KR102035643B1 - Device for operating a pumping device connected to a thermally insulating barrier of a tank used for storing a liquefied gas - Google Patents

Abstract

The invention relates to a method of controlling a pumping device associated with an enclosed adiabatic tank (2) in which the tank (2) comprises a liquefied gas (8) having a liquid phase and a vapor phase and which contacts the liquefied gas (8). Has a multilayer structure comprising a sealing membrane (7) and an insulating barrier (6) disposed between the sealing membrane (7) and the supporting structure (4), wherein the insulating barrier (6) comprises a solid material and a gas phase; The pumping device comprises a vacuum pump 16 connected to the adiabatic barrier 6 for placing the gas phase at a negative relative pressure, the method comprising a pressure on the gas phase of the adiabatic barrier 6. (P ₁ ) controls the vacuum pump 16 in accordance with the measured value and the setpoint pressure P ₁ , the method further comprising:
Measuring the temperature T of the liquid phase of the liquefied gas 8; And
Determining a set pressure P _c1 via the relationship −P _c1 = f ₁ (T), where f ₁ is an increasing monotonous function.

Description

DEVICE FOR OPERATING A PUMPING DEVICE CONNECTED TO A THERMALLY INSULATING BARRIER OF A TANK USED FOR STORING A LIQUEFIED GAS}

The present invention relates to the field of sealed adiabatic membrane tanks for storing liquefied gas.

Closed insulating membrane tanks are used, in particular, for the storage of liquefied natural gas (LNG).

Closed insulating membrane tanks with walls of multilayer construction are known in the art. This multi-layered structure is supported against the secondary hermetic barrier, the secondary hermetic membrane supported against the secondary insulation barrier, the secondary hermetic membrane, including the insulating elements supported against the support structure, from the outside of the tank to the inner direction. A primary insulating barrier comprising insulating elements, and a primary hermetic membrane in contact with the liquefied gas contained in the tank and supported against the primary insulating barrier.

Membrane tanks of this type are sensitive to the pressure difference between the opposite sides of each of the membranes, in particular the pressure difference between the opposite sides of the primary hermetic membrane. Indeed, the pressure of the primary insulating barrier increased relative to the interior of the tank makes the primary hermetic membrane easy to peel off. Thus, in order to ensure the integrity of the primary hermetic barrier, the pressure inside the primary insulation barrier is kept lower than the pressure inside the tank, so that the pressure difference between the opposite sides of the primary hermetic membranes causes the secondary insulation membranes to be insulated. It is desirable to press against the barrier and not to separate it from the secondary insulating barrier.

The basic idea of the present invention is to provide a method of controlling a pumping device connected to a thermal insulation barrier of a hermetic insulation tank, which enables effective protection of at least one hermetic membrane of the tank.

An embodiment of the present invention is a method of controlling a pumping device associated with a closed adiabatic tank, wherein the tank includes a liquefied gas having a liquid phase and a vapor phase and is supported by the sealed membrane and the closed membrane in contact with the liquefied gas. A wall having a multi-layered structure comprising a thermal insulation barrier disposed between the structures, the thermal insulation barrier comprising solid materials and a gas phase, wherein the pumping device applies a negative relative pressure to the gas phase. And a vacuum pump connected to the thermal barrier for placing it therein, the method comprising:

Measuring the pressure P ₁ of the gas phase of the adiabatic barrier;

Determining the setpoint pressure P _c1 through the equation P _c1 = f ₁ (T); And

Controlling the vacuum pump to subordinate the pressure P ₁ on the gas phase of the adiabatic barrier to the set point pressure P _c1 ,

f ₁ is an increasing monotonous function and T is the minimum temperature limit which can be reached as the liquid phase of the liquefied gas or the temperature of the liquid phase of the liquefied gas measured and corresponding to the operating state of the liquefied gas cooling device Is a variable representing.

This type of method is particularly effective for protecting the hermetic membrane when the pressure of the tank is below atmospheric pressure (this was not possible in the prior art). This is particularly likely to occur if the liquefied gas is first stored in the tank at a temperature below the liquid-vapor equilibrium temperature of the gas considered at the subcooled thermodynamic state, ie the pressure at which the gas is stored in the tank.

Applicants have recently developed cooling devices that can lower the temperature of some liquefied gas stored in a tank below its liquid-vapor equilibrium temperature, limiting the natural evaporation of the liquefied gas and allowing its long-term storage. Thus, this type of method is particularly suitable for meeting the specific requirements of tanks equipped with cooling devices of this type.

Indeed, in liquefied gas storage applications using subcooling of liquefied gas, the vapor phase in the gas sky of the tank and the liquid phase of the liquefied gas do not equilibrate everywhere in the tank. The vapor phase is easy to heat up and tends to layer within the tank. Thus, if the tank is not full and there is no agitation in the tank to homogenize the temperature of the gas phase, a temperature change of approximately 100 ° C. in the gas phase can be seen.

The interface between the vapor phase and the liquid phase is fixed at equilibrium. At this interface, the vapor phase condenses or the liquid phase evaporates depending on local temperature and pressure conditions.

In addition, when the tank is placed in the vessel, and the vessel becomes large, the position and configuration of the interface between the vapor phase and the liquid phase tend to change suddenly. Thus, the sudden movement of cargo in the tank makes it easy to condense a large amount of gas phase immediately, which in turn can suddenly reduce the pressure in the space inside the tank.

Now, to ensure the integrity of the hermetic membrane, it is necessary to ensure that the pressure in the tank interior space is never significantly lower than the pressure in the insulation barrier, and if this fails, the pressure drop in the tank interior space of this type, By detaching, it is easy to damage the sealing membrane.

Thus, by setting the target pressure inside the adiabatic barrier taking into account the temperature of the liquid phase stored in the tank or the minimum temperature limit that can be reached as the liquid phase of the liquefied gas, upon immediate condensation of a portion of the vapor phase of the cargo, without unnecessary energy costs, The pressure inside the thermal barrier can be lowered sufficiently to remain below the pressure to reach in the interior space.

