"Two-phase fluid flow meter with extended measuring range"

Abstract

A flow meter (1) for cryogenic liquid / gas two-phase fluids, with overflow, comprising a vertical internal tank, tank surrounded by a device, tank into which a supply pipe for the fluid whose flow rate is to be measured opens, and where the tank has one of the following configurations: a wall of the internal tank is provided with a system of multiple fluid discharge slots, forming a "spillway" system, from the tank to the space inside the device surrounding the tank, where the slots have a different width distributed over the height of the tank; or; the internal tank comprises several successive spillway systems, the fluid supply pipe opening inside a first spillway, the spillways successively discharging into one another, until discharging into the space inside the device surrounding the tank. Abstract figure: Fig.3

Description

Title of the invention: Flow meter for two-phase fluid with extended measuring range

[0001] The present invention relates to the field of flow meters for two-phase gas / liquid cryogenic fluids.

[0002] Measuring the flow rate of a two-phase fluid composed of a liquid and a gas is a difficult operation when seeking to measure a mass flow rate. Indeed, all sensors measuring a flow rate are hampered when they are placed in the presence of a two-phase liquid whose density changes at any time. This is particularly valid for measuring the flow rate of cryogenic fluids such as liquid nitrogen.

[0003] Some flow meters listed in the literature are based on the measurement of fluid velocity. These include, for example: - turbine flow meters: a turbine is installed in the moving fluid and the rotation speed of the turbine gives an image of the speed of the fluid. - Pitot tube flow meters: two tubes are installed in the moving fluid to be measured. One tube is installed perpendicular to the flow and gives the static pressure, the other is installed parallel to the flow and gives the total dynamic pressure. The difference in dynamic pressure between these two measurements is used to calculate the flow rate. - ultrasonic flow meters: some use the Doppler effect (analysis of the frequency reflected by the particles of the fluid which gives an image of the speed of the particle and therefore of the fluid) while others measure a difference in travel time of an ultrasonic wave from upstream to downstream and from downstream to upstream (image of the speed of the fluid).

[0004] In all these cases, when the density of the fluid varies continuously, the transition from volume flow to mass flow is difficult to achieve precisely.

[0005] Other systems use the measurement of pressure drop (loss of load) to deduce the flow rate. These are, for example, calibrated orifice flow meters which measure the pressure drop upstream and downstream of a calibrated orifice placed in the moving fluid. The measurement of these devices is very disturbed when the fluid does not have a constant density and when the gas level increases in the liquid.

[0006] Electromagnetic flow meters, applicable only to fluids with sufficient electrical conductivity, use the principle of electromagnetic induction: An electromagnetic field is applied to the fluid and the electromotive force created (force proportional to the fluid flow rate) is measured. In the case of for flow measurement of cryogenic (non-conductive) fluids such as liquid nitrogen, this principle is not applicable.

[0007] Vortex flow meters are based on the phenomenon of vortex generation that occurs behind a fixed, non-profiled body placed in a moving fluid (Karman effect). Measuring the pressure variations created by these vortices gives the frequency of the vortices, which is proportional to the speed of the fluid when the fluid maintains constant properties. When the density of the fluid varies, the measurement is distorted.

[0008] Thermal flow meters are based on measuring the temperature increase created by a constant supply of energy. A system with two temperature probes measures the temperature difference between the flow entering and leaving the flow meter. Between these two probes, a resistance provides a known quantity of energy. When the heat capacity of the fluid in motion is known, the flow rate can be calculated from these measurements. However, this principle is not applicable to two-phase liquids whose thermal behavior (vaporization of the liquid) is completely different from single-phase liquids.

[0009] Only the Coriolis mass flow meter gives an accurate measurement of the mass flow of a fluid. The flow meter consists of a U-shaped or omega-shaped or curved tube, in which the fluid circulates. The U is subject to lateral oscillation and the measurement of the phase shift of the vibrations between the two branches of the U gives an image of the mass flow. However, its cost is quite high and when it is used at very low temperatures (liquid nitrogen at -196°C for example) and with a fluid whose density varies enormously and includes a significant part in the gas phase, it is necessary to strongly isolate the system (high-performance insulation such as vacuum insulation for example) and despite everything, the measurements are distorted when the gas content exceeds a few percent by mass. It should also be noted that the measurement is often made impossible when the fluid speed is low or zero (in the first half of the measurement range).

[0010] As can be seen, measuring the flow rate of a two-phase liquid and in particular measuring the flow rate of a cryogenic fluid with acceptable accuracy is not easy to achieve with the devices currently available on the market.

[0011] It can nevertheless be noted that systems are currently being marketed.

[0012] For example, we can cite the case of systems based on the principle of measuring the level of a liquid flowing in a channel just before a restriction of the passage section. This system, described in document US-5,679,905, operates essentially as follows: the two-phase fluid is first separated into a gas phase which is not measured and a liquid phase whose flow rate is measured. This liquid passes into a channel which has a reduction in section at its outlet. The greater the flow rate, the greater the The liquid level in the channel is important and a level measurement in this channel then makes it possible to deduce the instantaneous flow rate. As can be seen, this system does not take into account the gas flow rate which in certain applications is not negligible. On the other hand, this system makes it possible to measure the liquid flow rate with relatively good precision without being disturbed by the gas level, which is the desired goal.

[0013] It should be noted in passing that for this system to function correctly, it must be well insulated from heat inputs which could vaporize part of the isolated liquid and thus disrupt the level measurement. This is why vacuum insulation is used in this system.

[0014] It will also be noted that for the system to work, there must be the presence of two phases in the flow meter, which prohibits its operation with a subcooled liquid (clear liquid without gas phase).

