HEAT EXCHANGER AND METHOD FOR HEATING A FRACTURING FLUID

Abstract

A heat exchanger comprises a shell internally divided into a hot fluid vessel and a cold fluid vessel by a pipe retaining plate having a plurality of apertures sealingly retaining a corresponding number of heat pipes, each of which has a hot end in the hot fluid vessel and a cold end in the cold fluid vessel. The hot fluid vessel is internally configured to direct a hot fluid through a porous dispersion plate that distributes the hot fluid amongst the hot ends of the heat pipes. The cold fluid vessel has an internal baffle that defines a serpentine channel that guides a cold fluid through the cold fluid vessel. Fracturing fluid may be heated by streaming flue gas exhausted from an incinerator through the hot fluid vessel while simultaneously streaming the fracturing fluid through the cold fluid vessel.

Description

FIELD OF THE INVENTION

[0001] The present invention relates to a heat exchanger and method for using the heat exchanger to heat a fracturing fluid using flue gas.

BACKGROUND OF THE INVENTION

[0002] Combustion devices such as incinerators used for waste management, power generation and industrial processes typically produce an exhaust stream of hot flue gases. The venting of hot flue gases into the atmosphere is potentially undesirable in that it wastes the thermal energy of the flue gas, and can heat the environment surrounding the combustion device. If instead the waste heat can be extracted from the flue gas before venting, then the energy efficiency of the overall system can be increased by recycling the extracted heat for heating the combustion device or other uses of the heat, while mitigating the environmental impact of the hot flue gas.

[0003] In the prior art, many heat exchangers for extracting waste heat from flue gases, such as "shell and tube" heat exchangers, operate on the principle of streaming the hot flue gas inside a tube, and streaming a cooling medium on the outside of the tube, or vice versa, and relying upon the thermal conductivity of the tube wall to transfer heat directly from the hot flue gas to the cooling medium: for examples, see U.S. Pat. No. 3,960,992; U.S. Pat. No. 4,151,874; U.S. Pat. No. 5,510,087; U.S. Pat. No. 6,142,218; and U.S. Pat. No. 7,036,563. The use of the tube to transfer the hot flue gas or the cooling medium presents potential design problems. The tubes preferably have a high ratio of wall surface area to interior volume to optimize heat transfer from the hot flue gas to the cooling medium. This can be achieved by decreasing the tube diameter, increasing the tube length and selecting a tortuous tube layout. However, such design selections also tend to increase the tube's susceptibility to internal fouling and internal resistance to fluid flow. In order to achieve a desired flow rate through the tubes, either more tubes are required thereby increasing the size and complexity of the heat exchanger, or more pressure is required to urge the fluid through the tubes. If the fluid pressure is increased, however, the tubes must be constructed to withstand such pressures. Although heat exchangers in the prior art fulfill the objective of extracting heat from the hot flue gas, their effectiveness may be limited by practical design considerations.

[0004] Hydraulic fracturing operations involving the injection of fracturing fluid into subterranean formations to propagate rock fractures have become widely adopted in the oil and gas industry. For optimal effectiveness and to prevent freezing of the fracturing fluid in cold weather, the fracturing fluid may be heated before injection into formation. Practically speaking, fracturing operations require relatively large volumes of fracturing fluid to be heated relatively quickly to moderate temperatures of approximately 50° C. prior to injection into the formation.

[0005] Accordingly, there remains a need for a heat exchanger for extracting waste heat from hot flue gases that is effective, efficient, simple to manufacture and use, reliable in operation, and is suited to quickly heating large volumes of fracturing fluid.

SUMMARY OF THE INVENTION

[0006] In one aspect, the present invention provides a heat exchanger for exchanging heat from a hot fluid to a cold fluid. The heat exchanger comprises a shell having a hot fluid inlet, a hot fluid outlet, a cold fluid inlet, and a cold fluid outlet; a pipe retaining plate internally dividing the shell into a hot fluid vessel defining a hot fluid flow path from the hot fluid inlet to the hot fluid outlet, and a cold fluid vessel defining a cold fluid flow path from the cold fluid inlet to the cold fluid outlet; a plurality of spaced-apart heat pipes, each of the heat pipes sealingly retained through a corresponding aperture in the pipe retaining plate, and having a hot end disposed in the hot fluid vessel, and a cold end disposed in the cold fluid vessel; and a porous dispersion plate in the hot fluid vessel for dispersing the hot fluid among the hot ends of the plurality heat pipes. The hot fluid vessel is internally configured so that the hot fluid flow path passes through the porous dispersion plate before passing about the hot ends of the heat pipes and through the hot fluid outlet.

