JP4073445B2 - Evaporative gas supply system for liquefied natural gas carrier - Google Patents

Description

  The present invention naturally occurs from liquefied natural gas stored in a tank in a liquefied natural gas carrier ship (also referred to as LNG tanker) that carries a liquefied natural gas (hereinafter also referred to as LNG) by mounting a tank. The evaporative gas is supplied to a main propulsion engine such as a gas engine that uses evaporative gas (hereinafter also referred to as BOG) as a main component of methane, and the liquefied natural gas evaporates when the evaporative gas is insufficient. The present invention relates to an evaporative gas supply system that can use evaporative gas that is forcibly evaporated by a vessel as fuel.

  BOG is naturally generated from the LNG stored in the tank. For this reason, conventionally, BOG is supplied to a steam boiler for combustion, steam is generated, and the steam is supplied to the main engine of the steam turbine to navigate an LNG carrier. However, since a steam turbine uses BOG once converted into steam, fuel efficiency is low. Therefore, an LNG carrier equipped with a gas engine that can directly use BOG as fuel has been developed. That is, a gas engine such as a gas-fired diesel engine or a gas turbine engine is used as the main propulsion engine.

  By the way, when the main propulsion engine is a steam turbine, the pressure of the BOG supplied to the steam boiler is about 2 barA, and it is sufficient to pressurize about 1 bar. A compressor for BOG pressurization is exclusively a single stage compression stroke. A centrifugal compressor is used. Centrifugal compressors can supply BOG continuously to steam boilers, and the flow rate and discharge pressure can be controlled relatively easily by the rotation speed and vane operation at the inlet and outlet. It is used for the LNG carrier equipped.

  As a prior art, a facility for supplying BOG to a power generation system of an LNG tanker, which is driven by a motor, and the inlet performs suction on the liquid level in the tank, and the outlet discharges into the supply manifold of the power generation system. A return pipe having a compressor and a submerged pump connected by a pipe to the evaporator inlet at the bottom of the tank, the evaporator outlet being connected to the manifold, returning the liquid to the tank and equipped with a regulating valve; A structure in which a submerged pump is connected to a pipe that connects to an evaporator has been proposed. This equipment is particularly intended to reduce the power of the compressor (see, for example, Patent Document 1).

Further, as shown in FIG. 7, BOG naturally generated from the LNG stored in the two tanks 53 is cooled by the LNG spray cooler 55 and then supplied to the two-stage centrifugal compressor 54 for pressurization. An evaporative gas supply system 51 that adjusts the temperature required by the diesel engine 52 with a steam heater 56 and a seawater-use cooler 57 and supplies BOG to the four diesel engines 52 has been proposed (for example, non-patented). Reference 1). FIG. 8 shows a more basic system diagram of the evaporative gas supply system of FIG. 7. As shown in FIG. 8, the BOG of the pipe 60 for supplying BOG naturally generated from the tank 53 to the BOG compressor 54 is shown. A BOG cooler 57 is interposed on the upstream side of the compressor 54. The LNG stored in the tank 53 is pumped up by the spray pump 58 and supplied to the forced evaporator 56 and the BOG cooler 57, and a part of the flow rate is adjusted. A BOG supply system configured to be able to return to the tank 53 via the return line 61 can be considered. The LNG is sprayed into the BOG in the BOG cooler 57 to cool the BOG and the BOG evaporated by the forced evaporator 59 and supply the BOG to the BOG compressor 54. Since the other configuration is common to the supply system 51 of FIG. 7, the description thereof is omitted, and common constituent members are denoted by the same reference numerals.
JP-A-2004-36608 (2 pages, 4-5 pages and FIG. 1) Alstorm, France 2005 GASTECH (published March 2005, system diagram)

  By the way, in the state where BOG has just been generated naturally from LNG in the tank, it is extremely low temperature (around −150 to −130 ° C.) as LNG, but this BOG is sucked through the gas supply pipe and compressed by BOG When reaching the machine, it is heated by the intrusion heat from the surroundings into the gas supply pipe, and the temperature rises to approximately −120 to −80 ° C. depending on the flow rate of BOG. However, when the temperature rises in this way, the power necessary for the compressor to pressurize and feed a certain mass of gas to a certain discharge pressure also increases, so the BOG temperature at the inlet of the BOG compressor is The lowest possible is desirable.

