Search International and National Patent Collections
Some content of this application is unavailable at the moment.
If this situation persists, please contact us atFeedback&Contact
1. (WO2007008851) FLUID VAPORIZER
Note: Text based on automatic Optical Character Recognition processes. Please use the PDF version for legal matters

FLUID VAPORIZER

FIELD OF THE INVENTION
This invention relates to the field of heating cryogenic fluids to ambient temperature. The
invention is particularly applicable to the
vaporizing of liquefied natural gas.

BACKGROUND INFORMATION
Liquefied Natural Gas (LNG) is a hydrocarbon mixture comprised primarily of methane, but typically also contains some lower hydrocarbons c2 through c4. This liquid, in the existing technology, is transported at sea by special tanker vessels at near atmospheric pressure and a temperature of approximately -161 degrees C.

These tanker vessels typically discharge their cargo at in-harbor ordinary piers into storage tanks. The gas is then typically dispatched from the storage tanks via ambient temperature and moderately high-pressure pipelines to consumers. The distribution pipeline pressure is usually in the range of 5 MPa to 12 MPa. Before being dispatched, the gas must be heated.

The heating is ordinarily done in heat exchangers using seawater if this is available at a suitable temperature or by using some of the gas to heat the warming fluid used in the heat exchangers . US
Patents 6,739,140 and 5,806,470 exemplify heat exchangers using water as the warming fluid. These heat exchangers require large surfaces for the transfer of the heat. Furthermore the surfaces must be made from costly materials such as for example stainless steel, aluminum, or titanium that retain ductility in the presence of the cryogenic fluid. It is important to avoid the formation of ice in the heat exchangers that use water as the warming fluid;

otherwise the capacity of the heat exchanger will be degraded. Heat exchangers using ambient temperature water from the sea may suffer difficulty in being permitted because they may discharge large volumes of cold water into a warmer body of water causing a potential environmental problem.

Another class of cryogenic fluid vaporizers uses other warming fluids such as dry air, dry nitrogen, or other fluids that cannot solidify in presence of the cold from the cryogenic fluids . US Patent
6,367,429 exemplifies these heat exchangers. The warming fluid in this type of vaporizer may be indirectly heated in a heater of known design such as a furnace or may be indirectly heated by another fluid -such as water in a second heat exchanger.

Vaporizers of cryogenic fluids in the known art are characterized by having large surfaces that are subjected to the low temperature of the cryogenic fluid and which must be made from high cost
materials. One application of cryogenic fluid vaporizers is to vaporize LNG on the tanker
delivering the LNG. The tanker in this application converts by onboard heat exchangers the LNG to ambient temperature Compressed Natural Gas (CNG) before discharging the CNG from the tanker into a delivery pipeline system. This is exemplified by the system just taken into use (early 2005) by the firm Excelerate in the Gulf of Mexico. In the Excelerate system the boilers of the vessel are used to deliver the heat to the LNG vaporizers thereby limiting the capacity for heat exchange to that of the boilers on the vessel. This capacity limitation increases the discharge time of the tanker from a normal one-day at typical LNG receiving terminals to about 5 days. The added cost is on the order of US$300,000 per shipload or about US$6 per tonne of LNG delivered.

This is a very significant cost penalty considering that the value of the gas may be about US$200 per tonne .

An alternative would be to deliver the LNG from the ship at a high rate and then heat the LNG using the heat content of the seawater such as proposed in US Patent 6,880,348 and in PCT application WO
2004/080790. These systems entail large heat
exchanger surfaces of costly materials and possible environmental objections from discharging large volumes of cold water into the sea. Another
alternative would be to deliver LNG to a heat exchanger adjacent to the delivery tanker and provide the warming from a furnace or from electric power provided by a sub sea cable. In both cases high operating costs result possibly in the order of US$200,000 per tanker load. In addition costly maintenance of complex systems placed offshore results .

The present invention is applicable to all
situations in which cryogenic fluids are vaporized and delivered to a pipeline; however, it is
particularly advantageous in connection with the discharge of LNG from a ship into an ambient
temperature pipeline.

The invention described in PCT application WO
2004/080790 requires large quantities of materials suitable for direct contact with cryogenic fluids such as titanium, aluminum, and stainless steel . The present invention makes it possible to construct such heat exchangers largely from low cost materials such as carbon steel .

SUMMARY OF THE INVENTION The present invention relates to a system for vaporizing a fluid comprising a cryogenic source of a fluid, the fluid from the cyogenic source being at a temperature no greater than -90 degrees C and a first pump receiving the fluid from the cryogenic source and discharging the fluid into a mixing chamber in combination with a warmed source of the fluid and an outlet from the warmed source of the fluid into the mixing chamber, wherein a temperature of a mixture of the fluid from the warmed and cryogenic sources in the mixing chamber is no less than -80 degrees C.

In other aspects the invention relates to the heating of cryogenic fluids to ambient temperature using the sea or atmospheric air to indirectly heat the cryogenic fluid conveyed in pipes . A specific example is the heating of LNG from its atmospheric boiling temperature, approximately -161 degrees C to ambient temperature. The heated gas will normally be delivered to a gas pipeline with an operating pressure in the range of 5 to 12 MPa.

The heating of the LNG is in this invention achieved by mixing natural gas with the LNG in such
proportions that the mixture achieves a temperature suitable for conveyance in carbon steel pipes forming part of a heat exchanger to heat the gas .

The natural gas used for mixing may be obtained by re-circulating a portion of the heated gas.

