JP4425090B2 - Fuel gas supply system to LNG carrier engine - Google Patents

Description

  The present invention relates to a system for supplying fuel gas to a diesel engine of an LNG carrier.

  Conventionally, a cargo tank of an LNG carrier has been subjected to a heat treatment to keep the temperature of the internal LNG (Liquefied Natural Gas) at about −160 ° C. to prevent excessive LNG evaporation. A part of the LNG liquid layer spontaneously evaporates due to intrusion heat from the outside, and evaporative gas (boil off gas; natural gas) is generated. Since this evaporative gas has a low boiling point and is difficult to reliquefy, it is used as fuel for steam boilers installed on the ship.

  The amount of the evaporative gas varies depending on the temperature and pressure during the voyage, but the heat treatment is applied so that it does not occur excessively, and the natural amount of evaporative gas is less than the normal required amount of the engine. Designed to be

  In the conventional LNG carrier, the steam boiler is used for the treatment of this evaporative gas. Recently, a marine gas-fired diesel engine that uses natural gas as a fuel and consumes less fuel has been developed. It is beginning to become.

  As this gas-fired diesel engine, there are a two-cycle engine that injects evaporative gas into the cylinder at a high pressure of 20 Mpa or more, and a four-cycle engine that ignites after being sucked into the cylinder and compressed at about 0.5 Mpa. In the case of a two-cycle engine, a large-sized compressor is required to compress the evaporative gas at a high pressure as described above, and therefore a four-cycle engine is preferable for marine use.

  On the other hand, when such a gas-fired diesel engine is used, the fuel gas required by the engine is larger than the amount of evaporated gas obtained by natural evaporation from the cargo tank in a range where the engine output is large during normal voyage or the like. . In such a case, there is an idea to forcibly evaporate LNG in the cargo tank and use it for fuel gas.

  As conventional technology for forcibly evaporating LNG in the cargo tank and using it as fuel gas, the LNG in the cargo tank is evaporated by the LNG evaporator and the evaporated gas sucked and pressurized from the gas layer of the cargo tank by the gas compressor. There is a gaseous fuel supply facility that is used as a fuel gas for a gas engine by mixing the evaporated gas obtained in this way (see, for example, Patent Document 1).

In this gaseous fuel supply facility, the evaporated gas sucked from the tank surface and compressed by the compressor and the evaporated gas supplied from the bottom of the tank to the evaporator by the pump and evaporated are included through the same manifold. LNG supplied to the power generation system and supplied to the evaporator is returned to the tank by a return adjustment valve according to the pressure.
JP 2004-36608 A (page 2-4, FIG. 1)

  By the way, the evaporation gas in the liquid layer of the cargo tank occupies about 100% with methane which is a component having a low boiling point in LNG as a main component and nitrogen as an impurity. However, as in Patent Document 1, a gas obtained by forcibly evaporating LNG with an evaporator has the same components as LNG, and thus contains a large amount of heavy components such as ethane and propane. Although it varies depending on the production area of LNG, the content of nitrogen is as low as 1% or less in terms of mole fraction, but the content of ethane, propane and other heavy components is not uncommon as 10% or more in terms of mole fraction.

  Therefore, when evaporating gas obtained by evaporating LNG pumped up by a pump as in Patent Document 1 is supplied to the engine, the evaporating gas contains many heavy components.

  In the conventional steam boiler described above, the restrictions on the components and supply pressure of the evaporative gas were loose. Therefore, the forced evaporative gas containing heavy components is mixed with the naturally evaporated gas and used as fuel gas. Was relatively easy.

  However, in the case of the above-mentioned gas-fired diesel engine, particularly a 4-cycle engine, the output decreases as the ratio of heavy components such as ethane and propane contained in the combustion gas increases to induce knocking in the compression stroke after inhalation. May be forced to drive.

  In addition, if the fluctuation of the supply pressure exceeds the range of the allowable pressure fluctuation, combustion may become unstable, and it may be necessary to switch from the gas operation mode to the fuel oil operation mode.

  Therefore, a complicated device configuration and a control system are required to solve these problems.

