KR20180090369A - Ship - Google Patents

Abstract

The ship includes a gas engine, a tank for storing the liquefied natural gas, a supply line for delivering the boil-off gas generated in the tank to the gas engine with the fuel gas, a branch line from the supply line downstream of the compressor, And a transfer valve provided at a portion upstream from the expansion device in the transfer line and capable of changing the opening degree and a heat exchange medium between the boiling off gas flowing between the transfer valve and the expansion device in the transfer line and the heat transfer medium A pressure gauge for detecting the pressure of the boil-off gas flowing between the transfer valve and the expansion device in the transfer line, and a control device for controlling the transfer valve so that the pressure of the boil-off gas detected by the pressure gauge becomes the set pressure do.

Description

Ship

The present invention relates to a ship comprising a gas engine.

Conventionally, there is known a vessel including a tank for storing liquefied natural gas and a gas engine for propulsion in which a boil-off gas generated in the tank is supplied as fuel gas. The boil-off gas is boosted to the pressure range required by the gas engine by the compressor and then supplied to the gas engine. In such a vessel, it is known that when the amount of boil-off gas generated is larger than the amount of fuel gas consumed by the gas engine, the surplus gas is transported to a tank or incinerated by a gas combustion device or the like.

For example, Patent Document 1 discloses a ship 100 that boosts boil-off gas delivered from a tank 110 to a high-pressure gas compressor 120 and supplies the boil-off gas to a gas combustion engine as shown in FIG. The ship 100 has a return line 130 that partially liquefies the compressed gas in the high pressure gas compressor 120 and returns it to the liquefied natural gas inside the tank 110. A flow control valve 131, a heat exchanger 132, an expansion valve 133, and a gas-liquid separator 134 are provided in the return line 130 in this order from the upstream side. The flow control valve 131 adjusts the flow rate of the boil-off gas delivered to the heat exchanger 132 in accordance with the speed of the ship. The boil-off gas compressed in the high-pressure gas compressor 120 passes through the flow control valve 131, is cooled in the heat exchanger 132 to be at least partially liquefied, and expanded in the expansion valve 133. The boil-off gas that has become low in pressure as it expands is separated into a gas component and a liquid component in the gas-liquid separator 134, and only the liquid component is returned to the tank 110 by the transfer pump 135. The gas component joins the boil-off gas led from the tank 110 to the high-pressure gas compressor 120 via the recirculation line 137 with the pressure regulating valve 136 from the gas-liquid separator 134.

Japanese Patent Laid-Open No. 2015-158263

4 is connected to a line where the downstream end of the recirculation line 137 is led from the tank 110 to the high-pressure gas compressor 120. Therefore, when there is a limitation in the capacity of the high-pressure gas compressor 120 due to a large amount of boil-off gas recirculated through the recirculation line 137 without being liquefied in the return line 130, Resulting in an increase in the pressure of the off-gas. Therefore, it is preferable that the re-liquefaction rate of the boil-off gas flowing through the return line 130 (the ratio of the amount of liquefied to the amount of transport of the boil-off gas) is as large as possible.

Accordingly, it is an object of the present invention to provide a vessel capable of improving the re-liquefaction velocity of the boil-off gas carried to the tank through the return line.

In order to solve the above problems, the inventors of the present application have been intensively studied, and as a result, by optimizing the pressure of the boil-off gas on the upstream side of the expansion device such as an expansion valve, The rate is improved. The present invention has been made in view of this.

For this purpose, a ship according to the present invention comprises a gas engine, a tank for storing liquefied natural gas, a supply line for delivering the boil-off gas generated in the tank to the gas engine with a fuel gas and equipped with a compressor, A delivery line which branches from the supply line on the downstream side to the tank and is provided with an expansion device, a delivery valve provided on a part upstream of the expansion device in the delivery line and capable of changing the opening degree, A pressure gauge for detecting the pressure of the boil-off gas flowing between the transfer valve and the expansion device in the transfer line, and a pressure gauge for detecting the pressure of the boil- Off gas so that the pressure of the detected boiling-off gas becomes the set pressure And a control device for controlling the transfer valve.

According to the above arrangement, the control device controls the transfer valve so that the pressure of the boil-off gas flowing between the transfer valve and the expansion device in the transfer line becomes the set pressure, thereby improving the re-liquefaction rate of the boil- .