The LNG may be maintained at all times above the critical pressure during the heating process such that it is converted to. pressurized gas at near ambient temperature without changing into two phases at any time during the heating process . In this event the pressures remain nearly constant in the system under steady state flow conditions, however, the invention is also applicable to systems where the pressures are maintained below the critical pressure. For systems where the pressure is below the critical pressure of the cryogenic fluid being heated pressure fluctuations and surging may result in the system.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is a diagram of a first embodiment of the invention in which all motive power comes from a high-pressure cryogenic fluid pump.
Figure 2 is a side view of an application of the first embodiment in which the heat for vaporization is obtained from a body of water such as the sea. Figure 3 is a side view of an application of the first embodiment in which the heat for vaporization is obtained from the atmosphere.
Figure 4 is a diagram of a second embodiment of the invention similar to the first embodiment except that a separate pump or compressor is used to re-circulate a part of the warmed gas instead of a jet pump .
Figure 5 is a diagram of a third embodiment of the invention similar to the second embodiment in which the heating of the cryogenic fluid takes place in multiple stages.
Figure 6 is a partial side view of an application of the third embodiment to a vessel delivering gas through an offshore mooring.
Figure 7 is a diagram of the application of the third embodiment shown on figure 6.
Figure 8 is a drawing showing a floating LNG import terminal .
Figure 9 is a drawing an application of the second embodiment of the invention showing the mounting of the heat exchanger in the sea below the waterline of the floating LNG import terminal on its hull.
Figure 10 is a drawing of the second embodiment of the invention showing the mounting of the heat exchanger in the air above the waterline of the floating LNG import terminal outside the hull.
Figure 11 is a drawing of the third embodiment of the invention in which the LNG is only partly heated aboard the floating LNG import terminal
Figure 12 is a diagram of a fourth embodiment of the invention in which the cryogenic fluid is
pressurized to a pressure substantially above that of the receiving pipeline and the warmed gas is then used to extract energy from the system upon
depressurization to the pipeline pressure.
Figure 13 shows a diagram of a fifth embodiment of the invention similar to the third embodiment in which the invention is employed to increase the capacity of an existing or conventional vaporizer.

DETAILED DESCRIPTION
Calculations in the following are all based on a computer program by the US National Institute of Standards and Technology REFPROP version 7.0
(Reference Fluid Thermodynamic and Transport
Properties), hereinafter referred to as Reference 1.

Figure 1 shows a first embodiment of the invention. A pump 11 takes suction of a cryogenic fluid from a source (not shown) through the pipe 10. Those skilled in the art will understand that the term cryogenic fluid may refer to any fluid with a temperature below 0 degrees C. However, for the purposes of this application, cryogenic fluids refer to fluids that have a temperature of no more than -90 degrees C. The pump 11 delivers the cryogenic fluid to jet pump 19 through pipe 20. Jet pump 19 takes suction through pipe 24 and delivers the combined flows from pipes 20 and 24 to mixing chamber 21, which delivers the mixture to pipe 22. There is virtually no flow of heat into pump 19 and mixing chamber 21; therefore there must be
conservation of enthalpy such that the sum of the enthalpies flowing into the pump 19 from pipes 20 and 24 almost equals the enthalpy flowing out through mixing chamber 21, which delivers the mixture to pipe 22. Thermal effects of expansion and contraction are ignored in this context, because they would normally be small in the practical application of this invention. As a result the temperature in pipe 22 is higher than the
temperature in pipe 20 but lower than the
temperature in pipe 24. Pipe 20 must be made of a materiel that can safely carry the cryogenic fluid at temperatures that may be as low as -161 deg C or even lower. As taught in this invention the
temperatures in pipes 22 and 24 will be maintained at levels that permit the use of low cost carbon steels in all pipes shown on figure 1 except pipes 20 and 10. With present technologies of steel making high quality low cost carbon steel pipes capable of safely conveying fluids under high pressure can be obtained in the market for temperatures to at least as low as -58 deg C and possibly as low as -80 degrees C or lower. The term low cost is in
comparison to the cost of cryogenic piping typically made from stainless steel, aluminum, or titanium. Pipe 22 conveys the1 fluids to manifold 30, which distributes the flow among a number of parallel pipes 23. Pipes 23 are immersed in a heating fluid taking its heat from nature such as the sea or the atmosphere. Pipes 23 would typically comprise a large number of pipes such as 10 or even 50 or more. However pipes 23 may also comprise a single pipe. Heat will flow from the warming fluid, which may be either a body of water or the atmosphere or both into pipes 23 thereby warming the fluid flowing through pipes 23. Because the temperature at
manifold 30 is below 0 deg C, ice (not shown) will normally form on the outside of pipes 23. The ice (not shown) acts as a thermal insulator and
therefore reduces the efficiency of heat transfer into pipes 23. This factor is overcome in this invention by simply making the total surface area of pipes 23 large enough that the temperature of fluids reaching manifold 31 is only a few degrees (e.g., 3 degrees C) below the temperature of the warming fluid in which the pipes 23 are immersed.

Pipes 23 terminate in a manifold 31 that delivers the fluid to pipe 26. If the warming fluid is the ocean at a location where the ocean water never becomes colder than 8 degrees C, then the system in Figure 1 will always deliver the fluid to export pipeline 29 at 5 degrees C or higher. It is a common requirement for the inlet temperature to a pipeline that the temperature be 5 deg C or higher. In the event the warming fluid is the atmosphere, reliable heating to +5 degrees C may always be achieved with proper sizing of the pipes 23 in tropical locations. However, in subtropical or temperate climates and in locations where the seawater temperature dips below 8 degrees C it may be necessary to place a heater 28 between the pipe 26 and the export pipeline 29.
Heater 28 is heated from a source (not shown) which may be a small portion of the fluid carried in pipe 26 which may for example burned in an indirectly fired heat exchanger 28 as is known in the art.
Heater 28 is thus optional depending on the warming fluid in which the pipes 23 are immersed. Downstream from heater 28 there is a tee 33 at which a portion of the warmed fluid is returned to jet pump 19 via pipe 24. Heater 28 limits the capacity of the system in cold climates, because heater 28 can always deliver the gas at a specified temperature such as 5 degrees C. Therefore the performance of jet pump 19 is invariant and the temperature of pipe 24 always remains within a narrow range. Tee 33 could also be placed upstream of heater 28 (not shown) . In this case the capacity of the system will decrease as the temperature of the warming fluid decreases because the temperature of pipe 22 will decrease with reduced temperature of the warming fluid and may reach the low temperature limit for the materials in pipes 22, 26 or 23. In this case the flow through pump 11 must be reduced to reduce the negative enthalpy introduced into the jet pump 19. The jet pump 19 provides all the power for overcoming the fluid friction in the loop comprised of pipe 22, manifold 30, pipes 23, manifold 31, pipe 26, heater 28, tee 33, and pipe 24. Ordinary heaters used as heater 28 typically have fairly high fluid flow resistance. For this reason in some applications it may be advantageous to place heater 28 in pipe 29 downstream (not shown) of tee 33.