  Further, in the case of an LNG carrier, a small amount of LNG is left in the cargo tank to generate fuel gas during ballast voyage in which LNG is unloaded at the landing site and then returned to the loading site. In this case, methane or nitrogen having a low boiling point evaporates preferentially in the tank, so that the ratio of heavy components tends to gradually increase, and there is a possibility of causing a “weathering” phenomenon in which the LNG composition changes. In addition, since the evaporated gas from which LNG having a high ratio of heavy components has evaporated contains a lot of heavy components, it causes knocking in the engine as described above.

  Accordingly, an object of the present invention is to provide a system capable of stably supplying a high-quality fuel gas containing almost no heavy components as a fuel gas supply system for an LNG carrier employing a gas-fired diesel engine.

In order to achieve the above object, the present invention provides a system for supplying evaporative gas generated from LNG in a cargo tank of an LNG carrier as fuel gas to an engine for LNG carrier, wherein the LNG in the cargo tank is LNG evaporated by a pump. A fuel gas forced evaporation device that increases the amount of evaporated gas from the cargo tank liquid layer by returning the forced evaporated gas forcedly evaporated by the LNG evaporator back to the LNG liquid in the cargo tank and re-liquefying it. A return pipe for returning the forced evaporative gas from the LNG evaporator into the LNG liquid in the cargo tank is located at the bottom of the tank where the lower end of the return pipe is in the liquid during ballast voyage, and the return pipe the lower portion forced evaporation gas provided with a plurality of openings finely released into LNG liquid from the liquid layer to increase in the fuel gas forced evaporation device Evaporation gas amount is provided a control unit for controlling the vapor pressure in the cargo tank so as to control the vapor amount in the cargo tank. As a result, good quality fuel gas can be stably supplied, and good quality fuel gas can be stably supplied to the gas-fired engine even when performing ballast voyage with a small amount of LNG in the cargo tank.

  Also, in this fuel gas supply system to the LNG carrier engine, when the controller detects that the evaporation gas pressure in the cargo tank has reached the set pressure, the pump adjusts the amount of LNG sent to the LNG evaporator. You may comprise.

  In the fuel gas supply system to any of the LNG carrier engines, a compressor for pressurizing the evaporative gas to a set pressure in a path for supplying the evaporative gas in the cargo tank to the engine, and pressurizing by the compressor Before supplying fuel gas to the engine by providing a fuel gas supply device comprising a heater for heating the evaporated gas to a predetermined temperature and a buffer tank for supplying the evaporated gas heated by the heater to the engine at a set pressure The pressure and temperature may be adjusted.

  Further, in this fuel gas supply system to the LNG carrier engine, a controller for adjusting the discharge amount of the compressor so as to keep the inside of the buffer tank at a set pressure may be provided.

  Further, in the fuel gas supply system to the LNG carrier engine, a controller may be provided for adjusting the evaporation gas supplied to the buffer tank back to the cargo tank so as to keep the inside of the buffer tank at a set pressure. .

  Further, in the fuel gas supply system to the LNG carrier engine, adjustment of the discharge amount of the compressor and adjustment of returning the evaporated gas supplied to the buffer tank to the cargo tank so as to keep the inside of the buffer tank at a set pressure. It is also possible to provide a controller that performs both of these adjustments and to combine both of these adjustments.

  The present invention can increase the amount of the liquid layer gas by returning the forced evaporative gas obtained by forcibly evaporating the LNG in the cargo tank by the evaporator to the LNG liquid and re-liquefying it by the means described above. Therefore, it is possible to stably supply a high-quality evaporative gas containing almost no heavy components as a fuel gas supplied to the gas-fired engine.

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings. In the following embodiments, an LNG carrier equipped with two cargo tanks will be described as an example. FIG. 1 is a configuration diagram showing a fuel gas supply system according to a first embodiment of the present invention, and FIG. 2 is an enlarged cross-sectional view of a portion II shown in FIG.

  As shown in the figure, the overall system requires a fuel gas supply device 3 that supplies natural evaporative gas generated in the cargo tank 1 to the gas-fired diesel engine 2 as fuel gas, and the engine 2 is required only with this natural evaporative gas. The fuel gas forced evaporation device 4 is configured by two independent systems that forcibly generate evaporative gas to supplement the gas amount when the gas amount is insufficient. As the gas-fired diesel engine 2, a four-cycle diesel engine is employed in which fuel gas at a set pressure is sucked and compressed, and diesel fuel serving as ignition fuel is injected and ignited.

