Classifications

• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F17—STORING OR DISTRIBUTING GASES OR LIQUIDS
  • F17C—VESSELS FOR CONTAINING OR STORING COMPRESSED, LIQUEFIED OR SOLIDIFIED GASES; FIXED-CAPACITY GAS-HOLDERS; FILLING VESSELS WITH, OR DISCHARGING FROM VESSELS, COMPRESSED, LIQUEFIED, OR SOLIDIFIED GASES
  • F17C13/00—Details of vessels or of the filling or discharging of vessels
  • F17C13/02—Special adaptations of indicating, measuring, or monitoring equipment
  • F17C13/021—Special adaptations of indicating, measuring, or monitoring equipment having the height as the parameter
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F17—STORING OR DISTRIBUTING GASES OR LIQUIDS
  • F17C—VESSELS FOR CONTAINING OR STORING COMPRESSED, LIQUEFIED OR SOLIDIFIED GASES; FIXED-CAPACITY GAS-HOLDERS; FILLING VESSELS WITH, OR DISCHARGING FROM VESSELS, COMPRESSED, LIQUEFIED, OR SOLIDIFIED GASES
  • F17C13/00—Details of vessels or of the filling or discharging of vessels
  • F17C13/02—Special adaptations of indicating, measuring, or monitoring equipment
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F17—STORING OR DISTRIBUTING GASES OR LIQUIDS
  • F17C—VESSELS FOR CONTAINING OR STORING COMPRESSED, LIQUEFIED OR SOLIDIFIED GASES; FIXED-CAPACITY GAS-HOLDERS; FILLING VESSELS WITH, OR DISCHARGING FROM VESSELS, COMPRESSED, LIQUEFIED, OR SOLIDIFIED GASES
  • F17C13/00—Details of vessels or of the filling or discharging of vessels
  • F17C13/02—Special adaptations of indicating, measuring, or monitoring equipment
  • F17C13/023—Special adaptations of indicating, measuring, or monitoring equipment having the mass as the parameter
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F17—STORING OR DISTRIBUTING GASES OR LIQUIDS
  • F17C—VESSELS FOR CONTAINING OR STORING COMPRESSED, LIQUEFIED OR SOLIDIFIED GASES; FIXED-CAPACITY GAS-HOLDERS; FILLING VESSELS WITH, OR DISCHARGING FROM VESSELS, COMPRESSED, LIQUEFIED, OR SOLIDIFIED GASES
  • F17C13/00—Details of vessels or of the filling or discharging of vessels
  • F17C13/02—Special adaptations of indicating, measuring, or monitoring equipment
  • F17C13/025—Special adaptations of indicating, measuring, or monitoring equipment having the pressure as the parameter
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F17—STORING OR DISTRIBUTING GASES OR LIQUIDS
  • F17C—VESSELS FOR CONTAINING OR STORING COMPRESSED, LIQUEFIED OR SOLIDIFIED GASES; FIXED-CAPACITY GAS-HOLDERS; FILLING VESSELS WITH, OR DISCHARGING FROM VESSELS, COMPRESSED, LIQUEFIED, OR SOLIDIFIED GASES
  • F17C13/00—Details of vessels or of the filling or discharging of vessels
  • F17C13/02—Special adaptations of indicating, measuring, or monitoring equipment
  • F17C13/028—Special adaptations of indicating, measuring, or monitoring equipment having the volume as the parameter
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F17—STORING OR DISTRIBUTING GASES OR LIQUIDS
  • F17C—VESSELS FOR CONTAINING OR STORING COMPRESSED, LIQUEFIED OR SOLIDIFIED GASES; FIXED-CAPACITY GAS-HOLDERS; FILLING VESSELS WITH, OR DISCHARGING FROM VESSELS, COMPRESSED, LIQUEFIED, OR SOLIDIFIED GASES
  • F17C5/00—Methods or apparatus for filling containers with liquefied, solidified, or compressed gases under pressures
  • F17C5/02—Methods or apparatus for filling containers with liquefied, solidified, or compressed gases under pressures for filling with liquefied gases
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01F—MEASURING VOLUME, VOLUME FLOW, MASS FLOW OR LIQUID LEVEL; METERING BY VOLUME
  • G01F23/00—Indicating or measuring liquid level or level of fluent solid material, e.g. indicating in terms of volume or indicating by means of an alarm
  • G01F23/14—Indicating or measuring liquid level or level of fluent solid material, e.g. indicating in terms of volume or indicating by means of an alarm by measurement of pressure
