stream to form an air gas product using a system of columns, wherein the purified and compressed air stream is at a feed pressure P.sub.F when entering the cold box, wherein the air gas product is selected from the group consisting of oxygen, nitrogen, and combinations thereof; withdrawing the air gas product at a product pressure P.sub.PO; delivering the air gas product at a delivery pressure P.sub.DO to an air gas pipeline, wherein the air gas pipeline has a pipeline pressure P.sub.PL; monitoring the pipeline pressure P.sub.PL; wherein during the first mode of operation, the method further comprises the steps of: reducing the difference between the pipeline pressure P.sub.PL and the delivery pressure P.sub.DO; wherein during the second mode of operation, the method further comprises the steps of: reducing the difference between the pipeline pressure P.sub.PL and the delivery pressure P.sub.DO; and adjusting liquid production from the cold box.

15. The method as claimed in claim 14, wherein the step of reducing difference between the pipeline pressure P.sub.PL and the delivery pressure P.sub.DO further comprises adjusting the product pressure P.sub.PO.

16. The method as claimed in claim 14, wherein the step of reducing difference between the pipeline pressure P.sub.PL and the delivery pressure P.sub.DO further comprises the step of adjusting the feed pressure P.sub.F.

17. The method as claimed in claim 14, wherein the step of adjusting liquid production from the cold box further comprises the step of maintaining the feed pressure P.sub.F substantially constant.

18. The method as claimed in claim 14, wherein the product pressure P.sub.PO and the delivery pressure P.sub.DO are substantially the same.

19. The method as claimed in claim 14, wherein the air gas product is oxygen, wherein the cold box comprises a main heat exchanger, a system of columns having a double column composed of a lower pressure column and a higher pressure column, a condenser disposed at a bottom portion of the lower pressure column, and a liquid oxygen pump.

20. The method as claimed in claim 19, wherein the cold box further comprises a gaseous oxygen (GOX) feed valve, wherein the GOX feed valve is in fluid communication with an outlet of the liquid oxygen pump and an inlet of the air gas pipeline.

21. The method as claimed in claim 20, wherein the step of reducing the difference between the pipeline pressure P.sub.PL and the delivery pressure P.sub.DO comprises an absence of adjusting the GOX feed valve.

22. The method as claimed in claim 20, wherein the step of reducing the difference between the pipeline pressure P.sub.PL and the delivery pressure P.sub.DO includes maintaining the GOX feed valve fully open.

23. The method as claimed in claim 19, wherein in both modes of operation, the method further comprises the step of providing a main air compressor upstream the cold box, wherein during the first mode of operation, the step of reducing the difference between the pipeline pressure P.sub.PL and the delivery pressure P.sub.DO further comprises the step of adjusting the operation of the liquid oxygen pump and the operation of the main air compressor, such that the product pressure P.sub.PO and the feed pressure P.sub.F are adjusted, wherein during the second mode of operation, the step of reducing the difference between the pipeline pressure P.sub.PL and the delivery pressure P.sub.DO further comprises the step of adjusting the operation of the liquid oxygen pump while maintaining the operation of the main air compressor substantially constant, such that the product pressure P.sub.PO is adjusted while keeping the feed pressure P.sub.F substantially constant.

24. The method as claimed in claim 19, wherein in both modes of operation, the method further comprises the step of providing a booster compressor downstream a main air compressor and upstream the cold box, wherein during the first mode of operation, the step of reducing difference between the pipeline pressure P.sub.PL and the delivery pressure P.sub.DO further comprises the step of adjusting the operation of the liquid oxygen pump and the operation of the booster compressor, such that the product pressure P.sub.PO and the feed pressure P.sub.F are adjusted, wherein during the second mode of operation, the step of reducing the difference between the pipeline pressure P.sub.PL and the delivery pressure P.sub.DO further comprises the step of adjusting the operation of the liquid oxygen pump while maintaining the operation of the booster compressor substantially constant, such that the product pressure P.sub.PO is adjusted while keeping the feed pressure P.sub.F substantially constant.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0087] 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.

[0088] FIG. 1 provides an embodiment of the present invention operating in a variable energy mode.

[0089] FIG. 2 provides another embodiment of the present invention operating in a variable energy mode.

[0090] FIG. 3 provides a graphical representation of data for an embodiment of the present invention operating in a variable energy mode.