According to still further advantageous embodiments, the method of the type described above may comprise one or more of the following features:

The variable T is obtained by measuring the temperature of the liquid phase of the liquefied gas or by measuring the operating parameter of the liquefied gas cooling device indicative of the minimum temperature limit that can be reached as the liquid phase of the liquefied gas.

The variable T is obtained by receiving an operating parameter of the liquefied gas cooling device which represents the minimum temperature limit that can be reached as the liquid phase of the liquefied gas.

The function f ₁ is in the temperature-pressure plot of the component of the liquefied gas having the lowest evaporation temperature among the components constituting the liquefied gas 8 or the liquefied gas present in a molar ratio greater than 5%. It is an affine transformation of a function that represents a liquid-vapor equilibrium curve.

The function f ₁ is of the form f ₁ (T) = g (T) −ε ₁ , g is the lowest evaporation temperature among the liquefied gases or components of the liquefied gas present in a molar ratio greater than 5% Is a function representing the liquid-vapor equilibrium curve in the temperature-pressure plot of the components of the liquefied gas having

The integer ε ₁ comprises, for example, 10 to 30 mbar.

The hermetic membrane is a primary hermetic membrane and the insulation barrier is a primary insulation barrier, the multilayer structure is supported against the support structure and comprises a secondary insulation barrier comprising solid materials and a gas phase, and the secondary insulation And a secondary hermetic membrane disposed between the barrier and the primary insulating barrier.

The pumping device comprises a second vacuum pump connected to the secondary thermal barrier for placing the gas phase of the secondary thermal barrier at a negative relative pressure, the method comprising:

Measuring the pressure P ₂ of the gas phase of the secondary thermal barrier; And

Controlling the second vacuum pump to subordinate the pressure P ₂ on the gas phase of the adiabatic barrier to a set point pressure P _c2 .

According to one embodiment, the second set point pressure P _c2 is determined through the equation P _c2 = f ₂ (T), and f ₂ is a monotonically increasing function.

The function f ₂ is the lowest of the liquid-vapor equilibrium curve of a plurality of components of the liquefied gas in a temperature-pressure plot among the components constituting the liquefied gas or the liquefied gas present in a molar ratio greater than 5%. It is the affine transformation of the function representing the liquid-vapor equilibrium curve in the temperature-pressure plot of the components of the liquefied gas with the evaporation temperature.

The function f ₂ has the form f ₂ (T) = g (T) −ε ₂ , and g is the lowest evaporation of the liquefied gas or components of the liquefied gas present in a molar ratio greater than 5%. In the temperature-pressure plot of the components of the liquefied gas having a temperature, it is a function representing the liquid-vapor equilibrium curve, ε ₂ is a positive constant.

The integer ε ₂ comprises, for example, 10 to 30 mbar.

According to another embodiment, the second set point pressure P _c2 is set through the equation P _c2 = h (P ₁ ), where h is a monotonically increasing function.

The function h has the form of h (P ₁ ) = P ₁ -ε'2, and ε ' ₂ is a constant.

The integer ε ' ₁ comprises, for example, 10 to 30 mbar.

According to one embodiment, the invention relates to a control method, the method,

Controlling the vacuum pump according to a measured value and a set point pressure P _c1 of the gas phase pressure P ₁ of the adiabatic barrier;

Measuring the temperature T of the liquid phase of the liquefied gas; And

Determining the setpoint pressure P _c1 through the equation P _c1 = f ₁ (T), where f ₁ is an increasing monotonic function.

Another basic idea of the present invention is to provide a method for controlling a liquid gas cooling device, which enables effective protection of at least one hermetic membrane of a tank.

According to one embodiment, the present invention is a method for controlling a liquefied gas cooling device associated with a facility for liquefied gas storage, the facility,

A closed insulated tank for containing the liquefied gas in the form of a liquid phase and a vapor phase in two phases;

A pressure sensor arranged to measure the pressure P ₁ on the gas in the thermal barrier; And

A vacuum pump connected to the adiabatic barrier and arranged to place the gas phase of the adiabatic barrier at a negative relative pressure, and the vacuum to subordinate the pressure P ₁ of the gas phase of the adiabatic barrier to a setpoint pressure P _c1 . A pumping device including a control module arranged to control the pump;

The tank comprises walls having a multilayer structure comprising a hermetic membrane in contact with the liquefied gas, and the insulating barrier disposed between the hermetic membrane and the support structure, the insulating barrier comprising solid materials and the gas phase. Including,

The cooling device is arranged to lower the temperature of the portion of the liquefied gas below the liquid-vapor equilibrium temperature of the liquefied gas at a pressure stored in the tank, the method of controlling the liquefied gas cooling device,

Equation T _min = determining a minimum temperature limit T _min of the liquefied gas via f ₃ (P _c1 ); And

Controlling the cooling device according to the minimum temperature limit T _{min such} that the temperature of the liquefied gas is not lowered below the minimum temperature limit T _min , where f ₃ is an increasing forging function.

According to still further advantageous embodiments, the method of the type described above may comprise one or more of the following features:

The function f ₃ is the liquid-vapor equilibrium curve in the temperature-pressure plot of the component of the liquefied gas having the lowest evaporation temperature among the components constituting the liquefied gas or liquefied gas present in a molar ratio of greater than 5%. Is a function representing.

In other words, in other words, the minimum temperature limit (T _min ) means that the temperature of the liquid phase of the liquefied gas contained in the tank is greater than the reduced pressure in the thermal barrier when the cargo moves abruptly. It is determined to correspond to the liquid-vapor equilibrium temperature of the liquefied gas or multiple components of the liquefied gas at the setpoint pressure P _{c1 such} that it does not reach a temperature low enough to cause a decrease in pressure in space.

According to one embodiment, the present invention also provides a facility for storing liquefied gas, the facility,

A closed insulated tank for containing the liquefied gas in the form of a liquid phase and a vapor phase in two phases;

A pressure sensor arranged to measure the pressure P ₁ on the gas in the thermal barrier; And

A pumping device connected to the adiabatic barrier and provided with a vacuum pump arranged to place the gas phase of the adiabatic barrier at a negative relative pressure, and a control module,

The tank comprises a hermetic membrane in contact with the liquefied gas, an adiabatic barrier disposed between the hermetic membrane and the support structure, the adiabatic barrier comprising a solid material and a gas phase,

The control module

Determine the setpoint pressure P _c1 via the equation P _c1 = f ₁ (T);

-To control the vacuum pump to subordinate the pressure P ₁ on the gas phase of the thermal insulation barriers 3, 6 to the set point pressure P _c1 ,

f ₁ is an increasing monotonic function, and T is a variable indicating the actual temperature of the liquid phase of the liquefied gas, or the minimum temperature limit achievable as the liquid phase of the liquefied gas for a specific operation of the liquefied gas cooling device.