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01F—MEASURING VOLUME, VOLUME FLOW, MASS FLOW OR LIQUID LEVEL; METERING BY VOLUME
  • G01F23/00—Indicating or measuring liquid level or level of fluent solid material, e.g. indicating in terms of volume or indicating by means of an alarm
  • G01F23/80—Arrangements for signal processing
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F17—STORING OR DISTRIBUTING GASES OR LIQUIDS
  • F17C—VESSELS FOR CONTAINING OR STORING COMPRESSED, LIQUEFIED OR SOLIDIFIED GASES; FIXED-CAPACITY GAS-HOLDERS; FILLING VESSELS WITH, OR DISCHARGING FROM VESSELS, COMPRESSED, LIQUEFIED, OR SOLIDIFIED GASES
  • F17C2221/00—Handled fluid, in particular type of fluid
  • F17C2221/01—Pure fluids
  • F17C2221/011—Oxygen
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F17—STORING OR DISTRIBUTING GASES OR LIQUIDS
  • F17C—VESSELS FOR CONTAINING OR STORING COMPRESSED, LIQUEFIED OR SOLIDIFIED GASES; FIXED-CAPACITY GAS-HOLDERS; FILLING VESSELS WITH, OR DISCHARGING FROM VESSELS, COMPRESSED, LIQUEFIED, OR SOLIDIFIED GASES
  • F17C2221/00—Handled fluid, in particular type of fluid
  • F17C2221/01—Pure fluids
  • F17C2221/014—Nitrogen
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F17—STORING OR DISTRIBUTING GASES OR LIQUIDS
  • F17C—VESSELS FOR CONTAINING OR STORING COMPRESSED, LIQUEFIED OR SOLIDIFIED GASES; FIXED-CAPACITY GAS-HOLDERS; FILLING VESSELS WITH, OR DISCHARGING FROM VESSELS, COMPRESSED, LIQUEFIED, OR SOLIDIFIED GASES
  • F17C2221/00—Handled fluid, in particular type of fluid
  • F17C2221/01—Pure fluids
  • F17C2221/016—Noble gases (Ar, Kr, Xe)
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F17—STORING OR DISTRIBUTING GASES OR LIQUIDS
  • F17C—VESSELS FOR CONTAINING OR STORING COMPRESSED, LIQUEFIED OR SOLIDIFIED GASES; FIXED-CAPACITY GAS-HOLDERS; FILLING VESSELS WITH, OR DISCHARGING FROM VESSELS, COMPRESSED, LIQUEFIED, OR SOLIDIFIED GASES
  • F17C2221/00—Handled fluid, in particular type of fluid
  • F17C2221/01—Pure fluids
  • F17C2221/016—Noble gases (Ar, Kr, Xe)
  • F17C2221/017—Helium
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F17—STORING OR DISTRIBUTING GASES OR LIQUIDS
  • F17C—VESSELS FOR CONTAINING OR STORING COMPRESSED, LIQUEFIED OR SOLIDIFIED GASES; FIXED-CAPACITY GAS-HOLDERS; FILLING VESSELS WITH, OR DISCHARGING FROM VESSELS, COMPRESSED, LIQUEFIED, OR SOLIDIFIED GASES
  • F17C2223/00—Handled fluid before transfer, i.e. state of fluid when stored in the vessel or before transfer from the vessel
  • F17C2223/01—Handled fluid before transfer, i.e. state of fluid when stored in the vessel or before transfer from the vessel characterised by the phase
  • F17C2223/0146—Two-phase
  • F17C2223/0153—Liquefied gas, e.g. LPG, GPL
  • F17C2223/0161—Liquefied gas, e.g. LPG, GPL cryogenic, e.g. LNG, GNL, PLNG
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F17—STORING OR DISTRIBUTING GASES OR LIQUIDS
  • F17C—VESSELS FOR CONTAINING OR STORING COMPRESSED, LIQUEFIED OR SOLIDIFIED GASES; FIXED-CAPACITY GAS-HOLDERS; FILLING VESSELS WITH, OR DISCHARGING FROM VESSELS, COMPRESSED, LIQUEFIED, OR SOLIDIFIED GASES
  • F17C2223/00—Handled fluid before transfer, i.e. state of fluid when stored in the vessel or before transfer from the vessel
  • F17C2223/03—Handled fluid before transfer, i.e. state of fluid when stored in the vessel or before transfer from the vessel characterised by the pressure level
  • F17C2223/035—High pressure (>10 bar)
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F17—STORING OR DISTRIBUTING GASES OR LIQUIDS
  • F17C—VESSELS FOR CONTAINING OR STORING COMPRESSED, LIQUEFIED OR SOLIDIFIED GASES; FIXED-CAPACITY GAS-HOLDERS; FILLING VESSELS WITH, OR DISCHARGING FROM VESSELS, COMPRESSED, LIQUEFIED, OR SOLIDIFIED GASES
  • F17C2250/00—Accessories; Control means; Indicating, measuring or monitoring of parameters
