CN103883446A

CN103883446A - Fuel Supply System And Method For Operating The Same

Info

Publication number: CN103883446A
Application number: CN201310708153.7A
Authority: CN
Inventors: A.科佩尔; A.弗兰克; B.佩克尔
Original assignee: MAN Diesel and Turbo SE
Current assignee: MAN Energy Solutions SE
Priority date: 2012-12-20
Filing date: 2013-12-20
Publication date: 2014-06-25
Anticipated expiration: 2033-12-20
Also published as: JP5922085B2; DE102012025020A1; FI125999B; JP2014122632A; FI20136280A; ITMI20132051A1; CN103883446B; KR102038713B1; KR20140080426A

Abstract

The system (1) flows heavy oil fuel and distillate fuel from fuel tanks (12,13) in the direction of mixing tank (14) and circulates oil fuel and distillate fuel in a feeder fuel circuit (4). A pump unit (21) flows fuel from mixing tank towards marine diesel engine (2,3) with second volume flow which is greater than the first volume flow. Diesel engine return backs fuel to the mixing tank and draws fuel from fuel tank (13) at third volume flow which is greater than the first volume flow, such that operation of the diesel engine is changed from first fuel type to second type. An independent claim is included for method for operating fuel supply system.

Description

Fuel supply system and method for operating the same

Technical Field

The present invention relates to a fuel supply apparatus for at least one marine diesel internal combustion engine according to the preamble of claim 1. The invention further relates to a method for operating such a fuel supply system.

Background

It is known from practice that marine diesel internal combustion engines can be operated on different fuel types. It is thus possible, for example, to operate a marine diesel internal combustion engine on the one hand with heavy oil fuel and on the other hand with distillate fuel (Destillatkraftstoff). Heavy oil fuels, while cost effective, nevertheless result in relatively high fuel emissions due to their high sulfur content. Distillate fuels cause lower exhaust emissions, however are more expensive. On open sea, marine diesel internal combustion engines are operated for cost reasons with heavy oil fuels. If, on the other hand, the ship is to be operated in the near-shore region in the so-called SECA (sulfur Emission Control area), the operation of the marine diesel internal combustion engine must be switched over for Emission reasons, i.e. from heavy oil fuel to distillate fuel. Only when the marine diesel internal combustion engine meets the emission regulations of the SECA region in terms of the emission of harmful substances as a result of the combustion of distillate fuels can the ship then enter such an SECA region.

According to practice, fuel supply apparatuses for marine diesel internal combustion engines, by means of which either heavy oil fuels or distillate fuels can be supplied, have a so-called Feeder-fuel circulation system (Feeder-kraft ffkreislauf) and a so-called Booster-fuel circulation system (Booster-kraft ffkreislauf).

The first fuel or the second fuel can be supplied by the feeder fuel circulation system in the direction of the mixing tank by means of the first pump device. The fuel can be delivered by means of the second pump device of the booster circulation system starting from the mixing tank in the direction of the particular or each marine diesel internal combustion engine. The first pump device of the feeder fuel circulation system sucks in this case the respective fuel in a first delivery volume flow, wherein a first partial delivery volume flow of the first delivery volume flow is delivered in the direction of the mixing tub, and wherein a second partial delivery volume flow of the first delivery volume flow is circulated in the feeder fuel circulation system. The second pump arrangement of the booster fuel circulation system draws fuel from the mixing tank at a second delivery volume flow (which is significantly larger than the first delivery volume flow). More fuel than is actually consumed by the marine diesel engine is therefore delivered through the particular or each marine diesel engine, in order to thus provide excess fuel, in particular for cooling purposes and lubrication purposes. The fuel not consumed by the specific or each internal combustion engine is led back into the mixing tank via the return (ru klauf) of the booster fuel circulation system.

