WO2006002030A1

WO2006002030A1 - Apparatus and methods for converting a cryogenic fluid into gas

Info

Publication number: WO2006002030A1
Application number: PCT/US2005/020829
Authority: WO
Inventors: Ned P. Baudat
Original assignee: Mustang Engineering, L.P.
Priority date: 2004-06-15
Filing date: 2005-06-12
Publication date: 2006-01-05
Also published as: US7155917B2; AU2005257930A1; US20080053110A1; EP1756469A1; US20100043452A1; US20050274126A1; EP1756469A4; US20070186565A1

Abstract

Method and apparatus for vaporizing cryogenic fluids in which an intermediate heat transfer fluid is first heated across a heat transfer surface with ambient air, and then the heat transfer surface provides heat to vaporize the cryogenic fluid.

Description

INVENTION TITLE APPARATUS AND METHODS FOR CONVERTING A CRYOGENIC FLUID INTO GAS DESCRIPTION

Heading BACKGROUND OF THE INVENTION [Para l ] The present invention relates to cryogenic fluids. In another aspect, the present invention relates to apparatus and methods for processing, transporting and/or storing cryogenic fluids. In even another aspect, the present invention relates to apparatus and methods for converting a cryogenic fluid into a gas. In even another aspect, the present invention relates to methods and apparatus for processing, transporting and/or storing liquified natural gas ("LNG"). In still another aspect, the present invention relates to apparatus and methods for modifying and/or retrofitting cryogenic vaporization systems. [Para 2] Most conveniently, natural gas is transported via pipeline from the location where it is produced to the location where it is consumed. However, given certain barriers of geography, economics, and/or politics, transportation by pipeline is not always possible, economic or permitted. Without an effective way to transport the natural gas to a location where there is a commercial demand, the gas may be burned as it is produced, which is wasteful. [Para 3] Liquefaction of the natural gas facilitates storage and transportation of the natural gas (a mixture of hydrocarbons, typically 65 to 99 percent methane, with smaller amounts of ethane, propane and butane). When natural gas is chilled to below its boiling point (in the neighborhood of -260 F depending upon the composition) it becomes an odorless, colorless liquid having a volume which is less than one six hundredth (1 /600) of its volume at ambient atmospheric surface temperature and pressure. Thus, it will be appreciated that a 150,000 cubic meter LNC tanker ship is capable of carrying the equivalent of 3.2 billion cubic feet of natural gas. [Para 4] It is not uncommon for natural gas to be produced in remote locations, such as Algeria, Borneo, or Indonesia, and then liquefied and shipped overseas in this manner to Europe, Japan, or the United States. Typically, the natural gas is gathered through one or more pipelines to a land-based liquefaction facility. The LNG is then loaded onto a tanker equipped with cryogenic compartments (such a tanker may be referred to as an LNC carrier or ("LNCC") by pumping it through a relatively short pipeline. After the LNGC reaches the destination port, the LNG is offloaded by cryogenic pump to a land-based regasification facility, where it may be stored in a liquid state or regasified. If regasified, the resulting natural gas then may be distributed through a pipeline system to various locations where it is consumed. [Para 5] In many circumstances, hot water or steam is used to heat the liquefied gas for vaporization. Unfortunately, such hot water or steam often freezes so as to give rise to the hazard of clogging up the evaporator. Various improvements in this process have heretofore been made. The evaporators presently used are mainly of the open rack type, intermediate fluid type and submerged combustion type. [Para 6] Open rack type evaporators use sea water as a heat source for the vaporization of liquefied natural gas. These evaporators use once-through seawater flow on the outside of a heat exchanger as the source of heat for the vaporization. They do not block up from freezing water, are easy to operate and maintain, but they are expensive to build. They are widely used in Japan. Their use in the USA and Europe is limited and economically difficult to justify for several reasons. First the present permitting environment does not allow returning the seawater to the sea at a very cold temperature because of environmental concerns for marine life. The present permitting environment allows only a small decrease in temperature before returning the seawater back to the sea, which would require a very large sea water quantity to be pumped through the system, if the terminal vaporization capacity was designed for a commercial size as economics would require. Also coastal waters like those of the southern USA are often not clean and contain a lot of suspended solids, which could require filtration. In addition the sea water intake structure would have to be located far away from the evaporators in most cases because of location restraints or to get to deep and clean sea water at the intake. With these restraints the use of open rack type vaporizers in the USA is environmentally and economically not feasible. [Para 7] Instead of vaporizing liquefied natural gas by direct heating with water or steam, evaporators of the intermediate fluid type use propane, fluorinated hydrocarbons or like refrigerant having a low freezing point. The refrigerant is heated with hot water or steam first to utilize the evaporation and condensation of the refrigerant for the vaporization of liquefied