WO2023247693A1

WO2023247693A1 - Methanol fuel supply system for a marine internal combustion engine

Info

Publication number: WO2023247693A1
Application number: PCT/EP2023/066936
Authority: WO
Inventors: Daniele Casartelli; Nicoletta Spazzadeschi
Original assignee: Alfa Laval Corporate Ab
Priority date: 2022-06-24
Filing date: 2023-06-22
Publication date: 2023-12-28

Abstract

A fuel supply system (10) is disclosed for supplying a methanol-based fuel from a fuel tank (12) to an internal combustion engine (14). The fuel supply system (10) comprises: a main fuel conduit (16), which fluidly connects the fuel tank (12) to the internal combustion engine (14); a first fuel pump (18), which is placed along the main fuel conduit (16) and which is designed for sucking fuel from the fuel tank (12) at a first pressure value (P1) and delivering the fuel along the main fuel conduit (16) at a second pressure value (P2), which is higher than the first pressure value (P1); a second fuel pump (20), which is placed along the main fuel conduit (16) downstream of the first fuel pump (18) and which is designed for receiving fuel from the first fuel pump (18) at the second pressure value (P2) and delivering the fuel along the main fuel conduit (16) at a third pressure value (P3), which is higher than the second pressure value (P2) and which is equal to the operative pressure value of the fuel required by the internal combustion engine (14); a heat exchanger device (22), which is placed along the main fuel conduit (16) and which is designed to exchange heat with the fuel to bring it to a temperature value within a predefined temperature range (ΔT), which is equal to the operative temperature range of the fuel required by the internal combustion engine (14); and a fuel filtering unit (24), which is placed along the main fuel conduit (16) downstream of the second fuel pump (20) and which is designed for20 filtering the fuel before being supplied to the internal combustion engine (14) at the third pressure value (P3) and within the predefined temperature range (ΔT).

Description

METHANOL FUEL SUPPLY SYSTEM FOR A MARINE INTERNAL COMBUSTION ENGINE

Field of the invention

The present invention refers in general to a fuel supply system for an internal combustion engine and, more specifically, to a fuel supply system wherein the fuel is methanol and the internal combustion engine is a marine internal combustion engine.

Background of the invention

Large ships are typically driven by marine engines operating on fuels like Heavy Fuel Oil (HFO) or Diesel Oil (DO). These fuels are all carbon-based fossil fuels which emit high amounts of carbon dioxide when combusted. Therefore, one of the ambitions of the International Maritime Organization (IMO) is that the shipping industry should reduce carbon dioxide emissions by 40% by 2030 and by 70% by 2050.

An alternative fuel for marine engines is methanol, also known as methyl alcohol, a chemical with the formula CH3OH (often abbreviated as MeOH). Existing marine engines operating on fossil fuel can typically be modified relatively easily so as to, instead/additionally, be operable on methanol and/or fuels containing methanol. Methanol has the advantage of being less polluting than carbon-based fossil marine fuels. However, methanol also has the disadvantage of being toxic, and therefore procedures must be in place for its neutralization when used as a fuel for marine engines.

Methanol fuel supply systems for marine combustion engines are known in the state of the art. However, these systems are usually complex, thus requiring sometimes oversized, complicated and expensive components. An example of a known system is disclosed by CN114320688. The methanol fuel system of the document requires the use of two heat exchangers along the main fuel supply line. Additionally, the system requires the use of a mixing chamber, which makes the system complicated and space demanding. Therefore, there is a need for a more compact and simple system which can be readily connected to existing fuel tanks and internal combustion engine of a marine vessel. Summary of the invention

One object of the present invention is therefore to provide a methanol fuel supply system for a marine combustion engine which is capable of resolving the drawbacks of the prior art in a simple, inexpensive and particularly functional manner.

In detail, one object of the present invention is to provide a methanol fuel supply system for a marine combustion engine which is compact, easy to install and easy to operate if compared with the fuel supply systems according to the prior art.

Another object of the present invention is to provide a methanol fuel supply system for a marine combustion engine which does not require numerous and complex components in order to operate correctly.

A further object of the present invention is to provide a methanol fuel supply system for a marine combustion engine which is safe and risk-free for operators.