[0091] FIG. 4 provides an embodiment of the present invention operating in a variable liquid mode.

[0092] FIG. 5 provides another embodiment of the present invention operating in a variable liquid mode

[0093] FIG. 6 provides a graphical representation of simulation data showing increases in liquid production as a function of gaseous oxygen product pressure for an embodiment operating in a variable liquid mode.

DETAILED DESCRIPTION

[0094] 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.

[0095] Now turning to FIG. 1, which represents an embodiment operating in a variable energy mode. Air 2 is introduced into main air compressor 10 and compressed, preferably to a pressure of at least 55 psig to 75 psig (or around 5 psig higher than the pressure of the higher pressure column). In an embodiment without booster air compressor 30, the pressure coming out of MAC 10 is preferably 400-450 psig. The resulting compressed humid air stream 12 is then purified of water and CO.sub.2 in front end purification system 20, thereby producing dry air stream 22. In one embodiment, all of dry air stream 22 passes via line 26 into cold box 40. The pressure of dry air stream 22 is measured by first pressure indicator PI1a. Within cold box 40, the air is cooled and cryogenically treated in order to separate the air into air gas product 42. Air gas product 42 is then removed from cold box 40 and passed through product control valve 50 before entering air gas pipeline 60. In a preferred embodiment, the pressure and flow rate of air gas product 42 can be measured by second pressure indicator PI2 and flow indicator FI1, respectively. The pressure of air gas pipeline 60 can be measured by pressure indicator PI3.

[0096] In one embodiment, the various pressure and flow indicators/sensors are configured to communicate (e.g., wirelessly or wired communication) with process controller 55, such that the various flow rates and pressures can be monitored by process controller 55, which is configured to adjust various settings throughout the process based on the measured flows and pressures.

[0097] Additionally, an embodiment of the present invention may also include booster air compressor 30. This embodiment is represented by dashed lines, since it is an optional embodiment. In this embodiment, a portion of dry air stream 22 is sent to booster air compressor 30 via line 24 and further compressed to form boosted air stream 32 before being introduced to cold box 40. The addition of booster air compressor 30 allows for additional freedoms in fine tuning the process, as will be explained in more detail later. In this embodiment, first pressure indicator PI1b is located on line 32 instead of line 26. Similarly, pressure controller 14b is in communication with booster air compressor 30 as opposed to pressure controller 14a for main air compressor 10. While the embodiment of FIG. 1 shows booster air compressor 30 as a single compressor, those of ordinary skill in the art will recognize that booster air compressor 30 can be more than one physical compressor. Additionally, booster air compressor 30 can also be a multi-stage compressor.

[0098] While the figures show direct lines of communication from the various pressure and flow indicators to the process controller 55, embodiments of the invention should not be so limited. Rather, those of ordinary skill in the art will recognize that embodiments of the invention may include instances in which certain indicators communicate directly with a related pressure controller.

[0099] FIG. 2 provides a more detailed view of cold box 40 for the optional embodiment that includes booster air compressor 30. In this embodiment, cold box 40 also includes heat exchanger 80, turbine 90, valve 100, double column 110, higher pressure column 120, auxiliary heat exchanger 130, lower pressure column 140, condenser/reboiler 150, and liquid oxygen pump 160. Turbine 90 can be attached to booster 70 via a common shaft. Just like in FIG. 1, air 2 is introduced into main air compressor 10 and compressed, preferably to a pressure of at least 55 psig to 75 psig (or around 5 psig higher than the pressure of the higher pressure column). The resulting compressed humid air stream 12 is then purified of water and CO.sub.2 in front end purification system 20, thereby producing dry air stream 22. A first portion of dry air stream 24 is sent to booster air compressor 30, with the remaining portion of dry air stream 26 entering cold box 40, wherein it is fully cooled in heat exchanger 80 before being introduced to higher pressure column 120 for separation therein. Following pressurization in booster air compressor 30, boosted air stream 32 is preferably fully cooled in heat exchanger 80 and then expanded across valve 100, before being introduced into a bottom portion of higher pressure column 120.

[0100] Partially boosted air stream 37 is preferably removed from an inner stage of booster air compressor 30 before being further compressed in booster 70 and then cooled in after cooler 75 to form second boosted stream 72. Second boosted stream 72 undergoes partial cooling in heat exchanger 80, wherein it is withdrawn from an intermediate section of heat exchanger 80 and then expanded in turbine 90 thereby forming expanded air stream 92, which can then be combined with second portion of dry air stream 26 before introduction to higher pressure column 120.

