CN101245897A

CN101245897A - LNG tank, LNG conveying tool, safety valve and method for setting the same

Info

Publication number: CN101245897A
Application number: CNA2007101631434A
Authority: CN
Inventors: 李正汉; 崔廷豪; 韩成坤; 崔东圭; 文荣植
Original assignee: Daewoo Shipbuilding and Marine Engineering Co Ltd
Current assignee: Hanhua Ocean Co ltd
Priority date: 2007-02-12
Filing date: 2007-10-10
Publication date: 2008-08-20
Anticipated expiration: 2027-10-10
Also published as: CN101245893A; EP1956287A3; JP2008196682A; JP2010261595A; CN101245892A; CN103398284B; CN103398284A; EP1956287A2; CN101245897B; CN101245892B; KR100805022B1; CN101245893B

Abstract

The invention provides a LNG storage tank, a LNG carrier, a safety valve and method for setting the safety valve. The set pressure of the safety valve during the loading of LNG differs from the set pressure of the safety valve during the voyage of the LNG carrier, and the set pressure of the safety valve during the loading of LNG is higher than the set pressure of the safety valve during the voyage of the LNG carrier.

Description

The method of LNG storage tank, LNG means of transportation, safety valve and setting safety valve

Technical field

(it has and is used for handling boil-off gas (boil-off gas, member BOG) that the LNG storage tank produces for liquefied natural gas, LNG) means of transportation to the present invention relates to a kind of LNG Liquefied natural gas.

Background technique

In general, in liquefaction device with rock gas (natural gas, NG) be transformed into liquid (being also referred to as LNG Liquefied natural gas or LNG), transport for long-distance and by floating storage and (the floating storage and re-gasification unit of the unit that gasifies again by the LNG means of transportation, FSRU) or land unloading harbour gasify again, to be supplied to the Consumer.

Gasifying by LNG at LNG, (LNG re-gasification vessel, LNG-RV) under Yun Shu the situation, LNG through gasification again, and without FSRU or land unloading harbour, and then directly is supplied to the Consumer to boats and ships in LNG-RV itself again.

Because the liquefaction of rock gas is to take place under-163 ℃ the cryogenic temperature approximately under external pressure, so even when the temperature of LNG under external pressure a little more than-163 ℃, LNG also is vaporized probably.Under the situation of existing LNG means of transportation with adiabatic LNG storage tank, because heat constantly is delivered to the LNG the LNG storage tank from the outside, so during by existing LNG means of transportation transportation LNG, LNG constantly is vaporized and produces boil-off gas in the LNG storage tank.

If in the LNG storage tank, produce boil-off gas as mentioned above, just the pressure of LNG storage tank can increase and become comparatively dangerous so.

Conventionally, in order to keep constant pressure in the LNG storage tank of using at the LNG means of transportation, the boil-off gas that produces in the LNG storage tank can be consumed as the fuel that advances the LNG means of transportation in the past.That is to say, the existing LNG means of transportation that is used for the liquid LNG of transfer of cryogenic maintains-163 ℃ approximately with the temperature of the LNG of LNG storage tank at LNG between the delivery period basically under external pressure, promptly, LNG in the LNG storage tank is maintained almost stationary temperature and pressure, handle boil-off gas so the former meeting of described LNG means of transportation is discharged into the outside by the boil-off gas that will be produced.

The problem of the steam turbine propulsion system that drives by the steam that produces in the boiler by the boil-off gas that produces in the burning LNG storage tank is that propulsive efficiency is lower.

In addition, after the boil-off gas that the dual-fuel diesel engine electric propulsion system produces described boil-off gas is used as the fuel of diesel engine in compression LNG storage tank, its propulsive efficiency is higher than the steam turbine propulsion system, but the complexity integration in described system is difficult to maintenance owing to medium speed diesel engine and electronic propulsion unit.In addition, this system that supplies of boil-off gas must being acted as a fuel must the using gases compression method, and needed installation of this method and running cost are higher than the liquid compression method.

In addition, this use boil-off gas can't be realized the efficient of employed two-stroke low speed diesel engine in the common ship as the conventional method of propellant.

Also exist and a kind ofly the boil-off gas that produces in the LNG storage tank is liquefied again and make again the boil-off gas of liquefaction turn back to method in the LNG storage tank.Yet the problem of this method that boil-off gas is liquefied again is, complicated boil-off gas liquefaction device again is installed in the LNG means of transportation.

In addition, when the amount of the boil-off gas that produces in the LNG storage tank surpasses propulsion system or boil-off gas again during the capacity of liquefaction device, unnecessary boil-off gas must be burnt by gas combustion unit.Therefore, described method has the problem of the auxiliary unit of for example gas combustion unit that need be used to handle unnecessary boil-off gas.

For instance, illustrated as Fig. 4, under the existing situation of keeping the LNG means of transportation of constant compression force almost basically in the LNG storage tank, the LNG storage tank is in first period (after wherein having loaded LNG 3 to 5 days) some warm.Therefore, solid line as place, figure middle and upper part is indicated, with natural boil-off gas (natural boil-off gas, NBOG) amount is compared, can produce quite a large amount of unnecessary boil-off gas at LNG between the delivery period, and this unnecessary boil-off gas surpasses boiler or dual fuel diesel electromechanics moves the fuel quantity that propulsion system is consumed.Therefore, (described oblique line represents to be different from the dotted line of figure middle and lower part, is used for illustrating the employed boil-off gas scale of construction of boiler or engine for gas combustion unit, GCU) burning must to pass through gas combustion unit corresponding to the boil-off gas scale of construction of oblique line.In addition, when LNG means of transportation TC (for example, be 5 to 6 days among Fig. 4), owing to do not consume the boil-off gas (when the wait of LNG means of transportation enters the canal) of any amount in boiler or the engine, the perhaps boil-off gas scale of construction of Xiao Haoing less (when LNG means of transportation TC) is so be used to advance the but not used up as yet unnecessary boil-off gas of engine must be burned to fall.In addition, in addition when the LNG means of transportation that wherein is mounted with LNG when wait enters the harbour or is just entering the harbour, therefore do not consume the boil-off gas of any amount or consume a small amount of boil-off gas, and must burn unnecessary boil-off gas.

At capacity is 150,000m ³The situation of LNG means of transportation under, the boil-off gas of burning is annual nearly 1500 to 2000 tons as mentioned above, spend about 700,000 dollars, and the burning of boil-off gas causes environmental pollution problem.

KR 2001-0014021 number, KR 2001-0014033 number, KR 2001-0083920 number, KR 2001-0082235 number and KR 2004-0015294 Korean Patent in early days openly case disclose and be suppressed at the technology that produces boil-off gas in the LNG storage tank by the following method: the pressure of the boil-off gas in the LNG storage tank is maintained under the high pressure of about 200 crust (gauge pressure), and need not as above-mentioned low-pressure tank, in the LNG storage tank, adiabatic wall to be installed.Yet this LNG storage tank must have big thickness so that storage has the boil-off gas that about 200 Bagaos are pressed, and therefore its problem is that manufacture cost increases, and for example needs that the additional assemblies of high pressure compressor maintains about 200 crust with the pressure with boil-off gas.Also have a kind of technology that is called pressure reservoir, described technology is different from above-mentioned technology.When at room temperature storing the liquid of highly volatile in the ultrahigh pressure basin, this ultrahigh pressure basin does not have the problem of handling boil-off gas, but has other problem, should can not improve than big and manufacture cost such as basin.

As mentioned above, conventionally, the LNG storage tank that the LNG means of transportation is used and allows to produce boil-off gas near LNG between the delivery period maintains the constant pressure of cryogenic liquide external pressure, so described LNG storage tank has the problem that consumes a large amount of boil-off gas or extra liquefaction device again is installed.In addition, different with the basin that transports described cryogenic liquide with low atmospheric pressure, use the LNG means of transprotation of basins such as pressure reservoir for example under slightly high temperature, to bear high pressure,, but aspect basin big or small, have restriction and need higher manufacture cost so it does not need to handle boil-off gas.

