KR20180048572A - Ship fuel gas supply system - Google Patents

Abstract

A low speed diesel engine capable of gas combustion is used as the main engine 12 and first and second fuel gas supply lines 14 and 21 for supplying fuel gas to the main engine 12 are provided. First and second controllers 17 and 28 for controlling the pressures of the fuel gas supplied from the first and second fuel gas supply lines 14 and 21 to the main engine 12 are provided. The pressure control in the first and second controllers 17 and 28 is performed based on the rotation number set value SN. The control of the first and second controllers 17 and 28 is controlled based on the fuel gas demand pressure output from the main engine control device 20 over the transient period when the revolution speed set value SN is changed .

Description

Ship fuel gas supply system

The present invention relates to a fuel gas supply system applied to a liquefied gas carrier or liquefied gas fuel line equipped with a low speed diesel engine capable of gas combustion as a main engine.

From the viewpoint of reducing environmental load and improving energy consumption, recently, a gas combustion low-speed diesel engine is adopted as the main engine of an LNG carrier, and a boil-off gas (NATURAL BOG) naturally generated in the LNG cargo tank is used as fuel The configuration to be used is known. However, in the gas combustion low speed diesel engine, the fuel gas pressure required at the fuel gas inlet of the main engine is determined according to the load of the main engine, and it is necessary to supply the fuel gas at the required pressure. Therefore, when the boil-off gas is used for the fuel, it is necessary to compress the boil-off gas to the required pressure by the high-pressure gas compressor. Further, as a method of generating high-pressure fuel gas with low power consumption, there is known a configuration in which liquefied natural gas is pressurized by a high-pressure liquid pump and heated to a high-pressure gas of a required pressure (Patent Document 1).

Patent Document 1: Japanese Unexamined Patent Application Publication No. 2012-177333

Since the load of the main engine of the ship is constantly fluctuated by the weather or the sea during the operation, if the supply pressure of the fuel gas to the main engine is controlled in accordance with the required pressure of the main engine, the control becomes unstable, It does not follow the pressure or, for example, exceeds the performance range of the control depending on the configuration of the device, and a continuous deviation occurs between the set pressure and the actual pressure.

An object of the present invention is to supply the fuel gas at a stable pressure to the inlet of a main engine capable of gas combustion even under a load fluctuation.

The present invention provides a fuel gas supply system for supplying fuel gas to a low-speed diesel engine capable of combusting gas which is used as a main engine, comprising: gas supply means for supplying fuel gas to a main engine; And the pressure control means sets the supply pressure based on the set number of revolutions of the main engine.

When the rotational speed set value is changed, the pressure control means sets the supply pressure without being based on the rotational speed set value. The period during which the supply pressure is set based on the set number of revolutions, for example, corresponds to the transient period according to the transition of the number of revolutions of the main engine. The pressure control means delays the change from the supply pressure set based on the set rotational speed value before the change to the supply pressure set based on the set rotational speed value after the change in the transient period. In the transient period, the supply pressure is, for example, the required pressure of the main engine.

The fuel gas is, for example, a boil-off gas in the cargo tank. The gas supply means includes a high-pressure gas compressor which compresses the fuel gas to supply it to the main engine, and the pressure control means controls the discharge pressure of the high-pressure gas compressor to control the supply pressure. Further, the gas supply means includes a high-pressure liquid pump that pressurizes the liquefied gas and supplies it as fuel gas to the main engine, and the pressure control means controls the supply pressure by controlling the discharge pressure of the high-pressure liquid pump.

The ship of the present invention is characterized by including the fuel gas supply system.

According to the present invention, it is possible to supply the fuel gas at a stable pressure to the inlet of the main engine capable of burning gas even when the load fluctuates.

1 is a block diagram showing a configuration of a fuel gas supply system according to an embodiment of the present invention.
2 is a block diagram showing the configuration of the first and second controllers.
3 is a graph showing the relationship between the engine load and the required pressure.
4 is a block diagram showing the configuration of the fuel gas supply system of the first modification.
5 is a block diagram showing the configuration of the fuel gas supply system of the second modification.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

1 is a block diagram showing a configuration of a fuel gas supply system according to an embodiment of the present invention.

The fuel gas supply system 10 of the present embodiment is applied to a ship that carries a liquefied gas such as natural gas, and a liquefied gas (LNG in this embodiment) is loaded in a cargo tank 11 installed in the hull. The main engine 12 is a low speed diesel engine capable of burning gas and is connected to the main engine 12 via a first fuel gas supply line 14 including a high pressure gas compressor 13, It is possible to supply off-gas (NATURAL BOG).

