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Title:
PUMP SYSTEM FOR DELIVERING LIQUEFIED GASEOUS FLUID
Document Type and Number:
WIPO Patent Application WO/2016/112462
Kind Code:
A1
Abstract:
A pump system for pumping a liquefied gas fluid from a cryogen space defined by a thermally insulated fluid storage vessel having a first pump with an inlet and an outlet, and a second pump with an inlet in fluid communication with the outlet of the first pump and an outlet, where the first and second pumps are each spaced apart, one from the other, and each disposed within the storage vessel.

Inventors:
COLDREN DANA R (US)
LEW DAVID ANDREW (CA)
Application Number:
PCT/CA2016/050030
Publication Date:
July 21, 2016
Filing Date:
January 14, 2016
Export Citation:
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Assignee:
WESTPORT POWER INC (CA)
International Classes:
F04B23/04; F02M21/02; F04B23/08; F04B37/08; F17C7/02
Foreign References:
KR100639892B12006-11-01
US7284543B22007-10-23
US20110290220A12011-12-01
EP1314927A12003-05-28
US6904896B22005-06-14
JP2003293883A2003-10-15
Attorney, Agent or Firm:
WESTPORT POWER INC. (Vancouver, British Columbia V6P 6G2, CA)
Download PDF:
Claims:
What is claimed is:

1. A pump system for pumping a liquefied gaseous fluid from a cryogen space defined by a thermally insulated fluid storage vessel, comprising:

a. a first pump having an inlet and an outlet, and

b. a second pump having an inlet in fluid communication with the outlet of the first pump, and an outlet,

wherein the first and second pumps are each spaced apart, one from the other, and each pump is disposed within the storage vessel. 2. The pump system of claim 1 , wherein a fluid pressure change in the second pump is greater than a fluid pressure change in the first pump.

3. The pump system of any of the preceding claims, wherein the first pump is a centrifugal-type pump.

4. The pump system of any of the preceding claims, wherein the second pump is a reciprocating piston pump.

5. The pump system of any of the preceding claims, wherein the first pump is disposed near a bottom of the storage vessel, and the inlet of the first pump has an intake near the bottom of the storage vessel.

6. The pump system of any of the preceding claims, wherein the second pump is disposed near a top of the storage vessel.

7. The pump system of any of the preceding claims, wherein a second particulate filter is disposed upstream from the inlet of the second pump.

8. The pump system of claim 7, wherein the second particulate filter has a pore size as small as three microns.

9. The pump system of claim 7, wherein the second particulate filter has a pore size between four and five microns.

10. The pump system of claim 7, wherein a first particulate filter is disposed upstream from the inlet of the first pump.

11. The pump system of any of the preceding claims, wherein the first pump and second pump are disposed within a common socket in the storage vessel.

12. The pump system of claim 11, wherein the common socket is thermally insulated from an ambient environment external to the storage vessel.

13. The pump system of any of claims 11 or 12, wherein the common socket extends from near a bottom of the storage vessel to a top of the storage vessel.

14. The pump system of any of claims 11, 12 or 13, wherein the common socket includes an overflow such that any fluid above a predetermined fluid level can flow into an upper portion of the cryogen space.

15. The pump system of any of claims 1 to 10, wherein the first pump is disposed within a separate socket from the second pump.

16. The pump system of claim 15, wherein the first pump and the second pump are co-axially aligned.

17. The pump system of any of the preceding claims, wherein the liquefied gaseous fluid is liquefied natural gas.

18. The pump system of any of the preceding claims, wherein liquefied gaseous fluid from the second pump is directed to a high pressure fluid utilization system.

The pump system of claim 18, wherein the high pressure fluid utilization system is a fuel injector system for an internal combustion engine.

Description:
PUMP SYSTEM FOR DELIVERING LIQUEFIED GASEOUS FLUID Technical Field

[0001] The present application relates to a pump system for delivering liquefied gaseous fluid that can start up without a cool down procedure and that allows reduced cost, weight and higher efficiency. A particularly useful application for the presently disclosed pump system relates to pumping a gaseous fuel in liquefied form to a high pressure for fuelling an internal combustion engine.

