Device and method for determining the mass of liquefied gas contained in a liquefied gas tank

Abstract

The invention relates to a device for determining the mass of liquefied gas contained in a liquefied gas tank, wherein the device comprises a first pressure sensor, which is designed to measure the geodetic pressure of liquefied gas contained in the liquefied gas tank, and wherein the device comprises an evaluation apparatus, which is designed to determine, from the measured geodetic pressure as well as from the liquid phase density and the gas phase density of the liquefied gas in the liquefied gas tank, the height of the liquid phase level of the liquefied gas in the liquefied gas tank, and to determine, from the determined height of the liquid phase level, the liquid phase mass and the gas phase mass of the liquefied gas contained in the liquefied gas tank. The invention also relates to a method for determining the mass of liquefied gas contained in a liquefied gas tank.

Description

[0001] Device and method for determining the liquid gas mass contained in a liquid gas tank

[0002] The invention relates to a device and a method for determining the mass of liquefied gas contained in a liquefied gas tank. liquefied gas tanks for liquefied gas can be mounted, for example, on tank vehicles. These can be single-walled low-temperature or normal-temperature liquefied gas tanks or double-walled liquefied gas tanks, in particular cryogenic liquefied gas tanks. Cryogenic liquefied gas tanks are intended for cryogenic liquefied gases, such as LIN, LOX, LAR, or LNG.

[0003] There is a need to reliably determine the mass of liquefied gas in the liquefied gas tank. For example, it must be ensured that the permissible total weight of a tanker vehicle is not exceeded during a filling process. Detection of changes in inventory quantities in the liquid tank is also desirable, for example, to detect losses or to be able to perform billing based on changes in inventory quantities.

[0004] It is difficult to install internal sensors in LPG tanks, especially in double-walled LPG tanks for cryogenic LPGs. The installation of approved sight glasses is not possible. A physical connection for a measuring point in or on the tank room causes an energy or temperature input, resulting in constant local evaporation and, subsequently, a constant pressure increase. The vacuum insulation of the LPG tank must not be compromised. Installing electronics inside the LPG tank cannot withstand the sometimes extremely low temperatures of, for example, close to -200°C. Explosion protection cannot be guaranteed, verified, or certified at these extreme temperatures. Likewise, the pressure resistance or leak tightness of measuring points cannot be monitored, and testing and maintenance access required under binding regulations (e.g., ADR) cannot be carried out.This applies in particular to LPG liquid gas tanks.

[0005] As a result, no practical electronic LPG mass measurement systems currently exist. The use of load cells, for example, is difficult due to the influence of external parameters. Imminent overfill and the resulting safe shutdown or change detection are not satisfactorily implemented. Another problem is that LPG in the LPG tank regularly contains both a liquid and a gas phase. Both phases must be considered to determine the LPG mass.

[0006] It has been proposed to implement a manual visual inspection for product leaks in the liquid phase by means of installed sounding pipe valves. However, this inevitably results in a leak of product, particularly hazardous goods, possibly containing flammable, environmentally harmful or life-threatening media. There is also no automatic shutdown. Using external systems to monitor tank pressure and thus prevent filling is based on the assumption that a pressure increase can be detected and that filling must be stopped. In practice, however, it is possible that a pressure increase is only detected when the gas phase quantity is already too low and there is therefore insufficient shutdown time. As a result, a permissible tank working pressure of, for example, 3 bar will very likely be exceeded.Safety valves that then trigger are generally only designed for gaseous phase quantities and not for the required cross-section for liquid phases. In a special application for LPG tanks, which cannot be used for cryogenic or ultra-low temperature tanks, it has been proposed to use a float that would enable a mechanical display. Based on the described prior art, the object of the invention is to reliably determine the mass of liquefied gas contained in a liquefied gas tank, for example, to reliably prevent exceeding a maximum filling quantity, to reliably detect and account for changes in inventory quantities or losses of goods.

[0007] The invention solves this problem through the independent claims. Advantageous embodiments can be found in the dependent claims, the description, and the figures.

[0008] For a device of the type mentioned at the outset, the invention achieves the object in that the device comprises a first pressure sensor which is designed to measure the geodetic pressure of liquefied gas contained in the liquefied gas tank, and in that the device comprises an evaluation device which is designed to determine the height of the liquid phase level of the liquefied gas in the liquefied gas tank from the measured geodetic pressure and from the liquid phase density and the gas phase density of the liquefied gas in the liquefied gas tank, and to determine the liquid phase mass and the gas phase mass of the liquefied gas in the liquefied gas tank from the determined height of the liquid phase level.

[0009] For a method of the type mentioned at the outset, the invention solves the problem by the following steps: measuring the geodetic pressure of liquefied gas contained in the liquefied gas tank, determining the height of the liquid phase level of the liquefied gas in the liquefied gas tank from the measured geodetic pressure and from the liquid phase density and the gas phase density of the liquefied gas in the liquefied gas tank, determining the liquid phase mass and the gas phase mass of the liquefied gas in the liquefied gas tank from the determined height of the liquid phase level. As explained at the outset, the liquefied gas tank can be a single-walled low-temperature or normal-temperature liquefied gas tank or a double-walled liquefied gas tank, in particular a cryogenic tank. The liquefied gas can in particular be a cryogenic liquefied gas, such as LEST, LOX, LAR, LNG.The liquefied gas is present in the liquefied gas tank in both the liquid and gaseous phases.