natural gas. Evaporators of this type are less expensive to build than those of the open rack-type but require heating means, such as a burner, for the preparation of hot water or steam and are therefore costly to operate due to fuel consumption. [Para 8] Evaporators of the submerged combustion type comprise a tube immersed in water which is heated with a combustion gas injected thereinto from a burner. Like the intermediate fluid type, the evaporators of the submerged combustion type involve a fuel cost and are expensive to operate. [Para 9] The patent art is replete with a number of patents directed to processes and apparatus for the vaporization of liquefied natural gas. [Para 10] For example, U.S. Pat. No. 4, 170, 1 1 5, issued on Oct. 9, 1979 to Ooka et al., describes an apparatus for vaporizing liquefied natural gas using estuarine water. This system is arranged in a series of heat exchangers of the indirect heating, intermediate fluid type. A multitubular concurrent heat exchanger is also utilized in conjunction with a multitubular countercurrent heat exchanger. As a result, salt water is used for the vaporization process. U.S. Pat. No. 4,224,802, issued on Sep. 30, 1980 to the same inventor, describes a variation on this type and also uses estuarine water in a multitubular heat exchanger. [Para 1 1] U.S. Pat. No. 4,331 ,129, issued on May 25, 1982 to Hong et al., teaches the utilization of solar energy for LNG vaporization. The solar energy is used for heating a second fluid, such as water. This second fluid is passed into heat exchange relationship with the liquefied natural gas. The water contains a anti-freeze additive so as to prevent freezing of the water during the vaporization process. [Para 12] U.S. Pat. No. 4,399,660, issued on Aug. 23, 1983 to Vogler, Jr. et al., describes an atmospheric vaporizer suitable for vaporizing cryogenic liquids on a continuous basis. This device employs heat absorbed from the ambient air. At least three substantially vertical passes are piped together. Each pass includes a center tube with a plurality of fins substantially equally spaced around the tube. [Para 13] U.S. Pat. No. 5,251 ,452, issued on Oct. 12, 1993 to L Z. Widder, also discloses an ambient air vaporizer and heater for cryogenic liquids. This apparatus utilizes a plurality of vertically mounted and parallelly connected heat exchange tubes. Each tube has a plurality of external fins and a plurality of internal peripheral passageways symmetrically arranged in fluid communication with a central opening. A solid bar extends within the central opening for a predetermined length of each tube to increase the rate of heat transfer between the cryogenic fluid in its vapor phase and the ambient air. The fluid is raised from its boiling point at the bottom of the tubes to a temperature at the top suitable for manufacturing and other operations. [Para 14] U.S. Pat. No. 5,819,542, issued on Oct. 1 3, 1998 to Christiansen et al._f teaches a heat exchange device having a first heat exchanger for evaporation of LNG and a second heat exchanger for superheating of gaseous natural gas. The heat exchangers are arranged for heating these fluids by means of a heating medium and having an outlet which is connected to a mixing device for mixing the heated fluids with the corresponding unheated fluids. The heat exchangers comprise a common housing in which they are provided with separate passages for the fluids. The mixing device, constitutes a unit together with the housing and has a single mixing chamber with one single fluid outlet. In separate passages, there are provided valves for the supply of LNG in the housing and in the mixing chamber. [Para 15] U.S. Patent No. 6,622,492, issued September 23, 2003, to Eyermann, discloses apparatus and process for vaporizing liquefied natural gas including the extraction of heat from ambient air to heat circulating water. The heat exchange process includes a heat exchanger for the vaporization of liquefied natural gas, a circulating water system, and a water tower extracting heat from the ambient air to heat the circulating water. To make the process work throughout the year the process may be supplemented by a submerged fired heater connected to the water tower basin. [Para 16] U.S. Patent No. 6,644,041 , issued November 1 1 , 2003 to Eyermann, discloses a process for vaporizing liquefied natural gas including passing water into a water tower so as to elevate a temperature of the water, pumping the elevated temperature water through a first heat exchanger, passing a circulating fluid through the first heat exchanger so as to transfer heat from the elevated temperature water into the circulating fluid, passing the liquefied natural gas into a second heat exchanger, pumping the heated circulating fluid from the first heat exchanger into the second heat exchanger so as to transfer heat from the circulating fluid to the liquefied natural gas, and discharging vaporized natural gas from the second heat exchanger. [Para 17] In spite of the advancements of the prior art, there is still a need in the art for improved apparatus and methods for processing, transporting, and/or storing LNG. [Para 1 8] There is another need in the art for apparatus and methods for converting a liquified cryogenic fluid into a gas. [Para 19] There is even another need in the art for apparatus and methods for converting a liquified natural gas into gaseous natural gas. [Para 20] This and other needs in the art will become apparent to those of skill in the art upon review of this specification, including its drawings and claims. Heading

