JP2018047753A - Ship - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve re-liquefaction ratio of BOG which is returned to a tank through a return line.SOLUTION: A ship comprises: a main gas engine 12; an LNG tank 11; an air feeding line 14 for guiding BOG in the tank to a compressor 15; a first supply line 16 for guiding the BOG discharged from the compressor to the main gas engine; a return line 41 which is branched from the first supply line, connected to the tank, and has an expansion device 42; a sub gas engine 13 for power generation; a liquid feeding line for guiding an LNG from the tank to a compulsion vaporizer; a second supply line 20 for guiding a vaporization gas to the sub gas engine from the compulsion vaporizer 19; a heat exchanger 43 for performing heat exchange between the LNG flowing to the liquid feeding line 18 and the BOG flowing to an upstream side part of the expansion device on the return line; a bypass line 51 whose upstream end is connected to the return line on the upstream side of the heat exchanger, whose downstream end is connected to the return line between the heat exchanger and the expansion device; and an adjustment device for adjusting a flow rate of the BOG flowing to the bypass line.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a ship including a gas engine for propulsion.

  Conventionally, a ship including a tank for storing liquefied natural gas and a propulsion gas engine in which boil-off gas generated in the tank is supplied as fuel gas is known. Such ships include a mechanical propulsion type in which a gas engine directly drives a propeller for propulsion and an electric propulsion type in which a gas engine rotates and drives a propeller for propulsion through a generator and a motor. is there.

  For example, Patent Document 1 discloses a mechanical propulsion type ship 100 as shown in FIG. In this ship 100, the boil-off gas generated in the tank 110 is guided to the MEGI engine (two-stroke engine) by the supply line 120 as fuel gas. The supply line 120 is provided with a multistage compressor 121 that compresses the boil-off gas to a high pressure of 15 to 40 MPa. A branch line 130 branches from the supply line 120 inside the compressor 121, and this branch line 130 is connected to the DF engine. The DF engine is used for propulsion and power generation.

  Further, a return line 140 branches from the supply line 120 on the downstream side of the compressor 121, and the return line 140 is connected to the tank 110. The return line 140 is provided with an expansion valve 141 and a gas-liquid separator 142 in order from the upstream side. The high-pressure and high-temperature boil-off gas returned to the tank 110 through the return line 140 is cooled and at least partially liquefied by the low-pressure and low-temperature boil-off gas flowing in the supply line 120 in the heat exchanger 160, and then the expansion valve 141. Is expanded into a low-pressure and low-temperature gas-liquid two-phase state. The gas-liquid two-phase boil-off gas is separated into a gas component and a liquid component by the gas-liquid separator 142, and only the liquid component is returned to the tank 110. On the other hand, the gas component is led from the gas-liquid separator 142 to the supply line 120 through the recirculation line 150 and merges with the boil-off gas flowing into the heat exchanger 160. Further, in the ship 100 shown in FIG. 7, the boil-off gas cooled by the heat exchanger 160 is additionally cooled by the gas component flowing in the recirculation line 150 by the cooler 170.

Special table 2015-505941 gazette

  The ship 100 shown in FIG. 7 is configured such that the boil-off gas returned to the tank 110 through the return line 140 is cooled by the cold heat of the boil-off gas flowing through the supply line 120 and the recirculation line 150. The present inventors are a ship configured to guide liquefied natural gas in a tank to a forced vaporizer through a liquid feed line, and to guide the vaporized gas generated in the forced vaporizer to a secondary gas engine, the liquid feed line A ship having a structure in which a heat exchanger is provided and the boil-off gas returned to the tank through the return line as shown in FIG. 7 is cooled by the liquefied natural gas flowing through the liquid supply line has been invented.

  By the way, in the ship 100 shown in FIG. 7, the boil-off gas returned to the tank 110 through the return line 140 is cooled only by the cold heat of the boil-off gas flowing through the supply line 120 and the recirculation line 150. Therefore, the reliquefaction rate of the boil-off gas flowing through the return line 140 (the ratio of the reliquefaction amount to the return amount of the boil-off gas) is not so high.

  Then, an object of this invention is to provide the ship which can improve the reliquefaction rate of the boil-off gas returned to a tank through a return line.