Due to the different delivery volumes in the feeder fuel circulation system and in the booster fuel circulation system, the replacement of the heavy oil fuel by the distillate fuel is relatively slow when transferring the fuel delivery in the feeder fuel circulation system from the heavy oil fuel to the distillate fuel in the booster fuel circulation system. In the transition from the operation with the heavy oil fuel to the operation with the distillate fuel, only as much distillate fuel as heavy oil fuel consumed in the booster circulation system is introduced into the mixing tank starting from the feeder circulation system. Therefore, the dilution of the heavy oil fuel with the distillate fuel in the booster fuel circulation system is only performed relatively slowly. Then, in order that the emission regulation in the SECA region may be satisfied, until the heavy oil fuel is replaced with the distillate fuel to a sufficient degree in the booster circulation system, which causes a relatively long time to be required.

Thus, with the fuel supply apparatuses known from practice, this may continue for up to more than 10 hours after the fuel delivery in the feeder circulation system has been switched from heavy oil fuel to distillate fuel, until the emission regulations of the SECA region can be met due to sufficient fuel replacement in the booster fuel circulation system.

Disclosure of Invention

Starting from this, the object of the invention is to provide a novel fuel supply for at least one marine diesel internal combustion engine and a method for operating the fuel supply. This object is achieved by a fuel supply apparatus according to claim 1. According to the invention, the first pump device of the feeder fuel circuit is designed in such a way that it sucks in the second fuel in a changeover operating mode (in which a changeover is made from the first fuel type to the second fuel type for the operation of the particular or each marine diesel internal combustion engine) starting from the second fuel tank with a third delivery volume flow which is greater than the first delivery volume flow.

According to the invention, the first pump device of the feeder fuel circulation system is designed in such a way that it draws a third delivery volume flow from the fuel tank for the second fuel type in the changeover operating mode, which is greater than the first delivery volume flow in the normal operating mode. The first fuel (in particular the heavy oil fuel) can thereby be replaced in the booster fuel circulation system by the second fuel (in particular by the distillate fuel) significantly more quickly, so that the particular or each marine diesel internal combustion engine can follow the emission regulations of the SECA region significantly faster, since this was possible up to now according to practice. A ship with a fuel supply according to the invention can thus be driven into the SECA region more quickly after the start of the fuel transition from heavy oil fuel to distillate fuel in the feeder fuel circulation system.

Preferably, the first pump device of the feeder fuel circulation system is designed such that it draws the second fuel in the changeover operating mode with such a third delivery volume flow: the first partial delivery volume flow of the third delivery volume flow, which is delivered in the direction of the mixing tank, corresponds to the second delivery volume flow of the booster fuel circulation system. This allows a particularly advantageous and rapid replacement of the first fuel type by the second fuel type in the booster fuel circulation system and thus a particularly rapid meeting of emission regulations of the SECA region after a fuel delivery transition from the first fuel type to the second fuel type

According to an advantageous further development of the invention, a first shut-off valve is connected upstream of the mixing tank in the return portion of the booster fuel circulation system, which first shut-off valve is open in the normal operating mode and closed in the changeover operating mode, wherein preferably a fuel outlet line from the return portion upstream of the first shut-off valve is connected to the second shut-off valve, which is closed in the normal operating mode and open in the changeover operating mode.

With these two shut-off valves, it is particularly advantageously possible to: the first fuel present in the booster fuel circulation system is quickly removed from the booster fuel circulation system after the feeder fuel circulation system is transitioned onto the third delivery volume flow in the transition mode of operation, and the first fuel is quickly replaced with the second fuel in the booster fuel circulation system.

A method according to the invention for operating such a fuel supply device is set forth in claim 7.

Drawings

Preferred developments of the invention result from the dependent claims and the following description. Embodiments of the invention are further elucidated by means of the drawing, without the invention being limited thereto. Wherein,

fig. 1 shows a schematic representation of a fuel supply device according to the invention for at least one marine diesel internal combustion engine.