[0015] It may also be noted that this document implements a V-shaped slot which has the disadvantage of being difficult to produce with great precision. A variation of 5% on the width of the slot has very serious consequences because it makes the measurement imprecise in the same proportions.

[0016] We can also cite the case of flow meters with phase separator.

[0017] Indeed, in the case where the measurement of liquid and gas flow rates is necessary, a system is sometimes used which uses the same principle of phase separation before the flow rate measurement.

[0018] Thus, commercially available devices have the following arrangement: - The two-phase liquid first passes through a phase separator which separates the liquid phase from the gas phase; - The gas phase is directed towards a volume flow meter (turbine type for example) with temperature compensation; - The liquid phase is also directed towards a volume flow meter (turbine type for example); - These two flow measurements are then converted into a mass measurement and added.

[0019] A priori, this device is more expensive than the previous one, one can think that it will be very precise. In practice, it is found that the measurement of the liquid flow rate is affected by errors which fluctuate according to the pressure and temperature conditions of the liquid entering the flow meter. These measurement errors are due to the presence of gas in the liquid phase which passes through the flow meter. Indeed, when the liquid leaves the phase separator to go towards the flow meter, a part of the liquid vaporizes, either because of the heat inputs or because of the pressure drop due to a rise of the liquid, or because of a pressure drop due to the pressure loss created by the flow meter itself.

[0020] Finally, to measure the flow rate of a cryogenic liquid, one can also overcome the problems mentioned above by creating pressure and temperature conditions different from the equilibrium pressure (boiling limit). In this field, the most commonly used method is, for example, a flow meter at the outlet of a cryogenic pump (high pressure side). In this case, the liquid is, for example, pumped into a tank where it is at equilibrium and it is pressurized by the pump, with almost no increase in temperature. The pipes and the flow meter that follow can then create a pressure drop; this will not result in vaporizing the liquid provided that the pressure drop is significantly lower than the increase in pressure created by the pump.

[0021] In this case, a conventional vortex, turbine or other type flow meter can be used as long as it can withstand low temperatures.

[0022] This technique is, for example, perfectly suited to measuring the flow rate of nitrogen delivery trucks. It is reliable and cost-effective since the cryogenic pump is required for other reasons.

[0023] On the other hand, when it is necessary to measure the flow rate of liquid nitrogen at a point where there is no cryogenic pump, then this technique is no longer interesting.

[0024] A solution for simultaneous or alternating measurement of the liquid and gas phases is also known, as described in document FR-3 013 446 in the name of the Applicant, based on the following principle: - the fluid arrives in a tank acting as a phase separator; - the gas phase is evacuated from the top of the tank via a bitmeter operating on a pure gas phase; - the liquid phase is evacuated from the bottom of the tank via a flow meter operating on a pure liquid phase; - the two phases are then combined at a three-way valve and continue on their way; - equipped with the two measured flow rates as well as the pressure and temperature of the fluid, the system can calculate the mass flow rate of the fluid passing through the flow meter.

[0025] This system proves to be precise and works regardless of the two-phase rate present in the fluid. It works precisely when the fluid is totally gaseous or when it is totally liquid or sub-cooled, but it also works in all intermediate situations.

[0026] However, this system is penalized by the fact that it is relatively expensive and its installation is relatively complex.

[0027] It must be installed horizontally and its size is quite large (typically 1 meter wide, 1 meter long, 2 meters high).

[0028] The Applicant then attached itself during previous work, described in the document WO 2023 / 011836, to propose a new, simple and reliable solution for measuring the flow rate of cryogenic gas / liquid two-phase fluids, making it possible to solve all or part of the technical problems mentioned above, a solution which was based on the implementation of the following measures (one can refer to the attached [Fig.l] to better visualize this previous solution): 1. A measurement of the flow rate of the non-subcooled liquid phase with a so-called "overflow" system. For this, the two-phase fluid is first naturally separated into a gas phase which is not measured and a liquid phase whose flow rate is measured.

[0029] The principle of the spillway is as follows: An obstacle (partition perforated with one or more slots) is installed in the liquid passage, it slows the flow of the liquid. The greater the flow, the more the level upstream of the obstacle will rise. With a calibrated obstacle it is then possible to calculate the flow rate based on the liquid level measured upstream of the obstacle.

[0030] To measure the height of liquid upstream of the obstacle, a differential pressure measurement is used. Among the differential pressure sensors available on the market, it is possible to use sensors which can measure low pressure values.

[0031] However, to achieve this pressure level with a cryogenic fluid height, a height of the order of 300 mm must be obtained. For this reason, it is advantageous to orient the spillway in the vertical direction so that it allows the creation of a high liquid height, and so that the differential pressure measurement is therefore also quite high. 2. A measurement of the flow rate of the subcooled liquid phase with a calibrated orifice (8): when the cryogenic fluid is subcooled, then the flow rate measurement is carried out using a calibrated orifice located upstream or downstream of the spillway.

[0032] The liquid passes through the calibrated orifice and generates a pressure difference. By calculation, it is then possible to obtain the flow rate of the subcooled cryogenic fluid.

[0033] It should be noted here that this flow measurement system does not work when the fluid is not subcooled. When it is saturated (or at equilibrium), the presence of gas in the liquid distorts the measurement, the measured pressure variation generates more two-phase flow. The measured pressure difference is not representative of the quantity of cryogenic fluid passing through the calibrated orifice. It is therefore necessary to know at all times the state of the cryogenic fluid, subcooled or not. 3. A measurement of the subcooling state of the cryogenic fluid (determination of the state of the cryogenic fluid: subcooled or gas-liquid equilibrium): to know the state of the cryogenic fluid evaluated, we measures the subcooling state of the cryogenic fluid whose flow rate is to be measured.