According to still further advantageous embodiments, the method of the type described above may comprise one or more of the following features:

The installation further comprises a temperature sensor arranged to measure the temperature T of the liquid phase of the liquefied gas and to convey the measured temperature T to the control module.

The installation further comprises an apparatus for cooling the liquefied gas arranged to lower the temperature of a portion of the liquefied gas below the liquid-vapor equilibrium temperature of the liquefied gas at a pressure stored in the tank.

The cooling device is arranged to meet the minimum temperature limit for the liquid phase of the liquefied gas, the control module is connected to the cooling device and the set point pressure P with the minimum temperature limit as the variable T _c1 ).

The installation comprises a sensor arranged to measure operating parameters of the liquefied gas cooling device indicative of the minimum limit which can be reached as the liquid phase of the liquefied gas.

The hermetic membrane is a primary hermetic membrane and the insulation barrier is a primary insulation barrier, the multilayer structure is supported against the support structure and comprises a secondary insulation barrier comprising solid materials and a gas phase, and the secondary insulation And a secondary hermetic membrane disposed between the barrier and the primary insulating barrier.

- and the equipment further comprises a second pressure sensor arranged to measure the secondary insulating barrier pressure (P _2).

The pumping device further comprises a second vacuum pump connected to the secondary thermal barrier for placing the gas phase of the secondary thermal barrier at a negative relative pressure.

The control module is arranged to control the second vacuum pump in accordance with the measured value of the pressure P ₂ on the gas phase of the secondary thermal barrier and the set point pressure P _c2 .

According to one embodiment, the liquefied gas cooling device is an evaporation device for cooling the liquefied gas, the evaporation device,

An evaporation chamber disposed in the interior space of the tank,

An intake leading to the interior space of the tank to exhaust the flow of liquefied gas on the liquid in the tank and a head loss member leading to the interior space of the evaporation chamber to extend the gas flow discharge Inflow circuit;

A discharge circuit arranged to escape the gas flow discharge from the evaporation chamber to the vapor utilization circuit on the gas,

The evaporation chamber includes heat exchange walls that enable heat exchange between the internal space of the evaporation chamber and the liquefied gas present in the internal space of the tank,

The discharge circuit comprises a vacuum pump arranged to vent the gas flow in the evaporation chamber, to discharge the gas flow into the gas in the vapor phase utilization circuit, and to maintain an absolute pressure below atmospheric pressure in the evaporation chamber.

According to yet another embodiment, the liquefied gas cooling device comprises a circuit for outgassing the vapor phase, the device comprising:

-An intake port which is connected to an inner space of the tank higher than the maximum filling height of the tank, so that when the tank is filled, it is filled into an area of the vapor phase in contact with an interface area separating the lower liquid phase and the upper vapor phase; And

Venting the gas stream in the vapor phase present in the vapor phase region through the inlet, evacuating the gas flow to the vapor phase utilization circuit, and maintaining a pressure below the atmospheric pressure in the vapor phase region. Evaporation is encouraged at the interface region height, and the vacuum pump is arranged such that the liquid gas in contact with the interface is in a two-phase liquid-vapor equilibrium, wherein the temperature of the liquefied gas in the two-phase liquid-vapor equilibrium Is below the liquid-vapor equilibrium temperature of the liquefied gas at the atmospheric pressure.

Plants of the type described above form part of a terrestrial storage facility for storing LNG, for example, or can be floated offshore or in deep waters, in particular methane tanker ships, floating storage and regasification units (FSRUs), floating production storage and unloading ( FPSO) unit or the like.

According to one embodiment, the vessel comprises a double hull, and the aforementioned equipment, the tank of the equipment for liquefied gas storage is arranged in the double hull.

According to one embodiment, the invention also provides a method of loading or unloading a vessel of the type described above, wherein the fluid is supplied between the floating or above ground storage facility and the tank of the vessel via insulating pipes.

According to one embodiment, the present invention also provides a fluid transfer system, which system is provided with insulating pipes arranged to connect the aforementioned vessel, a tank installed in the hull of the vessel, to a floating or ground storage facility, and the A pump for driving fluid between the floating or above ground storage facility and the tank of the vessel through the insulation pipes.

The invention and other objects, details, features and advantages of the invention will become more apparent in the course of describing particular embodiments of the invention for purposes of non-limiting illustration with reference to the accompanying drawings.
1 illustrates a liquefied gas storage and cooling system according to a first embodiment.
2 illustrates a liquefied gas storage and cooling system according to a second embodiment.
3 illustrates a liquefied gas storage and cooling system according to a third embodiment.
4 illustrates a liquefied gas storage and cooling system according to a fourth embodiment.
5 is a methane liquid-vapor equilibrium diagram.
FIG. 6 shows a methane tanker ship with a tank provided and a terminal for loading / unloading such a tank.

In the description and claims of the present invention "gas" is a generic term and can be used interchangeably to refer to a gas consisting of a single body or to a gas mixture consisting of a plurality of components. Thus, liquefied gas refers to a chemical body or mixture of chemical bodies that is in the liquid phase at low temperatures and in the vapor phase at normal temperature and pressure conditions.

1 shows a liquefied gas storage and cooling facility 1 according to a first embodiment. This type of installation 1 can be installed on a floating structure, such as a methane tanker ship or a liquefied or regasified barge.

Such a facility 1 includes a hermetic sealed membrane tank 2. The tank 2 is supported against the secondary insulating barrier 3, the secondary insulating barrier 3, which is supported against the supporting structure 4 and includes the insulating elements and the gas phase, from the outside of the tank to the inner direction. Contacting the secondary hermetic membrane 5, the primary insulating barrier 6 comprising the gaseous phase and the insulating elements supported against the secondary hermetic membrane 5, and the liquefied gas 8 contained in the tank. Walls with a multi-layered structure comprising a primary hermetic membrane (7). For example, membrane tanks 2 of this type are patent applications WO14057221, FR2691520 and FR2877638.