List of reference numerals

1 feeder fuel circulation system

2 marine diesel internal combustion engine

3 diesel internal combustion engine for ship

4 feeder fuel circulation system

5-booster fuel circulation system

6 pump device

7 fuel pump

8 fuel pump

9 stop valve

10 stop valve

11 valve

12 heavy oil fuel tank

13 distillate fuel tank

14 mixing tank

15 circulation pipeline

16 pressure limiting valve

17 flow measuring device

18 valve

19 bypass line

20 valve

21 pump device

22 initial flow part (Vorlauf)

23 reflux section

24 preheating device

25 valve

26 bypass line

27 valve

28 viscosity measuring device

29 valve

30 valve

31 bypass line

32 bypass valve

33 valve

34 cooling device

35 bypass line

36 coarse filter

37 coarse filter

38 stop valve

39 fuel lead-out line

40 stop valve

41 regulating valve.

Detailed Description

The invention relates to a fuel supply system for at least one marine diesel internal combustion engine of a ship and to a method for operating such a fuel supply system.

Fig. 1 shows a schematic representation of a fuel supply system 1, which in the exemplary embodiment shown is used for the fuel supply of two marine diesel internal combustion engines 2 and 3. The fuel supply device 1 can also supply fuel to only one marine diesel internal combustion engine or more than two marine diesel internal combustion engines, unlike the embodiment shown.

The fuel supply apparatus 1 includes a feeder fuel circulation system 4 and a booster fuel circulation system 5.

The feeder fuel circulation system 4 has a first pump device 6, which in the embodiment shown is formed by two fuel pumps 7 and 8 connected in parallel. In the embodiment shown, each of the two pumps 7 and 8 is located before the shut-off

valve

9 or 10, respectively. It should be noted that the first pump device 6 may also have only one fuel pump or more than two fuel pumps connected in parallel instead of the two fuel pumps 7 and 8.

By means of the first pump device 6 of the feeder fuel circulation system 4, depending on the switching position of the valve 11, either a first fuel can be pumped starting from the first fuel tank 12 (more particularly, in the embodiment shown, a heavy oil fuel) or a second fuel can be pumped starting from the second fuel tank 13 (more particularly, in the embodiment shown, a distillate fuel), wherein the fuel pumped by means of the first pump device 6 of the feeder fuel circulation system 4 can be conveyed in the direction towards the mixing tub 14.

In a normal operating mode of the fuel delivery system 1, the first pump device 6 of the feeder fuel circulation system 4 draws in a defined first delivery volume flow of the respective fuel from one of the two

fuel tanks

12 or 13, wherein a first partial delivery volume flow of the first delivery volume flow can be delivered in the direction of the mixing tub 14, and wherein a second partial delivery volume flow of the first delivery volume flow circulates in the feeder fuel circulation system 4 via the circulation line 15, into which the pressure limiting valve 16 is integrated.

When the marine diesel internal combustion engines 2 and 3 are operated at full load, consuming a total of 100% of the fuel, the first delivery volume flow which is then drawn by the pump device 6 from one of the two

fuel tanks

12 or 13 is typically 160% of the fuel consumption, the first delivery volume flow delivered in the direction of the mixing tub 14 then being 100%, and the second delivery volume flow which is conducted through the circulation line 15 then being 60%.

According to fig. 1, a first partial delivery volume flow of the first delivery volume flow, which is delivered in the direction of the mixing tank 14 via the first pump device 6 of the feeder fuel circulation system 4, can be conducted through the flow measuring device 17, i.e. when the valve 18 disposed upstream of the flow measuring device 17 is opened.

Alternatively, for example, when the flow measuring device 17 is defective, a first partial delivery volume flow of the first delivery volume flow can then be guided past the flow measuring device 17 via the bypass line 19, wherein the valve 18 is then closed and the valve 20 integrated into the bypass line 19 is opened.

In this regard, it should be noted that the second partial delivery volume flow of the first delivery volume flow, which is circulated in the feeder fuel circulation system 4 via the circulation line 15, is set by means of the pressure limiting valve 16 in such a way that a constant pressure level is established for the first partial delivery volume flow delivered to the mixing tank 14. The pressure level may be, for example, 7 bar.