[0007] In one embodiment of the heat exchanger first described above, the heat exchanger comprises a pressure vessel.

[0008] In one embodiment of the heat exchanger first described above, the heat exchanger comprises a vacuum chamber with a vapor port.

[0009] In embodiments of the heat exchanger first described above, the heat exchanger further comprises at least one baffle in the cold fluid vessel and configured to define a serpentine channel for the cold fluid flow path. The serpentine channel may be formed by a baffle oriented substantially perpendicular to the pipe retaining plate. Alternatively, the baffle may be oriented substantially parallel to the pipe retaining plate. The cold ends of the heat pipes may be evenly distributed throughout substantially the entire length of the serpentine channel.

[0010] In one embodiment of the heat exchanger first described above, each heat pipe comprises a sealed tube containing a heat transfer substance that migrates from the hot end to the cold end when the heat transfer substance at the hot end is at a first temperature, and migrates from the cold end to the hot end when the heat transfer substance at the cold end is at a second temperature less than the firs temperature.

[0011] In embodiments of the heat exchanger first described above, the hot fluid inlet and the hot fluid outlet are disposed on opposite ends of the shell, the cold fluid inlet and the cold fluid outlet are disposed on opposite ends of the shell, the hot fluid inlet and the cold fluid inlet are on the same end of the shell, and the hot fluid outlet and the cold fluid outlet are on the same end of the shell.

[0012] In embodiments of the heat exchanger first described above, the hot fluid inlet is adapted for connection to the exhaust of an incinerator and the dispersion plate is adapted for dispersing a flue gas.

[0013] In embodiments of the heat exchanger first described above, the heat pipes have a finned internal surface, a finned external surface, or both. The finned external surface may be adapted for oil emulsion breaking or waste water treatment.

[0014] In another aspect, the present invention provides a method of heating a fluid with flue gas. The method comprises the steps of:

[0015] (a) providing a heat exchanger comprising:

[0016] (i) a shell having a hot fluid inlet, a hot fluid outlet, a cold fluid inlet, and a cold fluid outlet;

[0017] (ii) a pipe retaining plate internally dividing the shell into a hot fluid vessel defining a hot fluid flow path from the hot fluid inlet to the hot fluid outlet, and a cold fluid vessel defining a cold fluid flow path from the cold fluid inlet to the cold fluid outlet;

[0018] (iii) a plurality of spaced-apart heat pipes, each of the heat pipes sealingly retained through a corresponding aperture in the pipe retaining plate, and having a hot end disposed in the hot fluid vessel, and a cold end disposed in the cold fluid vessel;

[0019] (iv) a porous dispersion plate disposed in the hot fluid vessel for dispersing the hot fluid among the hot ends of the plurality heat pipes;

[0020] wherein the hot fluid vessel is internally configured so that the hot fluid flow path passes through the porous dispersion plate before passing about the hot ends of the heat pipes and through the hot fluid outlet;

[0021] (b) using an incinerator to combust a fuel to generate a flue gas exhaust stream;

[0022] (c) streaming the flue gas exhaust stream through the hot fluid flow path from the hot fluid inlet to hot fluid outlet;

[0023] (d) streaming the fluid through the cold fluid flow path from the cold fluid inlet to the cold fluid outlet;

[0024] (e) controlling the flow rate of the flue gas exhaust stream through the hot fluid path, or the flow rate of the fluid stream through the cold fluid path, or both so that the fluid at the cold fluid outlet is heated to a target temperature.

[0025] In one embodiment of the method first described above, the incinerator is a cyclonic incinerator.

[0026] In one embodiment of the method first described above, the fluid is fracturing fluid and the target temperature is at about 50° C. In one embodiment of the method first described above, the fluid is an oil emulsion or a sour fluid.

[0027] In one embodiment of the method first described above, the heat exchanger used has a shell that comprises a vacuum chamber with a vapor port, and a vapor is drawn from the cold fluid vessel through the vapor port. This may be done to create a vacuum in the cold fluid vessel. The vapor drawn through the vapor port may be flowed to the incinerator for combustion.

