JP2018103955A - Ship - Google Patents

Abstract

PROBLEM TO BE SOLVED: To keep a high re-liquefaction rate of excess gas returned to a tank.SOLUTION: A ship comprises: a main gas engine for propulsion; a tank storing LNG; a compressor including a main flow passage, a plurality of compression mechanisms, a plurality of circulation passages, and a plurality of bypass valves; an air feed line introducing BOG (Boil Off Gas) generated in the tank to the compressor; a supply line introducing the BOG discharged from the compressor to the main gas engine; a return line returning excess gas from the supply line to the tank; at least one heat exchanger cooling the excess gas flowing to the return line; and a control device controlling the plurality of bypass valves. The control device, even if the BOG is not supplied to the main gas engine, when the excess gas is returned to the tank through the return line, controls the bypass valves that are provided in the circulation passages bypassing the final stage compression mechanism so that a discharge pressure of the final stage compression mechanism detected by a pressure gauge becomes a target pressure.SELECTED DRAWING: Figure 1

Description

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

  Conventionally, a ship including a main gas engine for propulsion is known. For example, Patent Document 1 discloses a ship 100 as shown in FIG.

  Specifically, in the ship 100, boil-off gas generated in the tank 110 that stores liquefied natural gas is guided to the compressor 130 by the air supply line 121, and is compressed to high temperature and high pressure by the compressor 130. The boil-off gas discharged from the compressor 130 is guided to the propulsion main gas engine (MEGI engine) through the first supply line 122. In addition, the extracted gas extracted during the compression from the compressor 130 is guided to the sub-gas engine (DF engine) for inboard power by the second supply line 131.

  Further, a return line 140 branches from the first supply line 122, and this return line 140 is connected to the tank 110. The return line 140 plays a role of returning the surplus gas that is not consumed by the main gas engine in the boil-off gas from the first supply line 122 to the tank 110. The return line 140 is provided with an expansion valve 141.

  Excess gas flowing through the return line 140 is cooled by the heat exchanger 150. The heat exchanger 150 performs heat exchange between the surplus gas flowing through the return line 140 and the boil-off gas flowing through the air supply line 121. In this way, since the surplus gas is cooled on the upstream side of the expansion valve 141, the surplus gas that has passed through the expansion valve 141 is partially liquefied.

Special table 2015-505941 gazette

  In the ship 100 shown in FIG. 4, there is room for improvement in the reliquefaction rate of the surplus gas returned to the tank 110 (the ratio of the reliquefaction amount to the surplus gas return amount).

  Accordingly, an object of the present invention is to maintain a high reliquefaction rate of surplus gas returned to the tank.

  In order to solve the above problems, the present invention provides a main gas engine for propulsion, a tank for storing liquefied natural gas, a main flow path extending from the suction port to the discharge port, and a plurality of compression mechanisms arranged in series on the main flow channel. A compressor including a plurality of circulation paths that respectively bypass the plurality of compression mechanisms, and a plurality of bypass valves provided in the plurality of circulation paths, and boil-off gas generated in the tank to the compressor An air supply line that leads, a supply line that guides boil-off gas discharged from the compressor to the main gas engine, a return line provided with an expansion device that returns surplus gas from the supply line to the tank, and the return At least one heat exchanger that cools excess gas flowing in the line, a control device that controls the plurality of bypass valves, and the most downstream of the plurality of compression mechanisms A pressure gauge that detects a discharge pressure of a final stage compression mechanism that is installed, and when the boil-off gas is not supplied to the main gas engine, the control device returns the excess gas to the tank through the return line. In addition, a bypass valve provided in a circulation path that bypasses the final stage compression mechanism among the plurality of bypass valves is controlled so that the discharge pressure of the final stage compression mechanism detected by the pressure gauge becomes a target pressure. Provide a ship.

According to said structure, even when boil-off gas is not supplied to a main gas engine, the pressure of surplus gas is maintained high. Therefore, the reliquefaction rate of the surplus gas returned to the tank can be kept high. The supply line is a first supply line, and the ship is disposed in the tank with a sub-gas engine for ship power. A liquid feed line that leads liquefied natural gas discharged from the pump to the forced vaporizer, and a second supply line that leads the vaporized gas generated by the forced vaporizer to the auxiliary gas engine, One heat exchanger may include a heat exchanger that performs heat exchange between surplus gas flowing in the return line and liquefied natural gas flowing in the liquid supply line. According to this configuration, the fuel gas can be stably supplied to the auxiliary gas engine. In addition, since the surplus gas is cooled using liquefied natural gas at a temperature lower than that of the boil-off gas, the reliquefaction rate of the surplus gas can be improved as compared with the case where the surplus gas is cooled using only the boil-off gas.