[0101] Higher pressure column 120 is configured to allow for rectification of air within, thereby producing an oxygen-rich liquid at the bottom and a nitrogen-rich gaseous stream at the top. Oxygen-rich liquid 122 is withdrawn from the bottom of higher pressure column 120 before exchanging heat with low pressure waste nitrogen 114 and low pressure nitrogen product 112 in auxiliary heat exchanger 130, and then expanded across a valve and introduced into lower pressure column 140. As is well known in the art, higher pressure column 120 and lower pressure column 140 are part of double column 110, and the two columns are thermally coupled via condenser/reboiler 150, which condenses rising nitrogen rich gas from higher pressure column 120 and vaporizes liquid oxygen that has collected at the bottom of lower pressure column 140. In the embodiment shown, two nitrogen-rich gas streams 126, 128 are withdrawn from higher pressure column 120, exchange heat with low pressure nitrogen product 112 and low pressure waste nitrogen 114, subsequently expanded across their respective valves, and then introduced into lower pressure column 140. Higher pressure nitrogen product 129 can also be withdrawn from higher pressure column 120 and then warmed in heat exchanger 80.

[0102] Liquid oxygen collects at the bottom of lower pressure column 140 and is withdrawn and pressurized to an appropriate pressure by liquid oxygen pump 160 to form liquid oxygen product 162. Liquid oxygen product 162 is then vaporized within heat exchanger 80 to form air gas product 42. The pressure and flow rate of air gas product 42 can be measured via second pressure sensor PI2 and FI1, respectively. As in FIG. 1, air gas product 42 flows across product control valve 50 and into air gas pipeline 60.

[0103] As noted previously, the pressure of air gas pipeline 60 tends to drift over time. In methods known heretofore, this problem was solved by adjusting the openness of product control valve 50 to create the appropriate pressure drop. However, there are inefficiencies in doing this. Instead, embodiments of the present invention can adjust the pressure set points within the cold box, for example, the discharge pressure of liquid oxygen pump 160. By reducing this pressure an appropriate amount, product control valve 50 can be left fully open, thereby resulting in minimal expansion losses across product control valve 50. In one embodiment, the appropriate amount yields a difference between PI2 and PI3 to be less than 5 psi, preferably less than 3 psi.

[0104] In another embodiment, by changing the pressure of liquid oxygen product 162, its vaporization temperature will also change. Furthermore, it is preferred that liquid oxygen product 162 vaporizes against a condensing air stream (e.g., boosted air stream 32). As such, in a preferred embodiment, the discharge pressure of booster air compressor 30 is also changed an appropriate amount. In one embodiment, an appropriate amount is preferably the amount that results in improved heating curves between liquid oxygen product 162 and boosted air stream 32.

[0105] In an embodiment in which the air gas product is nitrogen, the embodiment may include withdrawing higher pressure nitrogen product 129 as a liquid from higher pressure column 120, and pressurizing it to an appropriate pressure using a liquid nitrogen pump (not shown) before warming in heat exchanger 80. The resultant warmed nitrogen gas product would then be introduced to a nitrogen pipeline in similar manner as described with respect to the gaseous oxygen product. Alternatively, a liquid nitrogen stream can be removed from the lower pressure column instead of the higher pressure column.

[0106] FIG. 3 provides a graphical representation of pressures as a function of time for an embodiment of the present invention. As can be seen from FIG. 3, the ASU GOX pressure is kept slightly above (e.g., between 3-4 psi) the GOX pipeline pressure. This is accomplished by altering both the LOX discharge pressure from the LOX pump, as well as altering the booster air compressor (BAC) discharge pressure. By operating the LOX pump and BAC in variable pressure mode, embodiments of the present invention are able to save on power consumption without any losses in flow rate production, and therefore, present an incredible advantage over the methods known heretofore.

[0107] Table I and Table II below, show comparative data of the various streams for oxygen production at 610 psig and 400 psig.