Summary of the invention

[the present invention is with the technical problem that solves]

In order to solve the problems referred to above that prior art proposes, the invention provides the basin that a kind of pressure that is used for the LNG of transfer of cryogenic liquid state omits high (near external pressure).The purpose of this invention is to provide a kind of jumbo LNG storage tank that has, it can be made under the situation that does not improve manufacture cost and can reduce waste to boil-off gas, and a kind of method that is used to use described LNG storage tank transportation LNG is provided or a kind ofly is used to use described LNG storage tank to handle the method for boil-off gas.

[technological means]

To achieve these goals, the invention provides the LNG storage tank of the LNG that is used for the transfer of cryogenic liquid state of a kind of slightly high pressure (near external pressure), it is characterized in that allowing pressure in the LNG storage tank that to a certain degree change is arranged between the delivery period at LNG.

One embodiment of the present of invention are handled in the LNG means of transportation of member a kind of LNG means of transportation and a kind of method with following feature are provided having the boil-off gas that is used for handling the boil-off gas that the LNG storage tank produces: during transportation LNG in the LNG storage tank, allow vapor pressure in the LNG storage tank and the temperature of LNG to increase.

In general, known following method is the means that are used to handle boil-off gas: will be used for boiler (for example, steam turbine advances boiler) from the boil-off gas that the LNG storage tank produces; Use the fuel of boil-off gas as the gas engine of for example DFDE and MEGI; Boil-off gas is used for gas turbine; And boil-off gas liquefied again, and make the boil-off gas of liquefaction again turn back to LNG storage tank (openly case, number of registration are 0489804 and 0441857 Korean Patent and the open case of 2006-0000158 Korean Utility Model in early days referring to the 2004-0046836 Korean Patent).These methods have for example gas combustion unit (gas combustion unit, the problem of the boil-off gas waste that boil-off gas combustion structure GCU) produces, described boil-off gas combustion structure be used for surpassing general boil-off gas handle member capacity unnecessary boil-off gas (for example, after loading LNG), the perhaps boil-off gas of (for example, when the LNG means of transportation enters or leave harbour and Dang Qi TC) when boil-off gas can't be handled member and handled by boil-off gas.

The present invention has by improving flexibility that boil-off gas handles and eliminates advantage to this waste of boil-off gas.According to LNG means of transportation of the present invention needs GCU not, perhaps may need to improve and in case of emergency handle or the flexibility of management boil-off gas with GCU.

LNG means of transportation of the present invention is equipped with boil-off gas to handle member, for example boiler, liquefaction device and gas engine again, and the LNG storage tank is outside handles described boil-off gas by being discharged into from the boil-off gas that the LNG storage tank produces to be used for.

Another embodiment of the present invention provides a kind of method of setting safety valve in the method that is used for controlling the safety valve that place, LNG storage tank top that the LNG means of transportation uses provides, and described method is characterised in that safety valve is different in the setting pressure of LNG means of transportation term of voyage with safety valve in the setting pressure of LNG loading days.The LNG means of transportation that the present invention also provides a kind of safety valve, LNG storage tank and has described feature.

Conventionally, by the LNG storage tank top of using at the LNG means of transportation of the LNG of transfer of cryogenic liquid state safety valve is installed and is managed pressure in the LNG storage tank safely.Some known methods of managing the pressure in the LNG storage tank safely are: avoid the contingent blast of LNG storage tank by safety valve; And after loading LNG, handle the boil-off gas that produces from the LNG storage tank by above-mentioned method, described method comprises: boil-off gas is used for boiler (for example, steam turbine advance boiler), boil-off gas is used for gas turbine as the fuel of the gas engine of for example DFDE and MEGI, with boil-off gas and the boil-off gas and make the boil-off gas of liquefaction again turn back to the LNG storage tank of liquefying again.These methods have for example problem of the boil-off gas combustion structure waste boil-off gas of GCU, described member is used for surpassing the unnecessary boil-off gas that general boil-off gas is handled the capacity of member after LNG is loaded in the LNG means of transportation, perhaps is used for the boil-off gas when the LNG means of transportation enters or leave harbour and Dang Qi TC.Pressure in the LNG storage tank of the LNG means of transportation being used by these methods maintains in the prespecified range.

In this LNG means of transportation, when the setting value of safety valve was 0.25 crust, maximum was had an appointment and 98% is mounted with LNG in all told of LNG storage tank, and all the other about 2% remain empty.Be mounted with LNG more than 98% if having in all told of LNG storage tank, then when the pressure of LNG storage tank reached 0.25 crust, the LNG in the LNG storage tank may overflow from the dome on storage tank top.As shown in another embodiment of the present invention, if after loading LNG, constantly allow the pressure of the LNG in the LNG storage tank to increase, even so when loading a small amount of LNG, because the LNG temperature raises and causes LNG to expand under according to the setting pressure of safety valve of the present invention, so the LNG in the LNG storage tank still may overflow.For instance, found that even if having 97% to be mounted with LNG in all told of LNG storage tank, the LNG in the LNG storage tank still may overflow when the vapor pressure in the LNG storage tank is 0.7 crust.This directly causes needs to reduce the amount of the LNG that will load.

Therefore, not that the setting pressure of safety valve that LNG storage tank top is provided is fixed on the slightly high pressure near external pressure all the time, but can need not in the following manner to reduce initial LNG useful load and reduce the waste of boil-off gas or increase the flexibility that boil-off gas is handled: at the LNG loading days, the same setting pressure with safety valve with existing LNG means of transportation than low pressure (for example is fixed on, 0.25 crust), and then begin the navigation back by (for example using some boil-off gas at the LNG means of transportation, with the fuel of boil-off gas as boiler or engine) and when reducing LNG amount in the LNG storage tank, improve the setting pressure of safety valve as another embodiment of the present invention.The present invention is being applied to (for example to be equipped with boil-off gas processing member, boiler, liquefaction device or gas engine again) the LNG means of transportation time, be used for handling the boil-off gas that produces from the LNG storage tank, and have big effect aspect the waste of eliminating volatilization gas by volatilization gas being discharged into LNG storage tank outside.

Therefore, in the present invention, be discharged into the outside LNG amount that reduces in the LNG storage tank of storage tank by the boil-off gas that produces in the LNG storage tank after, increase the setting pressure of safety valve: preferable case is, the LNG loading days setting pressure is set at 0.25 cling to or below; And LNG means of transportation term of voyage with pressure be set at from be higher than 0.25 cling to 2 the crust, and more preferably from be higher than 0.25 cling to 0.7 the crust.Here, safety valve can for example cling to 0.7 crust from 0.4 according to increasing gradually according to the employed boil-off gas scale of construction of navigation condition in the setting pressure of LNG means of transportation term of voyage.

Therefore, in the present invention, the expression of " at LNG means of transportation term of voyage " mean when the LNG means of transportation loading LNG therein and after beginning to navigate by water the volume of the LNG in the LNG storage tank owing to used some boil-off gas and when reducing slightly.For instance, the LNG volume that is desirably in the LNG storage tank is that 98.5% o'clock setting pressure with safety valve is set at 0.25 crust, when the LNG volume is 98.0%, be set at 0.4 crust, when the LNG volume is 97.7%, be set at 0.5 crust, and when the LNG volume is 97.1%, be set at 0.7 crust.

The LNG storage tank that another embodiment of the present invention provides a kind of LNG means of transportation that is used for the liquid LNG of transfer of cryogenic to use, it is characterized in that, with the setting pressure that is provided at the safety valve on described LNG storage tank top be set at from be higher than 0.25 cling to 2 the crust, preferably cling to 0.7 crust, and be more preferably 0.7 crust from being higher than 0.25.The present invention also provides a kind of method of setting safety valve, LNG storage tank and having the LNG means of transportation of described technical characteristics of being used to.