  The ship of the present invention includes a main gas engine that rotationally drives a propeller for propulsion, a tank that stores liquefied natural gas, an air supply line that guides boil-off gas generated in the tank to a compressor, and a discharge from the compressor. A first supply line for leading the boil-off gas to the main gas engine, a return line provided with an expansion device branched from the first supply line and connected to the tank, a sub-gas engine for power generation, A liquid feed line that leads liquefied natural gas discharged from a pump disposed in the tank to a forced vaporizer, a second supply line that leads vaporized gas generated in the forced vaporizer to the auxiliary gas engine, and A heat exchanger for exchanging heat between the liquefied natural gas flowing in the liquid feed line and the boil-off gas flowing in the upstream side portion of the expansion device in the return line, and an upstream end A liquefaction led to the forced vaporizer, and a bypass line connected to the return line upstream of the heat exchanger and having a downstream end connected to the return line between the heat exchanger and the expansion device And an adjusting device that adjusts the flow rate of the boil-off gas flowing through the bypass line so that the natural gas is not vaporized.

  According to the above configuration, the high-pressure and high-temperature boil-off gas returned to the tank through the return line is cooled by the heat exchanger by the liquefied natural gas flowing through the liquid supply line. The liquefied natural gas flowing in the liquid supply line has a lower heat than the boil-off gas flowing in the air supply line. For this reason, since the boil-off gas having a lower temperature can be expanded by the expansion device, the reliquefaction rate of the boil-off gas returned to the tank through the return line can be improved.

  By the way, it is desirable to introduce liquefied natural gas which is completely in a liquid state to the forced vaporizer. However, in the configuration in which the liquefied natural gas flowing in the liquid feeding line is heated by the heat exchanger, the liquefied natural gas is partially evaporated by the heat exchanger to be in a gas-liquid two-phase state and led to the forced vaporizer. There is a fear. On the other hand, it is conceivable that a gas-liquid separator is provided in front of the forced vaporizer to guide only the liquid component to the forced vaporizer. However, if the flow rate of the boil-off gas flowing in the bypass line is adjusted so that the liquefied natural gas guided to the forced vaporizer does not vaporize as in the above configuration, the liquid state is completely in a liquid state without using a gas-liquid separator. Liquefied natural gas can be directed to a forced vaporizer.

  The heat exchanger is a first heat exchanger, and the ship exchanges heat between the boil-off gas flowing in the air supply line and the boil-off gas flowing into the first heat exchanger in the return line. You may further provide the 2nd heat exchanger to perform. According to this configuration, the high-pressure and high-temperature boil-off gas returned to the tank through the return line is cooled by the low-pressure and low-temperature boil-off gas flowing in the air supply line in the second heat exchanger, and then the first heat exchanger. It is cooled by liquefied natural gas flowing in the liquid feed line. For this reason, the reliquefaction rate of the boil-off gas returned to the tank through the return line can be improved.

  The ship includes a thermometer for detecting an outlet temperature of the heat exchanger provided in a portion downstream of the heat exchanger in the liquid supply line, and an outlet temperature detected by the thermometer is a target temperature. And a control device for controlling the adjusting device. According to this configuration, the outlet temperature can be maintained at a temperature at which the liquefied natural gas does not vaporize by setting the target temperature within a temperature range in which the liquefied natural gas guided to the forced vaporizer does not vaporize.

  In the ship, the control device adjusts the flow rate of the boil-off gas flowing in the bypass line to increase when the flow rate of the boil-off gas flowing from the first supply line to the return line exceeds a threshold value. The device may be controlled. Since there is a time loss from when the flow rate of boil-off gas flowing into the return line from the first supply line increases until the outlet temperature rises, the adjustment device is controlled based only on the outlet temperature detected by the thermometer. In such a case, there is a concern that the temperature controllability will be reduced. However, according to the above configuration, when the flow rate of the boil-off gas flowing into the return line from the first supply line increases from the threshold value, the flow rate of the boil-off gas flowing through the bypass line increases prior to the rise in the outlet temperature. Thus, since the adjusting device is controlled, an increase in the outlet temperature can be quickly suppressed.