  When the main propulsion engine is a gas engine other than the turbine described above, it is necessary to increase the pressure of the BOG to about 5 to 7 barA before the main propulsion engine (upstream side). However, there is room for improvement in the following points when trying to pressurize to about 5-7 barA using a centrifugal compressor.

  -The BOG pressure required by the main propulsion engine is higher than that of conventional general steam turbines, and the compression ratio (discharge pressure) of the compressor is high, so the BOG temperature at the discharge port is higher than before, It may exceed the range where safe operation of the compressor is possible. In order to avoid this, it is necessary to provide a gas cooling device on the inlet side of the compression stroke of each stage of the multistage compressor to keep the BOG temperature at the inlet as low as possible. However, the temperature of the gas handled is extremely low. It is difficult to obtain a cryogenic refrigerant other than LNG on the ship for cooling the BOG.

  When the temperature of the BOG at the compressor inlet rises, the gas specific gravity decreases, the gas volume expands and increases, and the power required for the compressor increases while the discharge pressure tends to decrease. In order to avoid this, the discharge pressure is adjusted to be constant at the vane opening of the compressor. However, if the difference from the design point increases, the flow control range becomes narrower, and in some cases, the constant discharge required by the gas engine. Operation may become impossible due to pressure.

  Therefore, as a solution for solving the above problems, as shown in FIG. 8, LNG was used as a refrigerant for cooling the BOG and lowering the temperature on the inlet side of the centrifugal compressor 54. It is conceivable to provide a cooler 53. However, this type of cooler 53 has a structure in which LNG is sprayed into the BOG in the sealed cooler body, and the BOG is cooled by the latent heat of vaporization when the droplets evaporate. There is a problem.

  ・ If the set temperature for cooling is lowered, the heavy components (ethane, propane, butane, etc.) in the LNG after spraying hardly evaporate and accumulate in the cooler as so-called drain. Processing work and processing equipment for it are required.

  ・ When LNG (natural gas) gasified when sprayed is mixed into the BOG, the mass (flow rate) of the BOG changes, so both the temperature and mass (flow rate) of the BOG at the outlet side of the cooler Complex control is required.

  ・ Because the temperature difference between the gas to be cooled (BOG) and the LNG to be cooled is small, the cooling efficiency by spraying is poor, and a considerable amount of droplets after spraying do not evaporate and BOG There is a risk of contamination. For this reason, if BOG mixed with LNG droplets is sucked into the compressor, the compressor may be adversely affected.

  The present invention has been made in view of the above points, and can solve the problems described in the following 1) to 5), in a liquefied natural gas carrier ship, in a gas engine using BOG mainly composed of methane as fuel. The evaporative gas supply system of the liquefied natural gas carrier ship which supplies

  1) The BOG temperature at the entrance of each compression stroke of the BOG compressor for increasing the discharge pressure to around 5-7 barA is made as low as possible by the cold heat of LNG to increase the density, and the volume flow rate of BOG flowing into the compressor is reduced. Thus, the volume of the compressor can be reduced and a predetermined discharge pressure can be easily secured.

  2) By passing the BOG through a heat exchanger using LNG as the refrigerant and keeping the inlet BOG of each compression stroke at a constant low temperature regardless of the flow rate, the gas density can also be kept high, and the discharge pressure The discharge pressure can be easily controlled over a wide flow range of BOG.

  3) The BOG temperature at the exit of each compression stroke can be kept low enough to enter the operating range of the compressor, and troubles such as trips can be avoided.

