US3726101A - Method of continuously vaporizing and superheating liquefied cryogenic fluid - Google Patents

Abstract

The present invention relates to an improved method of continuously vaporizing and superheating a stream of liquefied cryogenic fluid wherein the stream is vaporized and then superheated to a desired temperature level by exchange of heat with gas turbine exhaust gases. By the present invention, the vaporized cryogenic fluid is passed in heat exchange relationship with the turbine exhaust gases in successive serially connected heat exchange stages. A quantity of liquefied cryogenic fluid is combined with the vaporized cryogenic fluid passing through each of the stages so that the liquefied cryogenic fluid is vaporized and the resulting combined vapor is cooled prior to passing through the next successive heat exchange stage. By the present invention, smaller and less expensive heat exchange apparatus is required and the maximum heating capacity of the turbine exhaust gases is utilized for vaporizing and superheating the cryogenic fluid.

Description

atet

Arenson METHOD OF CONTINUOUSLY VAPORIZING AND SUPERHEATING LIQUEFIED CRYOGENIC FLUID Inventor: Edwin M. Arenson, El Reno, Okla.

Assignee: Black, Sivalls & Bryson Inc.,

Oklahoma City, Okla.

Filed: May 20, 1971 Appl. No.: 145,217

[52] U.S. Cl. ..62/52, 48/190, 60/3907, 60/3946, 62/53, 261/145 [51] Int. Cl ..Fl7c 7/02, F02m 31/00 [58] Field of Search ..62/52, 53; 261/145; 48/190; 60/3946, 39.07

[56] References Cited UNITED STATES PATENTS 3,154,928 11/1964 Harmens ,.62/53 3,438,216 4/1969 Smith ..62/52 3,552,134 1/1971 Arenson ..60/95 R Primary ExaminerWilliam F. ODea Assistant ExaminerPeter D. Ferguson Attorney-Dunlap, Laney, Hessin & Dougherty 5 7 ABSTRACT The present invention relates to an improved method of continuously vaporizing and superheating a stream of liquefied cryogenic fluid wherein the stream is vaporized and then superheated to a desired temperature level by exchange of heat with gas turbine exhaust gases. By the present invention, the vaporized cryogenic fluid is passed in heat exchange relationship with the turbine exhaust gases in successive serially connected heat exchange stages. A quantity of liquefied cryogenic fluid is combined with the vaporized cryogenic fluid passing through each of the stages so that the liquefied cryogenic fluid is vaporized and the resulting combined vapor is cooled prior to passing through the next successive heat exchange stage. By the present invention, smaller and less expensive heat exchange apparatus is required and the maximum heating capacity of the turbine exhaust gases is utilized for vaporizing and superheating the cryogenic fluid.

9 Claims, 2 Drawing Figures 54, ,/56 we I60 METHOD OF CONTINUOUSLY VAPORIZING AND SUPEREIEATING LIQUEFIED CRYOGENIC FLUID BACKGROUND OF THEINVENTION 1. Field of the Invention The present invention relates generally to an improved method of continuously vaporizing and superheating liquefied cryogenic fluid, and more particularly, but not by way of limitation, to a method of vaporizing and superheating a stream of liquefied cryogenic fluid wherein the fluid is heat exchanged with turbine exhaust gases.

2. Description of the Prior Art Many various methods and systems have been developed for vaporizing and superheating cryogenic fluids. The term cryogenic fluid is used herein to mean those fluids which exist in the liquid state at a temperature below about 150 F at pressures up to about 1000 psia, e.g., liquefied natural gas.

In recent years the use of liquefied natural gas as a source of fuel in areas where natural gas is unavailable has increased. In these areas, a continuous stream of liquefied natural gas is vaporized, superheated and distributed by pipeline to points of use. Many various methods and systems have been developed and used for vaporizing and superheating liquefied cryogenic fluids.

Generally, the methods and systems have required elaborate heating equipment involving high operating costs. Recently, in order to improve the economics of such systems, it has been proposed to utilize ambient water as the heating medium for vaporizing and superheating liquefied natural gas. The term ambient water is used herein to mean water contained in large bodies such as oceans, lakes, rivers, etc. Further, in order to vaporize and superheat a stream of liquefied cryogenic fluid utilizing ambient water without incurring a detrimental temperature drop in the ambient water and in order to generate power for pumping the liquefied cryogenic fluid and ambient water streams, a method utilizing ambient water to vaporize the stream of liquefied cryogenic fluid and utilizing turbine exhaust gases for superheating the vaporized cryogenic fluid to a desired level of superheat was developed and is described in my co-pending application Ser. No. 150,448 filed June 7, 1971. While methods and systems utilizing ambient water and turbine exhaust gas heat exchange for vaporizing and superheating a liquefied cryogenic fluid stream are highly advantageou economically, in certain applications inadequate temperature control of the superheated cryogenic fluid stream may be experienced.

By the present invention an improved method of continuously vaporizing and superheating a stream of liquefied cryogenic fluid wherein the stream is vaporized and then superheated to a desired temperature level by exchange of heat with gas turbine exhaust gases is provided wherein maximum temperature control of the superheated cryogenic fluid is provided and utilization of the maximum heating capacity of the turbine exhaust gases is achieved.

