JP2006348752A - Evaporated-gas supply system for liquefied natural gas-carrying vessel - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an evaporated-gas supply system supplying BOG to a gas engine using BOG containing methane as major component of LNG stored in a tank mounted on a liquefied natural gas carrier by using an oil cooled screw compressor for a BOG compression means. <P>SOLUTION: This evaporated-gas supply system 1 supplies BOG to the gas engine 2 using BOG containing methane as the major component of LNG stored in the tank 3 mounted in the liquefied natural gas carrier. The oil cooled screw compressor 4 is used for a compression means for compressing BOG, and a heater 8 for BOG supplied to the screw compressor 4 is installed in a middle of a BOG supply piping from the tank 3 to the screw compressor 4. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention mainly uses methane of 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 present invention relates to an evaporative gas supply system that supplies evaporative gas to a gas engine that uses evaporative gas as a component (hereinafter also referred to as BOG) 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 use BOG directly as fuel has been developed. That is, the main engine uses a gas engine such as a gas-fired diesel engine or a gas turbine engine.

  By the way, when the main 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 barA. The compressor for BOG pressurization consists of a single stage compression stroke. A centrifugal compressor is used. Since the centrifugal compressor can continuously supply BOG to the steam boiler, 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 has almost all the steam turbine main engines. Used for LNG carriers.

  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).

Also, as shown in FIG. 3, BOG naturally generated from 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).
JP-A-2004-36608 (2 pages, 4-5 pages and FIG. 1) Alstorm, France 2005 GASTECH (published March 2005, system diagram)

  When the main engine is the gas engine as described above, it is necessary to increase the pressure of the BOG to about 5 to 7 barA before the main engine (upstream side). However, when trying to pressurize to about 5-7 barA using a centrifugal compressor, there are the following problems.

  -Because the compression ratio is high, the compression process must be multistage.

-Since the temperature of the gas to be handled is extremely low, it is difficult to obtain a cryogenic refrigerant on board and an intermediate cooling device cannot be adopted.

  -Since the intermediate cooling device cannot be provided, if the temperature of the BOG rises at the discharge port, it may exceed the proper temperature of the centrifugal compressor and break during operation. The temperature of the BOG at the first stage compression stroke inlet Must be kept as low as possible (for example, below -120 ° C). Incidentally, BOG is at a very low temperature (-150 ° C. to -130 ° C.) as that of LNG when it is generated from LNG stored in the gas tank, but the BOG is sucked from the gas tank through the gas pipe. When it reaches the suction port of the compressor, it is heated by the intrusion heat from the surroundings into the gas pipe, so that the temperature rises to about −120 ° C. to −80 ° C.

  -When the temperature of the BOG at the compressor inlet rises, the gas specific gravity decreases, the power required for the compressor increases, and 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. Operation may become impossible due to pressure.

  Therefore, as a solution to solve the above problems, as shown in FIG. 2, cooling using LNG as a refrigerant for cooling the BOG on the inlet side of the centrifugal compressor 54 to lower the temperature. It is conceivable to provide a device 53. This type of cooler 53 sprays LNG into the BOG in the sealed cooler body, and cools the BOG with latent heat of vaporization when the droplets evaporate. New problems arise. FIG. 2 shows an evaporative gas supply system that supplies BOG to a gas engine 2 that uses BOG mainly composed of methane generated from LNG stored in a tank 3 mounted on a liquefied natural gas carrier as fuel. FIG. 2 is a system diagram showing an overall configuration when a two-stage centrifugal compressor 54 is used to pressurize BOG. In FIG. 2, reference numeral 55 is a mist separator, 56 is a BOG cooler, 57 is a drain tank, 58 is a drain pump, and 59 is a pressure reducing valve. In FIG. 2, members common to FIG. 1 described later are denoted by the same reference numerals.

  ・ If the cooling temperature is lowered, the weight (ethane, propane, etc.) in the LNG after spraying hardly evaporates and accumulates in the cooler as so-called drain. I need it.

  -When the 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.

  -There is a possibility that the sprayed LNG droplets are mixed into the BOG and may be sucked into the compressor, which may adversely affect the compressor.

  The present invention has been made in view of the above-mentioned points, and the inside of a tank mounted on a liquefied natural gas carrier ship that has solved the above problems of a centrifugal compressor by using an oil-cooled screw compressor as a compression means of BOG. It is an object of the present invention to provide an evaporative gas supply system that supplies BOG to a gas engine that uses BOG mainly composed of methane as fuel as the LNG stored in the tank.