  4) By performing heat exchange between LNG and BOG in a liquid-to-gas state and in a non-contact manner, there is no risk of accumulation of heavy components such as spray cooling, and there are no LNG droplets. There is no risk of being carried to the compressor.

  5) To save the heat source necessary for heating and evaporation of LNG when the LNG stored in the tank is forcibly evaporated by the evaporator to generate BOG, and the BOG generated in the tank alone is insufficient as fuel. Can do.

In order to solve the above problems, the evaporative gas supply system for a liquefied natural gas carrier according to the present invention mainly uses methane, which is naturally generated from liquefied natural gas stored in a tank mounted on the liquefied natural gas carrier. Forced generation evaporation in which the naturally occurring evaporation gas is supplied to a main propulsion engine that uses natural evaporation gas as a fuel as a fuel, and the liquefied natural gas is forcibly evaporated when the naturally occurring evaporation gas is insufficient In an evaporative gas supply system that uses gas as fuel , a forced evaporative gas supply system that supplies the forced evaporative gas from a forced evaporator to an evaporative gas supply pipe that supplies the naturally generated evaporative gas from the tank. Connecting the piping, the naturally occurring evaporative gas, or the naturally occurring evaporative gas and the forced evaporative gas, Other supplies to the compressor for pressurizing to feeding the spontaneous evaporation gas and the forced generation evaporative gas as fuel to the main propulsion engines, the spontaneous evaporation gas to the vapor supply pipe or the spontaneous, A heat exchanger for cooling the evaporative gas and the forcibly generated evaporative gas is interposed, the evaporative gas supply pipe is branched near the entrance of the heat exchanger, a bypass line is provided, and one end of the bypass line is connected to the heat exchanger. It is connected to a pipe connecting the outlet side of the heat exchanger and the inlet side of the compressor, and the temperature of the naturally occurring evaporative gas or the naturally occurring evaporative gas and the forced evaporative gas is adjusted to the bypass line. By using liquefied natural gas pumped from the tank by a pump device as a refrigerant for the heat exchanger, Raw evaporative gas or After cooling the spontaneous evaporation gas and the forced generation evaporated gas to a predetermined temperature, characterized in that to guide the liquefied natural gas to force the evaporator.

According to the evaporative gas supply system having the above configuration, the LNG stored in the tank is used for cooling the BOG before being pressurized by a compressor (for example, a centrifugal type) before being led to the forced evaporator. LNG is heated by intrusion heat while passing through the pipe, and is also heated by heat exchange with BOG. As a result, the amount of heat required for evaporating LNG with a forced evaporator is reduced, and the amount of steam used is saved correspondingly. Moreover, since the cooled BOG is introduced into the compressor and pressurized, the power of the compressor can be saved and the temperature of the BOG discharged from each stage outlet (particularly the second stage) of the compressor can be lowered. The trip of the compressor can be avoided and the operation becomes easy.

3. The compressor according to claim 2, wherein the compressor is a multi-stage compressor that performs a multi-stage compression stroke, and the heat exchanger is provided at least at one position between the inlet of the first-stage compressor and the multi-stage compressor. ,
By using the liquefied natural gas as a refrigerant for the heat exchanger, the naturally occurring evaporative gas or the naturally occurring evaporative gas and the forced evaporative gas are cooled to a predetermined temperature, and then the most downstream heat exchanger. The liquefied natural gas that has passed through can be guided to the forced evaporator.

  In this way, when the BOG is pressurized to, for example, about 5 to 7 barA by a centrifugal compressor, a multi-stage compressor is used and a heat exchanger is also provided at the compressor inlet of each stage to sufficiently cool the efficiency. It is possible to pressurize BOG well to a predetermined pressure.