SUMMARY OF THE INVENTION The present invention relates to an improved method of continuously vaporizing and superheating a stream of liquefied cryogenic fluid wherein the stream is vaporized and then superheated to a desired temperature level by exchange of heat with gas turbine exhaust gases. By the present invention, the vaporized cryogenic fluid is passed in heat exchange relationship with the turbine exhaust gases in successive serially connected heat exchange stages. Quantities of liquefied cryogenic fluid are combined with the vaporized cryogenic fluid passing through each of said stages so that the liquefied cryogenic fluid is vaporized and the resulting combined vapor is cooled prior to passing through the next successive heat exchange stage thereby utilizing the maximum heating capacity of said turbine exhaust gases.

It is, therefore, a general object of the present invention to provide an improved method of continuously vaporizing and superheating liquefied cryogenic fluid.

A further object of the present invention is the provision of an improved method of vaporizing and superheating a liquefied cryogenic fluid stream wherein the cryogenic fluid stream is heated and vaporized by exchange of heat with ambient water and then superheated to a desired temperature level by exchange of heat with turbine exhaust gases.

Yet a further object of the present invention is the provision of an improved method of vaporizing and superheating a stream of liquefied cryogenic fluid by exchange of heat with turbine exhaust gases wherein smaller and less expensive heat exchange apparatus is required and the maximum heating capacity of the turbine exhaust gases is utilized.

Other and further objects of the present invention will be apparent from the following detailed description of the presently preferred embodiments of the invention when read in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 illustrates, in diagrammatic form, one system which may be utilized for carrying out the improved method of the present invention, and

FIG. 2 illustrates, in diagrammatic form, a preferred arrangement of heat exchange and gas turbine apparatus for the system of FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to the drawings, and particularly to FIG. 1, one system which may be utilized for carrying out the method of the present invention is illustrated in diagrammatic form, and generally designated by the numeral 10. A stream of liquefied cryogenic fluid from a conventional liquefied cryogenicfluid storage tank 12, or other source, is pumped by pump 14 into one or more ambient water-cryogenicfluid heat exchangers 18 by way ofconduit 16. Theheat exchangers 18 may be a plurality of conventional open rack water heat exchangers or other conventional heat exchangers suitable for use with large volumes of ambient water. Aconduit 20 having one end disposed beneath the surface of the ambient water source is connected to one or moreconventional water pumps 22. The discharge of thepumps 22 is connected by aconduit 24 to the water inlet connection of theheat exchangers 18. After passing through theexchangers 18, the water is returned or recycled to its source by way of aconduit 26. As the liquefied cryogenic fluid stream passes through theheat exchangers 18, heat is exchanged between it and the water passing therethrough causing the cryogenic fluid stream to be heated and vaporized. The volume of water passed through theexchangers 18 is controlled so that the temperature drop in the water is maintained at a level meeting thermal pollution standards, e.g., 1 to 2 F.

A pair ofconventional gas turbines 28 and 30 are provided, each of which generates large volumes of hot exhaust gases through the combustion of fuel and air. Two gas turbines are provided in order to insure that one of the turbines is operable at all times and that a continuous stream of vaporized and superheated natu ral gas is produced. However, as will be described further hereinbelow, both of thegas turbines 28 and 30 are continuously operated.

The exhaust gases generated by thegas turbine 28 are conducted by way of a conduit orduct 32 to aheat exchanger 34. The cryogenic fluid stream heated and vaporized in the heat exchangers l8 exits theexchangers 18 by way of a conduit 36. The conduit 36 is connected to a pair ofconduits 38 and 40 and conventional controls are provided therein (not shown) for dividing the vaporized cryogenic fluid stream into two portions, the first portion passing intoconduit 38 and the second portion passing into theconduit 40. The first portion passes by way ofconduit 38 to a pair ofconduits 42 and 44 and conventional controls are provided (not shown) for dividing the first portion of the vaporized cryogenic fluid into two streams which pass through theconduits 42 and 44.

The stream of vaporized cryogenic fluid passing through theconduit 42 is conducted to heating tubes disposed within theheat exchanger 34. While passing through the heating tubes within theexchanger 34, heat is exchanged between the turbine exhaust gases and the vaporized cryogenic fluid stream so that the cryogenic fluid stream is heated to a predetermined temperature level. In addition, as will be described further hereinbelow, a quantity of liquefied cryogenic fluid is combined with the vaporized cryogenic fluid stream passing through theheat exchanger 34 so that the maximum heating capacity of the turbine exhaust gases is utilized. The superheated cryogenic fluid vapor exiting theheat exchanger 34 passes into aconduit 48 connected thereto.