Because the problem that the manufacture cost that this method has boil-off gas bigger waste and LNG means of transportation increases, so the present invention has solved described problem in the following manner: the setup pressure value that increases the safety valve of LNG storage tank, thereby allow after loading LNG to the LNG means of transportation term of voyage of unloading LNG, the pressure in the LNG storage tank increase and the LNG storage tank in the temperature increase of LNG.

The LNG storage tank that another embodiment of the present invention provides a kind of LNG means of transportation that is used for the liquid LNG of transfer of cryogenic to use, it is characterized in that the vapor pressure in the LNG storage tank is controlled near in the external pressure, and allow to increase vapor pressure in the LNG storage tank and the pressure of the LNG in the LNG storage tank between the delivery period at LNG.The feature of LNG storage tank is that also the scope of the vapor pressure in the LNG storage tank is clung to 2 crust from being higher than 0.25, preferably clings to 0.7 crust from being higher than 0.25, and is more preferably 0.7 crust.In addition, the LNG storage tank is characterised in that the boil-off gas on LNG storage tank top mixes with the LNG of LNG storage tank bottom, distributes so that keep even temperature in the LNG storage tank.On the one hand, because more LNG is evaporated probably when the temperature of a part of LNG storage tank is higher than the temperature of its another part, so be desirably in the uniform temperature distribution of keeping LNG or boil-off gas in the LNG storage tank.On the other hand, because the thermal capacity of the boil-off gas on LNG storage tank top is less than the LNG of LNG storage tank bottom, the local sharply increase of the temperature that LNG storage tank top causes because of the heat from the outside to the LNG storage tank enters may cause the pressure the LNG storage tank sharply to increase.Can mix the pressure that prevents in the LNG storage tank with the LNG of LNG storage tank bottom by the boil-off gas with LNG storage tank top sharply increases.

In addition, according to another embodiment of the present invention, the vapor pressure in the LNG storage tank that the LNG means of transportation is used can through control with the LNG storage tank in pressure coupling so that admit LNG at the LNG harbour.For instance, higher (for example in order to the pressure that is in the LNG storage tank of wherein admitting LNG at LNG unloading harbour, LNG-RV or FSRU, about 0.4 to 0.7 crust) under the situation, the pressure in the LNG storage tank that the LNG means of transportation is used continues to increase at LNG means of transportation term of voyage; With prior art under the situation of the same pressure lower (about 0.2 crust) that is used for being in the LNG storage tank of wherein admitting LNG at LNG unloading harbour, by according to the present invention utilization can reduce to boil-off gas waste in the flexibility aspect the boil-off gas processing, can make the pressure coupling of pressure and the LNG storage tank that is used to admit LNG in the LNG storage tank that the LNG means of transportation uses.

In addition, another embodiment of the present invention provides a kind of method with liquid LNG of transfer of cryogenic of described technical characteristics, and the LNG means of transportation with described LNG storage tank.

Exactly, according to another embodiment of the present invention, be used for liquid the having of LNG of transfer of cryogenic and be characterised in that, allow pressure in the LNG storage tank that to a certain degree change is arranged between the delivery period at LNG near the slightly high film LNG storage tank of the pressure of external pressure.The membrane according to the invention basin is an IGC rule 2000) cargo hold of the LNG basin that defines.More particularly, membrane tank is a kind of non-self-bearing type basin, and it has the adiabatic wall in the main body of being formed on, and has the film that is formed on basin top.In the application's case, membrane tank is in order to comprise half membrane tank.

Some examples of membrane tank are following GTT NO 96-2 and MARK III, and the basin of describing in No. 499710 and No. 644217 Korean Patent.

Membrane tank can be through design standing pressure up to 0.7 crust (gauge pressure) by strengthening basin, but the regulation membrane tank should be through design to have the pressure that be no more than 0.25 crust usually.All existing membrane tanks all meet this regulation, and the vapor pressure in management makes basin be 0.25 crust or below, and the temperature and pressure of LNG almost is constant at term of voyage.On the contrary, the invention is characterized in, 0.25 crust or above, preferably cling to 2 crust or following and more preferably cling under 0.7 crust or the following pressure from being higher than 0.25 from being higher than 0.25, allow pressure in the basin and the temperature of LNG to increase.In addition, be characterised in that by the method for using the LNG storage tank to handle boil-off gas, in the LNG storage tank, keep even temperature and distribute according to of the present invention.

According to another embodiment of the present invention, the invention provides a kind of big LNG means of transportation, and have about 100,000m ³Or the LNG means of transportation of above LNG storage capacity.Under situation, for the LNG storage tank is manufactured pressure storage tank, because the thickness of basin increases, so manufacture cost sharply increases with jumbo LNG means of transportation.Make in as the present invention under the situation near the basin of the relative pressure of atmospheric pressure with about 1 crust, manufacture cost does not sharply increase, and basin can transport LNG, and stands the pressure that boil-off gas produces in fact and do not handle boil-off gas.

Description of drawings

Fig. 1 illustrates according to the preferred embodiment of the invention the schematic representation that absorbs the principle that enters the heat in the LNG storage tank that the LNG means of transportation uses.

Fig. 2 is the schematic representation of the LNG storage tank that illustrates that LNG means of transportation is according to the preferred embodiment of the invention used.

To be explanation handle the schematic representation of the configuration of boil-off gas (BOG) according to the preferred embodiment of the present invention to Fig. 3 at the unloading harbour by the LNG storage tank that uses the LNG means of transportation and use.

Fig. 4 is that explanation is kept the almost figure of the waste boil-off gas of the LNG means of transportation of constant compression force basically according to prior art in the LNG storage tank.

Fig. 5 is the figure of the pressure operation type of the LNG storage tank that illustrates that the LNG means of transportation term of voyage that is mounted with LNG is therein used according to the pressure of LNG storage tank and to the LNG means of transportation at LNG unloading harbour place.

Fig. 6 is the figure that explanation is used for the method that the LNG towards LNG storage tank bottom injects from LNG storage tank top with boil-off gas.

Fig. 7 is explanation by receiving related data at term of voyage in real time and suitably handling and calculate described data and show the figure of system of current allowance maximum set pressure of the safety valve of the LNG storage tank that the LNG means of transportation is used in real time.

Fig. 8 explanation is according to the gas meter of LNG means of transportation of the present invention.

Fig. 9 illustrates the gas meter of conventional LNG means of transportation.

Figure 10 explanation is fed to LNG storage tank bottom with it according to the embodiment of the invention after the boil-off gas compression.

Figure 11 is the schematic representation of explanation according to the fuel gas supply system of the LNG means of transportation of the embodiment of the invention.

The LNG storage tank 2 that the 1:LNG means of transportation is used: the LNG storage tank that the unloading harbour is used

3: compressor 4: after-condenser

5: vaporizer 11:LNG pump

13:LNG sparger 21: boil-off gas (BOG) injection nozzle

23: boil-off gas (BOG) compressor P: high-pressure service pump

Embodiment

Below will describe the preferred embodiments of the present invention in detail referring to accompanying drawing.

LNG storage tank according to the present invention can be applicable to the storage of LNG means of transportation, LNG floating and the unit (FSRU) that gasifies again, land unloading harbour and the LNG boats and ships (LNG-RV) etc. that gasify again.The LNG storage tank has the following advantages: reduce waste to boil-off gas by allow to increase the pressure and temperature in the LNG storage tank and solved the problem of handling boil-off gas; And increased the flexibility (for example transporting and store LNG) that LNG handles, because consider the LNG demand, can in all types of LNG storage tanks, store LNG chronically.

To mainly embodiments of the invention be described by the example that can be applicable to the LNG storage tank that the LNG means of transportation uses.

