WO2008085005A1

WO2008085005A1 - Tank for holding a cryogenic liquid and a conduit assembly, and a system for effecting flow control and pressure management of a cryogenic liquid held in the tank

Info

Publication number: WO2008085005A1
Application number: PCT/KR2008/000185
Authority: WO
Inventors: Roy E. Adkins; Jason Young Cho
Original assignee: Cryo-Nevico Inc.; Nevico Co., Ltd.
Priority date: 2007-01-12
Filing date: 2008-01-11
Publication date: 2008-07-17
Also published as: KR100844223B1

Abstract

A tank for a cryogenic liquid is fitted with a conduit assembly that provides for flow of the cryogenic liquid into and out of the tank, venting of the tank and control of the fill level in the tank. The conduit assembly includes serpentine tubes that extend into an upper region within the inner shell. Within the inner shell, one of the tubes extends downwardly to a lower opening and provides for liquid flow into and out the tank; the other tube has an end with a downwardly facing opening in the upper region whereby vapor can be conducted out of the tank and the fill level is established. A system for effecting pressure management of the cryogenic liquid in the tank includes a conduit network that provides for pressure build as pressure in the conduit network drops and provides for delivery of liquid only to, e.g., a vehicle engine.

Description

TANK FOR HOLDING A CRYOGENIC LIQUID AND A

CONDUCT ASSEMBLY, AND A SYSTEM FOR EFFECTING

FLOW CONTROL AND PRESSURE MANAGEMENT OF A

CRYOGENIC LIQUID HELD IN THE TANK Technical Field

[1] The present invention is directed to an assembly for effecting filling, withdrawal and fill level control of a cryogenic liquid held in a tank and to a flow control and pressure management system for a cryogenic liquid. More particularly, the present invention is directed to such an assembly and system applied to a vehicle-mounted tank for receiving and holding a cryogenic liquid fuel and for delivering the liquid fuel to the vehicle engine. The liquids intended for transfer by the apparatus and method of this invention exist in a cryogenic state. The present invention is particularly adapted for, but not limited to, a vehicle-mounted tank for efficiently holding liquefied natural gas (LNG), or methane, and a control assembly for efficiently introducing the LNG into the tank and transferring the LNG to the vehicle engine. Background Art

[2] Cryogenic containers that are designed and manufactured for end-use as vehicular fuel tanks used to store extremely cold liquids require a means to fill the container and deliver product from the container. Typically, LNG vehicle fuel tanks are of double wall construction. The inner shell, a pressure vessel containing LNG fuel, is supported within the outer shell. Radiation shielding, such as wraps of polyester sheet aluminized on both sides, is placed in the space between the inner and outer shells, and the space is placed under a high vacuum to provide particularly effective insulation between the inner shell and the ambient. Since LNG is a cryogenic fuel that boils at -258⁰F (at normal atmospheric pressure), the pressure vessel support structure must exhibit a very low conductive heat leak. Tank "heat leak" has a dramatic effect on the pressure temperature and density relationships of the LNG thus making it very difficult to control the fuel tank pressure and maintain consistent fuel quality for delivery to the engine. Low heat leak minimizes tank pressure build-up during vehicle non-operational time periods and prevents venting of fuel during a designed "no vent" standby time.

Disclosure of Invention Technical Problem

[3] LNG is a dynamic fuel exhibiting fluid characteristics that vary with pressure and corresponding amount of internal energy. These variable fluid characteristics coupled with a cryogenic liquid temperature of -258⁰F at normal atmospheric pressure necessitate specific equipment and a system design that will enable efficient introduction of LNG into the tank(s) with an effective control of fill level in the tank. Also, the system controls must maintain a specified fuel supply flow rate to a vehicle engine within a specified pressure range during all modes of vehicle operation.

[4] An object of the invention is to effect the fill of the tank, the delivery of liquid from the tank and achieve pressure management of the tank with a single line thus providing a multi- function capability and reducing the number of tank penetrations and therefore a significant reduction in heat transfer.

[5] Another object of the present invention is to provide a reliable means of controlling the ullage space within the tank in order to comply with applicable Federal and State codes in the United States. The vent return line, as employed in the invention, serves as a device that provides an indication of when the tank is filled to the maximum allowable liquid level and will allow for the expansion of the LNG after the fill of the tank. This is accomplished by means of a tubular elbow welded to the end of the vent line serpentine tube in the interior of the tank, in a position perpendicular to the liquid surface of the LNG. With the entrant tube housing assembly installed in the upper part of the tank head it is possible to establish the exact elevation of this elbow above the liquid level and thereby provide a flow path for the liquid out of the tank while at the same time establishing a pressure pad at the top of the tank that prevents the tank from being overfilled.

[6] An object fulfilled by the invention is that, due to improved thermal protection design, "liquid only" can be delivered from the tank, thus assuring consistent fuel quality and pressure from the tank to an external heat exchanger for vaporization and delivery to an engine.