SUMMARY OF THE INVENTION [Para 21 ] It is an object of the present invention to provide for improved apparatus and methods for processing, transporting, and/or storing LNG. [Para 22] It is another object of the present invention to provide for apparatus and methods for converting a liquified cryogenic fluid into a gas. [Para 23] It is even another object of the present invention to provide for apparatus and methods for converting a liquified natural gas into gaseous natural gas. [Para 24] This and other objects of the present invention will become apparent to those of skill in the art upon review of this specification, including its drawings and claims. [Para 25] According to one embodiment of the present invention, there is provided a method of vaporizing a cryogenic fluid. The method includes providing heat from ambient air to a heat transfer fluid across a heat transfer surface, wherein the ambient air and heat transfer fluid are not in direct contact. The method also includes providing heat from the heat transfer fluid to a cryogenic fluid sufficient to vaporize the cryogenic fluid. [Para 26] According to another embodiment of the present invention, there is provided an apparatus for vaporizing a cryogenic fluid. The apparatus comprises a heat transfer fluid closed circulation loop defined by an ambient air heat exchanger, a heater and a vaporizer; and an LNC flow path defined thru the vaporizer. [Para 27] According to even another embodiment of the present invention, there is provided a method of modifying a vaporizing system in which a heat transfer fluid is circulated thru a heater to heat up the fluid and then circulated thru a vaporizer to vaporize the cryogenic fluid. The method includes the addition of a ambient air heat exchanger to provide heat to the heat exchange fluid. [Para 28] According to still another embodiment of the present invention, there is provided a modified system for vaporizing a cryogenic fluid comprising a heat transfer fluid heater and vaporizer, and comprising an ambient air heat exchanger added after the heat transfer fluid heater and vaporizer have been in operation in the system. [Para 29] These and other embodiments of the present invention will become apparent to those of skill in the art upon review of this specification, including its drawings and claims. Heading

BRIEF DESCRIPTION OF THE DRAWINGS [Para 30] In the drawings, it should be understood that like reference numbers refer to like members. [Para 31 ] FIG. 1 is a process flow schematic showing regasification system 100 having air exchange pre-heater 101 , economizer 103, heater 105, water knockout 1 1 1 , vaporizer 1 14, produced water pump 1 17, circulating fluid surge tank 1 19, and circulating fluid pump 121. [Para 32] FIC. 2 is a process flow schematic showing regasification system 200 having tube-in-tube air exchanger 201 , economizer 203, vaporizer 214, produced water knockout 21 1 , produced water pump 217, warming medium accumulator 219 and warming medium pump 221. [Para 33] FICs. 3 and 4 are schematics showing a retrofit of a typical ethylene glycol LNG vaporization system 300 having heater 302, LNG vaporizer 301 , accumulator 303, and circulation pump 307. [Para 34] FIG. 5 is a schematic showing a retrofit of a water bath or submerged combustion system. [Para 35] FIGs. 6 and 7 are schematics showing a retrofit of a typical cooling tower vaporization system 400, having cooling tower 401 , pump 403, exchanger 404, tank 405, LNG vaporizer 406, pump 407 and submerged bath heater 408.