Wherein the pressure gauge is a first pressure gauge and the vessel further comprises a second pressure gauge for detecting a pressure of the boil-off gas flowing in a portion downstream of the compressor in the supply line, When the pressure of the boil-off gas detected by the pressure gauge exceeds the threshold value, the opening degree of the conveying valve may be increased in priority to the control based on the set pressure. According to this configuration, when the pressure of the boil-off gas detected by the second pressure gauge is too high, the increase of the pressure can be suppressed, and in other cases, the effect of improving the re-liquefaction ratio can be obtained.

In the vessel, the heat exchanger may perform heat exchange between a boil-off gas flowing between the delivery valve and the expansion device in the return line and a boil-off gas flowing in a part upstream of the compressor in the supply line. According to such a configuration, the boil-off gas flowing through the return line can be cooled by using the boil-off gas flowing in the supply line upstream of the compressor.

Wherein the gas engine is a main gas engine and the supply line is a first supply line, the vessel comprising: a sub-gas engine for power generation; and a gas engine for extracting liquefied natural gas from the tank, Off gas flowing between the transfer valve and the expansion device in the transfer line and a boil-off gas flowing between the transfer valve and the expansion device in the second supply line Heat exchange may be performed between the liquefied natural gas. With this arrangement, the boil-off gas flowing through the return line can be cooled by using the liquefied natural gas flowing through the second supply line.

According to the present invention, the re-liquefaction ratio of the boil-off gas carried to the tank through the return line can be improved.

1 is a schematic configuration diagram of a ship according to a first embodiment.
2 is a Mollier diagram of the boil-off gas flowing in the first supply line and the return line in the first embodiment.
3 is a schematic configuration diagram of a ship according to the second embodiment.
4 is a schematic configuration diagram of a conventional ship.

(Embodiment 1)

FIG. 1 shows a ship 1A according to an embodiment of the present invention. This ship 1A is provided with a tank 11 for storing liquefied natural gas (hereinafter referred to as LNG), a main gas engine 12 for propulsion, and a sub gas engine 13 for power generation ).

In the illustrated example, only one tank 11 is provided, but a plurality of tanks 11 may be provided. For example, when the ship 1A is an LNG carrier, a plurality of tanks 11 are mounted on the ship 1A as cargo tanks. Although one main gas engine 12 and one sub gas engine 13 are provided in the example of the drawings, a plurality of main gas engines 12 may be provided, and a plurality of sub gas engines 13 may be installed .

In this embodiment, the ship 1A is a mechanical propulsion type, and the main gas engine 12 rotates the propeller (not shown) directly. However, it is also possible that the ship 1A is of the electric propulsion type and the main gas engine 12 rotates the propeller through an electric motor.

The main gas engine 12 is a diesel cycle type two-stroke engine in which the fuel gas injection pressure is as high as about 20 to 35 MPa. However, the main gas engine 12 may be an autocycle type two-stroke engine having a fuel gas injection pressure of, for example, about 1 to 2 MPa and a medium pressure. Alternatively, in the case of electric propulsion, the main gas engine 12 may be an autocycle type four-stroke engine in which the fuel gas injection pressure is as low as, for example, 0.5 to 1 MPa. Further, the main gas engine 12 may be a gas combustion engine that burns only fuel gas, or a dual fuel engine that burns fuel gas and / or fuel oil (in the case of a dual fuel engine, The cycle may be a diesel cycle when the fuel oil is burned).

The sub-gas engine 13 is an autocycle type four-stroke engine having a low fuel gas injection pressure of, for example, 0.5 to 1 MPa, and is connected to a generator (not shown). The sub gas engine 13 may be a gas combustion engine that burns only fuel gas, or a dual fuel engine that burns fuel gas and / or fuel oil.

A boil-off gas (hereinafter referred to as BOG) generated in the tank 11 by natural heat through the first supply line 14 is introduced into the main gas engine 12 as main fuel gas. The LNG-vaporized gas (hereinafter referred to as VG) extracted from the inside of the tank 11 through the second supply line 15 is delivered to the sub-gas engine 13 as main fuel gas.