  The cargo tank 1 is provided with a heat treatment prevention 11 around the inside to keep the temperature of the internal LNG at about −160 ° C. to prevent excessive LNG evaporation. A part of the layer evaporates spontaneously to become evaporating gas and accumulates in the upper part of the cargo tank 1. The pressure in the cargo tank 1 varies depending on the design pressure and operational state of the cargo tank 1, but it is necessary to increase the pressure in order to supply this evaporated gas to the gas-fired engine.

  In this embodiment, the fuel gas supply device 3 sucks the evaporated gas G evaporated from the LNG liquid layer in the cargo tank 1 and supplies the fuel gas (hereinafter referred to as “evaporated gas” in the process of supplying the engine 2) to the engine 2. Gas compressor 5 for sending as "fuel gas"), a gas heater 6 for adjusting the fuel gas to a temperature required by the engine 2, and an outlet side of the gas heater 6 to set the fuel gas at a set pressure. And a buffer tank 7 for supplying the engine 2 as a fuel gas having a stable pressure. These are connected by piping 8-10. The type of the gas compressor 5 and the type of the gas heater 6 are not limited.

  The fuel gas pressure supplied to the gas-fired engine 2 as fuel gas by such a fuel gas supply device 3 differs depending on the model of the gas-fired engine 2, but in the case of a 4-cycle engine, it is around 0.5 Mpa, Further, since the fuel gas temperature is about 0 ° C. to 50 ° C., the fuel gas in the buffer tank 7 is compressed by the compressor 5 and heated by the heater 6 so as to reach this pressure and temperature.

  In this embodiment, the adjustment of the fuel gas supply amount by the fuel gas supply device 3 is performed by controlling the operation of the gas compressor 5 following the required gas amount of the engine 2. In this control, a pressure gauge 12 is installed downstream of the compressor 5 (in this example, the buffer tank 7). When the pressure detected by the pressure gauge 12 exceeds the set pressure, the controller 13 controls the discharge amount of the compressor 5. When the pressure is reduced and the set pressure is not reached, the discharge amount of the compressor 5 is increased. Reference numeral 23 denotes a control circuit. Thus, the fuel gas pressure in the buffer tank 7 is kept at the set pressure, and the necessary gas amount (gas pressure) of the engine 2 is ensured.

  On the other hand, the fuel gas forced evaporation device 4 is configured to forcibly increase the evaporation gas from the LNG liquid layer in the cargo tank 1. This fuel gas forced evaporation device 4 is used to reduce the shortage when the fuel gas is insufficient with only the evaporative gas obtained by natural evaporation from the LNG liquid layer, such as when sailing when the gas-fired engine 2 is operated at a high load. Used to obtain additional fuel gas to supplement.

  The fuel gas forced evaporation device 4 is forced to evaporate by sending a pump 15 for sending LNG from the cargo tank 1 to the LNG evaporator 14 and heating the pump 15 via the pipe 16 to the LNG evaporator 14. And a return pipe 17 for releasing the forced evaporative gas thus discharged into the liquid in the cargo tank 1. The forced evaporative gas is released into the LNG liquid in the cargo tank 1 through the return pipe 17, thereby mixing the forced evaporative gas with the LNG in the cargo tank 1. As the pump 15, a spray pump provided in the cargo tank 1 may also be used.

  Further, in this embodiment, the lower end of the return pipe 17 is opened at the lowest possible position of the cargo tank 1 so that the forced evaporation gas forcedly evaporated and the LNG in the cargo tank 1 can be sufficiently mixed. Yes. In addition, the lower end of the return pipe 17 is positioned at the bottom of the cargo tank 1 that remains in the liquid during ballast voyage when the cargo LNG is lowered at the unloading site and only the fuel remains in the cargo tank 1. Even at times, the forced evaporative gas is discharged into the liquid in the cargo tank 1.