[Para 36] FIG. 8 is a process flow schematic showing vaporization process system 800 having air exchange pre-heater 801 , accumulator 804, auxiliary heater 805, vaporizer 814, air exchange feeder line valve 816, heater feeder line valve 818 and temperature controller 825.

[Para 37] FIG. 9 is a process flow schematic showing vaporization process system 900 having air exchange pre-heater 901 , auxiliary heater vaporizer 903, cold separator 904, auxiliary heater 905, second fluid pump 910, pre- heater vaporizer 914, pre-heater vaporizer LNG feed valve 916, auxiliary heater vaporizer LNG feed valve 918, second air exchange heater 920 and temperature controller 925. Heading

DETAILED DESCRIPTION OF THE INVENTION [Para 38] While some descriptions of the present invention may make reference to liquified natural gas ("LNC), it should be understood that the present invention is not limited to utility with LNC, but rather has broad utility with cryogenic fluids in general, preferably cryogenic fluids formed from flammable gases. ' [Para 39] The apparatus of the present invention will find utility for processing, storing, and/or transporting (i.e., including but not limited to, receiving, dispensing, distributing, moving) cryogenic fluids, a non-limiting example of which is liquified natural gas ("LNC"). More specifically.the present invention provides apparatus and methods for converting a cryogenic fluid into a gas, which apparatus and methods may be used not along in a stand alone manner, but which may also be utilized with and/or incorporated into apparatus and methods for processing, storing, and/or transporting cryogenic fluids. [Para 40] According to the present invention, there is an unexpected advantage obtained using a standard air cooler as a heater while passing a fluid through the tubes to pick up heat from the air, preferable on a continuous basis. While ambient vaporizers have been used to heat LNC, but require alternating between a number of units as they freeze up from water vapor in the air. The present invention employs an intermediate heat transfer fluid and selected temperatures, wherein frost does not inhibit the transfer surface, to vaporize LNG. [Para 4I] A first non-limiting embodiment of the apparatus and methods of the present invention is best described by reference to FIG. 1 , a process flow schematic showing regasification system 100 having air exchange pre- heater 101 , economizer 103, heater 105, water knockout 1 1 1 , vaporizer 1 14, produced water pump 117, circulating fluid surge tank 1 19, and circulating fluid pump 121. [Para 42] LNG is provided to vaporizer 1 14 via piping 21 at around -252F, and exits vaporizer 1 14 via piping 22 as gaseous natural gas at about 4OF. A circulating heat transfer fluid is provided to vaporizer 1 14 via piping 31 , and exits vaporizer 1 14 via piping 32 as a cooled heat transfer fluid. [Para 43] Heat transfer fluids suitable for use in the present invention include hydrocarbons, non-limiting examples of which include propane and butane, ammonia, glycol-water mixtures, formate-water mixtures, methanol, propanol, and other suitable heat transfer fluids as may be useful under the operating conditions. [Para 44] The heat transfer fluid is circulated in a closed system through air exchange pre-heater 101 where it is first heated after being cooled in vaporizer 1 14, then through economizer 103/heater 105 where it may be further heated if necessary, then through vaporizer 1 14 where it is utilized to provide heat of vaporization to the LNG, before returning to pre-heater 101. This heat transfer circulation system may be provided with one or more surge tanks 1 19 as necessary. Circulation of the heat transfer fluid is maintained by one or more circulation pumps 121. A nitrogen line 51 and pressure controller 55 maintain pressure of the heat transfer circulation system as desired. [Para 45] In the practice of the present invention, heat is provided from ambient air to the heat transfer fluid across a heat transfer surface rather than by direct contact between the ambient air and heat transfer fluid. For example, the heat transfer fluid is passed through the tubes of a heat exchanger while the ambient air passes through the shell side. [Para 46] Under certain conditions (see Examples 1 , 2 and 3 below), ambient air will provide all of the heating necessary without the need for the economizer 103/heater 105 providing any heating duty. [Para 47] When heater 105 is necessary it will be most efficiently run in conjunction with economizer 103, in which the exit effluent from heater 105 routed to economizer 103 to heat the LNG or other cryogenic fluid. The cooled effluent exits economizer 103 and flows to water knockout tank 111. Pump 1 17 eliminates produced water from the system. [Para 48] A second non-limiting embodiment of the apparatus and methods of the present invention is best described by reference to FIG. 2, which is a process flow schematic showing regasification system 200 having tube-in- tube air exchanger 201 , economizer 203, vaporizer 214, produced water knockout 21 1 , produced water pump 217, warming medium accumulator 219 and warming medium pump 221. [Para 49] In this embodiment, heat exchanger 201 is a tube-in-tube air exchanger (i.e, two tubes arranged in a concentric fashion), in which the cryogenic fluid passes through the inner most tube, pump 221 circulates the heat transfer fluid through the annular space between the two tubes, and ambient air passes over the surface of the outer tube. Accumulator 219 provides volume