The first supply line 14 is provided with a compressor 16 for compressing the BOG delivered from the tank 11 to a high pressure. In the present embodiment, the compressor 16 is a multi-stage high pressure compressor for stepping down the delivered BOG. However, the compressor 16 may also be a low-pressure compressor if the fuel gas injection pressure of the main gas engine 12 is low.

In this embodiment, the compressor 16 is designed to increase the BOG to a supercritical state, i. E., To a pressure higher than the supercritical pressure Pc (the point of intersection of the saturated liquid line L1 and the saturated vapor line L2) Compress. For example, the pressure of the BOG discharged from the compressor 16 is about 20 to 35 MPa, and the temperature is about 45 to 55 ° C.

In the first supply line 14, the conveying line 2 branches at a portion 14b downstream of the compressor 16. The transfer line 2 extends from the branch point 14c of the first supply line 14 and is connected to the tank 11. The tip of the transfer line 2 may be located above the liquid level of the LNG in the tank 11 or below the liquid level.

The transfer line 2 is provided with a transfer valve 21, a heat exchanger 22 and an expansion device 23 in this order from the upstream side. The transfer valve 21 is a pressure control valve that can change its opening degree. The transfer valve 21 may be a flow control valve instead of the pressure control valve. The transfer valve 21 reduces the BOG conveyed to the tank 11 through the transfer line 2. The BOG decompressed by the transport valve 21 flows into the heat exchanger 22. In the present embodiment, the BOG is conveyed through the conveying line 2 by the opening and closing of the conveying valve 21, but the conveying line 2 may be provided with an opening / closing valve separately from the conveying valve 21.

The heat exchanger 22 is connected to the BOG flowing from the first supply line 14 to the upstream portion 14a of the compressor 16 and the BOG flowing between the transfer valve 21 of the transfer line 2 and the expansion device 23. [ Heat exchange is performed between them. The BOG passing through the return line (2) is cooled by the BOG passing through the first supply line (14). The temperature of the BOG flowing from the heat exchanger 22 in the return line 2, that is, the temperature T1 of the BOG in the portion 2c between the heat exchanger 22 and the expansion device 23 of the return line 2, The flow rate and pressure of the BOG passing through the heat exchanger 22 of the transfer line 2, the flow rate and temperature of the BOG flowing into the heat exchanger 22 in the first supply line 14, and the like.

The expansion device 23 inflates the BOG flowing from the heat exchanger 22 along the return line 2. As a result, the BOG of the part downstream of the expansion device 23 in the conveying line 2 becomes a vapor-liquid two-phase state of low pressure and low temperature. Thus, the BOG introduced into the return line in the first supply line 14 is partly liquefied and transported to the tank 11. The expansion device 23 is, for example, an expansion valve or an ejector, an expansion turbine or the like.

A pump 31 is disposed in the tank 11 and a forced vaporizer 32 for forcibly vaporizing the LNG extracted from the pump 31 in the tank 11 is installed in the second supply line 15 have. The forced vaporizer 32 forcibly vaporizes LNG as a heat source, for example, steam generated in a boiler to produce VG. It is preferable that equipment (for example, a cooler and a gas-liquid separator) for removing heavy components such as ethane from the VG is installed on the downstream portion 15b of the second supply line 15 rather than the forced vaporizer 32 Do. Thus, the VG having a high methane content can be supplied to the sub-gas engine 13.

A flow control valve 33 is provided in the second supply line 15 at a portion 15a upstream of the forced vaporizer 32. The flow control valve 33 regulates the amount of evaporative gas generated by the forced vaporizer 32.

From the second supply line 15, a first bridge line 41 is connected to the first supply line 14. The first bridge line 41 is configured such that if the BOG is insufficient for the fuel gas consumption amount Q1 of the main gas engine 12, the first bridge line 41 is supplied from the second supply line 15 to the first branch line 41 from the downstream portion 15b rather than the forced vaporizer 32 And directs the VG to the upstream portion 14a of the compressor 16 in the supply line 14. As a result, BOG and VG are supplied to the main gas engine 12 as fuel gas. The first bridge line 41 is provided with a first control valve 42 that can change its opening degree.

The second bridge line 43 from the middle of the compressor 16 is connected to the downstream portion 15b of the second vaporizer 32 in the second supply line 15. The second bridge line 43 directs the BOG from the compressor 16 to the second supply line 15 when the BOG remains for the fuel gas consumption Q1 of the main gas engine 12. As a result, VG and BOG (and only BOG in some cases) are supplied to the sub-gas engine 13 as fuel gas. The second bridge line (43) is provided with a second adjustment valve (44) capable of opening change.