The boil-off gas generated in the cargo tank 11 is sent to the high-pressure gas compressor 13 through the upstream line of the first fuel gas supply line 14 and is compressed by the high-pressure gas compressor 13. The compressed boil-off gas is sent as "high-pressure gas" to the main engine 12 through the first fuel gas supply line 14 on the downstream side. The high-pressure gas compressor 13 is, for example, a multi-stage compressor and has a low-pressure stage 13A on the upstream side and a final stage 13B on the downstream side. For example, in the low-pressure stage 13A, the fuel gas can be fed as the "low-pressure gas" having a relatively low pressure through the branch line 15, and the fuel gas can be supplied to the gas- The surplus BOG that can not be completely consumed by the main engine 12 or the generator engine is also supplied as fuel gas to the BOG treatment device (boiler, gas combustion device, refueling device, etc.) via the branch line 15. The line for sending the surplus gas to the BOG processing device may be configured to be supplied at a reduced pressure from the discharge side of the final stage 13B of the high-pressure gas compressor 13 to the required pressure of the BOG processing device. In this embodiment, the low-pressure stage to the high-pressure stage are described as one multi-stage high-pressure gas compressor, but the low-pressure stage may be used as another compressor and the low-pressure gas compressor and the high-pressure gas compressor may be provided in series.

A first circulation line 16 for refluxing the fuel gas to the suction side of the final stage 13B is provided on the discharge side of the final stage 13B in the high-pressure gas compressor 13. The first circulation line 16 is provided with a first valve 16V for controlling the flow rate of the gas to be refluxed and the opening degree of the first valve 16V is controlled by the first controller 17. A pressure sensor 18 is provided on the discharge side of the final stage 13B and a pressure value PV1 on the discharge side of the fuel gas supplied to the main engine 12 is measured. On the other hand, on the upstream side of the first fuel gas supply line 14, a pressure sensor 19 for measuring the pressure PV2 of the boil-off gas in the cargo tank 11 is provided. In the present embodiment, the pressure PV2 is measured at one point in a common pipe of a plurality of cargo tanks 11. In this embodiment, However, the pressure may be measured at a plurality of locations and the average thereof may be determined as the pressure (PV2).

The first controller 17 inputs these measured pressure values PV1 and PV2 and also receives the fuel gas required pressure SP1 and the rotational speed of the main engine 12 from the main engine control device 20 ) Set value SN, a pressure set value SP2 in the cargo tank 11 set by the operator, and the like are input. The first controller 17 adjusts the opening of the first valve 16V of the first circulation line 16 based on these values and controls the opening of the main engine 12 of the boil-off gas.

The fuel gas supply system 10 of the present embodiment is also provided with a second fuel gas supply line 21. The second fuel gas supply line 21 has a pump 22 disposed in the vicinity of the bottom of the cargo tank 11. The liquefied gas in the cargo tank 11 is supplied to the pump 22 Pull up by. In the second fuel gas supply line 21, the pumped liquefied gas is temporarily stored in the suction drum 23. A high-pressure liquid pump 24 is connected to the downstream side of the suction drum 23, and the liquefied gas in the suction drum 23 is pressurized and sent out to the gas heater 25. In the gas heater 25, the liquefied gas pressurized by the high-pressure liquid pump 24 is heated and vaporized and supplied to the main engine 12 as a high-pressure gas. Further, even when the first fuel gas supply line 14 is not used, since the liquefied gas is used for the fuel of the gas-fired power generator engine, the fuel gas is supplied to the gas- Line may be provided or a line for supplying gas to the gas combustion generator organs in front of the suction drum 23 may be branched.

The high-pressure liquid pump 24 is driven by a motor 26 and the motor 26 is driven and controlled by a second controller 28 via an inverter 27. A second circulation line 29 for returning the liquefied gas to the suction drum 23 is provided on the downstream side of the high pressure liquid pump 24 and a second circulation line 29 for controlling the flow rate of the liquefied gas Two valves 29V are installed. The second controller 28 is supplied with the fuel gas required pressure SP1 and the rotation speed set value SN from the main engine control device 20 and the high pressure liquid pump 24 of the second fuel gas supply line 21 And the pressure value PV3 measured by the pressure sensor 30 provided between the gas heater 25 and the gas heater 25 are input. The second controller 28 adjusts the opening of the second valve 29V according to the operation mode and the operation state and controls the drive of the motor 26 as will be described later. The motor 26 may be a hydraulic drive motor. In this case, the motor 26 controls the drive of the hydraulic drive motor via the hydraulic drive source instead of the inverter 27. In the present embodiment, the second circulation line 29 is delivered to the suction drum 23, but may also be delivered to the cargo tank 11.