TABLE-US-00001 TABLE I 610 psig GOX Flow Pressure Temp Stream # (kscfh) (psig) (° F.)  2 7430 0 72 12 7430 71 87 24 3200 69 64 26 4143 69 64 32 2188 966 87 37 1012 525 87 42 1413 615 69 72 1012 794 87 92 1012 66 −280 94 5155 66 −260.5 162  1413 620 −287 MP Col — 66 — LP Col — 6 —

TABLE-US-00002 TABLE II 400 psig GOX Flow Pressure Temp Stream # (kscfh) (psig) (° F.)  2 7430 0 72 12 7430 71 87 24 3200 69 64 26 4143 69 64 32 2188 929 87 37 1012 513 87 42 1413 405 71 72 1012 794 87 92 1012 66 −280 94 5155 66 −266.5 162  1413 409 −289 MP Col — 66 — LP Col — 6 —

[0108] As is shown in the tables above, when the pipeline pressure changes, the pressures of streams 32, 37, 42 and 162 can be adjusted, while maintaining all other conditions substantially the same. As will be readily appreciated, being able to reduce compression needs for the LOX pump 160 and BAC 30 can result in significant power savings. Furthermore, this is accomplished without any loss of production in terms of flow rate and without any significant upset to the operating conditions of the double column.

[0109] Now turning to FIG. 4, which represents an embodiment operating in a variable liquid mode. Air 2 is introduced into main air compressor 10 and compressed, preferably to a pressure of at least 55 psig to 75 psig (or around 5 psig higher than the pressure of the MP column). In an embodiment without booster air compressor 30, the pressure coming out of MAC 10 is preferably 400-450 psig. The resulting compressed humid air stream 12 is then purified of water and CO.sub.2 in front end purification system 20, thereby producing dry air stream 22. In one embodiment, all of dry air stream 22 passes via line 26 into cold box 40. Within cold box 40, the air is cooled and cryogenically treated in order to separate the air into air gas product 42. Air gas product 42 is then removed from cold box 40 and passed through product control valve 50 before entering air gas pipeline 60.

[0110] In a preferred embodiment, the pressure and flow rate of air gas product 42 can be measured by second pressure indicator PI2 and flow indicator FI1, respectively. The pressure of air gas pipeline 60 can be measured by pressure indicator PI3. First liquid air gas product 44 and/or second liquid air gas product 48 can also be removed from cold box 40 in certain modes of operation. The flow rate of first liquid air gas product 44 can be measured by flow indicator FI2, and the flow rate of second liquid air gas product 48 can be measured by flow indicator FI3. In the embodiment shown, control valves 46, 47 can be used to control the flow rates of fluids 44, 48.

[0111] In one embodiment, the various pressure and flow indicators/sensors are configured to communicate (e.g., wirelessly or wired communication) with process controller 55, such that the various flow rates and pressures can be monitored by process controller 55, which is configured to adjust various settings throughout the process based on the measured flows and pressures.

[0112] Additionally, an embodiment of the present invention may also include booster air compressor 30. This embodiment is represented by dashed lines, since it is an optional embodiment. In this embodiment, a portion of dry air stream 22 is sent to booster air compressor 30 via line 24 and further compressed to form boosted air stream 32 before being introduced to cold box 40. While the embodiment of FIG. 4 shows booster air compressor 30 as a single compressor, those of ordinary skill in the art will recognize that booster air compressor 30 can be more than one physical compressor. Additionally, booster air compressor 30 can also be a multi-stage compressor.

[0113] While the figures show direct lines of communication from the various pressure and flow indicators to the process controller 55, embodiments of the invention should not be so limited. Rather, those of ordinary skill in the art will recognize that embodiments of the invention may include instances in which certain indicators communicate directly with a related pressure controller.

[0114] FIG. 5 provides a more detailed view of cold box 40 for the optional embodiment that includes booster air compressor 30. In this embodiment, cold box 40 also includes heat exchanger 80, turbine 90, valve 100, double column 110, higher pressure column 120, auxiliary heat exchanger 130, lower pressure column 140, condenser/reboiler 150, and liquid oxygen pump 160. Turbine 90 can be attached to booster 70 via a common shaft. Just like in FIG. 4, air 2 is introduced into main air compressor 10 and compressed, preferably to a pressure of at least 55 psig to 75 psig (or around 5 psig higher than the pressure of the MP column). The resulting compressed humid air stream 12 is then purified of water and CO.sub.2 in front end purification system 20, thereby producing dry air stream 22. A first portion of dry air stream 24 is sent to booster air compressor 30, with the remaining portion of dry air stream 26 entering cold box 40, wherein it is fully cooled in heat exchanger 80 before being introduced to higher pressure column 120 for separation therein. Following pressurization in booster air compressor 30, boosted air stream 32 is preferably fully cooled in heat exchanger 80 and then expanded across valve 100, before being introduced into a bottom portion of higher pressure column 120.