[0034] For this purpose, the level of liquid present downstream of the spillway is measured. When this level is zero, the cryogenic fluid is not undercooled, whereas in the opposite case, the cryogenic fluid is undercooled: - Case No. 1: If the sensor measuring the liquid height in the device (delta P2, downstream of the spillway) indicates a near-zero value, the fluid therefore has a gas phase and a liquid phase. The sensor measuring the pressure difference across the calibrated orifice (Delta P3) will also indicate a non-zero value (gas + liquid). - Case No. 2: If the sensor measuring the liquid height in the device (AP2, downstream of the spillway) indicates a non-zero value, the fluid therefore only has a liquid phase. The sensor measuring the pressure difference on the calibrated orifice (AP3) will indicate a value representative of the flow rate in pure liquid.

[0035] To reliably detect whether the fluid is in case No. 1 or in case No. 2, a pressure difference measurement is carried out in a second volume downstream of the spillway (AP2) as seen previously. This volume is either filled with gas (case No. 1) or filled with liquid (case No. 2), due to the difference in density between the liquid and gas phases, and thus makes it possible to define whether the fluid is pure liquid or a two-phase fluid.

[0036] And when AP3 is negative, this means that the fluid flow is reversed (from downstream to upstream): In this case, this flow is neutralized and not taken into account by the flow meter. The error is thus minimized. - 4. calculation of an estimate of the two-phase rate: using the system described below above in accordance with the prior art, we can, as we have understood, measure the liquid phase whatever the conditions, but we can go further and carry out calculations based on the two measurements (via weir and calibrated orifice) and then estimate the two-phase rate. This rate makes it possible to determine the gas phase and thus refine the measurement of total fluid flow rate.

[0037] The advantages of this prior flow meter can be summarized as follows: - moderate cost; - a measurement offering very good precision (typically 2%); - a system that cannot give rise to an erroneous measurement when the flow rate is zero or slightly negative and the cryogenic fluid is boiling in the flowmeter; - ease of installation; - it provides reliable measurements when the gas level in the fluid varies from 0 to 100%, the system even allows the flow rate to be measured when the liquid is sub-cooled.

[0038] The present invention seeks to improve the flow meter of the prior art described above, because in fact, if until recently, it had been thought of dedicating a flow meter to a given range of flow rates, for this the idea was to size the diameter of the calibrated orifice and the width of the slots according to the flow rate range.

[0039] But in fact, for slots ([Fig.l]) sized for a given flow rate range, if the flow rate to be measured turns out to be higher than the maximum value of the planned sized range, then an overflow from the top of the device will be observed.

[0040] We can in fact consider several very broad flow rate ranges of interest: - From 100kg / h to 500kg / h - Up to 1000kg / h - Up to 2000kg / h - etc...

[0041] According to the present invention, it is then desired to allow the same flow meter to cover several flow ranges, and this based on the initial structure of the flow meter described in the document cited above WO 2023 / 011836.

[0042] However, if we could initially propose working with a spillway having a much greater height, but the disadvantage would then be that the manufacture of the boiler part would be larger, more restrictive, and therefore more expensive.

[0043] It is then proposed according to the present invention, for a maximum liquid flow rate, and to limit the height of the device within reasonable limits, to implement: - not one but several successive spillways, these spillways having slots of different widths, which flow into one another; or - a single spillway but with slots whose width varies along the height of the spillway.

[0044] A first embodiment of such a structure is illustrated by the attached [Fig.2], which uses 3 successive spillways, provided with rectangular slots.

[0045] Spillway 1 (first spillway encountered by the fluid stream whose flow rate is to be measured): the slots (small width) are sized for the smallest flow rate range of interest. If the flow rate to be measured is higher than the maximum value of this first range, an overflow will be observed (arrow Fl)

[0046] If no overflow occurs, the measurements made on this spillway will be considered valid.

[0047] Spillway 2: the slots (average width) are sized for the flow rate range of interest which can be described as average. If the flow rate to be measured is higher than the maximum value of this second range, an overflow will be observed (arrow F2) towards the 3rd spillway.

[0048] If no overflow is observed, the measurements made on this spillway will be considered valid but less precise than those obtained on spillway No. 1 in the absence of overflow.

[0049] Spillway 3: The slots (width “high”) are sized for the range of interest with the highest flow rate.

[0050] It can be considered that in this [Fig.2], the pressure differences can be read in the following way: the pressure differences AP1A = P1A - P1A', AP1B= PIB -PIB', and AP1C= PIC- PIC' correspond to the API represented and used in the previous mode of [Fig.l] (respectively for the three spillways implemented in this [Fig.2]).

[0051] In a two-phase situation, the measurement of the liquid phase is made in the spillway: • For spillway 1, the measurement should ideally be taken between PI A and PI A'. This measurement will be converted into the height of liquid in spillway 1. A mathematical formula, classic in this field of overflows: • explained below, will then convert this level into the flow rate of liquid passing through the slot. When the level measurement is too close to a high limit, this spillway will be considered overflowing and this measurement will not be taken into account. • For spillway 2, the measurement should ideally be made between PIB and PIB'. Similarly, this measurement will give us the liquid level as well as the liquid flow rate crossing the slot of spillway 2. When the level measurement is too close to a high limit, this spillway will be considered overflowing and this measurement will not be taken into account. • For spillway 3, the measurement should ideally be made between PIC-PIC'. Similarly, this measurement will give us the liquid level as well as the liquid flow rate passing through the slot of spillway 3. When the level measurement is too close to a high limit, this spillway will be considered overflowing. In this case, the flow rate will be higher than the measuring capacity of the device and all measurements will be neutralized.