  ADVANTAGE OF THE INVENTION According to this invention, the reliquefaction rate of the boil off gas returned to a tank through a return line can be improved.

1 is a schematic configuration diagram of a ship according to a first embodiment of the present invention. It is a block diagram which shows an example of a functional structure of the control apparatus with which the ship shown in FIG. 1 is provided. It is an example of the characteristic curve which shows the relationship between a return gas flow rate and a correction value. It is a figure which shows the modification of the ship shown in FIG. It is a schematic block diagram of the ship which concerns on 2nd Embodiment of this invention. It is a schematic block diagram of the ship which concerns on 3rd Embodiment of this invention. It is a schematic block diagram of the conventional ship.

(First embodiment)
FIG. 1 shows a ship 1A according to an embodiment of the present invention. The ship 1A includes a tank 11 that stores liquefied natural gas (hereinafter referred to as LNG), a main gas engine 12 for propulsion, and a sub gas engine 13 for power generation (that is, for inboard power).

  In the illustrated example, only one tank 11 is provided, but a plurality of tanks 11 may be provided. In the present embodiment, the ship 1A is an LNG carrier, and the ship 1A is equipped with a plurality of cargo tanks. That is, the tank 11 shown in FIG. 1 is each of a plurality of cargo tanks. In the illustrated example, one main gas engine 12 and one sub gas engine 13 are provided, but a plurality of main gas engines 12 may be provided, or a plurality of sub gas engines 13 may be provided. Good.

  In the present embodiment, the ship 1A is a mechanical propulsion type, and the main gas engine 12 directly rotates and drives a screw propeller (not shown). However, the ship 1A may be an electric propulsion type, and the main gas engine 12 may rotationally drive the screw propeller via a generator and a motor.

  The main gas engine 12 is a diesel cycle type two-stroke engine having a high fuel gas injection pressure of, for example, about 20 to 35 MPa. However, the main gas engine 12 may be an Otto cycle type two-stroke engine having an intermediate pressure of, for example, a fuel gas injection pressure of about 1 to 2 MPa. Alternatively, in the case of electric propulsion, the main gas engine 12 may be an Otto cycle type four-stroke engine having a low fuel gas injection pressure of, for example, about 0.5 to 1 MPa. The main gas engine 12 may be a gas-only combustion engine that burns only fuel gas, or may be a dual fuel engine that burns one or both of fuel gas and fuel oil (binary fuel engine). In this case, the fuel gas may be burned by the Otto cycle, and the fuel oil may be burned by the diesel cycle).

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

  The fuel gas of the main gas engine 12 is mainly boil-off gas (hereinafter referred to as BOG) generated in the tank 11 due to natural heat input, and the fuel gas of the auxiliary gas engine 13 is mainly forced by LNG. The vaporized gas (hereinafter referred to as VG).

  Specifically, the tank 11 is connected to a compressor 15 by an air supply line 14, and the compressor 15 is connected to the main gas engine 12 by a first supply line 16. Further, a pump 17 is provided in the tank 11, and the pump 17 is connected to a forced vaporizer 19 through a liquid feed line 18. The forced vaporizer 19 is connected to the auxiliary gas engine 13 by the second supply line 20.

  The air supply line 14 guides BOG generated in the tank 11 to the compressor 15. In the present embodiment, the compressor 15 is a multistage high-pressure compressor. The compressor 15 compresses the BOG to a high pressure. The first supply line 16 guides the high-pressure BOG discharged from the compressor 15 to the main gas engine 12. However, the compressor 15 may be a low-pressure compressor when the fuel gas injection pressure of the main gas engine 12 is low, for example.

  The liquid supply line 18 guides LNG discharged from the pump 17 to the forced vaporizer 19. The liquid feed line 18 is provided with an adjustment valve 21 whose opening degree can be changed. The forced vaporizer 19 forcibly vaporizes LNG to generate VG. The second supply line 20 guides the VG generated by the forced vaporizer 19 to the auxiliary gas engine 13.