  • F17C2250/03—Control means
  • F17C2250/032—Control means using computers
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F17—STORING OR DISTRIBUTING GASES OR LIQUIDS
  • F17C—VESSELS FOR CONTAINING OR STORING COMPRESSED, LIQUEFIED OR SOLIDIFIED GASES; FIXED-CAPACITY GAS-HOLDERS; FILLING VESSELS WITH, OR DISCHARGING FROM VESSELS, COMPRESSED, LIQUEFIED, OR SOLIDIFIED GASES
  • F17C2250/00—Accessories; Control means; Indicating, measuring or monitoring of parameters
  • F17C2250/04—Indicating or measuring of parameters as input values
  • F17C2250/0404—Parameters indicated or measured
  • F17C2250/0408—Level of content in the vessel
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F17—STORING OR DISTRIBUTING GASES OR LIQUIDS
  • F17C—VESSELS FOR CONTAINING OR STORING COMPRESSED, LIQUEFIED OR SOLIDIFIED GASES; FIXED-CAPACITY GAS-HOLDERS; FILLING VESSELS WITH, OR DISCHARGING FROM VESSELS, COMPRESSED, LIQUEFIED, OR SOLIDIFIED GASES
  • F17C2250/00—Accessories; Control means; Indicating, measuring or monitoring of parameters
  • F17C2250/04—Indicating or measuring of parameters as input values
  • F17C2250/0404—Parameters indicated or measured
  • F17C2250/0421—Mass or weight of the content of the vessel
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F17—STORING OR DISTRIBUTING GASES OR LIQUIDS
  • F17C—VESSELS FOR CONTAINING OR STORING COMPRESSED, LIQUEFIED OR SOLIDIFIED GASES; FIXED-CAPACITY GAS-HOLDERS; FILLING VESSELS WITH, OR DISCHARGING FROM VESSELS, COMPRESSED, LIQUEFIED, OR SOLIDIFIED GASES
  • F17C2250/00—Accessories; Control means; Indicating, measuring or monitoring of parameters
  • F17C2250/04—Indicating or measuring of parameters as input values
  • F17C2250/0404—Parameters indicated or measured
  • F17C2250/0426—Volume
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F17—STORING OR DISTRIBUTING GASES OR LIQUIDS
  • F17C—VESSELS FOR CONTAINING OR STORING COMPRESSED, LIQUEFIED OR SOLIDIFIED GASES; FIXED-CAPACITY GAS-HOLDERS; FILLING VESSELS WITH, OR DISCHARGING FROM VESSELS, COMPRESSED, LIQUEFIED, OR SOLIDIFIED GASES
  • F17C2250/00—Accessories; Control means; Indicating, measuring or monitoring of parameters
  • F17C2250/04—Indicating or measuring of parameters as input values
  • F17C2250/0404—Parameters indicated or measured
  • F17C2250/043—Pressure
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F17—STORING OR DISTRIBUTING GASES OR LIQUIDS
  • F17C—VESSELS FOR CONTAINING OR STORING COMPRESSED, LIQUEFIED OR SOLIDIFIED GASES; FIXED-CAPACITY GAS-HOLDERS; FILLING VESSELS WITH, OR DISCHARGING FROM VESSELS, COMPRESSED, LIQUEFIED, OR SOLIDIFIED GASES
  • F17C2250/00—Accessories; Control means; Indicating, measuring or monitoring of parameters
  • F17C2250/04—Indicating or measuring of parameters as input values
  • F17C2250/0404—Parameters indicated or measured
  • F17C2250/043—Pressure
  • F17C2250/0434—Pressure difference
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F17—STORING OR DISTRIBUTING GASES OR LIQUIDS
  • F17C—VESSELS FOR CONTAINING OR STORING COMPRESSED, LIQUEFIED OR SOLIDIFIED GASES; FIXED-CAPACITY GAS-HOLDERS; FILLING VESSELS WITH, OR DISCHARGING FROM VESSELS, COMPRESSED, LIQUEFIED, OR SOLIDIFIED GASES
  • F17C2260/00—Purposes of gas storage and gas handling
  • F17C2260/02—Improving properties related to fluid or fluid transfer
  • F17C2260/024—Improving metering
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F17—STORING OR DISTRIBUTING GASES OR LIQUIDS
  • F17C—VESSELS FOR CONTAINING OR STORING COMPRESSED, LIQUEFIED OR SOLIDIFIED GASES; FIXED-CAPACITY GAS-HOLDERS; FILLING VESSELS WITH, OR DISCHARGING FROM VESSELS, COMPRESSED, LIQUEFIED, OR SOLIDIFIED GASES
  • F17C2270/00—Applications
  • F17C2270/01—Applications for fluid transport or storage

Definitions