The exhaust gases generated by theturbine 30 are conducted by way of a conduit orduct 50 to aheat exchanger 52. The stream of vaporized cryogenic fluid passing through theconduit 44 is conducted to heating tubes disposed within theheat exchanger 52. While passing through theexchanger 52, heat is exchanged between the turbine exhaust gases and the vaporized cryogenic fluid stream so that the cryogenic fluid stream is heated to a predetermined level of superheat. As in the case ofheat exchanger 34, a quantity of liquefied cryogenic fluid is combined with the cryogenic fluid vapor passing through theheat exchanger 52 and the resultant superheated cryogenic fluid exits theheat exchanger 52 by way of aconduit 56. The spent turbine exhaust gases exit theexchangers 34 and 52 by way of conduits orducts 58 and 60 from where the exhaust gases are vented to the atmosphere.

The second portion of the vaporized cryogenic fluid from theexchangers 18 passes through theconduit 40 to a pair ofconduits 62 and 64. Conventional controls are provided in theconduits 62 and 64 (not shown) for dividing the second portion of vaporized cryogenic fluid stream into two streams, one of which passes through theconduit 64 and the other through theconduit 62. The stream of vaporized cryogenic fluid passing through theconduit 64 is conducted to a plurality of heating tubes disposed within aheat exchanger 68. Combustion air for theturbine 28 is drawn from the atmosphere by way of a conduit through theheat exchanger 68 and then by way of aconduit 72 into thegas turbine 28. While passing through theheat exchanger 68, heat is exchanged between the stream of vaporized cryogenic fluid and the combustion air so that the combustion air is cooled. As has been heretofore known, the cooling of the combustion air utilized in thegas turbine 28 is advantageous in that the power output of theturbine 28 is increased accordingly. After passing through theheat exchanger 68 the vaporized cryogenic fluid stream is conducted by aconduit 74 to aconduit 76.

The stream of vaporized cryogenic fluid passing through theconduit 62 is conducted to a plurality of heating tubes disposed within aheat exchanger 80. Combustion air is drawn from the atmosphere by way of aconduit 82 through the heat exchanger and then by way of theconduit 84 to thegas turbine 30. The vaporized cryogenic fluid stream exiting theexchanger 80 is conducted by way of aconduit 86 to theconduit 76 where it is combined with the stream of vaporized cryogenic fluid passing through theconduit 76 from theheat exchanger 68. As will be described further herein, quantities of liquefied cryogenic fluid are combined with the vaporized cryogenic fluid streams passing through theexchangers 68 and 80 to prevent the formation of excessive quantities of ice in the exchangers. The combined vaporized cryogenic fluid stream is conducted by theconduit 76 to aconduit 88.

Theconduits 48 and 56 connected to theheat exchangers 34 and 52 respectively are connected to theconduit 88. Thus, the superheated cryogenic fluid streams passing from theexchangers 34 and 52 are combined in theconduit 88 with the stream of vaporized cryogenic fluid passing thereto by way ofconduit 76. From theconduit 88 the composite stream of vaporized and superheated cryogenic fluid is conducted by aconduit 90 to a vapor-liquid contactor 92. A stream of liquefied cryogenic fluid is conducted to thecontactor 92 by way of aconduit 94 connected thereto and connected to theconduit 16. The quantity of liquefied cryogenic fluid passed to thecontactor 92 by way of theconduit 94 is controlled such that the resultant combined stream exiting thecontactor 92 by way of the conduit 96 is at a desired specific temperature. That is, thecontactor 92 is utilized to combine a controlled quantity of liquefied cryogenic fluid with the stream of superheated cryogenic fluid passing therethrough so that the combined stream is produced at a desired temperature. Thus, in the event of operational fluctuations in the system 10 and load changes on theturbines 28 and 30, the temperature of the vaporized and superheated cryogenic fluid stream produced is maintained at a constant level. From the conduit 96 the vaporized and superheated cryogenic fluid is conducted to a point of use or distribution. Fuel for thegas turbines 28 and 30 may be drawn from the composite vaporized and superheated cryogenic fluid stream passing through theconduit 88 by way of aconduit 98 attached thereto.

Referring now to FIG. 2, a preferred arrangement of thegas turbines 28 and 30 andheat exchangers 34, 52, 68 and 80 is illustrated.

As shown in FIG. 2, the stream of cryogenic fluid heated and vaporized in theheat exchangers 18 is passed by way of conduit 36 to a-pair ofconduits 38 and 40. Theconduit 40 leads a portion of the vaporized cryogenic fluid to a pair ofconduits 62 and 64. Theconduit 64 leads a stream of the cryogenic fluid vapor to theheat exchanger 68 associated with thegas turbine 28. As previously described, atmospheric air is drawn through theheat exchanger 68 by way of the conduit 70 wherein it is cooled by heat exchange with the vaporized cryogenic fluid, and then passed by way ofconduit 72 to theturbine 28. A conventional temperature controller 100 is disposed in the air conduit orduct 72. The temperature controller 100 senses the temperature of the input air to theturbine 28 and opens or closes aconventional control valve 102 disposed in theconduit 64 accordingly. That is, if the temperature of the air passing through theconduit 72 is too high, the temperature controller 100 opens thecontrol valve 102 so that more cryogenic fluid vapor is passed through theheat exchanger 68 thereby providing additional cooling to the air, and vice versa.