  Furthermore, as shown in FIG. 2, the lower end of the return pipe 17 is provided with a plurality of small holes 18 around the lower end surface and the lower end portion. The forced evaporative gas FG is finely discharged into the liquid by forming a plurality of openings 18 for releasing the forced evaporative gas FG thus forcibly evaporated into the LNG liquid in the cargo tank 1. The contact area is increased to make it easy to melt. That is, for this reason as well, the lower end of the return pipe 17 is provided as low as possible in the cargo tank 1, and a number of fine holes are provided at the lower end so as to increase the contact area of the forced evaporative gas in the liquid. preferable. In FIG. 2, the small holes 18 are schematically illustrated. In this embodiment, the plurality of openings are configured by the small holes 18, but other configurations may be used as long as the forced evaporation gas can be finely discharged into the liquid.

  Further, as shown in FIG. 1, in this embodiment, a branch return pipe 19 that branches from a pipe 16 that connects the pump 15 and the LNG evaporator 14 and opens into the cargo tank 1 is provided. The branch return pipe 19 is provided with a control valve 20. By opening the control valve 20, the LNG sent to the LNG evaporator 14 can be returned to the cargo tank 1 to adjust the feed amount. Yes.

  In the case of this configuration, if the amount of evaporative gas generated by returning the forced evaporative gas evaporated by the LNG evaporator 14 into the LNG liquid is larger than the amount of evaporative gas consumed by the engine 2, Since the pressure rises, if the pressure is monitored by the pressure gauge 21 and it is detected that the pressure exceeds the set range, the controller 22 opens the control valve 20 of the branch return pipe 19 and sends the LNG to the LNG evaporator 14. Controlled to reduce the amount. Reference numeral 24 denotes a control circuit. Further, when this configuration is provided, the amount of LNG flowing through the LNG evaporator 14 is controlled to be reduced, so that the fine heating amount can be adjusted.

  In this embodiment, the amount of LNG sent to the LNG evaporator 14 is adjusted. However, when the amount of LNG is sufficiently in the cargo tank 1, the pressure in the cargo tank 1 is adjusted. It is also possible to simply switch between operation and stop of the pump 15 and the LNG evaporator 14 while monitoring. In this case, the operation / stop of the pump 15 and the LNG evaporator 14 is controlled by the controller 22.

  According to the fuel gas forced evaporation device 4 configured as described above, the LNG sent from the cargo tank 1 to the LNG evaporator 14 is forcibly evaporated by the LNG evaporator 14 which is a heat exchanger, and the forced evaporation gas. At this time, latent heat of vaporization and sensible heat due to temperature rise are obtained.

  The forced evaporating gas FG thus forcibly evaporated is returned to the LNG liquid in the cargo tank 1 to be discharged into the LNG liquid from the small hole 18 of the return pipe 17 opened at the bottom of the cargo tank 1. Then, it is diluted and cooled in LNG, dissolved and reliquefied. At this time, latent heat and sensible heat obtained by the LNG evaporator 14 are absorbed by the LNG in the tank. The thermal energy absorbed by the LNG is transported to a layer close to the liquid surface by convection, and promotes evaporation of methane and nitrogen having a low boiling point in the LNG. Thereby, the evaporation of the liquid layer gas in the cargo tank 1 is promoted, and the amount of the evaporated gas in the upper part of the cargo tank liquid layer can be increased.

  Moreover, the liquid layer evaporating gas obtained in this way is different from the forced evaporating gas obtained by directly evaporating LNG by the LNG evaporator 14, and is a gas mainly composed of methane having a low boiling point. It becomes a high-quality fuel gas that contains almost no causative heavy components. That is, the obtained vaporized gas in the liquid layer becomes a high-quality gas having an ideal component for the gas-fired engine 2 using fuel gas as fuel.

  In addition, although LNG is used as a heating medium, it is accompanied by evaporation and liquefaction to return the vaporized LNG to a liquid, so that only sensible heat without it (that is, a heating medium in the state of gas or LNG). Compared to the use of as a), it involves the exchange of latent heat with large energy per unit weight (the sensible heat of methane is the product of specific heat (2 kJ / kg ° C.) and temperature change. Even at 100 ° C., it is relatively small at 200 kJ / kg, while the latent heat is 510 kJ / kg.) By sending a small amount of liquid from the tank to the LNG evaporator 14, a sufficient amount of evaporating gas can be obtained in the tank. Can be generated.

