JP2018529049A - Method for controlling a pump connected to an insulated barrier of a liquefied gas storage tank - Google Patents

Abstract

The present invention is an apparatus for controlling a pump device related to a sealed heat insulating tank (2) for storing a liquefied gas (8) having a liquid phase and a gas phase, and is a sealed membrane (7) in contact with the liquefied gas. ), And a thermal barrier (6) disposed between the sealing membrane (7) and the support structure (4), the thermal barrier (6) comprising a solid and a gas phase, and the pump device being a thermal barrier (6). With the vacuum pump (16) connected to the vacuum chamber (16), the gas phase is placed at a negative relative pressure, and the method is based on the measured values of the set pressure P1 and the gas phase pressure P1 of the adiabatic barrier (6). 16), the method determines the liquid phase temperature T of the liquefied gas (8) and the setpoint pressure Pc1 is determined by the relationship Pc1 = f1 (T), where f1 is a monotonically increasing function Steps. [Selection] Figure 1

Description

  The present invention relates to the field of sealed insulated membrane tanks for storing liquefied gas, and in particular to sealed insulated membrane tanks used for the storage of liquefied natural gas (LNG).

  2. Description of the Related Art Conventionally, a sealed heat insulating film tank having a multilayer wall structure is known. The multilayer structure includes a secondary heat insulating barrier including a heat insulating element that contacts the support structure from the outside to the inside of the tank, a secondary sealing film that contacts the secondary heat insulating barrier, and a heat insulating element that contacts the secondary sealing film. A primary insulation barrier that includes a primary sealing membrane that abuts the primary insulation barrier intended to contact the liquefied gas contained in the tank.

  This type of membrane tank is sensitive to the pressure difference between the opposing sides of each membrane, in particular the pressure difference across the first sealing membrane. In fact, if the pressure of the primary insulation barrier increases with respect to the pressure inside the tank, the primary sealing film may be separated. Therefore, in order to ensure the integrity of the primary sealing barrier, it is preferable to keep the pressure inside the primary insulating barrier lower than the inside of the tank, so that the pressure difference across the primary sealing membrane The primary sealing film is pressed against the secondary insulation barrier and is not separated from the secondary insulation barrier.

  The basic idea of the present invention is to propose a method for controlling a pump device connected to an insulating barrier of an insulating tank, which effectively protects at least one sealing membrane of the tank. Seal.

In one embodiment, the present invention is a method of controlling a pump device associated with a hermetically insulated tank, wherein the tank stores a liquefied gas having a liquid phase and a vapor phase and is sealed with a sealed membrane in contact with the liquefied gas. A wall having a multilayer structure with a thermal barrier disposed between the membrane and the support structure, the thermal barrier comprising a solid material and a gas phase, and the pumping device placing the gas phase at a negative relative pressure Including a vacuum pump coupled to the adiabatic barrier for the method, wherein the method measures the gas-phase pressure P ₁ of the adiabatic barrier and determines the setpoint pressure P _c1 by the formula P _c1 = f ₁ (T) Where f ₁ is a monotonically increasing function and T represents the measured temperature of the liquid phase of the liquefied gas or the minimum temperature threshold that can be reached by the liquid phase of the liquefied gas, the operating state of the device for cooling the liquefied gas Is the variable corresponding to A method comprising the steps of controlling the vacuum pump so as to restrain the pressure P ₁ of the wall of the gas phase to the set pressure P _c1, a.

  This type of method is particularly effective in protecting the sealing membrane when the tank is at a pressure below atmospheric pressure (which was not previously in the prior art). This is particularly likely when the liquefied gas is initially stored in the tank at a temperature below the liquid-vapor equilibrium temperature of the gas considered in the supercooled thermodynamic state, i.e. the pressure at which the gas is stored.

  In recent years, the present applicant has reduced the temperature of a part of the liquefied gas stored in the tank below the liquid-vapor equilibrium temperature, thereby limiting the natural evaporation of the liquefied gas and enabling cooling for long-term storage. A device was developed. This type of method is therefore particularly suitable for addressing the specific requirements of tanks with this type of cooling device.

  In fact, in liquefied gas storage applications where liquefied gas subcooling is used, the vapor phase of the tank gas air and the liquid phase of the liquefied gas are not in equilibrium anywhere in the tank. The vapor phase tends to be heated and tends to stratify inside the tank. Therefore, if the tank is not fully filled and stirring is not used in the tank to homogenize the temperature of the vapor phase, a temperature gradient on the order of 100 ° C. can occur in the vapor phase.

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

  Moreover, when a tank is arrange | positioned in a ship and a ship expand | swells, the shape of the interface of a vapor phase and a liquid phase, a position, and a structure will change easily. Therefore, the sudden movement of cargo in the tank tends to cause a momentary condensation of a large amount of gas phase, and as a result, tends to cause a sudden drop in pressure in the interior space of the tank.

  Here, in order to guarantee the integrity of the sealing membrane, it is necessary to ensure that the pressure in the internal space of the tank does not become much lower than the pressure in the insulation barrier, and if this fails, this type of internal space tank May break and damage the sealing membrane.

  Therefore, in order to achieve the target pressure, either the temperature of the liquid phase stored in the tank or the minimum temperature threshold that can be reached by the liquid phase of the liquefied gas inside the adiabatic barrier is taken into account. It is possible to ensure that the pressure inside the thermal barrier is kept sufficiently lower than the pressure that can reach the interior space in the case of some instantaneous condensation, and this is the extra energy Not costing.

  According to another advantageous embodiment, a method of the above kind can have one or more of the following features:

  The variable T is obtained by measuring the liquid phase temperature of the liquefied gas or by measuring operating parameters of the apparatus for cooling the liquefied gas that represents the minimum temperature threshold that can be reached by the liquid phase of the liquefied gas.

  The variable T is obtained by receiving the operating parameters of the device for cooling the liquefied gas that represents the lowest temperature threshold at which the liquid phase of the liquefied gas can be reached.

The function f ₁ is a function representing the liquid-vapor equilibrium curve in the component temperature-pressure diagram of the liquefied gas or the liquefied gas having the lowest evaporation temperature of the component constituting the liquefied gas present in a molar ratio greater than 5%. This is the affine transformation.

