IT202200026550A1 - METHOD FOR REFUELLING LIQUEFIED NATURAL GAS VEHICLES - Google Patents

Description

Patent Description for Industrial Invention entitled: ?METHOD FOR REFUELLING VEHICLES WITH LIQUEFIED NATURAL GAS?.

DESCRIPTION

The present invention relates to a method for refueling vehicles with liquefied natural gas.

Liquefied natural gas (LNG) is a mixture of hydrocarbons, generally present in nature in a gaseous state, the main component of which is methane, but which normally also contains other gaseous hydrocarbons such as ethane, propane and butane. The gaseous mixture of hydrocarbons is subjected to a liquefaction process, that is, consecutive cooling cycles at significantly reduced temperatures (around -165?C) and pressurization to obtain a mixture in a liquid state. This process allows for an increase in the storage efficiency of these hydrocarbons, significantly reducing their volume and allowing for the storage of a much greater mass for the same volume.

For these reasons, liquefied natural gas is increasingly used as a fuel in vehicles that require large quantities of fuel, such as trucks.

Liquefied natural gas, however, heats up at normal ambient temperatures and tends to gradually pass into a gaseous state.

The vehicle tank, therefore, always contains a certain quantity of gaseous natural gas resulting from the heating of the liquefied natural gas and which causes an increase in the internal pressure of the tank. For this reason, vehicle tanks are generally equipped with a safety valve that allows the venting of gaseous natural gas beyond a certain pressure value.

When refueling, filling the tank with LNG causes a further increase in pressure, caused by the presence of residual gaseous natural gas. Also in this case, when a certain pressure threshold is reached, special safety valves cause the gaseous natural gas to escape, resulting in fuel loss and the release of dangerous substances into the environment.

Therefore, known refueling methods involve an initial intake of gaseous natural gas and then delivery of LNG. The recovered gaseous natural gas can be re-liquefied for subsequent delivery, for example by bubbling into liquefied natural gas.

However, the suction does not allow the total removal of the gaseous natural gas, which remains partly in the tank. Consequently, for the above reasons, the subsequent delivery does not allow a total filling of the tank with LNG.

In detail, it is estimated that, using known refueling methods, the volume of residual gaseous natural gas remaining in the tank would be occupied by approximately 5-10kg of LNG, equal to approximately 20-40km of vehicle travel. This inconvenience requires more frequent visits to service stations, resulting in inconvenience for the driver. This inconvenience is even more felt in some geographical areas where LNG stations are not very widespread.

The driver must therefore also evaluate deviations in his route in order to be able to refuel, sometimes even with a tank that is not completely empty.

The main aim of the present invention is to provide a method for refueling liquefied natural gas vehicles which allows the maximum use to be made of the vehicle's tank capacity.

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

Another purpose of the present invention is to devise a method for refueling liquefied natural gas vehicles that allows the aforementioned drawbacks of the known art to be overcome within the scope of a simple, rational, easy and effective solution with a low cost. The above-mentioned purposes are achieved by the present method for refueling liquefied natural gas vehicles having the characteristics of claim 1.

Other features and advantages of the present invention will become more evident from the description of a preferred, but not exclusive, embodiment of a method for refueling vehicles with liquefied natural gas, illustrated by way of example, but not of limitation, in the attached drawings in which:

Figure 1 is a schematic representation of a refueling system for carrying out the method according to the invention;

Figures 2 and 3 are schematic representations of a vehicle fuel tank according to two different embodiments;

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

With particular reference to these figures, the symbol 1 generally indicates a system for the refueling of liquefied natural gas vehicles through which the method can be implemented.

In the context of this discussion, the term "liquefied natural gas" refers to a mixture of hydrocarbons, generally present in nature in a gaseous state, the main component of which is methane, but which normally also contains other gaseous hydrocarbons such as ethane, propane and butane. The gaseous mixture of hydrocarbons is subjected to a liquefaction process, that is, to successive cooling cycles at significantly reduced temperatures (around -165?C) and pressurization to obtain, precisely, a mixture in a liquid state. This process allows for an increase in the storage efficiency of these hydrocarbons, significantly reducing their volume and allowing for the storage of a much greater mass with the same volume.

