CA2860682A1

CA2860682A1 - Gaseous fluid supply system with subsystem for isolating a storage vessel from an end user

Info

Publication number: CA2860682A1
Application number: CA2860682A
Authority: CA
Inventors: Brian A. Girard; Gregory C. Harper; Gregory A. Batenburg
Original assignee: Westport Power Inc
Current assignee: Westport Fuel Systems Canada Inc
Priority date: 2014-08-22
Filing date: 2014-08-22
Publication date: 2014-10-17
Anticipated expiration: 2034-08-22
Also published as: WO2016026054A1; CA2860682C

Abstract

A gaseous fluid supply system is disclosed comprising a subsystem for isolating the storage vessel from an end user when the end user is not operating. The subsystem comprises a recirculation loop fluidly connecting the fluid discharge line with the storage vessel and a switching device operable between a first position associated with when the end user is shut down, in which fluid is stopped from flowing from the pump to the end user, and fluid can be returned to the storage vessel through the recirculation loop and a second position associated with when the end user is running, in which fluid is supplied to the end user and fluid is stopped from flowing from the fluid discharge line to the recirculation loop. A method is also disclosed for detecting the operation state of the switching device when the end user is started.

Description

GASEOUS FLUID SUPPLY SYSTEM WITH SUBSYSTEM FOR ISOLATING A
STORAGE VESSEL FROM AN END USER
Technical Field [0001] The present disclosure relates to a gaseous fluid supply system which comprises a subsystem for isolating the storage vessel from an end user when the end user is not operating. The disclosed system and method is particularly beneficial in a gaseous fuel supply system for an internal combustion engine when the engine is shut down and fuel remains in the fuel system.
Background [0002] Natural gas or other gaseous fuels have been used to fuel vehicle engines for many years. The gaseous fuel in such fuel systems can be any fuel which is in a gaseous phase at standard pressure and temperature conditions (an absolute pressure of 1 bar (14.5 psig) and 0 C (32 F)). By way of example, typical gaseous fuels that can be stored in liquefied form include, among others, natural gas, propane, hydrogen, methane, butane, ethane, or mixtures comprising at least one of these fuels. Natural gas is in itself a mixture of gases and is often chosen as a fuel for internal combustion engines because, compared to conventional liquid fuels like diesel and gasoline, it is cleaner burning, abundant, and usually less expensive.

[0003] When natural gas is the selected fuel, it can be stored in a liquefied form, as liquefied natural gas (LNG) or in a gaseous form, as compressed natural gas (CNG).
LNG is normally stored in a cryogenic storage vessel at temperatures between about -150 C and -115 C (between about -240 F and -175 F) and at pressures of between about 1 bar and 14 bar (between about 15 psig and 200 psig). An advantage of storing a gaseous fuel in liquefied form is higher energy density, which means that less storage space is needed to store the same amount of fuel. By way of example, LNG has an energy density that is about four times that of CNG.

[0004] Engines fuelled with gaseous fuels, such as natural gas, can operate by injecting the gaseous fuel into the engine's air intake manifold or by injecting the fuel directly into the engine's combustion chamber. When the gaseous fuel is injected into the engine's air intake system the required fuel supply pressure is relatively low, typically around 7 bar (about 100 psig), whereas in systems which inject the fuel directly into the engine's combustion chamber, the fuel injection pressure needs to be higher than the in-cylinder pressure, and typically the fuel injection pressure is at least 200 bar (3000 psig) to enable injection late in the compression cycle (when the engine piston is near top dead center).
Both types of gaseous fuelled internal combustion engine systems can comprise a fuel pump located inside the storage vessel, or an external fuel pump located outside of the storage vessel to ensure that fuel is delivered to the engine at the required injection pressure at all times and during different engine operating modes, including during transients.

[0005] In such gaseous fuelled internal combustion engine systems, when the engine is not operating, for example during servicing, a fuel shut-off valve, positioned downstream of the fuel storage vessel, is closed to stop any fuel flow to the engine and thereby fluidly isolate the storage vessel, as described, for example, in applicant's co-pending Canadian patent application number 2,796,794. During engine shut down, some gaseous fuel can remain in the fuel system, and the pressure within the fuel supply line can increase, for example, as a result of heat transfer from the surrounding environment to the fuel trapped in the supply line. Fuel systems are designed with safety measures which protect against over-pressurization of the fuel systems, and if the pressure within the fuel supply line increases over a predetermined limit fuel, a pressure relief valve will operate to vent gaseous fuel until the fuel pressure is reduced. Vented gaseous fuel can be captured, burned or otherwise oxidized, but if the gaseous fuel is vented to atmosphere or consumed in a non-productive way, venting even small amounts of fuel is undesirable and wasteful.