[0052] The symbols of the mathematical formulas cited below must be understood as follows: - Q is the flow rate in m3.s 1 - p is the spillway flow coefficient - Ls is the width of the overhanging threshold, in mm - h is the liquid height, in mm - g is the acceleration of gravity in m.s2

[0053] To simplify the system, the measurement can be made between P1A and PIC' for spillway 1, between PIB and PIC' for spillway 2 and between PIC and PIC' for spillway 3.

[0054] A single calibrated orifice (diameter) can be used to measure the entire fluid in two-phase (the liquid phase represents more than 95% of the total flow, it is therefore essential that the measurement in the spillway is precise) and in pure liquid. The constraint is linked to the fact of using a precise sensor to measure the differential pressure.

[0055] According to another example of an embodiment of the invention illustrated in [Fig.3] attached, a single spillway is implemented, provided with rectangular slots of different width distributed over the height of the spillway: - “Low” thickness cracks on the first third (hl) in the lower part of the spillway - Slots of “medium” thickness on the 2nd third (h2-hl) of the spillway - And “high” thickness slots on the 3rd third (h3-h2) in the upper part of the spillway

[0056] As will then be clear to those skilled in the art, for measuring small flow rates the liquid passes through the portion of slots at the bottom of the tank, for measuring medium flow rates the liquid passes through the small and medium slots of the spillway, while for measuring large flow rates the liquid passes through all of the slots available on the spillway.

[0057] As an example here, a slot width of 1mm at the bottom of the spillway, 2mm in the middle and 4mm at the top of the spillway can be adopted. A greater width difference can also be adopted from one spillway to another, such as 0.2mm for the bottom, 1mm for the middle and 5mm for the top. Depending on the requirements, the difference can also be smaller, for example 1mm at the bottom, 1.5mm in the middle and 2mm at the top. Finally, variable width differences can also be adopted between the slots, such as 0.5mm at the bottom, 1mm in the middle and 3mm at the top.

[0058] According to another example of an embodiment of the invention, illustrated in the context of the attached [Fig.4], a single spillway is implemented, provided with triangular-shaped slots of different widths distributed over the height: slots of “low” thickness in the lower part of the spillway and progressively slots of increasingly greater thickness up to the upper part of the reservoir.

[0059] For example, the slot may have a width of 0 mm at the bottom and 5 mm at the top. Generally speaking, this slot will advantageously have a width varying from 0 to 2mm at the bottom and 1 to 10mm at the top.

[0060] In order to better assist in understanding the different embodiments of reservoirs and spillways in accordance with the present invention illustrated here, the following will be found in the attached [Fig.5]: In view a): a partial schematic view facing the slots of the widths implemented in the 3 successive spillways of [Fig.2]. In view b): a partial schematic view facing the slots of the single spillway of [Fig.3], with its slot width decreasing from the top to the bottom of the spillway. In view c): a partial schematic view facing the slots of the single spillway of [Fig.4].

[0061] Let us explain in the following an example of calculation of the flow rate for the example of the mode implementation of [Fig.3] (single spillway, slots of decreasing width from the top to the bottom of the spillway).

[0062] As seen above, the flow rate can be expressed by the following classic formula:

[0063] Where Q is the flow rate in m3 / s

[0064] p is the spillway flow coefficient

[0065] Ls is the width of the overhanging threshold, in mm

[0066] h is the liquid height, in mm

[0067] g is the acceleration of gravity in m.s2

[0068] If the calculated height is less than hl, the flow rate in the spillway must be calculated with the “low” slot width (1st third), therefore by applying the formula with the low slot width of the 1st third.

[0069] If the calculated height h is less than hl (a height h of liquid corresponds to a flow rate, as we have understood): Calculate the flow rate through the lower slit for the slit width of the first third and the height h. The total flow rate is equal to this flow rate.

[0070] If the calculated height h is between h1 and h2: Calculate the flow rate through the lower slit for the slit width of the first third and the height h1, and Calculate the flow rate through the middle slit for the slit width

[0071]

[0072]

[0073]

[0074]

[0075]

[0076]

[0077] of the second third and the height h2 - h1, The total flow rate is then the sum of these two flow rates. If the calculated height h is between h2 and h3: - Calculate the flow rate through the lower slit for the slit width of the first third (bottom) and the height h1, - The flow rate flowing through the average slot is calculated for the slot width of the 2nd (intermediate) third and the height h2-hl, - We calculate the flow rate flowing through the wide slot for the slot width of the 3rd third (top) and the height h3-h2, The total flow rate is then the sum of these 3 flow rates. The heights hl, h2 and h3, the low, medium and high slot widths can be adapted to “tier” measuring ranges as desired. Let us explain in the following an example of flow rate calculation for the example of the implementation mode of [Fig.2]. It will be recalled that in this [Fig.2], the pressure differences API A = PI A - PI A', AP1B= PIB - PIB', and AP1C= PIC- PIC' can be compared to the API represented and used in the previous mode of [Fig.l] (for the three spillways implemented in this [Fig.2]), therefore for each of these three spillways there is a pressure difference between the bottom of the tank considered and the atmosphere surrounding the tank within the interior space within the device. A data acquisition and processing system is capable of carrying out the following evaluations: - a. a determination of the information on the state of the incoming fluid: gaseous, two-phase or sub-cooled, from the pressure difference data between P1A' and PIC (i.e. two points located in the space surrounding the tank within the interior space, making it possible to deduce the height of liquid downstream of the tank, in order to determine the state of the fluid, gaseous, two-phase or sub-cooled, and giving the level of liquid invasion downstream of the tank); - b. based on this status information, the determination of said flow rate using either the pressure differential measured on both sides of the calibrated orifice present on the supply pipe of the fluid whose flow rate is to be measured to the equipment, or when the fluid is 100% gaseous or 100% liquid (subcooled), or when we are in the presence of a two-phase fluid, by applying the following approach: - when the pressure difference AP1A = P1A - P1A' characterizing the first spillway encountered by the fluid is between a given minimum level and a given maximum level (maximum corresponding to a level of border (for example, this maximum level could be a value between 50mm and 500mm), we then have a flow rate that can be described as "low" or "weak" flow rate: the pressure differential between P1A and PI A' makes it possible to deduce the height of liquid in tank No. 1 and subsequently the flow rate of fluid passing through the slots of tank No. 1, using the coefficients related to the width of the slots of tank No. 1. - when the pressure difference AP1A = P1A - P1A' is greater than the given maximum level (causing an overflow of the Nol tank) and the pressure difference AP1B = PIB - PIB' is between a given minimum level and a given maximum level (there is then no overflow of the No 2 tank) (for example, this maximum level could be a value between 50mm and 500mm), we then have a flow rate that can be described as an "average" flow rate: the pressure differential between PIB and PIB' makes it possible to deduce the height of liquid in the No 2 tank and subsequently the flow rate of fluid passing through the slots of the No2 tank, this by using the coefficients linked to the width of the slots of the No2 tank. - when the pressure difference AP1B = PIB - PIB' is greater than a given maximum level (sign of an overflow of tank No. 2) (for example, this maximum level could be a value between 50mm and 500mm) and the pressure difference AP1C = PIC - PIC' is between a minimum and a maximum (sign that no overflow of tank 3 is observed, flow rate that can then be described as "high average"): the pressure differential between PIC and PIC' makes it possible to deduce the height of liquid in tank No. 3 and subsequently the flow rate of fluid passing through the slots of tank No. 3, using the coefficients linked to the width of the slots of tank No. 3.