Figure 2 shows a practical example of a system to vaporize LNG constructed as per the first embodiment of the invention. A tank 101 contains LNG at
atmospheric pressure and a temperature of -161 deg C. A high-pressure pump 11 is placed inside tank 101 in order to maintain it cold. Pump 11 takes suction through pipe 10 from within tank 101 and delivers the high-pressure fluid through pipe 20 to jet pump 19.' Jet pump 19 takes suction from pipe 24 and delivers the combined flow from pipes 20 and 24 to mixing chamber 21, which delivers the mixture to pipe 22. Pipe 22 terminates in manifold 30 that distributes the flow between a plurality of pipes 23, of which only two are shown. Pipes 23 are immersed in seawater 103 and are attached to a trestle 104 supported on piles 107 which in turn are supported on the seabed 109. Most traditional LNG terminals are equipped with a trestle 104 leading to a wharf (not shown) where LNG tankers (not shown) are typically moored to discharge their cargo into tank 101 through a system of pipes (not shown) . The pipes 23 are attached to the piles 107 below the sea surface 105 and are continually immersed in the seawater 103. Trestle 104 may be quite long on the order of one km or more or very short on the order of 100 m or less all depending on local
circumstances at the terminal. Suppose trestle 104 is 1000 m long, then each pipe 23 making a single loop can be 2000 m long. Pipes 23 terminate at the downstream end at manifold 31, connecting via pipe 26 to indirectly fired heater 28. In the event the fluid conveyed in pipe 26 is warmer than the minimum inlet temperature to pipeline 29 then heater 28 will not be fired and will therefore not consume any fuel . In the event the temperature of the fluid in pipe 26 is below that specified for pipeline 29 the heater 28 will be fired just sufficiently to bring the temperature of the fluid flowing into pipeline 29 up to the specified temperature. A substantial portion or all the heat to vaporize the LNG is provided by the seawater 103, thereby minimizing loss of gas to heating. This loss is usually on the order of 1.5% of the flow in pump 11 at facilities that exclusively use the heat from firing the gas to vaporize the LNG. A portion of the vaporized gas is returned to jet pump 19 through pipe 24. The mass flow in pipeline 29 is equal to the mass flow through pump 11 less any gas used to fire heater 28.

Assume that in the example shown in figure 2 that the mass flow rate in pipe 22 is 250 kg/sec and the pressure in pipe 20 is 11 Mpa. Assume further that the backpressure in pipe 29 is 10 MPa.

If the temperature in the delivery pipe 29 is +5 deg C and the backpressure 10 MPA then the enthalpy increase from pipe 22 to pipe 29 can be determined from Reference 1 to be 660 kJ/kg. In this
calculation the enthalpy change in the liquid from friction losses in pump 11 and the piping system are ignored. Suppose further that the minimum
permissible temperature in pipes 22, manifold 30 and pipes 23 is -60 deg C. Then from Reference 1 the required enthalpy increase in the flow from pipe 20 to pipe 22 increasing the temperature from -161 deg. C to -60 deg C is 380 kJ/kg and the enthalpy
decrease in the flow from pipe 24 to pipe 22
lowering the temperature from +5 deg C to -60 deg C is 280 kJ/kg. In order to achieve a temperature of -60 deg C in pipe 22 the ratio of mass flows in pipes

22 and 24 must be 380/280. Thus the required mass flow in pipe 24 is 250*380/280= 340 kg/sec. The mass flow through manifold 30 is then 250 + 340 = 590 kg/sec. In order to heat the mass flow of 590 kg/sec from -60 deg C to +5 deg C the enthalpy increase is 290 kJ/kg from Reference 1. The power requirement is thus 290*590 = 171000 kW. Assume that the pipes 23 are immersed in a sea with a minimum temperature of 12 deg C and an average current of 0.1 m/sec. Assume further that the pipes 23 are 6 inch pipes then a calculation not given here shows that the heat transfer between the seawater and the ice (not shown) on pipes 23 is approximately 6 kW/m. Thus the approximate length of pipes 23 required is 171000/6 = 28500 meters. Assume that each pipe 23 is 2000 m long. 15 pipes 23 in parallel are thus required. To reduce the pressure loss in pipes 23 it may be elected to substitute the 15 parallel 6-inch pipes

23 with 20 parallel 10-inch pipes 23 each only 1000 m long. Calculations show that the system of 20 10-inch pipes 23, each 1000 m long, has approximately the same thermal performance as the 15 parallel S-inch pipes 23, each 2000 m long, but have a much reduced pressure loss due to flow resistance such that jet pump 19 can circulate the gas through pipes 23 with a pressure differential of approximately 1 Mpa between pipe 20 and 24. If the system of 15 parallel 6-inch pipes 23 were used to heat the fluids then a compressor (not shown) need to be incorporated in pipe 24, 28 or 22 to supplement or replace the pumping power of jet pump 19.