  In the present embodiment, the second supply line 20 is provided with a cooler 22, a gas-liquid separator 23, and a heater 24 in order from the upstream side. The cooler 22 cools the VG generated by the forced vaporizer 19, generates a liquid component whose main component is a component other than methane, and is collected by the gas-liquid separator 23. As a result, most of the heavy components (for example, ethane, propane, butane, etc.) are removed from VG, so that VG having a high methane number can be supplied to sub-gas engine 13. The liquid component collected by the gas-liquid separator 23 is returned to the tank 11 through the drain line. The VG that has passed through the gas-liquid separator 23 is heated by the heater 24. As a result, VG having an appropriate temperature can be supplied to the auxiliary gas engine 13.

  Further, a first bridge line 31 is connected to the air supply line 14 from the second supply line 20. In the present embodiment, the upstream end of the first bridge line 31 is connected to the second supply line 20 between the gas-liquid separator 23 and the heater 24, but the upstream end of the first bridge line 31 is a cooler. The second supply line 20 may be connected to the upstream side of 22, between the cooler 22 and the gas-liquid separator 23, or downstream of the heater 24. The first bridge line 31 guides VG from the second supply line 20 to the air supply line 14 when the BOG is insufficient with respect to the fuel gas consumption Q1 of the main gas engine 12. As a result, BOG and VG are supplied as fuel gas to the main gas engine 12.

  From the middle of the compressor 15, the second bridge line 33 is connected to the second supply line 20. In the present embodiment, the downstream end of the second bridge line 33 is connected to the second supply line 20 on the downstream side of the heater 24, but the downstream end of the second bridge line 33 is on the upstream side of the heater 24. It may be connected to the second supply line 20. The second bridge line 33 guides the BOG from the compressor 15 to the second supply line 20 when the BOG is greater than the fuel gas consumption Q1 of the main gas engine 12. As a result, VG and BOG (in some cases, only BOG) are supplied to the auxiliary gas engine 13 as fuel gas.

  The first bridge line 31 is provided with an adjustment valve 32 capable of changing the opening degree, and the second bridge line 33 is provided with an adjustment valve 34 capable of changing the opening degree. The adjustment valve 32 adjusts the flow rate Q2 of VG flowing through the first bridge line 31. The adjustment valve 34 adjusts the flow rate Q3 of BOG flowing through the second bridge line 33. In the present embodiment, each of the regulating valves 32 and 34 plays a role of opening or closing the bridge line (31 or 33). However, each of the first bridge line 31 and the second bridge line 33 may be provided with an open / close valve separately from the adjustment valve (32 or 34).

  A return line 41 is connected to the tank 11 from the first supply line 16. The tip of the return line 41 may be located above the liquid level of LNG in the tank 11 or may be located below the liquid level. The return line 41 is provided with an expansion device 42 such as an expansion valve.

  A heat exchanger 43 is provided in the return line 41 and the liquid supply line 18. The heat exchanger 43 cools a part or all of the BOG flowing in the return line 41 on the upstream side of the expansion device 42 by LNG flowing in the liquid supply line 18. By being expanded after this cooling, the BOG returned to the tank 11 is partially reliquefied.

  On the upstream side of the expansion device 42 in the return line 41, an opening / closing valve 44 for opening and closing the return line 41 and an adjusting valve 45 capable of changing the opening degree are provided in order from the upstream side. However, one or both of the opening / closing valve 44 and the regulating valve 45 may not be provided in the return line 41.

  Further, the return line 41 is provided with a bypass line 51 that causes the BOG to bypass the heat exchanger 43. The upstream end of the bypass line 51 is connected to the return line 41 between the heat exchanger 43 and the regulating valve 45, and the downstream end of the bypass line 51 is a return line between the heat exchanger 43 and the expansion device 42. 41. However, the upstream end of the bypass line 51 may be connected to the return line 41 upstream of the regulating valve 45. In this case, the bypass line 51 may be provided with one or both of an on-off valve and an adjustment valve whose opening degree can be changed.

  In the present embodiment, a distribution valve 52 is provided at the upstream end of the bypass line 51 as an adjusting device for adjusting the flow rate Qb of the BOG flowing through the bypass line 51. The distribution valve 52 supplies a BOG flow rate (hereinafter referred to as “return gas flow rate”) Qr flowing from the first supply line 16 to the return line 41 to the bypass line 51 and the BOG flow rate Qa flowing to the heat exchanger 43. Distribute to the flow rate Qb (= Qr−Qa) of the flowing BOG.