These objects are achieved according to the present invention by providing a methanol fuel supply system for a marine combustion engine as set forth in the attached claims.

Further features of the invention are underlined by the dependent claims, which are an integral part of the present description.

The methanol fuel supply system for a marine combustion engine according to the present invention is designed for supplying a methanol-based fuel from at least one fuel tank to at least one internal combustion engine and the system comprises a fuel inlet connected to a main fuel conduit, which fluidly connects the fuel tank to the internal combustion engine. At least one first fuel pump is placed along the main fuel conduit and is designed for sucking fuel from the fuel tank at a first pressure value and delivering the fuel along the main fuel conduit at a second pressure value, wherein the second pressure value is higher than the first pressure value. At least one second fuel pump is placed along the main fuel conduit, downstream of the first fuel pump, and is designed for receiving fuel from the first fuel pump at the second pressure value and delivering the fuel along the main fuel conduit at a third pressure value, wherein the third pressure value is higher than the second pressure value and wherein the third pressure value is adapted to the operative pressure value of the fuel required by the internal combustion engine.

The methanol fuel supply system also comprises a heat exchanger device, which is placed along the main fuel conduit. The heat exchanger device is designed or configured to exchange heat with the fuel to bring it to a temperature value within a predefined temperature range. This temperature range is adapted to the operative temperature range of the fuel required by the internal combustion engine. The temperature of the methanol fuel from the tank can be from -20 to + 45 degrees. The present fuel supply system can be configured to be operable for handling methanol fuel for this temperature range. The methanol fuel supply system further comprises a first fuel filtering unit, which is placed along the main fuel conduit, downstream of the second fuel pump, and which is designed for filtering the fuel before being supplied to the internal combustion engine at the third pressure value and within the predefined temperature range.

According to a preferred and advantageous aspect of the present invention, the methanol fuel supply system comprises at least one purging circuit, which is hydraulically connected to the main fuel conduit and which comprises in turn at least one inerting agent source, which is designed to supply an inerting agent to the methanol fuel supply system, and at least one purging conduit, which connects the inerting agent source to the main fuel conduit.

According to a variant, the inerting agent is nitrogen.

According to a further variant, a first fuel recirculation conduit can be connected to the main fuel conduit, downstream of the first fuel pump and upstream of the second fuel pump. The first fuel recirculation conduit connects back the main fuel conduit to the fuel tank. A second fuel recirculation conduit can also be connected to the main fuel conduit downstream of the second fuel pump and preferably upstream of the first fuel filtering unit. The second fuel recirculation conduit is designed to return, upstream of the second fuel pump, the fuel pumped by said second fuel pump.

According to a preferred aspect of the present invention, at least one pressure control device is placed along the first fuel recirculation conduit and/or the second fuel recirculation conduit. More preferably, the type of the pressure control devices is chosen from: - a mechanical valve;

- a variable frequency drive placed on the first fuel pump and/or the second fuel pump. Variable frequency drive option included in this invention ensures to achieve energy savings with respect to the pressure control compared to a the state-of-the art system.

According to another preferred and advantageous aspect of the present invention, the first heat exchanger device is a single heat exchanger device of the system, which is placed along the main fuel conduit. The single heat exchanger device can be provided with a fuel heat control equipment for adjusting the temperature of the fuel flowing through the main fuel conduit at the first heat exchanger device. The fuel heat control equipment comprises at least one container, for containing at least one heat exchanger medium, at least one loop conduit, for connecting in closed circuit the container to the single first heat exchanger device, a second heat exchanger device, which is placed along the loop conduit, and at least one heat exchanger medium pump, for pumping the heat exchanger medium within the loop conduit and into the second heat exchanger device.

Preferably, the heat exchanger medium is a glycol-water solution.

Also preferably, the methanol fuel supply system comprises at least one second fuel filtering unit, which is placed along the main fuel conduit downstream of the fuel tank and upstream of the first fuel pump. At least one connection conduit, provided with a differential pressure indicator, can be connected to the main fuel conduit downstream and upstream of the second fuel filtering unit.

Preferably, the first fuel filtering unit comprises at least two filter elements and filter valves configured to provide, and thus making it possible to, have a continuous filtration of the fuel through the first fuel filtering unit also during maintenance of one or more of the filter elements.