The method according to the invention first comprises a supply phase of a refueling system 1 equipped with a delivery line 2 suitable for delivering liquefied natural gas L and a withdrawal line 3 suitable for withdrawing gaseous natural gas G.

The method also includes a supply stage of a liquefied natural gas vehicle 4 L equipped with a refueling tank 5.

In accordance with the embodiment shown in the figures, the refueling system 1 is of the type of a service station for road vehicles and the vehicle 4 is of the type of a truck. However, it is not excluded that the refueling system and/or the vehicle are of a different type.

In greater detail, the supply system 1 comprises a supply apparatus 6 equipped with the supply line 2 and the withdrawal line 3. The supply system 1 also comprises a supply unit 7 connected to the supply apparatus 6 and suitable for supplying the liquefied natural gas L through the supply line 2 and a recovery unit 8 connected to the supply apparatus 6 and suitable for receiving the gaseous natural gas G withdrawn through the withdrawal line 3.

The supply unit 7 may comprise a liquefied natural gas storage tank L and/or a gaseous natural gas liquefaction unit G.

The recovery unit 8 may include a gaseous natural gas storage tank G and may be directly connected to the liquefaction unit, if present.

Conveniently, the delivery line 2 and the withdrawal line 3 are equipped with relative passage valves 9, designed to allow the passage of the respective fluid, and with relative safety valves 10, designed to allow the venting of gaseous natural gas G when a predefined pressure is reached.

The 9-way valves are of the pneumatic valve type and are configured to open/close the respective lines.

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 supply line 2 and the withdrawal line 3.

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

For this purpose, the refueling system 1 also comprises at least a first mass meter 14 connected to the delivery line 2 and capable of measuring the mass of liquefied natural gas L entering the dispenser 6 and at least a second mass meter 15 connected to the withdrawal line and capable of measuring the mass of gaseous natural gas G withdrawn.

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 process the final price of the liquefied natural gas L dispensed, as will be better described later in this paper. Specifically, the electronic processing and control unit 16 comprises a processing unit 17 operatively connected to the mass meters 14, 15.

The method comprises a connection step I of the refueling system 1 to the refueling tank 5.

In detail, the refueling system 1 comprises a first connection nozzle 18 connected to the delivery line 2 and a second connection nozzle 19 connected to the withdrawal line 3, both of which can be connected to the refueling tank 5.

Suitably, the vehicle 4 comprises at least one connection for the first connection nozzle 18, and possibly an connection for the second connection nozzle 19, connected to the refueling tank 5, respectively through a first conduit 20 suitable for transporting the liquefied natural gas L and a second conduit 21 suitable for transporting the gaseous natural gas G.

In this regard, it is appropriate to specify 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 connection nozzle 18 and a second attachment 23 connected to the refueling tank 5 through the second conduit 21 and connectable to the second connection nozzle 19.

In accordance with a second embodiment shown in figure 3, instead, the vehicle 4 comprises a single attachment 24 connectable to the first connection gun 18 and the first duct 20 and the second duct 21 coincide in a single connection duct.

For this purpose, the refueling system 1 comprises a connection line 25 fluid-dynamically connected to the delivery line 2 and to the withdrawal line 3 and suitable for placing the refueling tank 5 in fluid communication with the withdrawal line itself. The connection line 25 comprises a relative passage valve 9 which can also be operated to allow or not the passage of fluid depending on the type of vehicle 4 connected.

Conveniently, the sampling line 3 includes at least one non-return valve 26 configured to allow only the passage of gaseous natural gas G from the supply tank 5 to the recovery unit 8 and not vice versa.

