Method and device for transferring cryogenic fluid

Abstract

To provide a method and a device for transferring liquefied cryogenic fluid, such as liquid hydrogen, from a cryogenic tank containing liquefied cryogenic fluid having a gas phase in equilibrium with the liquid phase.SOLUTION: Transfer of fluid to a receiver is realized at least in part by a pressure difference between a tank (1) and a fluid receiver. The method according to the present invention comprises the steps of: pressurizing a fluid contained in the tank (1); withdrawing the liquid from the pressurized tank; measuring a volume flow rate of the withdrawn fluid; and determining mass of the withdrawn liquid from the measured volume flow rate of the withdrawn fluid and density of the withdrawn fluid. Therein the density of the withdrawn fluid is determined from pressure of the fluid in the tank (1) measured before the pressurization step.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method and apparatus for transferring cryogenic fluids.

[0002] The present invention more particularly relates to a method for transferring a liquefied cryogenic fluid, e.g., liquid hydrogen, from a cryogenic tank containing the liquefied cryogenic fluid having a gas phase in equilibrium with a liquid phase, wherein the transfer of the fluid to a receiver is achieved at least in part by a pressure differential between the tank and the fluid receiver, the method comprising the steps of pressurizing the fluid contained in the tank, withdrawing liquid from the pressurized tank, measuring the volumetric flow rate of the withdrawn fluid, and determining the mass of the withdrawn liquid from the measured volumetric flow rate of the withdrawn fluid and the density of the withdrawn fluid. [Background technology]

[0003] Measuring the flow rate of liquid hydrogen faces several challenges. Currently used turbine flow meters provide volumetric flow values, but the invoice of liquid volume is based on mass. Coriolis mass flow meters are more expensive and difficult to install in a vacuum chamber. Furthermore, the mass flow readings provided by mass flow meters can be disturbed by the presence of gas bubbles in the liquid. Summary of the Invention

[0004] SUMMARY OF THE INVENTION It is an object of the present invention to overcome all or some of the above-mentioned drawbacks of the prior art.

[0005] To this end, the method according to the invention, which otherwise complies with the generic definition given in the preamble above, is essentially characterized in that the density of the extracted fluid is determined from the pressure of the fluid in the tank measured before the pressurization step.

[0006] Further, embodiments of the present invention include: - the method includes measuring the pressure of the fluid in the tank and detecting an increase in pressure corresponding to a pressurizing step, wherein the pressure of the fluid in the tank measured before the pressurizing step is a pressure value measured before the detected increase in pressure; - the density of the extracted fluid is calculated from the formula D = -2.36P + 72.8 (D is the density in kg / m3 and P is the pressure in bar (abs)) and / or from a determined table giving the density of the fluid as a function of the pressure of the fluid, - determining the mass of the withdrawn liquid comprises calculating the mass by multiplying the density by the value of the measured volumetric flow rate of the withdrawn fluid; - determining the mass of liquid drawn off comprises, for example, correcting the measured volumetric flow rate value by a multiplying coefficient; The method may have one or more of the following characteristics: the step of measuring the volumetric flow rate of the drawn fluid is achieved using a positive displacement flow meter.

[0007] The present invention also relates to an apparatus for transporting a liquefied cryogenic fluid, for example liquid hydrogen, comprising a cryogenic tank intended to contain a liquefied cryogenic fluid having a gas phase in equilibrium with a liquid phase, and a liquid transfer duct having an upstream end connected to the tank and a downstream end intended to be connected to a receiver, the liquid transfer duct comprising a positive displacement flow meter, the apparatus comprising a system for pressurizing the fluid contained in the tank, a pressure sensor for the fluid in the tank, a temperature sensor, and an electronic data storage and processing component comprising a microprocessor, the electronic component being configured to determine the density of the fluid withdrawn by the transfer duct from the pressure value of the fluid measured by the pressure sensor.

[0008] The invention may also relate to any alternative device or method comprising any combination of the above or below features within the scope of the claims.

[0009] Further particular features and advantages will become apparent from the following description, which is provided with reference to the drawings.