Also preferably, the main fuel conduit comprises a plurality of fuel control and/or monitoring devices for acquiring data related to the fuel supplied from the fuel tank to the internal combustion engine and/or for sending these data to a central processing unit. Always preferably, the type of the fuel control and/or monitoring devices is chosen from:

- a fuel pressure value sensor and transmitter; a fuel temperature value sensor and transmitter; a fuel flow rate sensor and transmitter.

A single skid-mounted assembly, provided with a single frame, can be conveniently arranged to support the components of the methanol fuel supply system. The fuel supply system of the present disclosure is located within a battery limit of the fuel supply system and thus downstream of the fuel tank and upstream of the internal combustion engine. In this way, a compact methanol fuel supply system provided as a modular unit, is provided.

Further, the system described above may be configured to supply fuel having an atmospheric pressure and temperature of -20 to 45°C at the inlet of the system.

Brief description of the drawings

The features and advantages of a methanol fuel supply system for a marine combustion engine according to the present invention will be clearer from the following exemplifying and non-limiting description, with reference to the enclosed schematic drawings, in which:

Figure 1 is a schematic view showing the main components of the methanol fuel supply system for a marine combustion engine according to the present invention; and

Figure 2 is another schematic view of the fuel supply system of figure 1 , wherein further components of the system are shown.

Detailed description of the invention

With reference to Figures 1 and 2, a preferred embodiment of a methanol fuel supply system for a marine combustion engine according to the present invention is shown. The fuel supply system is indicated as a whole with reference numeral 10. In the Figure 1 , a frame surrounding components of the fuel supply system is illustrated to show the battery limit of the system, i.e. the boundaries of the present fuel supply system. Thus, for example a fuel tank and 12, fuel injection valves and internal combustion engine are outside the scope of the present fuel supply system.

The fuel supply system 10 is designed for supplying a methanol-based fuel from at least one fuel tank 12 to at least one internal combustion engine 14, more precisely a marine internal combustion engine. The system 10 is suitably configured to supply fuel having an atmospheric pressure and temperature of -20 to 45°C at an inlet 11 of the system.

The fuel supply system 10 comprises at least one main fuel conduit 16, which fluidly connects the methanol-based fuel tank 12 to the marine internal combustion engine 14. An inlet 11 to the fuel supply system 10 is connected to the main fuel conduit 16 downstream of the fuel tank 12. At least one first fuel pump 18 is placed along the main fuel conduit 16. This first fuel pump 18 is designed for sucking the methanol-based fuel from the fuel tank 12 at a first pressure value P1 and delivering the methanol-based fuel along the main fuel conduit 16 at a second pressure value P2. The second pressure value P2 is higher than the first pressure value P1 .

The first fuel pump 18 thus operates as a supply pump for the methanolbased fuel, which is contained in the fuel tank 12 at a first pressure value P1. This first pressure value P1 can preferably range from atmospheric pressure to 0.5 barG. This first fuel pump 18, which is preferably equipped with an electric motor, and which can be for example of centrifugal type (although different pumping technologies are suitable as well), is thus capable of increasing the first pressure value P1 of the methanol-based fuel up to a second pressure value P2. This second pressure value P2 can be comprised, for example, between 6 barG and 8 barG. However, different pressure can also apply depending on the operating conditions of the marine internal combustion engine 14.

The fuel supply system 10 also comprises at least one second fuel pump 20, which is placed along the main fuel conduit 16 downstream of the first fuel pump 18. This second fuel pump 20 is designed for receiving the methanol-based fuel from the first fuel pump 18 at the second pressure value P2 and delivering the methanol-based fuel along the main fuel conduit 16 at a third pressure value P3. The third pressure value P3 is higher than the second pressure value P2 and is equal to the operative pressure value of the methanol-based fuel required by the marine internal combustion engine 14.

The first fuel pump 18 and the second fuel pump 20 thus form a two-stage (low-pressure stage and high-pressure stage) pumping system. The second fuel pump 20, which is preferably equipped with an electric motor and which can be for example of centrifugal type (although different pumping technologies are suitable as well), then operates as a high-pressure pump for the methanol-based fuel and is capable of feeding the marine internal combustion engine 14 with the methanolbased fuel at a third pressure value P3 of about 13 barG (pressure at skid battery limit) at any required flow rate inside the duty data range.