The function f ₁ is of the form f ₁ (T) = g (T) −ε ₁ , where g is the liquefied gas or the liquefied gas having the lowest evaporation temperature of the liquefied gas component present in a molar ratio greater than 5%. It is a function representing a liquid-vapor equilibrium curve of a component in a temperature-pressure diagram, and ε ₁ is a positive constant.

The constant ε ₁ is, for example, between 10 and 30 mbar.

  The hermetic membrane is a primary hermetic membrane, the thermal barrier is a primary thermal barrier, a multilayer structure is further abutted against the support structure and includes a solid material, a gas phase, a secondary thermal barrier, a secondary thermal barrier, and 1 And a secondary sealing film disposed between the secondary insulation barrier.

The pump device includes a second vacuum pump connected to the secondary insulation barrier to place the gas phase of the secondary insulation barrier at a negative relative pressure, the method comprising the pressure of the gas phase of the secondary insulation barrier Measuring P ₂ and controlling the second vacuum pump to constrain the gas phase pressure P ₂ of the secondary adiabatic barrier to a set point pressure P _c2 .

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

The function f ₂ in the temperature-pressure diagram of the liquefied gas, the component of the liquefied gas having the lowest evaporation temperature in the liquid-vapor equilibrium curve of the liquefied gas, or the component constituting the liquefied gas present in a molar ratio greater than 5% It is an affine transformation of the function showing the liquid-vapor equilibrium curve in the temperature-pressure diagram of the main components of the liquefied gas.

The function f ₂ is of the form f ₁ (T) = g (T) −ε ₂ , where g is the liquefied gas or the liquefied gas having the lowest evaporation temperature of the components of the liquefied gas present in a molar ratio greater than 5%. It is a function representing a liquid-vapor equilibrium curve of a component in a temperature-pressure diagram, and ε ₂ is a positive constant.

The constant ε ₂ is, for example, between 10 and 30 mbar.

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

Function h, h (P1) = P1- ε ' is the _second type, epsilon' ₂ are constants.

The constant ε ′ ₂ is, for example, between 10 and 30 mbar.

According to one embodiment, the present invention relates to a control method, the step of controlling a vacuum pump as a function of a measured value of the set pressure P _c1 and the pressure P ₁ in the gas phase of the adiabatic barrier, and the temperature of the liquid phase of the liquefied gas Measuring T and determining the setpoint pressure P _c1 by the equation P _c1 = f ₁ (T), where f ₁ is a monotonically increasing function.

  Another basic idea of the present invention is to propose a method for controlling an apparatus for cooling liquid gas that can effectively protect at least one sealing membrane of a tank.

According to one embodiment, the present invention is a method for controlling an apparatus for cooling a liquefied gas associated with a facility for storing liquefied gas, wherein the facility has a liquid phase and a gas phase in a two-phase form. A wall having a multilayer structure with a sealed membrane in contact with the liquefied gas and a thermal barrier comprising a solid material and a gas phase disposed between the sealed membrane and the support structure And a pressure sensor adapted to measure the gas phase pressure P ₁ in the insulation barrier, and configured to place the gas phase of the insulation barrier at a negative relative pressure connected to the insulation barrier. A pump device comprising a vacuum pump and a control module for controlling the vacuum pump to constrain the gas phase pressure P ₁ of the insulation barrier to a set point pressure P _c1; and at a pressure at which the liquefied gas is stored in the tank The temperature of a portion of the liquefied gas And a cooling device adapted to lower the liquid phase equilibrium temperature of the liquefied gas, and a method of controlling the device for cooling the liquefied gas includes the equation T _min = f ₃ (P _c1 ), where f ₃ controlling and determining the lowest temperature threshold value T _min of the liquefied gas, so that the temperature of the liquefied gas does not fall below a minimum temperature threshold value T _min, the cooling device as a function of the minimum temperature threshold T _min is monotonically increasing function, the And are included.

According to other advantageous embodiments, a method of the above kind can have one or more of the following characteristics: That is, the function f ₃ represents the liquid-vapor equilibrium curve in the temperature-pressure diagram of the component of the liquefied gas or the component of the liquefied gas having the lowest evaporation temperature of the component constituting the liquefied gas present in a molar ratio of more than 5%. In other words, the minimum temperature threshold value T _min corresponding to the liquid-gas equilibrium temperature of the liquefied gas or the main component of the liquefied gas at the set temperature P _c1 is determined. The liquid phase of the liquefied gas in the tank does not reach a sufficiently low temperature, leading to a decompression of the internal space of the tank, which is greater than the reduced pressure of the adiabatic barrier.

According to one embodiment, the present invention also provides a facility for storing liquefied gas, which is sealed and liquefied intended to contain a liquefied gas in a two-phase form having a liquid phase and a gas phase. Sealing comprising a sealing membrane in contact with a gas and a wall having a multilayer structure with a thermal barrier comprising a solid material and a gas phase disposed between the sealing membrane and the support structure, wherein the sealing membrane contains the solid material and the gas phase and insulated tank, and a pressure sensor adapted to measure the pressure P ₁ of the gas phase in the heat insulating barrier, the vacuum pump that is configured to place the gas phase is connected to the insulating barrier insulating barrier to negative relative pressure And a pump device comprising a pump device comprising a control module, wherein the control module determines the setpoint pressure P _{c1 according} to the formula P _c1 = f ₁ (T), f ₁ is a monotonically increasing function, T is the actual temperature of the liquid phase of the liquefied gas or Restraining a step which is a variable representing the minimum temperature that can be reached by the liquid phase of the liquefied gas for the operation state of the apparatus for cooling the gases, the pressure P ₁ of the gas phase of the insulating barrier in the set pressure P _c1 And controlling the vacuum pump (16).

  According to another embodiment, such a facility has one or more of the following features.

  The facility further includes a temperature sensor adapted to measure and send the liquid phase temperature T of the liquefied gas to the control module.

  The facility further includes a device for cooling the liquefied gas, the device reducing the temperature of a portion of the liquefied gas to a temperature below the liquid-vapor equilibrium temperature of the liquefied gas at the pressure at which the liquefied gas is stored in the tank. To be adapted.