  According to the present invention, the reliquefaction rate of the surplus gas returned to the tank can be kept high.

It is a schematic structure figure of a ship concerning one embodiment of the present invention. It is a schematic block diagram of the compressor of the ship shown in FIG. It is a schematic block diagram of the ship of a modification. It is a schematic block diagram of the conventional ship.

  FIG. 1 shows a ship 1 according to an embodiment of the present invention. The ship 1 includes a tank 11 that stores liquefied natural gas (hereinafter referred to as LNG), a main gas engine 13 for propulsion, and a sub gas engine 16 for inboard power.

  In the illustrated example, only one tank 11 is provided, but a plurality of tanks 11 may be provided (for example, the ship 1 may be an LNG carrier). In the illustrated example, one main gas engine 13 and one sub gas engine 16 are provided, but a plurality of main gas engines 13 or a plurality of sub gas engines 16 may be provided.

  The main gas engine 13 may directly rotate and drive a screw propeller (not shown) (mechanical propulsion), or may indirectly rotate and drive the screw propeller via a generator and a motor (electricity). Promotion).

  In the present embodiment, the main gas engine 13 is a reciprocating engine having a high fuel gas injection pressure. The main gas engine 13 may be a gas 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 (for example, a MEGI engine). However, the main gas engine 13 may be a reciprocating engine whose fuel gas injection pressure is medium or low. Alternatively, the main gas engine 13 may be a gas turbine engine.

  The auxiliary gas engine 16 is a reciprocating engine having a low fuel gas injection pressure, and is connected to a generator (not shown). The auxiliary gas engine 16 may be a gas 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.

  The main gas engine 13 is mainly supplied with boil-off gas (hereinafter referred to as “BOG”) generated in the tank 11 by natural heat input as fuel gas, and the sub-gas engine 16 is forced to be LNG as fuel gas. Vaporized gas (hereinafter referred to as VG) is mainly supplied.

  Specifically, the tank 11 is connected to the compressor 12 by an air supply line 21, and the compressor 12 is connected to the main gas engine 13 by a first supply line 22. Further, a pump 14 is disposed in the tank 11, and the pump 14 is connected to the forced vaporizer 15 by a liquid feed line 31. The forced vaporizer 15 is connected to the auxiliary gas engine 16 by the second supply line 32.

  The air supply line 21 guides BOG generated in the tank 11 to the compressor 12. The compressor 12 compresses the BOG to a high pressure. The first supply line 22 guides BOG discharged from the compressor 12 to the main gas engine 13. The compressor 12 will be described in detail later.

  A return line 23 branches from the first supply line 22, and this return line 23 is connected to the tank 11. The return line 23 plays a role of returning surplus gas (hereinafter referred to as EG), which is not consumed by the main gas engine 13 in the BOG, from the first supply line 22 to the tank 11. An expansion device 24 is provided in the return line 23. The expansion device 24 is, for example, an expansion valve, an expansion turbine, or an ejector.

  The liquid feed line 31 guides LNG discharged from the pump 14 to the forced vaporizer 15. The forced vaporizer 15 forcibly vaporizes LNG to generate VG. The second supply line 32 guides the VG generated by the forced vaporizer 15 to the auxiliary gas engine 16. The pump 14 discharges LNG such that the pressure of VG generated by the forced vaporizer 15 (that is, the outlet pressure of the forced vaporizer 15) is higher than the fuel gas injection pressure of the sub gas engine 16. However, a compressor may be provided in the second supply line 32, and the compressor may make the pressure of VG higher than the fuel gas injection pressure of the auxiliary gas engine 16 instead of the pump 14.

  The second supply line 32 is provided with a cooler 33, a gas-liquid separator 34, and a heater 35 in order from the upstream side. The cooler 33 cools the VG generated by the forced vaporizer 15. Most of heavy components in VG (for example, ethane, propane, butane, etc.) become liquid by cooling in the cooler 33, removed by the gas-liquid separator 34, and returned to the tank 11. As a result, VG having a high methane number is supplied to the auxiliary gas engine 16. The heater 35 heats the VG that has passed through the gas-liquid separator 34 to a temperature suitable for supply to the auxiliary gas engine 16.

  Further, in the present embodiment, three heat exchangers (first heat exchanger 51, second heat exchanger 52, and third heat exchanger 53) for cooling the EG flowing through the return line 23 are provided. . In the illustrated example, the first to third heat exchangers 51 to 53 are separate, but any two or all of the first to third heat exchangers 51 to 53 are integrated. Also good.