At this point, the method involves the following phases:

- first delivery II of liquefied natural gas L into the supply tank 5 via delivery line 2;

- withdrawal III of residual gaseous natural gas G from the supply tank 5 via the withdrawal line 3;

- second delivery IV of liquefied natural gas L into the supply tank 5 via delivery line 2.

Specifically, in accordance with the second implementation form, sampling phase III is performed through connection line 25.

The withdrawal phase III is performed after the first dispensing phase II.

In practice, the method involves an extraction of gaseous natural gas G following an initial delivery of liquefied natural gas L in order to reduce the internal pressure of the supply tank 5 and allow a second delivery so as to fill the tank itself substantially completely.

As explained above, in fact, at the time of refueling, the refueling tank 5 has a minimum volume of liquefied natural gas L and the remaining volume occupied by gaseous natural gas G. Refueling in such conditions quickly causes an increase in pressure inside the refueling tank 5 caused by the compression of the gaseous natural gas G as the volume of liquefied natural gas L increases. It follows that, for safety reasons, the refueling tank 5 can only be partially filled in order to avoid venting and the consequent loss of gaseous natural gas G.

Usefully, the method comprises a detection step V of at least one pressure datum representative of the pressure of gaseous natural gas G inside the supply tank 5 which is performed concurrently with the first delivery step II.

The detection phase V is performed by a first pressure sensor 27 associated with the delivery line 2.

The first delivery phase II is interrupted when the pressure data is equal to or higher than a predefined threshold value.

The default threshold value is chosen based on a safety pressure value to which the safety valves generally used in such systems are set and which is generally equal to 16 bar.

In accordance with the preferred embodiment, the default threshold value is between 12 bar and 15 bar.

Usefully, the method also includes an acquisition phase VI of at least one flow rate data representative of the flow rate of the liquefied natural gas L which is performed concurrently with the first delivery phase II.

The acquisition phase VI is performed by means of the first mass meter 14.

The first delivery phase II can also be interrupted with the flow rate equal to or lower than a predefined minimum flow rate value. This circumstance can occur when the pressure data is still lower than the predefined threshold value but, however, the presence of gaseous natural gas G hinders the filling of the supply tank 5 with liquefied natural gas L, resulting in excessively long filling times.

The next phase of extraction III of gaseous natural gas G is performed for a predefined time interval.

Usefully, the method also includes at least one measurement step VII of at least one flow rate data representative of the flow rate of gaseous natural gas G which is performed concurrently with sampling step III.

Measuring phase VII is performed by means of the second mass meter 15.

Alternatively or in combination, sampling phase III is interrupted when the flow rate is equal to or lower than a predefined minimum flow rate value, i.e. when the mass of gaseous natural gas G is small.

The method then involves the second dispensing phase IV, which is performed in a similar manner to the first dispensing phase II.

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

The detection phase V and the acquisition phase VI are repeated during the second delivery phase IV, so that the latter can be interrupted with the pressure data equal to or higher than the predefined threshold value and/or with the flow rate data equal to or lower than the minimum predefined flow rate value.

The acquisition phases VI are also performed in order to measure the total mass of liquefied natural gas L delivered.

Similarly, the measurement phase VII is also performed in order to measure the total mass of gaseous natural gas G withdrawn. This value is then subtracted from the mass of liquefied natural gas L supplied in order to obtain a figure that is then converted, thanks to the electronic processing and control unit 16, into a figure to be paid by the user following refueling. This allows the price to be adjusted to the actual quantity of liquefied natural gas L supplied to the user.

In accordance with one possible implementation form, the withdrawal phase III of gaseous natural gas G is performed at the same time as the delivery phases II, IV. In this way, it is possible to further reduce the refueling times.

Advantageously, prior to the first delivery phase II, the method comprises a pre-detection phase VIII of at least one pressure datum representative of the residual gaseous natural gas pressure G inside the supply tank 5.

The pre-detection phase VIII is performed by a second pressure sensor 31 present on the sampling line 3.