A first pressure gauge 51 is provided between the expansion device 23 and the transfer valve 21 in the transfer line 2. The first pressure gauge 51 detects the pressure p1 of the BOG between the expansion device 23 and the transfer valve 21 in the transfer line 2. 1, the first pressure gauge 51 is disposed in the portion 2c between the expansion device 23 and the heat exchanger 22 in the transfer line 2, but the present invention is not limited thereto. For example, The pressure gauge 51 may be disposed in the portion 2b between the transfer valve 21 and the heat exchanger 22 in the transfer line 2. [

A second pressure gauge 52 is provided on the upstream side portion 2a of the return line 2 from the transfer valve 21. The second pressure gauge 52 detects the pressure p2 of the BOG of the upstream portion 2a from the carry valve 2 in the carry line 2. The upstream portion 2a of the return line 2 of the return line 2 is communicated with the downstream portion 14b of the first supply line 14 rather than the compressor 16. The pressure p2 of the BOG detected by the second pressure gauge 52 is thus the BOG of the downstream portion 14b of the compressor 16 in the first supply line 14, BOG " The pressure values detected by the first pressure gauge 51 and the second pressure gauge 52 are sent to the control device 5, respectively.

The above-described transfer valve 21, the flow control valve 33, the first regulating valve 42 and the second regulating valve 44 are controlled by the control device 5. [

The control device 5 is provided with a first gas engine controller (not shown) for controlling the fuel gas injection timing of the main gas engine 12 and a second gas engine controller (not shown) for controlling the fuel gas injection timing of the sub- Not shown). For example, the control device 5 calculates the fuel gas consumption amount Q1 of the main gas engine 12 from the signal transmitted from the first gas engine controller, and calculates the fuel gas consumption Q1 of the main gas engine 12 from the signal transmitted from the second gas engine controller, (Q2) of the fuel gas consumed by the fuel cell (13). However, the control device 5 may directly acquire the fuel gas consumption amount Q1 from the first gas engine controller or may directly acquire the fuel gas consumption amount Q2 from the second gas engine controller.

Next, the control when the BOG is transported to the tank 11 through the transport valve 21 will be described.

For example, the control device 5 opens the transfer valve 21 when it satisfies at least one of the following conditions (A) to (D).

(A) When the BOG is not supplied from the second bridge line 43 to the sub-gas engine 13, the use of the BOG calculated from the amount of LNG in the tank 11 and the pressure of the BOG in the tank 11 The possible amount Qa is larger than the fuel gas consumption amount Q1 of the main gas engine 12;

(B) When BOG is supplied from the second bridge line 43 to the sub-gas engine 13, the fuel gas consumption Q1 of the main gas engine 12 and the fuel gas consumption Q2 of the sub-gas engine 13 When the available amount of BOG (Qa) is larger than the total of BOG;

(C) when the pressure of the BOG inside the tank 11 is higher than a predetermined pressure;

(D) When the load of the main gas engine 12 is lower than a predetermined ratio (for example, 70%).

The control device 5 controls the opening degree of the conveying valve 21 so that the pressure p1 of the BOG detected by the first pressure gauge 51 becomes the set pressure Ps while the conveying valve 21 is opened . Here, the set pressure Ps is the flow rate of the BOG passing through the heat exchanger 22 in the return line 2, the flow rate of the BOG passing through the first supply line 14 in the return line 2 so that the refill rate of the BOG passing through the expansion device 23 is increased, The flow rate of the BOG flowing into the heat exchanger 22 and the temperature. In the present embodiment, as shown in Fig. 2, the set pressure Ps is set to a pressure larger than the supercritical pressure Pc. However, the set pressure Ps may be a pressure equal to or less than the supercritical pressure Pc.

The pressure p2 of the downstream portion 14b of the compressor 16 in the first supply line 14 may excessively rise due to, for example, a sudden drop in the load of the main gas engine 12 or the like. In this case, the control device 5 increases the opening degree of the conveying valve 21 in preference to the control based on the set pressure Ps described above. Specifically, the control device 5 increases the opening degree of the conveying valve 21 when the pressure p2 of the BOG detected by the second pressure gage 52 exceeds the threshold value PTH. For example, in relation to the above-described control, when the control start is in the middle of the conveyance control and the conveyance valve 21 starts at the middle opening degree, the control start is before the conveyance control is started and the conveyance valve 21 is fully closed, May be started.