The fuel supply system 10 further comprises a heat exchanger device 22, which is placed along the main fuel conduit 16. The heat exchanger is a single and sole heat exchanger placed along the main fuel conduit 16. It can beplaced downstream or upstream of the second fuel pump 20. The heat exchanger device is configured to be in fluid contact with the fuel and another fluid used for the heat exchange. By providing only one heat exchanger along the main fuel conduit, the fuel supply system will become more compact.

The first heat exchanger device 22 is designed to exchange heat with the methanol-based fuel to bring the latter to a temperature value within a predefined temperature range AT. This temperature range AT is equal to the operative temperature range of the methanol-based fuel required by the marine internal combustion engine 14. In other words, before the injection into the marine internal combustion engine 14, the temperature T of the methanol-based fuel has to reach the correct value required at skid battery limit.

Preferably but not exclusively, depending on the operating conditions of the marine internal combustion engine 14, the temperature range AT varies between 25°C and 50°C, whereas the temperature T of the methanol-based fuel contained in the fuel tank 12 can vary between -20°C and 45°C. The first heat exchanger device 22 can be, for example, a shell-and-tube heat exchanger or a semi-welded gasketed plate type heat exchanger (although different heat exchange technologies are suitable as well). It has been discovered that the compact design involving only one heat exchanger along the main fuel supply line is especially suitable, when the fuel supplied to the system has an atmospheric pressure and temperature of -20 to 45°C at an inlet 11 of the system.

At least one first fuel filtering unit 24 is placed along the main fuel conduit 16 downstream of the second fuel pump 20, preferably downstream of the first heat exchanger device 22. The first fuel filtering unit 24 is designed for filtering the methanol-based fuel before being supplied to the marine internal combustion engine 14 at the third pressure value P3 and within the predefined temperature range AT. More specifically, the first fuel filtering unit 24 allows to remove every particle present in the methanol-based fuel that could cause engine damage.

Preferably, as shown in Figure 2, the first fuel filtering unit 24 comprises a plurality of filter elements 52, as well as a plurality of filter valves 54. The filter valves 54 make it possible to have a continuous filtration of the methanol-based fuel through the first fuel filtering unit 24 also during maintenance of one or more of the filter elements 52. Filter elements 52 can be of a type capable of ensuring high efficiency of the first fuel filtering unit 24 and minimum maintenance requirement. Preferably, filtration degree of the first fuel filtering unit 24 can be of at least 10 microns.

Advantageously, the fuel supply system 10 according to the present invention can comprise at least one purging circuit 26, which is hydraulically connected to the main fuel conduit 16 and which comprises in turn at least one inerting agent source 28, which is designed to supply an inerting agent to the fuel supply system 10. For example, the inerting agent source 28 can be the inerting agent grid of the ship on which the fuel supply system 10 is installed. This inerting agent grid can thus be hydraulically connected to the main fuel conduit 16, but it does not have to be part of the fuel supply system placed on a single frame. Alternatively, the inerting agent source 28 can comprise one or more dedicated vessels, each containing a predefined amount of an inerting agent. The purging circuit 26 also comprises at least one purging conduit 30, which connects the inerting agent source 28 to the main fuel conduit 16. Preferably, the inerting agent is nitrogen.

Actually, since methanol is an inflammable and toxic liquid, a dangerously high vapor concentration can be reached in the main fuel conduit 16 in case of leakage, thus creating a dangerous condition. This may lead to an explosion if all the following conditions are met:

- the temperature T of the methanol-based fuel is above the flash point;

- a certain concentration of oxygen is present in the methanol-based fuel;

- the ratio of fuel vapour/oxygen is within a certain range;

- there is an ignition source with a sufficiently high temperature and energy.