The evaporative gas supply system of the liquefied natural gas carrier ship according to claim 3 is a naturally generated evaporative gas mainly composed of methane, which is naturally generated from the liquefied natural gas stored in a tank mounted on the liquefied natural gas carrier ship. Evaporation using forcibly generated evaporative gas, which is obtained by forcibly evaporating the liquefied natural gas when the naturally generated evaporative gas is in short supply, to the main propulsion engine that uses In the gas supply system, the forced generation evaporative gas supply pipe for supplying the forced generation evaporative gas from the forced evaporator is connected to the evaporative gas supply pipe for supplying the naturally generated evaporative gas from the tank, The naturally occurring evaporative gas, or the naturally occurring evaporative gas and the forced evaporative gas, are converted into the naturally occurring evaporative gas or the naturally occurring evaporative gas. And supplying the force generated vapor to the pressurizing compressor to feed the fuel to the main propulsion engines, the spontaneous evaporation gas to the vapor supply pipe or the spontaneous evaporation gas and the forced generation evaporated, A heat exchanger for gas cooling is interposed, and the compressor is composed of a multistage compressor that performs a multistage compression stroke, and the heat is provided at least at one position between the inlet of the first stage compressor and the multistage compressor. By providing a heat exchanger as a single plate-fin type heat exchanger and using liquefied natural gas pumped from the tank by a pump device as a refrigerant for the heat exchanger The naturally occurring evaporative gas, or the naturally occurring evaporative gas and the forced evaporative gas are cooled to a predetermined temperature, and then liquefied through the heat exchanger at the most downstream position. Characterized in that the gas was guided to the forced evaporator.

Thus, it drains unlike the case where it is possible to cool the BOG due to LNG in a liquid state body gas and without contact, cool by spraying with LNG directly into BOG as in the prior art It does not occur, and the processing and equipment necessary for the processing are not required, and the LNG droplet does not enter the compressor and adversely affect the operation.

  According to claim 4, there is provided a circulation pipe for branching a pipe that leads the liquefied natural gas used as a refrigerant in the heat exchanger to the forced evaporator and returning it to the tank, and a branch position of the pipe A switching valve can be interposed upstream.

  In this way, when the main propulsion engine has a low load and the amount of gas required as fuel is less than the amount of naturally occurring evaporative gas in the tank, there is no need to forcibly evaporate LNG. LNG after being used as a refrigerant for BOG can be returned to the tank. Since the LNG returned to the tank is heated and the temperature rises, as a result, the amount of BOG naturally generated from the LNG increases.

  The evaporative gas supply system for a liquefied natural gas carrier according to the present invention has the following excellent effects. That is, the LNG stored in the tank can be cooled to a temperature required for the BOG centrifugal compressor, and the BOG can be pressurized safely and efficiently by the compressor, and the fuel of the main propulsion engine can be naturally When the generated BOG alone is insufficient, the amount of steam for heating when the LNG is forcibly evaporated by the evaporator can be saved, and the LNG carrier can be navigated economically.

  Embodiments of an evaporative gas supply system for a liquefied natural gas carrier according to the present invention will be described below with reference to the drawings.

  FIG. 1 is a system diagram showing the most basic first embodiment of the evaporative gas supply system of the present invention. As shown in FIG. 1, the BOG supply system 1 of the present embodiment includes a DFD (gas-fired diesel engine) 2 as a gas engine in the engine room of an LNG carrier, and an LNG tank 3 having a heat insulating structure is mounted on the cargo section. ing. A centrifugal compressor 4 is installed in the cargo portion, and an upper end portion of the tank 3 and an inlet of the centrifugal compressor 4 are connected by a BOG supply pipe 11. Further, the centrifugal compressor 4 and the gas engine 2 are connected by a BOG supply pipe 12. A shell and tube type BOG cooler (heat exchanger) 7 is interposed in the pipe 11 to the centrifugal compressor 4. The BOG cooler 7 uses LNG stored in the tank 3 as a refrigerant, for example, by flowing it to the tube side, and cools the BOG flowing through the shell side. Further, in order to easily control the discharge pressure at the outlet of the compressor 4, the pipe 11 is branched near the inlet of the BOG cooler 7 so that the gas temperature at the inlet of the BOG compressor 4 can be kept constant. The bypass line 13 connected to the outlet of the BOG cooler 7, in other words, near the inlet of the BOG compressor 4 is connected to the pipe 11. Further, the bypass line 13 is provided with a bypass valve 8 for adjusting the temperature of the BOG.