[0028] In one embodiment of the method first described above, the cold fluid may be flowed through the cold fluid outlet to a vacuum chamber that maintains a vacuum and drawing a vapor may be drawn from the cold fluid in the vacuum chamber. The vapor may be flowed from the vacuum chamber to incinerator for combustion.

BRIEF DESCRIPTION OF THE DRAWINGS

[0029] The invention will now be described by way of an exemplary embodiment with reference to the accompanying simplified, diagrammatic, not-to-scale drawings. In the drawings:

[0030] FIG. 1 is a side elevation view of one embodiment of the heat exchanger of the present invention; and

[0031] FIG. 2 is a top view of one embodiment of the heat exchanger shown in FIG. 1, as viewed along section A-A in FIG. 1.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0032] The present invention relates to a heat exchanger and method for heating a fluid with flue gas. To the extent that the following description is of a specific embodiment or a particular use of the invention, it is intended to be illustrative only, and not limiting of the claimed invention. As will be apparent to those skilled in the art, various modifications, adaptations and variations of the foregoing specific disclosure can be made without departing from the scope of the invention claimed herein.

[0033] When describing the present invention, all terms not defined herein have their common art-recognized meanings. To facilitate understanding of the invention, the following terms are defined.

[0034] As used herein, the term "fluid" refers to any flowable substance that continually deforms under an applied shear stress, and includes substances in the liquid and gas phase. Fluid may include, without limitation, fracturing fluid and flue gas.

[0035] As used herein, the term "hot fluid" refers to the fluid from which heat is being extracted by use of the heat exchanger, and the term "cold fluid" refers to the fluid to which heat is being transferred by use of the heat exchanger. It will be understood that the terms hot fluid and cold fluid are relative terms indicating an initial temperature differential between the fluids which may change as the fluids are processed by the heat exchanger and method, and do not limit the invention to any particular temperature range.

[0036] As used herein, the nominal descriptors "hot" and "cold" in respect to the components of the heat exchanger are provided only to facilitate the description of the invention, and do not import any limitations as to the temperature of the components or the fluids in contact with these components.

[0037] A detailed description of an embodiment of the heat exchanger of the present invention is now provided with reference to FIG. 1, which is a side elevation view of one embodiment of the heat exchanger, and FIG. 2 which is a top view of one embodiment of the heat exchanger, as viewed along section A-A in FIG. 1. In FIG. 1, dashed lines depict elements hidden from view, such as internal elements and elements on the opposite side of the view.

[0038] As seen in FIG. 1, the heat exchanger (10) comprises a shell (12), a pipe retaining plate (14), a plurality of spaced-apart heat pipes (50), and a porous dispersion plate (40).

[0039] The shell (12) provides a fluid-tight walled chamber. The shell (12) is provided with openings for a hot fluid inlet (32), a hot fluid outlet (34), a cold fluid inlet (22) and a cold fluid outlet (24). The inlets (22, 32) and outlets (24, 34) may be placed in a variety of locations on the shell (12). In the embodiment shown in FIGS. 1 and 2, the hot fluid inlet (32) and the cold fluid inlet (22) are both disposed at the same end of the shell (12), while the hot fluid outlet (34) and the cold fluid outlet (24) are both disposed at an opposing end of the shell (12).

[0040] It will be understood that the shell (12) may be constructed of any suitable material and may comprise either a single continuous wall, or be constructed from a plurality of wall elements. In one embodiment, as shown in FIGS. 1 and 2, the shell (12) is a rectangular prismatic vessel. In one embodiment, not shown, the shell (12) is constructed as a pressure vessel (for example, one with a cylindrical wall and domed ends) designed to sustain a net positive pressure exerted by the fluid contained in the vessel. In one embodiment, the shell (12) is constructed as a vacuum chamber to sustain a net negative pressure within the shell (12), and having a vapor port (13) to remove vapor from the cold fluid vessel (20). A rectangular prismatic shell (12) allows for the placement of a plurality of uniform height baffles (26) to direct the cold fluid in a serpentine channel (as described below). Further, a rectangular prismatic shell (12) permits heat pipes (50) of uniform height to be distributed throughout the entire cross-section and height of the cold fluid vessel (20) (as described below).