  The return line 23 passes through the first heat exchanger 51, the second heat exchanger 52, and the third heat exchanger 53 in this order on the upstream side of the expansion device 24. The air supply line 21 passes through the second heat exchanger 52, the liquid supply line 31 passes through the third heat exchanger 53, and the second supply line 32 is between the gas-liquid separator 34 and the heater 35. Passes through the first heat exchanger 51. That is, the first heat exchanger 51 uses VG as a cold heat source, the second heat exchanger 52 uses BOG as a cold heat source, and the third heat exchanger 53 uses LNG as a cold heat source. The EG flowing in the return line 23 is partially liquefied by being expanded by the expansion device 24 after being cooled by the first to third heat exchangers 51 to 53.

  The compressor 12 described above is connected to the second supply line 32 by the extraction line 43. The extraction line 43 introduces the extracted gas (BG) extracted during compression from the compressor 12 to the second supply line 32 on the downstream side of the heater 35. The extraction line 43 is provided with a flow rate control valve 44.

  The second supply line 32 is connected to the air supply line 21 by a supply line 41. The replenishment line 41 branches from the second supply line 32 between the gas-liquid separator 34 and the first heat exchanger 51 and joins the air supply line 21 on the downstream side of the second heat exchanger 52. However, the replenishment line 41 may branch from the second supply line 32 between the cooler 33 and the gas-liquid separator 34. A flow control valve 42 is provided in the supply line 41.

  The expansion device 24 and the flow rate control valves 42 and 44 described above are controlled by the control device 6. However, in FIG. 1, only a part of the signal lines is drawn for simplification of the drawing. For example, the control device 6 has a memory such as a ROM and a RAM and a CPU, and a program stored in the ROM is executed by the CPU. The control device 6 may be a single device or may be divided into a plurality of devices.

  The control device 6 is electrically connected to a pressure gauge 61 provided on the air supply line 21 and a pressure gauge 62 provided on the first supply line 22. The pressure gauge 61 detects the pressure of the BOG in the air supply line 21, and the pressure gauge 62 detects the pressure of the BOG in the first supply line 22.

  The control device 6 calculates an available amount Qa of BOG based on the amount of LNG in the tank 11 and the pressure of BOG detected by the pressure gauge 61. Specifically, the control device 6 adds the pressure loss from the intake port that is the upstream end of the air supply line 21 to the position of the pressure gauge 61 to the pressure of the BOG detected by the pressure gauge 61, and the tank 11. The pressure of the BOG inside is calculated. However, the pressure gauge 61 may be provided in the tank 11 and directly detect the pressure of the BOG in the tank 11. Then, the control device 6 calculates the usable amount Qa of BOG from the amount of LNG in the tank 11 and the pressure of BOG in the tank 11. For example, when the tank 11 is a cargo tank and the capacity of the tank 11 is very large, the amount of LNG in the tank 11 can be handled as a fixed value. On the other hand, when the capacity of the tank 11 is small, a level meter that detects the amount of LNG in the tank 11 may be provided in the tank 11, and the amount of LNG in the tank 11 may be treated as a variable.

  After calculating the usable amount Qa of BOG, the control device 6 compares the fuel gas consumption amount Q1 of the main gas engine 13 with the usable amount Qa of BOG. The control device 6 opens the flow control valve 42 provided in the supply line 41 when Qa <Q1, and opens the flow control valve 44 provided in the extraction line 43 when Qa> Q1. In the case of Qa> Q1, the control device 6 determines the available amount Qa of BOG as the sum of the fuel gas consumption amount Q1 of the main gas engine 13 and the fuel gas consumption amount Q2 of the auxiliary gas engine 17. When Qa> Qt as compared with the consumption Qt, the operation of the forced vaporizer 15 is stopped (the LNG discharged from the pump 14 is returned to the tank 11 through a return line not shown), and the flow rate control valve 42 is turned on. It may be fully closed.

  Further, the control device 6 opens the expansion device 24 when the pressure of the BOG in the first supply line 22 detected by the pressure gauge 62 exceeds the upper limit value. As a result, the EG is returned to the tank 11 through the return line 23.

  Next, the compressor 12 will be described in detail with reference to FIG.

  The compressor 12 includes a main flow path 7 extending from the suction port 12 a to the discharge port 12 b and five compression mechanisms 71 to 75 arranged in series on the main flow path 7. However, the number of compression mechanisms may be 2 to 4, or 6 or more.

  Furthermore, the compressor 12 includes five circulation paths 81 to 85 that respectively bypass the compression mechanisms 71 to 75 and five bypass valves 91 to 95 provided in the circulation paths 81 to 85, respectively. For this reason, the BOG discharged from each of the compression mechanisms 71 to 75 can be returned to the suction side of the compression mechanism and circulated. That is, each of the bypass valves 91 to 95 defines the circulation amount of the corresponding compression mechanism (71 to 75).