  Further, a spray pump 6 is disposed near the bottom of the tank 3, one end of the LNG supply pipe 14 is connected to the discharge port of the spray pump 6, and the other end is connected to the refrigerant inlet of the BOG cooler 7. . One end of the LNG supply pipe 15 is connected to the refrigerant outlet of the BOG cooler 7, and the other end is connected to the inlet of the forced evaporator 5. One end of a forced BOG supply pipe 16 is connected to the outlet of the forced evaporator 5, and the other end is connected to the pipe 11 before the upstream side of the BOG cooler 7. The LNG supply pipe 14 is branched upstream from the refrigerant inlet of the BOG cooler 7, and one end of the branched temperature adjusting circulation line (circulation pipe) 17 is inserted into the LNG liquid in the tank 3. ing. Further, a return flow rate adjusting valve 9 is interposed in the temperature adjusting circulation line 17. Furthermore, the LNG supply pipe 15 to the forced evaporator 5 is branched and a circulation line (circulation pipe) 18 to the tank 3 is provided. An open / close valve 19 is provided in the LNG supply pipe 15 before the entrance. The evaporator 5 is a shell-and-tube type heat exchanger, and the steam in the ship is used as the heat / heating medium.

  The BOG supply system 1 according to the embodiment of the present invention configured as described above will be described with reference to FIG.

  In FIG. 1, BOG generated by spontaneous evaporation from LNG in the tank 3 is about 1 barA · temperature (at the top of the tank 3) −130 to −120 ° C., but in the fuel supply part of the gas engine 2 BOG with a pressure of about 6 barA and a temperature of 0-50 ° C. is required. Therefore, in this example, the centrifugal compressor 4 is used to meet the requirements of the gas engine 2. In addition, since NBOG naturally generated from LNG stored in the tank 3 is insufficiently supplied during normal LNG transportation, a part of the LNG is supplemented with FBOG that is forcibly evaporated.

  Specifically, the temperature of NBOG naturally generated from LNG is around −130 to −120 ° C. at the top of the tank 3, and the temperature rises due to intrusion heat while being sent to the centrifugal compressor 4 through the pipe 11. In this state, that is, when cooling is not performed, the temperature is about −80 to −60 ° C. at the inlet of the compressor 4. In the centrifugal compressor 4 in this case, in order to prevent an excessive increase in the BOG temperature at the outlet of the centrifugal compressor 4, a cooling process to around −120 ° C. is desired at the inlet. Therefore, the BOG is cooled in a non-contact manner by the cold heat of the LNG stored in the tank 3 in the BOG cooler 7 on the upstream side of the inlet of the compressor 4. The cooled BOG is pressurized by the compressor 4, but the temperature is adjusted by mixing uncooled BOG so that the temperature after cooling the BOG does not become too low. Is adjusted by the opening degree of the bypass valve 8. The cooling capacity of the BOG in the cooler 7 by LNG is adjusted by the opening degree of the return flow rate adjusting valve 9 of the temperature adjusting circulation line 17. On the other hand, the temperature of LNG increases due to heat absorption from the BOG, and is sent to the forced evaporator 5 through the pipe 15. Then, it is heated without contact with the inboard steam, evaporated and gasified to become BOG. The FBOG is mixed with the NBOG from the tank 3 in the pipe 11, cooled by the BOG cooler 7, and then sent to the compressor 4. Here, the pressure is increased to about 6 barA, and the temperature is raised and supplied to the gas engine 2.

  However, when the LNG carrier can be navigated only by the BOG that naturally occurs from the tank 3, the open / close valve 19 of the LNG supply pipe 15 is closed and the open / close valve 10 of the circulation line 18 is opened. The LNG in the tank 3 is sent to the BOG cooler 7 and used for cooling the BOG, and then returned to the tank 3 through the circulation line 18.