  The regulating valves 21, 32, 34, 45, the on-off valve 44 and the distribution valve 52 described above are controlled by the control device 6. In FIG. 1, only some signal lines are drawn for the sake of simplicity.

  A pressure gauge 71 provided in the first supply line 16 is connected to the control device 6. The pressure gauge 71 detects the pressure P of the BOG flowing through the first supply line 16. However, the pressure gauge 71 may be provided on the upstream side of the opening / closing valve 44 in the return line 41. The control device 6 controls the on-off valve 44 and the adjustment valve 45 based on the pressure P detected by the pressure gauge 71, for example.

  The controller 6 is connected to a thermometer 72 provided on the downstream side of the heat exchanger 43 in the liquid feeding line 18. The thermometer 72 detects the outlet temperature T of the heat exchanger 43 in the liquid feeding line 18. In the present embodiment, the control device 6 controls the distribution valve 52 based on the outlet temperature T detected by the thermometer 72.

  Below, the control apparatus 6 is demonstrated with reference to FIG. FIG. 2 is a block diagram illustrating an example of a functional configuration of the control device 6. In FIG. 2, only functional blocks related to the control of the distribution valve 52 are shown, and other functional blocks related to the control are omitted.

  As shown in FIG. 2, the control device 6 includes a return gas flow rate acquisition unit 61 and an adjustment device control unit 62 as functional blocks. The control device 6 is, for example, a computer, and includes an arithmetic processing unit such as a CPU, and a storage unit such as a ROM and a RAM (all not shown). Moreover, each functional block with which the control apparatus 6 is provided is realizable when the arithmetic processing part of the control apparatus 6 reads and executes the program stored in the memory | storage part, for example.

  The return gas flow rate acquisition unit 61 acquires the return gas flow rate Qr. In this embodiment, the return gas flow rate Qr is calculated from the pressure P detected by the pressure gauge 71, the opening degree of the adjustment valve 45, and the like. However, the method for obtaining the return gas flow rate Qr is not particularly limited. For example, the return gas flow rate acquisition unit 61 includes the fuel gas consumption Q1 of the main gas engine 12, the flow rate Q2 of VG flowing through the first bridge line 31, the flow rate Q3 of BOG flowing through the second bridge line 33, and the tank 11. The return gas flow rate Qr may be calculated by subtracting the BOG flow rate Q3 and the fuel gas consumption amount Q1 from the BOG generation amount Q4 obtained by adding the BOG generation amount Q4 and the VG flow rate Q2. Alternatively, the return gas flow rate acquisition unit 61 may provide a flow meter in a portion upstream of the distribution valve 52 in the return line 41 and directly acquire the return gas flow rate Qr from the flow meter. The return gas flow rate acquisition unit 61 sends the acquired return gas flow rate Qr to the adjustment device control unit 62.

  The adjustment device control unit 62 controls the distribution valve 52 so that the LNG guided to the forced vaporizer 19 is not vaporized by the heat exchanger 43. Specifically, the adjustment device control unit 62 acquires the outlet temperature T detected by the thermometer 72. Then, the adjusting device control unit 62 performs feedback control (for example, PID) on the distribution valve 52 so that the acquired outlet temperature T becomes a predetermined target temperature Ts in a temperature range where LNG guided to the forced vaporizer 19 is not vaporized. Control, PI control).

Further, in the present embodiment, the adjustment device control unit 62 performs control in which the above feedback control based on the outlet temperature T is combined with the feedforward control based on the return gas flow rate Qr. Regarding this feedforward control, regulator control unit 62, when the return gas flow rate Qr increases the threshold Q _TH, controls the distribution valve 52 to increase the flow rate Qb of the BOG flowing through the bypass line 51.

  Hereinafter, the control of the distribution valve 52 by the adjustment device control unit 62 will be described in more detail. The adjusting device control unit 62 calculates a command value X1 for controlling the distribution valve 52 so that the outlet temperature T becomes the target temperature Ts. The adjusting device control unit 62 adds the correction value X2 acquired based on the return gas flow rate Qr to the calculated command value X1. The adjustment device control unit 62 sends the output command value X3 obtained by adding the correction value X2 to the command value X1 to the distribution valve 52. The larger the output command value X3 sent to the distribution valve 52, the larger the BOG flow Qb flowing in the bypass line 51.