The suction drum 23 is provided with a third circulation line 31 for returning the boil-off gas in the drum to the upstream side (the cargo tank 11 side) of the first fuel gas supply line 14, The third valve (31V) is installed in the third circulation line (31). A fourth valve (21V) for keeping the load of the pump constant is provided at a very close position of the second fuel gas supply line (21) from the cargo tank (11) A branch line 32 for adjusting the supply pressure of the liquefied gas to be supplied to the pump 24 is provided and the branch line 32 is provided with the fifth valve 32V.

Further, even if the suction drum 23 is not provided, the NPSH (effective suction head) of the high-pressure liquid pump 24 is sufficiently secured and the gas vaporized between the cargo tank 11 and the high-pressure liquid pump 24 is gas- It is not absolutely necessary to install the suction drum 23. In this case, the third circulation line 31 is not provided, and the second circulation line 29 is not provided in the cargo And is delivered to the tank 11.

In the present embodiment, supply of surplus (BOG) through the branch line 15 to the BOG processing apparatus (boiler, gas combustion apparatus, refueling apparatus, etc.) ) By the third controller 33. [0053] The third controller 33 receives the cargo tank pressure value PV2 and the pressure setting value SP2 set by the operator and adjusts the opening degree of the sixth valve 15V based on these values, BOG) to the BOG processing device.

In the present embodiment, when the liquefied gas carrier is operated on the higher side (high-speed operation region) than the reference operating point in which the BOG generation amount and the fuel consumption amount in the main engine 12 are balanced in a state in which liquefied gas is loaded, The operation mode (hybrid mode) is selected. In the first operation mode, the boil-off gas compressed by the high-pressure gas compressor 13 is supplied to the main engine 12 through the first fuel gas supply line 14, and the boil- We supply the deficient fuel. That is, in the first operation mode, the pump 22, the high-pressure liquid pump 24 and the gas heater 25 are driven to generate high-pressure gas from the liquefied gas in the cargo tank 11, And supplies it to the main engine 12 together with the boil-off gas.

The first controller 17 controls the first valve 16V of the high-pressure gas compressor 13 so that the measured pressure value PV2 on the cargo tank 11 side becomes the pressure SP2 set by the operator . The second controller 28 controls the second fuel gas supply line 21 such that the discharge pressure of the second fuel gas supply line 21 becomes a pressure determined from the fuel gas required pressure SP1 or the rotation speed set value SN of the main engine 12 Side pressure value PV3 of the high-pressure liquid pump 24, and controls the driving of the high-pressure liquid pump 24. The high-

The second operation mode (compressor mode) is selected when the liquefied gas is loaded and operated in the low speed side (the deceleration operation area) than the reference operation point or the reference operation point, and the high pressure gas compressor 13 is used Only the first fuel gas supply line 14 is used. That is, the main engine 12 is operated using only the boil-off gas. When there is surplus gas, the gas is supplied to the BOG treatment device (boiler, gas combustion device, liquefaction device, etc.) through the branch line 15 .

In the second operation mode, the first controller 17 determines whether the discharge pressure of the first fuel gas supply line 14 is determined from the fuel gas required pressure SP1 or the rotation speed set value SN of the main engine 12 (To be described later), and controls the first valve 16V of the high-pressure gas compressor 13 by monitoring the pressure value PV1 on the discharge side.

Further, when spraying is performed in the operation in the liquefied gas unloading operation, the amount of the boil-off gas per unit time generated in the spraying operation changes vertically according to the amount of the liquid used in the spraying operation. Therefore, the first operation mode (hybrid mode) is selected on the higher side than the spraying reference operation point in which the amount of boil-off gas generated by the spraying operation is balanced with the fuel consumption amount in the main engine 12, Or the second operation mode (compressor mode) is selected at the lower speed side than the reference operating point at the time of spraying. That is, either the first or the second operation mode is selected in relation to the fuel consumption amount of the low-speed diesel engine and the amount of boil-off gas generation.

Further, when the amount of boil-off gas generated by the spraying operation exceeds the consumption amount by the main engine 12 and the generator engine, excess boil-off gas is supplied to the BOG processing device (boiler, Liquefying device or the like). Even in the case of the operation of the liquefied gas, the liquefied gas is stored in a certain degree in order to use the liquefied gas as the spray liquid for cooling the cargo tank and as the fuel of the main engine, It does not mean that it is empty.