Fig. 1 illustrates according to the present invention the principle that absorbs the heat that enters the LNG storage tank that the LNG means of transportation uses.In the prior art, pressure in the LNG storage tank that the LNG means of transportation is used is maintained in the prespecified range, and therefore, the most of heats that enter the LNG storage tank from the outside can cause producing boil-off gas, and all evapn gas all should be handled in the LNG means of transportation.On the contrary, according to the present invention, pressure in the LNG storage tank that permission LNG means of transportation is used increases, thereby increased saturation temperature, and therefore, most of heats are increased (it is to cause because of saturation temperature increases) and absorb by the tangible heat of LNG in the LNG storage tank or rock gas (NG), thereby significantly reduce the generation of boil-off gas.For instance, the pressure of the LNG storage tank of using when the LNG means of transportation is when the initial pressure of 0.06 crust is increased to 0.7 crust, and saturation temperature increases about 6 ℃.

Fig. 2 schematically illustrates the LNG storage tank that LNG means of transportation is according to the preferred embodiment of the invention used.Be formed with therein in the LNG storage tank 1 that the LNG means of transportation of adiabatic wall uses, under the situation of normal load LNG, pressure when the LNG means of transportation begins to navigate by water in the LNG storage tank 1 is about 0.06 crust (gauge pressure), and at LNG means of transportation term of voyage, because the generation of boil-off gas, described pressure increases gradually.For instance, after the position that is producing LNG is loaded into LNG in the LNG storage tank 1, pressure in the LNG storage tank 1 that the LNG means of transportation is used just in time is 0.06 crust, and rises to 0.7 crust when the LNG means of transportation arrives the destination after about 15-20 days navigation of process.

About the temperature aspect, the boiling point that generally contains the LNG of many impurity is lower than pure methane liquid.The boiling point of pure methane is-161 ℃ approximately under 0.06 crust, and to transport for example contain that the boiling point of the LNG of impurity such as nitrogen, ethane is-163 ℃ approximately.Based on pure methane, the temperature of the LNG in the LNG storage tank after in being loaded into the LNG storage tank is-161 ℃ approximately under 0.06 crust.If the vapor pressure in the LNG storage tank is controlled to be 0.25 crust, then consider the consumption of transportation range and boil-off gas, the temperature of LNG is increased to-159 ℃ approximately; If the vapor pressure in the LNG storage tank is controlled to be 0.7 crust, then the temperature of LNG is-155 ℃ approximately; If the vapor pressure in the LNG storage tank controls to 2 crust, then the temperature of LNG is increased to-146 ℃ approximately.

The LNG storage tank that LNG means of transportation according to the present invention is used comprises adiabatic wall, and considers that in its design the pressure that generation caused of boil-off gas increases.That is to say that the LNG storage tank increases with the pressure that generation was caused that has full intensity and stand boil-off gas through design.Therefore, the boil-off gas that produces in the LNG storage tank 1 that the LNG means of transportation is used is accumulated therein at LNG means of transportation term of voyage.

The LNG storage tank of using according to the LNG means of transportation of the embodiment of the invention 1 preferably includes adiabatic wall, and through design standing from being higher than 0.25 pressure that clings to 2 crust (gauge pressure), and more preferably, the pressure of 0.6 to 1.5 crust (gauge pressure).Considering the transportation range of LNG and current IGC rule, the LNG tank designs need be become stand to be higher than 0.25 and cling to 0.7 pressure that clings to, exactly is the pressure of about 0.7 crust.Yet, make hypotony and non-required, too short because the transportation range of LNG can become, and make overpressure can cause being difficult to make the LNG storage tank.

In addition, because the LNG storage tank 1 that LNG means of transportation according to the present invention is used can demonstrate fully in the following manner: during initial designs, LNG storage tank 1 is designed to have than big thickness, perhaps only by in the general LNG storage tank that existing LNG means of transportation is used, adding hardening agent suitably to strengthen existing storage tank, and need not bigger change is made in the design of existing LNG storage tank, so it is economical aspect manufacture cost.

The LNG storage tank that the LNG means of transportation that wherein has adiabatic wall of various routines is used is known in following correlation technique.Therefore, omitted adiabatic wall among Fig. 1.

The LNG storage tank that is installed in the LNG means of transportation can be divided into the basin of independent type and the basin of film type, and followingly will make detailed description it.

GTT NO 96-2 in the following table 1 and GTT Mark III merge into GTT (Gaztransport ﹠amp in Gaz Transport (GT) company and Technigaz (TGZ) company in nineteen ninety-five; Technigaz) rename by GT and TGZ respectively during company.

The classification of (table 1) LNG storage tank

Classification	Film type		Independent type
	Film type		Independent type		?GTT?Mark?III	GTT?No.96-2	MOSS	IHI-SPB
	Basin material--thickness	?SUS?304L ?--1.2mm	Invar--0.7mm	Aluminium alloy (5083)--50mm	?GTT?Mark?III	GTT?No.96-2	MOSS	IHI-SPB	Aluminium alloy (5083)--maximum 30mm
Heat sink material--thickness	Basin material--thickness	?SUS?304L ?--1.2mm	Invar--0.7mm	Aluminium alloy (5083)--50mm	Enhancement mode polyurethane foam--250mm	Plywood Case+perlite--530mm	Polyurethane foam--250mm	Polyurethane foam--250mm	Aluminium alloy (5083)--maximum 30mm

US 6,035, No. 795, No. 6,378,722, US and 5,586, No. 513 U. S. Patents of US; U.S. Patent Publication case US 2003-0000949, KR 2000-0011347 number and KR2000-0011346 Korean Patent have openly disclosed the basin of GT type and TGZ type in early days in the case.

No. 499710 and No. 0644217 Korean Patent have disclosed the adiabatic wall that is embodied as other principle.

Prior art has disclosed the LNG storage tank that LNG means of transportation with various types of adiabatic walls is used, and it will suppress the generation of boil-off gas as much as possible.

The present invention can be applicable to the conventional LNG storage tank that aforesaid LNG means of transportation with various types of adiabatic functions is used.These LNG storage tanks that the LNG means of transportation is used cling to or following pressure to stand 0.25 through design mostly, and the boil-off gas that produces in the LNG storage tank is fallen as the fuel consumption that advances the LNG means of transportation to use, perhaps boil-off gas is liquefied again the pressure in the LNG storage tank is maintained 0.2 crust or following (for example 0.1 crust), if and the pressure in the LNG storage tank is increased to and surpasses described value, then burn part or all of boil-off gas.In addition, have safety valve in these LNG storage tanks, and if the LNG storage tank fail to control as mentioned above wherein pressure, then boil-off gas is discharged into LNG storage tank outside by safety valve (in most cases its setting pressure is 0.25 crust).

Comparatively speaking, in the present invention, the pressure of safety valve is set to 2 crust from being higher than 0.25 crust, preferably clings to 0.7 crust from 0.25, and more preferably about 0.7 crust.

In addition, LNG storage tank according to the present invention is configured to increase by the part of the temperature and pressure that reduces the LNG storage tank, and reduces the pressure in the LNG storage tank.The LNG storage tank is kept its even temperature in the following manner and distributed: the LNG that LNG storage tank bottom is had a lower temperature has higher temperature towards LNG storage tank top boil-off gas sprays, and the boil-off gas that LNG storage tank top is had a higher temperature has a lower temperature towards LNG storage tank bottom LNG sprays.

In Fig. 2, the LNG storage tank 1 that the LNG means of transportation is used possesses LNG pump 11 and boil-off gas injection nozzle 21 in its underpart, and possesses LNG sparger 13 and boil-off gas compressor 23 at an upper portion thereof.LNG pump 11 and boil-off gas compressor 23 can be installed in LNG storage tank top or bottom.The LNG that LNG storage tank 1 bottom is had lower temperature is fed to the LNG sparger 13 that is provided at LNG storage tank top by LNG pump 11, and then spray towards the top that LNG storage tank 1 has high temperature, and the boil-off gas with higher temperature on LNG storage tank 1 top is fed to the boil-off gas injection nozzle 21 that is provided at LNG storage tank 1 bottom by boil-off gas compressor 23, and then inject towards the bottom with lower temperature of LNG storage tank 1, thereby the even temperature of keeping LNG storage tank 1 distributes, and finally reduces the generation of boil-off gas.