• the present invention relates to a method for determining in real time the filling level of a cryogenic tank.
• the invention also relates to a method for determining in real time the quantity of fluid available at each moment.
• This process requires knowing the parameters (geometry) of the tank. These parameters can be known to the system or estimated according to an estimation method (radius, height %) independent.
• the invention relates more particularly to a method of determining in real time the filling level of a cryogenic tank intended to contain a two-phase liquid-gas mixture in which is calculated at each time step for the liquid and possibly for the gas at least one of: the level, the volume or the mass contained in the tank, the method measuring at each time step the pressure differential between the high and low parts of the tank and at least one of the pressures of said differential.
• the invention thus relates to the improvement of level measurement in cryogenic tanks in order to improve the efficiency of the liquid supply logistics chain of these tanks.
• the reservoirs concerned comprise an internal reservoir for storing the fluid (or inner casing) disposed in an external reservoir (or outer casing) with a vacuum between these reservoirs.
• the tanks store cryogenic liquids such as oxygen, argon, nitrogen with capacities of 100 liters to 100000 liters for example. Storage pressures can be between 3 bar and 35 bar.
• deliveries of cryogenic liquid by truck are based on two pieces of information: the time of delivery and the quantity available.
• the delivery time is based on the liquid crossing of a fixed threshold (delivery threshold usually 30% of the tank capacity). This threshold incorporates measurement uncertainty to prevent the user from drying out. By making reliable the liquid level measurement in the tank it is possible to lower this trigger threshold and thus reduce the delivery frequency and therefore the associated costs.
• the knowledge of the quantity of fluid available in each tank makes it possible to determine the routes of the delivery trucks. The more the expected quantity of delivery will be close to that actually delivered, the more the tour plan will be respected thus making it possible to fully exploit the potential benefits generated by the many improvements made on the logistics part.
• the volume measurement is determined using in general an average liquid density for each range of pressure tanks. In practice, this density depends on the evolution of the internal pressures and the temperature. As a result, the higher the pressure in the tank, the greater the volume measurement error.
• the total mass measurement depends less on the density, hence a better measurement. However, this measure is not sufficient to determine the mass capacity of a tank at the time of delivery (it would be necessary to know the density of the fluid as for the calculation of the volume).
• a known technique for measuring the level of fluid in a cryogenic tank is to determine a liquid level using the principle of the pressure difference on the height of the tank.
• volume measurement (% V) is simply obtained from the measurement of a pressure differential (DP) as follows:
• the density of the liquid k 0 is in fact not constant. It varies over time depending on the internal pressure and the temperature of the liquid when it is not saturated, or when filling with a subcooled liquid. Therefore, the volume result given by the known technique is not always relevant (0-10% error approximately). This phenomenon is especially felt for high pressure (HP) tanks, that is to say greater than 10 bar and especially greater than 15 bar.
• Liquid level estimates are usually based on regular measurements of the pressure differential (eg every hour), pressure, and reservoir geometry (diameter, height, and maximum level).