Background

[0002] Because of its ready availability, low cost and potential for reducing particulate emissions, liquefied natural gas (LNG) is increasingly used as a gaseous fuel choice to fuel a range of industrial and vehicle engines, including mine trucks, locomotives, ships and other heavy goods vehicles (HGVs). Piston pumps have been developed in order to transfer the LNG from a storage vessel to the vehicle's engine. Some prior art LNG pump systems have the pump located outside the storage vessel so as not to introduce a heat leak source to the LNG environment, also referred to herein as the cryogen space, in which liquefied gaseous fluid can be stored at cryogenic temperatures. With such an arrangement it is possible to thermally insulate the piping to the pump and the pump itself, but by being located in the ambient environment, when the system is shut down and no fluid is flowing through it, the temperature of the pump and piping typically rises above cryogenic temperatures when idle. Pumps for handling liquefied gaseous fluids need to be cooled to cryogenic temperatures before they can be operated efficiently so if a pump has been idle and has warmed to ambient temperatures, a cool down procedure is needed to lower the temperature of the pump before it can be operated, for example to deliver fuel to the engine, and this cool down procedure introduces a start-up delay.

[0003] In this disclosure, for fluids that are normally in gaseous form at standard atmospheric pressure and temperature, cryogenic temperatures are defined as the temperature at which the pumped fluid can be maintained in a liquefied form, including fluids that are in a supercritical state. In situations where such a start-up delay is not acceptable, there needs to be a means for keeping the pump in a standby mode, at a cryogenic temperature, ready for immediate operation. [0004] Other prior art pump systems locate a pump inside the thermally insulated LNG storage vessel so that the pump is kept in a continuously cooled down state and ready for immediate operation, with sufficient insulation to prevent excessive heat leak into the storage vessel; for example, see U.S. Patent 4,472,946 and U.S. Patent 7,293, 418.

[0005] Some engines fuelled with natural gas introduce the fuel into the intake air system upstream from the engine combustion chamber, and engines that follow this approach generally have lower performance in terms of power and efficiency compared to engines that inject gaseous fuel directly into the combustion chamber in a manner that enables gaseous fuelled engines to emulate the power and performance of conventional diesel cycle engines. To achieve the higher pressures needed for direct injection a positive displacement pump such as the reciprocating piston pump disclosed in co-owned Patent Application EP 2,541,062 Al may be used, and by being immersed in the LNG storage vessel, the engine can be started without the delay caused by a cool down procedure. The pump typically has a "cold end" adapted to be immersed in the LNG in the storage vessel with an inlet close to the bottom of the storage vessel, and a drive unit opposite the cold end, with a drive shaft connecting the pump at the cold end with the drive unit. In addition, mounting the drive unit near the top of the fuel storage vessel can facilitate access for maintenance as well as keep the drive unit further away from the road surface and out of harm's way. For smaller vessels, rather than a vertical shaft, a long inclined shaft can be beneficial to reduce heat transfer from the drive unit to the pump. It is also necessary to thermally insulate the drive unit, both to reduce heat transfer to the stored liquefied gaseous fluid and to prevent freezing in the drive unit. Arrangements like those described in the referenced co-owned application can be effective for a certain size of LNG storage vessel designed for engines of a certain size. However for large HGVs, as the size of the fuel storage vessel increases, this type of arrangement becomes more costly because of the length of the shaft between the pump and the drive unit, and the size and strength required to deliver high pressure fuel at higher flow rates without buckling or otherwise failing. Furthermore, the increased weight of a scaled up shaft and drive system requires more power to drive the pump and reduces overall efficiency.

[0006] In addition, for vehicular applications, because the pump is mounted with an inlet near the bottom of the storage vessel, there is often little space to mount the pump drive unit below the storage vessel, especially if an elongated shaft is desired to reduce heat transfer. Known pump arrangements for storage tanks of a certain size often position the drive unit above the pump, and as noted herein, this can be problematic for large-scale fuel storage vessels such as those employed by large HGVs.