The heating tubes disposed within theheat exchanger 68 are arranged in successive serially connected stages. That is, a first bank of heating tubes 104 is provided connected to theconduit 64. Asecond tube bank 106 is provided connected externally of theexchanger 68 in series with the tube bank 104 and athird tube bank 108 is connected externally of theexchanger 68 to thetube bank 106. The cryogenic fluid vapor stream exiting theheat exchanger 68 passes by way ofconduit 74 into theconduit 76 as previously described.Shutoff valves 110 and 112 are disposed in theconduits 64 and 74 respectively.

A quantity of liquefied cryogenic fluid is combined with the cryogenic fluid vapor stream passing through thetube bank 106 and a quantity of liquefied cryogenic fluid is combined with the vapor stream passing through thetube bank 108 in order to cool the resulting combined streams prior to their passage through the tube banks. This stage injection of liquefied cryogenic fluid is used to maintain the temperature of the cryogenic fluid vapor stream passing through theexchanger 68 at a relatively constant level thereby preventing the formation of excessive ice on the outside surfaces of the heating tubes. This method of cooling the turbine combustion air is described in detail in my US. Pat. No. 3,552,134 dated Jan. 5, 1971.

As shown in FIG. 2, the liquefied cryogenic fluid combined in theexchanger 68 is conducted by way of aconduit 114 to aheader 116. Theconduit 114 is connected to a source of liquefied cryogenic fluid which may be theconduit 16 downstream of the pump 14. A conduit 118 is connected to theheader 116 and to the outlet of the tube bank 104 of theexchanger 68. A conventional temperature control assembly 120 is disposed in the conduit 118 for controlling the quantity of liquefied cryogenic fluid injected. A block valve 122 is provided in the conduit 118. A conduit 124 is connected to theheader 116 and to the outlet of thetube bank 106. A temperature control assembly 126 and block valve 128 are disposed in the conduit 124.

As will be apparent from FIG. 2, theheat exchanger 80. associated with thegas turbine 30 is identical to theheat exchanger 68 described above. A portion of the cryogenic fluid vapor from theconduit 40 passes by way of theconduit 62 to theheat exchanger 80. Atemperature control valve 132 disposed within theconduit 62 is operably connected to aconventional temperature controller 134 disposed in the air conduit orduct 84. Successive serially connectedtube banks 130, 138 and 140 are provided in the heat exchanger and a block valve 142 is disposed in theoutlet conduit 86 which is connected to theconduit 76.Conduits 144 and 146 are provided connected to the liquefiedcryogenic fluid header 116 and to the tube banks and 138.Temperature control assemblies 148 and 150 and block valves 152 and 154 are provided in theconduits 144 and 146 respectively.

The portion of the vaporized cryogenic fluid passing throughconduit 38 is divided between theconduits 42 and 44 as previously described. As shown in FIG. 2, theconduit 42 is connected to heating tubes disposed within theheat exchanger 34 associated with theturbine 28. Theconduit 44 is connected to heating tubes disposed within theheat exchanger 52 associated with theturbine 30. As described above for the heat exchan'gers 68 and 80, each of theheat exchangers 34 and 52 include banks of heating tubes arranged in successive serially connected stages. That is, theheat exchanger 34 includes three serially connectedtube banks 156, 158 and 160 and theheat exchanger 52 includes three serially connectedtube banks 166, 168 and 170. Theconduit 42 is connected to the inlet of thetube bank 156 of theexchanger 34 and the outlet of the tube bank 160 thereof is connected by theconduit 48 to theconduit 88. Theconduit 44 is connected to the inlet of thetube bank 166 of theexchanger 52 and the outlet of thetube bank 170 thereof is connected by theconduit 56 to theconduit 88. Quantities of liquefied cryogenic fluid are injected or combined with the cryogenic fluid vapor passing through each stage or tube bank of each of theexchangers 34 and 52 so that the resulting composite vapor streams are cooled and the maximum heating capacity of the exhaust gases passing through theheat exchangers 34 and 52 are utilized. For this purpose, a pair ofconduits 162 and 164 are connected to theheader 116 and to the outlets of thetube banks 156 and 158 of theexchanger 34 and a pair of conduits 172 and 174 connect theheader 116 to the outlets of thetube banks 166 and 168. Conventionaltemperature control assemblies 176 and 178 and block valves 180 and 182 are disposed in theconduits 162 and 164 respectively. Similarly, conventional temperature controllers 184 and 186 and block valves 188 and 190 are disposed in the conduits 172 and 174 respectively. Shutofi or blockvalves 192, 194, 196 and 198 are disposed in theconduits 42, 48 44 and 56 respectively.

Theturbines 28 and 30 drive conventionalelectric generators 200 and 202 respectively.