 According to one embodiment, the tank has an unshown vapor collection device that passes through the tank's ceiling wall and extends to the top of the interior space of the tank. An apparatus of this type has a valve arranged to allow the escape of steam from the inside of the tank to the outside when the pressure in the internal space of the tank 2 is higher than the limit. Thus, this type of steam collecting device prevents the increase in pressure from occurring inside the tank 2. The valve is also configured to prevent the gas flow flowing in the vapor collection device from flowing out of the tank 2 to the inside, thereby allowing the pressure in the internal space of the tank 2 to decrease. For example, a steam collection device of this type is described in WO2013093261.

The liquefied gas 8 is a combustible gas. The liquefied gas 8 is in particular one of liquefied natural gas (LNG), ie, ethane, propane, n-butane, i-butane, n-pentane, i-pentane, neopentane and nitrogen together with most of methane. The above other hydrocarbons may be gas mixtures mixed in small proportions. The combustible gas may also be a hydrocarbon mixture obtained by refining ethane or liquefied crude gas (LPG), ie crude oil mainly comprising propane and butane.

The liquefied gas 8 is stored in the internal space of the tank 2 in a liquid-vapor two phase state. Thus, the liquefied gas 8 is present in the vapor phase at the top of the tank 2 and in the liquid phase at the bottom of the tank 2.

This installation 1 also lowers the temperature of a portion of the liquid phase of the liquefied gas 8 below the liquid-vapor equilibrium temperature of the liquefied gas 7 at the pressure at which the liquefied gas 8 is stored in the tank 2. It further comprises a liquefied gas cooling device stored in the tank (2) provided to be. Thus, part of the liquefied gas is placed in a subcooled thermodynamic state.

For this purpose, in the embodiment shown in FIG. 1, the installation draws the gas flow in the liquid phase from the tank 2, expands it and evaporates using the latent heat of gas evaporation to liquefy the gas remaining in the tank 2. Cool (8).

The principle of operation of this type of evaporator 20 is shown in FIG. 5, which shows a liquid-vapor equilibrium diagram of methane. This plot shows the area labeled L where methane is in the liquid phase and the area labeled V where methane is in the vapor phase as a function of the pressure plotted on the abscissa and the temperature plotted on the ordinate.

Point P ₁ represents a two-phase equilibrium corresponding to the state of methane stored in tank 2 at atmospheric pressure and at a temperature of about −162 ° C. When this equilibrium methane is taken out of the tank 2 and expanded in the evaporator 20 to an absolute pressure of, for example, about 500 mbar, the equilibrium of the expanded methane moves in the direction of the left P ₂ point. Thus, the expanded methane will experience a temperature decrease of about 7 ° C. The discharged methane is then at least partially evaporated as it is in thermal contact with the methane remaining in the tank 2 via the evaporator 20 and, as such evaporation takes place, the liquid methane stored in the tank 2 The heat required for its evaporation is extracted from it, which allows cooling of the remaining liquid methane in the tank 2.

Therefore, the methane remaining in the tank 2 is disposed at a temperature below the equilibrium temperature at the pressure at which the methane in the tank 2 is stored.

Referring back to FIG. 1, the evaporator 20 is

An inlet circuit comprising an intake port 21 which is immersed in the liquid phase of the liquefied gas 8 stored in the tank 2;

Heat exchange walls which are immersed in the liquid phase and / or vapor of the liquefied gas 8 and in the liquefied gas stored in the tank 2 so that the discharged gas stream is in thermal contact with the remaining liquefied gas in the tank 2. One or more evaporation chambers 22; And

A discharge circuit 23 for escaping the gaseous flow in the vapor phase into the gas in the vapor phase utilization circuit 25.

The inlet circuit is provided with one or more head loss members, not shown, to generate head loss and lead into the evaporation chamber 22 to expand the discharged liquefied gas stream.

The evaporator is also provided with a vacuum pump 24 arranged outside the tank and associated with the discharge circuit 23. The vacuum pump 24 allows the liquefied gas stream stored in the tank 2 to be drawn into the evaporation chamber 22 and discharged to the gas in the vapor phase utilization circuit 25 in the vapor state. For liquefied natural gas, the absolute working pressure inside the evaporation chamber 22 is between 120 and 950 mbar, advantageously between 650 and 850 mbar, such as about 750 mbar.

In the case of installations on ships, the gases in the vapor phase utilization circuit 25 may in particular be connected to propulsion energy generation equipment, not shown, to allow the ship to be propelled. This type of energy generation equipment is chosen in particular in heat engines, fuel cells and gas turbines.

In FIG. 2, there is shown an installation 1 in which another liquefied gas cooling device is provided, which allows the liquefied gas 8 to be arranged in a subcooled thermodynamic state.

For this purpose, the installation 1 comprises a circuit 9 here for evacuating the gas in the vapor phase. The circuit 9 for evacuating the vapor phase vapor comprises a conduit 10 passing through the wall of the tank 2 to form a passage for vapor phase escape from the interior of the tank 2 to the outside. The pipe 10 comprises a water intake 11 leading into the internal space of the tank 2, in a reduced pressure bell 31. The decompression bell 31 has its upper part in contact with the vapor phase of the liquefied gas 8 stored in the tank 2 and filled with the vapor phase, the lower part of which is a liquid phase of the liquefied gas 8 stored in the tank 2. It is a hollow body disposed above the inner space of the tank 2 to be contained in. The intake port 11 of the circuit 9 for discharging the gas in the vapor flows to the top of the evaporation bell 31.

The discharge circuit 9 also comprises a vacuum pump 12 which is connected to the pipe upstream and to the circuit 13 on the downstream side for gas utilization in the vapor phase. Thus, the vacuum pump 12 is provided to suck the gas flow in the vapor phase present in the decompression bell 31 through the conduit 10 and supply it to the gas in the vapor phase utilization circuit 13. Here, the discharge circuit 9 includes a valve 19 or a confirmation valve disposed upstream or downstream of the vacuum pump 12 to prevent the gaseous flow in vapor from returning back to the internal space of the tank 2. Do it.

