Method for refueling liquefied natural gas vehicles

Abstract

The method for refueling liquefied natural gas vehicles comprises the following phases: supply of a refueling system (1) provided with a dispensing line (2) adapted to dispense liquefied natural gas (L) and with a withdrawal line (3) adapted to withdraw gaseous natural gas (G); supply of a liquefied natural gas (L) vehicle (4) provided with a refueling tank (5); connection (I) of the refueling system (1) to the refueling tank (5); first dispensing (II) of liquefied natural gas (L) into the refueling tank (5) through the dispensing line (2); withdrawal of residual gaseous natural gas (G) from the refueling tank (5) through the withdrawal line (3); second dispensing of liquefied natural gas (L) into the refueling tank (5) through the dispensing line (2).

Description

[0001] METHOD FOR REFUELING LIQUEFIED NATURAL GAS VEHICLES

[0002] Technical Field

[0003] The present invention relates to a method for refueling liquefied natural gas vehicles.

[0004] Background Art

[0005] Liquefied natural gas (LNG) is a mixture of hydrocarbons, generally found in nature in the gaseous state, of which the main component is methane, but which normally also contains other gaseous hydrocarbons such as ethane, propane and butane. The gaseous hydrocarbon mixture undergoes a liquefaction process, that is, consecutive cycles of cooling to very low temperatures (of about -165 °C) and pressurization to obtain, precisely, a mixture in the liquid state. This process makes it possible to increase the storage efficiency of these hydrocarbons, greatly reducing their volume and allowing storing a much greater mass for the same volume.

[0006] For these reasons, liquefied natural gas is increasingly being used as a fuel in vehicles that require large amounts of fuel such as trucks.

[0007] Liquefied natural gas, however, at normal ambient temperatures, heats up and tends to gradually pass to the gaseous state.

[0008] The vehicle tank, therefore, always contains a certain amount of gaseous natural gas resulting from the heating of the liquefied natural gas and causing an increase in the internal pressure of the tank. For this reason, vehicle tanks are generally provided with a safety valve that allows the gaseous natural gas to be vented beyond a certain pressure value.

[0009] Upon refueling, filling the tank with LNG results in a further increase in pressure, caused by the presence of the residual gaseous natural gas. Again, when a certain pressure threshold has been reached, special safety valves cause the gaseous natural gas to escape, resulting in the loss of fuel and the release of hazardous substances into the environment.

[0010] Therefore, known refueling methods involve an initial intake of gaseous natural gas and, later, LNG dispensing. The recovered gaseous natural gas can be subjected to a liquefaction process again for subsequent dispensing, e.g. by bubbling in liquefied natural gas.

[0011] However, intake does not allow for the total removal of the gaseous natural gas, some of which remains in the tank. As a result, for the aforementioned reasons, the subsequent dispensing does not allow for total filling of the tank with LNG. In detail, it is estimated that, by means of known refueling methods, the volume of residual gaseous natural gas remaining in the tank would be occupied by about 5-10 kg of LNG, equivalent to about 20-40 km of vehicle mileage.

[0012] This drawback results in the need to travel more frequently to service stations with consequent inconvenience for the driver. This drawback is even more pronounced in some geographical areas where LNG stations are not widespread. Drivers must, therefore, also consider detours in their road route in order to be able to refuel, sometimes even with a tank which is not completely empty.

[0013] Description of the Invention

[0014] The main aim of the present invention is to devise a method for refueling liquefied natural gas vehicles which allows making maximum use of the fuel tank capacity of the vehicle.

[0015] Another object of the present invention is to devise a method for refueling liquefied natural gas vehicles which allows reducing the frequency of refueling operations by the driver.

[0016] Another object of the present invention is to devise a method for refueling liquefied natural gas vehicles which allows the aforementioned drawbacks of the prior art to be overcome within the framework of a simple, rational, easy and efficient to use as well as cost-effective solution.