OPERATION OF THE SYSTEM 10 The system 10 includes twoconventional gas turbines 28 and 30 which provide power for operating two conventionalelectric generators 200 and 202. The primary purpose of including two gas turbines and electric generators is to provide a standby turbine for providing hot exhaust gases and electric power in the event one of the turbines fails thereby insuring the production of a continuous stream of vaporized and superheated cryogenic fluid. However, in operation of the system 10, both of thegas turbines 28 and 30 are continuously operated. The electric power output of one of theelectric generators 200 or 202 is advantageously used for operating the liquefied cryogenic fluid pumps 14 and the ambient water pumps 22. The electric power output from the other electric generator may be sold to a power company or other electric power consumer.

The system 10 is designed so that the required minimum rate of vaporized and superheated cryogenic fluid may be produced utilizing the exhaust gases generated from one of theturbines 28 and 30. Thus, if one of the turbines fails and is taken out of service, the exhaust gases generated by the other turbine are used to vaporize and superheat the required minimum rate of cryogenic fluid and the power output of the electric generator associated therewith is utilized to operate thepumps 14 and 22.

During normal operation of the system 10, a stream of liquefied cryogenic fluid is pumped by the pump 14 through the ambient water cryogenicfluid heat exchangers 18 by way ofconduit 16. While passing through theexchangers 18 the stream of cryogenic fluid is heated and vaporized. As described above, the vaporized stream is split into two portions, the major portion of which passes by way ofconduit 38 to theconduits 42 and 44 where it is divided into two portions, one portion passing by way ofconduit 42 through theheat exchanger 34 and the other portion passing by way ofconduit 44 through theheat exchanger 52. While passing through theexchangers 34 and 52 the vaporized cryogenic fluid streams are combined with quantities of liquefied cryogenic fluid and the combined streams are superheated to desired temperature levels. The superheated streams then pass by way ofconduits 48 and 56 into theconduit 88. The particular quantities of liquefied cryogenic fluid injected in theheat exchangers 34 and 52 is controlled by thetemperature control assemblies 176, 178, 184 and 186. That is, thetemperature controllers 176 and 178 associated with theheat exchanger 34 are set so that the temperature of the combined stream exiting the exchanger by way ofconduit 48 is at a desired level, and the controllers 184 and 186 associated with theexchanger 52 are set similarly. Thus, during normal operation of the system 10, theheat exchangers 34 and 52 are each handling one-half the stream of cryogenic fluid heated and vaporized in theambient water exchangers 18. In order to utilize the full heating capacity of the exhaust gases produced by theturbines 28 and 30, liquefied cryogenic fluid is injected into theexchangers 34 and 52.

The minor portion of the vaporized cryogenic fluid stream from theexchangers 18 passes by way ofconduit 40 to theconduits 62 and 64 wherein it is divided into two portions, one of which passes through theheat exchanger 68 and the other through theheat exchanger 80. As described above, theheat exchangers 68 and cool the input combustion air to theturbines 28 and 30 respectively. The heated combined vaporized cryogenic fluid streams exiting theexchangers 68 and 80 are combined in theconduit 76 and conducted to theconduit 88 where they combine with the superheated cryogenic fluid streams from theexchangers 34 and 52. The composite stream is conducted byconduit 90 to thecontactor 92 wherein a small additional quantity of liquefied cryogenic fluid is combined with the composite stream to trim out the temperature of the stream. From thecontactor 92, the stream is conducted to a point of use or distribution.

As shown in FIG. 2, the portion of vaporized cryogenic fluid from theexchangers 18 which is routed to thecombustion air coolers 68 and 80 is controlled by the temperature controllers and 134 andcontrol valves 102 and 132. That is, the quantity of vaporized cryogenic fluid passed to theexchangers 68 and 80 is increased or decreased by thetemperature controllers 100 and 102 in accordance with the temperatures of the combustion air streams passing to theturbines 28 and 30. The remaining portion of the vaporized cryogenic fluid stream is divided substantially equally betweenconduits 42 and 44. The division of the stream may be accomplished through the utilization of con-.ventional flow controllers 43 and 45 disposed in theconduits 42 and 44. As will be understood by those skilled in the art, many various other control apparatus may be used for dividing the vaporized cryogenic fluid stream exiting theheat exchangers 18 into the various portions required.

In the event one of theturbines 28 or 30 either fails or must be shut down for other reasons, the required minimum rate of vaporized and superheated cryogenic fluid is produced by the system 10. Specifically, let it be assumed that theturbine 28 is shut down. Upon shut down of theturbine 28, the block valves disposed in the conduits to and from theheat exchangers 68 and 34 are closed. That is, thevalves 110, 112, 122 and 128 associated with theexchanger 68 are closed, and the valves 180, 182, 192 and 194 associated with theexchanger 34 are closed. Additionally, the flow of liquefied cryogenic fluid to theexchanger 52 by way of the conduits 172 and 174 is reduced or stopped. Thus, in operation of the system 10 with theturbine 28 and relating heat exchangers shut down, the stream of vaporized cryogenic fluid exiting the ambientwater heat exchangers 18 passes by way of the conduit 36 to theconduit 38 and 40. A minor portion of the vaporized cryogenic fluid stream passes by way of theconduit 40 to theheat exchanger 80 wherein it is utilized to cool the input combustion air to theturbine 30 in the same manner as described above. The major portion of the vaporized cryogenic fluid passes by way ofconduit 38 to theheat exchanger 52. As the vaporized cryogenic fluid stream passes through theexchanger 52 it is superheated to as high a temperature as possible without the addition of liquefied cryogenic fluid. Normally, the system 10, and specifically theheat exchangers 34 and 52 are designed so that when the entire superheating load is handled by one of theexchangers 34 or 52, the stream of cryogenic fluid is heated to a temperature only slightly higher than the desired temperature. In order to trim out the temperature, i.e., reduce the temperature of the cryogenic fluid stream to a desired level and allow for operational fluctuations and load changes, the stream is passed to the contactor 92 (FIG. 1) wherein a quantity of liquefied cryogenic fluid is combined therewith as described above. The quantity of liquefied cryogenic fluid combined in thecontactor 92 is controlled by conventional temperature control instruments (not shown) so that the resulting com bined stream exiting thecontactor 92 by way of the conduit 96 is at the desired temperature.