Next, the state change of the BOG flowing through the first supply line 14 and the return line 2 will be described with reference to Figs. 1 and 2. Fig. 2 shows a change in the state of BOG when the BOG is conveyed to the tank 11 through the conveying line 2 without decompression by the conveying valve 21 for the sake of comparison with a one-dot chain line. In Fig. 2, the isotherms LT1 to LT3 of the temperatures T1 to T3 (T1 < T2 < T3) of the BOG are shown by thin solid lines.

First, the BOG in a low-pressure low-temperature saturated state (point A) flows into the heat exchanger 22 from the tank 11 through the first supply line 14 and flows into the heat exchanger 22 in the high- And superheated by exchanging (point A → point B). Thereafter, the BOG is compressed to a supercritical state by the compressor 16 (point B → point C). The BOG flowing into the return line 2 from the first supply line 14 is depressurized to the set pressure Ps by the transport valve 21 and the temperature of the BOG drops from the temperature T3 to the temperature T2 (Point C → point D). Thereafter, the BOG decompressed by the return valve 21 is cooled in the heat exchanger 22, and the temperature of the BOG is lowered from the temperature T2 to the temperature T1 (point D? Point E). Here, the BOG is liquefied by cooling in the heat exchanger 22. The BOG in the liquid state flowing from the heat exchanger 22 becomes a gas-liquid two-phase state of low pressure and low temperature (point E? Point F) as it is expanded in the expansion device 23. 2, the BOG re-liquefaction ratio in the present embodiment is the same as that in the case where BOG is conveyed to the tank 11 through the return line 2 without pressure reduction by the conveying valve 21 → point E '→ point F').

As described above, in the ship 1A according to the present embodiment, the control device 5 determines that the pressure p1 of the BOG flowing between the transfer valve 21 and the expansion device 23 in the transfer line 2 is Since the control valve 21 is controlled so as to achieve the set pressure Ps, it is possible to improve the re-liquefaction rate of BOG after passing through the expansion device 23. [ For example, if the absolute amount of cold heat is the same, the amount of the carrier gas that can be cooled down to the point E is reduced, but the liquefaction rate is increased and the amount of liquefaction is increased.

In the present embodiment, when the controller 5 determines that the pressure p2 of the BOG detected by the second pressure gauge 52 exceeds the threshold value PTH, the opening degree of the transfer valve 21 is increased Therefore, when the pressure p2 rises excessively, the rise of the pressure p2 is suppressed, and in the other cases, the above effect can be obtained.

In the present embodiment, the BOG flowing through the transfer line 2 can be cooled by using the BOG flowing from the first supply line 14 to the upstream portion 14a rather than the compressor 16.

(Second Embodiment)

Next, the ship 1B according to the second embodiment of the present invention will be described with reference to Fig. Here, in the present embodiment, the same components as those in the first embodiment are denoted by the same reference numerals, and redundant description will be omitted.

In this embodiment, BOG flowing between the transport valve 21 and the expansion device 23 in the transport line 2 and LOG 2 flowing in the second supply line 15 are used instead of the heat exchanger 22 shown in Fig. A heat exchanger 24 for exchanging heat is provided. This embodiment is characterized in that a heat exchanger through which the BOG delivered from the tank 11 to the compressor 16 is not installed or a BOG flowing between the transfer valve 21 and the expansion device 23 is cooled Is different from the first embodiment in that the heat transfer medium is LNG. Therefore, the state change of the BOG in this embodiment is different from the state change of the BOG in the first embodiment shown in Fig. Therefore, in the present embodiment, the set pressure Ps, which is different from that of the first embodiment, is appropriately set according to various factors described above such that the re-liquefaction ratio of the BOG passing through the expansion device 23 is increased.

In this embodiment, the same effect as that of the first embodiment can be obtained. Further, in this embodiment, the BOG flowing through the transfer line 2 can be cooled by using the LNG flowing through the second supply line 15.

