JACKETED FIRETUBE SYSTEM FOR A PROCESS VESSEL
A jacketed firetube system for use in a process vessel such as a heater or heater/treater has a jacket which extends along the firetube, at a flame inlet end. The jacket can be external to the firetube or internal to the firetube. A heat transfer fluid is circulated along the firetube between the jacket and the firetube for recovering heat from the firetube and reducing the firetube's temperature. The recovered heat is reintroduced into the system.
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This application claims the benefit of U.S. provisional application 61/434,258, filed Jan. 19, 2011, the entirety of which is incorporated herein by reference.
FIELD OF THE INVENTIONEmbodiments of the invention relate to firetubes for use in process vessels, such as heaters or heater/treaters used in the oil and gas industry, and more particularly, to apparatus and systems for maximizing heat recovery from the firetube and for minimizing fouling and localized overheating.
BACKGROUND OF THE INVENTIONIt is known to heat process fluids in a variety of vessels, such as ASME code process vessels, atmospheric bath heaters and tanks. Generally a “U” tube heat exchanger is fit within the process vessel. Heat is transferred from the heat exchanger to the process fluids therein for heating the process fluids as part of the handling and refining operation.
In the oilfield, U-tube heat exchangers or U-shaped “firetubes” are common for use in separation vessels such as heater-treaters and free-water knockout vessels and in line heaters and tanks. Traditionally, the firetube, generally made of one or more sections of round, steel pipe, is heated by a burner which is connected to an inlet end of the firetube and discharges flame and exhaust gases to the firetube for passage therethrough. A vent or exhaust stack at an outlet end of the firetube discharges heat-depleted exhaust gases therefrom. Any heat remaining in the exhaust gases is typically lost to the exhaust stack.
In a direct-fired vessel, the firetube is immersed in process fluid contained in the vessel. An external surface of the firetube is in direct contact with the process fluid for effecting the heat transfer thereto. Heat is transferred from the hot gases passing through in the firetube by transfer through the firetube's wall and directly to the process fluid.
Conventional firetubes are built in a “U”-shape, having the burner end and the exhaust stack end fit at a common wall. The “U”-shape extends into the vessel from the common wall. The common walls of one or more firetubes are installed inside the vessel through one or more obround or oval shaped manways in a front wall of the vessel.
It is known in the oil and gas industry that hydrocarbon-based process fluids, such as hydrocarbon emulsions, contain not only hydrocarbon and water, but may also contain contaminants such as polymers, solids, sand and the like. Polymer additives are often used in operations on subterranean hydrocarbon-bearing formations including water flood recovery. Accordingly, fluids returned from the formation contain not only oil and water, but also contain significant amounts of polymer. In fluid recovery vessels, clean, dry product oil is recovered from contaminant-rich, hydrocarbon returned fluids including emulsions. The returned fluids are directed to a conventional heater/treater vessel for separation therein. In the case of a direct-fired heater vessel, contaminants and particularly the polymers, are susceptible to attaching to the very hot external surfaces of the firetube, resulting in a coating or fouling of the firetube's surfaces and reducing the ability to effectively exchange heat to the process fluids.
Further, in automated operations, as the monitored temperature of the process fluid does not increase to desired operational temperatures or even lowers, the control system increases the burner input in response. Increased burner input results in a larger flame which can cause flame impingement at inside walls of the firetube, impingement creating localized hot spots. Hot spots can ultimately result in burn-through of the firetube walls. Applicant is aware that in some cases, firetubes in polymer-contaminated process vessels can be changed out as frequently as every two weeks.
Clearly there is a need for means to extend the service life of the firetube, particularly when the process fluid to be heated is a contaminant or polymer-rich fluid emulsion.
SUMMARY OF THE INVENTIONEmbodiments of a jacketed firetube system efficiently utilize and conserve heat within a direct-fired heater and protect the firetube from developing hotspots, by circulating a heat transfer fluid, externally or internally, along at least the portion of the firetube which is at greatest temperature.
In one broad aspect, a method for recovering heat from a firetube immersed in a process fluid in a process vessel, for heating the process fluid, comprises circulating a cool heat transfer fluid in a circulation circuit in thermal communication with and extending along at least a portion of the firetube and therewith. Heat is recovered from the firetube for heating the heat transfer fluid therein and thereafter heat is transferred from the heated, heat transfer fluid to the process fluid.