to the system to aid in heat transfer. For those times when the ambient air is too cool, extra heating may be provided by heater 214/economizer 203. Hot exit effluent from heater 214 routed to economizer 203 to heat the LNC or other cryogenic fluid. The cooled effluent exits economizer 203 and flows to water knockout tank 21 1. Pump 217 eliminates produced water from the system. [Para 50] The methods and apparatus of the present invention also provide for retrofitting of pre-existing cryogenic regassification apparatus. [Para 5I] In its simplest aspect, regassification which involves closed loop circulation of a heat transfer fluid thru a heater and then into a vaporizer to heat and vaporize a cryogenic fluid, may be modified by placing an ambient air heat exchanger ahead of the heater to either pre-heat or fully heat the heat transfer fluid. Of course, there will not be direct contact of the heat transfer fluid with the ambient air, but rather indirect contact across a heat transfer service. [Para 52] For example, referring now to FIG. 3, there is shown a retrofit of a typical ethylene glycol LNG vaporization system 300 having heater 302, LNG vaporizer 301 , accumulator 303, and circulation pump 307. In a method of retrofitting/modifying the system to form a retrofitted /modified system, air pre-heater 315 is added just upstream of heater 302 to serve as a pre- heater and/or heater. [Para 53] Referring now to FIG. 6, there is shown a retrofit of a typical cooling tower vaporization system 400, having cooling tower 401 , pump 403, exchanger 404, tank 405, LNG vaporizer 406, pump 407 and submerged bath heater 408. In a method of retrofitting/modifying the system to form a retrofitted/modified system, air pre-heater 415 is added. However, instead of preheating the LNG, this heater 415 serves to heat the heat transfer fluid flowing through vaporizer 406. [Para 54] More complex modification/retrofitting of such existing systems involve taking a side stream of the cryogenic fluid and routing it thru a vaporizer in which the vaporizer heat transfer fluid has been heated by ambient air in the manner of the present invention. Essentially, such a retrofit is the addition of the apparatus and method of the present invention to handle at least a portion of the vaporization. [Para 55] For example, the typical ethylene glycol/water system shown in FIG. 3 and modified /retrofitted by the addition of air pre-heater 315, may instead be modified/retrofitted as shown in FIG. 4 by the addition of system 500 in which a heat transfer fluid is circulated in a closed circuit via pump 505 through air heater 502 where it is heated, through exchanger 501 where it heats LNG, through accumulator 503, and back to heater 502 to complete the circuit. Controller 509 regulates flow of LNG to the pipeline and/or back to the LNG Vaporizer. [Para 56] As another example, the typical cooling tower vaporization system shown in FIG. 6 and modified /retrofitted by the addition of air exchanger 415, may instead be modified/retrofitted as shown in FIG. 7 by the addition of system 500 in which a heat transfer fluid is circulated in a closed circuit via pump 505 through air heater 502 where it is heated, through exchanger 501 where it heats LNG₁ through accumulator 503, and back to heater 502 to complete the circuit. Controller 509 regulates flow of LNG to the pipeline and /or back to the LNG Vaporizer. [Para 57] FIG. 5 is a schematic showing the retrofit of a water bath or submerged combustion vaporizer by the addition of system 500 as described above. [Para 58] Another non-limiting embodiment of the apparatus and methods of the present invention is best described by reference to FIG. 8, which is a process flow schematic showing vaporization process system 800 having air exchange pre-heater 801 , accumulator 804, auxiliary heater 805, vaporizer 814, air exchange feeder line valve 816, heater feeder line valve 818 and temperature controller 825. [Para 59] In this embodiment, temperature controller 825 monitors the temperature of the heat transfer fluid. If the temperature of the heat transfer fluid is not sufficiently high, then controller 825 operates valves 816 and 818 to achieve a desired heat transfer fluid temperature, by utilizing pre-heater 801 , auxiliary heater 805, or a combination thereof with the heating duty shared between heaters 801 and 805 in any suitable ratio. Controller 825 can be equipped with suitable algorithms in the form of either software and/or hardware to carry out this temperature control. [Para 60] Another embodiment of the present invention is shown in FIC. 9, which is a process flow schematic showing vaporization process system 900 having air exchange pre-heater 901 , auxiliary heater vaporizer 903, cold separator 904, auxiliary heater 905, second fluid pump 910, pre-heater vaporizer 914, pre-heater vaporizer LNC feed valve 916, auxiliary heater vaporizer LNC feed valve 918, second air exchange heater 920 and temperature controller 925. [Para 61] This embodiment contains a pair of vaporizers in which vaporizer 903 receives heat transfer liquid from heater 905 and the other vaporizer 914 receives heat from heater 901. Temperature controller 925 monitors the temperature of gas 930 and operates valves 916 and 918 according to an algorithm to achieve the desired temperature of gas 930. The vaporization load is carried by the auxiliary heater vaporizer 903 and pre- heater vaporizer 914, or a combination thereof with the vaporization load shared between vaporizers 903 and 914 in any suitable ratio.