[0078] Let us now consider the case of the mode of [Fig.3] implementing a single spillway with a slot width decreasing from the top to the bottom of this spillway.

[0079] As described above, a single spillway is used here, provided with rectangular slots of different widths distributed over the height of the spillway: - “Low” thickness cracks on the first third (hl) in the lower part of the spillway - “Medium” thickness cracks on the 2nd intermediate third (h2-hl) of the spillway - And “high” thickness slots on the 3rd third (h3-h2) in the upper part of the spillway

[0080] A data acquisition and processing system is then capable of carrying out the following assessments: - a. determining the state information of the incoming fluid: gaseous, two-phase or subcooled, from the pressure difference data between P1A' and PIC (i.e., two points located in the space around the reservoir within the interior space, allowing the liquid height downstream of the reservoir to be deduced, in order to determine the state of the fluid, gaseous, two-phase or subcooled, and giving the liquid invasion level downstream of the reservoir); - b. based on this state information, determining said flow rate by using either the measured pressure differential across the calibrated orifice present on the fluid supply pipeline to the equipment for which the flow rate is to be measured, when the fluid is 100% gaseous or 100% liquid (subcooled), or when dealing with a two-phase fluid by applying the following procedure: - when the pressure difference between PIC and PIC on the one hand, and between PIB and PIB' on the other hand are zero and the pressure difference between PI A and PI A' is not zero (we are then dealing here with what can be described as a "small" flow rate): the pressure differential AP1A = P1A - P1A' allows us to deduce the height of liquid in the first lower third of the spillway, and subsequently the flow rate of fluid passing through the slots of this first lower third, this by using the coefficients related to the width of the slots of this first lower third of the reservoir. - when the pressure difference between PIC and PIC is zero, but the pressure difference between PIB and PIB' is not (we are then dealing here with what can be described as an "average" flow rate: the pressure differential between PIB and PIB' makes it possible to deduce the height of liquid in the lower two thirds of the spillway (h2) and subsequently the flow rate of fluid passing through the slots of the lower reservoir, this by using the coefficients linked to the width of the slots of the lower reservoir (1st third), and we add to this flow rate the flow rate of fluid passing through the slots of the intermediate reservoir, this by using the coefficients linked to the width of the slots of this intermediate reservoir (h2-hl). - when the pressure difference between PIC and PIC is not zero (here we can speak of a “large” flow rate, this pressure difference between PIC and PIC makes it possible to deduce the height of liquid in the Nol, No2 and No3 reservoirs and subsequently the flow rate of fluid passing through the slots of the Nol (low) reservoir, this using the coefficients linked to the width of the slots of this low reservoir, flow rate to which we add the flow rate of fluid passing through the slots of the No2 (intermediate) reservoir, this using the coefficients linked to the width of the slots of this intermediate reservoir, and to which we finally add the flow rate of fluid passing through through the slots of tank No. 3 (upper third), this using the coefficients linked to the width of the slots of this tank No. 3.

[0081] The present invention then relates to a flow meter for cryogenic liquid / gas two-phase fluids, comprising: - A fluid supply pipe whose flow rate is to be measured, in the flow meter, pipe fitted with a calibrated orifice; - A vertical internal tank, a tank surrounded by a device, a tank into which said supply pipe opens, and where the tank has one of the following configurations: - i. According to a first embodiment, a wall of the internal tank is provided with a system of multiple fluid discharge slots, forming a “spillway” system, from the tank to the space inside the apparatus surrounding the tank, where the slots are rectangular or triangular in shape, having a different width distributed over the height of the tank: - Small width slots located in a low flow rate range on a lower part of the tank, for example on the first third of the lower part of the tank; - Medium width slots located in a medium flow range on an intermediate part of the tank, for example on the 2nd third of the tank; and - Wide slots located in a high flow range on the upper part of the tank, for example on the 3rd third in the upper part of the tank.