[0041] The pipe retaining plate (14) divides the inside of the shell (12) into two fluid-tight vessels on either side of the pipe retaining plate (14). On one side, a cold fluid vessel (20) defines a cold fluid flow path from the cold fluid inlet (22) to the cold fluid outlet (24). On the other side, a hot fluid vessel (30) defines a hot fluid flow path for a hot fluid from the hot fluid inlet (32) to the hot fluid outlet (34). The cold fluid inlet (22), cold fluid outlet (24), hot fluid inlet (32) and hot fluid outlet (34) may be adapted with fluid-tight couplings as are well known in the art for connection to fluid supply and discharge lines. It will be understood that the pipe retaining plate (14) may conduct heat between the fluids contained in the hot fluid vessel (30) and the cold fluid vessel (20), but this amount of heat transfer is likely insignificant in comparison to the amount of heat transfer effected by the heat pipes (50).

[0042] The plurality of heat pipes (50) are spaced apart from each other. In one embodiment as shown in FIG. 2, the heat pipes (50) are arranged in an array of evenly spaced rows and columns extending throughout the length and width of the shell (12). Each heat pipe (54) has a hot end (54) disposed in the hot fluid vessel (30) and a cold end (52) disposed in the cold fluid vessel (20). Each of the heat pipes (50) is sealingly retained through a corresponding aperture (16) in the pipe retaining plate (14). In one embodiment, the heat pipes (50) are sealingly retained through the apertures (16) by using a hammer union. A bottom sub of the hammer union is sealingly welded to the bottom of the pipe retaining plate (14). On the top side of the pipe retaining plate (14), a compression nut is used to connect a top sub to the bottom sub. The heat pipe (60) is passed through the two subs of the hammer union. A circumferential weld between the exterior wall of the heat pipe (50) and the top sub is used to provide a fluid tight barrier between the cold fluid vessel (20) and the hot fluid vessel (30). As will be apparent to those skilled in the art, other types of suitable connections may be used so that the aperture (16) sealingly retains the heat pipe (50) that passes through it.

[0043] The plurality of heat pipes (50) transfer heat from their hot ends (54) to their cold ends (52). In one embodiment, each heat pipe (50) comprises a sealed tube containing a heat transfer substance that may migrate from the hot end (54) to the cold end (52) when the heat transfer substance is at a higher temperature, and migrates from the cold end (52) to the hot end (54) when the heat transfer substance is at a lower temperature, as is well known in the art. The tube wall is preferably constructed from a material that has both high thermal conductivity and sufficient strength to contain the heat transfer substance under pressure. Non-limiting examples of suitable materials may include steel, copper, aluminum or other metals or alloys thereof. Non-limiting examples of the heat transfer substance include water, alcohol, acetone, sodium or mercury. Suitable heat pipes (50) are commercially available, such as those manufactured by Econotherm® (United Kingdom).

[0044] In one embodiment, the heat transfer substance is introduced into at least a partial vacuum so as to eliminate or reduce non-heat transfer gases in the tube.

[0045] In one embodiment, the heat transfer substance and the internal pressure of the pipe are selected so that the heat transfer substance is in the liquid phase at the design temperature of the cold end (52), and in a gas phase at the design temperature of the hot end (54). At the hot end (54), the heat transfer substance vaporizes and migrates to the cold end (52), where it will condense and migrate back to the hot end (54) so that it can be re-vaporized. Thus, the heat pipe (50) uses both thermal conductivity and the heat of phase transition of the heat transfer substance to transfer heat from the hot end (54) to the cold end (52).

[0046] In one embodiment, the migration of the heat transfer substance in the liquid phase from the cold end (52) to the hot end (54) is gravity-assisted by disposing the heat tube vertically with the cold end (52) above the hot end (54). In one embodiment, the migration of the heat transfer substance in the liquid phase from the cold end (52) to the hot end (54) is assisted by an internal wicking element (not shown).

[0047] In one embodiment, the heat pipes (50) may have a finned external surface, a finned internal surface, or both, to provide additional surface area on the heat pipe (50) available to conduct heat to and from the heat transfer substance. In one embodiment (not shown), the finned external surface is adapted for heavy oil emulsion breaking or waste water treatment.

