US3552134A

US3552134A - Process and apparatus for vaporizing liquefied natural gas

Info

Publication number: US3552134A
Authority: US
Inventors: Edwin M Arenson
Original assignee: Black Sivalls and Bryson Inc
Current assignee: Black Sivalls and Bryson Inc
Priority date: 1969-07-22
Filing date: 1969-07-22
Publication date: 1971-01-05
Anticipated expiration: 1988-01-05
Also published as: DE2035488B2; JPS4915921B1; FR2055358A5; DE2035488C3; DE2035488A1; GB1285123A; AT311929B

Abstract

THE PRESENT INVENTION RELATES TO AN IMPROVED PROCESS AND APPARATUS FOR VAPORIZING LIQUEFIED NATURAL GAS WITH TURBINE EXHAUST GASES WHEREIN THE VAPORIZED NATURAL GAS IS PASSED THROUGH HEAT EXCHANGE TUBES IN A HEAT EXCHANGER FOR COOLING THE INPUT AIR TO THE TURBINE. A STREAM OF LIQUEFIED NATURAL GAS IS VAPORIZED AND HEATED WITH THE TURBINE EXHAUST GASES TO A TEMPERATURE WHICH WILL BRING ABOUT THE FORMATION OF A MINIMUM QUANTITY OF ICE ON THE OUTSIDE SURFACES OF A FIRST BANK OF SAID HEAT EXCHANGE TUBES, AND IS PASSED THROUGH SAID FIRST BANK OF HEAT EXCHANGE TUBES TO COOL THE TURBINE INPUT AIR. A SECOND STREAM OF LIQUEFIED NATURAL GAS IS THEN COMBINED WITH THE VAPORIZED NATURAL GAS STREAM TO COOL THE RESULTING COMBINED STREAM TO A TEMPERATURE WHICH WILL BRING ABOUT

THE FORMATION OF A MINIMUM QUANTITY OF ICE ON THE OUTSIDE SURFACES OF A SECOND BANK OF SAID HEAT EXCHANGE TUBES. THE COMBINED STREAM IS THEN PASSED THROUGH THE SECOND BANK OF HEAT EXCHANGE TUBES SO THAT THE TURBINE INPUT AIR IS COOLED FURTHER. AS MANY ADDITIONAL BANKS OF HEAT EXCHANGE TUBES MAY BE PROVIDED AS ARE REQUIRED TO COOL THE AIR TO A DESIRED TEMPERATURE, AND THE STREAM OF NATURAL GAS RECOOLED WITH ADDITIONAL STREAMS OF LIQUEFIED NATURAL GAS IN THE MANNER DESCRIBED ABOVE BEFORE IT ENTERS EACH BANK.

Description

Jim 5, 1971 E. M.ARENsoN Y 3,552,134

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Jan. 5, 1971 E. M.-ARENsoN 3,552,134

PROCESS AND APPARATUS FOR `VPORIZING LIQUEFIED NATURAL GAS Filed July 22, 1969 v v 2 sheets-sheet z United States Patent Ofice 3,552,134 Patented Jan. 5, 1971 PROCESS AND APPARATUS FOR VAPORIZING LIQUEFIED NATURAL GAS Edwin M. Arenson, El Reno, Okla., assignor to Black,

Sivalls & Bryson, Inc., Oklahoma City, Okla., a corporation of Delaware Filed July 22, 1969, Ser. No. 843,413 Int. Cl. F17c 7/02, F02m 3l /00 U.S. Cl. 62-53 14 Claims ABSTRACT OF THE DISCLOSURE The present invention relates to an improved process and apparatus for vaporizing liquefied natural gas with turbine exhaust gases wherein the vaporized natural gas is passed through heat exchange tubes in a heat exchanger for cooling the input air to the turbine. A stream of liquefied natural gas is vaporized and heated with the turbine exhaust gases to a'temperature which will bring about the formation of a minimum quantity of ice on the outside surfaces of a first bank of said heat exchange tubes, and is passed through said first bank of heat exchange tubes to cool the turbine input air. A second stream of liquefied natural gas is then combined with the vaporized natural gas stream to cool the resulting combined stream to a temperature which will bring about the formation of a minimum quantity of ice on the outside surfaces of a second bank of said heat exchange tubes. The combined stream is then passed through the second bank of heat exchange tubes so that the turbine input air is cooled further. As many additional banks of heat exchange tubes may be provided as are required to cool the air to a desired tempertaure,` and the stream of natural gas recooled with additional streams of liquefied natural gas in the manner described above before it enters each bank.