[0115] Partially boosted air stream 37 is preferably removed from an inner stage of booster air compressor 30 before being further compressed in booster 70 and then cooled in after cooler 75 to form second boosted stream 72. Second boosted stream 72 undergoes partial cooling in heat exchanger 80, wherein it is withdrawn from an intermediate section of heat exchanger 80 and then expanded in turbine 90 thereby forming expanded air stream 92, which can then be combined with second portion of dry air stream 26 before introduction to higher pressure column 120.

[0116] Higher pressure column 120 is configured to allow for rectification of air within, thereby producing an oxygen-rich liquid at the bottom and a nitrogen-rich gaseous stream at the top. Oxygen-rich liquid 122 is withdrawn from the bottom of higher pressure column 120 before exchanging heat with low pressure waste nitrogen 114 and low pressure nitrogen product 112 in auxiliary heat exchanger 130, and then expanded across a valve and introduced into lower pressure column 140. As is well known in the art, higher pressure column 120 and lower pressure column 140 are part of double column 110, and the two columns are thermally coupled via condenser/reboiler 150, which condenses rising nitrogen rich gas from higher pressure column 120 and vaporizes liquid oxygen that has collected at the bottom of lower pressure column 140. In the embodiment shown, two nitrogen-rich gas streams 126, 128 are withdrawn from higher pressure column 120, exchange heat with low pressure nitrogen product 112 and low pressure waste nitrogen 114, subsequently expanded across their respective valves, and then introduced into lower pressure column 140. Medium pressure nitrogen product 129 can also be withdrawn from higher pressure column 120 and then warmed in heat exchanger 80.

[0117] Liquid oxygen collects at the bottom of lower pressure column 140 and is withdrawn and pressurized to an appropriate pressure by liquid oxygen pump 160 to form liquid oxygen 162. Liquid oxygen 162 is then vaporized within heat exchanger 80 to form air gas product 42. The pressure and flow rate of air gas product 42 can be measured via second pressure sensor PI2 and FI1, respectively. As in FIG. 4, air gas product 42 flows across product control valve 50 and into air gas pipeline 60. Liquid oxygen product 44 from liquid oxygen pump 160 is delivered to the storage (not shown). Liquid nitrogen product 48 from top of lower pressure column 140 is delivered to the storage (not shown).

[0118] As noted previously, the pressure of air gas pipeline 60 tends to drift over time. In methods known heretofore, this problem was solved by adjusting the openness of product control valve 50 to create the appropriate pressure drop. However, there are inefficiencies in doing this. Instead, embodiments of the present invention can adjust the pressure set points within the cold box, for example, the discharge pressure of liquid oxygen pump 160. By reducing this pressure an appropriate amount, product control valve 50 can be left fully open, thereby resulting in minimal expansion losses across product control valve 50. In one embodiment, the appropriate amount yields a difference between PI2 and PI3 to be less than 5 psi, preferably less than 3 psi.

[0119] By reducing the pressure of liquid oxygen product 162 and keeping the pressure of the incoming air streams at the same pressure set points (e.g., BAC and MAC maintained at constant set points), additional liquid production can be achieved. For example, for an ASU process that is built to produce gaseous oxygen at 610 psig (e.g., stream 42), approximately 51 kscfh LOX and 91 kscfh LIN can be produced. However, this same process can produce approximately 57 kscfh more LIN or 54 kscfh more LOX if the discharge pressure of the LOX pump is reduced to produce a gaseous oxygen product stream at approximately 400 psig.

[0120] Tables IV-VI below show comparative data for various streams with Table IV being a base case at 610 psig GOX production, Table V being an embodiment in which LIN production was maximized with GOX production being at 400 psig, and Table VI being an embodiment in which LOX production was maximized with GOX production also being at 400 psig. While these examples only show LIN and LOX production being maximized, respectively, those of ordinary skill in the art will recognize that embodiments of the invention are not so limited. Rather, embodiments of the invention can also include instances in which both LOX and LIN production could be both increased at the same time. Those of ordinary skill in the art will recognize that in these embodiments, the increase for each LIN or LOX will not be as much individually as is shown in Table V or Table VI.