[0006] Similarly, in other gaseous fluid supply systems which store a gaseous fluid in liquefied form and supply it in gaseous form to an end user, during the time when the end user is not operating, some gaseous fluid can remain in the supply system and the pressure in the fluid supply line can increase. Such gaseous fluid supply systems have to be provided with safety measures to protect the system from over-pressurization and at the same time to reduce fluid losses by reducing the amount of fluid vented from the system.

[0007] Accordingly, there is a need for an improved gaseous fluid supply system and method of operating same to isolate the storage vessel from the end user when the end user is not operating and to better manage pressure and reduce the times when gaseous fluid is vented from the system.
Summary [0008] A gaseous fluid supply system is disclosed having a subsystem for isolating a storage vessel from the end user. The gaseous fluid supply system comprises a fluid storage vessel, a fluid discharge line fluidly connected with the storage vessel, wherein one-way fluid flow is permitted out from the storage vessel, and a supply line in fluid communication with the fluid discharge line for supplying fluid to an end user. The subsystem for isolating the storage vessel from the end user comprises a recirculation loop fluidly connecting the fluid discharge line with the storage vessel, and a switching device operable between two positions. When the switching device is in a first position, associated with the time when the end user is shut down, fluid is stopped from flowing from the fluid discharge line to the supply line, and the fluid discharge line is in fluid communication with the recirculation loop and when the switching device is in a second position, associated with the time when the end user is running, the fluid discharge line is in fluid communication with the supply line and fluid is stopped from flowing from the fluid discharge line to the recirculation loop.

[0009]
The switching device can be a three-way valve which can be a manual valve or an automatically controlled valve. Alternatively, the switching device can comprise a first two-way valve disposed on the supply line and a second two-way valve disposed on the recirculation loop. The first and second two-way valves can be automatic valves controlled by a system controller.

[0010]
The recirculation loop comprises a recirculation line that is fluidly connected to the storage vessel. In some embodiments the recirculation loop comprises a recirculation line and a portion of a pressure relief line which is fluidly connected to the storage vessel such that the recirculation line is fluidly connected to the storage vessel through that portion of the pressure relief line. The pressure relief line is provided with a pressure relief valve which opens when a preset pressure threshold is exceeded. The preset pressure threshold is determined as a function of a maximum design pressure limit associated with the storage vessel.

[0011] In some embodiments, the recirculation loop is in direct fluid communication with a vapor space within the storage vessel.

[0012] The gaseous fluid supply system can further comprise a vapor supply line in fluid communication with a vapor space of the storage vessel for delivering fluid in a gaseous state from the vapor space to the fluid discharge line when certain predetermined conditions are met.

[0013] In preferred embodiments, the gaseous fluid supply system comprises a heat exchanger placed in the fluid discharge line or in the supply line for increasing the temperature of the fluid being supplied to the end user and converting it into gaseous form.

[0014] In preferred embodiments, the gaseous fluid supply system comprises a pump which supplies fluid from the storage vessel to the end user through the fluid discharge line and the supply line. The pump can be actuated by a hydraulic drive or by an electric motor. The pump can be disposed within a cryogenic space of the storage vessel.

[0015] In preferred embodiments, the present system is a system for supplying a gaseous fuel to an internal combustion engine. The engine can be the prime mover for a vehicle.

[0016] In some embodiments, the gaseous fluid supply system can further comprise a backpressure generating device located in the recirculation loop, and sensors for detecting the pressure in the supply line and for detecting the pressure in the fluid discharge line or, in preferred embodiments, for detecting at least one parameter indicative of the activation status of a pump which supplies fluid from the storage vessel to the end user through the fluid discharge line and the supply line. The system further comprises a controller which receives signals from the sensors and is programmed to compare the received signals to signals characteristics of a normal operation of the end user to determine if the switching device is in a position that allows fluid communication between the fluid discharge line and the recirculation loop when the end user is started.

[0017] In some embodiments, the backpressure generating device is a spring loaded valve which is set to open at a predetermined pressure. The predetermined pressure can be set to be the difference between the maximum allowable pressure in the supply line and the maximum allowable pressure in the storage vessel.