In order to achieve the above object, the evaporative gas supply system according to the present invention uses liquefied natural gas, which is stored in a tank mounted on a liquefied natural gas carrier ship, as evaporative gas mainly composed of methane. In the evaporative gas supply system for supplying the evaporative gas to the gas engine, an oil-cooled screw compressor is used as a compression means for pressurizing the evaporative gas, and the evaporative gas supplied to the screw compressor is heated. The means is provided in the middle of an evaporative gas supply path from the tank to the screw compressor.

According to the evaporative gas supply system of the liquefied natural gas carrier having the above configuration, since the oil-cooled screw compressor is used for the compression of the BOG, the performance of the compressor can be improved even if the intake gas properties and the operating conditions vary. Stable and hardly changes. That is, even if the temperature of the BOG sucked into the compressor rises somewhat, the influence on the temperature on the discharge port side is small, and operation is possible in a flow rate control range of 0 to 100%. In addition, in a centrifugal compressor without a cooling device, it is necessary to maintain the BOG inlet temperature at a low temperature of around -120 ° C., so a spray type cooler using LNG as a refrigerant is required on the upstream side. However, according to the present invention, since the inlet temperature condition of the BOG of the screw compressor is a relatively high temperature of −60 ° C. or more, if heating is performed using the general-purpose steam that can be used in the ship, Since it is good, heat exchange is easy, and facilities for drain treatment (drain tank, drain pump, etc.) generated from LNG become unnecessary. Furthermore, when the BOG is pressurized to 5 to 7 barA, the centrifugal compressor has a two-stage configuration, whereas the screw compressor may have a single stage, so the configuration of the compressor body is simplified.

  According to a second aspect of the present invention, a pressure measuring device is interposed in the evaporative gas supply path to the gas engine downstream of the screw compressor, and the pressure of the evaporative gas supplied to the gas engine is maintained at a predetermined pressure. It is desirable to feedback control the flow rate of the evaporative gas from the screw compressor based on the measurement value of the pressure measuring device.

In this way, the flow rate of the BOG supplied from the screw compressor to the gas engine is controlled so that the pressure of the BOG supplied to the gas engine becomes a pressure value required by the gas engine (for example, about 6 barA). Thus, the pressure of the BOG can be reliably adjusted to the pressure required by the gas engine. Specifically, as shown below, the BOG supply path from the screw compressor to the gas engine is branched to provide a bypass path to the screw compressor, and a bypass valve is interposed in the bypass path. Thus, the flow rate of the BOG to be bypassed to the screw compressor according to the increase / decrease of the pressure value by the pressure measuring instrument can be controlled by adjusting the opening degree of the bypass valve.

  The evaporator for forcibly evaporating the liquefied natural gas stored in the tank as defined in claim 3 is provided on the upstream side of the tank and the oil-cooled screw compressor or the upstream side of the gas engine. Can be interposed between the two.

  In this way, when the BOG that is naturally generated from the LNG stored in the tank is insufficient for the navigation fuel, a part of the LNG is pumped up and supplemented with the BOG that is forcibly evaporated by the evaporator. Can do. Further, the forcibly evaporated BOG can be adjusted to some extent with respect to temperature and pressure, and can therefore be supplied to a gas engine without being pressurized by a compressor.

The evaporative gas supply system for a liquefied natural gas carrier according to the present invention has the following excellent effects. That is, since an oil-cooled screw compressor is used for compression of BOG, even if the temperature of BOG sent to the compressor rises slightly, the influence on the temperature on the discharge port side is small, and the flow rate is 0 to 100%. The control range remains unchanged and the driving performance is stable. Moreover, the inlet temperature of the BOG of the screw compressor must be -60 ° C or higher due to the low temperature resistance of the lubricating oil. In contrast to the centrifugal compressor, heating using general-purpose steam used in the ship Since it is only necessary to provide means and heat with a heater, heat exchange is easy, and when a centrifugal compressor is used, a facility for drain treatment generated from LNG used for cooling becomes unnecessary. Furthermore, when pressurizing BOG to 5 to 7 barA, a centrifugal compressor has a two-stage configuration, whereas a screw compressor may have a single stage.
The configuration of the compressor body is simplified.