When the heavy-oil fuel, which typically has a temperature of approximately 90 ℃ in the first partial delivery volume flow delivered into the mixing tank 14, is delivered via the feeder fuel circulation system 4 starting from the first fuel tank 12 as the first fuel type in the direction of the mixing tank 14, it is then preheated in the first fuel tank 12.

The booster circulation system 5 has a second pump device 21, by means of which fuel can be drawn from the mixing tank 14 and can be conveyed in the direction of the particular or each marine diesel internal combustion engine 2, 3. This part of the booster fuel circulation system 5 via which fuel can be delivered onto the particular or each marine diesel internal combustion engine 2,3 starting from the mixing tank 14 is also referred to as the start flow portion 22 of the booster fuel circulation system 5. The fuel which is supplied via the start flow 22 to the specific or each marine diesel internal combustion engine 2,3 but is not combusted in the specific or each marine diesel internal combustion engine 2,3 can be returned via the return flow 23 of the booster fuel circulation system 5 in the direction of the mixing tank 14.

As can be gathered from fig. 1, the fuel drawn from the mixing tank 14 by the second pump device 21 of the booster fuel circulation system 5 can be conveyed through a preheating device 24, more particularly when the particular or each marine diesel internal combustion engine 2,3 is operated with heavy oil fuel. When the particular or each marine diesel internal combustion engine 2,3 is operated with distillate fuel, the valve 25 which is arranged upstream of the preheating device 24 is closed, in order to then guide the distillate fuel through the bypass line 26 with the valve 27 open. A viscosity measuring device 28 is integrated into the flow start portion 22 of the booster fuel circulation system 5 downstream of the preheating device 24, the viscosity measuring device 28 adjusting the operation of the preheating device 24 when the heavy oil fuel is led through the preheating device 24 so as to influence the viscosity of the heavy oil fuel by the preheating device 24.

Typically, the heavy oil fuel is heated by the preheating device 24 in order to set a viscosity of 12-14 cst (Stokes), wherein the pressure level in the booster fuel circulation system 5 downstream of the second pump device 21 may be 12bar, for example.

As already implemented, the second pump device 21 of the booster fuel circulation system 5 draws fuel from the mixing tank 14 and delivers it in the direction of the particular or each marine diesel internal combustion engine 2,3 — more specifically, depending on the open position of the

valves

29, 30 placed in front of the marine diesel internal combustion engines 2, 3. The second pump means 21 of the booster fuel circulation system 5 draws fuel from the mixing tank 14 at a second delivery volume flow (which is significantly higher than the first delivery volume flow of the feeder fuel circulation system 4).

In a specific embodiment, therefore, it is provided that: when the first delivery volume flow of the feeder fuel circulation system 4 is 160%, then the second delivery volume flow of the booster fuel circulation system 5 is 300%, wherein when the two

valves

29, 30 are open, then 150% of the sub-delivery volume flow is respectively directed through each marine diesel internal combustion engine 2, 3.

However, the two marine diesel internal combustion engines 2,3 together can burn a maximum of 100% fuel at full load, i.e. a maximum of 50% fuel for each marine diesel internal combustion engine 2,3 individually. More fuel than can be burned in the marine diesel engine is therefore fed through the two marine diesel engines 2,3, the excess fuel being used for cooling and lubrication and being able to be returned via the return 23 in the direction of the mixing tub 14.

When one of the two

valves

29, 30 is closed, i.e. when one of the two marine diesel internal combustion engines 2,3 is disengaged from the flow start 22 of the booster fuel circulation system 5, such fuel that is not then deliverable through the disengaged marine diesel internal combustion engine 2,3 can be conducted via a bypass line 31 bypassing the other marine diesel internal combustion engine 3, 2, wherein then a bypass valve 32 integrated into this bypass line 31 is opened.