[0018] In some embodiments, the pump supplying fluid to the end user from the storage vessel is a hydraulically actuated pump and the parameter indicative of the activation status of the fluid pump is a pressure in a hydraulic circuit of the pump.

[0019] In some other embodiments the pump is actuated by an electric motor.
In this case the parameter indicative of the activation status of the pump is the current and/or the voltage of the electric motor.

[0020] A method is disclosed for fluidly isolating a storage vessel from an end user in a fluid supply system comprising a fluid discharge line and a supply line for supplying fluid from the storage vessel to the end user when the end user is operating, a recirculation loop for recirculating fluid to the storage vessel and a switching device operable to fluidly connect or to stop fluid flow between the fluid discharge line, the supply line and the recirculation loop. The method comprises:
when shutting down the end user setting the switching device to a position that prevents fluid from flowing from the fluid discharge line to the supply line and allows fluid flow from the fluid discharge line through the recirculation loop to the storage vessel; and directing fluid from the fluid discharge line through the recirculation loop to the storage vessel when pressure within the recirculation loop is higher than pressure within the storage vessel.

[0021]
The method can further comprise detecting an operation state of the switching device when the end user is started. The step of detecting the operation state of the switching device comprises:
a) measuring the pressure in the supply line;
b) measuring the pressure in the fluid discharge line or measuring a parameter characteristic of an activation circuit of a pump which supplies fluid to the end user through the fluid discharge line and supply line;
c) sending signals of the measured pressure in the supply line and of the measured pressure in the fluid discharge line or of the measured parameter characteristic of the activation circuit to a controller;
d) determining that the switching device is in a position that allows fluid flow from the fluid discharge line through the recirculation loop to the storage vessel when the end user is started by detecting an increase in value of the pressure in the fluid discharge line or of the parameter indicative of the actuation state of the pump and no increase in measured pressure in the supply line; and e) indicating the position of the switching device through an alarm system.

[0022]
In this method the parameter indicative of the actuation state of the pump can be a pressure within a hydraulic circuit of a hydraulic pump which actuates the pump which supplies fluid to the end user or it can be the current and/or the voltage in an electric motor which actuates the pump.

Brief Description of the Drawings [0023] Figure 1 is schematic diagram of a first embodiment of a gaseous fluid supply system comprising a subsystem for isolating the storage vessel from the end user.

[0024] Figure 2 is schematic diagram of a second embodiment of a gaseous fluid supply system comprising a subsystem for isolating the fluid storage vessel from the end user.

[0025] Figure 3 is a schematic diagram of a third embodiment of a gaseous fluid supply system comprising a subsystem for isolating the fluid storage vessel from the end user.

[0026] Figure 4 is a schematic diagram of a fourth embodiment of a fluid supply system comprising a subsystem for isolating the fluid storage vessel from the end user.
Detailed Description [0027] Figure 1, schematically illustrates a first embodiment of fluid supply system 100 for delivering a gaseous fluid to an end user (not shown). Gaseous fluid supply system 100 comprises storage vessel 102 which stores gaseous fluid in liquefied form and pump 105, which in the illustrated embodiment is shown disposed inside liquid space 114 of storage vessel 100. An advantage of this arrangement is that the pump is immersed in the liquefied gas where it is always primed and kept at the same temperature as the fluid being pumped, so that there is no delay associated with cooling it to cryogenic temperatures before it is able to do useful work. Pump 105 delivers fluid from storage vessel 102 to the end user through fluid discharge line 103, which extends from the discharge outlet of pump 105 to an inlet of flow switching device 110, and from flow switching device 110, on to the end user through supply line 104. Check valve 112 allows fluid flow in only one direction, to prevent back flow of fluid towards the discharge outlet of pump 105. Pump 105 can be actuated by hydraulic drive 115, as illustrated by the embodiment shown in Figure 1, or can be driven by other known actuators, such as an electric motor. The illustrated embodiment further comprises heat exchanger 116 and check valve 118 located along fluid discharge line 103 to vaporize and deliver the fluid that is pumped from storage vessel 102 in gaseous form to the end user.

[0028] Gaseous fluid supply system 100 further comprises a subsystem for isolating storage vessel 102 from the end user when the end user is shut down and this subsystem comprises a switching device 110 and a recirculation loop to connect fluid discharge line 103 with storage vessel 102. The recirculation loop comprises fluid recirculation line 108, which in this first embodiment extends from an outlet of switching device 110 to a junction with pressure relief line 120. Pressure relief line 120 is fluidly connected to a location near the top of storage vessel 102 which is normally filled in vapor, and referred to in this disclosure as vapor space 122.