• the estimation errors are therefore mainly due to: a poor conversion of a pressure differential measured in the corresponding liquid level, to the difference between the measured pressure differential and the real pressure differential (effects of the measuring conduits connecting tank sensors), calibration errors (density of the liquid).
• the measurement of the pressure differential DP is the image of a mass, one thus obtains measurements independent of the evolution of the density. Nevertheless, two masses must be distinguished: the total mass before filling (gas + liquid) and the mass capacity (mass of liquid after filling). The first can be easily obtained by measuring the differential pressure DP.
• the second requires knowing the characteristics and quantity of the product remaining in the tank in order to estimate the quantity of liquid actually deliverable by a truck.
• a filling level at 100% that corresponding to the maximum mass that can be placed in the reservoir. This mass corresponds of course to a complete filling of the tank with the sub-cooled liquid. With such a calibration of 100%, we will be sure to never exceed 100%. However, we will never know what is the value corresponding to a full filling, this will depend on the conditions at the time of filling. Therefore we join the constraints of using the value of the volume.
• the single level of liquid or the mass of liquid is not sufficient to meet both issues: trigger threshold of a delivery and quantity deliverable.
• An object of the present invention is to overcome all or part of the disadvantages of the prior art noted above.
• the method according to the invention is essentially characterized in that it calculates: by a thermal model at each time step the average temperatures of the liquid and the gas in the tank from the measured pressure differential and at least one of the pressures of said differential,
• dP - pl.g.dhl from the calculated density of liquid (with dP the variation of pressure of the liquid, pi the density of the liquid, g the terrestrial acceleration, and dhl the variation in the height of the liquid).
• embodiments of the invention may include one or more of the following features:
• the method calculates the density of the gas at each instant from a part of the average temperature of the gas obtained and estimated at the previous instant and, secondly, from the pressure differential and from at least one of the measured pressures of said differential.
• the thermal model calculates, at each time step, the average temperatures of the liquid and the gas in the tank from a part of the measured pressure differential and at least one of the pressures of said differential and from the liquid and gas temperatures known from the previous moment,
• the model uses as initial value for the temperature of the liquid and the gas, the initial temperature values obtained during a complete filling of the tank, the level of the liquid at this known instant of complete filling being the known level of the weir of the tank,
• the model uses the following calculation approximation: the gas after complete filling is at equilibrium liquid-vapor at the pressure of the tank,
• the model uses the following calculation approximation: the liquid and the gas are constantly isothermal, each in its respective volume, but at respective temperatures which may be different, the model calculates at each time step the mean temperatures of the liquid and the gas in the tank from the mass and energy balances modeled and applied separately to the liquid and the gas contained in the reservoir,
• the mass and energy balances modeled and applied separately to the liquid and the gas contained in the reservoir are made at a given instant on the basis of the density values and the volume of liquid and gas calculated from an estimate of the the instant and the model iterates the calculation of the average liquid and gas temperatures in the reservoir until the average liquid and a predetermined value towards the temperatures estimated at the preceding instant and in that after convergence the process resumes the steps of calculating the density and liquid level temperatures for the following instant,
• - mass and energy budgets modeled and applied to gas use the enthalpy equation according to which the variation of the enthalpy of the gas corresponds to the thermal and mass exchanges applied to the gas, that is to say in taking into account at least one of the following exchanges: the exchange of heat between the liquid and the gas, the heat exchange between the outside of the tank and the gas, the heat exchange provided by a possible vaporization heater located usually below the tank, the vaporization of liquid in the tank,
• the mass and energy balances modeled and applied to the liquid use the enthalpy equation according to which the variation of the enthalpy of the liquid corresponds to the heat and mass exchanges applied to the gases, that is to say in taking into account at least one of the following exchanges: the exchange of heat between the outside and the liquid, the heat exchange between the gas and the liquid, the heat exchange provided by a possible vaporization heater located in general below the tank, the vaporization of liquid in the tank, the consumption of liquid withdrawn by a user of the tank,
• the method comprises measuring the temperature in the vicinity of the tank, to calculate the heat exchange between the outside and the tank,