The cooling device is applied to meet the minimum temperature threshold of the liquid phase of the liquefied gas, and the control module is connected to the cooling device and adapted to determine a set point pressure P _c1 that takes the minimum temperature threshold as a variable T. Is done.

  The equipment is adapted to measure the operating parameters of the device for cooling the liquefied gas, which represents the minimum threshold that can be reached by the liquid phase of the liquefied gas.

  The hermetic membrane is a primary hermetic membrane, the thermal barrier is a primary thermal barrier, the multilayer structure is further in contact with the support structure, a secondary thermal barrier including a solid material and a gas phase, and a secondary thermal barrier and a primary thermal barrier A secondary sealing film is disposed between the barrier.

The facility further includes a second pressure sensor adapted to measure the pressure P ₂ in the secondary insulation barrier.

  The pump device further includes a second vacuum pump connected to the secondary insulation barrier to place the gas phase of the secondary insulation barrier at a negative relative pressure.

The control module controls the second vacuum pump to constrain the gas phase pressure P ₂ of the secondary adiabatic barrier to the set pressure P _c2 .

  According to an embodiment, the device for cooling the liquefied gas is an evaporator for cooling the liquefied gas, and the evaporator is a liquefied gas existing in the internal space of the evaporation chamber and the internal space of the tank. An evaporation chamber that includes a heat exchange wall that allows heat exchange between the inlet, an inlet that leads to the liquid phase liquefied gas flow in the tank and evaporates to expand the extracted air Inlet circuit including a head loss member that communicates with the interior space of the chamber, and adapted to exhaust the gas flow from the vaporization chamber to the gas in the vapor phase utilization circuit, and sucks the gas flow in the vaporization chamber And an outlet circuit having a vacuum pump configured to discharge it into the gas in the vapor phase utilization circuit and maintain an absolute pressure below atmospheric pressure in the evaporation chamber.

  According to another embodiment, an apparatus for cooling a liquefied gas includes a circuit for withdrawing gas into the gas phase, the circuit leading to an interior space of the tank that exceeds a maximum fill height of the tank. An inlet that leads when the tank is filled to the region of the vapor phase that contacts the interface region that separates the lower liquid phase and the upper gas phase, and the flow of gas in the vapor phase that exists in the region of the vapor phase through the inlet It is adapted to aspirate and release it into the gas in the vapor phase utilization circuit and maintain it in the vapor phase region at a pressure lower than atmospheric pressure, so that the evaporation of the vacuum pump liquid phase is promoted at the level of the interface region A vacuum pump in which the liquefied gas in contact with the interface region is placed in a liquid-vapor equilibrium state where the liquefied gas has a temperature lower than the liquid phase equilibrium temperature of the liquefied gas at atmospheric pressure.

  A facility of the above kind forms part of an onshore storage facility, for example for storing LNG, or coastal or deep water, in particular a methane tanker ship, a floating storage and regasification unit (FSRU) It can be installed in a floating production storage and offloading unit (FPSO).

  According to one embodiment, the ship includes a double hull and the equipment described above, and a tank of equipment for storing liquefied gas is disposed within the double hull.

  According to one embodiment, the present invention also provides a method for unloading or unloading a vessel of the above kind, wherein the fluid is transferred from a floating or on-shore storage facility to or from the tank of the vessel via an insulated pipe. Supplied from there.

  According to one embodiment, the present invention also provides a system for transferring fluid, the system being adapted to connect the vessel and a tank installed on the hull to a floating or on-shore storage facility. Thermal insulation pipes and pumps that drive to or from the tanks of the ship to or from floating or land-based equipment.

  The invention will be better understood with reference to the following description of specific embodiments given by way of non-limiting illustration and the accompanying drawings, in which other objects, details, features and advantages will become clearer. .

It is a figure which shows typically the installation by 1st Embodiment for storing and cooling liquefied gas. It is a figure which shows typically the installation by 2nd Embodiment for storing and cooling liquefied gas. It is a figure which shows typically the installation by 3rd Embodiment for storing and cooling liquefied gas. FIG. 6 schematically shows an installation according to a fourth embodiment for storing and cooling liquefied gas. It is a liquid-vapor equilibrium curve of methane. 1 is a cross-sectional view of a methane tanker ship with a tank and a terminal for unloading / unloading the tank.

  In the specification and claims, the term “gas” refers generally to the exchange of a gas consisting of a single body or a gas mixture consisting of a plurality of components. Thus, a liquefied gas is a chemical or mixture of chemicals that is placed in the liquid phase at low temperatures and in the vapor phase under normal temperature and pressure conditions.

  FIG. 1 shows an installation 1 according to a first embodiment for storing and cooling liquefied gas. This type of equipment 1 can be installed in a floating structure such as a methane tanker ship or a liquefaction or regasification barge.

  The equipment 1 includes a hermetically sealed heat insulating membrane tank 2. The tank 2 includes a wall having a multi-layer structure, and from the outside to the inside of the tank 2, a secondary heat insulating barrier 3 including a heat insulating element that includes a gas phase and abuts against the support structure 4, and a secondary heat insulating barrier 3 A secondary sealing film 5 that abuts, a primary heat insulating barrier 6 including a heat insulating element that contacts the secondary sealing film 5, and a primary sealing film 7 that can contact a liquefied gas 8 stored in a tank. . As an example, a membrane tank 2 of the above kind is described in WO14057221, FR26991520 and FR28777638.

  According to one embodiment, the tank comprises a vapor collection device (not shown) that passes through the ceiling wall of the tank and leads to the upper part of the interior space of the tank. This type of device is provided with a valve that allows the vapor to be discharged from the inside of the tank to the outside when the pressure inside the internal space of the tank 2 exceeds a threshold value. This kind of vapor collecting device thus makes it possible to avoid the generation of increased pressure inside the tank 2. Further, the valve is configured to prevent the gas flowing in the vapor collecting device from flowing from the outside to the inside of the tank 2, and thus the pressure in the internal space of the tank 2 can be reduced. As an example, this type of vapor collection device is described in WO2013093261.