[0029] In a preferred embodiment, switching device 110, is a three-way valve, which can be a manually actuated valve or a valve with an electronically controlled actuator that is commanded by a controller to switch between different operating positions, under predetermined operating conditions, for example, when the end user is being shut down or started. Switching device 110 receives gaseous fluid through an inlet connected to fluid discharge line 103, and is operable to fluidly connect fluid discharge line 103 with either supply line 104 (to deliver gaseous fluid to the end user), or with recirculation line 108 so that fluid discharge line 103 is fluidly connected to storage vessel 102 by way of recirculation line 108 and a portion of pressure relief line 120. The volume of storage vessel 102 is much larger than the volume defined by fluid supply system 100, so storage vessel 102 is able to receive the relatively small quantities of gaseous fluid from the fluidly connected portion of fluid supply system 100 until the vapor pressure in the storage vessel exceeds the predetermined pressure threshold that triggers the opening of pressure relief valve 124. The method of isolating the storage vessel from the end user when the end user is shut down is described in more detail with respect to the embodiment shown in Figure 1.

[0030] When the end user is operating, fluid is delivered through fluid discharge line 103 and switching device 110 is operated to a first position that stops fluid flow from fluid discharge line 103 and supply line 104 to recirculation line 108 and that fluidly connects fluid discharge line 103 and supply line 104 so that all of the fluid delivered from storage vessel 102 flows to supply line 104. When the end user is shut down, switching device 110 is operated to a second position that fluidly isolates storage vessel 102 and fluid discharge line 103 from the end user and from supply line 104 and fluidly connects fluid discharge line 103 to recirculation line 108. When switching device 110 is in the second position, and the end user is shut down for a prolonged period of time, heat transfer from the ambient environment to the fluid remaining in fluid discharge line 103 and recirculation line 108 can cause the pressure of this gaseous fluid to increase, in which case, instead of being immediately vented, it will flow through a portion of pressure relief line 120 towards storage vessel 102 where the pressure is usually lower, and where the larger volume of stored liquefied fluid normally has some capacity to absorb small quantities of warmer higher pressure gas without elevating storage pressure within the storage vessel above the predetermined pressure threshold for opening pressure relief valve 124.

[0031] The first embodiment described above can be implemented in a gaseous fuelled internal combustion engine where fuel, for example, natural gas, is stored in liquefied form (LNG) in storage vessel 102 and delivered to the engine through fluid discharge line 103 and supply line 104.

[0032] LNG fuel storage vessels used to store fuel on board a vehicle are normally required to satisfy the local safety standards for the jurisdiction where the storage vessel is deployed. Such safety standards normally prescribe tests for surviving impacts of a severity reasonably expected, for example, as a result of a vehicle crash.
Accordingly, such fuel storage vessels are often manufactured with a shrouded space at one end of the vessel to protect the piping, valves and other fixtures associated with the storage vessel and fuel system. The elements of the presently disclosed system are located inside the protective shroud of the associated storage vessel, illustrated as dashed outline 126 in Figure 1.

[0033] The first embodiment can further comprise additional features for detecting the operation state of switching device 110 when the end user is started, namely backpressure device 140, located on recirculation line 108, pressure sensor 142, which measures the pressure in supply line 104, and pressure sensor 144, which measures the pressure in the hydraulic circuit of hydraulic drive 115. The measurement signals from sensors 142 and 144 are sent to system controller 130, which is programmed to detect the operation state of switching device 110 when the end user is started, as explained below. In the illustrated embodiment, backpressure device 140 is a spring loaded valve which opens at a predetermined pressure. In other embodiments the backpressure device can be another device which opens at a predetermined pressure, for example an electrically controlled valve. In the illustrated embodiment, the predetermined pressure for opening spring loaded valve 140 is determined to be the difference between the maximum allowable pressure in supply line 104 and the maximum allowable pressure in storage vessel 102, to ensure that backpressure device 140 opens before the pressure in supply line 104 reaches the maximum allowable limit while at the same time generating some backpressure in the recirculation line when the valve is closed.