[Para 62] It should be understood that any of the above systems may incorporate process controls/ methods as are known to those of skill in the art. For example, by-passes around any of the heat exchanges may be utilized. It should also be understood that much of the micro engineering/process detail is not shown in the above illustrations but would be well within the knowledge and understanding of those of skill in the art. Heading Examples [Para 63] The following non-limiting examples are provided merely to illustrate a few embodiments of the present invention, and there examples are not meant to and do not limit the scope of the claims of the present invention. These inventions are theoretical calculated examples. [Para 64] Example 1. This example utilizes the apparatus and method as shown in FIG. 1 (1 1 at -1 OF₁ 31 at 50F, 32 at -1 OF, and 1 19 at 16psig). The cryogenic fluid is a typical LNC. The circulating fluid utilized is propane. The duty percentage for the air cooler 101 , and the combined duty percentage for fired heater 105 and economizer 103 were calculated for ambient air temperatures of 35F, 45F, 65F, 7OF and 85F, with these percentages presented in the following TABLE 1. The propane circulation is about 1.7 Ib propane/lb LNC, with the rate depending upon the temperature and pressure of the LNC and propane. The propane circulation range is estimated to be from about 1 .0 to 2.5 Ib propane/lb LNG. [Para 65] TABLE 1. [Para 66] Duty Percentage at Various Ambient Air Temperatures

[Para 67] Example 2 [Para 68] This example also utilizes the apparatus and method as shown in FIC. 1 (1 1 @ -1 OF, 31 Φ 50F, 32 @ -1 OF. and 119 at 10Opsig). The cryogenic fluid is again a typical LNG. The circulating fluid utilized is propane. The duty percentage for the air cooler 101 , and the combined duty percentage for fired heater 105 and economizer 103 were calculated for ambient air temperatures of 35F, 45F, 65F, 7OF and 85F, with these percentages presented in the following TABLE 2. The propane circulation is about 7.6 Ib propane/ Ib LNG, with the rate depending upon the temperature and pressure of the LNG and propane. The propane circulation range is estimated to be from about 5.0 to 10.0 Ib propane/lb LNG. [Para 69] TABLE 2 [Para 70] Duty Percentage at Various Ambient Air-Tempβratu res