  FIG. 2 is a system diagram showing a second embodiment of the evaporative gas supply system of the present invention. As shown in FIG. 2, the BOG supply system 1-2 of this embodiment is different from the above embodiment in that a two-stage centrifugal compressor 4 or 4 is provided and an inlet of the first-stage compressor 4 is provided. BOG coolers 7 and 7 are interposed in the side piping and the piping 11 between the first and second stage compressors 4 and 4, and a bypass line 13 is provided between the inlet and outlet of each BOG cooler 7. The BOG temperature adjusting bypass valve 8 is provided. In each of the BOG coolers 7 and 7, LNG in the tank 3 is used as a refrigerant, and after use, the gas is guided to the forced evaporator 5 to make up for the shortage of BOG. The supply system 1-2 of this example is an embodiment in the case where the BOG required by the gas engine cannot be pressurized by the single-stage centrifugal compressor 4 in relation to the compression capacity of the BOG. In the case of this example, in order to make the BOG temperature at the entrance in each compression stroke substantially constant, a bypass valve 8 for temperature adjustment is provided for each BOG cooler 7. The setting of the BOG temperature at the entrance of each compression stroke using these is determined under the condition that the flow rate balance between the compression steps and the BOG temperature at the discharge port are below the limit values. Further, instead of the opening / closing valve 10 and the opening / closing valve 19, a switching valve 10 ′ is provided at a branch portion between the LNG supply pipe 15 and the circulation line 18. Since other configurations and supply modes are basically the same, a description thereof will be omitted, and common constituent members will be denoted by the same reference numerals. Although the present embodiment shows a two-stage compressor, the number of stages is not limited to this, and in that case, it is desirable to increase the BOG cooler 7 in accordance with the number of stages of the compressor.

  FIG. 3 is a system diagram showing a third embodiment of the evaporative gas supply system of the present invention. As shown in FIG. 3, the BOG supply system 1-3 of the present embodiment is different from the second embodiment in that one BOG cooler 7 is used instead of the two BOG coolers 7. In addition, the BOG supplied to the first-stage compressor 4 and the second-stage compressor 4 is cooled through the common BOG cooler 7. The BOG cooler 7 is a plate / fin type, which eliminates the contact between BOG and LNG, and also prevents the generation of drain as in a spray cooler. In this example, the installation space can be reduced by combining two BOG coolers 7 into one. In addition, the adoption of a plate-fin type heat exchanger has improved the efficiency of heat exchange, and has made it possible to reduce the size of the heat exchanger and save costs. Since other configurations and supply modes are basically the same, detailed description thereof is omitted, and common components are denoted by the same reference numerals.

  FIG. 4 is a system diagram showing a fourth embodiment of the evaporative gas supply system of the present invention. As shown in FIG. 4, the BOG supply system 1-4 of the present embodiment is different from that of the second embodiment in that the BOG cooler 7 and the BOG cooler 7 between the inlet and the outlet are for adjusting the temperature of the BOG. The bypass line 13 provided with the bypass valve 8 is provided between the first-stage compressor 4 and the second-stage compressor 4. In the case of this example, cost savings can be achieved by reducing the number of BOG coolers 7 to one. Further, the temperature control of the BOG cooler is facilitated because the number of coolers is small. However, since there is no BOG cooler at the inlet of the first stage compressor 4, the inlet temperature of the BOG changes in a considerable range, and the gas density of the BOG also changes accordingly. It is necessary to provide a sufficient capacity. Since other configurations and supply modes are basically the same, description thereof will be omitted, and common components will be denoted by the same reference numerals.