[0034] The method of detecting the operation state of the switching device involves determining if switching device 110 is in a position that allows fluid recirculation through recirculation line 108 and that stops fluid flow from the storage vessel to the end user when the end user starts to operate. In such cases, the presence of backpressure device 140 creates a backpressure when fluid flows through recirculation line 108, which triggers a pressure spike in the hydraulic circuit of hydraulic drive 105 if pump 105 is activated and if switching device 110 is in the position that blocks fluid from flowing into supply line 104, and diverts it to recirculation line 108. If system controller 130 determines through pressure sensor 144 that there is an increase in the pressure in the hydraulic circuit of hydraulic drive 115 and at the same time it records no change in value of the pressure in supply line 104, system controller 130 is able to determine that switching device 110 is set in the wrong position for starting the end user, and system controller 130 can activate an alarm system, for example through the OBD (on-board diagnostics) system to alert the operator to set switching device 110 to the position that allows fluid flow from the storage vessel to the end user (and that blocks fluid flow through recirculation line 108). When switching device 110 is a manually operated valve the operator will know to stop the start-up sequence for the end user, until the position of switching device 110 is changed. If the alarm system is activated and switching device 110 is one that is normally electronically operated, then the operator will need to troubleshoot the automatic control of the switching device.

[0035] In some other embodiments, pressure sensor 144 can be replaced by a pressure sensor placed in fluid discharge line 103, for example downstream of check valve 118, which can have the same function as pressure sensor 144 and can sense a pressure spike in the fluid discharge line indicating that fluid is supplied from storage vessel 102 to fluid discharge line 103 when the end user is started but that switching device 110 is set to a wrong position that allows fluid communication between fluid discharge line 103 and recirculation line 108 and stops fluid communication between fluid discharge line 103 and supply line 104.

[0036] Other embodiments of the present apparatus are illustrated in Figures 2, 3 and 4.
These embodiments have many elements that are functionally equivalent to like elements of the first embodiment presented in Figure 1, and such "like elements" are identified by like-numbered reference numbers.

[0037] With reference now to the second embodiment, shown in Figure 2, fluid supply system 200 comprises storage vessel 202 which stores a gaseous fluid in liquid form and pump 205 which is immersed in liquid space 214 of the storage vessel and which supplies fluid through fluid discharge line 203 and supply line 204 to an end user. In this embodiment, pump 205 is actuated by an electric motor 215 as illustrated.
Similar to the system illustrated in the first embodiment, the fluid supply system of Figure 2 comprises a heat exchanger 216 and one-way check valves 212 and 218 which have the same function as in the embodiment illustrated in Figure 1. The supply system in Figure 2 further comprises a vapor supply line 228 provided with a one-way check valve 232.
Through this vapor supply line fluid can be supplied from vapor space 222 of the storage vessel to fluid discharge line 203 when the pressure in the vapor space meets the demands required by the operation of the end user. As illustrated, vapor supply line 228 is fluidly connected to storage vessel 202 through a portion of pressure relief line 220.

[0038] The subsystem for isolating the storage vessel from the end user comprises a recirculation loop which in the present embodiment comprises recirculation line 208 and a switching device which in this embodiment is illustrated as three-way valve 210 which is operable to connect fluid discharge line 203, supply line 204 and recirculation line 208.

, In this embodiment, recirculation line 208 is connected directly to vapor space 222 of storage vessel 202. Pressure relief line 220 is also connected to storage vessel 202 to allow fluid to be vented through pressure relief valve 224 when the pressure within the storage vessel exceeds a predetermined allowable limit. Fluid vented from the system can be vented to the atmosphere, but it is preferably captured, burned or otherwise oxidized.
The elements of the second embodiment of the present system can be located in a protective shroud of the storage vessel illustrated with dashed outline 226.

[0039] For the embodiment illustrated in Figure 2, the method of isolating the storage vessel from the end user when the end user is shut down is similar with the method described for the first embodiment, whereby at shut-down, three-way valve 210 is set to a position which blocks fluid flow from fluid discharge line 203 to supply line 104 and to the end user, thereby fluidly isolating the storage vessel from the end user, and allowing fluid flow between fluid discharge line 203 and recirculation line 208 such that fluid remaining in fluid discharge line 203 and in recirculation line 208 when the end user is shut down can be returned directly to vapor space 222 of storage vessel 202 when the fluid pressure in recirculation line 208 becomes higher than the pressure in the storage vessel. Similar to the first embodiment, fluid is vented to the atmosphere or is preferably redirected elsewhere through pressure relief line 220 only when the pressure within the storage vessel rises over an admissible predetermined limit. Vented fluid can be captured in a separate vessel to be used later or can be burned or otherwise oxidized.