[0017] The aforementioned objects are achieved by this method for refueling liquefied natural gas vehicles having the characteristics of claim 1.

[0018] Brief Description of the Drawings

[0019] Other characteristics and advantages of the present invention will become more apparent from the description of a preferred, but not exclusive, embodiment of a method for refueling liquefied natural gas vehicles, illustrated by way of an indicative, yet non-limiting example in the accompanying tables of drawings in which: Figure 1 is a schematic representation of a refueling system for implementing the method according to the invention;

[0020] Figures 2 and 3 are schematic representations of the tank of a vehicle in accordance with two different embodiments;

[0021] Figure 4 shows a block diagram representing the phases of the method according to the invention.

[0022] Embodiments of the Invention

[0023] With special reference to these figures, reference numeral 1 globally denotes a system for refueling liquefied natural gas vehicles through which the method is implementable.

[0024] In the context of this disclosure, the term “liquefied natural gas” relates to a mixture of hydrocarbons, generally occurring in nature in the gaseous state, of which the main component is methane, but which normally also contains other gaseous hydrocarbons such as ethane, propane and butane. The gaseous hydrocarbon mixture undergoes a liquefaction process, that is, successive cycles of cooling to very low temperatures (of about -165°C) and pressurization to precisely obtain a mixture in the liquid state. This process allows increasing the storage efficiency of these hydrocarbons, greatly reducing their volume and allowing storing a much larger mass for the same volume.

[0025] The method according to the invention first comprises a phase of supplying a refueling station 1 provided with a dispensing line 2 adapted to dispense liquefied natural gas L and with a withdrawal line 3 adapted to withdraw gaseous natural gas G.

[0026] The method also comprises a phase of supplying a vehicle 4 running with liquefied natural gas L provided with a refueling tank 5.

[0027] In accordance with the embodiment shown in the figures, the refueling station 1 is of the type of a service station for road vehicles and the vehicle 4 is of the type of a truck. It cannot, however, be ruled out that the refueling station and / or the vehicle may be of a different type.

[0028] In more detail, the refueling station 1 comprises a dispensing apparatus 6 provided with the dispensing line 2 and with the withdrawal line 3. The refueling station 1 also comprises a supply unit 7 connected to the dispensing apparatus 6 and adapted to supply the liquefied natural gas L through the dispensing line 2 and a recovery unit 8 connected to the dispensing apparatus 6 and adapted to receive the gaseous natural gas G withdrawn through the withdrawal line 3.

[0029] The supply unit 7 may comprise a storage tank of the liquefied natural gas L and / or a liquefaction assembly of the gaseous natural gas G.

[0030] The recovery unit 8 may comprise a storage tank of the gaseous natural gas G and may be directly connected to the liquefaction assembly, if any.

[0031] Conveniently, the dispensing line 2 and the withdrawal line 3 are provided with relevant passage valves 9, adapted to allow the respective fluid to flow, and with relevant safety valves 10, adapted to allow the gaseous natural gas G to vent when a predefined pressure is achieved.

[0032] The passage valves 9 are of the type of pneumatic valves and are configured to open / close the respective lines.

[0033] The safety valves 10 are connected to a venting unit 11 by means of a safety line 12, through which the pressurized gas escapes from the dispensing line 2 and from the withdrawal line 3.

[0034] The dispensing apparatus 6 comprises a display 13 intended to indicate to a user the cost of the liquefied natural gas L per unit of mass, the mass of the dispensed liquefied natural gas L and the final price of the dispensed liquefied natural gas L.

[0035] For this purpose, the refueling station 1 also comprises at least a first mass meter 14 connected to the dispensing line 2 and adapted to measure the mass of the liquefied natural gas L entering the dispensing apparatus 6 and at least a second mass meter 15 connected to the withdrawal line and adapted to measure the mass of withdrawn gaseous natural gas G.