[0082] or: - j. according to a 2nd mode, the internal reservoir comprises several successive spillway systems, the fluid supply pipe opening into a first spillway, the spillways successively discharging into one another, until discharging into the space inside the apparatus surrounding the reservoir, a wall of each of the spillways being provided with a system of multiple fluid discharge slots, where the width of the slots increases between the first spillway into which the supply pipe opens and the last spillway in the series. - Pressure sensors to measure the following pressure differences: • A pressure difference (AP3) between the upstream and downstream of said calibrated orifice • One or more API pressure differences (AP1A, AP1B, etc.) between the bottom of each spillway and the atmosphere surrounding each spillway within the interior space within the apparatus, enabling the liquid level in each spillway to be measured; • A pressure difference AP2 (P1A'-P1C', ....) existing between two points located in the space surrounding the tank within said interior space, making it possible to deduce the height of liquid downstream of the tank, in order to determine the state of the fluid, gaseous, two-phase or sub-cooled, and giving the level of liquid invasion downstream of the tank. - a data acquisition and processing system, capable of carrying out the following evaluations: - a. determining the state information of the incoming fluid: gaseous, two-phase or subcooled, from the pressure difference data ΔP2; - b. based on this state information, determining said flow rate by using either the pressure differential ΔP3 when the fluid is 100% gaseous or 100% liquid (subcooled), or the pressure differential ΔP1 which allows to deduce the liquid height in the collector(s) and subsequently the fluid flow rate through the slots.

[0083] According to one of the embodiments of the invention, the flow meter is characterized in that a wall of the internal tank is provided with a system of multiple fluid discharge slots, forming a "spillway" system, from the tank to the space inside the device surrounding the tank, where the slots are rectangular or triangular in shape, having a different width distributed over the height of the tank: - Small width slots located in a low range of flow rates on a lower part of the tank, for example on the first third in the lower part of the tank; - Medium width slots located in a medium flow range on an intermediate part of the tank, for example on the 2nd third of the tank; and - Wide slots located in a high flow range on the upper part of the tank, for example on the 3rd third in the upper part of the tank.

[0084] and in that the flow rate of the fluid entering the flow meter is calculated in the following manner, the data acquisition and processing system being capable of carrying out the following evaluations: - a determination of the information on the state of the incoming fluid: gaseous, two-phase or sub-cooled, from the pressure difference data between two points located in the space surrounding the tank within the interior space within the device (AP2 (P1A'-P1C', ....)), making it possible to deduce the height of liquid downstream of the tank, and giving the level of liquid invasion downstream of the tank; - based on this status information, the determination of said flow rate in using either the pressure differential measured on both sides of said calibrated orifice present on the fluid supply pipe, when the fluid is 100% gaseous or 100% liquid (subcooled), or if we are in the presence of a two-phase fluid by applying the following approach: 1. when the pressure difference AP1C = PIC - PIC on the one hand, pressure difference existing between the bottom of the upper part of the tank and the atmosphere surrounding the tank within the interior space within the device, and when the pressure difference AP1B = PIB - PIB' on the other hand, pressure difference existing between the bottom of the intermediate part of the tank and the atmosphere surrounding the tank within the interior space within the device, are zero, but the pressure difference AP1A = P1A - P1A', pressure difference existing between the bottom of the lower part of the tank and the atmosphere surrounding the tank within the interior space within the device, is not zero, the pressure differential AP1A = P1A -P1A' makes it possible to deduce the height of liquid in the lower part of the tank, for example on the 1st third in the lower part of the tank,and subsequently the flow rate of fluid passing through the slots of this first lower third, this using the coefficients related to the width of the slots of this first lower third of the tank; 2. when the pressure difference AP1C = PIC - PIC, the pressure difference existing between the bottom of the upper part of the tank and the atmosphere surrounding the tank within the interior space within the device is zero, but the pressure difference AP1B = PIB - PIB', the pressure difference existing between the bottom of the intermediate part of the tank and the atmosphere surrounding the tank within the interior space within the device, is not, the pressure differential AP1B = PIB - PIB' allows the height of liquid in the lower two-thirds of the spillway (h2) to be deduced and subsequently the fluid flow rate passing through the slots of the lower tank, this by using the coefficients linked to the width of the slots of this lower tank, and the fluid flow rate passing through the slots of the intermediate tank is added to this flow rate, this by using the coefficients linked to the width of the slots of this intermediate tank (h2-hl). 3. when the pressure difference AP1C = PIC - PIC, pressure difference existing between the bottom of the upper part of the tank and the atmosphere surrounding the tank within the interior space within the device is not zero, this pressure difference AP1C = P1C-P1C makes it possible to deduce the height of liquid in the entire internal tank and subsequently the flow rate of fluid passing through the slots of the lower tank, this by using the co efficient linked to the width of the slots of this low reservoir, flow rate to which we add the flow rate of fluid passing through the slots of the intermediate reservoir, this using the coefficients linked to the width of the slots of this intermediate reservoir (h2-hl), and to which we finally add the flow rate of fluid passing through the slots of the high reservoir, this using the coefficients linked to the width of the slots of this high reservoir.