[0048] In the embodiment shown in FIGS. 1 and 2, the porous dispersion plate (40) is disposed in the hot fluid vessel (30) between the hot fluid inlet (32) and hot ends (54) of the plurality of heat pipes (50). The porous dispersion plate (40) functions to disperse the hot fluid more evenly among the hot ends (54) of the plurality heat pipes (50) by diffusing the hot fluid stream from the hot fluid inlet (32) into a plurality of smaller streams leading to the hot ends (54) of the heat pipes (50). In one embodiment, the porous dispersion plate (40) comprises a plate having a plurality of punched holes. The dimensions and spacing of the punched holes are selected to provide an even distribution of the hot fluid over the hot ends (54) of the plurality of heat pipes (50). The porosity of the dispersion plate (40) can be selected to affect the flow rate of hot fluid in the hot fluid vessel (40) to suit a particular application.

[0049] The hot fluid vessel (30) is internally configured so that the hot fluid flow path passes through the porous dispersion plate (40) before passing about the hot ends of the heat pipes (54) and through the hot fluid outlet (34). In one embodiment as shown in FIG. 2, a deflector (36) directs the hot fluid entering the hot fluid vessel (30) from the hot fluid inlet (32) in a downward direction beneath the porous dispersion plate (40), where a plurality of directional vanes (38) direct the hot fluid towards the porous dispersion plate (40). In this manner, the hot fluid is forced to diffuse evenly among the plurality of hot ends (54) of the heat pipes (50). It will be appreciated that if the flow rate of the hot fluid is sufficiently high, the temperature of the hot fluid will be fairly even among the hot ends (54) of the heat pipes (50) even though some of the heat pipes (50) may be more distal than others to the hot fluid inlet (32).

[0050] As will be appreciated by persons skilled in the art, if the dimension of the cold fluid vessel (20) is relatively large compared to the dimension of the cold fluid inlet (22), the cold fluid flow in the cold fluid vessel (20) may have regions in which the cold fluid moves at lower velocities or in a circulation pattern that is detrimental to the efficiency of the heat exchanger. To address this effect, in one embodiment as shown in FIG. 2, the cold fluid vessel (20) has a plurality of baffles (26) configured to direct the cold fluid flow path in a serpentine channel. The serpentine channel directs the cold fluid past the cold ends (52) of the heat pipes (50) in orderly succession and to ensure that the cold fluid flows in the immediate vicinity of each of the cold ends (52) of the heat pipes (50). In one embodiment as shown in FIG. 2, the serpentine flow path is created by a plurality of baffle plates (26) which are substantially perpendicular to the pipe retaining plate, thus having segments that overlap horizontally--that is, in a plane substantially parallel to the pipe retaining plate (14). The general flow path of the cold fluid is noted with the arrow-headed lines. In one embodiment, the cold ends (52) of the heat pipes (50) are evenly distributed throughout substantially the entire length of the serpentine channel. In another embodiment (not shown), the serpentine flow path has segments that overlap vertically--that is, in a plane perpendicular to the pipe retaining plate (14). In an alternative embodiment, the serpentine flow path is created by a plurality of baffle plates (26) which are substantially parallel to the pipe retaining plate, thus having segments that overlap vertically--that is, in a series of planes each of which is substantially parallel to the pipe retaining plate (14).

[0051] The operation of the heat exchanger (10) and an embodiment of the claimed method is now illustrated by its use to heat a fracturing fluid with the heat of a flue gas exhausted from an incinerator, but it will be understood that the hot fluid may comprise any suitable heated fluid.

[0052] The heat exchanger (10) is set up as follows. The hot fluid inlet (32) is connected to the flue gas exhaust stream of the incinerator. In one embodiment, the incinerator is a cyclonic incinerator such as one described in U.S. Patent Application Publication number 2010/0242812 A1. The hot fluid outlet (34) may be connected to a flue gas discharge line. A positive pressure differential between the hot fluid inlet (32) and the hot fluid outlet (34) urges the hot flue gas from the hot fluid inlet (32) to the hot fluid outlet (34), thereby streaming the hot flue gas through the hot fluid flow path. The cold fluid inlet (22) is connected to a fracturing fluid supply line. The cold fluid outlet (24) is connected to a fracturing fluid discharge line. A positive pressure differential between the cold fluid inlet (22) and the cold fluid outlet (24) urges the fracturing fluid from the cold fluid inlet (22) to the cold fluid outlet (24), thereby streaming the fracturing fluid through the cold fluid flow path simultaneously as the hot flue gas streams through the hot fluid flow path. The positive pressure differential may be created by pumping the fracturing fluid through the cold fluid inlet (22). It will be understood that the temperature of the flue gas at the hot fluid inlet (32) is higher than the temperature of the fracturing fluid at the cold fluid inlet (22).