  The liquefied gas 8 is a combustible gas. The liquefied gas 8 is in particular liquefied natural gas (LNG), ie mostly methane, one or more other hydrocarbons ethane, propane, n-butane, i-butane, n-pentane i-pentane, A small amount of mixed gas such as neopentane and nitrogen. The combustible gas may be ethane or liquefied petroleum gas (LPG), i.e. a mixture of hydrocarbons obtained from refining petroleum, essentially 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. Therefore, the liquefied gas 8 exists in the vapor phase at the upper part of the tank 2 and the liquid phase at the lower part of the tank 2.

  In order to cool the liquefied gas stored in the tank 2, the facility 1 sets the temperature of a part of the liquid phase of the liquefied gas 8 at the pressure at which the liquefied gas 8 is stored in the tank 2. Further included is a device for lowering the temperature below. In this way, a portion of the liquefied gas is placed in a supercooled thermodynamic state.

  For this purpose, in the embodiment shown in FIG. 1, the facility 1 removes the gas flow in the liquid phase from the tank 2, expands it and vaporizes it using the latent heat of vaporization and remains in the tank 2. It includes an evaporator 20 intended to cool the liquefied gas 8 being cooled.

  The operating principle of this type of evaporator 20 is explained in connection with FIG. 5, which shows a methane liquid-vapor equilibrium curve, which is a function of pressure plotted on the horizontal axis and temperature plotted on the vertical axis. As shown, a region where the methane indicated as L exists in the liquid phase and a region where the methane indicated as V exists in the gas phase are shown.

Point P ₁ represents a two-phase equilibrium state corresponding to the state of methane stored in tank 2 at atmospheric pressure and a temperature of about −162 ° C. When this equilibrium methane is withdrawn from the tank 2 and then expanded in the evaporator 20 to an absolute pressure of, for example, about 500 mbar, the equilibrium of the expanded methane moves to the point P ₂ towards the left. Therefore, the expanded methane has a temperature drop of about 7 ° C. The extracted methane evaporates at least partially when it comes into thermal contact with the methane remaining in the tank 2 via the evaporator 20, and the liquid methane stored in the tank 2 can be cooled when evaporating. The heat required for evaporation is taken from the liquid methane remaining in the tank 2.

  Accordingly, the methane remaining in the tank 2 is placed at a temperature lower than its equilibrium temperature at the pressure at which methane is stored in the tank 2.

  Referring again to FIG. 1, the evaporation device 20 is immersed in the inlet circuit having an inlet 21 immersed in the liquid phase of the liquefied gas 8 stored in the tank 2, and in the liquid phase and / or vapor phase of the liquefied gas 8. One or more evaporation chambers 22 having a heat exchange wall immersed in the liquefied gas stored in the tank 2 and in thermal contact between the gas and the entrained flow of gas remaining in the tank 2, and a vapor state And an outlet circuit 23 for exhausting the gas flow into the gas in the gas phase utilization circuit 25.

  The inlet circuit includes one or more head loss members (not shown) that generate head losses and direct them into the evaporation chamber 22 to expand the drawn liquefied gas stream.

  The evaporator also comprises a vacuum pump 24 associated with the outlet circuit 23, located outside the tank. The vacuum pump 24 sucks the flow of the liquefied gas stored in the tank 2 into the evaporation chamber 22 and discharges it to the gas in the gas phase utilization circuit 25 in a gas phase state. In the case of liquefied natural gas, the absolute operating pressure inside the evaporation chamber 22 is between 120 and 950 mbar, preferably between 650 and 850 mbar, for example on the order of 750 mbar.

  When installed on a ship, the gas in the gas phase utilization circuit 25 can be connected to a propulsion energy production facility (not shown), and the ship can be propelled. This type of energy production facility is selected in particular from heat engines, fuel cells and gas turbines.

  In FIG. 2, the facility 1 is provided with another device for cooling the liquefied gas, and the liquefied gas 8 can be placed in a supercooled thermodynamic state.

  For this purpose, the installation 1 here comprises a circuit 9 for extracting gas in the gas phase. The circuit 9 for extracting gas in the gas phase includes a conduit 10 that penetrates the wall of the tank 2, defining a passage for exhausting the gas phase from the inside of the tank 2 to the outside. The conduit 10 has an intake port 11 that communicates with the inside of the internal space of the tank 2 in the decompression bell 31. The decompression bell 31 is arranged in the upper part of the internal space of the tank 2, and the upper part thereof is filled in contact with the gas phase of the liquefied gas 8 stored in the tank 2, and the lower part is liquefied gas stored in the tank 2. 8 is immersed in the liquid phase. The inlet 11 of the circuit 9 for extracting the gas phase is led to the upper part of the evaporation bell 20.

  The extraction circuit 9 also includes a vacuum pump 12 connected to a pipe on the upstream side and connected to a circuit 13 for utilizing vapor phase gas on the downstream side. Therefore, the vacuum pump 12 sucks the flow of the gas in the vapor phase existing in the decompression bell 31 through the conduit 10 and supplies it to the gas in the vapor phase utilization circuit 13. Here, since the extraction circuit 9 includes a valve or a check valve 19 disposed upstream or downstream of the vacuum pump 12, it is possible to prevent the gas-phase gas flow from returning to the internal space of the tank 2. it can.

  The vacuum pump 12 is configured to generate a pressure lower than the atmospheric pressure at the upper part of the decompression bell 31, and can promote the evaporation of the liquefied gas in the evaporation bell 20. The gas phase inside the reduced bell 31 is placed at a pressure lower than the atmospheric pressure, the vaporization of the liquefied gas 8 is promoted at the liquid-vapor interface in the decompression bell 31, and the liquefied gas stored in the tank 2 is stored. 8 is in a two-layer vapor equilibrium state where the liquefied gas 8 has a temperature lower than the liquid phase equilibrium temperature of the liquefied gas at atmospheric pressure.

  In another embodiment shown in FIG. 3, the cooling device comprises a liquefier and the liquefier is adapted to collect vaporized liquefied gas in the interior space of the tank 2, and a liquid phase liquefied gas Is provided with an outlet 33 adapted to be introduced into the interior space of the tank 2. The liquefier further includes a cooling circuit 35 through which the cooling fluid circulates. The cooling circuit 35 includes a compressor 36, a condenser 37, a decompressor 38, and an evaporator 39 that removes heat from the liquefied gas circulating in the first circuit 34 and evaporates the cooling liquid. A cooling device of this kind is described in document EP2853479.

