PLATE FIN HEAT EXCHANGER ASSEMBLY

Abstract

A plate fin heat exchanger assembly (S) for a cryogenic air separation unit, comprising: a heat exchanger having at least two cryogenic liquid inlets (B,C) at least two cryogenic liquid outlets (B,C), at least one nitrogen-rich stream inlet (D) at a first end of the heat exchanger and at least one nitrogen-rich stream outlet at a second end of the heat exchanger, the heat exchanger configured to receive a flow of at least one nitrogen-rich stream (WN,LPGAN) of the air separation unit at the at least one nitrogen-rich stream inlet and separate flows of at least two cryogenic liquids (LOX,LIN,LR) at the at least two cryogenic liquid inlets; wherein the inlet of the first of the cryogenic liquids is closer to the first end than the outlet of the second of the cryogenic liquids.

Claims

1-12. (canceled)

13. A plate fin heat exchanger assembly (S) for a cryogenic air separation unit, comprising: a heat exchanger having at least two cryogenic liquid inlets (B,C) at least two cryogenic liquid outlets (B,C), at least one nitrogen-rich stream inlet (D) at a first end of the heat exchanger, and at least one nitrogen-rich stream outlet at a second end of the heat exchanger, the heat exchanger configured to receive a flow of at least one nitrogen-rich stream (WN,LPGAN) from the air separation unit at the at least one nitrogen-rich stream inlet and separate flows of at least two cryogenic liquids (LOX,LIN,LR) at the at least two cryogenic liquid inlets; the heat exchanger configured to receive a first flow of at least one cryogenic liquid of an air separation unit and further configured to channel the first flow of the at least one cryogenic liquid in a cross flow orientation from a first of the cryogenic liquid inlets to a first of the cryogenic liquid outlets; the heat exchanger configured to receive a second flow of at least one cryogenic liquid of an air separation unit and for channeling the second flow of the at least one cryogenic liquid from a second of the cryogenic liquid inlets to a second of the cryogenic liquid outlets; the heat exchanger configured to receive a portion of the flow of the at least one nitrogen-rich stream and for channeling a portion of the flow of the at least one nitrogen-rich stream in a first direction within the first heat exchange segment from the at least one nitrogen-rich stream inlet to the at least one nitrogen-rich stream outlet to sub-cool both the first flow of the at least one cryogenic liquid and the second flow of the at least one cryogenic liquid, wherein the first direction is generally orthogonal to the first flow of the at least one cryogenic liquid and wherein the inlet of the first of the cryogenic liquids is closer to the first end than the outlet of the second of the cryogenic liquids.

14. The plate fin heat exchanger assembly of claim 13, wherein the first direction is generally orthogonal to the second flow of the at least one cryogenic liquid.

15. The plate fin heat exchanger assembly of claim 13, wherein the outlet and/or inlet (C) of the first of the cryogenic liquids (LOX) is closer to the first end than any cryogenic liquid inlet and/or cryogenic liquid outlet (A,B) of the heat exchanger.

16. The plate fin heat exchanger assembly of claim 15, comprising a third cryogenic liquid inlet, a third cryogenic outlet, the first heat exchanger configured to receive a third flow of at least one cryogenic liquid of an air separation unit and for channeling the third flow of the at least one cryogenic liquid from a third of the cryogenic liquid inlets to a third of the cryogenic liquid outlets, wherein the inlet of the first of the cryogenic liquids is closer to the first end than the outlet of the third of the cryogenic liquids.

17. The plate fin heat exchanger assembly of claim 13, wherein the first flow of at least one cryogenic liquid comprises a flow of liquid oxygen (LOX) from the lower pressure column.

18. The plate fin heat exchanger assembly of claim 13, wherein the second flow of at least one cryogenic liquid comprises a flow of bottom liquid from the higher pressure column (LR) or a flow of nitrogen enriched liquid (LL) from the higher pressure column or a flow of liquefied air (AL) or a flow of liquefied nitrogen (LIN).

19. The plate fin heat exchanger assembly of claim 18, wherein the second or third cryogenic liquid inlet is closer to the second end than any other cryogenic liquid inlet or outlet.

20. The plate fin heat exchanger assembly of claim 13, wherein the flow of at least one nitrogen-rich stream in the first direction is a flow in an upward or downward orientation.

21. The plate fin heat exchanger assembly of claim 13, wherein the cryogenic liquid inlets are disposed vertically below the corresponding cryogenic liquid outlets such that the overall flow of the cryogenic liquids is in an upward flow orientation if the at least nitrogen-rich stream is a flow in a downward orientation.

22. The plate fin heat exchanger assembly of claim 13, wherein the cryogenic liquid inlets are above the corresponding liquid outlets if the nitrogen-rich stream flow is in an upward direction.

23. A process for cooling and warming streams from a cryogenic air separation unit in a plate fin heat exchanger assembly, the process comprising the steps of: providing the plate fin heat exchanger assembly of claim 13; warming at least one nitrogen-rich stream, selected from the group comprising of a waste nitrogen stream, a product nitrogen stream, a third nitrogen-rich return stream from the column system, and combinations thereof, by passing through the heat exchanger assembly from the nitrogen enriched fluid inlet to the nitrogen enriched fluid outlet; cooling a liquid oxygen stream (LOX) by passing from the first cryogenic liquid inlet to the first cryogenic liquid outlet; and cooling another cryogenic stream by passing from the second cryogenic liquid inlet to the second cryogenic liquid outlet, such that the liquid oxygen stream is cooled exclusively in the region of the heat exchanger proximate to the first end.