BACKGROUND OF THE INVENTION (l) Field of the invention The present invention relates generally to an improved process and apparatus for vaporizing liquefied natural gas, and more particularly, but not by way of limitation, to a process and apparatus for vaporizing liquefied natural gas with turbine exhaust gases wherein the turbine input air is cooled in stages with a strea/m of the vaporized natural gas. The stream of vaporized natural gas is maintained at a temperature level which will bring about the formation of a minimum quantity of ice within the apparatus.

(2) Background of the invention Liquefed natural gas is normally vaporized by the addition of heat to return into its natural gas state for use. For instance, natural gas may be liquefied and stored to provide gas for short periods of time during which demands are excessively high. This stored liquefied natural gas is at a temperature of 258 F., and must be heated in order to vaporize it and return it to its normal state for use.

A conventional turbine of the type used to generate electric power consumes enonmous quantities of air and generates large volumes of very hot exhaust gases. 'The horsepower output of the turbine may be increased by cooling the turbine input air.

Various processes have been proposed for vaporizing liquefied natural gas with turbine exhaust gases wherein the liquefied natural gas is used to cool the turbine input air. Also, processes hafve been proposed wherein the liquefied natural gas is rfirst vaporized with turbine exhaust gases, and then used to cool the turbine input air. These proposals have merit in that facilities embodying such processes may be used to both generate electricity and vaporize liquefied natural gas more economically than can separate facilities. However, a problem is encountered when it is attempted to cool turbine input air with liquefied natural gas in conventional heat exchange apparatus in that ice will form in the apparatus due to water vapor condensing and freezing therein. That is, liquefied natural gas at a temperature of 258 F. will cause the outside surfaces of heat exchanger tubes to have a temperature well below the temperature at which water vapor in atmospheric air will condense and freeze. Continued operation of such a heat exchanger will result in the formation of layers of ice within the heat exchanger until the pressure loss of the air passing through the heat exchanger is excessive, of the air flow is completely blocked olf by the ice in the heat exchanger.

Also, it has been found that a similar problem exists when it is attempted to cool turbine input air with a stream of vaporized natural gas. Since it is desirable to reduce the turbine input air from atmospheric conditions to a temperature of 30 F. to 40 F., if it is attempted to use vaporized natural gas to cool the air in a single stage of heat exchange, the vaporized natural gas must be at a temperature well below the condensing and freezing point of water vapor. Therefore, ice |will form in the heat exchange apparatus used in the same manner as described above.

The present invention is directed to an improved process and apparatus for vaporizing liquefied natural gas with turbine exhaust gases and cooling the turbine input air with the vaporized natural gas wherein the turbine air is cooled in two or more stages with a minimum of ice formed in the heat exchange apparatus used.

SUMMARY OF THE lINVENTION The present invention is directed to a process for vaporizing a stream of liquefied natural gas with turbine exhaust gases wherein vaporized natural gas is passed through heat exchange tubes in heat exchange relationship with the input air of the turbine thereby cooling the input air. A first stream of liquefied natural gas is vaporized and heated with turbine exhaust gases to a temperature which will bring about the formation of a minimum quantity of ice on the outside surfaces of the heat exchange tubes. The stream of vaporized natural gas is then passed through a first bank of the heat exchange tubes so that the turbine input air is cooled and the vaporized natural gas stream is heated. A second stream of liquefied natural gas is then combined with the streai of vaporized natural lgas so that the combined stream.- is cooled to said temperature and the second stream of liquelied natural gas is vaporized. The combined stream is then passed through a second bank of heat exchanger tubes so that said turbine input air is cooled further, and the combined stream is removed from the process. Apparatus is also provided by the present invention.

It is, therefore, a general object of the present invention to provide an improved process and apparatus for vaporizing liquefied natural gas.