The vacuum pump 12 makes it possible to encourage the evaporation of the liquefied gas inside the evaporation bell 31 by creating a pressure below atmospheric pressure on the upper part of the decompression bell 31. Since the vapor phase inside the decompression bell 31 is at a pressure lower than atmospheric pressure, evaporation of the liquefied gas 8 is promoted at the liquid / vapor interface inside the decompression bell 31, while the liquefied gas stored in the tank 2 ( 8 is placed in a two-phase liquid-vapor equilibrium, where the temperature of the liquefied gas 8 is lower than the liquid-vapor equilibrium temperature of the liquefied gas at atmospheric pressure.

According to another embodiment shown in FIG. 3, the cooling device includes a water intake port 32 provided to collect liquefied gas in the form of a vapor in the internal space of the tank 2, and a liquid liquefied gas in the tank 2. And a liquefaction apparatus including a first circuit (34) comprising an outlet (33) arranged to return into the interior space. The liquefaction apparatus further includes a cooling circuit 35 through which the cooling fluid circulates. The cooling circuit 35 includes a compressor 36, a condenser 37, a pressure reducer 38, and an evaporator 39 which takes heat from the liquefied gas circulated in the first circuit 34 by evaporating the cooling liquid. do. Cooling devices of this type are described in particular in EP2853479.

According to another embodiment shown in FIG. 4, the cooling device comprises a cooling unit 40 for circulating liquid nitrogen at about −196 ° C. in the hairpin tube 41, where the role is the tube 41. It is to cool the liquefied gas around. As the refrigeration liquefied gas is further increased in density, the refrigerated liquefied gas moves downward in the tank 2, and the liquefied gas not yet frozen is moved upward. This convection movement is carried by the convection well 42 to form this convection movement throughout the tank 2. As it circulates, liquid nitrogen evaporates, allowing the benefit of liquefied gas cooling from the latent heat of nitrogen evaporation. Nitrogen leaving tube 23 is re-liquefied in cooling unit 41. Cooling devices of this type are described in particular in application FR2785034.

Although various liquid gas cooling devices have been described above, the present invention is not limited to only one of them, but any cooling device capable of cooling the liquefied gas below the liquid-vapor equilibrium temperature can be used.

Referring again to FIG. 1, according to the illustrated embodiment, the installation 1 is a vacuum pump 16 and a secondary thermal insulation barrier 3 connected to a pipe 17 leading to the interior space of the primary thermal insulation barrier 6. And a pumping device comprising a vacuum pump 14 connected to the pipe 15 leading to the inner space. This type of pumping device aims to maintain the gas phases inside the primary thermal insulation barrier 6 and the secondary thermal insulation barrier 3 at a pressure lower than the pressure in the internal space of the tank 2. Therefore, the pressure difference between the membranes tends to press the membranes inward and not to separate in the inward direction of the tank 2.

Vacuum pumps 14, 16 refer to cryogenic pumps, ie pumps that are able to withstand cryogenic temperatures below -150 ° C. They also meet ATEX regulations. In other words, it is designed to avoid any explosion hazard. Vacuum pumps 14, 16 can be produced in a variety of ways, such as in Roots (ie, rotary lobes), or in pedals, liquid rings, screws, Venturi-like effectors, and the like.

The installation 1 also further comprises a control module 26 for controlling the vacuum pump 14 and the vacuum pump 16 to regulate the pressures in the primary thermal insulation barrier 6 and the secondary thermal insulation barrier 3. . The control module 26 may comprise a single element as in the illustrated embodiment, or may comprise two elements, in the latter case respectively linked to one and the other of the two vacuum pumps 14, 16. Can be.

The control module 26 is connected to at least one temperature sensor 27 immersed in the liquid phase of the liquefied gas 8 stored in the tank 2, and thus, of the liquefied gas 8 stored in the tank 2. It can deliver temperature measurements in the liquid phase. The temperature sensor 27 is advantageously placed near the bottom of the tank 2 in order to obtain a temperature measurement indicating the lowest temperatures in the tank 2. The temperature sensor 27 is also preferably located near the heat exchange walls of the evaporation chamber 22. The temperature sensor 27 can be used in any kind such as a thermocouple or a platinum resistance probe.

In addition, the installation 1 has at least one pressure sensor 28 capable of transmitting pressure P ₁ measurements of the liquid phase inside the primary thermal barrier 6 and the pressure on the gas inside the secondary thermal barrier 3. It further includes a pressure sensor 29 capable of transmitting the measured value of (P ₂ ).

The control module 26 controls the setpoint pressure P _c1 and the pressure P ₁ on the gas inside the primary thermal barrier 6 to subordinate the pressure P ₁ to the set point pressure P _c1 . It is arranged to generate a control value for the vacuum pump 16 according to the measurement. Similarly, the control module 26 controls the gas phase P ₂ inside the setpoint pressure P _c2 and the primary thermal barrier 6 in order to subordinate the pressure P ₂ to the set point pressure P _c2 . And a control value for the vacuum pump 14 in accordance with the measurement.

In addition, the control module 26 is arranged to continuously determine the setpoint pressure P _c1 for the primary thermal insulation barrier 6 in accordance with the temperature measured by the temperature sensor 27. In other words, the setpoint pressure P _c1 is determined by the equation:

P _c1 = f ₁ (T)

here:

f ₁ Is a monotonically increasing function

T is the temperature of the liquid phase of the liquefied gas 8 delivered by the temperature sensor 27.

The function f ₁ is in particular a temperature-pressure plot of the component of a liquefied gas having the lowest evaporation temperature at atmospheric pressure, among other components of the liquefied gas, or of other components of the liquefied gas present in an insignificant amount (ie molar ratio greater than 5%) Is the affine transformation of the function g representing the liquid-vapor curve at. In addition, the function f ₁ has the following form, for example:

P _c1 = f ₁ (T) = g (T)-ε ₁

here,

g is a function representing, in the temperature-pressure plot, the liquid-vapor equilibrium curve of the liquefied gas or the most volatile component of the negligible amount of liquefied gas, and

ε ₁ is a constant, for example approximately 10 to 30 mbar

The function g makes it possible to determine the saturated vapor pressure associated with the temperature of the measured liquid phase in the tank 2, thereby determining the pressure value as the lower limit of the absolute pressure that is easily reached when the vapor phase of the liquefied gas stored in the tank condenses. To be able.