Thus, by the present invention, both of theturbines 28 and 30 are continuously operated with the maximum heating capacity of the turbine exhaust gases being utilized to vaporize and superheat cryogenic fluid. Further, the electric power output of the generators associated with the turbines is utilized to operate the various pumps of the system 10, with a portion thereof being sold to an outside consumer or otherwise utilized. In the event of a turbine shut down, the

required vaporized and superheatedcryogenic fluid 1 rate is produced by the system 10.

As will be understood, the present invention wherein controlled quantities of liquefied cryogenic fluid are stage combined with a vaporized cryogenic fluid stream being superheated by exchange of heat with turbine exhaust gases is not limited to use in the specific system described above and may be utilized to advantage in a variety of systems. By the use of the present invention, the surface area required for the turbine exhaust gas heat exchanger is reduced due to the resulting higher log mean temperature difference achieved.

in order to present a clear understanding of the present invention, the following example is given:

EXAMPLE Let it be assumed that the system 10 must be capable of producing a 929 mmscf/day stream of natural gas at a temperature of 60 F. During normal operation, a 1,496,500 lb/hr stream of liquefied natural gas (LNG) at a temperature of 260 F is pumped from thestorage tank 12 by the pump 14 to theheat exchangers 18 at a pump discharge pressure of 1000 psig. A 476,000 gpm stream of ambient water at a temperature of 70 F is pumped by thepumps 22 through theheat exchangers 18. For a 2 temperature drop in the water, 476,380,000 btu/hr are transferred from the ambient water stream to the LNG stream causing the LNG to be vaporized and heated to a temperature of 0 F. The vaporized natural gas stream at a temperature of 0 F is conducted by the conduit 36 to theconduits 38 and 40. AS88560 lb/hr portion of the natural gas is passed by way ofconduit 40 to theconduits 62 and 66. A 294,280 lb/hr stream is passed by way of theconduit 64 through the heating tubes disposed within theheat exchanger 68, and a 294,280 lb/hr stream is passed by way of theconduit 62 through the heating tubes disposed in theheat exchanger 80. Each of theexchangers 68 and 80 are operated in an identical manner. That is, a 767,800 lb/hr stream of combustion air at a temperature of 80 F (50 percent saturated with water) is drawn through theconduits 70 and 82 to theexchangers 68 and 80 respectively. As the combustion air stream is passed through theheat exchangers 68*and 80, 12,190,000 btu/hr of heat is transferred from the air to the natural gas streams, causing the air to be cooled to a temperature of 40 F. 35,456 lb/hr of LNG are combined with the natural gas passing through theheat exchangers 68 and 80. That is, 35,456 lb/hr of LNG are combined with the natural gas passing through thetube banks 104, 106 and 108 of theexchanger 68 and a 329,736 lb/hr combined stream of natural gas exits theheat exchanger 68 at a temperature of 3 F. 35,456 lb/hr of LNG are combined with the natural gas stream passing through thetube banks 130, 138 and 140 of the exchanger and a 329,736 lb/hr combined stream of natural gas exits theheat exchanger 80 at a temperature of 3 F. The natural gas streams from theexchangers 68 and 80 are combined and a 659,472 lb/hr stream of natural gas at a temperature of 3 F passes by way of theconduit 76 to theconduit 88.

A 907,940 lb/hr portion of the natural gas stream exiting theexchangers 18 at a temperature of 0 F passes by way of theconduit 38 to theconduits 42 and 44. 453,970 lb/hr of the natural gas passes by way ofconduit 42 through theexchanger 34. 220,878 lb/hr of LNG are combined with the natural gas in theexchanger 34, which LNG is vaporized and the resulting combined stream (674,848 lb/hr) is heated to a temperature of 150 F.

453,970 lb/hr of the natural gas at 0 F is passed by way of theconduit 44 through theheat exchanger 52. 220,878 lb/hr of LNG are combined with the natural gas in theheat exchanger 52 and the resulting combined stream of 674,848 lb/hr exits theexchanger 52 at a temperature of 150 F.

