Removable Flow Diversion Baffles for Liquefied Natural Gas Heat Exchangers

Abstract

The invention relates to liquefied natural gas. Particularly, the invention relates to indirect heat exchange means utilized in liquefaction processes. Specifically, the invention relates to the utilization of flow diversion plates within heat exchangers.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority benefit under 35 U.S.C. Section 119(e) to U.S. Provisional Patent Ser. No. 61/219,640 filed on Jun. 23, 2009 the entire disclosure of which is incorporated herein by reference.

FIELD OF THE INVENTION

The invention relates to liquefied natural gas. Particularly, the invention relates to indirect heat exchange means utilized in liquefaction processes. Specifically, the invention relates to the utilization of flow diversion baffle plates within heat exchangers.

BACKGROUND OF THE INVENTION

The cryogenic liquefaction of natural gas is routinely practiced as a means of converting natural gas into a more convenient form for transportation and storage. Such liquefaction reduces the volume of the natural gas by about 600-fold and results in a product which can be stored and transported at near atmospheric pressure.

Natural gas is frequently transported by pipeline from the supply source to a distant market. It is desirable to operate the pipeline under a substantially constant and high load factor but often the deliverability or capacity of the pipeline will exceed demand while at other times the demand may exceed the deliverability of the pipeline. In order to shave off the peaks where demand exceeds supply or the valleys when supply exceeds demand, it is desirable to store the excess gas in such a manner that it can be delivered when demand exceeds supply. Such practice allows future demand peaks to be met with material from storage. One practical means for doing this is to convert the gas to a liquefied state for storage and to then vaporize the liquid as demand requires.

The liquefaction of natural gas is of even greater importance when transporting gas from a supply source which is separated by great distances from the candidate market and a pipeline either is not available or is impractical. This is particularly true where transport must be made by ocean-going vessels. Ship transportation in the gaseous state is generally not practical because appreciable pressurization is required to significantly reduce the specific volume of the gas. Such pressurization requires the use of more expensive storage containers.

In order to store and transport natural gas in the liquid state; the natural gas is preferably cooled to −240° F. to −260° F. where the liquefied natural gas (LNG) possesses a near-atmospheric vapor pressure. Numerous systems exist in the prior art for the liquefaction of natural gas in which the gas is liquefied by sequentially passing the gas at an elevated pressure through a plurality of cooling stages whereupon the gas is cooled to successively lower temperatures until the liquefaction temperature is reached. Cooling is generally accomplished by indirect heat exchange with one or more refrigerants such as propane, propylene, ethane, ethylene, methane, nitrogen, carbon dioxide, or combinations of the preceding refrigerants (e.g., mixed refrigerant systems).

Core-in-shell heat exchangers containing plate-fin heat exchangers (also known as brazed aluminum heat exchangers), are often utilized for such indirect heat exchange in the liquefaction process. It is often necessary for various reasons to alter the shellside refrigerant flow direction within core-in-shell heat exchangers using flow diversion plates. For example, flow diversion baffles are installed inside core-in-shell heat exchangers to direct incoming refrigerant in a downward direction and to meet process velocity specifications. However, in conventional core-in-shell heat exchangers flow diversion plates are permanently affixed to the inside of the exchanger shell. These non-removable flow diversion plates severely complicate inspection and repair access to the heat exchanger found inside the pressure vessel. Furthermore, the inability to remove the flow diversion plate creates a serious safety hazard for operators and employees performing maintenance and/or repairs inside the core-in-shell heat exchanger.

SUMMARY OF THE INVENTION

In one embodiment of the present invention, a heat exchanger includes: a pressure-containing shell defining an internal volume, wherein the shell further includes an interior radius and an exterior radius; at least one brazed aluminum heat exchanger core disposed in the internal volume; a plate strip, wherein the radius of plate strip is identical to the interior radius of the shell, wherein the plate strip is welded to the interior radius of the shell, said plate strip further includes a bolt pattern; a removable flow diversion plate, wherein the flow diversion plate includes a bolt pattern identical to the bolt pattern of the plate strip; a series of nuts and bolts, wherein the bolts are placed through the of bolt pattern of the plate strip and the flow diversion plate and the nuts are used to secure the bolts in plate.