Therefore, the function of the purging circuit 26 can be that of leak testing after maintenance of the fuel supply system 10, as well as that of reducing the oxygen content in said fuel supply system 10 before filling it with the methanolbased fuel. The likelihood of a flammable atmosphere being created in the fuel supply system 10 is thus reduced. Eventually a critical concentration is reached below which no ignition is possible. The purging circuit 26 may avoid this drawback by creating a non-flammable atmosphere inside the main fuel conduit 16 and inside any other piping connected to said main fuel conduit 16. Inerting is usually performed at startup of the fuel supply system 10, to remove air (and oxygen) from piping. Before maintenance operations on the fuel supply system 10, to push the methanol-based fuel back to the fuel tank 12 through one or more drain lines 66, avoiding contact with air and also with operating personnel, a purging operation can also be performed. The purging circuit 26 may be provided with one or more nitrogen inlets with filter, one or more pressure indicators and transmitters, one or more drain valves and one or more drain pumps (not shown in the drawings).

Preferably, as shown in the Figures, a first fuel recirculation conduit 32 can be connected to the main fuel conduit 16 downstream of the first fuel pump 18 and upstream of the second fuel pump 20. The first fuel recirculation conduit 32 connects back the main fuel conduit 16 to the fuel tank 12. A second fuel recirculation conduit 64 can also be connected to the main fuel conduit 16 downstream of the second fuel pump 20 and preferably upstream of the first fuel filtering unit 24. The second fuel recirculation conduit 64 is designed to return, upstream of the second fuel pump 20, the fuel pumped by said second fuel pump 20. Thus, in this way no mixing chambers or tanks are needed along the main fuel supply line, and the fuel system may be constructed in an even more compact manner than the known systems. This is a huge advantage, making the system easier to install, saving space when installed and making the system more light- weighed.

Additionally, at least one pressure control device 48, 50 can be placed along the first fuel recirculation conduit 32 and/or the second fuel recirculation conduit 64. For example, each pressure control device 48, 50 can be a mechanical valve or a variable frequency drive (VFD) 18’, shown in Fig. 1 but also being applicable in the embodiment of Fig. 2, and placed on the first fuel pump 18 and/or the VFD 20’ placed on the second fuel pump 20. One of the possible functions of each recirculation conduit 32, 64, together with the respective pressure control device 48, 50, is that of regulating the pressure of the methanol-based fuel at the outlet of the first fuel pump 18 and the second fuel pump 20. Another possible functions of each recirculation conduit 32, 64 is that of preventing the methanol-based fuel to reach the internal combustion engine 14 in certain operating conditions of said engine 14, while keeping the fuel supply system 10 ready to operate. For example, one of these operating conditions may be when the internal combustion engine 14 is running on a fuel other than the methanol-based fuel (e.g., a carbon-based fossil fuel), while the methanol-based fuel must be ready to be supplied to the internal combustion engine 14.

According to a preferred aspect of the invention, as shown in Figure 2, the first heat exchanger device 22 can be provided with a fuel heat control equipment 34 for adjusting the temperature T of the methanol-based fuel flowing through the main fuel conduit 16 at said single first heat exchanger device 22 along the main fuel conduit 16. The fuel heat control equipment 34 may comprise a container 36, for containing a heat exchanger medium, and a loop conduit 38, for connecting in closed circuit the container 36 to the single first heat exchanger device 22. A second heat exchanger device 40 is placed along the loop conduit 38. A heat exchanger medium pump 42 is also placed along the loop conduit 38. The function of this pump 42, which can be conveniently equipped with its own electric motor, is that of pumping the heat exchanger medium within the loop conduit 38 and into the second heat exchanger device 40.

Preferably, the heat exchanger medium contained in the container 36 is a glycol-water solution. However, in addition to or in place of the glycol-water solution, other heat exchanger media could also be used, for example steam. The container 36 therefore has the function of buffer and expansion tank of the heat exchanger medium. The second heat exchanger device 40 can be for example of the brazed plate type (although different heat exchange technologies are suitable as well).

As shown in Figure 2, the fuel supply system 10 can be provided with a second fuel filtering unit 44, which is placed along the main fuel conduit 16 downstream of the fuel tank 12 and upstream of the first fuel pump 18. A connection conduit 46 with a differential pressure indicator can be provided. This connection conduit 46 is connected to the main fuel conduit 16 downstream and upstream of the second fuel filtering unit 44 for checking any variation of the differential pressure of the methanol-based fuel before and after the passage through the second fuel filtering unit 44.