A further object of the present invention is the provision of a process and apparatus for vaporizing liquefied natural gas with turbine exhaust gases wherein the vaporized natural gas may be used to cool the turbine input air.

Yet a further object of the present invention is the provision of an improved process and apparatus for cooling turbine input air with natural gas vaporized with the turbine exhaust gases wherein a minimum quantity of ice is formed on the outside surfaces of heat exchange tubes used to cool said turbine input air.

Still a further object of the present invention is the provision of relatively inexpensive apparatus for vaporizing liquefied natural gas with turbine exhaust gases and cooling the turbine input air with said vaporized natural gas wherein a minimum of ice will form in said apparatus an excessive pressure loss or stoppage of the air will not result.

Other objects and advantages of the invention will be evident from the following detailed description when read in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. l is a view of apparatus for carrying out the process of the present invention in diagrammatic form.

FIG. 2 is a side elevational view of the apparatus of the present invention, and

FIG. 3 is a top view, partially in section, of the apparatus of FIG. l.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to the drawings and particularly to FIG. o

l, a stream of atmospheric air is drawn through conduit into an air cooler 12. Air cooler 12 basically comprises a plurality of heat exchange tubes 14 for cooling the air passing therethrough. The cooled air passes out of air cooler 12 through conduit 16 into a conventional turbine 18. Turbine 18 is of the type wherein large quantities of air are mixed with natural gas and combusted thereby generating large volumes of hot exhaust gases. The exhaust gases from such a turbine will normally be at temperatures in the range of from 900 F. to 1000 F.

Turbine 18 is used to operate a conventional electric generator 20. The hot combustion gases from turbine 18 pass through conduit 22 into a liquefied natural gas heater 24. From heater 24 the exhaust gases pass through conduit 26 from where they may be vented to the atmos- K phere.

A stream of liquefied natural gas stored in storage tank 28 is pumped through conduit 30 into conduit 32 by a conventional pump 34. A conventional hand-controlled throttling-type valve 36 is disposed in conduit 32, and a conduit 38 is connected to conduit 32 upstream of valve 36. As will be described further herein valve 36 is adjusted so that a portion of the liquefied natural gas pumped by pump 34 passes into conduit 38. The major portion of the liquefied natural gas stream passes through valve 36 and conduit 32 into a bank 40 of heat exchanger tubes 2S, connected in series, and disposed within heater 24. The liquefied natural gas passing through heat exchanger tube bank 40 is vaporized and heated to a desired temperature by the turbine exhaust gases passing on the outside of heat exchanger tubes 25. The vaporized and heated natural gas is conducted from heater 24 through conduit 42.

A conventional temperature controller 44 is connected to conduit 42 to sense the temperature of natural gas passing therethrough. Temperature controller 44 may be any pneumatic or electric temperature controller which will generate a signal proportional to the deviation of the temperature sensed from a selected temperature. A bypass conduit 46 is attached to conduit 42 and to conduit 32. A conventional control valve 48 is disposed within conduit 46 which may be any conventional automatic control valve which will open and close in response to the signal generated by temperature controller 44.

Conduit 42 is connected to a tirst bank 50 of heat exchange tubes 14 connected in series and disposed within air cooler 12. Vaporized natural gas conducted to heat exchange tube bank 50 by conduit 42 passes through bank 50 thereby cooling the air passing on the outside of bank 50. The vaporized natural gas, which is heated while passing through heat exchanger tube `bank 50, passes into a header 88 which is connected to header 98.

Conduit 38 is connected to conduit 54 which is in turn connected to header 98. A conventional control valve 56 is disposed within conduit 54. A portion of the liquefied natural gas stream passing through conduit 38 passes through conduit 54, control valve 56 into header 98 wherein it mixes with the heated natural gas passing into header 98 from header 88. The combined stream then passes into a second bank 58 of heat exchange tubes 14 connected in series and disposed within air cooler 12. A conventional temperature controller 60 is disposed within header 98 to sense the temperature of the combined stream passing therethrough. Temperature controller 60 may be any conventional pneumatic or electric temperature controller which will generate a signal proportional to the deviation of the temperature sensed from a desired set temperature. Control valve 56 may be any conventional automatic control valve which will open and close in accordance with the signal generated by temperature controller 60.