The generation of this minimizing boil-off gas is particularly useful for the pressure that increases gradually in the LNG storage tank, because the increase that does not have boil-off gas to handle the generation of the boil-off gas in the LNG means of transportation of member and the pressure in the LNG storage tank has contacts directly.Have at the LNG means of transportation under the situation of boil-off gas processing member, if the pressure in the LNG storage tank increases, then the boil-off gas with specified quantitative is discharged into the outside, thus the pressure in the control LNG storage tank, and therefore can need not to spray LNG or injection boil-off gas at LNG means of transportation term of voyage.

In addition, be loaded in the LNG means of transportation, then can during LNG is transported to the destination, further reduce the generation (or increase of pressure) of boil-off gas if LNG sentences supercooled liquid at the production harbour of producing LNG.After sentencing supercooled liquid loading LNG at the production harbour, the pressure in the LNG storage tank that the LNG means of transportation is used may be negative pressure (0 crust or following).In order to prevent that pressure is reduced to negative pressure, available nitrogen is filled the Steam area of LNG storage tank.

Below will describe the LNG storage tank that uses this LNG means of transportation to use and handle the method for boil-off gas.

At LNG means of transportation term of voyage, the LNG storage tank 1 that LNG means of transportation according to the present invention is used allows to have in the LNG storage tank 1 pressure to increase, and need not to handle in the LNG storage tank 1 boil-off gas that produces, thereby increase the temperature in the LNG storage tank 1, and be LNG in the LNG storage tank and the internal energy of NG, and then when arriving the destination, the LNG means of transportation manages the boil-off gas of accumulating in the LNG storage tank 1 that the LNG means of transportation uses everywhere at the unloading harbour with the most accumulation of heat that is entered.

Fig. 3 schematically illustrates the LNG storage tank that is used to use LNG means of transportation according to the preferred embodiment of the invention to use is managed boil-off gas everywhere at the unloading harbour configuration.

The unloading harbour is equipped with LNG storage tank 2, high pressure compressor 3a, low pressure compressor 3b, after-condenser 4, high-pressure service pump P and the vaporizer 5 that a plurality of unloading harbours are used.

Because accumulation has a large amount of boil-off gas in the LNG storage tank 1 that the LNG means of transportation is used, thus by high pressure compressor 3a the boil-off gas in the LNG storage tank 1 is compressed to the 70-80 crust at unloading harbour place usually, and then directly be supplied to the Consumer.Usually the part boil-off gas of accumulation is compressed to about 8 crust in the LNG storage tank 1 that can the LNG means of transportation be used by low pressure compressor 3b, and then by carrying out condensation again through after-condenser 4, and then gasify so that be supplied to the Consumer again by vaporizer 5.

When the LNG storage tank that LNG is used from the LNG means of transportation is unloaded to the LNG storage tank used of unloading harbour, because the pressure of the LNG storage tank that the LNG means of transportation is used is higher than the pressure of the LNG storage tank used of unloading harbour, can flow in the LNG storage tank used of unloading harbour so have the LNG of elevated pressures, therefore can produce extra boil-off gas.For the generation with extra boil-off gas minimizes, can in the following manner LNG be supplied to the Consumer: the LNG storage tank that LNG is used from the LNG means of transportation directly is transferred to the inlet of the high-pressure service pump of unloading harbour.Because the pressure in the LNG storage tank is higher during the LNG unloading,, the LNG storage tank that LNG means of transportation according to the present invention is used shortens 10% to 20% advantage than conventional LNG storage tank so having unloading time.

Be fed to substituting of LNG storage tank 2 that the unloading harbour uses as the LNG of storage in the LNG storage tank of the LNG means of transportation being used at unloading harbour place 1, described LNG can be fed to after-condenser 4 with boil-off gas condensation again, and then it is gasified again, thereby it directly is supplied to the Consumer by vaporizer 5.

On the other hand, if after-condenser is not installed, then LNG directly can be fed to the suction port of high-pressure service pump P at unloading harbour place.

As mentioned above, if unloading harbour place is equipped with the LNG storage tank 2 that a plurality of unloading harbours are used, and the LNG storage tank 1 that LNG uses from the LNG means of transportation is assigned to a plurality of LNG storage tanks 2 of using of unloading harbour each equably, then because the generation of boil-off gas is distributed to a plurality of LNG storage tanks 2 that the unloading harbour is used, so the influence of the generation of the boil-off gas in the LNG storage tank that the unloading harbour can be used minimizes.Because the amount of the boil-off gas that produces in the LNG storage tank that the unloading harbour is used is less, so by low pressure compressor 3b boil-off gas is compressed to about 8 crust usually, and then pass through through after-condenser 4 and with its condensation again, and then gasify again by vaporizer 5, so that be supplied to the Consumer.

In addition, according to the present invention, because the LNG storage tank used of LNG means of transportation to be being higher than the pressure operation of existing design pressure, during the LNG unloading, do not keep pressure in the LNG storage tank that the LNG means of transportation uses so do not need to be used in the process of filling boil-off gas or NG steam in the LNG storage tank that the LNG means of transportation uses.

In addition, if the conventional LNG storage tank to LNG harbour or the floating storage and unit (FSRU) usefulness that gasifies is again made amendment, perhaps build the new LNG storage tank of the storage of unloading harbour or floating and unit (FSRU) usefulness that gasifies again, so that the pressure of the LNG storage tank that the storage pressure of LNG storage tank is used corresponding to LNG means of transportation according to the present invention, then from the LNG means of transportation, extra boil-off gas can be do not produced during the unloading LNG, and therefore existing Unloading Technology can be used.

According to the present invention, the storage of LNG floating and the unit (FSRU) that gasifies again have more flexibility and therefore may not need after-condenser at the boil-off gas management aspect.

According to the present invention, the flash gasoline of generation will reduce in a large number or no longer exist be unloaded to the storage of LNG floating and the unit (FSRU) that gasifies again from LNGC during, and owing to saved the time of disposing flash gasoline, so the operating time will reduce in a large number.And the freighter pressure that therefore unloads LNGC will have more flexibility.

According to the present invention, LNG gasifies again, and boats and ships (LNG-RV) can have above-mentioned LNG means of transportation and the LNG floating is stored and both advantages of unit (FSRU) that gasify again.

Fig. 5 explanation is according to the pressure in the LNG unloading harbour LNG of the place storage tank, is mounted with the pressure operation type of the LNG storage tank that the LNG means of transportation term of voyage LNG means of transportation of LNG uses therein.The indication of F pattern is at the term of voyage of LNG means of transportation, (for example) if the authorized pressure scope of the LNG storage tank at unloading harbour place for from 0.7 cling to 1.5 crust or below, then allow pressure in the LNG storage tank that the LNG means of transportation uses increase continuously 0.7 to 1.5 crust or below, identical with the authorized pressure of the LNG storage tank at LNG unloading harbour place.This pattern is particularly useful in the LNG means of transportation that does not have boil-off gas processing member.

When the authorized pressure of the LNG storage tank at unloading harbour place is 0.4 crust or when following, S or V model are suitable.S and V model can be applicable to have the LNG means of transportation that boil-off gas is handled member.S pattern indication is at the term of voyage of LNG means of transportation, allows the pressure in the LNG storage tank of LNG means of transportation evenly and gradually to increase, and that is to say, increase continuously 0.4 crust or below, identical with the authorized pressure of the LNG storage tank of LNG unloading harbour.

V model is the operation width that enlarges the pressure in the LNG storage tank that the LNG means of transportation uses, and has the following advantages: be stored in the waste that reduces in the LNG storage tank that the LNG means of transportation uses boil-off gas by the unnecessary boil-off gas that will surpass the boil-off gas processing boil-off gas scale of construction that member consumed.For instance, when LNG means of transportation TC, because propulsion members (for example DFDE, MEGI and the gas turbine) inoperation of using boil-off gas to act as a fuel, so do not consume boil-off gas.Therefore, the boil-off gas that produces in the LNG storage tank that the LNG means of transportation can be used is stored in wherein, thus the pressure of the LNG storage tank that the LNG means of transportation can be used be increased to 0.7 to 1.5 the crust or below.Behind LNG means of transportation TC, the propulsion members complete operation of using boil-off gas to act as a fuel, thereby increase consumption to boil-off gas, and the pressure of the LNG storage tank that the LNG means of transportation is used be reduced to 0.4 crust or below.