  In another embodiment shown in FIG. 4, the cooling device includes a cooling unit 40 that circulates liquid nitrogen at about −196 ° C. in the hairpin tube 41, the effect of which is to cool the liquefied gas around the tube 41. It is. When the cooled liquefied gas becomes denser, it moves downward in the tank 2 and the refrigerated gas that has not been frozen rises. This convection motion is guided by the convection well 42 and causes this convection motion throughout the tank 2. As the liquid nitrogen circulates, the nitrogen evaporates and the liquefied gas can be cooled by the effect of the latent heat. Upon exiting the tube 23, the nitrogen is reliquefied in the cooling unit 41. A cooling device of this kind is described in particular in FR 2785034.

  Although various devices for cooling liquid gas have been described above, the present invention is not limited to any of these cooling devices and allows cooling below the liquid phase equilibrium temperature of the liquefied gas. Other cooling devices can be used.

  Referring again to FIG. 1, in the illustrated embodiment, the facility 1 includes a vacuum pump 16 connected to a pipe 17 leading to the interior space of the primary insulation barrier 6 and a pipe leading to the interior space of the secondary insulation barrier 3. It can be seen that a pump device having a vacuum pump 14 connected to 15 is provided. This type of pump device is intended to maintain the gas phase inside the primary heat insulation barrier 6 and the secondary heat insulation barrier 3 at a pressure lower than the pressure in the internal space of the tank 2. Thus, the pressure difference between the membranes presses the membranes inward so that they do not tear in the direction of the interior of the tank 2.

  The vacuum pumps 14 and 16 are low-temperature pumps, that is, can withstand extremely low temperatures of −150 ° C. or less. They are also compliant with ATEX regulations, i.e. designed to avoid all explosion hazards. The vacuum pumps 14, 16 can be manufactured in a variety of ways, for example, roots type (ie, rotating lobes) or types with paddle, liquid ring, screw, venturi type effectors.

  The apparatus 1 further includes a control module 26 that allows the vacuum pump 14 and the vacuum pump 16 to be controlled to regulate the pressure in the primary insulation barrier 6 and the secondary insulation barrier 3. The control module 26 includes a single element as in the illustrated embodiment, or two elements, the latter being associated with control of one and the other of the two vacuum pumps 14,16, respectively.

  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 transmits the measurement of the liquid phase temperature of the liquefied gas 8 stored in the tank 2. it can. In order to obtain a temperature measurement indicating the lowest temperature in the tank 2, the temperature sensor 27 is advantageously arranged near the bottom of the tank 2. The temperature sensor 27 is also preferably arranged near the heat exchange wall of the evaporation chamber 22. The temperature sensor 27 may be of any type, such as a thermocouple or a platinum resistance probe.

The facility 1 also includes at least one pressure sensor 28 that enables transmission of the measured value of the liquid phase pressure P ₁ inside the primary adiabatic barrier 6 and the gas phase pressure P inside the secondary adiabatic barrier 3. _And a pressure sensor 29 that allows transmission of _two measurements.

The control module 26 is adapted to generate a control value for the vacuum pump 16 as a function of the measurement of the setpoint pressure P _c1 and the gas phase pressure P ₁ inside the primary adiabatic barrier 6, the pressure P ₁ being the target pressure P _1. Restrain to _c1 . Similarly, the control module 26 is adapted to generate a control value for the vacuum pump 14 as a function of the measurement of the target pressure P _c2 and the gas phase pressure P ₂ inside the primary adiabatic barrier 6, and the pressure P ₂ Restrain to set pressure P _c2 .

The control module 26 is further adapted to continuously determine the set pressure P _c1 of the first adiabatic barrier 6 as a function of the temperature measured by the temperature sensor 27. In other words, the set pressure P _c1 is given by
P _c1 = f ₁ (T)
Here, f ₁ : monotonically increasing function and T: temperature of the liquid phase of the liquefied gas 8 delivered by the temperature sensor 27 are determined.

The function f ₁ is more specifically the liquefied gas or the liquefied gas with the lowest evaporation temperature at atmospheric pressure among other components of the liquefied gas present in a non-negligible amount (ie a molar ratio greater than 5%). It is an affine transformation of a function g representing a liquid-vapor equilibrium curve of a component in a temperature-pressure diagram. The function f ₁ is, for example, the following equation:
P _c1 = f ₁ (T) = g (T) −ε ₁
Where g: a function representing the liquid-vapor equilibrium curve of the most volatile component in a non-negligible amount of liquefied gas or liquefied gas in a temperature-pressure diagram, and ε ₁ : a constant, for example about 10-30 mbar. Represented.

  The function g can determine the saturated vapor pressure related to the temperature of the liquid phase measured in the tank 2, and thus lowers the absolute pressure that can be reached during the vapor phase condensation of the liquefied gas stored in the tank. The pressure value can be determined as

  According to one embodiment, when the liquefied gas is a gas mixture of components, the function g represents the liquid-vapor equilibrium curve of the most volatile component of components present in non-negligible amounts. For example, in the case of liquefied natural gas, the function g represents the liquid-vapor equilibrium curve of pure methane. Next, referring to the liquid-vapor equilibrium curve of the most volatile component, the saturated vapor pressure is determined as the lower limit of the saturated vapor pressure of the mixed gas. This approach is simple and robust and does not require real-time determination of the composition of the liquefied gas that can change over time.

  However, in another embodiment, the function g representing the liquid-vapor equilibrium curve of the actual gas mixture is used to more accurately determine the saturated vapor pressure associated with the measured temperature of the liquefied gas stored in the tank. It is possible to do as well.

For example, the equilibrium curve of methane in the temperature-pressure diagram can be approximated by the following function:
g (T) = 3.673776 × 10 ⁻² T ³ −9.597262T ²
+ 8.552665 × 10 ² T−2.568325 × 10 ⁴
Here, T is Kelvin and g (T) is millibar.

If the temperature of the liquid phase of the liquefied gas 8 stored in the tank is 105 K, this kind of temperature generated by the function g is typically 565 mbar. If the liquid phase temperature of the liquefied gas is 105K, the pressure in the tank will not theoretically fall below the absolute pressure of 565 mbar. In such a situation, if the constant ε ₁ is assumed to be 20 mbar in consideration of the uncertainty of the liquid phase temperature measurement and the liquid phase temperature non-uniformity inside the tank, the set pressure P _c1 is 545 mbar. is there.