(Other Embodiments)

The embodiments are to be considered in all respects as illustrative and not restrictive. It is intended that the scope of the invention be indicated by the appended claims rather than by the foregoing description, and that all changes that come within the meaning and range of equivalency of the claims are intended to be embraced therein.

For example, in the above embodiment, when the control device 5 increases the opening degree of the transfer valve 21 when the pressure p2 of the BOG detected by the second pressure gauge 52 exceeds the threshold value PTH It is not limited to this. For example, when the pressure p2 exceeds the threshold value PTH while the pressure p1 of the BOG detected by the first pressure gauge 51 is maintained at the set pressure Ps The BOG of the downstream portion 14b of the compressor 16 in the first supply line 14 may be controlled to escape from the gas combustion device or the like (not shown).

Although the compressor 16 compresses the BOG to a pressure higher than the supercritical pressure Pc in the above embodiment, the present invention is not limited to this. For example, when the fuel gas injection pressure of the main gas engine 12 is a medium pressure The pressure p2 supplied from the compressor 16 to the main gas engine 12 may be smaller than the supercritical pressure Pc in the case of a low pressure (for example, about 1 to 2 MPa or about 0.5 to 1 MPa) .

Further, both of the heat exchanger 22 of the first embodiment and the heat exchanger 24 of the second embodiment may be provided in the return line 2. In this case, the heat exchanger 22 and the heat exchanger 24 may be provided separately on the conveying line 2, or may be integrally provided on the conveying line 2.

The first bridge line 41 may be provided with a pressure reducing valve and a check valve for outputting a constant secondary pressure even if the primary pressure is changed, instead of the first adjusting valve 42. With this configuration, when the pressure of the BOG flowing through the upstream portion 14a of the first supply line 14 is lower than the secondary pressure of the pressure reducing valve, the VG is automatically supplied.

In addition, one or both of the main gas engine 12 and the sub gas engine 13 are not necessarily a reciprocating engine, and may be a gas turbine engine. The gas engine of the present invention may not be a main gas engine for propulsion, but may be, for example, a gas engine for in-line power supply.

The present invention is also applicable to ships that do not have the first bridge line 41 and / or the second bridge line 43. The present invention is also applicable to ships that do not include the secondary gas engine 13 and the second supply line 15 for supplying VG thereto.

1A, 1B: Ship
11: Tank
12: Main gas engine (gas engine)
13: Negative gas engine
14: first supply line (supply line)
15: second supply line
16: Compressor
2: return line
21: Return valve
22, 24: heat exchanger
5: Control device
51: First pressure gauge (pressure gauge)
52: Second manometer

Claims (4)

A gas engine,
A tank for storing liquefied natural gas,
Off gas generated in the tank to the gas engine with a fuel gas, a supply line provided with a compressor,
A return line branched from the supply line on the downstream side of the compressor and connected to the tank,
A transfer valve provided on a part of the transfer line upstream of the expansion device,
A heat exchanger for performing heat exchange between the boil-off gas flowing between the transfer valve and the expansion device and the heat transfer medium in the transfer line,
A pressure gauge for detecting the pressure of the boil-off gas flowing between the transfer valve and the expansion device in the transfer line,
And a control device for controlling the transport valve so that the pressure of the boil-off gas detected by the pressure gauge becomes a set pressure. The method according to claim 1,
Wherein the pressure gauge is a first pressure gauge and the vessel further comprises a second pressure gauge for detecting the pressure of the boil-off gas flowing in the supply line downstream of the compressor,
Wherein when the pressure of the boil-off gas detected by the second pressure gauge exceeds a threshold value, the control device increases the opening degree of the conveying valve in preference to the control based on the set pressure. 3. The method according to claim 1 or 2,
Wherein the heat exchanger performs heat exchange between a boil-off gas flowing between the delivery valve and the expansion device in the return line, and a boil-off gas flowing in a part upstream of the compressor in the supply line. 4. The method according to any one of claims 1 to 3,
Wherein the gas engine is a main gas engine, the supply line is a first supply line,
And a second supply line for extracting the liquefied natural gas from the inside of the tank and delivering the vaporized gas as liquefied natural gas to the sub-gas engine as fuel gas,
Wherein the heat exchanger performs heat exchange between the boil-off gas flowing between the delivery valve and the expansion device and the liquefied natural gas flowing through the second supply line in the return line.

Images