In another embodiment of the present invention, a method of transferring heat from a refrigerant to a cooled fluid, the method includes: introducing the refrigerant into an internal volume defined within a shell, the internal volume having a height-to-width ratio greater than 1; containing a removable flow diversion plate attached to a plate strip to divert the flow of the cooled fluid within the internal volume of the shell, wherein the radius of plate strip is identical to the interior radius of the shell, wherein the plate strip is welded to the interior radius of the shell, the plate strip further includes a bolt pattern, wherein the removable flow diversion plate includes a bolt pattern identical to the bolt pattern of the plate strip, wherein a series of bolts are placed through the of bolt pattern of the plate strip and the removable flow diversion plate and a series of nuts are used to secure the bolts in plate; introducing the cooled fluid into a plate-fin core disposed within the internal volume of the shell; transferring heat from the cooled fluid in the core to the refrigerant in the shell via indirect heat exchange; and withdrawing a stream of vapor refrigerant from dedicated vapor outlet nozzles defined in the shell, the core defining a plurality of shell-side flow passageways for receiving said refrigerant.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention, together with further advantages thereof, may best be understood by reference to the following description taken in conjunction with the accompanying drawings in which:

FIG. 1 illustrates the removable flow diversion plate of this invention.

DETAILED DESCRIPTION OF THE INVENTION

Reference will now be made in detail to embodiments of the invention, one or more examples of which are illustrated in the accompanying drawings. Each example is provided by way of explanation of the invention, not as a limitation of the invention. It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the scope or spirit of the invention. For instances, features illustrated or described as part of one embodiment can be used on another embodiment to yield a still further embodiment. Thus, it is intended that the present invention cover such modifications and variations that come within the scope of the appended claims and their equivalents.

Brazed-aluminum plate-fin heat exchangers, often referred to as plate-fin cores, plate-fin exchangers, plate-fin ecomonizers, plate-fin battery assemblies, or cold boxes, are used in process industries, particularly in gas separation processes at cryogenic temperatures. The brazed-aluminum plate fin heat exchanger is similar to the gasketed plate & frame heat exchanger with the exception that the brazed-aluminum plate-fin heat exchanger does not require gaskets, tightening bolts, frame, or carrying and guide bars. The brazed aluminum heat exchanger consists of heat transfer plates, parting sheets, cap sheets, spacer bars, end bars, and inlet and outlet headers, all constructed of various aluminum alloys. These heat exchangers are composed of a stack of square or rectangular, aluminum heat transfer fin plates stamped with a plain, serrated, perforated, or wave (herringbone) pattern designed to enhance heat transfer. Flat, aluminum parting sheets are located between the stamped heat transfer fin plates to create individual flow passages. Flat, aluminum cap sheets significantly thicker than the aluminum parting sheets, are located at the top and bottom of the plate stack. This completed core assembly is placed in a vacuum furnace and heated until all of the plates are securely brazed to one another. Flow passages are formed by adjacent plates so that the two streams exchange heat while passing through alternate channels, often referred to as cooling zones or stages. The fluid flowing through each passage fills the passage between the flat sheets which separate the passages and the space above and below the corrugated fin in each passage. The ends of the flow channels terminate into headers, which are necessary to ensure good flow distribution into the brazed aluminum heat exchanger, and are also used to change the direction of the fluid entering and exiting the brazed aluminum heat exchanger as required for external piping connections.

The length, width, height, and number of stacked plates found within in a plate fin core assembly is determined by the necessary process thermal duty, as well as the process and refrigerant flow rates, physical properties of both fluids, and pressure drop and temperature requirements. The pattern stamped into the heat transfer fins promotes turbulence and also supports the plates against differential pressure deformation. The stacks of plates are brazed together in a vacuum furnace to form a complete pressure-resistant unit.

Flow diversion plates are often utilized for separating or splitting a stream. Referring to FIG. 1, a removable flow diversion plate 10 is bolted to the interior wall of the shell of the heat exchanger. A bolting plate strip 12 matching the inside radius of an exchanger shell 8, containing a bolting pattern is welded to the inside of exchanger shell 8. Bolting plate strip 12 serves as a permanent bolting strip to hold removable flow diversion plate 10 in place during exchanger operations. In an embodiment, the bolting plate strip is approximately ¾″ thick and approximately 2″ radial width. Removable flow diversion plate 10 has an identical bolt pattern as bolting plate strip 12. In an embodiment, the bolting strip and the removable flow diversion plate are made of the same material. In another embodiment, the bolting strip and the removable flow diversion plate are made of the same material as the exchanger shell.

During heat exchanger operation, removable flow diversion plate 10 is securely attached to bolting strip 12 by a series of nuts and bolts 14 along the bolt pattern. Furthermore, the series of nuts and bolts utilized should be durable enough to ensure the removable flow diversion plate remains in place during exchanger operations. In an embodiment, stud bolts are used to attach the removable flow diversion plate to the welded bolting plate strip. In another embodiment, the removable flow diversion plate will be double-nutted to the welded bolting strip. In a further embodiment, the removable flow diversion plate is double-nutted using heavy hex nuts to ensure the removable flow diversion plate does not loosen during exchanger operations. Furthermore, the series of nuts and bolts utilized to secure removable flow diversion plate in place should be durable enough to withstand cryogenic temperatures. In an embodiment, the series of nuts and bolts are made of austenitic stainless steel. In another embodiment, the series of nuts and bolts are made of ASME SA-320 grade B8.