  The cargo tank 1 and the LNG in the cargo tank 1 have a large heat capacity, and the temperature and pressure in the cargo tank 1 do not change suddenly due to the heating of a part of the LNG by the LNG evaporator 14.

  According to the fuel gas supply system 25 configured as described above, by returning the evaporated gas obtained by forcibly evaporating the LNG in the cargo tank 1 using the LNG evaporator 14 to the LNG liquid by the fuel gas forced evaporator 4. The amount of evaporating gas G that evaporates from the liquid layer in the cargo tank 1 is increased. The increased evaporation gas G from the liquid layer is sucked into the compressor 5, heated to a predetermined temperature by the heater 6, and then supplied to the buffer tank 7. That is, only the evaporated gas from the LNG liquid layer is used as the fuel gas. As a result, a high-quality fuel gas (evaporated gas) containing almost no heavy components in the LNG liquid can be stored in the buffer tank 7 at a predetermined set pressure. Thus, the fuel gas stored in the buffer tank 7 at the set pressure is sucked into the engine 2.

  Then, the gas pressure in the buffer tank 7 changes depending on the operating status of the engine 2, and when the pressure in the buffer tank 7 increases, it is determined that the gas consumption of the engine is small and the amount of gas supplied by the compressor 5 is reduced. When the pressure in the buffer tank 7 decreases, the controller 13 determines that the amount of gas consumed by the engine is large and adjusts the controller 13 to increase the amount of gas supplied by the compressor 5.

  That is, according to the fuel gas supply system 25 of this embodiment, the fuel gas supply device 3 controls the compressor 5 according to the required gas amount of the engine 2 to adjust the supply amount to the buffer tank 7 side. 13 is adjusted.

  Even when the amount of gas supplied by the compressor 5 is adjusted according to the change in the pressure in the buffer tank 7, the fuel gas forced evaporation device 4 detects the pressure in the cargo tank 1 with the pressure gauge 21, When the pressure in the tank 1 is higher than the set pressure, the consumption of the engine is small. Therefore, by reducing the amount of LNG that is forcibly evaporated by the LNG evaporator 14, the amount of evaporated gas from the liquid layer in the cargo tank 1 is reduced. When the pressure in the cargo tank 1 is lower than the set pressure, the consumption of the engine is large. Therefore, by increasing the amount of LNG forcibly evaporated by the LNG evaporator 14, the amount of evaporated gas from the liquid layer in the cargo tank 1 is increased. The amount of LNG sent to the LNG evaporator 14 is adjusted by the controller 22 so as to increase.

  In this embodiment, the lower end of the return pipe 17 from the LNG evaporator 14 is positioned below the cargo tank 1 that is in liquid during ballast voyage, so that the LNG evaporator 14 forcibly evaporates during ballast voyage. The forced evaporative gas thus discharged can be discharged into the liquid in the cargo tank 1 to stably obtain a high quality evaporative gas with few heavy components.

  In addition, the adjustment of the amount of evaporative gas (fuel gas) performed in this way is independent of the fuel gas supply device 3 and the fuel gas forced evaporation device 4, so that each control is simple and both are combined. It can be adjusted with simple control.

  If the amount of heat in the LNG evaporator 14 of the forced evaporator 4 exceeds the required amount required for fuel consumption of the engine 2, the amount of evaporation temporarily increases, but the evaporated gas continues to be consumed by the engine 2. When the heating is stopped, the pressure in the cargo tank 1 gradually decreases. Conversely, even if the heating amount is temporarily insufficient, there is no problem because the temperature and pressure of the entire LNG are slightly lowered. Therefore, depending on the amount of LNG in the cargo tank 1, only simple control of performing and stopping heating in the LNG evaporator 14 may be performed.

  In addition, since the LNG in the cargo tank 1 having a large heat capacity is used, the temperature and pressure in the cargo tank 1 suddenly increases even when the forced evaporation device 4 temporarily performs excessive heating or the heating is insufficient. It does not change and stable operation is possible.

  Furthermore, since nitrogen, which is a light component, has a lower boiling point than methane, it preferentially evaporates and disappears from LNG. However, as mentioned above, nitrogen originally has a low content of 1 mol% or less in LNG and causes knocking. Therefore, the engine will not be knocked.