The fuel which can be returned via the return 23 of the booster fuel circulation system 5 in the direction of the mixing tank 14 can be guided either through the cooling device 34 or through the bypass line 35 depending on the position of the valve 33 integrated into the return 23.

When the heavy oil fuel is burned as fuel in the specific or each marine diesel internal combustion engine 2,3, the excess heavy oil fuel that is not combusted at that time is led via the bypass line 35 to bypass the cooling device 34. When the distillate fuel is burned as fuel in the particular or each marine diesel internal combustion engine 2,3, the excess distillate fuel that is not combusted can then be conducted through the cooling device 34 depending on its temperature.

According to fig. 1, in the embodiment shown, a

coarse filter

36, 37 is placed before each internal combustion engine 2,3 downstream of the

respective valve

29, 30 in order to filter out coarse contaminants from the fuel delivered into the booster fuel circulation system 5 and thus protect the particular or each marine diesel internal combustion engine 2,3 from damage.

In the sense of the invention here, it is now proposed: the first pump device 6 of the feeder fuel circuit 4 is designed such that, in a changeover operating mode, in which the or each marine diesel internal combustion engine 2,3 is switched from a first fuel (i.e. heavy oil fuel) to a second fuel (i.e. distillate fuel) for operation-starting from the second fuel tank 13, the second fuel is no longer pumped with the first delivery volume flow, but rather with a third delivery volume flow which is greater than the first delivery volume flow.

According to an advantageous embodiment of the invention, provision is made for: the first pump device 6 of the feeder fuel circulation system 4 is designed such that it draws the second fuel from the second fuel tank 13 in the changeover operating mode with such a third delivery volume flow; the first partial delivery volume flow of the third delivery volume flow delivered in the direction of the mixing tank 14 is greater than or equal to the second delivery volume flow of the booster fuel circulation system 5 (i.e. the delivery volume flow of the second pump device 21 of the booster fuel circulation system).

In a particular embodiment it is provided that: in the changeover operating mode, the first partial delivery volume flow of the third delivery volume flow (which is delivered starting from the pump device 6 of the feeder fuel circulation system 4 in the direction of the mixing tub 14) is 300%, i.e. corresponds to the second delivery volume flow of the booster fuel circulation system 5.

It may be provided here that a respective 160% of the second fuel is sucked from the second fuel tank 13 via each of the two pumps 7, 8 of the pump device 6 of the feeder fuel circulation system 4, in order to direct 300% to the mixing tub 14 and to circulate the remaining 20% in the feeder fuel circulation system 4 via the circulation line 15.

A first shut-off valve 38, which is open in the normal operating mode and closed in the changeover operating mode, is connected upstream of the mixing tank 14 in the return portion 23 of the booster fuel circulation system 5. Upstream of the first shut-off valve 38, a fuel outlet line 39 branches off from the return 23 of the booster fuel circulation system 5, which in the exemplary embodiment shown opens into the first fuel tank 12 for heavy oil fuel. A second shut-off valve 40 is connected into the fuel outlet line 39, which second shut-off valve 40 is closed in the normal operating mode and is open in the changeover operating mode.

By means of the present invention, it is thus possible to increase the delivery power of the first pump means 6 of the feeder fuel circulation system 4 when switching the fuel supply from heavy oil fuel to distillate fuel, in order thereby to quickly remove from the booster fuel circulation system the heavy oil fuel still present in the booster fuel circulation system 5 and quickly replace the heavy oil fuel by distillate fuel. For this purpose, after increasing the delivery power of the first pump device 6 of the feeder fuel circulation system 4, the second shut-off valve 40 is first opened and then the first shut-off valve 38 is closed.

Preferably, after the change into the changeover operating mode, the first pump device 6 of the feeder fuel circulation system 4 is operated with increased delivery power for a defined period of time or for a defined volumetric flow, so that the changeover operating mode is therefore kept active for a defined period of time or for a defined volumetric flow.