The main fuel conduit 16 can be equipped with a plurality of fuel control and/or monitoring devices 56, 58, 60. These control and/or monitoring devices 56, 58, 60 are suitably designed for acquiring various data related to the methanolbased fuel supplied from the fuel tank 12 to the internal combustion engine 14. At least some of these control and/or monitoring devices 56, 58, 60 can also be designed for sending these data to a central processing unit (not shown in the drawings) of the fuel supply system 10. For example, the fuel control and/or monitoring devices 56, 58, 60 can comprise one or more fuel pressure value sensors and transmitters 56, one or more fuel temperature value sensors and transmitters 58 and one or more fuel flow rate sensors and transmitters 60.

The fuel supply system 10 described so far can be provided in the form of a single skid-mounted assembly. This assembly is conveniently provided with a single frame 62 which supports the components, suitably all components, of the fuel supply system 10 within the battery limit.

The frame 62 can be designed to be as compact as possible and can be readily connected to any existing fuel tank 12 and any marine internal combustion engine 14 that can operate with a methanol-based fuel. This way it is possible to provide for easy installation of the fuel supply system 10 in any environment, for example inside a fuel preparation room of a ship.

It is thus seen that the methanol fuel supply system for a marine combustion engine according to the present invention achieve the previously outlined objects, resulting in a compact system, easy to install and easy to operate.

The methanol fuel supply system for a marine combustion engine of the present invention thus conceived is susceptible in any case of numerous modifications and variants, all falling within the same inventive concept; in addition, all the details can be substituted by technically equivalent elements. In practice, the materials used, as well as the shapes and size, can be of any type according to the technical requirements. The scope of protection of the invention is therefore defined by the enclosed claims. List of references

10: fuel supply system;

11 : inlet

12: fuel tank;

14: internal combustion engine;

16: main fuel conduit;

18: first fuel pump;

18’: VFD associated with the first fuel pump;

20: second fuel pump;

20’: VFD associated with the second fuel pump;

22: first heat exchanger device;

24: first fuel filtering unit;

26: purging circuit;

28: inerting agent source;

30: purging conduit;

32: first fuel recirculation conduit;

34: fuel heat control equipment;

36: heat exchanger medium container;

38: loop conduit;

40: second heat exchanger device;

42: heat exchanger medium pump;

44: second fuel filtering unit;

46: bypass conduit;

48: pressure control device;

50: pressure control device;

52: filter elements;

54: filter valves;

56: fuel pressure value sensor and transmitter;

58: a fuel temperature value sensor and transmitter;

60: a fuel flow rate sensor and transmitter;

62: skid-mounted assembly;

64: second fuel recirculation conduit;

66: drain line; P1 : first fuel pressure value;

P2: second fuel pressure value;

P3: third fuel pressure value;

T: fuel temperature value; AT: fuel temperature range.

Claims

1. A fuel supply system (10) configured for supplying a methanol-based fuel from at least one fuel tank (12) to at least one internal combustion engine (14), the fuel supply system (10) comprising:

- a fuel inlet (11) connected to a main fuel conduit (16), which is configured to fluidly connect said fuel tank (12) to said internal combustion engine (14);

- a first fuel pump (18), which is placed along said main fuel conduit (16) and which is configured to suck fuel from said fuel tank (12) at a first pressure value (P1 ) and delivering said fuel along said main fuel conduit (16) at a second pressure value (P2), wherein said second pressure value (P2) is higher than said first pressure value (P1 );

- a second fuel pump (20), which is placed along said main fuel conduit (16) downstream of said first fuel pump (18) and which is designed for receiving fuel from said first fuel pump (18) at said second pressure value (P2) and delivering said fuel along said main fuel conduit (16) at a third pressure value (P3), wherein said third pressure value (P3) is higher than said second pressure value (P2) and wherein said third pressure value (P3) is adapted to the operative pressure value of said fuel required by said internal combustion engine (14);

- a first heat exchanger device (22), which is placed along said main fuel conduit (16), and which is configured to bring said fuel to a temperature value within a predefined temperature range (AT), wherein said temperature range (AT) is adapted to the operative temperature range of said fuel required by said internal combustion engine (14); and

- a first fuel filtering unit (24), which is placed along said main fuel conduit (16) downstream of said second fuel pump (20) and which is designed for filtering said fuel before being supplied to said internal combustion engine (14) at said third pressure value (P3) and within said predefined temperature range (AT).