• the tank being of the jacketed type with inter-wall volume under vacuum, characterized in that the additional pressure difference value is calculated by adding or subtracting the gas and liquid levels in the measuring pipes by taking into account the calculated liquid level and neglecting the pressure influence of the pipe portions located in the inter-wall space,
• the additional pressure difference value is calculated according to a formula of the type:
• DPpipe pg_pipe.g. (2len_w + total_length)
• pg_pipe the density of the gas at room temperature (outside the tank)
• g the Earth's acceleration in m / s 2
• len_w the thickness of the tank wall and totaljength the total height of the inner tank and in that, when the upper pipe is located inside the tank in the inter-wall space, the additional pressure difference value (DPpipe) is calculated according to a formula of the type:
• DPpipe DPside_gas + DPsideJiq;
• DPside_gas being the pressure difference in the portion of the pipe connected to the upper part of the tank and facing the gas in the tank
• DPsideJiq being the pressure difference in the part of the upper pipe and facing the liquid in the tank
• the method for dynamically determining the filling level of a cryogenic tank is intended to contain a diphasic liquid-gas mixture, according to any one of the preceding claims, comprising a step of measuring a pressure differential between levels situated respectively at the low and high ends of the tank, characterized in that it comprises a calculation of a volume and / or a mass of liquid in the tank from the pressure differential measured, the known or estimated geometry of the reservoir and at least one density of liquid in the tank, the method further comprising the steps of calculating the following quantities for a moment (t + ⁇ t):
• a first step of calculating a density of the liquid in the reservoir from the pressure measurements at the level of the low and high ends of the reservoir respectively, and the value estimated at the preceding instant of a temperature Tl of the liquid in the tank, a second stage of calculating the level of liquid in the tank by applying the law in hydrostatic fluid type: dP - pl.g.dhl from the density of the liquid calculated in the previous step a third step of calculating the pressure level at the interface between the liquid phase and the gas phase in the reservoir from the calculated liquid level in the reservoir,
• a seventh step of calculating the temperature Tg of the gas from the energy balance of the fifth and sixth steps and an eighth step of comparing the temperature T (t + ⁇ t) calculated for the following moment at the seventh step; with and the temperature T (t) estimated for the preceding instant, and when the difference between the temperature T (t + ⁇ t) calculated for the following instant at the seventh stage and the temperature T (t) estimated for the moment preceding is greater than a determined threshold: a step of returning to the second step and of iteration until convergence, when the difference between the temperature T (t + ⁇ t) calculated for the following instant in the seventh step and the temperature T (t) estimated for the previous instant is less than a threshold (convergence): reiteration of the above steps for the moment (t + 2 ⁇ t) with the pressure values measured for this moment.
• FIG. 1 represents a schematic view illustrating a first example of a cryogenic reservoir for implementing the invention (conduits external to the walls of the tank),
• FIG. 2 represents a schematic view illustrating a second example of a cryogenic reservoir for implementing the invention (conduits internal to the walls of the tank),
• FIG. 3 is a simplified and partial representation of the steps implemented by the method according to the invention.
• FIG. 4 is a simplified and partial representation of the initialization steps implemented by the method according to the invention.
• the estimation method that will be described below may be implemented by a computer of a tank control system (local or remote).
• This method includes a pressure measurement (differential DP), an estimate and may include a remote transmission.
• the pressures are measured via conduits 11, 12 which may be in the inter-wall space of the reservoir (FIG. 2) or outside 11 (FIG. 1).
• the tank 1 comprises a pressurizing device such as a vaporizer heater 3 able to take liquid to vaporize and reinject it into the tank.
• This heater 3 conventionally regulates the pressure within the tank 1.
• tank which stores the fluid
• the liquid brought by truck when filling may also be considered in the steady state (temperature range of 0 10 K around the balance, for example from 77.2 to 87.9 ° K for nitrogen) .
• the pressure of the liquid in the truck is chosen, according to the pressure of the tank, between 1 and 2 bar.
• the liquid is introduced into the tank by pumping.
• gas and liquid-specific temperatures are considered in the tank but without these temperatures being a function of the location in the tank. That is, in the following the gas temperatures Tg and liquid T1 are average temperatures.
• the pressure at the interface between the liquid phase and the gaseous phase taken as the average of the pressures at the bottom and at the top (PB and PH), is considered.
• the energy balance equations are applied separately to the gas and liquid phases of the reservoir.