After the time period has elapsed or after the volume flow has been reached, a change is made back to the normal operating mode, wherein for this purpose the two shut-off

valves

38 and 40 are first actuated, i.e. the first shut-off valve 38 is opened and the second shut-off valve 40 is closed, in order to subsequently reduce the delivery capacity of the first pump device 6 of the feeder fuel circulation system 4, i.e. from the third delivery volume flow onto the first delivery volume flow, which is drawn by the first pump device 6 from the

respective fuel tank

12,13 in the normal operating mode.

The heavy oil fuel present in the booster fuel circulation system 5 can thus be removed quickly from this booster fuel circulation system 5 and replaced quickly by distillate fuel when switching from the heavy oil fuel supply to the distillate fuel supply by means of the invention, so that the ship can be driven into the SECA area after switching the fuel supply over to the distillate fuel supply in a very short time.

According to an advantageous development of the invention, a control valve 41 is connected in parallel to the second shut-off valve 40. The control valve 41 can be actuated as a function of the measurement signal of the flow measuring device 17. When the particular or each marine diesel internal combustion engine 2,3 is burning relatively little fuel and therefore relatively little fuel is replenished into the mixing tank 14 by the feeder fuel circulation system 4, then the regulating valve 41 can be used to draw fuel out of the return 23 in the direction of the fuel outlet line 39 by correspondingly opening the regulating valve 41, in order thus to set a constant consumption in the booster fuel circulation system 5, independently of the actual fuel consumption of the particular or each marine diesel internal combustion engine 2,3, in the booster fuel circulation system 5, in order thus to replenish a constant amount of fuel into the mixing tank 14 by the feeder fuel circulation system 4.

This is particularly advantageous if, when changing from the normal operating mode into the changeover operating mode, the temperature in the booster fuel circulation system 5 of the fuel supply system 1 is to be reduced before the delivery power of the first pump device 6 of the feeder fuel circulation system 4 is increased.

As set forth above, the temperature level in the booster fuel circulation system 5 during heavy oil fuel operation is approximately 140 ℃. But the temperature level in the booster fuel circulation system 5 should be reduced to about 45C before switching to distillate fuel operation.

According to practice, the duration required for such a cooling process depends on the actual fuel consumption of the particular or each marine diesel internal combustion engine 2, 3. By actuating the control valve 41 as a function of the measurement signal of the flow measuring device 17, the cooling process can be designed independently of the actual consumption of the particular or each marine diesel internal combustion engine 2, 3. The point in time in which it can be switched to distillate fuel operation is therefore also not dependent on the actual consumption of the particular or each marine diesel internal combustion engine 2, 3.

By opening the control valve 41, a constant high fuel consumption of the particular or each marine diesel internal combustion engine 2,3 can be simulated in order to deliver a constant delivery volume via the pump device 6 into the mixing tank 14. Thus, when the measurement signal of the flow measuring device 17 shows a relatively small consumption of the specific or each marine diesel internal combustion engine 2,3, the regulating valve 41 is then opened further, and when the measurement signal of the flow measuring device 17 shows a relatively high consumption of the specific or each marine diesel internal combustion engine 2,3, the regulating valve 41 is then closed further.

The control of the control valve 41 is preferably carried out as a function of the measurement signal of the flow measuring device 17 in such a way that the measurement signal of the flow measuring device 17 is compared with a setpoint value. If the measurement signal of the flow measuring device 17 is greater than or corresponds to a setpoint value, the actual consumption of the particular or each marine diesel internal combustion engine 2,3 is correspondingly high, and the control valve 41 is closed. If, conversely, the measurement signal of the flow measuring device 17 is smaller than the setpoint value, the actual consumption of the particular or each marine diesel internal combustion engine 2,3 is lower, the control valve 41 is opened as a function of the deviation between the setpoint value and the actual value of the measurement signal, in order to simulate a constant consumption and to deliver a constant volumetric fuel flow into the mixing tank 14 via the feeder fuel circulation system 4. This causes the temperature level in the booster fuel circulation system 5 to be rapidly lowered independently of the load.