According to one embodiment, when the liquefied gas is a gas mixture consisting of a plurality of components, the function g represents the liquid-vapor equilibrium curve of the most volatile components present in a negligible amount. For liquefied natural gas, for example, the function g represents the liquid-vapor equilibrium curve of pure methane. Then, referring to the liquid-vapor equilibrium curve of the most volatile component, the saturated steam pressure of the gas mixture is determined as the lower limit and the saturated vapor pressure is determined. This approach eliminates the need to determine in real time the composition of the liquefied gas, which is simple, robust and time-dependent.

However, according to another embodiment, to more accurately determine the saturated vapor pressure associated with the measured temperature for the stored liquefied gas in the tank, using a function g representing the liquid-vapor equilibrium curve of the actual gas mixture. The same is also possible.

For example, the equilibrium curve of methane in the temperature-pressure plot can be approximated by the following function:

       here,

T is the Kelvin temperature,

g (T) is in millibars.

Considering the temperature 105K of the liquid phase of the liquefied gas 8 stored in the tank, this type of temperature image generated by the function g above is 565 millibars. In addition, if the temperature of the liquid phase of the liquefied gas is 105 Kelvin, the pressure in the tank is theoretically unlikely to drop below the absolute pressure of 565 millibars. In this situation, the setpoint pressure P _c1 becomes 545 millibars when the constant epsilon ₁ is equal to 20 millibars in order to take into account the uncertainty of the liquid phase measurement and the heterogeneity of the temperature of the liquid phase in the tank interior.

Thus, by placing the primary thermal insulation barrier 6 at this absolute pressure of 545 millibars, the pressure inside the tank 2 is always greater than the pressure inside the primary thermal insulation barrier 6, whereby the primary hermetic membrane ( 7) can be pressed against the secondary thermal barrier 3 and the collapse is prevented.

Using the function g representing the liquid-vapor equilibrium curve of the liquid gas, an ideal compromise can be made between the safety of plant operation and the energy costs required to ensure operational safety. Nevertheless, if it is acceptable to reduce safety and increase energy costs, very different functions g having the same general profile can be used.

In addition, the control module 26 is also arranged to determine the set point pressure P _c2 for the secondary thermal barrier 6.

According to one embodiment, the setpoint pressure P _c2 is determined according to the temperature T measured by the temperature sensor 27 in a manner similar to the set point pressure P _c2 . Therefore, the setpoint pressure P _c2 is determined by the following equation:

P _c2 = f ₂ (T)

here,

f ₂ is a monotonically increasing function

T is the temperature of the liquid phase of the liquefied gas 8 delivered by the temperature sensor 27.

Like function f ₁ , function f ₂ can also be written in the form:

P _c2 = f ₂ (T) = g (T)-ε ₂

here,

g is a function representing the liquid-vapor equilibrium curve of a liquefied gas or a plurality of components of a liquefied gas in a temperature-correction diagram,

ε ₂ is a constant, for example about 10 to 30 mbar.

According to another embodiment, the setpoint pressure P _c2 is determined not by the temperature measured by the temperature sensor but by the pressure P ₁ on the gas in the primary thermal barrier 6 via the following equation:

P _c2 = h (P ₁ )

here,

h is an increasing singular function,

P ₁ is the pressure measured in the gas phase of the primary insulating barrier 6.

Function h has the following form, for example:

P _c2 = h (P ₁ ) = P ₁ -ε ' ₂

here,

-ε ' ₂ is a constant.

According to one variant embodiment, ε ' ₂ Includes both positive constants, such as between 10 and 30 mbar. The method thus ensures that the gas phase of the secondary thermal barrier 3 is always greater than the pressure of the primary thermal barrier 6 such that the secondary hermetic membrane 5 is pressed against the secondary thermal barrier 3. do.

According to another modified embodiment, ε ' ₂ includes a negative constant, for example, between -10 and -30. The method thus ensures that the pressure on the gas of the secondary thermal barrier 3 is always greater than the pressure of the primary thermal barrier 6 so that the liquefied gas 8 in poor sealing of the sealing membranes 5, 7 The suction toward the secondary thermal barrier 3 can be prevented.

According to still other embodiments, the set point pressure P _c1 and / or set point pressure P _c2 for the primary thermal insulation barrier 6 is not in accordance with the temperature measurement of the liquefied gas 8, but rather liquefied. The variable corresponding to the lowest limit that can be reached as the liquid phase of the liquefied gas for a particular operating state of the gas cooling device is determined by the variable T in the preceding equations.

Thus, according to one embodiment with the liquefied gas cooling device shown and referenced in FIG. 1, the plant is arranged at the outlet of the evaporation chamber 22 and of the gas flow in the vapor circulating inside the evaporation chamber 22. A temperature sensor for measuring the temperature or the temperature of the wall of the evaporation chamber 22. Under the continuous operating conditions of the cooling device, the temperature measured in this way represents the lowest temperature attainable as the liquid phase of the liquefied gas 8 stored inside the tank 2. Then, by using the temperature measured in this manner as the T value in the foregoing equations, the vacuum pump 16 and the vacuum pump 14 control method also provide a primary thermal barrier 6 and a secondary thermal barrier 3. It is possible to ensure that the pressures of the gas phases in the interior of the tank are always below the pressure in the interior space of the tank 2.

In the same way, if the liquefied gas cooling device is a liquefied device comprising a liquefied gas circulation circuit cooperating with the cooling circuit shown in FIG. 3, the installation is arranged in the cooling circuit and at the outlet of the evaporator 39 the It may include a temperature sensor that measures the return temperature. Under continuous cooling device operating conditions, the temperature measured in this way also represents the lowest temperature attainable as the liquid phase of the liquefied gas 8 stored inside the tank 2, and thus the setpoint pressure P _c1 . May optionally be used to determine the setpoint pressure P _c2 .