[0036] The dispensing apparatus 6 also comprises an electronic processing and control unit 16 configured to control the electronic components of the apparatus itself and to determine the final price of the dispensed liquefied natural gas L, as will be better described later in this disclosure. Specifically, the electronic processing and control unit 16 comprises a processing unit 17 operationally connected to the mass meters 14, 15.

[0037] The method comprises a connection phase I of the refueling system 1 to the refueling tank 5.

[0038] In detail, the refueling system 1 comprises a first connecting gun 18 connected to the dispensing line 2 and a second connecting gun 19 connected to the withdrawal line 3, both of which connectable to the refueling tank 5.

[0039] Appropriately, the vehicle 4 comprises at least one attachment for the first connecting gun 18, and possibly one attachment for the second connecting gun 19, connected to the refueling tank 5 through a first conduit 20 adapted to carry the liquefied natural gas L and a second conduit 21 adapted to carry the gaseous natural gas G, respectively.

[0040] In this regard, it should be specified that, in accordance with a first embodiment shown in Figure 2, the vehicle 4 comprises a first attachment 22 connected to the refueling tank 5 through the first conduit 20 and connectable to the first connecting gun 18 and a second attachment 23 connected to the refueling tank 5 through the second conduit 21 and connectable to the second connecting gun 19. In accordance with a second embodiment shown in Figure 3, on the other hand, the vehicle 4 comprises a single attachment 24 connectable to the first connecting gun 18, and the first conduit 20 and the second conduit 21 coincide into a single connecting conduit.

[0041] For this purpose, the refueling system 1 comprises a connection line 25 connected to the dispensing line 2 and to the withdrawal line 3 in a fluid-operated maimer and adapted to set the refueling tank 5 in fluidic communication with the withdrawal line itself. The connection line 25 comprises a relevant passage valve 9 also operable to allow or prevent the fluid passage depending on the type of vehicle 4 connected.

[0042] Conveniently, the withdrawal line 3 comprises at least one check valve 26 configured to allow only gaseous natural gas G to flow from the refueling tank 5 to the recovery unit 8 and not vice versa.

[0043] At this point, the method involves the following phases: first dispensing II of liquefied natural gas L into the refueling tank 5 through the dispensing line 2; withdrawal III of residual gaseous natural gas G from the refueling tank 5 through the withdrawal line 3; second dispensing IV of liquefied natural gas L into the refueling tank 5 through the dispensing line 2.

[0044] Specifically, in accordance with the second embodiment, the withdrawal phase III is carried out through the connection line 25.

[0045] The withdrawal phase III is carried out after the phase of first dispensing II.

[0046] In actual facts, the method involves the extraction of gaseous natural gas G as a result of a first dispensing of liquefied natural gas L so as to reduce the pressure inside the refueling tank 5 and allow a second dispensing so as to fill the tank itself substantially full.

[0047] As stated above, in fact, upon refueling, the refueling tank 5 has a minimum volume of liquefied natural gas L and the remaining volume is occupied by the gaseous natural gas G. Refueling under such conditions shortly results in a pressure rise within the refueling tank 5 caused by the compression of the gaseous natural gas G as the volume of the liquefied natural gas L increases. As a result, for safety reasons, the refueling tank 5 can be only partly filled in order to avoid venting and subsequent leakage of the gaseous natural gas G.

[0048] Conveniently, the method comprises a sensing phase V of at least one pressure datum representative of the pressure of gaseous natural gas G within the refueling tank 5 which is carried out at the same time as the phase of first dispensing II.

[0049] The sensing phase V is carried out by means of a first pressure sensor 27 associated with the dispensing line 2.

[0050] The phase of first dispensing II is interrupted with the pressure datum being equal to or greater than a predefined threshold value.

[0051] The predefined threshold value is selected depending on a safety pressure value at which the safety valves generally used in such systems are set and which, generally, is 16 bar.