The combined natural gas stream passes into heat exchanger tube bank 58 from header 98 and is heated by the air passing through air cooler 12 while cooling the air correspondingly. From heat exchanger tube bank 58, the natural gas stream passes into header 100 which is connected to header 104. A conduit 64 is connected to conduit 38 and to header 104, and a conventional control valve 66 is disposed therein. Liqueed natural gas from conduit 38 passes through conduit 64 and control valve 66 into header 104 where it is combined with the natural gas stream passing into header 104 from header 100. A conventional temperature controller 68 of the same type as described above is disposed within header 62 to sense the temperature of the stream of natural gas therein, and to open and close control valve 66 accordingly.

From header 104 the combined stream of natural gas passes into a third bank 70 of heat exchanger tubes 14 connected in series and disposed within air cooler 12. The combined natural gas stream passing through bank 70 is heated by the air while the air is cooled correspondingly. From heat exchanger tube bank 70 the natural gas stream enters conduit 72.

A conduit 74 is attached to conduit 72 and to conduit 42. A conventional control valve 76 is disposed within conduit 74. A conventional temperature controller 78 of the same type as described above is disposed within conduit 16 to sense the temperature of the air passing therethrough and to open and close control valve 76 accordingly.

Conduit 72 is connected to a bank 78 of heat exchanger tubes 25 connected in series and disposed within heater 24. A conduit 80 is connected to the oulet of heat exchange tube bank 78 for conducting the natural gas to a point of distribution or use. A bypass conduit 75 is connected between

conduits

72 and 80 having a conventional control valve 77 disposed therein. A conventional temperature controller 79 is connected to conduit 80 to sense the temperature of the natural gas passing therethrough and open and close control valve 77 accordingly.

Referring now to FIGS. 2 and 3 the apparatus of the present invention is shown mounted on a skid 82. The skid mounted apparatus basically comprises air inlet conduit 10, air cooler 12, turbine 18, electric generator 20, heater 24 and liquefied natural gas pump 34. As can be seen best in FIG. 3, heat exchange tubes 14 of air cooler 12 are grouped in three

banks

50, 58 and 70, previously described. Heat exchange tubes 14 in bank 50 are connected in series having an inlet 84 and an outlet 86. The conduit 42 is connected to the inlet 84 of bank 50, and the outlet 86 of bank 50 is connected to the header 88. Heat exchange tube bank 58 has an inlet 90 and an outlet 92, and heat exchange tube bank 70 includes an inlet 94 and an outlet 96. The header 98 is connected to the inlet of heat exchange tube bank 58, the header is connected to the outlet 92 of heat exchange tube bank 58 and the header 104 is connected to the inlet 94 of heat exchange tube bank 70. Conduit 72 is connected to the outlet 96 of heat exchange tube bank 70.

Headers

88 and 98 are connected together at the lower ends thereof by conduit 101, and headers 100 and 104 are connected together at the lower ends thereof by conduit 102.

Conduits

54 and 56, described above are connected to headers 98 and 104, respectively.

Heater 24 comprises a bank 40 of heat exchange tubes 25, connected in series, and a bank 78 of heat exchange tubes 2S, connected in series. Heat exchange tube bank 40 includes an inlet 106 and an outlet 108. Heat exchange tube bank 78 includes an inlet 1101 and an outlet 112. Conduit 32 is connected to the inlet 106 of heat exchange tube bank 40, and conduit 42 is connected to the outlet 108 of heat exchange tube bank 40. Conduit 72 is connected to the inlet 110 of heat exchange tube bank 78 and conduit 80 is connected to the outlet 112 of heat exchange tube bank 78.

OPERATION Referring now to FIGS. 1 through 3, atmospheric air is drawn through conduit into air cooler 12 wherein it is cooled from atmospheric conditions to from about 30 F. to about 40 F. The cooled air then passes through conduit 16 into the air intake of turbine 18. Natural gas enters turbine 18 through conduit 81 which is connected to conduit 80. A conventional shutoff valve 83 and pressure regulator 85 are disposed in conduit 81. The natural gas and, air are combusted within turbine 18 to provide energy for operating electric generator 20. Hot exhaust gases having a temperature in the range from about 900i F. to about 1000 F. pass out of turbine 18 into conduit 22.' Conduit 22 leads the hot combustion gases into heater 24 from where the exhaust gases are vented to the atmosphere through conduit 26.