[0010] The invention will be better understood on reading the following description, given purely by way of example and with reference to the accompanying drawings, in which: [Brief explanation of the drawings]

[0011] [Figure 1] 1 is a schematic partial view illustrating an example of the structure and operation of a tank embodying the present invention; DETAILED DESCRIPTION OF THE INVENTION

[0012] Like reference numbers refer to like elements throughout the drawings.

[0013] In the detailed description of the invention, the following embodiments are examples. Although the description refers to one or more embodiments, this does not mean that the features apply only to a single embodiment. Individual features of different embodiments can also be combined and / or substituted to provide other embodiments.

[0014] FIG. 1 illustrates one example of an apparatus for transferring liquefied cryogenic fluids in which the present invention can be practiced.

[0015] The device comprises a cryogenic tank 1 intended to contain a liquefied cryogenic fluid (e.g. hydrogen) having a gas phase in equilibrium with a liquid phase. The tank 1 is preferably a double-shelled tank with an insulating space (preferably under vacuum) between the shells.

[0016] The device comprises a liquid transfer duct 2 having an upstream end connected to the tank 1 and a downstream end intended to be connected to a receiver for the withdrawn fluid.

[0017] The liquid transfer duct 2 is equipped with a positive displacement flow meter 4 .

[0018] The device comprises a system 3 for pressurizing the fluid contained in the tank 1 .

[0019] The pressurization device 3 comprises, for example, a pressure generating unit (pressure building unit (PBU)). The pressurization device 3 comprises, for example, a pressurization duct 13 connected in a loop to the tank (a first end is connected, for example, to the lower part of the tank 1 and a second end is connected, for example, to the upper part of the tank). Between these two ends, the pressurization duct 13 comprises a heat exchanger 33 (for example, for exchanging heat with air) and a set of one or more valves, for example two valves 23, 43 located on either side of the heat exchanger 33.

[0020] The transfer of liquid from tank 1 (mobile or stationary) to the receiver is achieved at least in part by a pressure difference. To this end, tank 1 may be pressurized to effect this transfer. Pressurization from a tank 1 in thermodynamic equilibrium can be conventionally achieved by withdrawing liquid from the tank through an opening in valve 23 upstream of heat exchanger 33, vaporizing this liquid in heat exchanger 33, and then returning the resulting hot gas by natural convection to the gas headspace of the tank through an opening in valve 43 downstream of heat exchanger 33.

[0021] This pressurization method increases the gauge pressure of the fluid by a determined amount (typically on the order of 0.2-3 bar). This increase in pressure does not significantly increase the temperature of the liquid in the tank. This means that the fluid in Tank 1 goes from a saturated state to a subcooled liquid state.

[0022] When the liquid is pressurized, it is transferred by the pressure difference to a receiver (one or more suitable valve openings in the transfer duct 2).

[0023] For billing purposes, a measurement is made of the withdrawn (volumetric) flow rate 4. As billing must be done using mass measurements, a correction for density of the volume reading is necessary.

[0024] Since the density of a liquid depends on its saturation pressure, measurement of the volumetric flow rate (for example with a turbine flow meter) is not possible without correcting for the density value.

[0025] The device comprises a pressure sensor 5 for the fluid in the tank 1 , for example located in the transfer duct 2 upstream of the flow meter 4 .

[0026] An indication of the pressure of the fluid at the time of withdrawal does not allow for reliable correction, since the liquid is not in thermodynamic equilibrium.

[0027] According to one advantageous particular feature, the pressure in the tank is measured or determined when there is equilibrium between the gas and liquid phases. The increase in gauge pressure caused by pressurization is detected during start-up of the pressurization system 3 and / or by detecting a sudden increase in pressure (several bars per hour in the case of pressurization by PBU for 15 mbar / h) that is significantly faster than the pressure increase in the tank related to the heat input. The pressure sensor 5 can therefore detect the pressure increase related to pressurization, for example, by detecting an interruption (e.g., a discontinuity) in the measured pressure gradient. The value of the gauge pressure just before the start of this pressure increase can be retrieved (e.g., recorded), for example, by using a value offset in time with respect to the pressure increase.

[0028] This pressure value allows the density of the drawn liquid to be calculated or determined using a chart.