[0040] The second embodiment can further comprise additional optional features for detecting the operation state of switching device 210. When the end user starts to operate.
Backpressure device 240 is located on recirculation line 208 and allows fluid flow from fluid discharge line 203 to storage vessel 202 when the pressure within recirculation line 208 is higher than the pressure within the storage vessel. Pressure in supply line 204 is monitored by pressure sensor 242 which sends the measurement signals to system controller 230. Current and voltage feedback from electric motor 215 of pump 205 are collected and communicated through sensor 244 to system controller 230. The current and voltage of electric motor 215 represent parameters which are characteristic of the activation status of pump 205.

[0041] The method of detecting the operation state of switching device 210 in this second embodiment is similar with the method described in relation with the embodiment illustrated in Figure 1. System controller 230 receives signals from pressure sensor 242 and from sensor 244 regarding the pressure in the supply line and, respectively, regarding the current and/or voltage of the electric motor. The presence of backpressure device 240 creates a backpressure when fluid flows through recirculation line 208, which triggers a spike in the voltage and/or current of electric motor 215 if pump 205 is activated when the end user is started and if switching device 210 is in the position that blocks fluid from flowing into supply line 204 and diverts it to recirculation line 208. If system controller 230 determines that there is an increase in current and/or voltage of electric motor 215 and at the same time it records no pressure increase in supply line 204, system controller 230 is able to determine that switching device 210 is set in the wrong position for starting the end user. This operation state is indicated to an operator, who can then set the switching device 210 to the desired position manually or can troubleshoot the automatic control of the switching device to remedy the situation.

[0042] Another embodiment of the present gaseous fluid supply system is illustrated in Figure 3. As in the previous embodiments, in this third embodiment the subsystem for isolating storage vessel from the end user comprises recirculation line 308 and a switching device illustrated as three-way valve 310. The gaseous fluid supply system 300 further comprises fluid discharge line 303 connected to the discharge outlet of an external pump 305 and supply line 304. When the end user is operating, three-way valve 310 is set in a first position and fluid is supplied to the end user from liquid space 314 of storage vessel 302 through fluid discharge line 303 provided with one way valve check valve 312 connected to the discharge outlet of external pump 305 and through fluid supply line 304.
In this embodiment, pump 305 is an external pump placed outside of storage vessel 302 which is activated by hydraulic drive 315. Vapor can also be supplied from vapor space 322 inside storage vessel 302 to fluid discharge line 303 through vapor supply line 328, provided with one way check valve 332. During the operation of the end user, fluid in gaseous state can be supplied from the vapor space 322 to the end user through vapor supply line 328 and through fluid discharge line 303 when the pressure within vapor space 322 meets the required operation pressure of the end user as determined by the system controller.

[0043] Recirculation line 308 is fluidly connected to three-way valve 310 and to pressure relief line 320 which is provided with pressure relief valve 324. The recirculation loop in this embodiment comprises recirculation line 308 and a portion of pressure relief line 320 which fluidly connects recirculation line 308 to storage vessel 302.

[0044] In this third embodiment, heat exchanger 316 and one-way check valve which prevents any fluid backflow to the heat exchanger are placed in fluid supply line 304 and therefore some of the system components located upstream of the heat exchanger, for example switching device 310, have to be compatible to work in cryogenic conditions corresponding to the temperature of the fluid being delivered from the cryogenic space of storage vessel 302.

[0045] The components to the supply system can be enclosed in a shroud 326 of the storage vessel.

[0046] The operation of this third embodiment is similar with the operation of the other embodiments described here. When the end user is shut-down, three-way valve 310 is set to a second position which isolates the storage vessel from the end user and at the same time allows fluid communication between fluid discharge line 303 and recirculation line 308 such that fluid from the supply line can be returned to storage vessel 302 when the pressure of the fluid in the recirculation line increases and becomes higher than the pressure in the storage vessel. Similar to the first embodiment, fluid is vented through pressure relief line 320 only when the pressure within the storage vessel rises over an admissible predetermined limit. In this embodiment, a relatively large portion of the fluid returned to the storage vessel can be in liquid state. Three-way valve 310 can be a manual valve which is switched by an operator between the two positions, or it can be an automatic valve which is switched between the two positions by the system controller.

[0047] Similar to the other embodiments, the system illustrated in Figure 3 can comprise some additional components for detecting the position of switching device 310.
The system can comprise a backpressure device 340, illustrated as a spring loaded valve, pressure sensor 342 for measuring the pressure in supply line 304 and pressure sensor 344 which monitors the pressure within the hydraulic drive 315 which actuates pump 305. Controller 330 receives the measured signals from sensors 342 and 344.