[0085] According to another embodiment of the invention, the flow meter is characterized in that the internal reservoir comprises several successive overflow systems, the fluid supply pipe opening into a first overflow, the overflows successively discharging into one another, until discharging into the space inside the apparatus surrounding the reservoir, a wall of each of the overflows being provided with a system of multiple fluid discharge slots, where the width of the slots increases between the first overflow into which the supply pipe opens and the last overflow of the series, and in that the flow rate of the fluid entering the flow meter is calculated in the following manner, the data acquisition and processing system being capable of carrying out the following evaluations: - a) a determination of the information on the state of the incoming fluid: gaseous, two-phase or sub-cooled, from the pressure difference data between two points located in the space surrounding the tank within the interior space within the device (AP2 (P1A'-P1C', ....)), making it possible to deduce the height of liquid downstream of the tank, and giving the level of liquid invasion downstream of the tank; - b) based on this status information, the determination of said flow rate using either the pressure differential measured on both sides of the calibrated orifice present on the supply pipe of the fluid whose flow rate is to be measured to the equipment, when the fluid is 100% gaseous or 100% liquid (subcooled), or when there is a two-phase fluid by applying the following approach: - 1) when the pressure difference AP1A = P1A - P1A', difference of pressure existing between the bottom of said 1st spillway encountered by the fluid and the atmosphere surrounding the reservoir within the interior space within the device is between a given minimum level and a given maximum level, given maximum level corresponding to an overflow level, this pressure differential AP1A = P1A - P1A' makes it possible to deduce the height of liquid in this 1st spillway encountered by the fluid and thus the flow rate of fluid passing through the slots of this 1st spillway encountered by the fluid, this by using the coefficients related to the width of the slots of this first spillway. 2) when said pressure difference AP1A= P1A - P1A' is greater than said given maximum level, causing an overflow of this 1st spillway encountered by the fluid, and the pressure difference AP1B= PIB - PIB', pressure difference existing between the bottom of the 2nd spillway, spillway following the 1st spillway in the series and the atmosphere surrounding the reservoir within the interior space within the device, is between a given minimum level and a given maximum level, the pressure differential AP1B= PIB - PIB' makes it possible to deduce the height of liquid in spillway No. 2 into which said 1st spillway discharges, and subsequently the flow rate of fluid passing through the slots of this spillway No. 2, this by using the coefficients linked to the width of the slots of this spillway No. 2. 3) when said pressure difference AP1B = PIB - PIB' is greater than a given maximum level, and the pressure difference AP1C = PIC - PIC', the pressure difference existing between the bottom of the last spillway in the series, and the atmosphere surrounding the reservoir within the interior space within the device, is between a given minimum level and a given maximum level, this pressure differential AP1C = PIC - PIC' makes it possible to deduce the height of liquid in said last spillway (spillway No. 3) into which said spillway No. 2 discharges, and subsequently the flow rate of fluid passing through the slots of this last spillway, this by using the coefficients linked to the width of the slots of reservoir No. 3. 4) when the pressure difference AP1C = PIC - PIC' is greater than a given maximum level, the flow meter is then considered to be overcapacity, i.e. the flow rate passing through the device is greater than the measuring capacity of the equipment, and all measurements are then considered to be neutralized.

Claims

1. Claims A flow meter for cryogenic liquid / gas two-phase fluids, comprising: - A supply pipe (2) for the fluid whose flow rate is to be measured, in the flow meter, pipe fitted with a calibrated orifice (8); - A vertical internal tank, a tank surrounded by a device, a tank into which said supply pipe opens, and where the tank has one of the following configurations: - i) According to a first embodiment, a wall of the internal tank is provided with a system of multiple fluid discharge slots, forming a “spillway” system, from the tank to the space inside the device surrounding the tank, where the slots are rectangular or triangular in shape, having a different width distributed over the height of the tank: - Small width slots located in a low flow rate range on a lower part of the tank, for example on the first third of the lower part of the tank; - Medium width slots located in a medium flow range on an intermediate part of the tank, for example on the 2nd third of the tank; and - Wide slots located in a high flow range on the upper part of the tank, for example on the 3rd third in the upper part of the tank. or: - j) according to a 2nd mode, the internal tank comprises several successive overflow systems, the fluid supply pipe opening inside a first overflow, the overflows successively discharging into one another, until discharging into the space inside the device surrounding the reservoir, one wall of each of the spillways being provided with a system of multiple fluid discharge slots, where the width of the slots increases between the first spillway into which the supply pipe opens and the last spillway in the series. Pressure sensors to measure the following pressure differences: A pressure difference (AP3) between the upstream and downstream of said calibrated orifice One or more API pressure differences (AP1A, AP1B, etc.) between the bottom of each spillway and the atmosphere surrounding each spillway within the interior space within the device, enabling the liquid level in each spillway to be measured; A pressure difference AP2 (P1A'-P1C', ....) existing between two points located in the space surrounding the tank within said interior space, making it possible to deduce the height of liquid downstream of the tank, in order to determine the state of the fluid, gaseous, two-phase or sub-cooled, and giving the level of liquid invasion downstream of the tank. a data acquisition and processing system, capable of carrying out the following evaluations: a) a determination of the information on the state of the incoming fluid: gaseous, two-phase or sub-cooled, from the pressure difference data AP2; b) based on this status information, the determination of said flow rate using either the AP3 pressure differential when the fluid is 100% gaseous or 100% liquid (subcooled), or the API pressure differential which makes it possible to deduce the height of liquid in the spillway(s) and by the following the flow of fluid passing through the slots.