[0053] In the hot fluid vessel (30), the deflector (36) directs the flow of hot flue gas in a downward direction below the hot ends (54) of the heat pipes (50). The directional vanes (38) direct the flow of hot flue gas towards the dispersion plate (40). The openings of the dispersion plate (40) evenly diffuse the hot flue gas amongst the hot ends (54) of the heat pipes (50). In the cold fluid vessel (20), the baffles (26) direct the flow of fracturing fluid in a serpentine channel through the entire length and width of the cold fluid vessel (20). As the fracturing fluid flows through the cold fluid vessel (20), the fracturing fluid comes into contact with the cold ends (52) of the heat pipes (50) in succession.

[0054] The walls of the heat pipes (50) at the hot ends (54) conduct heat from the hot flue gas in the hot fluid vessel (30) to the heat transfer substance in the heat pipes (50). Each of the heat pipes (50) uses both thermal conductivity and the heat of phase transition of an internal heat transfer substance to transfer heat from the hot end (54) to the cold end (52). The walls of the heat pipes (50) at the cold ends (52) conduct heat to the fracturing fluid in the cold fluid vessel (20). This heat transfer from the hot flue gas to the fracturing fluid continuously repeats so long as flue gas and fracturing fluid are flowed through the hot fluid inlet (32) and the cold fluid inlet (22), respectively. The cooled flue gas exits the heat exchanger (10) through the hot fluid outlet (34), where it can be used for other purposes such as in a gas-to-air exchanger for a bottoming cycle of a combined heat recovery process for auxiliary heating or for power generation, or for venting to the atmosphere.

[0055] One or more of the flow rate of the flue gas or the fracturing fluid may be controlled to achieve a target temperature of the fracturing fluid cold fluid outlet (24). For example, a pump or restrictor may be used to control the flow rate of the fracturing fluid in the cold fluid vessel (20) or of the hot flue gas in the hot fluid vessel (30) so that fracturing fluid has a temperature of about 50° C. at the cold fluid outlet (24).

[0056] In addition to heating fracturing fluid, the heat exchanger (10) may also be used to enhance the efficiency of breaking oil emulsions, and stripping hydrogen sulfide from sour fluids produced during hydrocarbon extraction operations. In these applications, the cold fluid--being the oil emulsion or the sour fluid--is streamed through the cold fluid vessel (20). The rates of heat transfer and, as the case may be, oil separation or hydrogen sulfide stripping, may be enhanced by creating a vacuum in the cold fluid vessel (20) by removing gas through the vapor port (13). For example, such a vacuum may be created by supplying the cold fluid at a rate less than that required to completely fill the cold fluid vessel (20) and applying a suction at the vapor port (13) to evacuate any vaporized cold fluid in the cold fluid vessel (20). Lowering the total gas pressure in the cold fluid vessel (20) will depress the boiling point of the cold fluid, thus lowering the amount of heat transfer required to convert some of the cold fluid to the vapor phase so that it can be drawn through the vapor port (13). In the case of sour fluids, lowering the total gas pressure in the cold fluid vessel (20) will further encourage the liberation of hydrogen sulfide from the sour fluid by decreasing the solubility of the hydrogen sulfide in the sour fluid, beyond the decrease in solubility that would be achieved by only heating the sour fluid. The liberated hydrogen sulfide gas can be drawn through the vapor port (13) so that it can either be flared, or flowed to an incinerator for combustion to enhance the total efficiency of the stripping operation.

[0057] In an alternative embodiment (not shown), a separate vacuum chamber may be connected in line with the cold fluid vessel such that a vacuum inlet of the vacuum chamber is connected to the cold fluid outlet (24). A suction can be applied to the vacuum chamber to enhance the efficiency of breaking oil emulsions, and stripping hydrogen sulfide from sour fluids produced during hydrocarbon extraction operations, as described above, without having to provide a shell (12) that can withstand negative pressure. In like manner, the liberated gas in the vacuum chamber can be either liberated or flowed to an incinerator for combustion to enhance the total efficiency of the stripping operation.