Figure 3 shows a second practical example of the first embodiment of the invention. The example shown in figure 3 is largely identical to the example shown in figure 2 except that the pipes 23 are not heated by the sea but rather by the atmosphere.

A high-pressure pump 11 is placed inside tank 101 in order to maintain it cold. Pump 11 takes suction through pipe 10 from within tank 101 and delivers the high-pressure fluid through pipe 20 to jet pump 19. Jet pump 19 takes suction from pipe 24 and delivers the combined flow from pipes 20 and 24 to pipe 22. Pipe 22 terminates in manifold 30 that distributes the flow between a plurality of pipes

23, of which only 5 are shown. Pipes 23 are mounted on a rack (not shown) or pipe supports (not shown) above the ground 110, as is standard practice for above ground pipelines. As shown on figure 3 the pipes 23 extend away from tank 101 in the direction of the delivery pipeline 29, however they can also double back as shown on figure 2 or may be
configured in any suitable shape such as a spiral (not shown) , a helix (not shown) , or multiple double back shapes (not shown) . Pipes 23 terminate at the downstream end in manifold 31 that connects to the delivery pipeline 29 and the re-circulation pipe 26. Heater 28 is placed in the re-circulation line 26 and 24. This heater 28 adds any heat deficit if sufficient heat is not transferred through the walls of pipes 23 to the fluid. This may for example be the case on cold days or when the flow in pipeline 29 is high. The temperature of the fluid having been heated in heater 28 may be substantially above that required at the inlet to pipeline 29. It is often required that the minimum temperature in
transmission pipelines such as pipe 29 be 5 deg C or above, in contrast the temperature of the fluid leaving heater 28 in pipe 24 may be much higher, possibly as high as 100 deg C or higher.

Figure 4 shows a diagram of a second embodiment of the invention similar to the first embodiment except that an externally powered compressor 25 replaces the jet-pump 19 shown in figure 3. Pump 20 takes suction through pipe 10 of a cryogenic fluid from a source (not shown) . Pump 11 delivers pressurized cryogenic fluid to mixing chamber 21 through pipe 20. Mixing chamber 21 received warmed fluid from pipe 24 and cryogenic fluid from pipe 20 and
delivers the mixture to pipe 22. The temperature in pipe 22 will be above the temperature in pipe 20 and below the temperature in pipe 24. The mass flows in pipes 20 and 24 will be proportioned by a control system (not shown) as is known in the art such that the temperature in pipe 22 would be above the lowest allowable temperature for carbon steel formulated for low temperature service. Pipe 22 is in fluid connection with manifold 30 that is in fluid
connection with one or more pipes 23. Pipes 23 are immersed in a warming fluid (not shown) such as the sea or the atmosphere and serve as heat exchanger tubes. Pipes 23 are in fluid connection with
manifold 31 that receives the warmed mixture and conveys it through pipe 26 to tee 33. At tee 33 part of the warmed fluid is sent out through pipeline 29 to customers (not shown) and part is re-circulated back to mixing chamber 21 through pipe 27,
compressor 25, and pipe 24. Compressor 25 provides the power to overcome the fluid resistance in the flow circuit mixing chamber 21, pipe 22, manifold

30, pipes 23, manifold 31, pipe 26, tee 31, pipe27, compressor 25, and pipe 24.

Figure 5 shows a third embodiment of the invention. This embodiment is particularly applicable to situations involving high cost components such as risers to floating moorings where it may be
desirable to maintain a low total flow in the high cost components by permitting temperatures in the high cost components below those permitted for carbon steel conduits. Pump 11 takes suction through pipe 10 from a source of cryogenic fluid (not shown) and discharges the fluid at high pressure through pipe 20 to a mixing chamber 40. Mixing chamber 40 also receives warmed fluid via pipe 67 and deliver the combined flow to pipe 41 at a temperature above that of the fluid in pipe 20 and below that of the fluid in pipe 67. The temperature in pipe 41 is determined from the principle of conservation of enthalpy in mixer 40. Pipe 41 may be a flexible riser of the known technology as for example
manufactured by the firm COFLEXIP. The materials normally used in manufacturing flexible risers for cold hydrocarbon gases are ordinarily able to withstand temperatures of -80 degrees C or somewhat lower. Pipe 41 connects to mixing chamber 42. Mixing chamber 42 also receives warmed fluid via pipe 63 and delivers the combined flow to pipe 43. The temperature of the fluid in pipe 43 will be below that of the fluid in pipe 63 but above the
temperature of the fluid in pipe 41. Ordinarily the system will be designed such that the temperature in pipe 43 will be above the minimum permissible temperature in low cost carbon steel, i.e. with the present steel making technology above -60 deg C. Pipe 43 terminates downstream in manifold 44, which distributes the flow among a plurality of pipes 45. Pipes 45 are immersed in a warming fluid such as the ocean or the atmosphere. The warming fluid in which pipes 45 are immersed will heat the fluid flowing through pipes 45, however, ice (not shown) will normally form on the exteriors of pipes 45 thereby reducing the efficiency of heat transfer from the warming fluid into pipes 45. This is overcome in this invention by simply making pipes 45 long enough or by supplementing the heat from the environment by heat from heater 60. The pipes 45 terminate
downstream in manifold 46, which discharges into pipe 47. Pipe 47 is the inlet to heater 60 that raises the temperature of the fluids in pipe 47 to the required inlet temperature of delivery pipeline 48. Heater 60 is optional, if supplied it will usually only be used when the flow rates are very high such that insufficient heat is delivered to pipes 45 or when the warming fluid in which pipes 45 are immersed is not warm enough. The provision of heater 60 makes the delivery capacity of the system invariant from the heat transfer from the warming fluid to pipes 45, yet reduces greatly the energy consumption compared to a system where the fluid is vaporized by burning a fraction of the fluid.
Warmed gas is delivered to mixing chamber 40 by pipe 65, compressor 66 and pipe 67. Warmed gas is
delivered to mixing chamber 42 by pipe 61,
compressor 62 and pipe 63. The pressure in pipe 20 will normally be maintained above the critical pressure of the cryogenic fluid. By maintaining the pressure above the critical pressure in the mixing chambers 42 and 40 separation in phases is avoided and no pressure surges from unstable phase
separation occurs, however, the invention is also applicable to systems where the pressure is below the critical pressure. In this case the piping, pump 11 and compressors 62 and 66 must be designed to cope with the resulting rapid pressure fluctuations.