Whether the pressure operation type of the LNG storage tank that the LNG means of transportation is used can unload the harbour place according to LNG and install and be used to handle the flash gasoline treatment facility of a large amount of flash gasolines and decide.The pressure of the LNG storage tank that operation LNG means of transportation is used under the F pattern has been installed at LNG unloading harbour place under the situation of the flash gasoline treatment facility that is used to handle a large amount of flash gasolines; The pressure of the LNG storage tank that operation LNG means of transportation is used under S pattern or V model is not installed at LNG unloading harbour place under the situation of the flash gasoline treatment facility that is used to handle a large amount of flash gasolines.

The equipment that Fig. 6 explanation pressure by LNG storage tank that the boil-off gas on LNG storage tank top is used towards LNG injection the reducing LNG means of transportation of its underpart increases.

The equipment that being used for reducing the pressure of the LNG storage tank that the LNG means of transportation uses as shown in Figure 6 increases is configured to compress the boil-off gas on the top of the LNG storage tank 1 that the LNG means of transportation uses, and then will be through the LNG injection towards LNG storage tank 1 bottom of the boil-off gas of overcompression.

Boil-off gas suction port 31, the end that this equipment is included in LNG storage tank top that the LNG means of transportation uses to be provided is connected to the pipe 33 that boil-off gas suction port 31 and the other end are connected to LNG storage tank 1 bottom, and the compressor 35 that provides at pipe 33 part places.

Illustrated as Fig. 6 left side, pipe 33 can be installed in the LNG storage tank 1.Be installed in the LNG storage tank 1 if manage 33, then need the immersion compressor that compressor 35 should be to be provided in pipe 33 bottoms.

Illustrated as Fig. 6 right side, pipe 33 can be installed in LNG storage tank 1 outside.Be installed in LNG storage tank 1 outside if manage 33, then the common compressor of compressor 35 for providing at pipe 33 places.

Need should provide at boil-off gas suction port 31 places and prevent that liquid from entering member.Prevent that the example that liquid enters member from being demister.

The part that the equipment that being used for reducing the pressure of the LNG storage tank that the LNG means of transportation uses increases is configured to reduce the temperature and pressure of LNG storage tank increases, thereby reduces the pressure of LNG storage tank.Can reduce the generation of boil-off gas in the following manner: the bottom injection with lower temperature of the LNG storage tank 1 that the boil-off gas with higher temperature on LNG storage tank 1 top that the LNG means of transportation is used is used towards the LNG means of transportation, thereby the even temperature of keeping the LNG storage tank that the LNG means of transportation uses distributes, that is to say, prevent that the temperature in the LNG storage tank from increasing in the part.

Fig. 7 explanation is used for the figure of the system that shows in real time, and described system is by receiving related data in real time and suitably handling and calculate described data and show the maximum set pressure of the current permission of the LNG storage tank that the LNG means of transportation is used in real time at LNG means of transportation term of voyage.Can be by the safety valve of described security of system ground control LNG storage tank.

Relief valve (the safety reliefvalve that possesses the LNG storage tank at the LNG means of transportation therein, SRV) or under the situation of safety valve, originally the setting pressure with safety valve is set at lower, so that, but can reduce to increase according to the LNG volume that consumption caused of boil-off gas at term of voyage with the charging burden maximization.

Can set according to the SRV that volume and the density of IGC rule 15.1.2 by remaining LNG obtains to increase.Can calculate LNG density exactly by measuring the LNG temperature.

When the measured value of the LNG liquid level in the LNG storage tank for example frequently changes, the present invention includes: be used for eliminating the external noise that dynamically moving of ship caused and the system of fluctuation by suitable data processing; Be used for calculating the system of permission setting pressure of the safety valve of LNG storage tank by the actual volume that uses treated data to calculate the LNG of LNG storage tank 1; And the equipment that is used to show the result.

Fig. 7 illustrates through measuring the related data with the volume that calculates the LNG in the LNG storage tank 1 on the right side.By the LNG liquid level in existing level meter (not shown) the measurement LNG storage tank, measure the temperature of LNG storage tank by existing temperature transducer (not shown), measure the pressure of LNG storage tank by existing pressure transducer (not shown), by existing trim sensor (trim sensor, not shown) measure the trim of LNG means of transportation, and measure the heel of LNG means of transportation by existing heel sensor (list sensor, not shown).The inclination in the running direction of the trim indication LNG means of transportation of LNG means of transportation, and the lateral inclination of the heel of LNG means of transportation indication LNG means of transportation.

As Fig. 7 left side explanation be used to confirm that according to embodiment the system of setting pressure of the safety valve of LNG storage tank comprises data processing module 61, it is used to handle the survey data illustrated as Fig. 7 right side.

Need by using method processing data in data processing module 61 such as method of least squares, moving average or lower pass-filter.

In addition, be used to confirm that the system of setting pressure of the safety valve of LNG storage tank further comprises LNG volume computing module 63, it is used for calculating the volume of the LNG in the LNG storage tank 1 by calculating the data of handling at data processing module 61.

Be used to confirm that LNG volume that the system of setting pressure of the safety valve of LNG storage tank is calculated according to LNG volume computing module 63 calculates the permission setting pressure of the safety valve of LNG storage tank 1.

On the other hand, can measure the flow rate of combustion gas that is fed to the combustion gas propulsion members of LNG means of transportation from LNG storage tank 1, the initial carrying capacity of LNG and the amount of employed boil-off gas are compared, calculating the front volume of work as of LNG in the LNG storage tank, and in the volume of the LNG that LNG volume puocessing module 63 is calculated, reflect the volume of the LNG that calculates according to the above-mentioned fuel gas flow speed of measuring.

On display floater 65, show as the permission setting pressure of the safety valve of the above-mentioned and LNG storage tank that calculates and the LNG volume in the LNG storage tank.

Fig. 8 explanation is used to measure the gas meter of the fuel gas flow speed of LNG means of transportation according to the present invention.

Differential pressure flowmeter (differential pressure flow meter) is used to measure the flow rate of the combustion gas of LNG means of transportation.In flowmeter, measuring range is limited, and bigger measurement error may occur for the flow rate beyond the measuring range.In order to change measuring range, should change measuring hole (orifice) itself, this is a trouble and dangerous work.

Conventionally, a measuring hole only is installed, and therefore measuring range is limited, if but arrange two measuring holes continuously with different measuring scope, then can be simply by selecting according to flow rate and using the suitable measured value of measuring hole to enlarge effective range.

That is to say, in order to measure fuel gas flow speed in a big way, can enlarge effective range in the following manner simply: arrange at least two measuring holes continuously, each measuring hole has different measuring ranges, and selects and use the suitable measured value of measuring hole according to flow rate.In Fig. 8, each measuring hole 71,71 ' with different measuring scope is arranged in the centre of supply of fuel line pipe 70 continuously, and described supply of fuel line pipe 70 is used for the LNG storage tank that combustion gas is used from the LNG means of transportation is fed to the combustion gas propulsion members.Differential pressure type measuring appliance 73 is connected to the supply of fuel line pipe 70 of the front and rear of each measuring

hole

71,71 '.This differential pressure type measuring appliance 73 optionally is connected to flowmeter 77 by selector 75, and described selector 75 can be selected according to measuring range.

Can enlarge effective range simply in the following manner: the above-mentioned selector 75 that can select according to measuring range is installed, and is selected and use the suitable measured value of measuring hole according to flow rate between differential pressure type measuring appliance 73 and flowmeter 77.