According to yet another embodiment, the liquefied gas cooling device may be provided to meet the lowest temperature limit T _min for the liquid phase of the liquefied gas. In other words, the liquefied gas cooling device is controlled so that the temperature of the liquid phase of the liquefied gas does not drop below the temperature limit T _min . Thus, the operating parameters of the cooling device are set such that the temperature of the liquid phase of the liquefied gas does not fall below the previously described limits.

For example, in the case of an installation with a liquefied gas cooling device as shown and referenced in FIG. 1, the lowest temperature limit can be ensured by setting the corresponding limit pressure inside the evaporation chamber 22.

Likewise, in the case of a facility with a liquefied gas cooling device as shown and referred to in FIG. 2, the lowest temperature limit can be ensured by setting the corresponding limit pressure inside the decompression bell 31.

If the liquefied gas cooling device is a liquefaction device that includes a gas circulation circuit that cooperates with the cooling circuit, the lowest temperature limit can be met by setting the flow rate or the limit pressure for the cooling fluid in the cooling circuit. Alternatively, depending on the measured temperature, the temperature may meet the lowest temperature limit described above by measuring the temperature of the fins of the evaporator of the cooling circuit and the power of the cooling circuit which is regulated to a suitable safety limit.

According to another variant embodiment, the temperature limit T _min is preset and then transmitted to the control module 26. Then, it is determined by the control module 26 by setting the temperature limit T _min as the T value in the equation P _c1 = f ₁ (T) = g (T) − ε ₁ .

According to another variant, it is the set point pressure P _c1 that is preset and then delivered to the cooling device. In this case, the temperature limit T _min is determined by the equation:

T _min = f ₃ (P _c1 )

here,

f ₃ is a function representing the liquid-vapor equilibrium curve of a liquefied gas or a plurality of components of a liquefied gas in a pressure-temperature plot,

P _c1 is the setpoint pressure in the primary thermal barrier 6.

Referring to FIG. 6, a cutaway view of a methane tanker ship 70 shows a sealed insulated tank 71 of prismatic type, mounted on a double hull 72 of a ship. The walls of the tank 71 may include a primary containment barrier for contacting LNG contained in the tank, a secondary containment barrier disposed between the ship's double hull 72 and the primary containment barrier, and a primary containment barrier and two Two insulating barriers each disposed between the secondary sealing barrier and between the secondary sealing barrier and the double hull 72.

In a manner known per se, the loading / unloading pipes 73 disposed on the upper deck of the ship can be connected to the marine or port terminal via suitable connectors and used to unload or load LNG cargo from the tank 71. .

6 shows an example of a marine terminal that includes a loading and unloading station 75, an underwater pipe 76, and an aboveground installation 77. The loading and unloading station 75 is a stationary coastal installation that includes a mobile arm 74 and a tower 78 that supports the mobile arm 74. The movable arm 74 carries a bundle of insulated flexible pipes 79 that can be connected to the loading / unloading pipes 73. Reversible movable arm 74 is provided for methane tankers of all sizes. The connection pipe, not shown, extends inside the tower 78. The loading and unloading station 75 enables the loading of the methane tanker 70 into the ground facility 77 and the unloading from the ground facility 77. The ground installation 77 comprises a tank 80 for storing liquefied gas and connecting pipes 81 connected to the loading or unloading station 75 by an underwater pipe 76. Even when the loading or unloading station 75 and the ground installation 77 are far apart, such as 5 km, the water pipe 76 allows liquefied gas to be transported. I can keep it.

The pump provided on the vessel 70 and / or the pump provided in the ground installation 77 and / or the pump provided in the loading and unloading station 75 is used to generate the pressure required for liquefied gas movement.

Although the invention has been described in connection with a number of specific embodiments, it is obvious that the invention is not limited to such embodiments and, as long as it is within the scope of the invention, includes technical equivalents and combinations of all means described above. Do.

The use of the verb “comprises” and all verb conjugations does not exclude the presence of elements or steps other than those set forth in the claims. The use of the indefinite article "a" when referring to an element or step does not exclude the presence of a plurality of such elements or steps unless otherwise specified.

In the claims, any reference signs placed between parentheses shall not be construed as limiting the claim.

Claims (23)