[7] Another object of the present invention is to provide for the reliable installation of a capacitance gauge probe in combination with the liquid fill/withdrawal tube. The capacitance probe is attached to the entrant tube unit by fittings welded to the vertical portion of the fill/withdrawal tubing.

[8] The filling, venting, pressure management and flow control assembly and system provided by this invention will satisfy applicable codes for maximum allowable tank fill level as well as the fuel pressure and flow rate requirements of any vehicle engine. Technical Solution

[9] As shown in Figs. 1 and 2, a conduit assembly includes a pair of tubes 10, 12 that extend through an end wall of a tank 13 for a cryogenic liquid. A tank to which the conduit assembly is applicable is disclosed in U.S. Patent No. 6,880,719 Bl. The tank makes use of a double wall construction having an inner shell 14 that holds the liquid under pressure and an outer shell 16 that surrounds the inner shell and is spaced from it. A barrier to heat transfer into the inner shell is provided by an evacuated space 18 between the inner and outer shells.

[10] As shown, the tubes have a serpentine form and extend side-by-side horizontally within an upper region of the inner shell. As best shown in Fig. 1, the tubes extend through outer and inner housings 20, 22 forming an extension of the evacuated space between the inner and outer shells. In particular, the tubes extend through a closure plate 20a on the outer housing, through the evacuated space between the shells, through the inner housing and closure plate 22a and into an upper central region of the inner shell.

[11] One of the tubes 10, used for filling and withdrawal of liquid, includes a vertical section 10a that extends toward the bottom of the inner shell and has an opening at its lower end, Located adjacent to the vertical section 10a of tube 10 is a liquid level capacitance gauge 24.

[12] The other tube 12, used for venting and fill level control, terminates in the upper central region of the inner shell at an elbow 12a with a downwardly facing opening 12b. An electrical lead 24a from the capacitance gauge 24 is shown extending through the vent tube.

[13] A cryogenic liquid from a bulk supply flowing through the fill tube enters the inner shell at the bottom. As the liquid level rises, gases above the surface of the liquid can flow from the inner shell through the vent tube 12 and back to the bulk supply. When the liquid level rises to immerse the bottom of the elbow 12b, liquid will flow through the vent tube back to the bulk supply. A gas pressure pad established above the surface of the liquid will prevent further rise of the liquid in the inner shell. The elbow 12a is located so that the downwardly facing opening is generally coincident with the fill level mandated by applicable codes. The position of the elbow also establishes the proper "ullage space" (tank space not occupied by liquid) in the container, to allow for expansion of the LNG after filling.

[14] Figs. 3 and 4 show a preferred embodiment of a system for effecting flow control and pressure management of a cryogenic liquid held in a tank. An elbow 12a of third conduit 30 is coupled to the outer end of fill and withdrawal conduit 10 that communicates with the bottom of tank 13. The other end of third conduit 30 is coupled to an outer end of tank vent tube 12 via a passage in manifold 32. A pressure regulator 34 is disposed in third conduit 30 between its couplings with conduits 10 and 12. Thus, third conduit 30 forms a loop between fill and withdrawal conduit 10 and vent tube 12, and the pressure regulator 34 is interposed in the loop. The pressure regulator incorporates a normally closed valve that opens in response to a drop in pressure in third conduit 30 below a predetermined level. A pressure regulator found to be suitable for this application is RegO Products Part No. RG 125.

[15] Fourth conduit 36 for conducting vapor from the tank to a bulk supply is coupled to third conduit 30 via a passage in the manifold 32 a shut off valve 38 (normally open) is disposed in fourth conduit 36. Also, coupled to the manifold are primary and secondary relief valves 40, 42. Teed into third conduit 30 between the coupling with conduit 10 and the pressure regulator 34 are fifth conduit 44 which receives cryogenic liquid from a bulk supply (not shown), and sixth conduit 46 which conducts cryogenic liquid to a point of use, such as a vehicle engine (not shown). As shown, an accumulator 48 and a check valve 50 are also disposed in third conduit 30 between the regulator 34 and the coupling with sixth conduit 46. A shut-off valve 52 (normally open) is disposed in third conduit 30 between the couplings with fill and withdrawal conduits 10 and fifth conduit 44. A solenoid valve 54 is disposed in sixth conduit 46 to allow or block flow of liquid to a point of use.

[16] The regulator 34 will maintain a constant delivery pressure to an engine. When liquid is being provided to an engine, the liquid level in the tank will fall and the pressure in third conduit 30 may also fall. When the pressure in the third conduit 30 falls below a predetermined level, the valve in the regulator 34 will open, liquid in the accumulator 48 will pass through check valve 50 and regulator 34 and into the third conduit 30 on the other side of the regulator. This section third of conduit 30 acts as a heat exchanger in which liquid in the conduit will be vaporized by heat from ambient, causing expansion of the fluid in the conduit which causes a pressure build. In practice, very small amounts of liquid passing through the check valve 50 and the regulator 34 effect a pressure build that returns the pressure in conduit to a required level. When the pressure reaches the predetermined level, the regulator shuts off, stopping vaporization and pressure build-up. As liquid is forced from the tank, pressure in the tank begins to drop and the pressure build regulator again begins operating.