The pre-detection phase VIII is performed in order to evaluate the quantity of gaseous natural gas G present in the supply tank 5 before delivering liquefied natural gas L.

With the pressure data higher than a predefined pressure value, the method involves a removal step IX of the residual gaseous natural gas G from the supply tank 5 through the sampling line 3.

In accordance with the preferred embodiment, the default pressure value is between 7 bar and 9 bar.

In other words, if the pressure inside the supply tank 5 is lower than the predefined pressure value, i.e., the quantity of gaseous natural gas G is not excessive, the first delivery phase II is performed directly and the gaseous natural gas G is eventually removed in one go during the withdrawal phase III.

If, however, the pressure inside the supply tank 5 is higher than the predefined pressure value, i.e. the quantity of gaseous natural gas G is high, the removal phase IX is performed before the first delivery phase II.

Measurement phase VII is also repeated during removal phase IX.

Again, measurement phase VII is performed in such a way as to measure the total mass of gaseous natural gas G withdrawn and the resulting data is subtracted from the mass of liquefied natural gas L delivered.

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

The determination phase X allows to verify whether the fluid contained inside the delivery line 2 is in the liquid state or in the solid state, i.e. whether the delivery line contains mainly liquefied natural gas L or gaseous natural gas G so as to avoid the introduction of further gaseous natural gas G into the supply tank 5.

The determination phase X is performed by means of a temperature sensor 28 installed along the delivery line 2.

The method also includes a removal phase XI of residual fluid contained within the delivery line 2 which is performed with the temperature data higher than a predefined temperature value.

In accordance with the preferred embodiment, the default temperature value is between -120?C and -140?C.

As explained above, liquefied natural gas L has a boiling point of -165?C, beyond which natural gas passes into a gaseous state. It follows that at temperatures above the predefined temperature value, delivery line 2 contains a high quantity of gaseous natural gas G which affects the subsequent delivery phase.

Therefore, delivery line 2 is first emptied of the fluid contained in it to ensure the delivery of only liquefied natural gas L.

For this purpose, the refueling system 1 comprises a recovery line 29 fluid-dynamically connected to the delivery line 2.

The recovery line 29 includes a relative passage valve 9 and a relative safety valve 10.

Usefully, the removal phase XI is performed by injecting liquefied natural gas L into the delivery line 2 and removing it through the recovery line 29.

In detail, the removal phase XI is performed by circulating liquefied natural gas L from the supply unit 7, to the delivery line 2, passing through the first mass meter 14, and finally recovered through the recovery line 29.

The XI removal phase is performed until a temperature value lower than the preset temperature value is reached.

The method may then include a cooling phase of the residual fluid to obtain liquefied natural gas L. The cooling phase allows the collected fluid to be recovered and reintroduced into circulation in the form of liquefied natural gas L. The cooling phase is performed by means of a cooling unit 30 connected to the recovery line 29. For example, the residual fluid may be cooled by bubbling in liquefied natural gas L.

Figure 4 shows a block diagram representing the various phases of the present method.

To carry out 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 connection nozzles 18, 19 or only the first connection nozzle 18 are connected.

By means of the second pressure sensor 31, the pressure of the residual gaseous natural gas G inside the supply tank 5 is detected (pre-detection phase VIII). If the pressure data is higher than the predefined pressure value, the gaseous natural gas G is removed from the supply tank 5 via the sampling line 3 (removal phase IX) until a flow rate equal to or lower than the minimum predefined flow rate value is measured (measurement phase VII).

Meanwhile, the temperature along the recovery line 29 is detected by the temperature sensor 28 (determination phase X). If the temperature data is higher than the predefined temperature value, the liquefied natural gas L is circulated inside the delivery line 2 and removed through the recovery line 29 (removal phase XI).

At this point, a first delivery of liquefied natural gas L is made (first delivery phase II), which is interrupted upon detection of a pressure value equal to or higher than the predefined threshold value (detection phase V) and/or upon acquisition of a flow rate value equal to or lower than the predefined minimum flow rate value (acquisition phase VI).