  Therefore, by placing the primary insulation barrier 6 at this absolute pressure of 545 mbar, the pressure inside the tank 2 is always higher than the pressure inside the primary insulation barrier 6 and the primary sealing membrane 7 is made secondary. It can be pressed against the thermal barrier 3 to prevent collapse.

  It is noted that by using the function g representing the liquid-vapor equilibrium curve of liquid gas, an ideal compromise between the safe operation of the facility and the energy costs required to ensure operational safety can be achieved. I want. Nevertheless, if it is permissible to reduce the safety margin or increase the energy cost, it is possible to use a significantly different function g with an equivalent general profile.

Furthermore, the control module 26 is adapted to determine the set pressure P _c2 of the secondary insulation barrier 6.

According to one embodiment, the setpoint pressure P _c2 is determined as a function of the temperature T measured by the temperature sensor 27 in a manner similar to the setpoint pressure P _c2 . Therefore, the target pressure P _c2 is given by the following equation:
P _c2 = f ₂ (T)
Here, f ₂ is determined by a monotonically increasing function, and T is a temperature of the liquid phase of the liquefied gas 8 delivered by the temperature sensor 27.

Like function f ₁ , function f ₂ has the following form:
P _c2 = f ₂ (T) = g (T) −ε ₂
Here, g: a function representing a liquid phase equilibrium curve of a liquefied gas or a liquid component of a liquefied gas in a temperature correction diagram, and ε ₂ : a constant, for example, about 10 to 30 mbar.

According to another embodiment, the setpoint pressure P _c2 is determined not as a function of the temperature measured by the temperature sensor 27 but as a function of the pressure P ₁ of the gas phase in the primary adiabatic barrier 6 by the following equation: And
P _c2 = h (P ₁ ) = P ₁ −ε ′ ₂
Here, h: monotonically increasing function and P ₁ : pressure measured in the gas phase of the primary adiabatic barrier 6.

The function h is, for example, of the form
P _c2 = h (P ₁ ) = P ₁ −ε ′ ₂
Here, ε ′ ₂ is represented by a constant.

According to a variant embodiment, ε ′ ₂ is a positive constant, for example between 10 and 30 mbar. Therefore, according to this method, the pressure of the gas phase of the secondary heat insulation barrier 3 is always lower than the pressure of the gas phase of the primary heat insulation barrier 6, and as a result, the secondary sealing film 5 is pressed against the secondary heat insulation barrier 3. Is guaranteed.

According to another variant embodiment, ε ′ ₂ is a negative constant, for example between −10 and −30 mbar. Therefore, according to this method, it is ensured that the gas phase pressure of the secondary heat insulation barrier 3 is always higher than the gas phase pressure of the primary heat insulation barrier 6, and liquefaction occurs when the sealing films 5 and 7 are poorly sealed. It makes it possible to prevent the gas 8 from being sucked towards the secondary insulation barrier 3.

According to another alternative embodiment, the set pressure P _c1 and / or the set pressure P _c2 of the primary adiabatic barrier 6 is not determined as a function of the measured value of the temperature of the liquefied gas 8, but liquefied gas. Is determined by substituting as a variable T in the above equation the variable corresponding to the minimum threshold that can be reached by the liquid phase of the liquefied gas for a particular operating state of the device for cooling the.

  Thus, as described with reference to FIG. 1, according to the embodiment comprising a device for cooling the liquefied gas, the device is arranged at the outlet of the evaporation chamber 22 and circulates inside the evaporation chamber 22. It includes a temperature sensor that measures either the temperature of the gas flow in the gas phase or the temperature of the walls of the evaporation chamber 22. Under the continuous operating conditions of the cooling device, the temperature measured in this way represents the lowest temperature that can be reached by the liquid phase of the liquefied gas 8 stored inside the tank 2. Next, assuming that the temperature measured in this way is the value of T in the above equation, the pressure in the gas phase inside the primary heat insulation barrier 6 and the secondary heat insulation barrier 3 is set to the tank by the control method of the vacuum pump 16 and the vacuum pump 14. It can be guaranteed that it is always lower than the pressure in the interior space of 2.

Similarly, if the device for cooling the liquefied gas is a liquefier that includes a liquefied gas circulation circuit cooperating with the cooling circuit as shown in FIG. A temperature sensor may be included that measures the return temperature of the cooling fluid at the outlet. Under the continuous operating conditions of the cooling device, the temperature measured in this way also represents the lowest temperature that can be reached by the liquid phase of the liquefied gas 8 stored inside the tank 2, and therefore the set pressure P _c1 It can also be used to determine and optionally to determine the set pressure P _c2 .

According to another embodiment, the device for cooling the liquefied gas is adapted to meet a minimum temperature threshold T _min for the liquid phase of the liquefied gas. In other words, device liquidus temperature of the liquefied gas to cool the liquefied gas so as not to fall below the temperature threshold value T _min is controlled. Therefore, the operating parameter of the cooling device is set so that the temperature of the liquid phase of the liquefied gas does not fall below the threshold value.

  By way of example, as described with reference to FIG. 1, in the case of an installation with a device for cooling the liquefied gas, the minimum temperature threshold is ensured by setting a corresponding threshold pressure inside the evaporation chamber 22. can do.

  Similarly, as described with reference to FIG. 2, in the case of equipment having a device for cooling liquefied gas, a minimum temperature threshold value can be guaranteed by setting a threshold pressure corresponding to the inside of the decompression bell 31. it can.

  If the device that cools the liquefied gas is a liquefier that includes a gas circulation circuit that cooperates with the cooling circuit, the minimum temperature threshold may be adapted by setting a threshold pressure or flow rate for the cooling fluid in the cooling circuit. . Alternatively, the temperature can be measured on the evaporator fin of the cooling circuit and the cooling circuit power is regulated with an appropriate safety margin as a function of the measured temperature to meet the aforementioned minimum temperature threshold. To do.