[0052] In accordance with the preferred embodiment, the predefined threshold value is of between 12 bar and 15 bar. Conveniently, the method also comprises an acquisition phase VI of at least one datum of flow rate representative of the flow rate of liquefied natural gas L carried out at the same time as the phase of first dispensing II.

[0053] The acquisition phase VI is carried out by means of the first mass meter 14.

[0054] The phase of first dispensing II can also be interrupted with the datum of flow rate equal to or less than a predefined value of minimum flow rate. This circumstance may occur when the pressure datum is still below the predefined threshold value but, nevertheless, the presence of the gaseous natural gas G hinders the filling of the refueling tank 5 with liquefied natural gas L, thus resulting in very long filling times.

[0055] The next withdrawal phase III of gaseous natural gas G is carried out for a predefined time interval.

[0056] Conveniently, the method also comprises at least one measurement phase VII of at least one datum of flow rate which is representative of the flow rate of gaseous natural gas G which is carried out at the same time as the withdrawal phase III. The measurement phase VII is carried out by means of the second mass meter 15. Alternatively or in combination thereof, the withdrawal phase III is interrupted with the datum of flow rate being equal to or less than a predefined value of minimum flow rate, i.e., when the mass of the gaseous natural gas G is small. Thereafter, the method involves the phase of second dispensing IV, which is carried out in a similar way as the phase of first dispensing II.

[0057] As anticipated, the phase of second dispensing IV allows the tank to be filled substantially completely.

[0058] The sensing phase V and the acquisition phase VI are repeated during the phase of second dispensing IV, so that the latter can be interrupted with the pressure datum being equal to or higher than the predefined threshold value and / or with the datum of flow rate being equal to or less than the predefined value of minimum flow rate.

[0059] In addition, the acquisition phases VI are carried out so as to measure the total mass of dispensed liquefied natural gas L.

[0060] Similarly, the measurement phase VII is also carried out so that the total mass of withdrawn gaseous natural gas G can be measured. This value is then subtracted from the mass of dispensed liquefied natural gas L so as to obtain a datum which is then converted, thanks to the electronic processing and control unit 16, into an amount to be paid by the user as a result of refueling. This allows the price to be adjusted to the actual amount of liquefied natural gas L supplied to the user.

[0061] In accordance with one possible embodiment, the withdrawal phase III of gaseous natural gas G is carried out at the same time as the dispensing phases II, IV. In this way, it is further possible to reduce the timing of refueling.

[0062] Advantageously, prior to the phase of first dispensing II, the method comprises a pre-sensing phase VIII of at least one pressure datum representative of the pressure of residual gaseous natural gas G within the refueling tank 5.

[0063] The pre-sensing phase VIII is carried out by means of a second pressure sensor 31 on the withdrawal line 3.

[0064] The pre-sensing phase VIII is carried out so as to assess the amount of gaseous natural gas G in the refueling tank 5 before dispensing the liquefied natural gas L.

[0065] With the pressure datum above a predefined value of pressure, the method involves a removal phase IX of the residual gaseous natural gas G from the refueling tank 5 through the withdrawal line 3.

[0066] In accordance with the preferred embodiment, the predefined value of pressure is of between 7 bar and 9 bar.

[0067] In other words, if the pressure within the refueling tank 5 is less than the predefined value of pressure, i.e., the amount of gaseous natural gas G is not excessive, the phase of first dispensing II is directly carried out, and the gaseous natural gas G is possibly removed at one time during the withdrawal phase III.

[0068] If, on the other hand, the pressure within the refueling tank 5 is higher than the predefined value of pressure, i.e., the amount of gaseous natural gas G is high, prior to the phase of first dispensing II, the removal phase IX is carried out.

[0069] The measurement phase VII is also repeated during the removal phase IX.

[0070] Again, the measurement phase VII is carried out so that the total mass of withdrawn gaseous natural gas G is measured, and the datum obtained is subtracted from the mass of dispensed liquefied natural gas L.