Subsequently, or concurrently, the gaseous natural gas G present in the supply tank 5 is withdrawn through the sampling line 3 (withdrawal phase III), for a predefined time interval and/or until the measurement of a flow rate equal to or lower than the predefined minimum flow rate value (measurement phase VII).

Finally, the second delivery of liquefied natural gas L is carried out (second delivery phase IV), which is interrupted upon detection of a pressure value equal to or higher than the predefined threshold value (detection phase V) and/or upon acquisition of a flow rate value equal to or lower than the predefined minimum flow rate value (acquisition phase VI).

In practice, it has been found that the described invention achieves the proposed aims and in particular it is highlighted that the method according to the present invention for refueling vehicles with liquefied natural gas allows the maximum use of the capacity of the vehicle's tank.

Furthermore, this method of refueling liquefied natural gas vehicles allows for a reduction in the frequency of refueling operations by the driver.

Claims (11)

1) Method for refueling liquefied natural gas vehicles characterised by the fact that it includes the following phases: - supply of a refueling system (1) equipped with a delivery line (2) suitable for supplying liquefied natural gas (L) and a withdrawal line (3) suitable for withdrawing gaseous natural gas (G); - supply of a vehicle (4) powered by liquefied natural gas (L) equipped with a refuelling tank (5); - connection (I) of said refueling system (1) to said refueling tank (5); - first delivery (II) of liquefied natural gas (L) into said supply tank (5) through said delivery line (2); - withdrawal of residual gaseous natural gas (G) from said supply tank (5) through said withdrawal line (3); - second delivery of liquefied natural gas (L) into said supply tank (5) through said delivery line (2). 2) Method according to claim 1, characterised in that it comprises a detection phase (V) of at least one pressure datum representative of the pressure of gaseous natural gas (G) residual inside said supply tank (5), carried out at the same time as said first delivery phase (II), said first delivery phase (II) being interrupted with said pressure datum equal to or greater than a predefined threshold value. 3) Method according to one or more of the preceding claims, characterised in that said predefined threshold value is between 12 bar and 15 bar. 4) Method according to one or more of the preceding claims, characterised in that it comprises an acquisition phase (VI) of at least one flow rate data representative of the flow rate of said liquefied natural gas (L), performed at the same time as said first delivery phase (II), said first delivery phase (II) being interrupted with said flow rate data equal to or lower than a predefined minimum flow rate value. 5) Method according to one or more of the preceding claims, characterised in that said phase of sampling (III) of gaseous natural gas (G) is carried out for a predefined time interval. 6) Method according to one or more of the preceding claims, characterised in that, prior to said first delivery phase (II), it comprises a pre-detection phase (VIII) of at least one pressure datum representative of the pressure of gaseous natural gas (G) residual inside said supply tank (5). 7) Method according to one or more of the preceding claims, characterised in that, prior to said first delivery phase (II), it comprises a removal phase (IX) of said residual gaseous natural gas (G) from said supply tank (5) through said sampling line (3), carried out with said pressure data higher than a predefined pressure value. 8) Method according to one or more of the preceding claims, characterised in that said predefined pressure value is between 7 bar and 9 bar. 9) Method according to one or more of the preceding claims, characterised in that, prior to said first dispensing phase (II), it comprises a determination phase (X) of a temperature datum representative of the temperature of said dispensing line (2). 10) Method according to one or more of the preceding claims, characterised in that, prior to said first delivery phase (II), it comprises a removal phase (XI) of residual fluid contained within said delivery line (2), carried out with said temperature data higher than a predefined temperature value, said removal phase (XI) being carried out by introducing liquefied natural gas (L) into said delivery line (2) and removal through a recovery line (29). 11) Method according to one or more of the preceding claims, characterised in that said predefined temperature value is between -120?C and -140?C.