2. The system (10) according to claim 1 , characterized in that it comprises at least one purging circuit (26) which is hydraulically connected to said main fuel conduit (16) and which comprises in turn:

- at least one inerting agent source (28), which is designed to supply an inerting agent to said system (10); and - at least one purging conduit (30), which connects said inerting agent source (28) to said main fuel conduit (16).

3. The system (10) according to claim 2, characterized in that said inerting agent is nitrogen.

4. The system (10) according to anyone of claims 1 to 3, characterized in that a first fuel recirculation conduit (32) is connected to said main fuel conduit (16) downstream of said first fuel pump (18) and upstream of said second fuel pump (20), said first fuel recirculation conduit (32) connecting back said main fuel conduit (16) to said fuel tank (12).

5. The system (10) according to any one of the preceding claims, characterized in that a second fuel recirculation conduit (64) is connected to said main fuel conduit (16) downstream of said second fuel pump (20) and preferably upstream of said first fuel filtering unit (24), said second fuel recirculation conduit (64) being designed to return, upstream of said second fuel pump (20), the fuel pumped by said second fuel pump (20)

6. The system (10) according to claim 4 or 5, characterized in that at least one pressure control device (48; 50) is placed along said first fuel recirculation conduit (32) and/or said second fuel recirculation conduit (64).

7. The system (10) according to claim 6, characterized in that the type of said pressure control device (48; 50) is chosen from:

- a mechanical valve;

- a variable frequency drive (18’; 20’) placed on said first fuel pump (18) and/or said second fuel pump (20).

8. The system (10) according to anyone of claims 1 to 7, characterized in that said first heat exchanger device (22) is a single heat exchanger device of the system placed along said main fuel conduit (16).

9. The system (10) according to claim 8, wherein the single heat exchanger device (22) is provided with a fuel heat control equipment (34) for adjusting the temperature (T) of said fuel flowing through said main fuel conduit (16) at said first heat exchanger device (22), said fuel heat control equipment (34) comprising:

- at least one container (36) for containing at least one heat exchanger medium;

- at least one loop conduit (38) for connecting in closed circuit said container (36) to the single heat exchanger device (22) along the main fuel conduit (16); - a second heat exchanger device (40), which is placed along said loop conduit (38); and

- a heat exchanger medium pump (42) for pumping said heat exchanger medium within said loop conduit (38) and into said second heat exchanger device (40).

10. The system (10) according to anyone of claims 1 to 9, characterized in that it comprises a second fuel filtering unit (44), which is placed along said main fuel conduit (16) downstream of said fuel tank (12) and upstream of said first fuel pump (18).

11. The system (10) according to claim 10, characterized in that at least one connection conduit (46) provided with a differential pressure indicator is connected to said main fuel conduit (16) downstream and upstream of said second fuel filtering unit (44).

12. The system (10) according to anyone of claims 1 to 11 , characterized in that said first fuel filtering unit (24) comprises at least two filter elements (52) and filter valves (54) configured to provide a continuous filtration of said fuel through said first fuel filtering unit (24) also during maintenance of one or more of said filter elements (52).

13. The system (10) according to anyone of claims 1 to 12, characterized in that said main fuel conduit (16) comprises a plurality of fuel control and/or monitoring devices (56; 58; 60) for acquiring data related to the fuel supplied from said fuel tank (12) to said internal combustion engine (14) and/or for sending said data to a central processing unit.

14. The system (10) according to claim 13, characterized in that the type of said fuel control and/or monitoring devices (56; 58; 60) is chosen from:

- a fuel pressure value sensor and transmitter (56);

- a fuel temperature value sensor and transmitter (58);

- a fuel flow rate sensor and transmitter (60).

15. The system (10) according to anyone of claims 1 to 14, characterized in that a single skid-mounted assembly provided with a single frame (62) is arranged to support the components of said system (10), which is located within a battery limit of the fuel supply system and downstream of the fuel tank (12) and upstream of the internal combustion engine (14).

16. The system (10) according to any one of the preceding claims, wherein the system is configured to supply fuel having an atmospheric pressure and temperature of -20 to 45°C at the inlet (11 ) of the system (10).