[17] In some cases, where the LNG saturation pressure is above the minimum tank operating pressure, the pressure build system, just described, will never be activated at any flow rate of fuel from the tank. Minimum pressure is controlled by the liquid saturation pressure. However, when liquid saturation pressure is below the specified minimum tank operating pressure, or in any case where pressure has decayed at low tank quantity with high flow rates, the pressure build system will maintain pressure within the required operating range.

[18] Excessive pressures in third conduit 30 are relieved by the opening of primary and/ or secondary relief valves 40, 42.

Claims

[1] In combination, a tank for holding a cryogenic liquid and a conduit assembly, wherein: the tank comprises an inner shell 14 for holding a cryogenic liquid, an outer shell 16 surrounding the inner shell 14 and an evacuated space between the inner shell 14 and the outer shell 16; the conduit assembly includes (1) a fill and withdrawal conduit 10 for conducting flow of cryogenic liquid into and out of the tank and (2) a vent tube 12 for discharging the air of the inner shell and fill level control in the inner shell; the first conduit includes (1) an extension extending generally horizontally through adjacent walls of both the inner shell 14 and the outer shell 16, through the evacuated space and within an upper region of the inner shell and (2) a vertical section 10a joined to an elbow 12a of the extension and extending downwardly within the inner shell toward the bottom of the inner shell and (3) an opening 12b located near the bottom of the inner shell; and the vent tube 12 includes (1) an extension extending generally horizontally through adjacent walls of both the inner shell 14 and the outer shell 16, through the evacuated space and within an upper region of the inner shell and (2) an elbow 12a with a downwardly facing opening 12b located in an upper region of the inner shell.

[2] The combination as recited in claim 1, wherein: the inner shell includes a housing extending generally horizontally within an upper region of the inner shell, the housing forming an extension of the evacuated space and having a closure plate 20a in an upper central region of the inner shell; and the extensions of the fill and withdrawal conduit 10 and the vent tube 12 extend through the housing and through the closure plate 20a into the interior of the inner shell 14.

[3] The combination as recited in claim 1 or claim 2, wherein at least portions of the extensions of the fill and withdrawal conduit 10 and the vent tube 12 are configured as serpentine tubes that extend alongside each other.

[4] The combination as recited in claim 1 or claim 2, and further comprising a liquid level capacitance gauge within the inner shell 14 adjacent to the vertical section 10a of the fill and withdrawal conduit 10.

[5] The combination as recited in claim 3, and further comprising a liquid level capacitance gauge within the inner shell 14 adjacent to the vertical section 10a of the fill and withdrawal conduit 10. [6] A system for effecting flow control and pressure management of a cryogenic liquid held in a tank, the system comprising: a fill and withdrawal conduit 10 communicating with the interior of the tank near the bottom of the tank; a vent tube 12 communicating with the interior of the tank at an upper region of the tank; a third conduit 30 communicating with the fill and withdrawal conduit 10 and the vent tube 12 and extending between the fill and withdrawal conduit 10 and vent tube 12 outside of the tank; a pressure regulator disposed in the third conduit 30, the pressure regulator comprising a normally closed valve that opens in response to a pressure drop in the third conduit 30 below a predetermined level; a check valve 50 disposed in the third conduit 30 between the fill and withdrawal conduit 10 and the pressure regulator; a fourth conduit for conducting vapor from the tank to a bulk supply, the fourth conduit being joined to the third conduit 30 between the vent tube 12 and the pressure regulator; a fifth conduit 44 for introducing cryogenic liquid from a bulk supply to the tank, the fourth conduit communicating with the third conduit 30 between the fill and withdrawal conduit 10 and the check valve 50; and a sixth conduit 46 for conducting cryogenic liquid to a point of use, the fifth conduit being joined to the third conduit 30 between the fill and withdrawal conduit 10 and the check valve 50. [7] The system as recited in claim 6, and further comprising a reservoir for holding cryogenic liquid in the third conduit 30, the reservoir being located in the third conduit 30 adjacent to the check valve 50 and between (1) the fifth conduit 44 and the sixth conduit 46 and (2) the check valve 50. [8] The system as recited in claim 6 or claim 7, and further comprising: a shut off valve 38 (normally open) in the fourth 36 conduit for allowing or blocking flow of vapor through the fourth conduit 36 between the tank and a bulk supply; and a solenoid valve 54 for allowing or blocking flow of cryogenic liquid through the third conduit 30 and the fourth conduit 36 between a bulk supply and the fill and withdrawal conduit 10. [9] The system as recited in claim 6 or claim 7, and further comprising a solenoid valve 54 in the sixth conduit 46 for allowing or blocking flow of cryogenic liquid through the sixth conduit 46 between the third conduit 30 and a point of use. [10] The system as recited in claim 8, and further comprising a solenoid valve 54 in the sixth conduit 46 for allowing or blocking flow of cryogenic liquid through the sixth conduit 46 between the third conduit 30 and a point of use.