[0007] It is also known to locate a low pressure transfer pump inside a storage vessel to transfer fluid from the storage vessel to an external high pressure pump. The drawback of this arrangement for liquefied gaseous fluids stored at cryogenic temperatures is the same as other systems that use an external pump, namely the need for a cool down procedure to cool down the temperature of the external pump to cryogenic temperatures before the liquefied gaseous fluid can be delivered to the end user. The cool down procedure normally involves flowing cryogenic fluid through the external piping and through the external pump and then venting the vaporized liquefied gaseous fluid either to atmosphere or back to the storage vessel. Venting to atmosphere for a cool down procedure is fine for liquefied gaseous fluids such as nitrogen or oxygen, but not acceptable for gaseous fuels like natural gas. Venting back to the storage vessel introduces heat to the cryogen space which could reduce hold time before the vapor pressure increases to a point higher than the pressure relief set point, simply postponing when venting to atmosphere occurs. [0008] Accordingly, there is a need for an improved cryogenic pump system suited for large-scale cryogenic storage vessels, especially for pump systems that deliver fuel to larger HGVs without significant increases in the pump system weight, cost and efficiency. Summary

[0009] A pump system for pumping cryogenic fluid from a cryogen space defined by a thermally insulated storage vessel, to a high pressure cryogenic fluid utilization system is disclosed. The pump system comprises two pumps both located within the storage vessel, being spaced apart from each other, with the outlet of the first pump in fluid communication with the inlet of the second pump.

[0010] In exemplary embodiments, the first pump is located near the bottom of the cryogenic storage vessel, to allow the intake of the inlet to be at the bottom of the cryogen space. The first pump is intended as a transfer pump, to transfer fluid from the bottom of the cryogen space toward the second pump, such that the inlet of the second pump is below the level to which the cryogenic fluid from the first pump is pumped. This ensures a constant positive pressure at the inlet of the second pump.

[0011] The second pump is preferably a reciprocating pump intended to pressurize the fluid from the outlet of the first pump and transfer it via the outlet to a high pressure cryogenic fluid utilization system. The second pump is located near the top of the cryogenic storage vessel such that the drive unit and pump outlet can be located at least partially outside of the vessel to reduce heat transfer from the drive unit to the cryogenic fluid in the storage vessel.

[0012] In an exemplary embodiment, the cryogenic fluid to be pumped is liquefied natural gas on board a vehicle, intended for use by a high pressure fluid utilization system, such as the vehicle's internal combustion engine. In some embodiments it can be advantageous for the first pump and the second pump to be disposed within a common socket, which is thermally insulated from the ambient environment external to the cryogenic storage vessel. The common socket can facilitate installation and removal through one opening into the storage vessel. The common socket extends from the bottom of the storage vessel to the top of the storage vessel, with the first pump located at the bottom of the common socket such that the inlet of the intake is at the bottom of the cryogen space. The second pump is located at the top of the common socket and thus at the top of the storage vessel.

[0013] With the first pump functioning as a transfer pump, the pressure change in the second pump is greater than the pressure change in the first pump, which can be a low pressure centrifugal-type pump.

[0014] The common socket can also include a drain port such that any fluid transferred from the first pump that rises above a predetermined level flows into the upper portion of the cryogen space, where it can help to collapse vapor.

[0015] The disclosed pump system optionally allows for a reciprocating piston pump with a shorter drive shaft compared to known arrangements where the high pressure pump is located near the bottom of the storage vessel. The shortened drive shaft reduces the overall pump system weight and requires less strength against buckling compared to arrangements with a longer shaft. Furthermore, the reduced weight of the shorter drive system requires less power to drive the pump and increases overall efficiency.

[0016] The provision of the first centrifugal pump and second reciprocating piston pump within a single common socket is advantageous in that the single column eliminates the need for additional fittings and lines between the pumps, further reducing potential failure sites and component and material cost.