In another broad aspect, a jacketed firetube system is used to transfer heat from a firetube to a process fluid in a process vessel where the firetube is adapted for connection to a burner at a first burner end and a vent stack at a second outlet end and having a passageway therebetween for directing hot gases from the burner to the vent stack. The firetube is immersed in the process fluid. The jacketed firetube system comprises a circulation circuit extending along at least a portion of the firetube for circulating a heat transfer fluid therein. The circulation circuit comprises a tubular jacket, extending along the firetube from the first burner end along at least a portion thereof, the jacket in thermal communication therewith and defining a circulation space therebetween. An inlet to the jacket delivers cool, heat transfer fluid to the circulation space. An outlet from the jacket discharges heated, heat transfer fluid therefrom. The heat transfer fluid is circulated through the circulation space for recovering at least a portion of the heat from the firetube.
Process vessels can be manufactured using embodiments of the jacketed firetube system and existing process vessels can be retrofit using embodiments which can be inserting internally into the conventional firetube or the conventional firetube can be removed and an external jacketed firetube embodiment inserted into the vessel.
Using embodiment of the jacketed firetube system, Applicant believes the efficiency of the firetube increases from a conventional efficiency in the range of about 60% to about 90%.
Having reference to
Applicant understands that, in a conventional U-tube firetube 12, this high temperature portion corresponds, at least in part, to the flame portion from the burner B, typically extending from the first burner end 14 of the firetube 12 about ⅓ of the outgoing length of the firetube 12. Longer firetubes 12 receive greater input with greater flame lengths, still being in the order of ⅓ of the outgoing length. Temperatures, in the first ⅓ of the firetube 12, can typically reach about 1300° F., depending upon system parameters.
As shown in
The system further comprises a circulation circuit 17 for recovering heat from the firetube 12, extending from about the first burner end 12. A heat transfer fluid P, such as an unheated or cool heat transfer fluid Pc, is circulated along at least a portion of the firetube 12, particularly along a high temperature portion TH, extracting heat therefrom and producing a heated heat transfer fluid Ph. As a result, the temperature of the firetube 12 along the high temperature portion TH is reduced, recovering maximal heat therefrom, and reducing the temperature below that temperature which is detrimental to the heat transfer fluid P and ultimately detrimental to the firetube 12. While shown in the context of a U-shaped firetube 12, conveniently supported from a common front wall 20, the heat recovery and embodiments herein can also be applied to other straight and arcuate firetubes having different interfaces with the vessel V.
The heat transfer fluid P may be a product fluid produced by a treatment of the process fluid, or may be another fluid, such as gycol.
The circulation circuit 17 comprises structure extending along at least the high temperature portion TH and forming a fluid passageway for placing the heat transfer fluid P in thermal contact with the firetube 12. The circulation structure comprises a tubular jacket 18 which extends from the firetube's first burner end 14, adjacent the burner B, and along the at least a portion of the firetube 12 where the temperature of the firetube 12 is highest. The jacket forms a circulation space C between itself and the firetube 12. The jacket 18 is closed, such as by an annular front wall 21 and an end wall 22. The circulation circuit 17 further comprises a jacket inlet 30 which receives and delivers the received, cool heat transfer fluid Pc to the circulation space C and a jacket outlet 32 which discharges heated heat transfer fluid Ph therefrom.
In the embodiment of
In an embodiment, best seen in
Having reference to
In yet another embodiment, shown in
Having reference to
The embodiment of
In one mode of operation, and having reference to
In an embodiment, the heat transfer fluid P is the product oil from the vessel 40. A pump 54 is fluidly connected between the vessel's second containment area 48 and the jacket inlet 30 for providing a slipstream of clean product oil as the cool heat transfer fluid PC to be circulated through the circulation space C. In an embodiment, the pump 54 is a variable speed pump which is controlled by operational parameters of the system, such as the temperature of the firetube 12. As the temperature of the heated fluid PH rises, the pump 54 increases the amount of the clean product oil P provided to the jacket 18 for regulating the temperature of the fluid P and the firetube 12. Maximum heat is removed from the firetube 12 and high temperatures are avoided for minimizing fouling and substantially preventing hotspots and firetube damage.
The cool product oil PC is circulated within the circulation space C from the jacket inlet 30 to the jacket outlet 32, heating the product fluid PH therein. As the product fluid P is compatible with the process fluid feedstream F, heat recovered from the firetube 12 by the heated product fluid PH can be transferred to the process fluid F in the vessel 40 by reintroducing the heated product fluid PH to the feedstream F.