[0048] The method of detecting the operation state of switching device when the end user is started in the system illustrated in Figure 3 is similar to the method described in relation to Figure 1. When pump 305 strokes and switching device 310 is set to a position that allows fluid flow from fluid discharge line 303 to recirculation line 308, spring loaded valve 340 generates a backpressure in recirculation line 308.
Controller 330 monitors the signals received from sensors 342 and 344. If, when the end user is started, there is a spike in pressure in the hydraulic circuit of hydraulic pump 315 and at the same time there is no pressure increase in supply line 304, controller 330 determines that switching device 310 is set in a position which stops fluid flow from fluid discharge line 303 to the end user and allows fluid flow through recirculation line 308. This operation state is indicated to the vehicle driver, for example through an OBD (on-board diagnostics) system and the situation can be corrected.

[0049] Figure 4 illustrates yet another embodiment of the present system.
Gaseous fluid supply system 400 comprises some similar components to the previously described embodiments, having similar reference numbers which will not be described here entirely, if at all. The difference between this fourth embodiment and the previous embodiments is that the switching device which is operable to connect fluid discharge line 403, supply line 404 and recirculation line 408 comprises two-way valves 406 and 407. Two-way valve 406 is positioned on supply line 404 and two-way valve 407 is positioned on recirculation line 408. These two two-way valves can be actuated manually or by the system controller 430.

[0050] When the end user is started, two-way valve 406 is opened to allow fluid flow from liquid space 414 of storage vessel 402 and pump 405 to the end user through fluid discharge line 403 provided with check valve 418 and through supply line 404.
The storage vessel can be isolated from the end user as further explained here.
When the end user is shut down, two-way valve 406 is closed to stop fluid flow from storage vessel 402 to the end user, and two-way valve 407 is opened to allow fluid flow from fluid discharge line 403 to recirculation line 408. Similarly to the previous embodiments, fluid from fluid discharge line 403 and from recirculation line 408 can be returned to vapor space 422 of storage vessel 402 through a portion of pressure relief line 420 when the pressure in recirculation line 408 is higher than the pressure in the storage vessel.
Fluid is vented through pressure relief line 420 and pressure relief valve 424 only when the pressure within the storage vessel rises over an admissible predetermined limit. Vented fluid can be captured in an auxiliary vessel or can be oxidized or burned.

[0051] The system illustrated in Figure 4 further comprises heat exchanger 416 positioned on fluid discharge line 403 and vapor supply line 428 and one way check valve 432 through which vapor can be supplied from vapor space 422 to fluid discharge line 403 under predetermined conditions. All the elements of the fluid supply system can be enclosed in shroud 426 of the storage vessel for a better protection.

[0052] In all the described embodiments, the system can be a fuel supply system of a gaseous fuelled internal combustion engine which can be the prime mover for a vehicle.
The gaseous fuel can be natural gas which is stored in liquefied form in a LNG
tank.

[0053] The present invention has been described with regard to a plurality of illustrative embodiments. However, it will be apparent to persons skilled in the art that a number of variations and modifications can be made without departing from the scope of the invention as defined in the claims.

Claims

1. A gaseous fluid supply system comprising:
a. a fluid storage vessel;
b. a fluid discharge line fluidly connected with said storage vessel wherein one-way fluid flow is permitted out from said storage vessel;
c. a supply line for supplying fluid from said fluid discharge line to an end user;
d. a recirculation loop fluidly connecting said fluid discharge line with said storage vessel; and e. a switching device operable between:
i. a first position associated with when said end user is shut down, in which fluid is stopped from flowing from said fluid discharge line to said supply line, and said fluid discharge line is in fluid communication with said recirculation loop; and ii. a second position associated with when said end user is running, in which said fluid discharge line is in fluid communication with said supply line and fluid is stopped from flowing from said fluid discharge line to said recirculation loop.

2. The gaseous fluid supply system of claim 1, wherein said switching device is a three-way valve.

3. The gaseous fluid supply system of claim 1 wherein said switching device comprises a first two-way valve disposed on said supply line and a second two-way valve disposed on said recirculation loop.

4. The gaseous fluid supply system of claim 3 wherein said first and second two-way valves are automatic valves controlled by a system controller.

5. The gaseous fluid supply system of claim 1 wherein said recirculation loop comprises a recirculation line that is fluidly connected to said storage vessel.