• the calculated liquid height hl1 (in m) is calculated according to the formula (equation 1):
• VlX Ti R 2 M - -
• the calculated liquid level hl1 is corrected taking into account an additional pressure difference value DPpipe created by the gas present in the measuring pipes 11, 12, both when the pipes 11 are located in the tank ( Figure 2) or out of the tank ( Figure 1). That is, the pressure sensors 4 are deported and "read" fluid-influenced pressures in the conduits 11, 12 connecting them to the upper and lower parts of the reservoir.
• DPwall is the pressure differential between the two ends of the vertical duct crossing the inter-wall (top or bottom).
• DPtotJength being the pressure difference due to the gas pressure in the pipe portion 11 connecting the highest point to the measuring member 4 (sensor) remote.
• DPamb is the pressure difference due to the gas pressure in the pipe portion 11 connecting the lowest point to the remote sensor member 4 (sensor).
• pg pipe being the density of the gas in the conduit thick_w being the thickness of the wall of the tank
• T (x) being the temperature at point x
• P the pressure.
• the pressure differential DPwall between the two ends of the vertical duct passing through the inter-wall (top or bottom) can be considered substantially identical to the upper and lower parts (only the fact of gas in the duct).
• the duct extends near the outer casing to "capture" the calories outside the tank and completely vaporize the fluid in the conduit 12 measurement. Between the upper and lower ends of this portion, the pressure is substantially the same (differential of 0.5 bar maximum).
• pg_pipe is the density of gas at asbestos temperature (the outer conduits 11, 12 are preferably not isolated).
• len_w being the thickness of the walls of the tank and totaljength being the total height of the tank forming the storage volume.
• the upper duct 11 Since the upper duct 11 is close to the outer casing, it can not be considered that it contains only gas at ambient temperature. Two temperatures are to be considered:
• Tside-gas the temperature of the gas in the upper part of the duct 11 (adjacent to the gas phase),
• Tsidejiq the temperature of the gas in the lower part of the duct 11 (adjacent to the liquid phase of the tank).
• dpipe being the distance (spacing) between the upper duct 11 and the wall of the inner tank.
• ⁇ PH PHr + DPside _ gas + DPside _ Uq - DPamb
• totaljength being the total height of the inner tank, hl and hg the actual heights of liquid and gas in that shell.
• DPipe being the additional pressure difference value created by the gas present in the measuring pipes 11, 12.
• equations 11 and 8 indicate that the measured pressure differential DP underestimates the real pressure differential DPreal. And since the liquid level in the internal reservoir and the real pressure differential DPreal are proportional, at low liquid levels this underestimation can be significant.
• fold being the density of the liquid calibrated by default according to the procedure mentioned above.
• pg being the density of the gas.
• the members A, B and C of equation 15 correspond respectively to the effects of the calibration, the effect of the measuring ducts 11, 12 and the effect of the gas in the tank.
• Equation 15 shows that the error in the liquid level due to the effect of the gas in the tank partially offsets the error due to the effect of the measuring ducts.
• the members A, B and C of equation 16 here also correspond respectively to the effects of the calibration, the effect of the measuring ducts and the effect of the gas in the tank.
• thermodynamic model makes it possible to calculate these values.
• the mass and energy variation is the sum of the incoming masses minus the sum of the outgoing masses.
• the tank can be divided into two working volumes: one for the gas phase and one for the liquid phase.
• m vap being the mass flow (in m / s) of incoming gas generated by the
• Mc m Hg (pec T) + ⁇ vap Hg (Teq) - ⁇ t g ai i e rhG (Tg) + Q - W o Jt prc ⁇ prc vap ⁇ ⁇ - * * "is""ga
• Hg being the enthalpy of the gas.
• Hg (T prc ) is the enthalpy of the gas coming from the vaporizer
• T 8 ⁇ ⁇ prc the temperature of the gas from the vaporizer T prc is substantially equal to the temperature (average) of the gas Tg in the tank (is verified if the return gas duct vaporized the inner tank).
• the flow m prc of incoming energy due to the vaporizer is relatively low.
• the gas passing through the vaporizer receives from the outside an energy estimated by H 1 PrC (Hg (TaItIb) -Hl (Tl)) and redistributes this energy by heat exchange against the reservoir towards the liquid and gaseous phases.
• the heat Q supplied to the gas phase can be evaluated as (equation 25):
• NI m cons mass flow leaving consumption by the user of the tank.