The preferred forms of the invention described above are to be used as illustration only, and should not be used in a limiting sense to interpret the scope of the present invention. Modifications to the exemplary embodiments, set forth above, could be readily made by those skilled in the art without departing from the spirit of the present invention.

Claims

1. A heat exchanger comprising:

a. a pressure containing shell defining an internal volume, wherein the shell further includes an interior radius and an exterior radius;

b. at least one brazed aluminum plate-fin core disposed in the internal volume;

c. a plate strip, wherein the radius of plate strip is identical to the interior radius of the shell, wherein the plate strip is welded to the interior radius of the shell, said plate strip further includes a bolt pattern;

d. a removable flow diversion plate, wherein the flow diversion plate includes a bolt pattern identical to the bolt pattern of the plate strip; and

e. a fastener means to secure the removable flow diversion plate to the plate strip.

2. The heat exchanger according to claim 1, wherein the fastener means includes at least one nut and at least one bolt.

3. The heat exchanger according to claim 2, wherein at least one bolt is placed through the bolt patter of the plate step and the flow diversion plate and at least one nut is used to secure at least one bolt in place.

4. The heat exchanger according to claim 1, wherein the plate strip is about ¾″ thick and about 2″ radial width.

5. The heat exchanger according to claim 1, wherein the series of nuts and bolts are made of the same material as the shell.

6. The heat exchanger according to claim 1, wherein the series of nuts and bolts are made of austenitic stainless steel.

7. The heat exchanger according to claim 1, wherein the series of nuts and bolts are made of the ASME SA-320 Grade B8 stainless steel.

8. The heat exchanger according to claim 1, wherein the series of bolts are stud bolts.

9. The heat exchanger according to claim 1, wherein the nuts are double-nutted using heavy hex nuts to ensure the removable flow diversion plates are securely attached to the plate strip.

10. The heat exchanger according to claim 1, wherein the internal volume has a height-to-width ratio greater than 1.

11. The heat exchanger according to claim 1, wherein the heat exchanger is a plate-fin heat exchanger.

12. The heat exchanger according to claim 1, wherein the heat exchanger is brazed aluminum heat exchanger.

13. A method of transferring heat from a refrigerant to a cooled fluid, said method comprising:

a. introducing the refrigerant into an internal volume defined within a shell, the internal volume having a height-to-width ration greater than 1;

b. utilizing a removable flow diversion plate attached to a plate strip to divert the flow of the cooled fluid within the internal volume of the shell, wherein the radius of plate strip is identical to the interior radius of the shell, wherein the plate strip is welded to the interior radius of the shell, said plate strip further includes a bolt pattern, wherein the removable flow diversion plate includes a bolt pattern identical to the bolt pattern of the plate strip, wherein a series of bolts are placed through the of bolt pattern of the plate strip and the removable flow diversion plate and a series of nuts are used to secure the bolts in plate;

c. introducing the cooled fluid into a plate-fin core disposed within the internal volume of the shell;

d. transferring heat from the cooled fluid in the core to the refrigerant in the shell via indirect heat exchange; and

e. withdrawing a predominately vapor stream of the refrigerant from dedicated vapor outlet nozzles in the shell, said core defining a plurality of shell-side flow passageways for receiving said refrigerant.

14. The method according to claim 13, wherein the height-to-width ratio being at least about 1.25.

15. The method according to claim 13, step (c) including vaporizing at least a portion of said refrigerant in said shell-side passageways.

16. The method according to claim 13; and (f) maintaining the level of liquid-phase refrigerant said in said shell where at least 50% of the height of the core is submerged in the liquid-phase refrigerant.

17. The method according to claim 13, according to step (f) including maintaining the level of liquid-phase refrigerant said in said shell where at least 75-95% of the height of the core is submerged in the liquid-phase refrigerant.

18. The method according to claim 17, step (a) including introducing said refrigerant into the internal volume at a location above the level of liquid phase refrigerant in the shell.

19. The method according to claim 13, wherein the plate strip is about ¾″ thick and about 2″ radial width.

20. The method according to claim 13, wherein the series of nuts and bolts are made of the same material as the shell.

21. The method according to claim 13, wherein the series of nuts and bolts are made of austenitic stainless steel.

22. The method according to claim 13, wherein the series of nuts and bolts are made of the ASME SA-320 Grade B8 stainless steel.

23. The method according to claim 13, wherein the series of bolts are stud bolts.

24. The method according to claim 12, wherein the nuts are double-nutted using heavy hex nuts to ensure the removable flow diversion plates are securely attached to the plate strip.

25. The method according to claim 13, wherein the internal volume has a height-to-width ratio greater than 1.

26. The method according to claim 13, wherein the heat exchanger is brazed aluminum heat exchanger.