A stream of liquefied natural gas is pumped from storage tank 28 or other source through conduit 30 into conduit 32 by pump 34. Valve 36 in conduit 32 is adjusted so that the stream of liquefied natural .gas is divided into two streams, one passing into conduit 38, and the other passing through conduit 32 into heat exchange tube bank 40 disposed within heater 24.

The stream' of liquefied natural gas passing through heat exchange tube bank -40 is heated and vaporized through exchange of heat with the exhaust gases passing through heater 24 on the outside of heat exchange tubes 25. The vaporized natural gas then passes into conduit 42. Temperature controller 44 senses the temperature of the vaporized natural gas passing into conduit 42, and opens or closes valve 48 accordingly. When valve 48 is opened a portion of the liquefied natural gas bypasses heat exchange tube bank 40 and mixes with the heated and vaporized natural gas entering conduit 42 from bank 40. Upon mixing the combined stream will be cooled and the portion of liquefied natural gas bypassed will be vaporized. In operation, temperature controller 44 is set to control the vaporized gases passing into conduit 42 at a ternperature of approximately -[10 F. The temperature of the liquefied natural

gas entering conduits

32 and 38 is approximately -258 F.

The vaporized natural gas stream passes through conduit 42 and enters bank 50 of heat exchange tubes 14 disposed within air cooler 12. Heat is exchanged between the natural gas within tubes 12 and the air passing on the outside of tubes 12 so that the air is cooled and the natural gas is heated.

As will be understood by those skilled in the art, natural gas at a temperature of |10 F. passing through heat exchange tubes 14 of bank 50 will result in an initial outside heat exchange tube wall temperature below 32 F. Thus, Water vapor contained within the air passing over the outside of heat exchange tubes 12 will condense and freeze on the outside surfaces of tubes 12. The ice formed on the outside surfaces of tubes 12 will build up and heat transferred from the inside of tubes 12 to the outside will be impeded proportionately. However, the formation of ice on the outside of heat exchange tubes 12 will reach a state of equilibrium when the ice reaches a thickness which will prevent the outside surface of the ice from having a temperautre below 32 F. Thus, by maintaining the temperature of the natural gas passing through the inside of heat exchange tubes 12 at a temperature approaching 32 F., such as a temperature of |10 F., only a thin layer of ice will be formed on the outside surfaces of the tubes 12 when equilibrium is reached. This thin layer will not impede the fiow of air over the tubes, or reduce the effective heat exchange area of the tubes appreciably. However, by maintaining the temperature of the natural gas passing through the heat exchange tubes 12 at a temperature of +10 F. or higher, the temperature of the air passing over tubes -12 can be reduced only a limited amount in a conventional single stage heat exchanger. Assuming an inlet air temperature of F., if it is attempted to reduce the temperature of the air to from 30 F. to 40 F. with +10 F. natural gas, a very large and expensive heat exchange apparatus would be required. The present invention provides a process and apparatus wherein the air is cooled in a plurality of stages thereby allowing relatively small inexpensive heat exchange apparatus to be used while at the same time preventing the formation of thick layers of ice on the outside of the heat exchange tubes.