[0017] In an alternate embodiment, the first and second pumps are located in a first and second socket respectively, rather than in a common socket, with each socket located at a distance from the other. The first and second sockets are fluidly connected so as to allow fluid from the first pump to be transferred out of the first socket and into the second socket for use by the second pump.

[0018] A high pressure cryogenic pump system can optionally include a single screening device disposed at the pump inlet, to prevent solid contaminants and other particles from entering the pump. For example, solid contaminants and other particles in the cryogenic fluid that may freeze to a solid state at cryogenic temperatures can cause damage if drawn into to the pump. This is particularly problematic for high pressure pumps that are built with very small tolerances between moving parts.

[0019] With known single stage high pressure cryogenic pumps, to reduce pressure drop and thereby ensure sufficient net positive suction head for operation of the pump, these requirements normally limit the type of screening device, for example to a wire mesh or perforated screen which are effective for relatively coarse screening to block large particles while allowing the passage of smaller particles. Because the disclosed pump system employs a first pump in series with a second pump, in preferred embodiments the first pump can be a relatively low pressure pump, with larger tolerances between moving parts so that it can handle more particulate matter than the second pump, which has smaller tolerances to enable generation of higher pressures.

[0020] A first particulate filter can be optionally included, disposed upstream from the inlet of the first pump, reducing the likelihood of contaminants and particulates damaging either the first or second pump.

[0021] The disclosed system arrangement optionally allows the insertion of a second particulate filter to filter out finer particulates in the piping between the outlet of the first pump and the inlet of the second pump. Because this placement is downstream from the outlet of the first pump, the first pump can be selected to provide enough pressure to push the pumped fluid through the second particulate filter and ensure enough fluid pressure at the inlet of the second pump; that is, the second pump relies solely on the static pressure of the fluid in the storage vessel to provide the necessary net positive suction head and this enables the selection of a particulate filter with a smaller pore size.

[0022] Because the first pump does rely solely on static fluid pressure within the storage vessel to provide the necessary set positive suction head, the first particulate filter can have a larger pore size than the second particulate filter, but even so, the pore size can be smaller than the openings in a wire mesh or perforated screen to provide better filtering compared to known arrangements for single stage high pressure pump systems. The second paiticulate filter will also catch debris that might be generated by the first pump, for example if a part in the first pump breaks.

[0023] Commercially available particulate filters with a pore size as small as three microns, such as the 4450 series filter manufactured by Norman Filter Company, are designed to filter fluids at cryogenic temperatures and are suitable to use in this application. In preferred embodiments a pore size between four and five microns can be specified for the second particulate filter.

[0024] The configurations described in the embodiments above are particularly suited for use on board vehicles with large cryogenic storage vessels, such as HGVs and locomotives. The described embodiments allow for a reciprocating pump with a shorter drive shaft, which reduces the overall strength of the drive system required to deliver high pressure fuel at higher flow rates without buckling or otherwise failing, and the reduced weight and the reduced weight of the shorter drive system requires less power to drive the pump and increases overall efficiency. Dual-socket embodiments can occupy less of the interior fluid storage space, thereby increasing fluid storage capacity.

[0025] However, these configurations are not limited to use in HGVs and locomotive vehicles, as it may be employed in any pump system for delivering liquefied gaseous fluid from a storage vessel. Brief Description of the Drawings

[0026] FIG. 1 illustrates a cross-sectional view of a prior art pump system with a pump disposed with an inlet near the bottom of the fluid storage space of the storage vessel. [0027] FIG. 2 illustrates a cross-sectional view of a preferred embodiment of the disclosed pump system with first and second pumps located in a common socket, both being disposed within a storage vessel.

[0028] FIG. 3 illustrates a cross-sectional view of an alternate embodiment with first and second pumps located in a common socket of a storage vessel that has a circular cross-section for a storage vessel with a shape that is spherical or generally cylindrical with a horizontal elongated axis.

[0029] FIG. 4 illustrates a cross-sectional view of another embodiment with the first and second pump located in discreet first and second respective sockets, which are spaced apart from each other. Detailed Description of Preferred Embodiment(s)

[0030] Throughout the following description, specific details are disclosed to provide a more thorough understanding of the invention. However, some well-known elements have not been shown or described in detail to avoid obscuring the presently disclosed invention. Accordingly, the specification and drawings are to be regarded in an illustrative, rather than restrictive, sense. The drawings are not to scale.