24. The process according to claim 23, wherein the liquid oxygen stream (LOX) is cooled to a temperature at most 15° C. above the temperature at which the at least one nitrogen rich stream (WN, LPGAN)enters the nitrogen-rich stream inlet.

25. The process according to claim 24, wherein the liquid oxygen stream (LOX) is cooled to a temperature at most 10° C. above the temperature at which the at least one nitrogen rich stream (WN, LPGAN)enters the nitrogen-rich stream inlet.

Description

[0039] The invention will now be described in greater detail with reference to FIGS. 2 and 3 which represent cross-sections of the plate fin heat exchanger used as a subcooler.

[0040] FIG. 2 is to be compared with FIG. 1 showing the same fluids but with the flow arrangement of the present invention.

[0041] FIGS. 2A and 2B show cross-sections of the sections of a subcooler arrangement according to the invention devoted to cooling the liquid streams. Each of the figures shows the arrangements for the layers devoted to cooling, each being used for two cooling streams, each layer for a stream or stream to be cooled being separated from the next layer for a stream or streams to be cooled by a layer for a stream to be warmed.

[0042] The stream C in this case is cooled in two different layers, this being an optional feature.

[0043] In this way heat is transferred from one layer to another. The stream D enters the top of the subcooler (crossed out arrow D) through an inlet, flows straight down through the subcooler and emerges in a warmed state from the warm end of the subcooler via an exit. Stream D is the cold stream, waste nitrogen, to which heat is transferred and comes from the low pressure column of an air separation unit. Streams A and B are liquid nitrogen and lean liquid from the higher pressure column, and stream C is liquid oxygen from the bottom of a low pressure column.

[0044] In FIG. 2A, liquid oxygen C enters the subcooling exchanger at the colder half of the subcooler and exits the exchanger at the cold end. Here it is the liquid oxygen C which is cooled exclusively in the coldest part of the subcooler. The liquid oxygen flows at substantially at right angles to the gaseous nitrogen flows and no liquid inlet is closer to the cold end of the subcooler and no liquid outlet is closer to the cold end of the subcooler.

[0045] The liquid oxygen stream is cooled to a temperature at most 15° C., preferably at most 10° C., above the temperature at which the at least one nitrogen rich stream enters the nitrogen-rich stream inlet

[0046] Lean liquid LL from the top of the higher pressure column is sent to the warm end of the subcooler in the same layer as liquid C and is removed in a cooled state from the middle of the subcooler.

[0047] In FIG. 3A, liquid oxygen C enters the subcooling exchanger at the colder half of the subcooler and exits the exchanger at the cold end. Here it is the liquid oxygen C which is cooled exclusively in the coldest part of the subcooler. The liquid oxygen flows at substantially at right angles to the gaseous nitrogen flows and no liquid inlet is closer to the cold end of the subcooler and no liquid outlet is closer to the cold end of the subcooler.

[0048] Liquid nitrogen LIN from the top of the higher pressure column is sent to the warm end of the subcooler in the same layer as liquid C and is removed in a cooled state from the middle of the subcooler.

[0049] The LOX will not necessarily be colder than in the prior art process, but may be so if the first section of the exchanger performs better than expected. As such, a partial bypass of LOX is installed (not shown) in order to control the temperature with this configuration. The LIN and LL will be warmer than in the prior art, as the WN and GAN have been warmed by the LOX. However the impact the oxygen recovery is minimal. Either the LIN and LL temperatures are only slightly changed or the LR and AL temperatures may be colder than hi the prior art, which has a compensating effect, depending on the ratio of the different warm and cold streams in the exchanger.

[0050] FIG. 3 shows a subcooler according the invention with two warming gases and four cooling liquids.

[0051] The subcooler comprises three regions 1,2,3, the region 1 operating below a temperature T1, the region 3 operating at a temperature T2, greater than T1 and region 2 operating between T1 and T2.

[0052] The warming gases are waste nitrogen WN and low pressure gaseous nitrogen LPGAN, both from the lower pressure column of the air separation unit.

[0053] The cooling streams are liquid oxygen LOX from the lower pressure column, liquid nitrogen LIN from the top of the higher pressure column, lean liquid LL from the top of the higher pressure column, containing more oxygen than liquid LIN and liquefied air AL taken from the higher pressure column, a conduit or a turbine outlet.

[0054] Here once again it is the liquid oxygen which is cooled exclusively in the coldest part 1 of the subcooler. The liquid oxygen flows at substantially at right angles to the gaseous nitrogen flows and no liquid inlet is closer to the cold end of the subcooler and no liquid outlet is closer to the cold end of the subcooler. The liquid oxygen stream is cooled to a temperature at most 15° C., preferably at most 10° C., above the temperature at which the at least one nitrogen rich stream enters the nitrogen-rich stream inlet

[0055] Liquefied air AL is sent exclusively to the warm end of the subcooler and removed exclusively from a section 3 operating at the warmest temperatures. Rich liquid LR taken from the higher pressure column sump is sent exclusively to the warm end of the subcooler and removed exclusively from a section 3 operating at the warmest temperatures.

[0056] Lean liquid LL is sent to central region 2 of the subcooler and removed from that region operating between temperatures T1 and T2. Liquid LIN taken from the higher pressure column sump is sent exclusively to the central region 2 of the subcooler and removed exclusively from that region operating between temperatures T1 and T2.