[0071] Advantageously, prior to the phase of first dispensing II, the method comprises a determination phase X of a temperature datum which is representative of the temperature of the dispensing line 2.

[0072] The determination phase X allows checking whether the fluid contained within the dispensing line 2 is in the liquid state or in the solid state, i.e., whether the dispensing line mainly contains the liquefied natural gas L or the gaseous natural gas G so as to avoid the introduction of additional gaseous natural gas G into the refueling tank 5.

[0073] The determination phase X is carried out by means of a temperature sensor 28 installed along the dispensing line 2.

[0074] The method also comprises a phase of taking off XI the residual fluid which is contained within the dispensing line 2 carried out with the temperature datum above a predefined value of temperature.

[0075] In accordance with the preferred embodiment, the predefined value of temperature is of between -120°C and -140°C.

[0076] As stated above, the liquefied natural gas L has a boiling point of -165 °C, beyond which the natural gas changes to the gaseous state. As a result, at temperatures above the predefined value of temperature, the dispensing line 2 contains a high amount of gaseous natural gas G, which invalidates the subsequent dispensing phase.

[0077] Therefore, the dispensing line 2 is first emptied of the fluid therein to ensure the dispensing of only liquefied natural gas L.

[0078] For this purpose, the refueling system 1 comprises a recovery line 29 connected to the dispensing line 2 in a fluid-operated maimer.

[0079] The recovery line 29 comprises a relevant passage valve 9 and a relevant safety valve 10.

[0080] Conveniently, the taking off phase XI is carried out by means of the introduction of liquefied natural gas L within the dispensing line 2 and taking off through the recovery line 29.

[0081] In detail, the taking off phase XI is carried out by means of the circulation of the liquefied natural gas L from the supply unit 7, to the dispensing line 2, passing through the first mass meter 14, and finally recovered through the recovery line 29.

[0082] The taking off phase XI is carried out until a value of temperature which is less than the predefined value of temperature is achieved.

[0083] The method can then comprise a cooling phase of the residual fluid to obtain the liquefied natural gas L. The cooling phase allows the withdrawn fluid to be recovered and returned to circulation in the form of liquefied natural gas L. The cooling phase is carried out by means of a cooling unit 30 connected to the recovery line 29. For example, the residual fluid can be cooled by bubbling in the liquefied natural gas L.

[0084] Figure 4 shows a block diagram representing the various phases of this method. To carry out the refueling operations, the refueling system 1 is connected to the vehicle 4 (connection phase I). In detail, depending on the type of vehicle 4, both connecting guns 18, 19 or only the first connecting gun 18 are connected.

[0085] By means of the second pressure sensor 31, the pressure of the residual gaseous natural gas G within the refueling tank 5 is sensed (pre-sensing phase VIII). If the pressure datum is higher than the predefined value of pressure, the gaseous natural gas G is removed from the refueling tank 5 through the withdrawal line 3 (removal phase IX) until a datum of flow rate being equal or less than the predefined value of minimum flow rate is measured (measurement phase VII).

[0086] In the meantime, the temperature along the recovery line 29 is sensed by means of the temperature sensor 28 (determination phase X). If the temperature datum is higher than the predefined value of temperature, the liquefied natural gas L is made to circulate within the dispensing line 2 and removed through the recovery line 29 (taking off phase XI).

