Cryogenic Pump

Abstract

A cryogenic pump is typically used to supply high pressure natural gas to an engine. The pump has a piston operable to discharge cryogenic liquid from a pumping chamber within a pump housing. The cryogenic liquid exits the chamber through an outlet port in which a check valve is positioned. The check valve has a valve member which is loaded by a spring and is retained by a retaining member accessible from outside the housing. The check valve has an inlet which is axial with the valve member and an outlet which is transverse to the axis of the valve member.

Description

FIELD OF THE INVENTION

The present invention relates to a cryogenic pump and particularly to a check valve for a cryogenic piston pump

BACKGROUND OF THE INVENTION

A cryogenic pump that utilizes a piston as the pumping member has a pumping chamber with an outlet port from the pumping chamber communicating with a conduit for the pumped liquid. Typically, a check valve is located in the conduit to prevent backflow of liquid from the conduit to the pumping chamber. A check valve typically has its inlet and outlet in axial alignment with one another.

Cryogenic pumps are typically used in industrial plants for example, in plant for the separation or liquefaction of industrial gases. Cryogenic liquefied gases are becoming increasingly widely used. For example, liquefied natural gas (LNG) is now being used as an automotive fuel, particularly for heavy goods vehicles (HGVs). Piston pumps have been developed in order to transfer the LNG from a storage vessel on board the vehicle to the vehicle's engine. Such a pump needs to be quite compact and easy to maintain. The pump typically has a vaporizer associated with it.

An example of a cryogenic pump suitable for use with LNG on an HGV is given in U.S. Pat. No. 7,293,418.

SUMMARY OF THE INVENTION

A cryogenic pump for pumping liquid natural gas comprises:

• • (a) a piston operable to discharge cryogenic liquid from a pumping chamber within a pump housing;
  • (b) an outlet port from the pumping chamber, the outlet port disposed in the pump housing; and
  • (c) a check valve in the outlet port, the check valve comprising:
    • (i) a valve member;
    • (ii) a demountable retaining member accessible from the exterior of the pump housing;
    • (iii) an inlet axial with the valve member and transverse to the axis of the pumping chamber of the cryogenic pump; and
    • (iv) an outlet transverse to the axis of the valve member and parallel to the axis of the pumping chamber of the cryogenic pump.

In one embodiment, the retaining member comprises a sleeve for guiding the valve member. The sleeve is preferably formed integrally with the retaining member.

In another embodiment, the valve member is spring-loaded. The valve member preferably comprises a cylindrical body and a frustoconical head, which, when the check valve is in its closed position, sealingly engages, under bias of the spring, a complementary valve seat formed in the pump housing. The head is preferably formed from plastic material or polytetrafluoroethylene (PTFE). The valve seat is preferably formed from metal such as stainless steel).

In another embodiment, the spring is a compression spring. The compression spring is preferably seated in a detent formed in the retaining member.

BRIEF DESCRIPTION OF THE DRAWINGS

A cryogenic pump according to the invention will now be described, by way of example, with reference to the accompanying drawings, in which:

FIG. 1 is a schematic perspective view of the pump;

FIG. 2 is a sectional side elevation of the warm end of the pump shown in FIG. 1;

FIG. 3 is a sectional elevation of the pumping chamber of the pump shown in FIG. 1; and

FIG. 4 is an enlarged sectional elevation of part of the pumping chamber shown in FIG. 3 illustrating the check valve in the outlet part of the pumping chamber.

The drawings are not to scale.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENT(S)

Referring to the drawings, there is shown generally a cryogenic pump 2 of the kind having a cold end 3 adapted to be immersed in a volume of cryogenic liquid, not shown, to be supplied to, for example, a combustion engine. Pump 2 is generally of the same kind as that disclosed in U.S. Pat. No. 7,293,418, save that it does not include an accumulator. Instead, pump 2 has a pumping chamber communicating directly with a vaporizer or like heater. The disclosure of U.S. Pat. No. 7,293,418 is hereby incorporated by reference herein in its entirety. Cryogenic pump 2 has a warm end 5 opposite cold end 3. Warm end 5 is not intended for immersion in the cryogenic liquid. Pump 2 has a housing 4 of generally elongate configuration with an axial piston 6 and piston shaft 7. Piston 6 is able, in operation, to draw cryogenic liquid into, and force cryogenic liquid out of, a pumping chamber 8 defined within housing 4. Pumping chamber 8 has an inlet 9 for cryogenic liquid communicating with a hollow cylindrical cryogenic liquid intake member 11 typically fitted with a filter 11a effective to prevent small solid particles from entering the pump.

Pumping chamber 8 has an outlet port 10 for the discharge of cryogenic liquid. With particular reference to FIGS. 3 and 4, outlet port 10 houses a check valve 12. Outlet port 10 is connected to a relatively small diameter conduit 13 which extends from cold end 3 to warm end 5 of pump 2. Conduit 13 terminates in an annular heat exchange device 15, in which the cryogenic liquid is vaporized by indirect heat exchange with a relatively high temperature heat exchange fluid. (If, for example, the cryogenic liquid is LNG, and pump 2 is intended to supply the natural gas to an engine (not shown), the heat exchange fluid can be the aqueous liquid that is used to cool the engine.) The heat exchange device 15 is provided with an outlet 99 (see FIG. 2) for vaporized natural gas and an inlet 19 and outlet 21 for the heat exchange fluid. Typically, there is within the heat exchange device a passage (not shown) for the cryogenic liquid in heat exchange relationship with another passage (not shown) for the heat exchange fluid. Flow of the cryogenic liquid through its passage causes it to vaporize.