In conventional system, with the capacity of combustion gas measuring hole be set in natural evaporation gas (naturalboil-off gas, NBOG) near.Therefore, the LNG means of transportation to the less situation of the consumption of boil-off gas under, the accuracy of measurement is lower.In order to remedy this inaccuracy, the invention provides a kind of extra continuously method that little measuring hole is installed.

This method can be measured the liquid level of the LNG in the LNG storage tank, thereby measures liquid level or the volume of measuring the LNG in the LNG storage tank according to used up LNG.

In addition, prior art is not also known the composition of boil-off gas, and this is the extra factor that reduces measurement accuracy.In order to remedy this point, can be by adding the composition that gas chromatography (gas chromatography) is studied boil-off gas.

In addition, if the measurement of the LNG liquid level in the LNG storage tank is become accurately by above-mentioned method, then it can improve the pressure with the LNG storage tank of the present invention and keeps a little more than the boil-off gas management method of prior art and the efficient of equipment.That is to say that the accurate measurement of the LNG volume in the LNG storage tank can help the setting changing of the safety valve of LNG storage tank is become a plurality of settings, and reduce the consumption of boil-off gas.

Fig. 9 illustrates the conventional gas meter that the LNG means of transportation is used.Conventional gas meter includes only one and is used for the measuring hole 71 that the differential pressure type flow rate is measured is carried out in combustion gas, and therefore has the shortcoming that can only obtain effective measured value in the particular measurement scope.

Figure 10 explanation is fed to boil-off gas the bottom of LNG storage tank after Compression Evaporation gas according to the embodiment of the invention.

If having the boil-off gas on the LNG storage tank top of using by compression LNG means of transportation, uses by the LNG means of transportation through the boil-off gas of overcompression combustion gas propulsion members as propellant, then described LNG means of transportation can't use combustion gas fully through the canal in for example canal, Zurich the time, and therefore the temperature and pressure of LNG storage tank the local possibility that increases to occur bigger.May need extra boil-off gas extraction equipment to solve this problem.That is to say, illustrated as Figure 10, extract and a small amount of boil-off gas of compression (about 3 to 5 crust) by the boil-off gas compressor, and then put it into the bottom of LNG storage tank 1.

In order to carry out this operation, installing in the middle of fuel gas supply conduit L1 is used to make boil-off gas to turn back to the boil-off gas branch line L2 of LNG storage tank 1, being used to compress the boil-off gas on LNG storage tank 1 top that the LNG means of transportation uses, and will be fed to the combustion gas propulsion members through the boil-off gas of overcompression.In addition, in the upstream, meeting point of fuel gas supply conduit L1 and boil-off gas arm L2, compressor 41 is installed in the middle of fuel gas supply conduit L1.

Buffering basin 43 is installed in the middle of boil-off gas arm L2.Owing to there are differences between the pressure of the boil-off gas of process compressor 41 and the pressure of LNG storage tank 1, so need to be stored in through the boil-off gas of compressor 41 in the buffering basin 43 temporarily, and become the pressure with LNG storage tank 1 to match the pressure control of boil-off gas, and then make boil-off gas turn back to LNG storage tank 1.

Need operate the equipment that the pressure that is used for reducing the LNG storage tank that the LNG means of transportation uses increases with per 2 hours about time lags of 10 minutes.

Some examples of combustion gas propulsion members be the dual-fuel diesel engine electric propulsion system (double fueldiesel electric propulsion system, DFDE), gas injection engine and gas turbine.

The LNG means of transportation of using DFDE, gas injection engine or gas turbine uses following principle: by boil-off gas compressor compresses boil-off gas, and then will be transported to engine through the boil-off gas of overcompression with the burning boil-off gas.Yet, if in the combustion gas propulsion members, do not consume combustion gas or consume a small amount of combustion gas, then cause violent pressure to increase because of the local increase of the temperature in the LNG storage tank in order to prevent, eliminate or reduce the LNG means of transportation Compression Evaporation gas of the boil-off gas discharging of LNG storage tank as being configured among the present invention, and then make boil-off gas turn back to the bottom of LNG storage tank by the boil-off gas branch line through overcompression, and will not be transported to the gas engine through the boil-off gas of overcompression.

Another embodiment of the present invention provides a kind of fuel gas supply system, and it is used for the LNG gasification with the LNG storage tank, and will arrive the combustion gas propulsion members as gas supply through the LNG of gasification.That is to say that in the prior art, the combustion gas propulsion members is used as fuel by using high pressure compressor with boil-off gas, but the present invention does not use boil-off gas fully.

As an alternative, the boil-off gas that can add the cold energy that uses LNG liquefaction device again.That is to say that boil-off gas carries out heat exchange through overcompression and with the LNG of fuel gas supply conduit, thereby (by after-condenser, not having the N2 refrigerator) is cooled.In the case, have only the NBOG of 40%-60% to be liquefied again, but this is unquestionable, because LNG means of transportation according to the present invention is configured to eliminate or reduce the discharging of the boil-off gas in the LNG storage tank.In addition, if necessary, can be especially at sailing in ballast and installed capacity is about 1 ton/hour little boil-off gas liquefaction device again.

Employed LNG means of transportation stands intensity that the pressure that by boil-off gas caused increase through design to have with LNG storage tank 1 in the fuel gas supply system according to present embodiment, so that allow LNG means of transportation term of voyage because the pressure increase that the boil-off gas that is produced in the LNG storage tank causes.

Fuel gas supply system among Figure 11 comprises: fuel gas supply conduit L11 is used for extracting LNG and the LNG that is extracted being fed to the combustion gas propulsion members from the LNG storage tank that the LNG means of transportation is used; And heat exchanger 53, it is provided in the middle of the fuel gas supply conduit L11, and wherein heat exchanger 53 carries out heat exchange between the boil-off gas of LNG and extraction from LNG storage tank 1.

First pump 52 is installed among the fuel gas supply conduit L11 of heat exchanger 53 upstreams, LNG is fed to the combustion gas propulsion members, flow rate and the pressure demand of described LNG overcompression to meet the combustion gas propulsion members.

Boil-off gas liquefaction pipeline L12 so that from LNG storage tank 1 top extraction boil-off gas, and makes the boil-off gas that is extracted turn back to a side of LNG storage tank 1 through over-heat-exchanger 53.

Will be fed to the combustion gas propulsion members, and make by carrying out the boil-off gas that heat exchange is liquefied and turn back to LNG storage tank 1 with LNG by carrying out the LNG that heat exchange increases temperature with heat exchanger 53.

Second pump 54 is installed among the fuel gas supply conduit L11 in heat exchanger 53 downstreams, so that carry out heat exchange and after overcompression is with the flow rate that meets the combustion gas propulsion members and pressure demand LNG is fed to the combustion gas propulsion members with boil-off gas in heat exchanger 53 at LNG.

Heater 55 is installed among the fuel gas supply conduit L11 in second pump, 54 downstreams, so that the LNG of heat exchange has been carried out in heating with boil-off gas in heat exchanger 53, thereby LNG is fed to the combustion gas propulsion members.

Gas compressor 56 and cooler 57 are installed among the boil-off gas liquefaction pipeline L12 of heat exchanger 53 upstreams successively, so that the boil-off gas that compression and cooling are extracted from the LNG storage tank, and then between boil-off gas and LNG, carry out heat exchange.

Gaseous-pressure demand at the combustion gas propulsion members is higher (for example, 250 crust) under the situation, by first pump 52 LNG is compressed to 27 crust, at LNG during through over-heat-exchanger 53, the temperature of LNG is increased to-100 ℃ approximately from about-163 ℃, and LNG is fed to second pump 54 with liquid state, and it is compressed to about 250 crust (because it is in supercritical state by second pump 54, so do not have the separatrix between liquid state and the gaseous state), then with its gasification, in heater 55, it is heated simultaneously, and then it is fed to the combustion gas propulsion members.In the case, though LNG during through over-heat-exchanger 53 its temperature increase, LNG is not gasified, because it is higher to be fed to the pressure of LNG of heat exchanger.