  FIG. 3 is a block diagram showing a fuel gas supply system according to a second embodiment of the present invention. The second embodiment is different from the first embodiment in the configuration for keeping the fuel gas pressure in the buffer tank 7 of the fuel gas supply device constant. In addition, the same code | symbol is attached | subjected to the structure same as the said 1st Embodiment, and the detailed description is abbreviate | omitted.

  As shown in the figure, in this second embodiment, instead of controlling the pressure in the buffer tank 7 in the first embodiment by controlling the discharge amount of the compressor 5, the discharge amount of the compressor 5 is a constant amount. The amount of gas supplied to the engine 2 is adjusted by returning the fuel gas downstream of the compressor 5 to the cargo tank 1 while maintaining it.

  In the fuel gas supply device 31 in this embodiment, a pressure gauge 7 provided in the buffer tank 7 and a pipe 9 leading from the gas heater 6 to the buffer tank 7 are connected to the cargo tank 1 via a return pipe 17. A branch pipe 32, a control valve 33 for opening and closing the branch pipe 32, and when the pressure detected by the pressure gauge 7 exceeds a set pressure, the control valve 33 is opened and the cargo tank 1 is opened from the branch pipe 32. And a controller 34 for controlling the return of the fuel gas. Since the fuel gas forced evaporation device 4 described above is the same as that of the first embodiment, a detailed description thereof will be omitted.

  According to the fuel gas supply system 35 of the second embodiment configured as described above, when the pressure in the buffer tank is detected by the pressure gauge 12 provided in the buffer tank 7 and this pressure exceeds the set pressure, The control valve 33 of the branch pipe 32 provided in the pipe 9 leading from the gas heater 6 to the buffer tank 7 is opened by the controller 34, and a part of the fuel gas supplied from the branch pipe 32 to the buffer tank 7 is a cargo tank. It is controlled to return to 1.

  Therefore, according to the second embodiment, the amount of gas supplied by the compressor 5 does not need to be controlled, and only a constant operation or switching between operation and stop may be performed. The amount of fuel gas supplied to the buffer tank 7 The amount of gas returned to the cargo tank 1 is adjusted by the controller 34 so as to keep the pressure at the set pressure.

  That is, normally, the control valve 33 of the branch pipe 32 leading from the pipe 9 to the cargo tank 1 is closed and operated, and when the pressure in the buffer tank 7 exceeds the set range, the control valve 33 of the branch pipe 32 is opened. By returning a part of the fuel gas supplied to the buffer tank 7 to the cargo tank 1, the flow rate to the buffer tank 7 is decreased.

  Also in this embodiment, since only the evaporative gas G containing nitrogen as the main component and methane obtained from the gas layer of the cargo tank 1 is used as the fuel gas, the engine 2 contains almost no heavy components in the LNG liquid. High quality fuel gas can be supplied. Moreover, even in ballast voyages where the amount of LNG in the cargo tank 1 is small, it is possible to supply a high-quality fuel gas that hardly contains heavy components that cause knocking.

  Further, in this embodiment as well, the fuel gas supply device 31 and the fuel gas forced evaporation device 4 are independent, so that the control of each is simple and the evaporation gas amount can be controlled by simple control even when both are combined. Can be adjusted.

  In the second embodiment, the fuel gas is returned from the pipe 9 between the gas heater 6 and the buffer tank 7 to the cargo tank 1, but it may be between the compressor 5 and the gas-fired diesel engine 2. For example, it is not limited to this embodiment.

  Further, since other functions and effects are the same as those of the fuel gas supply system 25 of the first embodiment described above, detailed description thereof is omitted.

  Further, in this second embodiment, the amount of evaporative gas sent to the buffer tank 7 is adjusted using the control valve 33, but the adjustment using this control valve 33 and the compressor 5 in the first embodiment are adjusted. The gas amount may be adjusted in combination with the adjustment based on the discharge amount, and the gas amount adjustment method may be determined according to the use conditions and the like.

  In the above embodiment, the LNG carrier provided with two cargo tanks 1 is described as an example, but the number of cargo tanks 1 is not limited.