This is Iaccomplished by passing natural gas at a ternperature of approximately {10 F. through the first bank 50 of the heat exchanger tubes 12. Heat is transferred out of the, air passing over the tube bank l50 and into the natural gas, cooling the air and heating the natural gas. The thus heated natural gas enters header #88 and passes through conduit into header 98. In order to cool the heated natural gas stream to a temperature of approximately +10 F. a controlled quantity of liquefied natural gas at a temperature of 258 F. is injected into header 98 through conduit 54. As will be understood, the liquefied natural gas will be vaporized when it mixes with the natural gas passing through header 98, and will cool the resulting combined stream of natural gas. Temperature controller y60 senses the temperature of the combined stream of natural gas and opens or closes valve 56 accordingly. That is, temperature controller 60 is set to maintain the combined stream of natural gas passing through header 98 at a temperature of approximately +l0 F., and controls the ow of liquefied natural gas into header 98 accordingly. The thus cooled combined natural gas stream passes into bank 518 of heat exchanger tubes 14. Additional heat is transferred from the air passing through air cooler 12 to the natural gas stream within tube bank 58 cooling the air further. The heated natural gas stream passing out of tube bank 58 enters header 100 and passes through conduit 102 into header 104. An additional quantity of liquefied natural gas is injected into header 104 to cool the natural gas passing therethrough. Temperature controller 68 is set to control the temperature of the combined stream of natural gas passing through header 104 at +10 F. The thus cooled gas passes from header 104 into tube bank 70 wherein additional heat is transferred to it from the air passing on the outside of tube bank 70. Thus, the air passing through air cooler '12 is cooled in successive stages so that a minimum quantity of ice is formed on the outside of heat exchanger tubes 14, and so that air cooler 12 may Ibe relatively small in size and cost.

Temperature controller 78 disposed in conduit 16 senses the temperature of the cooled air passing from air cooler 12 into turbine 18. If the temperature of the air is too cold, temperature controller 7&8 opens control valve 76 causing a portion of the natural gas passing through conduit 42 to bypass air cooler 42, thereby raising the temperature of the air passing through air cooler 12, and vice versa.

The stream of natural gas from -air cooler 12 passes through and mixes with natural gas bypassed through conduit 7'4. The natural gas stream then passes into heat exchanger tube bank 7|8 disposed in heater 24. While passing through tube bank 78, the natural gas contained therein is heated by the turbine exhaust gases passing on the outside of the tubes 25 to a desired temperature. The super heated natural gas passes out of tube bank 78 into conduit `80 from where it is conducted to a point of use or distribution. Temperature controller 79 senses the temperature of the gas stream passing through conduit 80 and opens or closes bypass valve 77 accordingly.

Thus, an improved process and apparatus for vaporizing liquefied natural gas with turbine exhaust gases is provided wherein the turbine input air is cooled in successive stages with vaporized natural gas, thereby preventing the formation of large quantities of ice on the air cooler heat exchange tubes and permitting relatively small inexpensive apparatus to be used.

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 embodiments of the invention are given for the purpose of disclosure, numerous changes can `be made which will readily suggest themselves t0 those skilled in the art, and which are encompassed within the spirit of the invention disclosed herein.

What is claimed is:

1. In a process for vaporizing a stream of liquefied natural gas with turbine exhaust gases wherein the vaporized natural gas stream is passed through heat exchange tubes in heat exchange relationship with the input air of said turbine to cool said input air, the improvement comprisvaporizing and heating a first stream of liquified natural gas with said turbine exhaust gases to a temperature which will bring about the formation of a minimum quantity of ice on the outside surfaces of said heat exchange tubes;

passing said first stream through a first bank of said heat exchange tubes so that said turbine input air is cooled and said stream is heated;

combining said first stream with a second stream of liquefied natural gas so that the resulting stream is cooled to said temperature and said second steam is vaporized;

passing said cooled combined stream through a second bank of said heat exchange tubes so that said turbine input air is cooled further; and

removing said combined stream from said process.

2. The process of claim 1 which is further characterized to include the additional step of z heating said combined stream with said turbine exhaust gases to a desired level of super heat.

3. The process of claim 1 which is further characterized to include the steps of 2 controlling the flow rate of said rst stream in proportion to the temperature of said cooled turbine input air, and

controlling the flow rate of said second stream in proportion to the temperature of said combined stream. 4. The process of claim 1 wherein is further characterized to include the additionals steps of:

combining a third stream of liquefied natural gas with said combined stream so that the resulting stream is cooled and said third stream is vaporized; and

passing said combined cooled stream through a third bank of said heat exchanger tubes so that said turbine input air is cooled further.

5. The process of claim 4 which is further characterized to include the additional steps of:

controlling the ow rate of said rst stream in proportion to the temperature of said cooled turbine input air;

controlling the ow rate of said second stream in proportion to the temperature of the combined stream comprised of said first stream and said second stream; and

controlling the flow rate of said third stream in pro- Cil portion to the temperature of the combined stream comprised of said first, second and third streams.