  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 an 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 an engine room A of an LNG carrier, and a LNG tank 3 having a heat insulating structure in a cargo section B. It is installed. In the cargo section B, two motor-driven oil-cooled screw compressors 4 and 4 are installed, and the upper end of the tank 3 and the inlets of the screw compressors 4 and 4 are connected by BOG supply pipes 21 respectively. Yes. The screw compressors 4 and 4 and the gas engine 2 are connected to each other by a BOG supply pipe 22. Although the illustration of the structure of the oil-cooled screw compressor 4 is omitted, a pair of male and female screw rotors are meshed with each other in the casing, and the volume in the twisted tooth gap is gradually rotated by rotating the rotor. It has a structure that compresses by reducing, and a large amount of lubricating oil is used for lubrication of the rotor drive surface, removal of compression heat, and sealing. Further, a slide valve is built in the main body, and the compression stroke volume itself can be increased or decreased. However, this oil-cooled screw compressor 4 is publicly known.

  Further, a spray pump 6 is disposed near the bottom in the tank 3, one end of the LNG supply pipe 23 is connected to the discharge port of the spray pump 6, and the other end is connected to the inlet of the forced evaporator 5. One end of a BOG supply pipe 24 is connected to the outlet of the forced evaporator 5, and the other end is connected to a mist separator 7 interposed in the pipe 21. Further, the entrance / exit of the forced evaporator 5 is connected by a bypass pipe 25 provided with a temperature control valve 11. The evaporator 5 is a shell and tube type heat exchanger, and uses steam in the ship as a heating medium.

  On the downstream side of the mist separator 7 of the pipe 21, the on-off valve 12 and the BOG heating heater 8 are interposed in this order. The heater 8 is a shell and tube type and uses steam in the ship as a heating medium.

  An oil recovery unit 9 is interposed on the downstream side of each screw compressor 4, 4 of the pipe 22, and a lubricating oil circulation pipe 26 is provided on the downstream side of the oil recovery unit 9 and the lubricating oil injection part of each screw compressor 4, 4. Are connected to each other. The lubricating oil circulation pipe 26 is provided with an oil cooler 13, an oil pump 14, and an oil filter 15 in this order from the downstream side of the oil recovery unit 9. An oil mist separator 16 is provided downstream of the oil recovery unit 9 in the pipe 22, the pipe 22 is branched downstream of the oil mist separator 16, and one end of the branched bypass pipe 27 is connected to the pipe 21. Connected to the downstream side of the heater 8. Further, a bypass valve 17 is interposed in the bypass pipe 27.

  A BOG cooler 18 is interposed between the downstream side of the oil mist separator 16 in the pipe 22 and the gas engine 3. The cooler 18 is a shell and tube type, and fresh water or seawater is used as a refrigerant.

  In addition, the flow rate adjusting valve 10 is interposed in the pipe 23. The pipe 24 is provided with a thermometer 31 and a pressure gauge 32, respectively. The thermometer 31 is connected to the temperature adjustment valve 11 via the temperature control device 19. Further, the thermometer 31 and the pressure gauge 32 are connected to the flow rate adjustment valve 10 via the forced evaporation control device 20. Further, a pressure gauge 33 is interposed on the downstream side of the cooler 18 of the pipe 22. The pressure gauge 33 is connected to the bypass valve 17 and the compressors 4 and 4 via a compressor control device 34.

  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 1 bar.
A • Temperature -150 to −130 ° C. The fuel supply part of the gas engine 2 requires BOG at a pressure of about 6 barA and a temperature of 0 to 50 ° C. Therefore, in this example, basically, one of the oil-cooled screw compressors 4 and 4 (the other compressor 4 is a spare) is used to meet the demand 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 −150 to −130 ° C., and the temperature rises due to intrusion heat while being sent to the screw compressor 4 through the pipe 21, so that it remains as it is, that is, cooling or When it is not heated, it becomes about −80 ° C. at the inlet of the compressor 4. On the other hand, the oil-cooled screw compressor 4 is circulated by mixing with BOG, and at the same time, the low temperature resistance of the lubricating oil to be cooled is -60 ° C. or higher, and is heated by the heater 8 (about + 20 ° C.). Also, the LNG in the tank 3 is fed to the forced evaporator 5 by the spray pump 6, heated and evaporated in the evaporator 5, converted into FBOG, and then the natural gas from the tank 3 in the mist separator 7. Mixed with NBOG. The FBOG contains drain such as butane and propane and is removed by the mist separator 7. The temperature of the FBOG before being sent to the mist separator 7 is about −40 ° C., but the temperature of the BOG is lowered to about −80 to −60 ° C. while being mixed with NBOG and sent from the mist separator 7. . Then, as described above, the BOG is heated by the heater 8 and supplied to the screw compressor 4 at −60 ° C. or higher.