[Para 71 ] Example 3 [Para 72] This example again utilizes the apparatus and method as shown in FIC. 1 (1 1 at range of -1 OF to 30F, 30 at -1 OF, 31 at 50F, 32 at 30F, and 1 19 at 16psig). The cryogenic fluid is a typical LNC. Rather than using propane as the circulating fluid, WBF is utilized. As with Examples 1 and 2, the duty percentage for the air cooler 101 , and the combined duty percentage for fired heater 105 and economizer 103 were calculated for ambient air temperatures of 35F, 45F, 65F, 7OF and 85F, with these percentages presented in the following TABLE 3. The WBF circulation is about 10-30 Ib WBF/lb LNG, with the rate depending upon the temperature and pressure of the LNG and propane. [Para 73] TABLE 3 [Para 74] Duty Percentage at Various Ambient Air Temperatures

[Para 75] Example 4 [Para 76] This example utilizes the apparatus and method as shown in FIG. 2. The cryogenic fluid is a typical LNC. The warming medium utilized is propane. The duty percentage for the tube-in-tube air exchange 201 , and the combined duty percentage for fired heater 214 and economizer 203 were calculated for ambient air temperatures of 35F, 45F, 65F, 7OF and 85F₁ with these percentages presented in the following TABLE 4. The economizer is used with the Water Bath Heater only. [Para 77] TABLE 4 [Para 78] Duty Percentage at Various Ambient Air Temperatures

[Para 79] Example 5 [Para 80] Potential savings utilizing present invention. [Para 81 ] Basis: 1000 MMBtu/Hr; Air exchanger designed assuming 7OF; $5.00/MMBtu; 365 days of operation/yr.

[Para 82] Month: Jan Feb Mar Apr May Jun JuI Aug Sep Oct Nov Dec [Para 831 T (F): 51 54 6i 67 75 βi 82 83 79 70 6i 55

[Para 84] AIR Htr %Duty: 77.5 81 90 94 100 100 100 100 100 100 90 so

[Para 85] Air Duty [Para 86] (MMBtu/Hr): 775 8io 900 940 1000 1000 1000 1000 1000 1000 900 800

[Para 87] Average Yearly Savings:927.1 x $5 X 24 X 365 = $40.6 MM/Yr. [Para 88] [Para 89] The above calculations are based on approximately 1 500 MMSCFD being vaporized. [Para 90] While the illustrative embodiments of the invention have been described with particularity, it will be understood that various other modifications will be apparent to and can be readily made by those skilled in the art without departing from the spirit and scope of the invention. Accordingly, it is not intended that the scope of the claims appended hereto be limited to the examples and descriptions set forth herein but rather that the claims be construed as encompassing all the features of patentable novelty which reside in the present invention, including all features which would be treated as equivalents thereof by those skilled in the art to which this invention pertains.

Claims

What is claimed is:

[Claim 1 ] A method of vaporizing a cryogenic fluid, the method comprising the steps of: providing heat from ambient air to a heat transfer fluid across a heat transfer surface, wherein the ambient air and heat transfer fluid are not in direct contact; providing heat from the heat transfer fluid to a cryogenic fluid sufficient to vaporize the cryogenic fluid. [Claim 2] The method of claim 1 , wherein the cryogenic fluid is LNC. [Claim 3] An apparatus for vaporizing a cryogenic fluid, comprising: a heat transfer fluid closed circulation loop defined by an ambient air heat exchanger, a heater and a vaporizer; and an LNG flow path defined thru the vaporizer. [Claim 4] A method of modifying a vaporizing system in which a heat transfer fluid is circulated thru a heater to heat up the fluid and then circulated thru a vaporizer to vaporize the cryogenic fluid, the method comprises addition of a ambient air heat exchanger to provide heat to the heat exchange fluid. [Claim 5] A modified system for vaporizing a cryogenic fluid comprising a heat transfer fluid heater and vaporizer, and comprising an ambient air heat exchanger added after the heat transfer fluid heater and vaporizer have been in operation in the system.