  In the main flow path 7, pressure gauges 63 to 67 are provided on the discharge side of the compression mechanisms 71 to 75, respectively. Each of the pressure gauges 63 to 67 detects the discharge pressure of the corresponding compression mechanism (71 to 75). For example, the pressure gauge 67 detects the discharge pressure of the final stage compression mechanism 75 located on the most downstream side of the compression mechanisms 71 to 75. The control device 6 described above is electrically connected to these pressure gauges 63 to 67. In the normal operation in which BOG is supplied to the main gas engine 13, the control device 6 bypasses the valves 91 to 95 so that each of the discharge pressures of the compression mechanisms 71 to 75 detected by the pressure gauges 63 to 67 becomes the target pressure. To control.

  Further, even when BOG is not supplied to the main gas engine 13, the control device 6 detects when the pressure of the BOG in the tank 11 detected indirectly by the pressure gauge 61 exceeds the upper limit value or by the pressure gauge 62. When the pressure of the BOG in the first supply line 22 exceeds the upper limit value, the expansion device 24 is opened. As a result, the EG is returned to the tank 11 through the return line 23. Before the pressure of the BOG in the tank 11 or the pressure of the BOG in the first supply line 22 exceeds the upper limit value, the compressor 12 may be operating or may not be operating.

  Then, even when BOG is not supplied to the main gas engine 13, the control device 6 performs compression detected by the pressure gauges 63 to 67 when the EG is returned to the tank 11 through the return line 23, as in normal operation. The bypass valves 91 to 95 are controlled so that each of the discharge pressures of the mechanisms 71 to 75 becomes a target pressure.

  By such control, even when BOG is not supplied to the main gas engine 13, the pressure of the EG is maintained high. Therefore, the liquefaction rate of the EG returned to the tank 11 can be kept high.

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

  For example, any one or two of the first to third heat exchangers 51 to 53 may be omitted. Further, as shown in FIG. 3, the liquid supply line 31, the forced vaporizer 15, the second supply line 32, and the auxiliary gas engine 16 may be omitted.

  However, if the liquid feed line 31, the forced vaporizer 15, the second supply line 32, and the auxiliary gas engine 16 are provided as in the above embodiment, the fuel gas is stably supplied to the auxiliary gas engine 16. Can do. Moreover, if at least the third heat exchanger 53 is provided in the configuration, the EG is cooled using LNG having a temperature lower than that of the BOG, so that the EG is cooled more than when the EG is cooled using only the BOG. The reliquefaction rate can be improved.

  Also, one of the pressure gauge 62 provided in the first supply line 22 and the pressure gauge 67 for detecting the discharge pressure of the final stage compression mechanism 75 of the compressor 12 is omitted, and the other is controlled and bypassed by the expansion device 24. It may be used in common with the control of the valve 95.

DESCRIPTION OF SYMBOLS 1 Ship 11 Tank 12 Compressor 12a Suction port 12b Discharge port 13 Main gas engine 14 Pump 15 Forced vaporizer 16 Sub gas engine 21 Air supply line 22 First supply line 23 Return line 24 Expansion device 31 Liquid supply line 32 Second supply Lines 51-53 Heat exchanger 6 Control device 63-67 Pressure gauge 7 Main flow path 71-75 Compression mechanism 81-85 Circulation path 91-95 Bypass valve

Claims (2)

A main gas engine for propulsion,
A tank for storing liquefied natural gas;
A main flow path extending from the suction port to the discharge port, a plurality of compression mechanisms arranged in series on the main flow path, a plurality of circulation paths that respectively bypass the plurality of compression mechanisms, and a plurality of bypasses respectively provided in the plurality of circulation paths A compressor including a valve,
An air supply line for guiding boil-off gas generated in the tank to the compressor;
A supply line for guiding boil-off gas discharged from the compressor to the main gas engine;
A return line provided with an expansion device for returning surplus gas from the supply line to the tank;
At least one heat exchanger for cooling excess gas flowing into the return line;
A control device for controlling the plurality of bypass valves;
A pressure gauge for detecting the discharge pressure of the final stage compression mechanism located at the most downstream among the plurality of compression mechanisms,
The controller controls the discharge pressure of the final stage compression mechanism detected by the pressure gauge when the surplus gas is returned to the tank through the return line even when boil-off gas is not supplied to the main gas engine. The ship which controls the bypass valve provided in the circulation path which bypasses the said last stage compression mechanism among these bypass valves so that it may become. The supply line is a first supply line;
A sub-gas engine for inboard power,
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 for guiding the vaporized gas generated in the forced vaporizer to the auxiliary gas engine,
The marine vessel according to claim 1, wherein the at least one heat exchanger includes a heat exchanger that exchanges heat between surplus gas flowing through the return line and liquefied natural gas flowing through the liquid supply line.

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