The BOG is compressed by the screw compressor 4 to a pressure of about 6 barA and a temperature of 70 to 80 ° C.
Then, the oil is supplied to the gas engine 2 through the pipe 22. During this time, the lubricating oil is removed by the oil recovery device 9, and the lubricating oil is further removed by the oil mist separator 16. Is cooled. In this way, a BOG having a pressure of about 6 barA and a temperature of 0 to 50 ° C. required by the gas engine 2 is supplied to the gas engine 2. The lubricating oil removed by the oil collector 9 is cooled by the oil cooler 13 while being circulated to the screw compressor 4 by the oil pump 14, and then dust and the like are removed by the oil filter 15. In addition, a part of the BOG supplied to the gas engine 2 after the lubricating oil is removed by the oil mist separator 16 is returned to the screw compressor 4 through the bypass pipe 27 before being cooled by the cooler 18. The amount is feedback controlled based on the pressure value measured by the pressure gauge 33 and automatically adjusted by the bypass valve 17. Further, the slide valve of the screw compressor 4 moves based on the pressure value by the pressure gauge 33, and the flow rate of the BOG is increased or decreased.

  Although one example of the evaporative gas supply system in the liquefied natural gas carrier ship of the present invention has been described above, the present invention is not limited to this and can be implemented as follows.

a) Instead of supplying the BOG produced by forcibly evaporating the LNG stored in the LNG stored in the gas tank 3 from the LNG stored in the forced tank 5 to the upstream side of the screw compressor 4, The BOG supplied to the upstream side of the gas engine 2 and compressed by the screw compressor 4 can be mixed. In this case, however, 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 0 to 50 ° C.

  b) In the above embodiment, the BOG compressed by the screw compressor 4 is only the natural evaporation in the tank 3, so the compressor capacity is reduced to about 1/2 of the compressor capacity in the above embodiment. it can.

It is a systematic diagram which shows the Example of the evaporative gas supply system in the liquefied natural gas carrier ship of this invention. In order to pressurize BOG in an evaporative gas supply system that supplies BOG to a gas engine that uses BOG mainly composed of methane as fuel as LNG stored in a tank mounted on a liquefied natural gas carrier. It is a systematic diagram which shows the whole structure in the case of using a centrifugal compressor of a stage. It is a systematic diagram which shows the supply system to the diesel engine using BOG naturally generated from LNG proposed by Alstorm.

Explanation of symbols

1 BOG supply system 2 Gas engine (gas-fired diesel engine)
3 Tank for LNG 4 Oil-cooled screw compressor 5 Forced evaporator 6 Spray pump 7 Mist separator 8 Heater (heating means)
DESCRIPTION OF SYMBOLS 9 Oil recovery device 10 Flow control valve 11 Temperature control valve 12 On-off valve 13 Oil cooler 14 Oil pump 15 Oil filter 16 Oil mist separator 17 Bypass valve 18 BOG cooler 19 Temperature control device 20 Forced evaporation control device 21,22,24 BOG Supply pipe 23 LNG supply pipe 26 Lubricating oil circulation pipe 27 Bypass pipe 31 Thermometer 32, 33, 35 Pressure gauge 34 Pressure control device

Claims (3)

In the evaporative gas supply system that supplies the evaporative gas to the gas engine that uses the evaporative gas mainly composed of methane as the fuel of the liquefied natural gas stored in the tank mounted on the liquefied natural gas carrier ship,
An oil-cooled screw compressor is used as the compression means for pressurizing the evaporative gas, and the evaporative gas heating means supplied to the screw compressor is connected to the evaporative gas supply path from the tank to the screw compressor. An evaporative gas supply system for a liquefied natural gas carrier characterized by being installed in the middle of A pressure measuring device is interposed in the evaporative gas supply path to the gas engine on the downstream side of the screw compressor, and the pressure measuring device is arranged so that the pressure of the evaporating gas supplied to the gas engine is maintained at a predetermined pressure. The evaporative gas supply system for a liquefied natural gas carrier according to claim 1, wherein the evaporative gas flow rate from the screw compressor to the gas engine is feedback-controlled based on a measured value. An evaporator for forcibly evaporating liquefied natural gas stored in the tank is interposed between the tank and the oil-cooled screw compressor upstream side or the gas engine upstream side. The evaporative gas supply system for a liquefied natural gas carrier according to claim 1 or 2.

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