TABLE-US-00003 TABLE IV 610 psig GOX Flow Pressure Temperature Stream # (kscfh) (psig) (° F.)  2 8073 0 72 12 8073 71 87 24 4010 69 64 26 3329 69 64 32 2663 928 87 37 1347 515 87 42 1487 610 74 44 51 30 −297 48 91 6 −315 72 1347 790 87 92 1347 66 −281 94 4676 66 −248 162  1487 614 −287 MP Col — 66 — LP Col — 6 —

TABLE-US-00004 TABLE V 400 psig GOX - - LIN Production Flow Pressure Temperature Stream # (kscfh) (psig) (° F.)  2 8073 0 72 12 8073 71 87 24 4010 69 64 26 3329 69 64 32 2663 928 87 37 1347 515 87 42 1487 400 75 44 51 30 −297 48 148 6 −315 72 1347 826 87 92 1347 66 −281 94 4676 66 −252 162  1487 404 −289 MP Col — 66 — LP Col — 6 —

TABLE-US-00005 TABLE VI 400 psig GOX - - LOX Production Flow Pressure Temperature Stream # (kscfh) (psig) (° F.)  2 8073 0 72 12 8073 71 87 24 4010 69 64 26 3329 69 64 32 2663 928 87 37 1347 515 87 42 1433 400 75 44 105 30 −297 48 91 6 −315 72 1347 826 87 92 1347 66 −281 94 4676 66 −248 162  1433 404 −289 MP Col — 66 — LP Col — 6 —

[0121] As is shown in the tables above, when the pipeline pressure changes, the pressure of stream 42 is adjusted to match the pipeline pressure and the flow rates of streams 44 or 48 are changed. The remaining streams remain largely unchanged. As will be readily appreciated, being able to produce additional amounts of liquid can be highly beneficial, particularly since liquid streams are at a premium on the market. Furthermore, this is accomplished without any loss of production in terms of flow rate, without any significant upset to the operating conditions of the double column, and with minimal additional capital expenses.

[0122] In an embodiment in which the air gas product is nitrogen, the embodiment may include withdrawing higher pressure nitrogen product 129 as a liquid from higher pressure column 120, and pressurizing it to an appropriate pressure using a liquid nitrogen pump (not shown) before warming in heat exchanger 80. The resultant warmed nitrogen gas product would then be introduced to a nitrogen pipeline in similar manner as described with respect to the gaseous oxygen product. Alternatively, a liquid nitrogen stream can be removed from the lower pressure column instead of the higher pressure column.

[0123] FIG. 6 presents a graphical representation of liquid production as a function of pressure of the air gas product (e.g., stream 42). As shown in the example, going from a pressure of about 650 psig to 400 psig can yield an almost two fold increase in LIN production (went from about 80 to about 150 kscfh). Similarly, liquid oxygen production was increased from around 40 to about 105 kscfh. While the graphical representation was developed with the assumption that only one of the liquid products was being adjusted at a time, the invention is not intended to be so limited. In fact, it is perfectly acceptable to increase both liquid products at the same time.

[0124] In another embodiment, process controller 55 can be configured to access spot pricing data (or the user can input data into the controller), such that process controller 55 can be configured to optimize/adjust the amount of increased LIN and/or LOX based upon the current spot pricing data. Similarly, process controller 55 can also be configured to keep track of local inventories of LIN and/or LOX, and make adjustments to the production of LIN and/or LOX based on this additional data.

[0125] In another embodiment, process controller 55 can determine whether to operate in power savings mode or additional liquid production mode based upon certain conditions. For example, if electricity is cheaper than normal, saving power might not be of great importance, and therefore, process controller 55 can make a determination to switch to liquid production mode. In a preferred embodiment, process controller 55 makes these decisions automatically based on input conditions. In another embodiment, process controller 55 can include a manual override.

[0126] 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.

[0127] 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.

[0128] The singular forms “a”, “an” and “the” include plural referents, unless the context clearly dictates otherwise.

[0129] “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.

[0130] “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.

[0131] 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.

[0132] 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.

[0133] 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.