6. 1n apparatus for vaporizing liquefied natural gas with turbine exhaust gases which includes a turbine input air heat exchanger wherein a stream of vaporized natural gas is passed through heat exchange tubes to cool said turbine input air, the improvement comprising:

means attached to said apparatus for controlling the temperature of said stream of vaporized natural gas at a level which will bring about the formation of a minimum quantity of ice on the outside surface of said heat exchange tubes;

said heat exchange tubes being arranged in a first bank and a second bank, each of said banks having an inlet and outlet;

a first conduit connected to the inlet of said first bank of heat exchange tubes for conducting said stream of vaporized natural gas therethrough;

a second conduit connected to the outlet of said first bank of heat exchange tubes and connected to the inlet of said second bank of heat exchange tubes for conducting said stream of vaporized natural gas therebetween;

means attached to said second conduit for injecting a stream of liquefied natural gas therein so that said stream of liquefied natural gas is vaporized and the resulting combined stream of natural gas is cooled; and

a third conduit connected to the outlet of said second bank of heat exchange tubes for removing said com- `bined stream of natural gas from said second bank of heat exchange tubes.

7. The apparatus of claim 6 which is further characterized to include means for heating said removed combined stream of natural gas to a desired level of super heat with said turbine exhaust gases.

8. The apparatus of claim 6 which is further characterized to include means for controlling the fiow rate of said stream of vaporized natural gas passing into said first conduit in proportion to the temperature of the cooled turbine input air.

9. The apparatus of claim 6 which is further characterized to include means for controlling the ow rate of said stream of liquefied natural gas injected into said second conduit in proportion to the temperature of said combined stream of natural gas passing from said second conduit into said second bank of heat exchange tubes.

10. In apparatus for vaporizing liquefied natural gas with turbine exhaust gases which includes a turbine input air heat exchanger wherein a stream of vaporized natural gas is passed through heat exchange tubes to cool said turbine input air, the improvement comprising:

means attached to said apparatus for controlling the temperature of said stream of vaporized natural gas at a level which will bring about the formation of a minimum of quantity of ice on the outside surface of said heat exchange tubes;

said heat exchange tubes being arranged in a first bank, a second bank, and a third bank, each of said banks having an inlet and an outlet;

a second conduit connected to the outlet of said rst bank of heat exchange tubes and connected to the inlet of said second bank of heat exchange tubes for conducting said stream of vaporized natural gas therebetween;

means attached to said second conduit for injecting a first stream of liquefied natural gas therein so that said first stream of liquefied natural gas is vaporized and the resulting combined stream of natural gas is cooled;

a third conduit connected to the outlet of said second bank of heat exchange tribes and connected to the inlet of said third bank of heat exchange tubes for conducting said combined stream of vaporized natural gas therebetween;

means attached to said third conduit for injecting a second stream of liquefied natural gas therein so that said second stream of liquefied natural gas is vaporized and the resulting combined stream is cooled;

a fourth conduit connected to the outlet of said third bank of heat exchange tubes for removing said combined stream of vaporized natural gas from said third bank of heat exchange tubes.

11. The apparatus of claim 10 which is further characterized to include means for heating said removed combined stream of natural gas to a desired level of super heat with said turbine exhaust gases.

12. The apparatus of claim 10 which is further characterized t0 include means for controlling the ow rate of said stream of vaporized natural gas passing into said irst conduit in proportion to the temperature of the cooled turbine input air.

13. The apparatus of claim 10 which is further characterized to include means for controlling the iiow rate of said stream of liquefied natural gas injected into said second conduit in proportion to the temperature of said combined stream of natural gas passing from said second conduit into said second bank of heat exchange tubes.

14. The apparatus of claim 10 which is further characterized to include means for controlling the ilow rate of said stream of liquefied natural gas injected into said third conduit in proportion to the temperature of said combined stream of natural gas passing from said third conduit into said third bank of heat exchange tubes.

References Cited UNITED STATES PATENTS 2,958,189 11/1960 Britton et al. 60-39.71X 3,438,216 4/1969 Smith 62-52 ALBERT W. DAVIS, JR., Primary Examiner U.S. Cl. X.R.