Figure 6 shows in partial side view a practical application of the third embodiment. A LNG tanker 121 is moored offshore to a mooring 122. Mooring 122 may be constructed according to large number of known technologies. Anchor lines 127 secured to anchors 125 in the seabed 135 moor the mooring 122. The illustration of the mooring 122 is but one example of many possible moorings known in the art . Pump 11 is a high-pressure pump shown for clarity above the vessel 121 although it would normally be mounted inside a cargo tank 128. Pump 11 delivers LNG from a cargo tank 128 to pipe 20. Pipe 20 includes a fluid swivel 120 because the vessel 121 may weathervane relative to the seabed 135 Pipe 20 delivers the LNG to mixing chamber 40, which is shown incorporated in the mooring buoy. However, mixing chamber 40 may also be carried on the vessel 121. Mixing chamber 40 is in fluid connection with a seabed pipeline 67 through flexible riser 167. The riser 167 is in fluid connection with pipe 67 at pipeline end manifold 130. Pipe 67 delivers warm gasified LNG from a source (not shown) . Mixing chamber 40 is also in fluid connection with a second riser 141, which is in fluid connection with a second mixing chamber 42 via pipeline end manifold

131 on the seabed 135. Riser 167 delivers sufficient warmed gas to mixing chamber 40 that the combined flow of the fluids from pipe 20 and pipe 167, which is discharged into riser 141, is of a temperature suitable for conveyance in the riser 141 and the piping upstream from mixing chamber 42. This
temperature would ordinarily be above -100 degrees C and below - 40 degrees C. Mixing chamber 42 receives warmed gas from a source (not shown) . The flows from riser 141 and from pipe 63 are combined in mixing chamber 42 and discharged into pipe 43, which conveys the fluids to a heater (not shown) . The temperature of the fluids in pipe 43 would be at a level suitable for conveyance in carbon steel pipe formulated for low temperature service, which with current technology of steel making is in the range of -40 degree C and - 60 degree C.

Figure 7 is a diagram in plan view showing the remainder of the system shown in partial view on figure 6. Riser 141 connects at pipeline end manifold 131 to pipe 41, which delivers a cryogenic fluid partially heated as shown on figure 6 from tanker 121 to mixing chamber 42. Mixing chamber 42 also receives warm fluid via pipe 63 and delivers a mixture of the two streams from pipes 41 and 63 to pipe 43. The mixture in pipe 43 has a temperature above the fluid in pipe 41 but below the fluid in pipe 63. It is an objective of the invention that the temperature of the fluid in pipe 43 be suitable for conveyance in carbon steel pipe formulated for low temperature service. The temperature of the fluid in pipe 43 will ordinarily be in the range of -40 deg C to - 60 Deg C, however it could be
somewhat higher such as - 30 deg C. Pipe 43 conveys the fluid to a manifold 44 on the seabed
distributing the flow among a plurality of parallel pipes 45. Figure 6 shows 6 such parallel pipes 45, however, the number of parallel pipes 45 may range from one single pipe 45 to a large number such a 100 or more. The required number of parallel pipes 45 depends on physical conditions at the site of application and on the capacity of the system. Pipes 45 are immersed in the sea. Ice (not shown) will normally form on the outside of pipes 45 at least at the upstream ends of pipes 45. As the fluid flows through pipes 45 it gets warmed from the seawater in which the pipes 45 are immersed. The pipes 45 delivers the warmed fluid to manifold 46 from where the fluid is delivered into the pipes 48, 61, and 65. The temperature of the fluids in pipes 45 at manifold 46 will in a properly designed system be a few degrees below that of the ambient seawater in which the pipes 45 are immersed. By making pipes 45 sufficiently long the temperature difference between the fluids inside pipes 45 and the exterior seawater at manifold 46 can be made arbitrarily small, however it will ordinarily be in the range of 1 degree C to 5 degrees C. In tropical areas said temperature difference may be substantially higher such as 10 and even 20 degrees C. Pipe 61 returns part of warmed fluids to mixing chamber 42 via compressor 62 and pipe 63. Compressor 62 may
conveniently be of the inline type contained
entirely within the pipes 61 and 63 as is known in the art and powered by an electric cable (not shown) . However, compressors 62 and 66 may also be of the conventional types placed on a platform (not shown) a suitable distance from vessel 121. Another part of the warmed fluids is returned to the mooring (not shown) for vessel 121 via pipe 65, compressor 66, pipe 67 and riser 167. The remainder of the fluids conveyed through pipes 45 is sent out from manifold 46 to the delivery pipeline 48.

The practical example of the third embodiment shown in figures 6 and 7 shows the pipes 45 in which the fluids are heated immersed in the sea. It should be understood that the third embodiment is applicable to systems where pipes 45 are heated in any body of water, in the atmosphere, or to system where the pipes 45 are partially immersed in a body of water and another part of pipes 45 are in the atmosphere.