• equation 28 the mechanical work is neglected because the liquid is considered incompressible.
• the power related to the vaporization is not taken into account because this equation is used only in the case where there is precisely no vaporization (liquid temperature below equilibrium temperature 7) ⁇ T eq ).
• the total thermal power entering the liquid phase is composed of three terms I, II, III (equation 30):
• hp the exchange coefficient between the ambient and the gas in the tank
• hlg the coefficient of heat exchange between the gas and the liquid in the tank.
• the first term (I) represents the natural convection between the outside ambient and the liquid located inside the tank.
• thermodynamic behavior of the tank between two fillings can be established on the basis of the following conditions:
• PH PH + pg_pipe.g (H max + of _ len - M)
• PB PB B - pg pipe.gMl
• Pr eal DP + pg_ pipe. g (H max-H of _ len)
• the density of liquid in the duct 9S-P ⁇ e is considered at room temperature in the first case ( Figure 1) and at the equilibrium temperature in the second case ( Figure 2).
• hp.Stot representing the power exchanged by degree of temperature difference can be calculated according to the mass flow rate of vaporized liquid and the latent heat of liquid oxygen at room temperature (298 ° K) according to the following equation 33:
• Hlatent being the latent heat of vaporization of oxygen O 2 under pressure
• fttioss ⁇ 2 being the mass flow rate of oxygen loss characteristic of the reservoir
• Tamb being the ambient temperature relative to the
• mlCpl hpStot (Tamb - Tl) - ⁇ ⁇ Tl ⁇ Teq dt
• equation 38 The solution of equation 37 is given by equation 38 below:
• the first effect is a condensation of the gas due to the cold liquid injected at the top.
• the second effect is a gas evacuation through the safety valve.
• the first effect is privileged while the second effect is privileged when filling from below.
• Model with condensation the gas evacuated by the valve (model with condensation) is neglected, or it is estimated that all the mass of lost gas is evacuated by the valve (non-condensing model).
• Hl _ affermi _ after + Hg _ after.mg _ after ml _ bef.Hl _ bef + ml _ deliv.Hl _ deliv + mg _ befilg _ bef
• the working hypotheses are as follows: the filling is at 100%, that is to say that the liquid level is at most Hmax, the volumes of gas and liquid are known, the temperature of the gas is at equilibrium after filling With these two assumptions it is possible to determine the temperature after filling and the mass delivered during filling. Model without condensation:
• Hlmix being the enthalpy of the liquid mixture after filling.
• This first model underestimates the mass actually delivered during filling because it does not consider gas losses (venting through the valve).
• the second model non-condensing will overestimate the mass actually delivered because the reduction in mass during filling is only due to venting, so it will replace this mass with liquid from the delivery truck.
• the numerical estimation can be conducted mathematically, we use: the letter u for the measured data used as input
• the liquid mass ml and the mass of mg gas in the tank are calculated at each time step on the basis of the measured input data.
• the calculation can comprise three phases:
• step 101 After initialization (101) the temperature and mass values are calculated by iteration for each time step since the last filling (step 102). If a filling is detected (step 103; "O", step 104), the method calculates the delivered liquid mass mdeliv and the liquid temperatures T1, gas Tg, masses of liquid ml and gas mg after filling according to the model above. As long as a filling is not detected (N, steps 103 and 105), the process continues to calculate by iteration for each time step the values of liquid temperature T1, gas temperature Tg, mass of liquid ml and mass of gas mg.
• the first assumption is based on the fact that liquid is evacuated during an overflow (the operator must make sure during a filling).
• the second hypothesis is based on the fact that during a filling a large part of the gas condenses (top filling in particular), the remaining gas can be considered at equilibrium.
• the real pressure differential value DPreal makes it possible to calculate the density of the liquid at this instant pi according to the formula of step 201.
• hg the height of gas
• pg the density of the gas
• hl the height of liquid
• g being the terrestrial attraction.
• a new temperature TM for the liquid can be calculated (step 202, for example applying an equation representing the liquid temperature T1 as a polynomial function of the pi density).
• the difference between the new calculated temperature value TM and the previous TIo is calculated. If this difference Diff is greater than a threshold S, the procedure starts again at step 200 using the new value of the calculated temperature TM. Otherwise the new temperature TM is adopted as the initial temperature.

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