Here, the correction value X2, when the return gas flow rate Qr increases the threshold Q _TH, a value for correcting the command value X1 to increase the flow rate Qb of the BOG flowing through the bypass line 51. That is, when the return gas flow rate Qr increases, the outlet temperature T is predicted to rise. For this reason, the flow rate Qb of the BOG flowing through the bypass line 51 is increased prior to the rise of the outlet temperature T by feedforward correction in which the correction value X2 is added to the command value X1. Thereby, the rise in the outlet temperature T due to the increase in the return gas flow rate Qr can be quickly suppressed.

In the present embodiment, a characteristic curve indicating the relationship between the return gas flow rate Qr and the correction value X2 is stored in the control device 6, and the adjustment device control unit 62 obtains the correction value X2 from this characteristic curve. FIG. 3 shows an example of a characteristic curve showing the relationship between the return gas flow rate Qr and the correction value X2. The adjusting device control unit 62 acquires a correction value X2 corresponding to the return gas flow rate Qr sent from the return gas flow rate acquisition unit 61 from the characteristic curve. In the characteristic curve shown in FIG. 3, when the return gas flow rate Qr is equal to or smaller than the threshold Q _TH, the correction value X2 is maintained at a value alpha. Further, in the characteristic curve shown in FIG. 3, when the return gas flow rate Qr is greater than the threshold value Q _TH, the correction value X2 as return gas flow rate Qr increases increases from the value α to a value beta. Here, the value α may be zero, in this case, until the return gas flow Qr exceeds the threshold Q _TH, a correction value X2 is zero, regulator control unit 62 outputs command of the command value X1 The value X3 is output to the distribution valve 52.

  As described above, in the ship 1 </ b> A of the present embodiment, the high-pressure and high-temperature BOG returned to the tank 11 through the return line 41 is cooled by the heat exchanger 43 by the LNG flowing through the liquid supply line 18. The LNG flowing through the liquid supply line 18 has a lower heat than the BOG flowing through the air supply line 14. For this reason, since the lower temperature BOG can be expanded by the expansion device 42, the reliquefaction rate of the BOG returned to the tank 11 through the return line 41 can be improved.

  By the way, it is desirable to introduce LNG in a completely liquid state to the forced vaporizer 19. However, in the configuration in which the LNG flowing through the liquid feeding line 18 is heated by the heat exchanger 43, the LNG is partially evaporated by the heat exchanger 43 to be in a gas-liquid two-phase state and led to the forced vaporizer 19. There is a fear. On the other hand, it is conceivable that a gas-liquid separator is provided in front of the forced vaporizer 19 to guide only the liquid component to the forced vaporizer 19. However, if the flow rate of BOG flowing through the bypass line 51 is adjusted so that the LNG guided to the forced vaporizer 19 does not vaporize as in the above configuration, the LNG that is completely in a liquid state without using a gas-liquid separator. Can be led to the forced vaporizer 19.

  Further, in the present embodiment, the distribution valve 52 is feedback-controlled so that the outlet temperature T becomes a predetermined target temperature Ts in a temperature range where LNG guided to the forced vaporizer 19 is not vaporized. For this reason, the outlet temperature T can be maintained at a temperature at which LNG does not vaporize.

Further, in the present embodiment, back when the gas flow rate Qr increases the threshold Q _TH, prior to the increase of the outlet temperature T, the dispensing valve 52 is feedforward to increase the flow rate Qb of the BOG flowing through the bypass line 51 Be controlled. For this reason, the rise in the outlet temperature T caused by the increase in the return gas flow rate Qr can be quickly suppressed. Further, in the present embodiment, when the return gas flow rate Qr is equal to or smaller than the threshold Q _TH, even when returning gas flow rate Qr increases, feedforward correction to increase the flow rate Qb of the BOG flowing through the bypass line 51 is not performed . As a result, as much BOG as possible can be allowed to flow through the heat exchanger 43 to be cooled.