Figures 5, 6 and 7 illustrate the third embodiment having two mixing chambers 40 and 42 in which the temperature of the mixture is increased in two stages . However it should be understood that a multiple mixing chambers in series (not shown) might be employed rather than two. The third embodiment of the present invention is particularly suitable for use in combination with the invention described in PCT application WO 2004/080790, which is hereby incorporated by reference. Moorings of the single point mooring type has been used as an illustration in this document, however all types of moorings, including conventional fixed berth and multi-buoy moorings may be used to moor LNG tankers discharging into a vaporizing system as described in this specification. This specification shows the high-pressure pump 11 to be located aboard the LNG vessel 121, however, it may be located away from tanker 121, in which case nearly all existing LNG tankers can use the invention.

Figure 8 shows schematically in plan view a floating LNG terminal. The floating terminal 160 is
permanently moored by means of mooring lines 164 to the seabed (not shown) . This drawing shows
schematically a so-called multi buoy mooring in which the floating terminal 160 is maintained in a nearly stationary position with a nearly fixed heading. It should be understood that the floating terminal 160 might be moored by almost any known mooring system such as single point moorings (not show) or sea island type berths (not shown) . The floating terminal 160 has storage tanks 161 to store the LNG. The LNG is vaporized by systems (not shown) aboard the floating terminal and is delivered at high pressure and at near ambient temperature by piping systems (not shown) to a flexible piping system 166 connecting to a delivery pipeline (not shown) . Figure 8 also illustrates the temporary mooring of a LNG tanker 150 by mooring lines 152 and fenders 163 to the storage tanker 160. Tanker 150 delivers LNG from its tanks 151 by pumps and piping systems (not shown) aboard tanker 150 through a flexible piping 162 to the floating terminal 160. The LNG is conveyed aboard the floating terminal 160 from the flexible piping 162 through piping systems (not shown) to the storage tanks 161.

Figure 9 shows in side view a floating storage vessel 160 with a heat exchanger as per the second embodiment of the invention mounted on the floating storage vessel 160. The equipment to vaporize the LNG: Cryogenic pump 11, mixing chamber 21, and compressor 25 are ordinarily placed inside the hull of floating storage vessel 160, however these items are shown outside the hull of floating storage vessel 160 for clarity. Pipe 10 in fluid connection with high-pressure LNG pump 11 takes suction from one or more of the LNG tanks 161. Pump 11 discharges into pipe 20 in fluid connection with mixing chamber 21. Mixing chamber 21 is in fluid connection with the discharge pipe 24 from compressor 25. Mixing chamber 21 receives warmed fluid from pipe 24 and cold fluid from pipe 20. The mixture having an intermediate temperature is discharged into pipe 22. The temperature of the mixture in pipe 22 is
ordinarily sufficiently high such as -40 Deg C to -60 deg C that this fluid may be safely conveyed in carbon steel pipes formulated for low temperature service. Pipe 22 is in fluid connection with
manifold 30 that distributes the flow among pipes 23 immersed in the sea outside the hull of storage vessel 160. Two pipes 23 are shown on figure 9 although the number of pipes 23 would ordinarily be above 10. However, pipes 23 may comprise any number of pipes including one single pipe. Pipes 23 are attached to vessel 160 through structural connectors 70 as is known in the art. Pipes 23 are shown attached to the bottom plating 171 of vessel 160, however, pipes 23 may instead or also be attached to the sides (not shown) of vessel 160 below the water line 172.

The downstream ends of pipes 23 are in fluid
connection with manifold 31 discharging into pipe 26. The temperature of the fluid in pipe 26 'is a few degrees C below that of the temperature of the seawater in which vessel 160 floats. Pipe 26 is in fluid connection with manifold 35 and compressor 25. A portion of the flow leaves the vessel 160 via manifold 35 that is in fluid connection with a pipeline (not shown) for delivery to customers (not shown) and the remainder of the flow in manifold 31 is re-circulated via compressor 25 and pipe 24 to mixing chamber 21.

Heat exchangers in the known art require that pipes 23 be made of expensive cryogenically capable materials such as stainless steel, aluminum, or titanium. This invention teaches a method whereby pipes made from low cost carbon steel pipes
formulated for low temperatures in the range of -40 degrees C to -100 degrees C may be used in lieu of pipes made from expensive materials suitable for cryogenic service at very low temperatures such as -161 degrees C. Heat exchangers in the known art using water from a body of water as the warming fluid require that the water be treated with
biocides to avoid biological fouling and require large powered water circulation systems. Both are avoided in the heat exchanger made in accordance with the present invention, thereby providing significant environmental benefits.

Figure 10 shows in side view a floating storage vessel 160 with a heat exchanger as per the second embodiment of the invention mounted on the floating storage vessel 160. Figure 10 shows an example of the second embodiment of the invention similar to the example in figure 9 except the warming is provided by the atmosphere instead of the sea. The equipment to vaporize the LNG: Cryogenic pump 11, mixing chamber 21, and compressor 84 are ordinarily placed inside the hull of floating storage vessel