[0031] While the disclosed pump system is described in relation to a particularly suited application, namely pumping a liquefied gaseous fluid from a storage vessel to an internal combustion engine, persons skilled in the technology will understand that other applications are also suitable.

[0032] FIG 1. shows a representative drawing, pump system 100, of the prior art. In a smaller vessel, it is advantageous to employ an extended drive shaft 10, to - Si - provide a better thermal barrier between drive unit 111, placed near the top of storage vessel 102 and pump 106, which has its inlet 110 located near the bottom of the vessel. However for large HGVs, as the size of the fuel storage vessel increases, this type of arrangement becomes more costly because of the length of the shaft between the pump and the drive unit, and the size and strength required to deliver high pressure fuel at higher flow rates without buckling or otherwise failing. Furthermore, the increased weight of a scaled up shaft and drive system requires more power to drive the pump and reduces overall efficiency.

[0033] FIG. 2 illustrates a cross-sectional view of a preferred embodiment of pump system 200 with common socket 204 disposed within storage vessel 202. First pump 208 is located at the bottom of common socket 204 such that the first inlet 214 is located at the bottom of storage vessel 202, which allows most of the stored fluid to be pumped therefrom with a positive static pressure at first inlet 214. Fluid pumped through pump system 200 is optionally filtered by a first particulate filter 215 located upstream of first inlet 214, to prevent particulates and contaminants from entering first pump 208 and second pump 206. Another optional second particulate filter 215a may be located upstream of second inlet 210 to further prevent contaminants and other solid particulates, that may damage seals and other parts of second pump 206, from entering the second pump. [0034] In this embodiment, first pump 208 serves as a transfer pump, to transfer fluid from storage vessel 202 to second pump 206 via second inlet 210, which is preferably a reciprocating piston type pump. With this arrangement, the fluid pressure change through second pump 206 can be greater than that through first pump 208, and the style of pumps need not be the same. By way of example, first pump 208 could be a centrifugal-type pump, or another type of pump known for efficiently transferring fluid when a relatively low pressure increase is needed, and second pump 206 can be of a type that is known for generating higher pressure increases, such as a piston pump or other positive displacement pump. [0035] First outlet 216 of first pump 208 pumps the fluid inside common socket 204 to a predetermined level above the second inlet 210, which allows for a constant positive pressure at second inlet 210. The fluid is then pressurized by second pump 206 and pumped through second outlet 212 to an end user such as to a combustion chamber of a vehicle's internal combustion engine.

[0036] While not indicated, a seal separating the drive end of the reciprocating piston pump, second pump 206, from the cryogenic fluid inside common socket 204, and thermal insulation is employed to minimize heat transfer between the drive unit and the stored fluid. Heat transfer from the drive unit to the stored fluid can result in vaporization of some of the liquefied gaseous fluid, resulting in an increase in the vapor pressure, which can lead to the undesirable venting of vapor if a predetermined relief pressure is exceeded. Additionally, it is undesirable for the drive unit to be cooled to cryogenic temperatures, particularly if the drive unit is hydraulically actuated because the cooling causes the hydraulic fluid to increase in viscosity or to freeze.

[0037] The space defined by common socket 204 can serve as a sump or a pipe from the outlet of first pump 208 that can deliver fluid to a sump with a smaller volume disposed near second pump 206. A predetermined fluid level allowable in the sump is at a point above second inlet 210. Any fluid pumped by first pump 208 that is in excess of the predetermined fluid level, flows out of the sump through overflow 218, and is returned to the main fluid storage space. By being returned into the upper portion of the main fluid storage space, the returning fluid can help to collapse some of the vapor, helping to reduce vapor pressure. In preferred embodiments, first pump 208 can be controlled to maintain a fluid level in the sump higher than a predetermined low level and lower than overflow 218. Where common socket 204 extends to outside storage vessel 202, and is thermally insulated from the ambient environment.