6. The gaseous fluid supply system of claim 1 wherein said recirculation loop comprises a recirculation line and a portion of a pressure relief line which is fluidly connected to said storage vessel, and wherein said pressure relief line is provided with a pressure relief valve which opens when a preset pressure threshold is exceeded.

7. The gaseous fluid supply system of claim 6 wherein said preset pressure threshold is determined as a function of a maximum design pressure limit associated with said storage vessel.

8. The gaseous fluid supply system of claim 1 wherein said recirculation loop is in direct fluid communication with a vapor space within said storage vessel.

9. The gaseous fluid supply system of claim 1 wherein said switching device is a manual valve.

10. The gaseous fluid supply system of claim 1 further comprising a vapor supply line in fluid communication with a vapor space of said storage vessel for delivering fluid in a gaseous state from said vapor space to said fluid discharge line.

11. The gaseous fluid supply system of claim 1 further comprising a heat exchanger placed in said fluid discharge line or in said supply line.

12. The gaseous fluid supply system of claim 1 further comprising a pump which supplies fluid from said storage vessel to said end user through said fluid discharge line and said supply line, said pump being actuated by a hydraulic drive.

13. The gaseous fluid supply system of claim 12 wherein said pump is disposed within a cryogenic space of said storage vessel.

14. The gaseous fluid supply system of claim 1 wherein said system is a gaseous fuel supply system for an engine.

15. The gaseous fluid supply system of claim 14 wherein said engine is the prime mover for a vehicle.

16. The gaseous fluid supply system of claim 1 further comprising:
a. a backpressure generating device located in said recirculation loop;
b. sensors for detecting the pressure in said supply line and for detecting the pressure in said fluid discharge line or for detecting at least one parameter indicative of the activation status of a pump which supplies fluid from said storage vessel to said end user through said fluid discharge line and said supply line; and c. a controller which receives signals from said sensors and is programmed to compare said received signals to signals characteristics of a normal operation of said end user to determine if said switching device is in a position that allows fluid communication between said fluid discharge line and said recirculation loop when said user is started.

17. The gaseous fluid supply system of claim 16 wherein said backpressure generating device is a spring loaded valve which is set to open at a predetermined pressure.

18. The gaseous fluid supply system of claim 17 wherein said predetermined pressure is the difference between the maximum allowable pressure in said supply line and the maximum allowable pressure in said storage vessel.

19. The gaseous fluid supply system of claim 16 wherein when said pump is a hydraulically actuated pump said parameter indicative of the activation status of said fluid pump is a pressure in a hydraulic circuit of said pump.

20. The gaseous fluid supply system of claim 16 wherein when said pump is actuated by an electric motor and said parameter indicative of the activation status of said pump is the current and/or the voltage of said electric motor.

21. A method for fluidly isolating a storage vessel from an end user in a fluid supply system comprising a fluid discharge line and a supply line for supplying fluid from said storage vessel to said end user when said end user is operating, a recirculation loop for recirculating fluid to said storage vessel and a switching device operable to fluidly connect or to stop fluid communication between said fluid discharge line, said supply line and said recirculation loop, said method comprising:
when shutting down said end user setting said switching device to a position that stops fluid flow from said fluid discharge line to said supply line and allows fluid flow from said fluid discharge line through said recirculation loop to said storage vessel; and directing fluid from said fluid discharge line through said recirculation loop to said storage vessel when pressure within said recirculation loop is higher than pressure within said storage vessel.

22. The method of claim 21 further comprising detecting an operation state of said switching device when said end user is started.

23. The method of claim 22 wherein the step of detecting said operation state of said switching device comprises:
a. measuring a pressure in said supply line;
b. measuring a pressure in said fluid discharge line or measuring a parameter characteristic of an activation circuit of a pump which supplies fluid from said storage vessel to said fluid discharge line;

c. sending signals of said measured pressure in said supply line and of said measured pressure in said discharge line or of said measured parameter characteristic of said activation circuit of said pump to a controller;
d. determining that said switching device is in a position that allows fluid flow from said fluid discharge line through said recirculation loop to said storage vessel when said end user is started by detecting an increase in value of said pressure in said fluid discharge line or of said parameter indicative of the actuation state of said pump and no increase in said measured pressure in said supply line; and e. indicating said position of said switching device through an alarm system.

24. The method of claim 23 wherein said parameter indicative of the actuation state of said pump is a pressure within a hydraulic circuit of a hydraulic pump which actuates said pump or the current and/or the voltage in an electric motor which actuates said pump.