[0058] It will be understood that the heat exchanger (10) can be used in the reverse configuration by flowing the hot fluid rather than the cold fluid through the cold fluid vessel (20), and flowing the cold fluid rather than the hot fluid through the hot fluid vessel (30). Accordingly, the internal features of the cold fluid vessel (20) and the hot fluid vessel (30) such as the layout of the heat pipes (50), the baffles elements (26, 36, 38) can be transposed between the hot fluid vessel (30) and the cold fluid vessel (20).

[0059] Although the present invention has been described with reference to specific embodiments, such embodiments are intended to be illustrative only and not limit the scope of the claims. The scope of the invention extends to all modifications, equivalents, and alternatives falling within the scope of the invention as defined by the appended claims.

Claims

1. A heat exchanger for exchanging heat from a hot fluid to a cold fluid, the heat exchanger comprising: (a) a shell having a hot fluid inlet, a hot fluid outlet, a cold fluid inlet, and a cold fluid outlet; (b) a pipe retaining plate internally dividing the shell into a hot fluid vessel defining a hot fluid flow path from the hot fluid inlet to the hot fluid outlet, and a cold fluid vessel defining a cold fluid flow path from the cold fluid inlet to the cold fluid outlet; (c) a plurality of spaced-apart heat pipes, each of the heat pipes seemingly retained through a corresponding aperture in the pipe retaining plate, and having a hot end disposed in the hot fluid vessel, and a cold end disposed in the cold fluid vessel; (d) a porous dispersion plate in the hot fluid vessel disposed between the hot fluid inlet and hot ends of the plurality of heat pipes for dispersing the hot fluid evenly among the hot ends of the plurality heat pipes; wherein the hot fluid vessel is internally configured so that the hot fluid flow path passes through the porous dispersion plate before passing about the hot ends of the heat pipes and through the hot fluid outlet.

2. The heat exchanger of claim 1 wherein the shell comprises a pressure vessel.

3. The heat exchanger of claim 1 wherein the shell comprises a vacuum chamber with a vacuum port.

4. The heat exchanger of claim 1 wherein the shell is substantially rectangular prismatic or cylindrical in shape.

5. The heat exchanger of claim 1 further comprising at least one baffle in the cold fluid vessel and configured to define a serpentine channel for the cold fluid flow path.

6-8. (canceled)

9. The heat exchanger of claim 1 wherein each heat pipe comprises a sealed tube containing a heat transfer substance that migrates from the hot end to the cold end when the heat transfer substance is at a higher temperature, and migrates from the cold end to the hot end when the heat transfer substance is at a lower temperature.

10-13. (canceled)

14. The heat exchanger of claim 1 wherein the hot fluid inlet is adapted for connection to the exhaust of an incinerator.

15. The heat exchanger of claim 1 wherein the dispersion plate is adapted for dispersing a flue gas.

16. The heat exchanger of claim 1 wherein the heat pipes have a finned internal surface, a finned external surface, or both.

17. The heat exchanger of claim 1 wherein the heat pipes have a finned external surface adapted for oil emulsion breaking or waste water treatment.

18. A method of using the heat exchanger of claim 1 to heat a fluid with flue gas, the method comprising the continuous and simultaneous steps of: (a) using an incinerator to combust a fuel to generate a flue gas exhaust stream; (b) directing the flue gas exhaust stream through the hot fluid inlet; (c) pumping a fluid stream through the cold fluid inlet; and (d) controlling the flow rate of the flue gas exhaust stream, the fluid stream, or both so that the fluid at the cold fluid outlet is heated to a target temperature.

19. The method of claim 18 wherein the incinerator is a cyclonic incinerator.

20. The method of claim 18 wherein the fluid is fracturing fluid and the target temperature is at about 50.degree. C.

21-22. (canceled)

23. The method of claim 18 further comprising the continuous and simultaneous step of drawing a vapor from the cold fluid vessel through a vapor port.

24. The method of claim 23 wherein the vapor is drawn through the vapor port to create a vacuum in the cold fluid vessel.

25. The method of claim 23 further comprising the step of flowing the vapor from the vapor port to the incinerator for combustion.

26. The method of claim 18 further comprising the steps of flowing the cold fluid through the cold fluid outlet to a vacuum chamber and drawing a vapor from the cold fluid.

27. The method of claim 26 wherein the vacuum chamber is maintained under a vacuum.

28. The method of claim 26 further comprising the step of flowing the vapor from the vacuum chamber to the incinerator for combustion.

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