  Further, although one system of the compressor 5 and the heater 6 is provided, two systems of these may be provided to prepare for a failure or the like.

  Furthermore, the above-described embodiment shows an example, and various modifications can be made without departing from the spirit of the present invention, and the present invention is not limited to the above-described embodiment.

  The fuel gas supply system to the engine for an LNG carrier according to the present invention can be used for an LNG carrier that is gasified so as to contain almost no heavy components in the LNG of the cargo as the fuel gas of the diesel engine.

It is a block diagram which shows the fuel gas supply system which concerns on 1st Embodiment of this invention. It is an expanded sectional view of the II section shown in FIG. It is a block diagram which shows the fuel gas supply system which concerns on 2nd Embodiment of this invention.

Explanation of symbols

1 ... Cargo tank
2. Gas-fired diesel engine
3. Fuel gas supply device
4 ... Fuel gas forced evaporation system
5. Gas compressor
6. Gas heater
DESCRIPTION OF SYMBOLS 7 ... Buffer tank 8-10 ... Piping 11 ... Heat-treatment 12 ... Pressure gauge 13 ... Controller 14 ... LNG evaporator 15 ... Pump 16 ... Pipe 17 ... Return pipe 18 ... Small hole 19 ... Branch return pipe 20 ... Control valve 21 ... Pressure gauge 22 ... Controller 23, 24 ... Control circuit 25 ... Fuel gas supply system 31 ... Fuel gas supply device 32 ... Branch pipe 33 ... Control valve 34 ... Controller 35 ... Fuel gas supply system
G ... Evaporated gas FG ... Forced evaporative gas

Claims (6)

In a system for supplying evaporative gas generated from LNG in a cargo tank of an LNG carrier to a LNG carrier engine as fuel gas,
Evaporation from the cargo tank liquid layer by sending LNG in the cargo tank to the LNG evaporator by a pump, and returning the forced evaporation gas forcedly evaporated by the LNG evaporator back to the LNG liquid in the cargo tank and re-liquefying it. Provide a fuel gas forced evaporation device to increase the gas volume,
A return pipe for returning forced evaporative gas from the LNG evaporator to the LNG liquid in the cargo tank is provided at the bottom of the tank where the lower end of the return pipe is in liquid during ballast voyage, and the lower end of the return pipe A plurality of openings for finely discharging forced evaporative gas into the LNG liquid are provided in the part,
To an LNG carrier engine provided with a controller for controlling the amount of evaporated gas from the liquid layer to be increased by the fuel gas forced evaporation device by the evaporated gas pressure in the cargo tank so as to control the amount of evaporated gas in the cargo tank. Fuel gas supply system. In the fuel gas supply system to the LNG carrier engine according to claim 1,
A fuel gas supply system to an LNG carrier engine configured to adjust the amount of LNG sent to the LNG evaporator by the pump when the controller detects that the evaporation gas pressure in the cargo tank has reached a set pressure. . In the fuel gas supply system to the LNG carrier engine according to claim 1 or 2 ,
A compressor that pressurizes the evaporated gas up to a set pressure, a heater that heats the evaporated gas pressurized by the compressor to a predetermined temperature, and an evaporation heated by the heater in a path for supplying the evaporated gas in the cargo tank to the engine. A fuel gas supply system to an LNG carrier engine provided with a fuel gas supply device including a buffer tank that supplies gas to the engine at a set pressure. In the fuel gas supply system to the LNG carrier engine according to claim 3 ,
A fuel gas supply system to an LNG carrier engine provided with a controller for adjusting a discharge amount of the compressor so as to keep the inside of the buffer tank at a set pressure. In the fuel gas supply system to the LNG carrier engine according to claim 3 ,
A fuel gas supply system for an LNG carrier engine provided with a controller for adjusting the evaporation gas supplied to the buffer tank to return to the cargo tank so as to keep the inside of the buffer tank at a set pressure. In the fuel gas supply system to the LNG carrier engine according to claim 3 ,
Fuel to the LNG carrier engine provided with a controller for adjusting the discharge amount of the compressor so as to keep the inside of the buffer tank at a set pressure and for returning the evaporated gas supplied to the buffer tank to the cargo tank Gas supply system.

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