2. A flow meter according to claim 1, characterized in that a wall of the internal tank is provided with a system of multiple fluid discharge slots, forming a "spillway" system, from the tank to the space inside the apparatus surrounding the tank, where the slots are rectangular or triangular in shape, having a different width distributed over the height of the tank: - Small width slots located in a low flow rate range on a lower part of the tank, for example on the first third of the lower part of the tank; - Medium width slots located in a medium flow range on an intermediate part of the tank, for example on the 2nd third of the tank; and - Wide slots located in a high flow range on the upper part of the tank, for example on the 3rd third in the upper part of the tank. and in that the flow rate of the fluid entering the flow meter is calculated in the following manner, the data acquisition and processing system being capable of carrying out the following evaluations: - a) a determination of the information on the state of the incoming fluid: gaseous, two-phase or sub-cooled, from the pressure difference data between two points located in the space surrounding the tank within the interior space within the device (AP2 (P1A'-P1C', ....)), making it possible to deduce the height of liquid downstream of the tank, and giving the level of liquid invasion downstream of the tank; - b) based on this status information, the determination of said flow rate using either the pressure differential measured on both sides of said calibrated orifice present on the fluid supply pipe, when the fluid is 100% gaseous or 100% liquid (subcooled), or if we are in the presence of a two-phase fluid by applying the approach next: 1) when the pressure difference AP1C = PIC - PIC on the one hand, pressure difference existing between the bottom of the upper part of the tank and the atmosphere surrounding the tank within the interior space within the device, and when the pressure difference AP1B = PIB - PIB' on the other hand, pressure difference existing between the bottom of the intermediate part of the tank and the atmosphere surrounding the tank within the interior space within the device, are zero, but the pressure difference AP1A = P1A - P1A', pressure difference existing between the bottom of the lower part of the tank and the atmosphere surrounding the tank within the interior space within the device, is not zero, the pressure differential API A = PI A - PI A' makes it possible to deduce the height of liquid in the lower part of the tank, for example on the 1st third in the lower part of the tank,and subsequently the flow rate of fluid passing through the slots of this first lower third, this using the coefficients related to the width of the slots of this first lower third of the tank;, 2) when the pressure difference AP1C = PIC - PIC, the pressure difference existing between the bottom of the upper part of the tank and the atmosphere surrounding the tank within the interior space within the device is zero, but the pressure difference AP1B = PIB - PIB', the pressure difference existing between the bottom of the intermediate part of the tank and the atmosphere surrounding the tank within the interior space within the device, is not, the pressure differential AP1B = PIB - PIB' makes it possible to deduce the height of liquid in the lower two-thirds of the spillway (h2) and subsequently the flow rate of fluid passing through the slots of the lower tank, this by using the coefficients linked to the width of the slots of this lower tank, and we add to this flow rate the flow rate of fluid passing through the slots of the intermediate tank, this by using the coefficients linked to the width of the slots of this intermediate tank (h2-hl). 3) when the pressure difference AP1C = PIC - PIC, pressure difference existing between the bottom of the upper part of the tank and the atmosphere surrounding the tank within the interior space within the device is not zero, this pressure difference AP1C = PIC - PIC makes it possible to deduce the height of liquid in the entire internal tank and subsequently the flow rate of fluid passing through the slots of the lower tank, this using the coefficients linked to the width of the slots of this lower tank, flow rate to which we add the flow rate of fluid passing through the slots of the intermediate tank, this using the coefficients linked to the width of the slots of this intermediate tank (h2-hl), and to which we finally add the flow rate of fluid passing through the slots of the upper tank, this using the coefficients linked to the width of the slots of this upper tank.

3. A flow meter according to claim 1, characterized in that the internal reservoir comprises several successive overflow systems, the fluid supply pipe opening into a first overflow, the overflows successively discharging into one another, until discharging into the space inside the apparatus surrounding the reservoir, a wall of each of the overflows being provided with a system of multiple fluid discharge slots, where the width of the slots increases between the first overflow into which the supply pipe opens and the last overflow of the series, and in that the flow rate of the fluid entering the flow meter is calculated in the following manner, the data acquisition and processing system being capable of carrying out the following evaluations: - a) a determination of the information on the state of the incoming fluid: gaseous, two-phase or sub-cooled, from the pressure difference data between two points located in the space surrounding the tank within the interior space within the device (AP2 (P1A'-P1C', ....)), making it possible to deduce the height of liquid downstream of the tank, and giving the level of liquid invasion downstream of the tank; - b) based on this status information, determining said flow rate using either the pressure differential measured on both sides of the calibrated orifice present on the supply pipe of the fluid whose flow rate is to be measured to the equipment, when the fluid is 100% gaseous or 100% liquid (subcooled), or when we are in the presence of a two-phase fluid by applying the following procedure: 1) when the pressure difference AP1A = P1A - P1A', the pressure difference existing between the bottom of said 1st spillway encountered by the fluid and the atmosphere surrounding the tank within the interior space within the device is between a given minimum level and a given maximum level, given maximum level corresponding to an overflow level, this pressure differential AP1A = PI A - PI A' makes it possible to deduce the height of liquid in this 1st spillway encountered by the fluid and thus the flow rate of fluid passing through the slots of this 1st spillway encountered by the fluid, this by using the coefficients related to the width of the slots of this first spillway. 2) when said pressure difference AP1A= P1A - P1A' is greater than said given maximum level, causing an overflow of this 1st spillway encountered by the fluid, and the pressure difference AP1B= PIB - PIB', pressure difference existing between the bottom of the 2nd spillway, spillway following the 1st spillway in the series and the atmosphere surrounding the reservoir within the interior space within the device, is between a given minimum level and a given maximum level, the pressure differential AP1B= PIB - PIB' makes it possible to deduce the height of liquid in spillway No. 2 into which said 1st spillway discharges, and subsequently the flow rate of fluid passing through the slots of this spillway No. 2, this by using the coefficients linked to the width of the slots of this spillway No.

2. 3) when said pressure difference AP1B = PIB - PIB' is greater than a given maximum level, and the pressure difference AP1C = PIC - PIC', pressure difference existing between the bottom of the last spillway in the series, and the atmosphere surrounding the reservoir within the interior space within the device, is between a given minimum level and a given maximum level, this pressure differential AP1C = PIC - PIC' makes it possible to deduce the height of liquid in said last spillway (spillway No. 3) into which said spillway No. 2 discharges, and subsequently the flow rate of fluid passing through the slots of this last spillway, this by using the coefficients linked to the width of the slots of tank No.

3. 4) when the pressure difference AP1C = PIC - PIC' is greater than a given maximum level, the flow meter is then considered to be overcapacity, i.e. the flow rate passing through the device is greater than the measuring capacity of the equipment, and all measurements are then considered to be neutralized.

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