[0087] At this point, a first dispensing operation of the liquefied natural gas L is carried out (phase of first dispensing II), which is interrupted upon sensing of a pressure datum being equal to or higher than the predefined threshold value (sensing phase V) and / or upon acquisition of a datum of flow rate being equal to or less than the predefined value of minimum flow rate (acquisition phase VI). Subsequently, or at the same time, the gaseous natural gas G in the refueling tank 5 is withdrawn through the withdrawal line 3 (withdrawal phase III), for a predefined time interval and / or until a datum of flow rate equal to or less than the predefined value of minimum flow rate is measured (measurement phase VII). Finally, the second dispensing operation of the liquefied natural gas L is carried out (phase of second dispensing IV), which is interrupted upon sensing of a pressure datum being equal to or higher than the predefined threshold value (sensing phase V) and / or upon acquisition of a datum of flow rate being equal to or less than the predefined value of minimum flow rate (acquisition phase VI). It has in practice been ascertained that the described invention achieves the intended objects, and in particular, the fact is emphasized that the method according to the present invention for refueling liquefied natural gas vehicles allows maximum utilization of the tank capacity of the vehicle.

[0088] In addition, this method for refueling liquefied natural gas vehicles makes it possible to reduce the frequency of refueling operations by the driver.

Claims

CLAIMS1) Method for refueling liquefied natural gas vehicles characterized by the fact that it comprises the following phases: supply of a refueling system (1) provided with a dispensing line (2) adapted to dispense liquefied natural gas (L) and with a withdrawal line (3) adapted to withdraw gaseous natural gas (G); supply of a liquefied natural gas (L) vehicle (4) provided with a refueling tank (5); connection (I) of said refueling system (1) to said refueling tank (5); first dispensing (II) of liquefied natural gas (L) into said refueling tank (5) through said dispensing line (2); withdrawal of residual gaseous natural gas (G) from said refueling tank (5) through said withdrawal line (3); second dispensing of liquefied natural gas (L) into said refueling tank (5) through said dispensing line (2).2) Method according to claim 1, characterized by the fact that it comprises a phase of sensing (V) of at least one pressure datum representative of the pressure of the residual gaseous natural gas (G) within said refueling tank (5), carried out at the same time as said phase of first dispensing (II), said phase of first dispensing (II) being interrupted with said pressure datum being equal to or greater than a predefined value of threshold.3) Method according to one or more of the preceding claims, characterized by the fact that said predefined value of threshold is of between 12 bar and 15 bar.4) Method according to one or more of the preceding claims, characterized by the fact that it comprises a phase of acquisition (VI) of at least one datum of flow rate representative of the flow rate of said liquefied natural gas (L), carried out at the same time as said phase of first dispensing (II), said phase of first dispensing (II) being interrupted with said datum of flow rate being equal to or less than a predefined value of minimum flow rate.5) Method according to one or more of the preceding claims, characterized by the fact that said phase of withdrawal (III) of gaseous natural gas (G) is carriedout for a predefined time interval.6) Method according to one or more of the preceding claims, characterized by the fact that, prior to said phase of first dispensing (II), it comprises a phase of pre-sensing (VIII) of at least one pressure datum representative of the pressure of residual gaseous natural gas (G) within said refueling tank (5).7) Method according to one or more of the preceding claims, characterized by the fact that, prior to said phase of first dispensing (II), it comprises a phase of removal (IX) of said residual gaseous natural gas (G) from said refueling tank (5) through said withdrawal line (3), carried out with said pressure datum above a predefined value of pressure.8) Method according to one or more of the preceding claims, characterized by the fact that said predefined value of pressure is of between 7 bar and 9 bar.9) Method according to one or more of the preceding claims, characterized by the fact that, prior to said phase of first dispensing (II), it comprises a phase of determination (X) of a temperature datum which is representative of the temperature of said dispensing line (2).10) Method according to one or more of the preceding claims, characterized by the fact that, prior to said phase of first dispensing (II), it comprises a phase of taking (XI) the residual fluid off which is contained within said dispensing line (2), carried out with said temperature datum above a predefined value of temperature, said phase of taking off (XI) being carried out by means of the introduction of liquefied natural gas (L) within said dispensing line (2) and taking off through a recovery line (29).11) Method according to one or more of the preceding claims, characterized by the fact that said predefined value of temperature is of between -120°C and - 140°C.

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