A method of controlling a pumping device associated with an hermetic insulated tank (2), wherein the tank (2) comprises a liquefied gas (8) having a liquid phase and a vapor phase and which is in contact with the liquefied gas (8). 7) and walls having a multi-layer structure comprising a thermal insulation barrier 3, 6 disposed between the hermetic membrane 7 and the support structure 4, the thermal insulation barrier 3, 6 being solid materials And a gas phase, wherein the pumping device comprises a vacuum pump (14, 16) connected to the adiabatic barrier (3, 6) to place the gas phase in a negative relative pressure state, Way,
Measuring the pressure P ₁ of the gas phase of the thermal barrier 3, 6;
Determining the setpoint pressure P _c1 via the equation P _c1 = f ₁ (T); And
Controlling the vacuum pumps 14, 16 to subordinate the pressure P ₁ on the gas phase of the thermal insulation barrier 3, 6 to the set point pressure P _c1 ;
f ₁ is an increasing monotonous function, T can be reached as a measured temperature of the liquid phase of the liquefied gas 8, or as a liquid phase of the liquefied gas 8 and the cooling device of the liquefied gas 8 And a variable representing a minimum temperature limit corresponding to the operating state of the. The method of claim 1,
The variable T is measured by measuring the temperature of the liquid phase of the liquefied gas 8 or by measuring the operating parameter of the liquefied gas cooling device representing the minimum temperature limit that can be reached as the liquid phase of the liquefied gas, Obtained. The method of claim 1,
The variable (T) is obtained by receiving an operating parameter of the liquefied gas cooling device indicative of the minimum temperature limit that can be reached as the liquid phase of the liquefied gas (8). The method according to any one of claims 1 to 3,
The function f ₁ is the temperature of the component of the liquefied gas 8 having the lowest evaporation temperature among the components constituting the liquefied gas present in the liquefied gas 8 or in a molar ratio greater than 5% − In the pressure plot, the affine transformation of the function representing the liquid-vapor equilibrium curve. The method of claim 4, wherein
The function f ₁ is of the form f ₁ (T) = g (T) −ε ₁ , and g is among the components of the liquefied gas present in the liquefied gas 8 or in a molar ratio greater than 5%. A function representing the liquid-vapor equilibrium curve in the temperature-pressure plot of the component of the liquefied gas (8) with the lowest evaporation temperature, and ε ₁ is a positive constant. The method according to any one of claims 1 to 3,
The hermetic membrane is a primary hermetic membrane 7, the adiabatic barrier is a primary adiabatic barrier 6 and the multilayer structure is supported against the support structure 4 and comprises solid materials and a gas phase. And a secondary hermetic membrane (5) disposed between the secondary insulation barrier (3) and the secondary insulation barrier (3) and the primary insulation barrier (6). The method of claim 6,
The pumping device comprises a second vacuum pump 14 connected to the secondary thermal barrier 3 for placing the gas phase of the secondary thermal barrier 3 at a negative relative pressure. , The method,
Measuring the pressure P ₂ of the gas phase of the secondary thermal barrier 3; And
Controlling the second vacuum pump (14) to subject the pressure (P ₂ ) on the gas phase of the adiabatic barrier to a second set point pressure (P _c2 ). The method of claim 7, wherein
And the second set point pressure (P _c2 ) is determined via the equation P _c2 = f ₂ (T), wherein f ₂ is an increasing monotonic function. The method of claim 8,
The function f ₂ is the temperature of the component of the liquefied gas 8 having the lowest evaporation temperature among the components constituting the liquefied gas present in the liquefied gas 8 or in a molar ratio greater than 5% − In the pressure plot, the affine transformation of the function representing the liquid-vapor equilibrium curve. The method of claim 9,
The function f ₂ has the form f ₂ (T) = g (T) −ε ₂ , and g is a component of the liquefied gas present in the molar ratio of the liquefied gas 8 or greater than 5%. In the temperature-pressure plot of the component of the liquefied gas (8) having the lowest evaporation temperature among them, a function representing the liquid-vapor equilibrium curve, and ε ₂ is a positive constant. The method of claim 7, wherein
And the second set point pressure (P _c2 ) is set via the equation P _c2 = h (P ₁ ) and h is a forging function that increases. The method of claim 11,
The function h is h (P1) = P1 - "it has the form of _2, ε 'ε ₂ is characterized in that a constant. As a facility (1) for storing liquefied gas,
A hermetic insulated tank for storing liquefied gas 8 in the form of a liquid phase and a vapor phase, arranged between the hermetic membrane 7 in contact with the liquefied gas, between the hermetic membrane 7 and the support structure 4. An enclosed thermal insulation tank (2) comprising walls having a multi-layered structure comprising a thermal insulation barrier (3, 6), the thermal insulation barrier comprising solid materials and a gas phase;
A pressure sensor 28 arranged to measure the pressure P ₁ on the gas in the thermal barrier 3, 6; And
A pumping device comprising a vacuum pump 14, 16 connected to the adiabatic barrier 3, 6 and arranged to put the gas phase of the adiabatic barrier 3, 6 at a negative relative pressure, and a control module 26. Including;
The control module 26
Determine the setpoint pressure P _c1 via the equation P _c1 = f ₁ (T);
To control the vacuum pump 16 to subordinate the pressure P ₁ on the gas phase of the thermal insulation barriers 3, 6 to the set point pressure P _c1 ,
f ₁ is an increasing monotonic function, T is the actual temperature of the liquid phase of the liquefied gas 8, or can be reached as the liquid phase of the liquefied gas 8 for a particular operation of the liquefied gas 8 cooling device. A facility characterized by a variable representing a minimum temperature limit. The method of claim 13,
And further comprising a temperature sensor (27) which measures the temperature (T) of the liquid phase of the liquefied gas (8) and which is arranged to transmit the measured temperature (T) to the control module (26). . The method of claim 13,
The liquefied gas (8) cooling device is a facility characterized in that the liquefied gas is a cooling device arranged to lower the temperature of a portion of the liquefied gas to less than the liquid-vapor equilibrium temperature of the liquefied gas at a pressure stored in the tank. . The method of claim 15,
The liquefied gas cooling device is arranged to meet the minimum temperature limit for the liquid phase of the liquefied gas, and the control module 26 is connected to the liquefied gas cooling device and sets the minimum temperature limit as the variable T. And determine the set point pressure (P _c1 ). The method of claim 15,
And a sensor arranged to measure operating parameters of the liquefied gas cooling device indicative of the minimum temperature limit achievable as the liquid phase of the liquefied gas. The method according to any one of claims 13 to 17,
The hermetic membrane is a primary hermetic membrane 7 and the adiabatic barrier is a primary adiabatic barrier 6 and the multilayer structure is supported against the support structure 4 and is a secondary comprising solid materials and a gas phase. And a secondary hermetic membrane (5) disposed between said secondary thermal barrier (3) and said primary thermal barrier (6). The method of claim 18,
And a second pressure sensor 29 arranged to measure the pressure P ₂ in the secondary thermal barrier, wherein the pumping device is adapted to place the gas phase of the secondary thermal barrier 3 at a negative relative pressure. And further comprising a second vacuum pump 14 connected to the secondary thermal barrier 3, wherein the control module 26 measures and sets point the pressure P ₂ on the gas phase of the secondary thermal barrier 3. And the second vacuum pump (14) according to the pressure (P _c2 ). A ship 70 comprising a double hull and a plant according to any of claims 13 to 17, characterized in that the tank 2 of the plant for storing the liquefied gas is arranged in the double hull. Ship. A method of loading and unloading a vessel (70) according to claim 20, comprising: insulating pipes (73, 79, 76, 81) between a floating or above ground storage facility (77) and the vessel's tank (2). Supplying a fluid. As a fluid delivery system, the insulated pipes 73, 79, 76, arranged to connect the vessel 70 according to claim 20, the tank 2 installed in the hull of the vessel, to a floating or above ground storage facility 77, 81), and a pump for transferring fluid through the insulation pipes between the floating or above ground storage facility and the tank of the vessel. delete

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