According to a variant embodiment, the temperature threshold T _min is preset and then transmitted to the control module 26. Next, the control module 26 determines the set point pressure by taking the temperature threshold T _min as the value of T in the formula P _c1 = f ₁ (T) = g (T) −ε ₁ .

According to an alternative variant embodiment, it is the target pressure P _c1 that is preset and then transmitted to the cooling device. In this case, the temperature threshold T _min is given by
T _min = f ₃ (P _c1 )
Here, it is determined by f ₃ : a function representing a liquid-vapor equilibrium curve of the main component of liquefied gas or liquefied gas in the pressure-temperature diagram, P _c1 : set pressure of the primary adiabatic barrier 6.

  Referring to FIG. 6, a cross-sectional view of a methane tanker ship 70 shows a prismatic, generally shaped, sealed and insulated tank 71 mounted within a double hull 72 of the ship. The wall of the tank 71 has a primary sealing barrier intended to contact the LNG contained in the tank, and a secondary sealing barrier disposed between the primary sealing barrier and the ship's double hull 72; It includes two insulating barriers, each disposed between the primary and secondary sealing barriers and between the secondary sealing barrier and the double hold 72.

  In a known manner, the unloading / unloading pipe 73 located on the upper deck of the ship is connected to the maritime terminal or port terminal by suitable connectors and can transfer LNG cargo from or to the tank 71. .

  FIG. 6 shows an example of a maritime terminal that includes a loading / unloading station 75, an underwater pipe 76, and an onshore facility 77. The unloading and unloading station 75 is a fixed offshore facility that includes a moving arm 74 and a tower 78 that supports the moving arm 74. The movable arm 74 carries a bundle of heat-insulating flexible pipes 79 that can be connected to the unloading / unloading pipes 73. An orientable movable arm 74 fits all sizes of methane tankers. The unloading / unloading station 75 allows the methane tanker 70 to be unloaded from or onto the land facility 77. The onshore facility includes a tank 80 for storing liquefied gas and a pipe 81 connected to an unloading / unloading station 75 by an underwater pipe 76. The underwater pipe 76 allows the transfer of liquefied gas between the unloading / unloading station 75 and the land facility 77 over a large distance, for example 5 km, so that the methane tanker 70 is shored during unloading and unloading operations. Keep a great distance from.

  Pumps on the ship 70 and / or pumps with land equipment 77 and / or pumps with a loading / unloading station 75 are used to generate the pressure required for the transfer of liquefied gas.

  The present invention has been described in connection with a number of specific embodiments, but is in no way limited thereto, and includes all technical equivalents of the means described and combinations thereof within the scope of the invention. It is clear.

  Use of the verbs “include”, “comprise”, and their conjugates does not exclude the presence of elements or steps other than those listed in a claim. The use of the indefinite article for an element or step, one (“a” or “an”), does not exclude the presence of a plurality of such elements or steps, unless otherwise indicated.

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

Claims (23)