  FIG. 5 is a system diagram showing a fifth embodiment of the evaporative gas supply system of the present invention. As shown in FIG. 5, the BOG supply system 1-5 of the present embodiment is different from the second embodiment in that the BOG cooler 7 and the BOG cooler 7 between the inlet and the outlet are for adjusting the temperature of the BOG. The bypass line 13 provided with the bypass valve 8 is provided on the inlet side of the first stage compressor 4. In the case of this example, in addition to cost savings by reducing the number of BOG coolers, by keeping the BOG temperature at the entrance of the first stage compression stroke almost constant, the gas density of the first stage and thereafter is almost constant. Since compression is performed, there is an advantage that control of the flow rate is somewhat easier than in the fourth embodiment. Since other configurations and supply modes are basically the same, description thereof will be omitted, and common components will be denoted by the same reference numerals.

6 is a system diagram showing a sixth real施例off gas supply system of the present invention. As shown in FIG. 6, the BOG supply system 1-6 of the present embodiment is different from the first embodiment in that LNG used as a refrigerant in the BOG cooler 7 is vaporized by the forced evaporator 5 and gasified. After that, the gas is supplied to the gas engine 2 without passing through the BOG cooler 7 and the compressor 4. In the case of this example, the BOG that naturally occurs in the tank 3 is exclusively pressurized by the BOG compressor 4, and the shortage as fuel for the main propulsion engine 2 is evaporated by the forced evaporator 5 to compensate. . Therefore, the amount of BOG handled by the BOG compressor 4 is reduced, and the power consumption is also reduced accordingly. The LNG guided to the forced evaporator 5 can be increased with a small amount of power until it reaches the pressure required as fuel for the main propulsion engine 2 while remaining in the liquid state by the spray pump 6. Therefore, the pressure of the BOG generated by the forced evaporator 5 is increased. Can be used as fuel without passing through the compressor 4. Since other configurations and supply modes are basically the same, description thereof will be omitted, and common components will be denoted by the same reference numerals. However, in this case, it is necessary to adjust the pressure and temperature of the BOG to be forcibly evaporated so that the pressure required by the gas engine 2 is about 6 barA and the temperature is 0 to 50 ° C.

1 is a system diagram showing a first embodiment of an evaporative gas supply system in a liquefied natural gas carrier of the present invention. It is a systematic diagram which shows 2nd Example of the evaporative gas supply system in the liquefied natural gas carrier ship of this invention. It is a systematic diagram which shows 3rd Example of the evaporative gas supply system in the liquefied natural gas carrier ship of this invention. It is a systematic diagram which shows 4th Example of the evaporative gas supply system in the liquefied natural gas carrier ship of this invention. It is a systematic diagram which shows 5th Example of the evaporative gas supply system in the liquefied natural gas carrier ship of this invention. It is a systematic diagram which shows 6th Example of the evaporative gas supply system in the liquefied natural gas carrier ship of this invention. It is a systematic diagram which shows the supply system to the diesel engine using BOG naturally generated from LNG proposed by Alstorm. It is a systematic diagram which shows the prior art example of the evaporative gas supply system in a liquefied natural gas carrier.

Explanation of symbols

1 BOG supply system 2 Gas engine (gas-fired diesel engine: main propulsion engine)
3 Tank for LNG 4 Centrifugal compressor 5 Forced evaporator 6 Spray pump (pump device)
7 BOG cooler (heat exchanger)
8 Temperature adjustment bypass valve 9 Return flow rate adjustment valve 10 Open / close valve 10 'switching valve 11, 12, 14 BOG supply piping 13 LNG bypass line 15 LNG supply piping 16 Forced BOG supply piping 17 Temperature adjustment circulation line ( (Circulation piping)
18 LNG circulation line (circulation piping)

Claims (4)