In an embodiment, the jacket outlet 32 is fluidly connected to the first containment area 46, such as through the vessel's feed inlet 50. Thus, the heated product oil PH is mixed with the contaminant-rich feedstream F within the first containment area 46 in the process vessel 40. Heat in the heated product oil PH is transferred to the incoming contaminant-rich feedstream F, thus conserving heat in the system and reducing energy consumption required to heat the contaminant-rich feedstream F in the vessel 40.
Having reference to
Process vessels 40, such as conventional heater/treater vessels, are retrofit using embodiments of the jacketed firetube system 10.
With reference again to
With reference again to
As is understood by one of skill in the art, additional retrofit is required to provide a fluid connection 31 between the jacket outlet 32 and the vessel's feed inlet 50 and to provide a fluid connection 33 between the vessel 40 and the pump 54 for removing the slipstream of clean product oil P to be pumped to the jacket inlet 30, if required.
As will be appreciated by one of skill in the art, reduction in the size of the firetube 12 and removal of the slipstream of clean product oil P from the vessel 40, for circulation through the jacket 18, with subsequent reintroduction with the feedstream F, will result in only a small percentage loss of the overall capacity of the heater/treater vessel 40.
As shown in
The cool heat transfer fluid PC in the jacket 18, circulated therein, is caused to pass through the thermal conducting passageways 60 enhancing heat transfer thereto. Applicant believes the cool heat transfer fluid PC flows generally upwardly through the thermal conducting passageways 60 as a result of a thermosiphon effect caused by a temperature differential between the heated heat transfer fluid PH above the firetube 12 and the cooler heat transfer fluid PC below the firetube 12. The cool heat transfer fluid PC flows from a fluid inlet 64 at a portion 66 of the circulation space C in the jacket 18 below the firetube 12 to a fluid outlet 68 at a portion 70 of the circulation space C in the jacket 18 above the firetube 12.
As one of skill will appreciate flow diverters may be positioned within the jacket 18 to enhance the thermosiphon effect urging the cooler heat transfer fluid PC to flow through the thermal conductive passageways 60.
In another embodiment, as shown in
Claims
1. A method for recovering heat from a firetube immersed in a process fluid in a process vessel, for heating the process fluid, the method comprising:
- circulating a cool heat transfer fluid in a circulation circuit in thermal communication with and extending along at least a portion of the firetube and therewith, for recovering heat from the firetube for heating the heat transfer fluid therein; and thereafter
- transferring the heat from the heated, heat transfer fluid to the process fluid.
2. The method of claim 1 comprising:
- circulating the cool heat transfer fluid along at least a portion of an external surface of the firetube for recovering heat from the firetube for heating the heat transfer fluid.
3. The method of claim 1 comprising:
- circulating the cool heat transfer fluid along at least a portion of an internal surface of the firetube for recovering heat from a flame therein for heating the heat transfer fluid and the at least a portion of the internal surface of the firetube.
4. The method of claim 1 further comprising:
- regulating the circulation of the heat transfer fluid in response to the temperature in the firetube.
5. The method of claim 1 wherein the heat transfer fluid compatible with the process fluid; and further comprising:
- mixing the heated, compatible heat exchange fluid with the process fluid in the vessel for recovering the heat therefrom.
6. The method of claim 5 comprising:
- introducing the heated, compatible heat exchange fluid to a feed stream of process fluid for mixing with the process fluid in the vessel.
7. The method of claim 5 wherein the compatible heat transfer fluid is a product fluid produced by the process vessel, the method further comprising:
- flowing a slipstream of the product fluid from the process vessel through the circulation circuit.
8. The method of claim 5 wherein the compatible heat transfer fluid is a product fluid produced by the process vessel, the method further comprising:
- flowing a slipstream of the product fluid from the process vessel through the circulation circuit; and
- introducing the heated, product fluid from the circulation circuit to a feed stream of process fluid for mixing with the process fluid in the vessel.
9. The method of claim 1 wherein the heat transfer fluid is a product fluid produced by the process vessel, the method further comprising:
- flowing a slipstream of the product fluid from the process vessel through the circulation circuit; and
- introducing the heated, product fluid from the circulation circuit to a feed stream of process fluid for mixing with the process fluid in the vessel.