A method for controlling a pump device associated with a hermetically sealed tank (2), wherein the tank (2) stores a liquefied gas (8) having a liquid phase and a gas phase and contacts the liquefied gas (8). Sealing wall (7) and a wall having a multilayer structure with a heat insulating barrier (3, 6) disposed between the sealing film (7) and the support structure (4), 3, 6) has a solid material and a gas phase, and the pumping device is connected to the adiabatic barrier (3, 6) in order to place the gas phase at a negative relative pressure. 16) and the method comprises:
Measuring the gas phase pressure P ₁ of the adiabatic barrier (3, 6);
The step of determining the setpoint pressure P _c1 by the formula P _c1 = f ₁ (T), where f ₁ is a monotonically increasing function, and T is the measured temperature of the liquid phase of the liquefied gas (8) or the liquefied gas (8 And a variable that represents the minimum temperature threshold that can be reached by the liquid phase of the liquid crystal and corresponds to the operating state of the device for cooling the liquefied gas (8);
Controlling the vacuum pump (14, 16) to constrain the gas phase pressure P ₁ of the adiabatic barrier (3, 6) to a set pressure P _c1 ;
A method for controlling a pump device comprising:   The variable T represents an operating parameter of the device for cooling the liquefied gas, which represents the minimum temperature threshold that can be reached by measuring the liquid phase temperature of the liquefied gas (8) or by the liquid phase of the liquefied gas. The method according to claim 1, which is obtained by measuring.   The variable T is obtained by receiving an operating parameter of the device for cooling the liquefied gas, which represents the minimum temperature threshold that can be reached by the liquid phase of the liquefied gas (8). Method. The function f ₁ is a temperature-pressure diagram of the component of the liquefied gas (8) having the lowest evaporation temperature of the component constituting the liquefied gas (8) or the component of the liquefied gas present in a molar ratio greater than 5%. The method according to claim 1, wherein the method is an affine transformation of a function representing a liquid-vapor equilibrium curve. The function f ₁ is represented by f ₁ (T) = g (T) −ε ₁ , where g is the lowest evaporation temperature of the liquefied gas (8) or a component of the liquefied gas present in a molar ratio greater than 5%. The method according to claim 4, wherein ε ₁ is a positive constant, a function representing a liquid-vapor equilibrium curve in a temperature-pressure diagram of a component of the liquefied gas (8) having   The sealing film is a primary sealing film (7), the heat insulation barrier is a primary heat insulation barrier (6), and the multilayer structure further abuts the support structure (4) and includes a solid material and a gas phase 2 6. A secondary insulation barrier (3) and a secondary sealing membrane (5) disposed between the secondary insulation barrier (3) and the primary insulation barrier (6). The method according to one item. The pump device includes a second vacuum pump (14) connected to the secondary insulation barrier (3) for placing the gas phase of the secondary insulation barrier (3) at a negative relative pressure. The way,
Measuring the gas phase pressure P ₂ of the secondary adiabatic barrier (3);
And controlling the second vacuum pump (14) so as to restrain the pressure P ₂ in the gas phase of the secondary insulation barrier setpoint pressure P _c2,
The method of claim 6 comprising: The method of claim 7, wherein the second setpoint pressure P _c2 is determined by the equation P _c2 = f ₂ (T), where f ₂ is a monotonically increasing function. The function f ₂ represents the liquid in the temperature-pressure diagram of the component of the liquefied gas (8) having the lowest evaporation temperature of the component constituting the liquefied gas (8) or the liquefied gas present in a molar ratio of more than 5%. 9. The method of claim 8, wherein the method is an affine transformation of a function representing a vapor equilibrium curve. The function f ₂ is of the form f ₁ (T) = g (T) −ε ₂ , where g is the liquefied gas (8) or the evaporation temperature of the components constituting the liquefied gas present in a molar ratio greater than 5%. The method according to claim 9, wherein is a function representing the liquid-vapor equilibrium curve in the temperature-pressure diagram of the component of the lowest liquefied gas (8), and ε ₁ is a positive constant. The method of claim 7, wherein the second set pressure P _c2 is determined by the equation P _c2 = h (P ₁ ), where h is a monotonically increasing function. The method of claim 11, wherein the function h is represented by h (P ₁ ) = P ₁ −e, where ε ′ ₂ is a constant. A method of controlling an apparatus for cooling a liquefied gas associated with a facility for storing liquefied gas, the facility comprising:
A sealed insulated barrier tank (2) configured to store a liquefied gas (8) having a two-phase form having a liquid phase and a vapor phase, the sealed membrane (7) in contact with the liquefied gas, and the sealed A wall having a multilayer structure with a thermal barrier (3, 6) disposed between the membrane (7) and the support structure (4), the sealed membrane comprising a solid material and a gas phase; An insulated barrier tank;
A pressure sensor (28) adapted to measure the pressure P _{1 of the} gas phase in the adiabatic barrier (3, 6);
A vacuum pump (14, 16) connected to the adiabatic barrier (3, 6) and configured to place the gas phase of the adiabatic barrier (3, 6) at a negative relative pressure; and the vacuum pump (3, 6) ) gas phase adapted control module to control the vacuum pump (16) so as to restrain the pressure P ₁ in the set pressure P _c1 of (26), a pump device including,
A cooling device adapted to lower the temperature of a portion of the liquefied gas below the liquid phase equilibrium temperature of the liquefied gas at a pressure at which the liquefied gas is stored in a tank;
A method of controlling the apparatus for cooling the liquefied gas comprises:
Determining the minimum temperature threshold T _min of the liquefied gas by the equation T _min = f ₃ (P _c1 ), where f ₃ is a monotonically increasing function;
The As temperature of the liquefied gas does not fall below the minimum temperature threshold value T _min, method and controlling the cooling device as a function of a minimum temperature threshold value T _min, it is included. A facility (1) for storing liquefied gas,
The equipment
A sealed heat insulating tank (2) configured to store a liquefied gas (8) having a two-phase form having a liquid phase and a vapor phase, the sealed membrane (7) in contact with the liquefied gas, and the sealed membrane (7 ) And a heat insulating barrier (3, 6) disposed between the support structure (4) and comprising a solid material and a gas phase, the sealing membrane comprising the solid material and the gas phase , A sealed insulation tank (2),
A pressure sensor (28) adapted to measure the pressure P ₁ of the gas phase in the adiabatic barrier (3, 6);
A vacuum pump (14, 16) connected to the adiabatic barrier (3, 6) and configured to bring the gas phase of the adiabatic barrier (3, 6) to a negative relative pressure; and a control module (26) A pump device,
The control module is
Determining the setpoint pressure P _c1 by the formula P _c1 = f ₁ (T), where f ₁ is a monotonically increasing function and T is the actual temperature of the liquid phase of the liquefied gas (8) or the liquefied gas ( A variable representing the minimum temperature that can be reached by the liquid phase of the liquefied gas (8) for the operating state of the device for cooling 8);
Controlling the vacuum pump (16) to constrain the gas phase pressure P ₁ of the adiabatic barrier (3, 6) to a set pressure P _c1 .
Equipment for storing liquefied gas (1).   15. Equipment according to claim 14, further comprising a temperature sensor (27) that measures the temperature T of the liquid phase of the liquefied gas (8) and sends it to the control module (26).   The apparatus further comprises an apparatus for cooling the liquefied gas adapted to lower the temperature of a portion of the liquefied gas below the liquid-vapor equilibrium temperature of the liquefied gas at a pressure at which the liquefied gas is stored in the tank. Item 14. The equipment according to Item 14 or 15. The cooling device is adapted to match the minimum temperature threshold of the liquid phase of the liquefied gas, and the control module (26) is connected to the cooling device and takes the minimum temperature threshold as a variable T and sets the setpoint pressure P _c1 . The facility of claim 16, wherein the facility is adapted to determine.   17. The facility of claim 16, comprising a sensor adapted to measure an operating parameter of an apparatus for cooling the liquefied gas that represents a minimum threshold that can be reached by the liquid phase of the liquefied gas.   The sealing membrane is a primary sealing membrane (7), the thermal barrier is a primary thermal barrier (6), the multilayer structure further abuts the support structure (4), and includes a solid material and a gas phase 19. A secondary insulation barrier (3) and a secondary sealing membrane (5) disposed between the secondary insulation barrier (3) and the primary insulation barrier (6). Equipment according to any one of the above. Further comprising a second pressure sensor for the adapted to measure the pressure P ₂ in the secondary insulating barrier (29), the pump device, the second insulation film vapor phase negative (3) A second vacuum pump (14) connected to the secondary insulation membrane (3) for placing at a relative pressure is further included, and the control module (26) sets the second vacuum pump (14) to a set value. pressure P _c2 and adapted to control as a function of the measured values of the pressure P ₂ in the gas phase of the secondary insulation barrier (3), Installation according to any one of claims 14 to 19.   A ship (70) for storing a liquefied gas comprising a double hull and the equipment according to any one of claims 14 to 20, wherein the tank (2) of the liquefied gas storage equipment is a double ship. A ship placed in the body.   22. Fluid according to claim 21, wherein the fluid is supplied from or to a floating or land-type facility (77) or to a tank of a ship (71) via an insulating pipe (73, 79, 76, 81). How to unload / unload a ship.   22. Ship (70) according to claim 21 and insulating pipes (73, 79) adapted to connect the tank (71) installed on the hull of the ship to a floating or land-type facility (77). 76, 81) and a pump for driving fluid from or to the floating or terrestrial facility to or from the tank of the ship via the insulating pipe.

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