(Modification)
The adjusting device for adjusting the flow rate Qb of the BOG flowing through the bypass line 51 is not particularly limited to the distribution valve 52. For example, like the ship 1B shown in FIG. 4, the adjustment device includes an adjustment valve 54 provided in the bypass line 51 and capable of changing the opening degree, a connection point between the bypass line 51 in the return line 41, and the heat exchanger 43. And an adjustment valve 53 that can be changed in opening degree. Further, the adjusting device may be configured by only the adjusting valve 54. Further, in the marine vessel 1B, the return line 41 may not be provided with one or both of the on-off valve 44 and the regulating valve 45.

(Second Embodiment)
Next, with reference to FIG. 5, the ship 1C which concerns on 2nd Embodiment of this invention is demonstrated. In the present embodiment and the third embodiment to be described later, the same components as those in the first embodiment are denoted by the same reference numerals, and redundant description is omitted.

  In the present embodiment, as a configuration for cooling the BOG returned to the tank 11 through the return line 41, in addition to the heat exchanger (hereinafter referred to as “first heat exchanger”) 43, the second heat exchanger is used. 81 is provided.

  The second heat exchanger 81 performs heat exchange between the BOG flowing in the air supply line 14 and the BOG flowing into the first heat exchanger 43 in the return line 41. More specifically, the second heat exchanger 81 is between the BOG flowing in the air supply line 14 and the BOG flowing in the upstream portion from the connection point (that is, the position of the distribution valve 52) between the return line 41 and the bypass line 51. Perform heat exchange at. However, the second heat exchanger 81 flows between the connection point between the BOG flowing in the air supply line 14 and the bypass line 51 in the return line 41 (that is, the position of the distribution valve 52) and the first heat exchanger 43. Heat exchange may be performed with the BOG.

  According to this configuration, the high-pressure and high-temperature BOG returned to the tank 11 through the return line 41 is cooled by the low-pressure and low-temperature BOG flowing in the air supply line 14 in the second heat exchanger 81, and then the first heat It is cooled by LNG flowing in the liquid feeding line 18 by the exchanger 43. For this reason, the reliquefaction rate of BOG returned to the tank 11 through the return line 41 can further be improved.

(Third embodiment)
Next, with reference to FIG. 6, the ship 1D which concerns on 3rd Embodiment of this invention is demonstrated. In the present embodiment, a third heat exchanger 82 is provided in addition to the first heat exchanger 43 as a configuration for cooling the BOG returned to the tank 11 through the return line 41.

  The third heat exchanger 82 exchanges heat between the VG that flows between the gas-liquid separator 23 and the heater 24 in the second supply line 20 and the BOG that flows into the first heat exchanger 43 in the return line 41. I do. More specifically, the third heat exchanger 82 has a connection point between the VG flowing between the gas-liquid separator 23 and the heater 24 in the second supply line 20 and the bypass line 51 in the return line 41 (that is, the distribution valve 52). The heat exchange is performed with the BOG flowing in the upstream portion of the position. However, the third heat exchanger 82 has a connection point between the VG flowing between the gas-liquid separator 23 and the heater 24 in the second supply line 20 and the bypass line 51 in the return line 41 (that is, the position of the distribution valve 52). ) And the BOG flowing between the first heat exchanger 43 may perform heat exchange.

  According to this configuration, the high-pressure and high-temperature BOG returned to the tank 11 through the return line 41 is cooled by the VG flowing in the second supply line 20 in the third heat exchanger 82, and then the first heat exchanger 43. Then, the liquid is cooled by LNG flowing in the liquid feed line 18. For this reason, the reliquefaction rate of BOG returned to the tank 11 through the return line 41 can further be improved.

(Other embodiments)
The present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the gist of the present invention.

  For example, the configurations in FIGS. 4 to 6 can be appropriately combined. For example, the configurations shown in FIGS. 5 and 6 may employ the regulating valves 53 and 54 shown in FIG. 4 instead of the distribution valve 52, and the second heat exchanger 81 and the third heat exchanger. A configuration with two or more of 82 is also possible. Moreover, said ship 1A-1D may further be equipped with the heat exchanger which performs heat exchange between BOG which flows into the air supply line 14, and BOG which flows into the bypass line 51. FIG.