On the other hand, gaseous-pressure demand at the combustion gas propulsion members is lower (for example, 6 crust) time, by first pump 52 LNG is compressed to 6 crust, partial L NG is gasified through over-heat-exchanger 53 time, LNG is fed to heater 55 and heating in heater 55, and then it is fed to the combustion gas propulsion members.In the case, second pump 54 is unnecessary.

This fuel gas supply system according to the LNG means of transportation, from the LNG storage tank, extract LNG, and the LNG that compression is extracted is so that it meets the flow rate and the pressure demand of combustion gas propulsion members, and will be fed to the combustion gas propulsion members through the LNG of overcompression, LNG is not fed to the combustion gas propulsion members afterwards but between LNG and the boil-off gas that from the LNG storage tank, extracts, carry out heat exchange.Therefore, fuel gas supply system has the following advantages: combustion gas is being fed to the process of combustion gas propulsion members from the LNG means of transportation, simplified configuration, reduced desired power, and prevented to cause the violent increase of the pressure of LNG storage tank because of boil-off gas accumulation wherein.

Though illustrated and described specific embodiment of the present invention in this article, but should be appreciated that the those skilled in the art can expect various modifications, change or correction easily, and therefore, description herein and graphic should the explanation with purpose of illustration, and can not limit the scope of the invention and spirit.

[effect of the present invention]

As mentioned above, the present invention has the following advantages: steam pressure and the LNG temperature processed by allowing to have boil-off gas in the LNG storage tank that the LNG means of transport of member uses increase at the LNG In transit, and reduce the waste of boil-off gas and increase the flexibility of boil-off gas processing aspect.

Exactly, according to the present invention, even the boil-off gas scale of construction that produces when the LNG In transit also can preserved unnecessary boil-off gas, thereby improve economic benefit when being surpassed the used up boil-off gas scale of construction in the LNG storage tank in the situation of not loss boil-off gas. For instance, possess at the LNG means of transport in the situation of the engine that the illustrated processing boil-off gas of Fig. 4 uses, in the LNG means of transport, load the unnecessary boil-off gas that produced in some days behind the LNG, when LNG means of transport TC or wait or move that accurate position surpasses the boil-off gas scale of construction that is consumed in the engine when entering the harbour with the LNG that wherein loads and the unnecessary boil-off gas that produces in the prior art mostly by the GCU burning, but can reduce this waste to boil-off gas by technology of the present invention.

In addition, use at the LNG means of transport in the situation of two combustion gas injection engines or gas turbine, can rather than pass through boil-off gas compressor supply combustion gas by liquid pump, thereby a large amount of the minimizing installed and running cost.

Claims

1, a kind of method that is used for being set in the safety valve that liquefied natural gas (LNG) tank top that LNG Liquefied natural gas means of transportation that conveying liquified natural gas uses installs provides, wherein said safety valve is different from the setting pressure of described safety valve at described LNG Liquefied natural gas means of transportation term of voyage in the setting pressure of LNG Liquefied natural gas loading days, and described safety valve is higher than the setting pressure of described safety valve at the LNG Liquefied natural gas loading days in the setting pressure of described LNG Liquefied natural gas means of transportation term of voyage.

2, method according to claim 1, wherein after being discharged into by boil-off gas that described liquefied natural gas (LNG) tank is outside and reducing the amount of the LNG Liquefied natural gas in the described liquefied natural gas (LNG) tank, increase the setting pressure of described safety valve with LNG Liquefied natural gas in the described liquefied natural gas (LNG) tank or generation.

3, method according to claim 2, wherein the LNG Liquefied natural gas loading days setting pressure of described safety valve is set at 0.25 crust or below, and at described LNG Liquefied natural gas means of transportation term of voyage the setting pressure of described safety valve is set at from being higher than 0.25 and clings to 2 crust.

4, method according to claim 3 wherein is set at the setting pressure of described safety valve from being higher than 0.25 at described LNG Liquefied natural gas means of transportation term of voyage and clings to 0.7 crust.

5, according to the described method of arbitrary claim in the claim 2 to 4, it comprises: measure the trim of the pressure of the liquid level of the LNG Liquefied natural gas in the liquefied natural gas (LNG) tank in the described LNG Liquefied natural gas means of transportation, the temperature of described liquefied natural gas (LNG) tank, described liquefied natural gas (LNG) tank, described LNG Liquefied natural gas means of transportation and the heel of described LNG Liquefied natural gas means of transportation; And handle and calculate the data measured to calculate the volume of the LNG Liquefied natural gas in the described liquefied natural gas (LNG) tank.

6, method according to claim 5 is wherein by the data processing module processing said data.

7, method according to claim 6, wherein said data processing module comes processing said data by method of least squares, moving average or lower pass-filter.

8, method according to claim 7, wherein the LNG Liquefied natural gas volume computing module of the volume of the LNG Liquefied natural gas by being used for calculating described liquefied natural gas (LNG) tank calculates handled data in the described data processing module.

9, method according to claim 5, it further comprises: measure the flow rate of combustion gas that is fed to the combustion gas propulsion members of described LNG Liquefied natural gas means of transportation from described liquefied natural gas (LNG) tank; The initial LNG Liquefied natural gas carrying capacity and the amount of employed boil-off gas are compared, and calculate the front volume of working as of the LNG Liquefied natural gas that contains in the described liquefied natural gas (LNG) tank; And the LNG Liquefied natural gas volume that reflection calculates according to the flow rate of measuring of described combustion gas in the LNG Liquefied natural gas volume that is calculated by described LNG Liquefied natural gas volume computing module.

10, according to the described method of arbitrary claim in the claim 2 to 4, it comprises: in the centre that is used for combustion gas is fed to from the described liquefied natural gas (LNG) tank of LNG Liquefied natural gas means of transportation the supply of fuel line pipe of described combustion gas propulsion members, arrange at least two measuring holes continuously, each described measuring hole has different measuring ranges; According to the measured value of described flow rate selection from a suitable measuring hole in described at least two measuring holes; Measure the flow rate of the combustion gas of described LNG Liquefied natural gas means of transportation, to measure the flow rate of employed combustion gas; And the volume of calculating the LNG Liquefied natural gas in the described liquefied natural gas (LNG) tank.

11, according to the described method of arbitrary claim in the claim 2 to 4, the device of differential pressure type gas meter as the fuel gas flow speed that is used to measure described LNG Liquefied natural gas means of transportation wherein is provided, wherein in the centre that is used for the described liquefied natural gas (LNG) tank that combustion gas is used from described LNG Liquefied natural gas means of transportation is fed to the supply of fuel line pipe of combustion gas propulsion members, arrange at least two measuring holes continuously, each described measuring hole has different measuring ranges.

12, the safety valve that provides of a kind of liquefied natural gas (LNG) tank top of in the LNG Liquefied natural gas means of transportation that conveying liquified natural gas is used, installing, wherein said safety valve is different from the setting pressure of described safety valve at described LNG Liquefied natural gas means of transportation term of voyage in the setting pressure of LNG Liquefied natural gas loading days, and described safety valve is higher than the setting pressure of described safety valve at the LNG Liquefied natural gas loading days in the setting pressure of described LNG Liquefied natural gas means of transportation term of voyage.

13, safety valve according to claim 12, wherein after being discharged into by the boil-off gas with LNG Liquefied natural gas in the described liquefied natural gas (LNG) tank or generation that described liquefied natural gas (LNG) tank is outside and reducing the amount of the LNG Liquefied natural gas in the described liquefied natural gas (LNG) tank, the setting pressure of described safety valve increases.

14, safety valve according to claim 12, wherein said safety valve the setting pressure of LNG Liquefied natural gas loading days be set to 0.25 crust or below, and described safety valve is set to from being higher than 0.25 in the setting pressure of described LNG Liquefied natural gas means of transportation term of voyage and clings to 2 crust.

15, a kind of liquefied natural gas (LNG) tank that has according to the described safety valve of arbitrary claim in the claim 12 to 14.

16, a kind of LNG Liquefied natural gas means of transportation with liquefied natural gas (LNG) tank according to claim 15.