160, however these items are shown outside the hull of floating storage vessel 160 for clarity. Pipe 10 in fluid connection with high-pressure LNG pump 11 takes suction from one or more of the LNG tanks 161. Pump 11 discharges into pipe 20 in fluid connection with mixing chamber 21. Mixing chamber 21 is also in fluid connection with the discharge of compressor 84. Mixing chamber 21 receives cold LNG at a
temperature of about -160 deg C from pipe 20 and receives warmed natural gas at a temperature a few degrees C below the ambient air temperature from compressor 84. The fluid streams from pipe 20 and compressor 84 are mixed in mixing chamber 21 and discharged into manifold 80 at an intermediate temperature between the temperatures in pipe 20 and compressor 84. The intermediate temperature would be above the minimum temperature permitted in piping 80 and 81 and would ordinarily be in the range of -40 deg C to - 60 deg C but could be outside this range. Manifold 80 distributes the flow received from mixing chamber 21 between a number of parallel pipes 81 of which only two are shown. Pipes 81 are in the atmosphere above vessel 160. Pipes 81 are supported by structural systems (not shown) well known in the art. Pipes 81 receive heat from the atmosphere.
Because of the low temperature in pipes 81 ice (not shown) may form on the outside of pipes 81. The ice acts as an insulator and reduces the efficiency of the heat transfer. This is overcome by making pipes 81 sufficiently long. The rate of heat transfer between the atmosphere and pipes 81 depends strongly upon the speed of the air flowing past pipes 81, therefore in order to enhance the heat transfer the vessel 160 may be equipped with fans (not shown) or blowers (not shown) to increase the air speed past pipes 81. These fans (not shown) or blowers (not shown) need not be operating at all times, but only at times when the wind speed and/or the air
temperature are low.

Pipes 81 are at the downstream end in fluid
connection with manifold 82. A portion of the flow in manifold 82 leaves the vessel 160 via manifold 90 that is in fluid connection with a pipeline (not shown) for delivery to customers (not shown) and the remainder of the flow in manifold 82 is re-circulated via pipe 83 and compressor 84 to mixing chamber 21.

Figure 11 shows an example of the third embodiment of the invention in which the natural gas from the storage vessel 160 is sent out at the intermediate temperature instead of the near ambient temperature. The equipment to vaporize the LNG: Cryogenic pump 11, mixing chamber 21, and compressor 25 are
ordinarily placed inside the hull of floating storage vessel 160, however these items are shown outside the hull of floating storage vessel 160 for clarity. Pipe 10 in fluid connection with high-pressure LNG pump 11 takes suction from one or more of the LNG tanks 161. Pump 11 discharges into pipe

20 in fluid connection with mixing chamber 21.
Mixing chamber 21 is in fluid connection with the discharge pipe 24 from compressor 25. Mixing chamber

21 receives warm fluid from pipe 24 and cold fluid from pipe 20. The mixture having an intermediate temperature is discharged into pipe 22. The
temperature of the fluid in the mixture in pipe 22 is ordinarily sufficiently high such as -40 Deg C to - 60 deg C that this fluid may be safely conveyed in carbon steel pipes formulated for low temperature service. Pipe 22 is in fluid connection with pipes 95 and 96. Pipe 95 is in fluid connection with pipe 23 immersed in the seawater outside the hull of storage vessel 160. Only one pipe 23 is shown on figure 11 although the number of pipes 23 would ordinarily be above 10. Pipes 23 are attached to vessel 160 through structural connectors 70 as is known in the art. Pipes 23 are shown attached to the bottom plating 171 of vessel 160; however, pipes 23 may instead or also be attached to the sides (not shown) of vessel 160 below the water line 172.
Transfer of heat from the seawater to pipes 23 takes place along the pipes 23 thereby warming the fluid conveyed through pipes 23. Pipes 23 are ordinarily made sufficiently long that the temperature at the downstream end at pipe 26 is only a few degrees C below that of the seawater.

Pipe 22 conveys part of the flow to pipe 95 as described above. The remainder is discharged into pipe 96 and manifold 97. Manifold 96 is in fluid connection with a delivery pipeline (not shown) to shore (not shown) . In this embodiment the delivery pipeline (not shown) must be able to convey a cold fluid at the temperature of the fluid in pipe 22.

This temperature is ordinarily around -40 degrees C. If the delivery pipeline (not shown) is sufficiently long then the heat inflow from the environment into the delivery pipeline (not shown) may heat the content sufficiently for entry into the pipeline system ashore (not shown) , which ordinarily requires a temperature of 5 degrees C or higher.
Alternatively the delivery pipeline (not shown) may be connected to a heat exchanger (not shown) on the seabed and/or to a heat exchanger (not shown) upstream of the pipeline system ashore (not shown) , said heat exchanger (not shown) placed onshore or on a platform in the sea.

Figure 12 shows a fourth embodiment of the
invention. This embodiment differs from the first, second and third embodiments by pump 11 raising the pressure of the cryogenic fluid delivered to pipe 20 to a pressure substantially above that of the export pipeline 29. Pipe 22 delivers the combined flow from pipes 24 and 20 to T 246 where it is split into a fraction equal to the flow in pipe 29 to be sent out to the pipeline 29 via pipe 249 and the remainder to be returned to the mixing chamber 21 via pipe 24. The pipe 249 connects to a heat exchanger 250 that raises the temperature of the conveyed fluid using a heat source (not shown) . A pipe 251 connects heat exchanger 250 to a turbine 252 that reduces the pressure of the conveyed fluid to that of the export pipeline 29. Turbine 252 is connected to an
electrical generator (not shown) . The generator (not shown) connected to turbine 252 may transmit power by electrical cables (not shown) to pump 11, to compressor 238, and to an electrical transmission system (not shown) exporting any surplus power generated. The fourth embodiment may operate at higher pressures than the first, second, and third embodiments, thus the pipes 22 and 24 can be of lower diameter as the volumetric flow is reduced because of the increased density of the conveyed gas. The temperature in pipe 22 is no longer
dictated by the required temperature in the export pipeline 29 but rather is limited by materials properties of the materials used to construct pipes 22, 249, 242, and 237.