When the spray operation is not performed in the operation of the liquefied gas supply, the third operation mode (pump mode) is selected, and the fuel gas is supplied to the main engine 12 only through the second fuel gas supply line 21. That is, high pressure gas is generated from the liquefied gas in the cargo tank 11 using the pump 22, the high-pressure liquid pump 24, and the gas heater 25, and is supplied to the main engine 12. Then, the first fuel gas supply line 14 is not used, and the high-pressure gas compressor 13 is turned off.

In the third operation mode, as in the first operation mode, the second controller 28 determines whether the discharge pressure of the second fuel gas supply line 21 is higher than the fuel gas required pressure SP1 of the main engine 12, (To be described later), the discharge-side pressure value PV3 of the high-pressure liquid pump 24 is monitored to control the driving of the high-pressure liquid pump 24. It is also necessary to supply the fuel gas to the main engine 12 at a supply amount lower than the fuel gas supply amount at the minimum operable capacity (the minimum number of rotations of the motor 26) of the high-pressure liquid pump 24 in the third operation mode The second controller 28 drives the high pressure liquid pump 24 to the minimum operable capacity while opening the second valve 29V to supply surplus fuel discharged from the high pressure liquid pump 24 to the suction drum 23 ) Through the second circulation line (29).

In addition, the cruise speed of the ship is set at the reference operating point, or at a slightly lower speed. In other words, the ship is cruising at the cruising speed most of the time, for example, it is operated near the reference operating point. Therefore, at the time of loading the liquefied gas, only the high-pressure gas compressor 13 is driven, and most of the boil-off gas is consumed as the fuel of the main engine 12. [ Only when operation in the high-speed operation region is required, the high-pressure liquid pump 24 is driven to generate high-pressure gas directly from the liquefied gas. In addition, since the spraying operation is not carried out for most of the time in the operation of the liquefied gas supply, the operation mode of the third operation mode is almost taken, and the high-pressure gas pump 13 is operated without operating the high- Fuel gas is supplied. On the other hand, when the spraying operation is performed and the boil-off gas is generated, the high-pressure gas compressor 13 is driven, and the boil-off gas is used as the fuel of the main engine 12.

Next, the configuration of the first and second controllers 17 and 28 will be described with reference to the block diagram of Fig. The configurations of both are common in the range shown in Fig.

The first and second controllers 17 and 28 are supplied with the fuel gas required pressure SP1 and the set rotational speed value SN. Here, the fuel gas required pressure SP1 is a value obtained by the main engine control device 20, and is a value obtained by multiplying the amount of fuel supplied to the main engine 12 of the main engine control device 20 Index), and is determined with reference to the calculated engine load and the graph or relationship of the sows as shown in Fig. The set rotational speed value SN is a value calculated in the main engine control device 20 based on the value input to the main engine control device 20 by the operator so as to set the number of revolutions of the main engine, The engine control device 20 controls the fuel supply amount such that the main engine 12 rotates at a constant speed by the number of revolutions. 2, the pressure measurement values PV1, PV2 and PV3 inputted to the first and second controllers 17 and 28 are represented by PV.

3, the abscissa is the engine load (%) and the ordinate is the fuel gas required pressure MPa of the main engine 12. In the main engine control device 20, the fuel gas required pressure SP1 changes in accordance with the change of the load of the main engine 12 corresponding to the graph S of Fig.

The first and second controllers 17 and 28 calculate the engine load based on the propeller law in which the load of the main engine is roughly proportional to the third power of the rotational speed of the main engine from the value of the set period revolution speed SN And the periodic speed set value SN is converted into the fuel gas required pressure SP0 at the main engine inlet by referring to the function 17A. The function 17A is equivalent to the graph of Fig. 3, and when the engine load (%) is determined, the required pressure (vertical axis) of the fuel gas is obtained from the graph S.

The fuel gas required pressure SP1 input to the first and second controllers 17 and 28 and the pressure SP0 calculated with reference to the function 17A are inputted to the changeover switch 17B, Is input to the pressure controller 17C of the fuel gas supply system. Based on the measured pressure value PV and the inputted pressure command value SP0 or SP1, the pressure controller 17C controls the operating system such as the valves 16V and 29V, the inverter 27, (MV) so that the pressure command value (PV) becomes the pressure command value.

Here, the changeover of the changeover switch 17B is performed by a command from the main engine control device 20, for example, in accordance with the change in the set value of the revolution number SN. That is, the changeover switch 17B is supplied with the pressure SP0 obtained at the normal cycle revolution set value SN into the pressure controller 17C, and when the set cycle revolution number SN is changed, The pressure command value input to the pressure controller 17C is switched over to the fuel gas required pressure SP1 over the transient period until transition to the revolution speed. Further, after the end of the transient period, the pressure SP0 obtained at the new revolution number set SN is again inputted to the pressure controller 17C.