10. The method of claim 1 wherein the heat transfer fluid is incompatible with the process fluid, further comprising:
- flowing the heated, incompatible heat transfer fluid to a heat exchanger for recovering heat therefrom; and
- transferring the heat recovered by the heat exchanger to the process fluid in the vessel.
11. The method of claim 10 further comprising:
- flowing a feed stream of process fluid through the heat exchanger for transferring the heat to the process fluid in the vessel.
12. The method of claim 10 wherein the incompatible heat transfer fluid is glycol.
13. A jacketed firetube system for transferring heat from a firetube to a process fluid in a process vessel, the firetube adapted for connection to a burner at a first burner end and a vent stack at a second outlet end and having a passageway therebetween for directing hot gases from the burner to the vent stack, the firetube being immersed in the process fluid, the system comprising:
- a circulation circuit extending along at least a portion of the firetube for circulating a heat transfer fluid therein, the circulation circuit comprising: a tubular jacket, extending along the firetube from the first burner end along at least a portion thereof, the jacket in thermal communication therewith and defining a circulation space therebetween; an inlet to the jacket for delivering cool, heat transfer fluid to the circulation space; and an outlet from the jacket for discharging heated, heat transfer fluid therefrom,
- wherein the heat transfer fluid is circulated through the circulation space for recovering at least a portion of the heat from the firetube.
14. The jacketed firetube system of claim 13, wherein the jacket is external to the at least a portion of the firetube.
15. The jacketed firetube system of claim 13, wherein the jacket is internal to the at least a portion of the firetube.
16. The jacketed firetube system of claim 13 wherein the tubular jacket extends along the at least a portion of the firetube that has a surface temperature detrimental to the process fluid.
17. The jacketed firetube system of claim 13 wherein the heat transfer fluid is compatible with the process fluid, the system further comprising:
- a fluid connection between the jacket outlet and the process vessel for flowing the heated, heat transfer fluid discharged from the jacket outlet for mixing with the process fluid in the vessel for recovering the heat therefrom.
18. The jacketed firetube system of claim 17 wherein the heat transfer fluid compatible with the process fluid is the vessel's product fluid.
19. The jacketed firetube system of claim 18 further comprising:
- a fluid connection between the process vessel and the jacket inlet for delivering the product fluid to the circulation space.
20. The jacketed firetube system of claim 13 wherein the vessel further comprises a feed inlet, the system further comprising:
- a fluid connection between the jacket outlet and the feed inlet for delivering the heated heat transfer fluid thereto.
21. The jacketed firetube system of claim 13 wherein the heat transfer fluid is incompatible with the process fluid, the system further comprising:
- a heat exchanger for flowing the heated, heat transfer fluid and a feed stream of the process fluid therethrough for transferring the heat from the heat transfer fluid to the process fluid in the vessel.
22. The jacketed firetube system of claim 21 wherein the heat transfer fluid is glycol.
23. The jacketed firetube system of claim 14 wherein the firetube further comprises:
- a plurality of thermal conducting passageways for circulating fluid therethrough, each thermal conducting passageway extending generally upwardly from a fluid inlet at a portion of the jacket below the firetube to a fluid outlet at a portion of the jacket above the firetube and having a thermal conductive wall extending through the firetube for conducting heat from the hot gases to the heat transfer fluid circulating therethrough.
24. The jacketed firetube system of claim 14 wherein the jacket further comprises:
- a plurality of thermal conducting passageways for circulating fluid therethrough, each thermal conducting passageway extending generally upwardly from a fluid inlet at a portion of the vessel below the jacket to a fluid outlet at a portion of the vessel above the jacket and having a thermal conductive wall extending through the jacket for conducting heat to the process fluid.
25. A method for retrofitting a firetube for transferring heat from a firetube to a process fluid in a process vessel, the firetube adapted for connection to a burner at a first burner end and a vent stack at a second outlet end and having a passageway therebetween for directing hot gases from the burner to the vent stack, the method comprising:
- inserting an insert into the first end in thermal communication with and extending along at least a portion of the firetube for forming a circulation circuit for circulating a cool heat transfer fluid therethrough for recovering at least a portion of the heat from the firetube for heating the heat transfer fluid therein.
Type: Application
Filed: Jan 16, 2012
Publication Date: Jul 19, 2012
Applicant: CHADWICK ENERGY SERVICES LTD. (Airdrie)
Inventor: Thomas CHADWICK (Airdrie)
Application Number: 13/351,084
International Classification: F28D 15/00 (20060101); F28D 1/047 (20060101);