[0038] The disclosed pump system, like the preferred embodiment described with reference to FIG. 2, allows for a reciprocating high pressure piston pump with a shorter drive shaft to be utilized because its inlet does not need to be located near the bottom of the storage vessel. The shortened drive shaft reduces the overall weight of the drive system for the high pressure pump, reducing the power to drive the pump, thereby increasing overall efficiency. [0039] Whereas the embodiment in FIG. 2 is representative of a pump system installed in a storage vessel with a generally cylindrical shape having a vertically oriented elongated axis, such as might be used in a mine truck, FIG. 3 illustrates an alternate embodiment. Pump system 300 has a similar configuration and advantage to that described in FIG. 2 and similar reference numerals have been used for equivalent components, however pump system 300 is installed in a storage vessel 302 with a circular cross section in the vertical plane. This configuration might be used in a marine application for an LNG carrier with spherical storage vessels or with a cylindrical vessel having an elongated horizontal axis that can be used for example to fuel a locomotive engine or for stationary industrial applications. [0040] FIG. 4 is a schematic illustration of an alternative embodiment. Pump system 400 comprises first pump 408 disposed within first socket 405, which is separate and spaced apart from second socket 404 which houses second pump 406. Pipe 420 fluidly connects first pump 408 to second pump 406, allowing first pump 408 to be located near the bottom of storage vessel 402 where it can transfer most of the fluid from the main storage space to second pump 406 housed within second socket 404, located near the top of storage vessel 402. Like in other embodiments, second particulate filter 415a is located upstream of second inlet 410, to prevent solid contaminants and other solid particulates from entering and damaging second pump 406. Another, first particulate filter 415 can be added, located upstream of first inlet 414 to further prevent contaminants and other solid particulates from entering and damaging first pump 408 and second pump 406.

[0041] First pump 408 can be a centrifugal-type pump that does not need to be connected to the reciprocating drive shaft that is used in preferred embodiments to drive second pump 406, which serves as a high pressure stage. Even though there are separate sockets for respective sockets 404 and 405, for double-walled vacuum insulated storage vessels, it is advantageous for the two sockets to be co-axial, to reduce structural stresses around the sockets where they are joined to the inner and outer walls of the storage vessel. [0042] Like in other embodiments, in operation of pump system 400, first pump 408 receives fluid through first inlet 414 and pumps fluid to a first pressure so that it flows from first outlet 416 through connecting pipe 420 to the sump in second socket 404. From the sump, fluid flows through second inlet 410 into second pump 406. The fluid level in the sump is controlled to be maintained within a predetermined range, above the level of the inlet and preferably at or below the level of the overflow 418. If the range includes the level of the overflow then a regular flow of liquefied gaseous fluid through the overflow can help to collapse vapor in the upper portion of the main storage space. Second pump 406 then compresses the fluid to a second pressure which is typically a greater pressure change than that produced by first pump 408, and pressurized fluid is then pumped through second outlet 412. When employed as part of a fuel storage and delivery system associated with an engine, in preferred embodiments the pumped fluid is a liquefied gaseous fuel that is delivered at a pressure suited for direct injection into an engine's internal combustion chamber.

[0043] In addition to the shortened drive shaft in reciprocating piston 406, because there is no common socket that extends from one side of the storage vessel to the other side, an advantage of this embodiment is that it allows a larger portion of the space inside storage vessel 402 to be used for fuel storage, increasing the time between refueling and ultimately increasing efficiency of pump system 400. However, a disadvantage is that two access points are required, one for each of sockets 404 and 405, for installing and servicing first pump 408 and second pump 406, making this embodiment better suited as the size of the storage vessel increases.

[0044] While particular elements, embodiments and applications of the present invention have been shown and described, it will be understood that preferred embodiments are disclosed herein as examples of the claimed concepts and described features, and the invention is not limited thereto since variations for practicing the same concepts can be made by those skilled in the ait without departing from the scope of the present disclosure, particularly in light of the foregoing teachings.