APPARATUS FOR OPERATING AN AIR SEPARATION PLANT

Abstract

An apparatus for the production of air gases with variable liquid production by the cryogenic separation of air can include a cold box having a heat exchanger, and a system of columns; a pressure monitoring device; and a controller. The cold box can be configured to receive a purified and compressed air stream under conditions effective for cryogenically separating the air stream to form an air gas product. The apparatus may also include means for transferring the air gas product from the cold box to an air gas pipeline. The pressure monitoring device is configured to monitor the pipeline pressure, and the controller is configured to adjust the product pressure of the air gas product coming out of the cold box based upon the pipeline pressure and to further adjust liquid production from the cold box based on the adjusted product pressure.

Claims

1. An apparatus for the production of air gases by the cryogenic separation of air, the apparatus comprising: a) a main air compressor configured to compress 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) a front end purification system configured to purify the compressed humid air stream of water and carbon dioxide to produce a dry air stream having reduced amounts of water and carbon dioxide as compared to the compressed humid air stream; c) a booster compressor in fluid communication with the front end purification system, wherein the booster compressor is configured to compress a first portion of the dry air stream to form a boosted air stream, the boosted air stream having a first boosted pressure P.sub.B1; d) a cold box comprising 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, wherein the cold box is configured to receive the boosted air stream and a second portion of the dry air stream 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) means for monitoring the pressure of a pipeline, wherein the pipeline is in fluid communication with the cold box, such that the pipeline is configured to receive the air gas product from the cold box, the air gas product having a first product pressure P.sub.P1; f) means for adjusting one or more pressure set points of the apparatus based on the monitored pipeline pressure, wherein the one or more pressure set points of the apparatus comprise a discharge pressure of the liquid oxygen pump; and g) means for adjusting liquid production from the cold box.

2. The apparatus as claimed in claim 1, wherein the first product pressure P.sub.P1 is adjusted such that the difference between the first product pressure P.sub.P1 and the first delivery pressure P.sub.D1 is below a given threshold.

3. The apparatus as claimed in claim 2, wherein the threshold is less than 5 psi.

4. The apparatus as claimed in claim 2, wherein the threshold is less than 3 psi.

5. The apparatus as claimed in claim 1, wherein the liquid production from the cold box is a liquid selected from the group consisting of liquid nitrogen, liquid oxygen, and combinations thereof.

6. The apparatus as claimed in claim 1, wherein means for adjusting liquid production from the cold box comprises a process controller, in communication with a plurality of flow indicators, pressure indicators, and control valves.

7. The apparatus as claimed in claim 1, wherein the air gas product is oxygen and the pipeline is an oxygen pipeline.

8. The apparatus as claimed in claim 7, wherein the liquid oxygen pump pressurizes liquid oxygen from the lower pressure column to the first product pressure P.sub.P1.

9. The apparatus as claimed in claim 1, wherein the air gas product is nitrogen and the pipeline is a nitrogen pipeline.

10. An apparatus for the production of air gases by the cryogenic separation of air, the apparatus comprising: a cold box configured to receive a purified and compressed air stream 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, wherein the cold box is configured to produce the air gas product at a product pressure P.sub.PO; means for transferring the air gas product from the cold box to an air gas pipeline; a pressure monitoring device configured to monitor the pipeline pressure P.sub.PL; and a controller configured to adjust the product pressure P.sub.PO of the air gas product coming out of the cold box based upon the pipeline pressure P.sub.PL, wherein the controller is also configured to adjust liquid production from the cold box based on the product pressure P.sub.PO of the air gas product coming out of the cold box.

11. The apparatus as claimed in claim 10, 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 air gas pump selected from the group consisting of a liquid oxygen pump, a liquid nitrogen pump, and combinations thereof.

12. The apparatus as claimed in claim 11, wherein the controller is configured to communicate with the liquid oxygen pump and adjust a discharge pressure of the liquid oxygen pump.

13. The apparatus as claimed in claim 10, wherein the product pressure P.sub.PO and the delivery pressure P.sub.DO are substantially the same.

14. The apparatus as claimed in claim 10, wherein the controller is in communication with the pressure monitoring device.

15. The apparatus as claimed in claim 10, further comprising means for withdrawing liquid oxygen from the cold box.

16. The apparatus as claimed in claim 10, further comprising means for withdrawing liquid nitrogen from the cold box.

17. The apparatus as claimed in claim 10, further comprising 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, wherein the controller is configured to maintain the GOX feed valve in a fully open position regardless of the pipeline pressure P.sub.PL.

18. The apparatus as claimed in claim 10, further comprising a main air compressor disposed upstream the cold box, wherein the controller is further configured to adjust 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.

19. The apparatus as claimed in claim 10, further comprising a booster compressor downstream a main air compressor and upstream the cold box, wherein the controller is further configured to adjust 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

[0070] 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.

[0071] FIG. 1 provides an embodiment of the present invention.

[0072] FIG. 2 provides another embodiment of the present invention.

[0073] FIG. 3 provides a graphical representation of simulation data showing increases in liquid production as a function of gaseous oxygen product pressure.

DETAILED DESCRIPTION

[0074] 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.

[0075] Now turning to 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 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. 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.

[0076] 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.

[0077] 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.

[0078] 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. 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.

[0079] 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.

[0080] 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 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.

[0081] 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.

[0082] 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 liquid 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.

[0083] 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. 1, 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). Those of ordinary skill in the art will recognize that both product LOX and LIN can be produced as high pressure at the discharge of the pump or low pressure from the columns either in the HP or LP column for UN or from the bottom of the LP column for LOX.

[0084] 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.

[0085] 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.

[0086] Tables I-III below show comparative data for various streams with Table I being a base case at 610 psig GOX production, Table II being an embodiment in which LIN production was maximized with GOX production being at 400 psig, and Table III 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 II or Table III.

TABLE-US-00001 TABLE I 610 psig GOX Flow Pressure Temp 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-00002 TABLE II 400 psig GOX -- LIN Production Flow Pressure Temp 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-00003 TABLE III 400 psig GOX -- GOX Flow Pressure Temp 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 —

[0087] 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.

[0088] 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.

[0089] FIG. 3 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.

[0090] 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.

[0091] 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.

[0092] As used herein, if the pressure of a stream is kept substantially constant, that is intended to mean that the pressure set point for the process equipment that affects said stream pressure remains unchanged. Normal variance due to typical process conditions is meant to be encompassed by this term.

[0093] 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.

[0094] The singular forms “a”, “an” and “the” include plural referents, unless the context clearly dictates otherwise.

[0095] “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.

[0096] “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.

[0097] 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.

[0098] 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.

[0099] 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.