As described above, according to the configuration of the present embodiment, since the pressure command value to the pressure controller is constant and does not affect the load fluctuation in the cycle during operation, unless the controller switches the set value of the revolution speed of the cycle , The gaseous fuel can be supplied to the cycle at a stable pressure.

Next, the first and second modified examples of the present embodiment will be described with reference to Figs. 4 and 5. Fig. The fuel gas supply system 10 'of the first modification shown in Fig. 4 removes the configuration of the second fuel gas supply line 21 using the high-pressure liquid pump 24 from the embodiment of Fig. 1, The fuel gas supply system is constituted by only the first fuel gas supply line 14 using the gas compressor 13. [ 5, the configuration of the first fuel gas supply line 14 using the high-pressure gas compressor 13 is removed from the embodiment of Fig. 1, and the configuration of the fuel gas supply system 10 " The fuel gas supply system is constituted by only the second fuel gas supply line 21 using the high-pressure liquid pump 24. [ Other configurations of the first and second modified examples are the same as those of the first and second modified examples.

In the first and second modified examples, the fuel gas can be supplied at regular intervals with a stable pressure as in the embodiment.

In this embodiment, the pressure command value is switched to the fuel gas required pressure during the transient period when the engine speed is changed. However, the pressure command value may be continuously changed over the transient period without using the required pressure It is also possible to adopt a configuration in which the delay is changed by moderately delaying, or the configuration is changed stepwise in a predetermined step. Also, the switching period is not limited to the transient period, and may be longer or slightly shorter. Further, the end of the transient period may be detected from the measured engine speed, or the time may be set in advance.

In addition, the main engine may be a low speed diesel engine of gas prior combustion (single fuel combustion), or may be a diesel fuel combustion low speed diesel engine with an oil fuel. In this case, for example, It may be used as a fuel. In the present embodiment, a liquefied gas carrier carrying LNG containing methane as a main component is described. However, the present invention is also applicable to a liquefied gas carrier carrying a cargo other than LNG. The gas pressure of the engine inlet required by the low speed diesel engine varies depending on the nature of the fuel gas (for example, ethane) used and the case where a higher pressure is required than when the LNG is used as the fuel (For example, from 40 MPa to 60 MPa), but the present invention can be applied similarly to the embodiment in which methane is the main component. Further, the present invention is not limited to a liquefied gas carrier as long as it is a ship that uses liquefied gas for cycle fuel.

10: fuel gas supply system
11: Cargo tank
12: Main engine
13: High pressure gas compressor
13A: Low pressure stage
13B: Final stage
14: First fuel gas supply line
16: first circulation line
16V: first valve
17: First controller
17A: Function
17B: Conversion switch
17C: Pressure controller
18, 19, 30: pressure sensor
20: Main engine control unit
21: a second fuel gas supply line
22: Pump
23: Suction drum
24: High-pressure liquid pump
25: Gas heater
28: second controller
29: second circulation line
29V: Second valve

Claims (9)

1. A fuel gas supply system for supplying a fuel gas to a gas-combustible low-speed diesel engine used as a main engine,
Gas supply means for supplying a fuel gas to the main engine,
And a pressure control means for controlling a supply pressure of the fuel gas supplied to the main engine,
Wherein the pressure control means sets the supply pressure based on a set number of revolutions of the main engine. The fuel gas supply system according to claim 1, characterized in that, when the rotational speed set value is changed, the pressure control means sets the supply pressure without being based on the rotational speed set value. 3. The fuel gas supply system according to claim 2, wherein a period during which the supply pressure is set based on the set rotational speed value corresponds to a transient period according to the transition of the rotational speed of the main engine. 4. The apparatus according to claim 3, wherein the pressure control means changes the supply pressure to be set based on the set rotational speed value from the supply pressure set based on the rotational speed set value before the change to the delay Fuel gas supply system. 4. The fuel gas supply system according to claim 3, wherein, in the transient period, the supply pressure is a required pressure of the main engine. The fuel gas supply system according to any one of claims 1 to 5, characterized in that the fuel gas is a boil off gas in a cargo tank. 7. The fuel cell system according to any one of claims 1 to 6, wherein the gas supply means includes a high-pressure gas compressor for compressing the fuel gas and supplying the fuel gas to the main engine, So as to control the supply pressure. 8. The fuel cell system according to any one of claims 1 to 7, wherein the gas supply means includes a high-pressure liquid pump which pressurizes the liquefied gas and supplies the liquefied gas as the fuel gas to the main engine, And the supply pressure is controlled by controlling the discharge pressure of the pump. 9. A ship comprising the fuel gas supply system according to any one of claims 1 to 8.

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