The fourth embodiment is illustrated by the
following example. Export pipeline 29 has a
backpressure of 5 MPa and it is required that the gas entering pipeline 29 has a minimum temperature of 5 deg. C. In this example pump 11 delivers 1000 kg/sec of methane at temperature -161 deg. C to the mixing chamber 21 at a pressure of 20 Mpa . The density of the methane is approximately 430 kg/m3 therefore the volumetric flow in pump 11 is 1000/430 = 2.3 m3/sec. The theoretical power of pump 11 is then 20*2.3= 46 MW. Assuming an overall efficiency of pump 32 of 65% then the required power input to pump 32 is 46/0.65 = 71 MW. Warmed methane is received in mixing chamber 21 from pipe 24. Pipe 22 is made from a steel quality that can tolerate -40 deg C. From Reference 1 it is calculated that the gas received from pump 11 requires an enthalpy increase of 470 kJ/kg to achieve this temperature. Assume that the mass flow from pipe 24 is also 1000 kg/sec. The stream of gas flowing in pipe 24 is cooled to -40 deg C. From reference 1 it is
determined that this stream must then have a
temperature of 90 deg. C to deliver the required enthalpy of 470 kJ/kg. The ambient temperature in the sea is ordinarily in the range of 0 deg C and 20 deg C. Therefore the temperature changes in pipes 44 and 35 when going from the ambient temperature to operating temperatures of -40 deg C and +90 Deg C respectively are no more than 90 deg C. Pipelines made from high strength carbon steels without expansion loops or other means to compensate for thermal movement can tolerate this temperature change .

Heat exchanger 250 is in this example assumed to heat the gas further to 115 deg C. Then by letting the pressure down from 20 MPa to 5 MPa in turbine 252 a theoretical power of 210 MW is generated.

Assume an overall efficiency of 65% of turbine 252 and its associated generator (not shown) then 137 MW power is generated at turbine 252. Assume further that compressor 238 requires 20 MW power for
operations then this example generates enough power to operate the machinery of 71 MW for pump 11 and 20 MW for compressor 238 and have an excess for sale of 137-71-20=46 MW.

All the heat is provided in the system by heat exchangers 250 and 243. Both heat exchangers 250 and 243 operate in temperature ranges that are within the allowable temperatures for carbon steels
formulated to operate in a temperature range above -40 deg C to -60 deg C. Both heat exchangers heat 1000 kg/sec. The temperature in heat exchanger 243 is raised from -40 deg C to +90 deg C, requiring an enthalpy increase of 470KJ/kg and heat exchanger 250 raises the temperature from -40 deg. C to +115 Deg. C requiring an enthalpy increase of 550 KJ/kg. Thus the heat input is 470+550 = 1020 MW.

From reference 1 it is determined that the density of the gas at -40 deg C and a pressure of 20 Mpa is 254 kg/m3. Thus the volumetric flow in pipe 22 is

(2000 kg/sec) /(254 kg/m3) = 8 m3/sec. The density of the gas in pipe 24 is 113 kg/m3 resulting in a volumetric flow of (1000 kg/sec) / (113 kg/m3) = 8.8 m3/sec. If the velocity in pipes 44 and 35 is restricted to about 8 meters per second an interior cross sectional area of 8.8/8 = 1.1 m2 results. This corresponds to a 48 -inch diameter pipe with a 35 mm wall thickness. It is therefore practical to make these pipes from single pipes. It is to be
understood that although this specification refers to mixing chamber 21, pump 11, heat exchangers 243 and 250, compressor 238 turbine 252, and pipes
22,249,251,29,246,242, and 24 as single units each may be comprised of multiple units in parallel operating in unison or independently.

Figure 13 shows a fifth embodiment of the invention. This embodiment is particularly adaptable to
increasing the capacity of existing vaporizers. A pump 11 mounted aboard a tanker 370 carrying
cryogenic fluids receives cryogenic fluid through pipe 10 and delivers through pipe 20 the cryogenic fluid to heat exchanger 374 where the cryogenic fluid is heated to a temperature usually about 5 deg . C. Heat exchanger 374 may not be able to accept a higher throughput delivering the warmed fluid at a lower temperature without freezing up. To achieve a higher delivery rate pump 11 is of increased
capacity and delivers part of the cryogenic fluid through pipe 380, valve 381, and pipe 382 to a mixing chamber 376 downstream from heat exchanger 374. Valve 381 is a regulator valve that proportions the fraction of the flow through pump 11 that bypasses the heat exchanger 374. The warmed fluid from mixing chamber 376 is delivered through a connector (not shown) from ship 370 to a pipe on the seabed 390 to an offshore platform 395 equipped with a heater 392 from where the warmed fluid is
delivered to delivery pipeline 29. The following example illustrates the performance of the fifth embodiment of the invention: Assume that pipe 390 can operate at -40 deg. C and pipeline 29 at +5 deg C. Assume further that heat exchanger 374 can only heat the cryogenic fluid to +5 deg C and above .
Assume further that pipe 390 operates at 10 Mpa. From reference 1 it is seen that an enthalpy
increase of 550 kJ/kg is required to heat methane from -161 to -40 deg. C and that an enthalpy
increase of 730 kJ/kg is required to heat methane from -161 deg. C to +5 deg. C. By applying the fifth embodiment of this invention the capacity to send out gas from ship 370 can be increased in this example by a factor of 730/550 = 1.3. The heat exchanger 392 must at least have a capacity of 30% of heat exchanger 374 to raise the temperature of the gas flowing in pipe 390 from -40 deg . C to the required +5 deg C for pipe 29.

Reference is made in this specification to the presently commercially available low cost carbon steel pipes having a minimum operating temperature in the range -40 deg C to - 60 Deg C. The present invention becomes more advantageous the lower the permissible operating temperature of low cost carbon steel pipes . Future improvements in carbon steel making technology may lower the minimum operating temperature of low cost carbon steel pipes to -80 deg C or possibly lower. Such a development will further increase the advantage of the present invention.

In the foregoing specification, the invention has been described with reference to specific exemplary embodiments thereof. It will, however, be evident that various modifications and changes may be made thereunto without departing from the broader spirit of the invention. The specification and drawings are accordingly to be regarded in an illustrative rather than a restrictive sense.