A 780,000 lb/hr stream of exhaust gases at a temperature of 950 F is produced by each of theturbines 28 and 30. The exhaust gases are conducted from theturbines 28 and 30 by theducts 32 and 50 respectively to theexchangers 34 and 52. 133,000,000 btu/hr are transferred from the turbine exhaust gases to the natural gas stream and injected LNG, and the spent exhaust gases exit theexchangers 34 and 52 at temperatures of 300 F. The superheated natural gas streams from theexchangers 34 and 52 pass by way of theconduits 68 and 56 respectively into theconduit 88 where they combine with the natural gas stream entering theconduit 88 by way of theconduit 76. The resultant composite stream (2,009,168 lb/hr) at a temperature of 100 F is conducted by way of the conduit to thecontactor 92. 135,016 lb/hr of liquefied natural gas is conducted to thecontactor 92 by way of theconduit 94 and the resultant natural gas stream exits the system 10 at a rate of l,l46,000,000 scf/day and a temperature of 60 F by way of the conduit 89.

In operation of the system 10 with one of theturbines 28 or 30 shut down, for example, with theturbine 28 shut down, the natural gas stream exiting theexchangers 18 at a temperature of 0 F is divided into major and minor portions, the minor portion (294,280 lb/hr) passing by way of theconduits 40 and 62 to theheat exchanger 80. A 329,736 lb/hr stream of natural gas exists theexchanger 80 by way of theconduits 86 and 76 at a temperature of 3 F. The major portion of the natural gas stream (1,202,220 lb/hr) at a temperature of 0 F passes by way of theconduits 38 and 44 to the turbine exhaustgas heat exchanger 52 associated with theturbine 30. While passing through theheat exchanger 52, 133,000,000 btu/hr is transferred from the turbine exhaust gases to the natural gas stream causing the natural gas stream to be superheated to a temperature of 175 F. Spent turbine exhaust gases at a temperature of 300 F are conducted from theexchanger 52 by way ofduct 60. The superheated natural gas stream from theexchanger 52 passes by way of theconduit 56 to theconduit 88 wherein it is combined with the natural gas passing into theconduit 88 by way of theconduit 76 making a total composite stream of 1,531,956 lb/hr at a temperature of 140 F. The composite stream is passed from theconduit 88 by way of theconduit 90 to thecontactor 92. A 205,971 lb/hr LNG stream is passed by way of theconduit 94 to thecontactor 92 wherein it intimately mixes with the natural gas stream. While within thecontactor 92, heat is transferred from the superheated natural gas stream to the LNG stream causing the LNG to be vaporized and combined with the natural gas stream resulting in a 929 mmscf/day stream of natural gas at a temperature of 60 F.

The present invention, therefore, is well adapted to carry out the objects and attain the ends and advantages mentioned as well as those inherent therein. While presently preferred systems for carrying out the method of the present invention are given for the purpose of disclosure, numerous changes can be made which will readily suggest themselves to those skilled in the art and which are encompassed within the spirit of the invention disclosed herein.

What is claimed is:

1. In a method of continuously vaporizing and superheating a stream of liquefied cryogenic fluid wherein the stream is vaporized and then superheated to a desired temperature level by exchange of heat with gas turbine exhaust gases, the improvement comprising:

passing said vaporized cryogenic fluid in heat exchange relationship with said turbine exhaust gases in successive serially connected heat exchange stages; and

combining a quantity of liquefied cryogenic fluid with the vaporized cryogenic fluid passing through each of said stages so that the liquefied cryogenic fluid is vaporized and the resulting combined vapor is cooled prior to passing through the heat exchange stage thereby utilizing the maximum heating capacity of said turbine exhaust gases.

2. The method ofclaim 1 wherein the liquefied cryogenic fluid is liquefied natural gas.

3. In a method of continuously vaporizing a stream of liquefied cryogenic fluid wherein the stream is vaporized and then superheated by exchange of heat with gas turbine exhaust gases, at least a portion of the vaporized cryogenic fluid stream being passed in heat exchange relationship with the turbine input air so that said air is cooled and the power output of the turbine increased, the improvement comprising:

dividing said stream of liquefied cryogenic fluid into first and second streams;

passing said first stream of liquefied cryogenic fluid in heat exchange relationship with a stream of ambient water so that said first stream is heated and vaporized;

passing said heated and vaporized stream in heat exchange relationship with said turbine exhaust gases in successive serially connected heat exchange stages; and

4. The method of claim 3 which is further characterized to include the steps of:

passing the portion of the vaporized cryogenic fluid stream heat exchanged with said turbine input air in successive serially connected heat exchange stages with said air; and

combining a portion of said second stream of liquefied cryogenic fluid with the vaporized cryogenic fluid passing through each of saidinput air heat exchange stages so that the resulting combined stream is cooled prior to passing through the stage thereby maintaining the formation of ice from water vapor contained in said air at a minimum.

5. The method of claim 4 wherein the liquefied cryogenic fluid is liquefied natural gas.

6. The method of claim 5 wherein a portion of the produced vaporized and superheated natural gas is utilized as fuel for said turbine.