Supplying the naturally-occurring evaporative gas to a main propulsion engine that uses as a fuel a naturally-occurring evaporative gas mainly composed of methane, which is naturally generated from liquefied natural gas stored in a tank mounted on a liquefied natural gas carrier. In addition, in the evaporative gas supply system that uses, as a fuel, forcibly generated evaporative gas obtained by forcibly evaporating the liquefied natural gas when the naturally generated evaporative gas is insufficient,
Connecting the forced generation evaporative gas supply pipe for supplying the forced generation evaporative gas from the forced evaporator to the evaporative gas supply pipe for supplying the naturally generated evaporative gas from the tank; Alternatively, the naturally occurring evaporative gas and the forced evaporative gas are supplied to a compressor that pressurizes the naturally occurring evaporative gas or the naturally occurring evaporative gas and the forced evaporative gas to be supplied to the main propulsion engine as fuel. The evaporative gas supply pipe is provided with a heat exchanger for cooling the spontaneously generated evaporative gas, or the naturally generated evaporative gas and the forced evaporative gas, and the evaporative gas supply pipe is connected to the heat exchanger. A branch line is provided near the entrance to provide a bypass line, and one end of the bypass line is connected between the outlet side of the heat exchanger and the inlet side of the compressor. After having connected, the spontaneous vapor or temperature adjusting bypass valve of the spontaneous evaporation gas and the forced generation evaporated gas, the bypass line is interposed,
By using the liquefied natural gas pumped from the tank by the pump device as the refrigerant of the heat exchanger, the naturally occurring evaporative gas or the naturally occurring evaporative gas and the forced evaporative gas are cooled to a predetermined temperature. An evaporative gas supply system for a liquefied natural gas carrier, characterized in that the liquefied natural gas is guided to a forced evaporator. The compressor is composed of a multistage compressor that performs a multistage compression stroke, and the heat exchanger is provided at least at one location between the inlet of the first stage compressor and the multistage compressor,
By using the liquefied natural gas as a refrigerant for the heat exchanger, the naturally occurring evaporative gas or the naturally occurring evaporative gas and the forced evaporative gas are cooled to a predetermined temperature, and then the most downstream heat exchanger. 2. The evaporative gas supply system for a liquefied natural gas carrier according to claim 1, wherein the liquefied natural gas that has passed through is guided to the forced evaporator. Supplying the naturally-occurring evaporative gas to a main propulsion engine that uses as a fuel a naturally-occurring evaporative gas mainly composed of methane, which is naturally generated from liquefied natural gas stored in a tank mounted on a liquefied natural gas carrier. In addition, in the evaporative gas supply system that uses, as a fuel, forcibly generated evaporative gas obtained by forcibly evaporating the liquefied natural gas when the naturally generated evaporative gas is insufficient,
Connecting the forced generation evaporative gas supply pipe for supplying the forced generation evaporative gas from the forced evaporator to the evaporative gas supply pipe for supplying the naturally generated evaporative gas from the tank; Alternatively, the naturally occurring evaporative gas and the forced evaporative gas are supplied to a compressor that pressurizes the naturally occurring evaporative gas or the naturally occurring evaporative gas and the forced evaporative gas to be supplied to the main propulsion engine as fuel. The evaporative gas supply pipe is provided with a heat exchanger for cooling the naturally occurring evaporative gas or the naturally occurring evaporative gas and the forced evaporative gas, and the compressor is operated in a plurality of stages of compression. A multi-stage compressor is provided, and the heat exchanger is provided in at least one place between the inlet of the first-stage compressor and the multi-stage compressor, and the heat exchanger is provided as a plate. In common with the one of the heat exchanger fin type,
By using the liquefied natural gas pumped from the tank by the pump device as the refrigerant of the heat exchanger, the naturally occurring evaporative gas or the naturally occurring evaporative gas and the forced evaporative gas are cooled to a predetermined temperature. An evaporative gas supply system for a liquefied natural gas carrier, characterized in that the liquefied natural gas that has passed through the heat exchanger at the most downstream is led to the forced evaporator. A circulation pipe for branching a pipe that leads the liquefied natural gas used as a refrigerant in the heat exchanger to the forced evaporator and returning it to the tank is provided, and a switching valve is provided upstream of the branch position of the pipe. The evaporative gas supply system of the liquefied natural gas carrier ship according to any one of claims 1 to 3.

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