At warm end 5 of pump 2 there is provided a drive chamber 23 for piston 6. Typically, a hydraulic drive is employed, there being an inlet port 25 and an outlet port 17 for hydraulic liquid, but an electrical, pneumatic or mechanical drive could alternatively be used. The drive arrangements may in general be similar to those disclosed in U.S. Pat. No. 7,293,418 for the pump described and shown therein. Piston 6 has two strokes. In its upward stroke (that is in its stroke away from cold end 3, a flow of cryogenic liquid through inlet 9 is induced. In its downward stroke (that is in its stroke away from warm end 5) a flow of cryogenic liquid through outlet port 10 is provided. Pump 2 is capable of generating a high delivery pressure, typically in the order of 300 bar, or higher.

Check valve 12 is best viewed in FIG. 4. Check valve 12 is located in pump housing 4 at outlet port 10. Check valve 12 has a spring-loaded valve member 14 which is retained within housing 4 by a demountable retaining member 16 accessible from the exterior of pump housing 4. Retaining member 16 may make a screw-threaded engagement with pump housing 4 and may have a configuration such that access can be gained to valve member 14 from outside housing 4 by means of a specific tool (not shown) to dismantle the part, in association with a standard wrench. In its normal position retaining member 16 comprises a resilient O-ring seal 40 to prevent leakage of fluid out of pump 16 via the screw-threads of retaining member 16. Retaining member 16 has a sleeve 22 for guiding valve member 14. Sleeve 22 is typically formed integrally with retaining member 16.

Valve member 14 has a cylindrical body 24 and a frustoconical head 26. During the delivery stroke check valve 12 remains open but it closes for the intake stroke of piston 6. If the pump is idle, check valve 12 remains closed. When check valve 12 is in its closed position, head 26 makes a sealing engagement, under the bias of a compression spring 28 and any fluid pressure in outlet 20, with a complementary valve seat 30 formed in pump housing 4. Typically, head 26 and the rest of valve member 14 are formed of a plastics material which is able to be used at cryogenic temperatures. PTFE is one such plastics material.

Similarly, housing 4 and, in particular, valve seat 30 is made of a material that in addition to being a metallic engineering material is suitable for use at cryogenic temperatures. Stainless steel is one such material. Compression spring 28 is seated in a detent 32 in retaining member 16. The bias of compression spring 28 acts in a valve-closing direction. Thus, when there is no cryogenic liquid pressure acting in the opposite direction, valve 12 remains in a closed position preventing back flow of fluid from conduit 13 into pumping chamber 8. Moreover, the basis of the spring is effective to keep check valve 12 closed when there is no cryogenic liquid pressure acting on valve member 14 irrespective of the attitude of cryogenic pump 2. (In practice, the cryogenic pump is typically positioned with its axis at angle to the vertical.)

Valve 12 has an inlet 18 which is axial with valve member 14 and a radial outlet 20 which is transverse to the axis of valve member 14. Check valve 12, when open, permits cryogenic liquid to flow from inlet 18 to outlet 20. The flow path has an axial element being defined between sleeve 22 and a complementary portion of housing 4 and a transverse radial element through outlet 20, there being a transverse radial passage 41 through sleeve 22 of retaining member 16 to aid flow of the cryogenic liquid.

The position of check valve 12 in housing 4 of cryogenic pump 2 keeps down the dead volume between piston 6 at the end of the downward stroke, namely, the stroke away from warm end 5, and the sealing area of check valve 12, and thereby avoids loss of pump efficiency.

Typically, valve member 14 undergoes wear in use, so is exchanged for an identical such member after a chosen period of time. In order to exchange valve member 14, pump 2 is withdrawn from the tank (not shown) containing cryogenic liquid in which it is typically located, pump 2 allowed to return to ambient temperature, and retaining member 16 removed.

While particular elements, embodiments and applications of the present invention have been shown and described, it will be understood, that the invention is not limited thereto since modifications can be made by those skilled in the art without departing from the scope of the present disclosure, particularly in light of the foregoing teachings.

Claims

1. A cryogenic pump for pumping liquid natural gas comprising: (a) a piston operable to discharge cryogenic liquid from a pumping chamber within a pump housing;(b) an outlet port from said pumping chamber, said outlet port disposed in said pump housing; and(c) a check valve in said outlet port, said check valve comprising: (i) a valve member;(ii) a demountable retaining member accessible from the exterior of said pump housing;(iii) an inlet axial with said valve member and transverse to the axis of said pumping chamber of said cryogenic pump; and(iv) an outlet transverse to the axis of said valve member and parallel to the axis of said pumping chamber of said cryogenic pump.

2. The cryogenic pump of claim 1, wherein said retaining member comprises a sleeve for guiding said valve member.

3. The cryogenic pump of claim 2, wherein said sleeve is integral with said retaining member.

4. The cryogenic pump of claim 1, wherein said valve member is spring-loaded.

5. The cryogenic pump of claim 4, wherein said valve member comprises a cylindrical body and a frustoconical head, which, when said check valve is in its closed position, sealingly engages, under bias of said spring, a complementary valve seat formed in said pump housing.

6. The cryogenic pump of claim 5, wherein said head is formed from plastic material.

7. The cryogenic pump of claim 5, wherein said head is formed from polytetrafluoroethylene.

8. The cryogenic pump of claim 5, wherein said valve seat is formed from metal.

9. The cryogenic pump of claim 8, wherein said valve seat is formed from stainless steel.

10. The cryogenic pump of claim 4, wherein said spring is a compression spring.

11. The cryogenic pump of claim 10, wherein said compression spring is seated in a detent formed in said retaining member.