7. In a method of continuously vaporizing a stream of liquefied cryogenic fluid wherein the stream is vaporized and then superheated by exchange of heat with gas turbine exhaust gases, at least a portion of the vaporized cryogenic fluid stream being passed in heat exchange relationship with the turbine input air so that said air is cooled and the power output of the turbine increased, the improvement comprising:

a. dividing said stream of liquefied cryogenic fluid into first, second and third streams;

b. passing said first stream of liquefied cryogenic fluid in heat exchange relationship with a stream of ambient water so that said first stream is heated and vaporized;

c. passing said heated and vaporized stream in heat exchange relationship with said turbine exhaust gases in successive serially connected heat exchange stages;

d. combining portions of said second stream of liquefied cryogenic fluid with the vaporized cryogenic fluid passing through each of said turbine exhaust gases heat exchange stages so that the liquefied cryogenic fluid is vaporized and the resulting combined stream is cooled prior to passing through the stage thereby utilizing the maximum heating capacity of said turbine exhaust gases; and

. combining said third stream of liquefied cryogenic fluid with the stream of heated and vaporized cryogenic fluid from step (d) so that the resultant composite vapor stream is produced at a desired temperature.

8. The method of claim 7 which is further characterized to include the steps of:

passing the portion of the vaporized cryogenic fluid stream heat exchanged with said turbine input air in successive serially connected heat exchange stages with said air; and

from water vapor contained in said air at a minimum. 9. The method of claim 8 wherein the liquefied cryogenic fluid is liquefied natural gas.

Claims (8)

1. 2. The method of claim 1 wherein the liquefied cryogenic fluid is liquefied natural gas.
2. 3. In a method of continuously vaporizing a stream of liquefied cryogenic fluid wherein the stream is vaporized and then superheated by exchange of heat with gas turbine exhaust gases, at least a portion of the vaporized cryogenic fluid stream being passed in heat exchange relationship with the turbine input air so that said air is cooled and the power output of the turbine increased, the improvement comprising: dividing said stream of liquefied cryogenic fluid into first and second streams; passing said first stream of liquefied cryogenic fluid in heat exchange relationship with a stream of ambient water so that said first stream is heated and vaporized; passing said heated and vaporized stream in heat exchange relationship with said turbine exhaust gases in successive serially connected heat exchange stages; and combining portions of said second stream of liquefied cryogenic fluid with the vaporized cryogenic fluid passing through each of said turbine exhaust gases heat exchange stages so that the liquefied cryogenic fluid is vaporized and the resulting combined stream is cooled prior to passing through the stage thereby utilizing the maximum heating capacity of said turbine exhaust gases to heat the combined stream to a desired level of superheat.
3. 4. The method of claim 3 which is further characterized to include the steps of: passing the portion of the vaporized cryogenic fluid stream heat exchanged with said turbine input air in successive serially connected heat exchange stages with said air; and combining a portion of said second stream of liquefied cryogenic fluid with the vaporized cryogenic fluid passing through each of said input air heat exchange stages so that the resulting combined stream is cooled prior to passing through the stage thereby maintaining the formation of ice from water vapor contained in said air at a minimum.
4. 5. The method of claim 4 wherein the liquefied cryogenic fluid is liquefied natural gas.
5. 6. The method of claim 5 wherein a portion of the produced vaporized and superheated natural gas is utilized as fuel for said turbine.
6. 7. In a method of continuously vaporizing a stream of liquefied cryogenic fluid wherein the stream is vaporized and then superheated by exchange of heat with gas turbine exhaust gases, at least a Portion of the vaporized cryogenic fluid stream being passed in heat exchange relationship with the turbine input air so that said air is cooled and the power output of the turbine increased, the improvement comprising: a. dividing said stream of liquefied cryogenic fluid into first, second and third streams; b. passing said first stream of liquefied cryogenic fluid in heat exchange relationship with a stream of ambient water so that said first stream is heated and vaporized; c. passing said heated and vaporized stream in heat exchange relationship with said turbine exhaust gases in successive serially connected heat exchange stages; d. combining portions of said second stream of liquefied cryogenic fluid with the vaporized cryogenic fluid passing through each of said turbine exhaust gases heat exchange stages so that the liquefied cryogenic fluid is vaporized and the resulting combined stream is cooled prior to passing through the stage thereby utilizing the maximum heating capacity of said turbine exhaust gases; and e. combining said third stream of liquefied cryogenic fluid with the stream of heated and vaporized cryogenic fluid from step (d) so that the resultant composite vapor stream is produced at a desired temperature.
7. 8. The method of claim 7 which is further characterized to include the steps of: passing the portion of the vaporized cryogenic fluid stream heat exchanged with said turbine input air in successive serially connected heat exchange stages with said air; and combining a portion of said second stream of liquefied cryogenic fluid with the vaporized cryogenic fluid passing through each of said input air heat exchange stages so that the resulting combined stream is cooled prior to passing through the stage thereby maintaining the formation of ice from water vapor contained in said air at a minimum.
8. 9. The method of claim 8 wherein the liquefied cryogenic fluid is liquefied natural gas.

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