Claims

1. A fuel supply apparatus (1) with: a feeder fuel circulation system (4), by means of which a first fuel, in particular a heavy-oil fuel, or a second fuel, in particular a distillate fuel, can be conveyed in the direction of a mixing tank (14) starting from a first fuel tank (12) for a first fuel type or starting from a second fuel tank (13) for a second fuel type via a first pump device (6); and a booster fuel circulation system (5) by means of which fuel can be conveyed starting from the mixing tank (14) in the direction of at least one marine diesel internal combustion engine (2,3) via a second pump device (21), wherein, in a normal operating mode, a first pump device (6) of the feeder fuel circulation system (4) sucks the first fuel or the second fuel out of the respective fuel tank (12,13) in a first delivery volume flow, conveys a first partial delivery volume flow of the first delivery volume flow in the direction of the mixing tank (14) and circulates a second partial delivery volume flow of the first delivery volume flow in the feeder fuel circulation system (4), and wherein, furthermore, in a normal operating mode, the second pump device (21) of the booster fuel circulation system (5) sucks fuel out of the mixing tank (14) in a second delivery volume flow which is greater than the first delivery volume flow, -transporting in the direction of the or each marine diesel internal combustion engine (2,3) and returning fuel that is not combusted in the or each marine diesel internal combustion engine (2,3) into the mixing tank (14), characterized in that the first pump device (6) of the feeder fuel circulation system (4) is designed such that it sucks up the second fuel in a changeover operating mode, in which the operation for the or each marine diesel internal combustion engine (2,3) is changed over from the first fuel type to the second fuel type, starting from the second fuel tank (13) with a third transport volume flow that is greater than the first transport volume flow.

2. Fuel supply arrangement according to claim 1, characterized in that the first pump means (6) of the feeder fuel circulation system (4) are designed such that: in the switching operating mode, the first pump device draws in the second fuel with a third delivery volume flow, such that a first partial delivery volume flow of the third delivery volume flow, which is delivered in the direction of the mixing tank (14), corresponds to a second delivery volume flow of the booster fuel circulation system (5).

3. The fuel supply apparatus according to claim 1 or 2, characterized in that a first shut-off valve (38) that is open in the normal operation mode and closed in the changeover operation mode is connected in the return portion (23) of the booster fuel circulation system (5) upstream of the mixing tank (14).

4. A fuel supply apparatus according to claim 3, characterized in that a fuel lead-out line (39) into which a second shut-off valve (40) is connected branches off from the return portion (23) upstream of the first shut-off valve (38), which second shut-off valve is closed in the normal operating mode and open in the changeover operating mode.

5. Fuel supply apparatus according to claim 4, characterized in that the fuel outlet line (39) leads to the first fuel tank (12).

6. Fuel supply installation according to claim 4 or 5, characterised in that a regulating valve (41) is connected in parallel with the second stop valve (40), which regulating valve can be actuated in the changeover operating mode depending on a measuring signal of a flow measuring device (17) in the feeder fuel circulation system (4).

7. Method for operating a fuel supply device according to one of claims 1 to 6, characterized in that, in order to change from a normal operating mode into a changeover operating mode, the first pump device (6) of the feeder fuel circulation system (4) is first switched from a first delivery volume flow to a third delivery volume flow, whereupon the second shut-off valve (40) is opened and the first shut-off valve (38) is closed.

8. Method according to claim 7, characterized in that for changing from the changeover operating mode into the normal operating mode, first the first shut-off valve (38) is opened and the second shut-off valve (40) is closed, and subsequently the first pump device (6) of the feeder fuel circulation system (4) is changed over from the third delivery volume flow onto the first delivery volume flow.

9. Method according to claim 7, characterized in that after a change from the normal operating mode into the changeover operating mode, the changeover operating mode remains active for a defined period of time or for a defined volume flow and changes back into the normal operating mode after the passage of this period of time or after reaching this volume flow.