[0029] The density can be obtained, for example, by calculation and the formula D=-2.36xP+72.8 (where D is the density in kg / m3 and P is the pressure in bar (abs)) and / or by a predetermined look-up table or table such as:

[0030] [Table 1]

[0031] This density value makes it possible to correct the volumetric flow rate value read by the flow meter 4.

[0032] For this purpose, the device may comprise an electronic data storage and processing component 6 having one or more microprocessors, which may be configured to determine the density of the fluid drawn by the transport duct 2 from the pressure value of the fluid measured by the pressure sensor 5.

[0033] If Tank 1 is mobile, during a multiple delivery round, the energy injected during delivery to pressurize the tank and the transport between the two delivery points will increase the temperature of the liquid (and therefore the saturation pressure of the system at equilibrium).

[0034] The present invention allows for the determination of the density of the liquid at the time of delivery, which is not correlated to the gauge pressure during withdrawal.

[0035] The present invention allows positive displacement flow meter measurements during cryogenic liquid delivery to be corrected for density.

[0036] Determining the mass of the withdrawn liquid may comprise calculating the mass by multiplying the density by a measured volumetric flow rate value of the withdrawn fluid.

[0037] This allows the mass quantity of liquid transferred to be determined, even though the gauge pressure during this delivery is uncorrelated with the density of the delivered fluid (which is subcooled).

Claims

1. 1. A method for transferring a liquefied cryogenic fluid, e.g., liquid hydrogen, from a cryogenic tank (1) containing the liquefied cryogenic fluid having a gas phase in equilibrium with a liquid phase, wherein transferring the fluid to a receiver is achieved at least in part by a pressure difference between the cryogenic tank (1) and the receiver, the method comprising the steps of pressurizing the fluid contained in the cryogenic tank (1), withdrawing liquid from the pressurized cryogenic tank, measuring a volumetric flow rate of the withdrawn fluid, and determining a mass of the withdrawn liquid from the measured volumetric flow rate of the withdrawn fluid and a density of the withdrawn fluid, characterized in that the density of the withdrawn fluid is determined from a pressure of the fluid in the cryogenic tank (1) measured before the pressurizing step.

2. 2. The method of claim 1, wherein the method comprises the steps of measuring the pressure of the fluid in the cryogenic tank (1) and detecting a pressure increase corresponding to a pressurization step, and wherein the pressure of the fluid in the cryogenic tank measured before the pressurization step is the pressure value measured before the detected pressure increase.

3. 3. A method according to claim 1 or 2, characterized in that the density of the extracted fluid is calculated from the formula D = -2.36P + 72.8, where D is the density in kg / m3 and P is the pressure in bar (abs), and / or from a determined table giving the density of the fluid as a function of the pressure of the fluid.

4. 4. The method of claim 1, wherein the step of determining the mass of the withdrawn liquid comprises calculating the mass by multiplying the density by the measured value of the volumetric flow rate of the withdrawn fluid.

5. 5. The method according to claim 1, wherein the step of determining the mass of liquid drawn off comprises, for example, correcting the measured volumetric flow rate value by a multiplication factor.

6. Method according to any one of claims 1 to 5, characterized in that the step of measuring the volumetric flow rate of the withdrawn fluid is achieved by means of a positive displacement flow meter.

7. 1. A device for transferring a liquefied cryogenic fluid, for example liquid hydrogen, comprising: a cryogenic tank (1) intended to contain a liquefied cryogenic fluid having a gas phase in equilibrium with a liquid phase; and a liquid transfer duct (2) having an upstream end connected to the cryogenic tank (1) and a downstream end intended to be connected to a receiver, the liquid transfer duct (2) being equipped with a volumetric flow meter; The device comprises: a system (3) for pressurizing the liquefied cryogenic fluid contained in the cryogenic tank (1), configured to pressurize the liquefied cryogenic fluid contained in the cryogenic tank (1) before withdrawal; a pressure sensor (5) for the liquefied cryogenic fluid in the cryogenic tank (1); a temperature sensor (5); and an electronic data storage and processing component (6) comprising a microprocessor, the electronic data storage and processing component (6) being configured to determine the density of the liquefied cryogenic fluid withdrawn by the liquid transfer duct (2) from a pressure value of the liquefied cryogenic fluid measured by the pressure sensor (5) before the pressurization.

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