  5 and 6, a plurality of heat exchangers for cooling the BOG are provided separately, but these heat exchangers may be integrally formed. For example, in the ship 1 </ b> C shown in FIG. 5, the first heat exchanger 43 and the second heat exchanger 81 may be integrally formed.

  In the above embodiment, the control device 6 calculates the command value X1 based on the outlet temperature T detected by the thermometer 72. However, in addition to or instead of the outlet temperature T, for example, the first heat exchanger 43 is used. The command value X1 may be calculated based on one or a plurality of other parameters that serve as indicators of the outlet temperature T, such as the inlet temperature T2. In the above embodiment, the control device 6 corrects the calculated command value X1 with the correction value X2 based on the return gas flow rate Qr. However, instead of the return gas flow rate Qr, for example, the return of the adjustment valve 45 or the like is returned. You may correct | amend by one or several another parameter used as the parameter | index of the gas flow rate Qr.

  In the above-described embodiment, the control device 6 performs control in which feedback control based on the outlet temperature T is combined with feedforward control based on the return gas flow rate Qr. However, the control device 6 performs feedback control based on the outlet temperature T. May only do. Even in this case, the control device 6 feedback-controls the distribution valve 52 so that the outlet temperature T becomes the target temperature Ts.

  The characteristic curve showing the relationship between the return gas flow rate Qr and the correction value X2 described in the above embodiment is not limited to the example shown in FIG. 3, and an appropriate characteristic curve is adopted according to the configuration of the heat exchanger 43 and the like. Is done.

  Further, the ships 1A to 1D may not include either or both of the first bridge line 31 and the second bridge line 33. Further, when the auxiliary gas engine 13 is not restricted by the methane number, the cooler 22, the gas-liquid separator 23, and the heater 24 may not be provided in the second supply line 20.

  Further, one or both of the main gas engine 12 and the auxiliary gas engine 13 are not necessarily a reciprocating engine, and may be a gas turbine engine.

1A to 1D Ship 11 Tank 12 Main gas engine 13 Sub gas engine 14 Air supply line 15 Compressor 16 First supply line 17 Pump 18 Liquid supply line 19 Forced vaporizer 20 Second supply line 41 Return line 42 Expansion device 43 Heat exchange (First heat exchanger)
51 Bypass line 52 Distributing valve 53, 54 Regulating valve 6 Control device 71 Pressure gauge 72 Thermometer 81 Second heat exchanger

Claims (4)

A main gas engine that rotationally drives the propeller for propulsion,
A tank for storing liquefied natural gas;
An air supply line for guiding boil-off gas generated in the tank to the compressor;
A first supply line for guiding boil-off gas discharged from the compressor to the main gas engine;
A return line provided with an expansion device, branched from the first supply line and connected to the tank;
A sub-gas engine for power generation,
A liquid feed line for guiding liquefied natural gas discharged from a pump disposed in the tank to a forced vaporizer;
A second supply line that leads the vaporized gas generated in the forced vaporizer to the sub-gas engine;
A heat exchanger for exchanging heat between the liquefied natural gas flowing in the liquid feed line and the boil-off gas flowing in the upstream portion of the return line from the expansion device in the return line;
A bypass line having an upstream end connected to the return line upstream of the heat exchanger and a downstream end connected to the return line between the heat exchanger and the expansion device;
An adjusting device that adjusts the flow rate of the boil-off gas flowing in the bypass line so that the liquefied natural gas guided to the forced vaporizer does not vaporize;
A ship equipped with. The heat exchanger is a first heat exchanger;
The ship further includes a second heat exchanger that exchanges heat between the boil-off gas flowing in the air supply line and the boil-off gas flowing into the first heat exchanger in the return line. The listed ship. A thermometer for detecting an outlet temperature of the heat exchanger, which is provided in a portion downstream of the heat exchanger in the liquid feeding line;
The ship according to claim 1, further comprising a control device that controls the adjusting device so that an outlet temperature detected by the thermometer becomes a target temperature.   The control device controls the adjusting device so that the flow rate of the boil-off gas flowing in the bypass line increases when the flow rate of the boil-off gas flowing from the first supply line into the return line exceeds a threshold value. The ship according to claim 3.

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