[0010] To determine the liquefied gas mass, the device according to the invention has a first pressure sensor that measures the geodetic pressure or the geodetic pressure head of the liquefied gas contained in the liquefied gas tank. As is known, the geodetic pressure describes the pressure at the lower end of the fluid column, which is created by the liquefied gas's own weight. It takes into account the liquid phase fraction and the gas phase fraction. The measured values ​​of the first pressure sensor are applied to an evaluation device of the device, which determines the height of the liquid phase level in the liquefied gas tank from the measured geodetic pressure, taking into account the liquid phase density and the gas phase density of the liquefied gas. From the height of the liquid phase level, the evaluation device determines the liquid phase mass and the gas phase mass of the liquefied gas contained in the liquefied gas tank. The volume and geometry of the liquefied gas tank are known.The type of liquefied gas contained therein is also known. The liquid phase level and / or the liquid phase and gas phase mass are determined taking into account the volume and / or geometry of the liquefied gas tank and / or the type of liquefied gas contained therein. The sum of the liquid phase mass and the gas phase mass can be determined as the total liquefied gas mass in the liquefied gas tank.

[0011] The data described above and below can be determined by the evaluation device, for example, before and / or after a filling or discharging process and / or repeatedly and / or continuously during a filling or discharging process.

[0012] Based on the measurement of the geodetic pressure and the resulting determination of the liquid phase level, the invention allows a reliable determination of the liquefied gas mass contained in the liquefied gas tank without the problems explained in the prior art, in particular without the need to install sensors or electronics inside the liquefied gas tank. By determining the liquefied gas mass, a filling process of the liquefied gas tank can be reliably stopped before the maximum permissible fill level is reached. Furthermore, by determining the liquefied gas mass, changes in inventory quantities during filling or emptying the liquefied gas tank, or even in the event of unwanted losses, can be detected, documented, and / or billed.

[0013] As explained, the invention allows the liquefied gas mass to be determined without requiring sensors to be located inside the liquefied gas tank. Accordingly, according to one embodiment, the first pressure sensor can be located outside the liquefied gas tank. This avoids problematic access to the tank interior.

[0014] According to a further embodiment, the first pressure sensor can be a differential pressure sensor that measures a pressure difference between a line connected to a top side of the LPG tank and a line connected to a bottom side of the LPG tank. In this way, the geodetic pressure head of the LPG in the LPG tank can be measured in a particularly reliable and practical manner.

[0015] According to a further embodiment, the device can comprise a second pressure sensor designed to measure the tank pressure in the liquefied gas tank. The evaluation device can then be further designed to determine the liquid phase density and the gas phase density of the liquefied gas in the liquefied gas tank from the measured tank pressure and the temperature of the liquefied gas or the temperature inside the liquefied gas tank. For certain liquefied gases, such as LPG, a density measurement is possible using a density sensor. However, for a large number of liquefied gases, measuring the density with such a density sensor is not possible. For this purpose, the aforementioned embodiment provides a reliable method for determining the liquid phase and gas phase density.

[0016] The second pressure sensor can also be located outside the LPG tank. It can measure the pressure in a line connected to the interior of the LPG tank. This design again eliminates the need for access to the tank interior, thus avoiding the disadvantages discussed in the prior art.

[0017] It is particularly possible that in the device according to the invention no sensors and / or no electronics are arranged in the interior of the liquid gas tank.

[0018] According to a further embodiment, the temperature of the liquefied gas taken into account in the aforementioned embodiment for determining the density of the liquefied gas can be calculated from the vapor pressure inside the liquefied gas tank measured by the second pressure sensor. The vapor pressure is known to be the pressure of the saturated vapor, i.e. the vapor that is in equilibrium with its liquid phase in the closed liquefied gas tank. For the liquefied gases concerned here, the vapor pressure generally only depends on the temperature, not on the ratio between the liquid phase and the gas phase. Accordingly, for example, based on previously stored vapor pressure curves, which could also be determined empirically, the temperature of the liquefied gas inside the liquefied gas tank can be reliably determined from the vapor pressure that arises in the liquefied gas tank, without the need for a temperature sensor.The steam pressure can be easily measured using the second pressure sensor explained above.

[0019] According to a further embodiment, it can be provided that the evaluation device is designed to adjust the vapor pressure inside the LPG tank by controlling a pressure relief valve connected to the LPG tank and / or by controlling a first filling valve arranged in a first filling line connected to an underside of the LPG tank and / or a second filling valve arranged in a second filling line connected to an upper side of the LPG tank. By means of the control explained, the vapor pressure can be precisely adjusted, for example, before, after, or during the determination of the LPG mass contained in the LPG tank. On the one hand, the pressure in the LPG tank can be reduced via the pressure relief valve for adjusting the vapor pressure.On the other hand, by filling the LPG tank from either the top or the bottom, the tank pressure inside the LPG tank can be influenced and the vapor pressure adjusted. Filling the LPG tank from the top causes the tank pressure to decrease, while filling from the bottom causes the tank pressure to increase.

[0020] According to a further embodiment, the evaluation device can be designed to regulate the tank pressure inside the LPG tank to a desired value during filling and / or emptying of the LPG tank by controlling the pressure relief valve and / or the first and second filling valves. Of course, it is also conceivable for the evaluation device to control a pump used for filling and / or emptying the LPG tank in order to regulate the tank pressure to the desired value. An automatically regulated tank pressure improves the determination of the LPG mass. Depending on the type of gas, sound-damped pressure relief can also be carried out via the pressure relief valve. This can prevent, for example, necessary safety valves from constantly and repeatedly responding to excess pressure, increasingly icing up due to constant and repeated opening, and subsequently failing or no longer being able to close.

[0021] According to a further embodiment, it can be provided that the evaluation device is designed to calculate the liquid phase mass below the liquid phase level and multiply it by the liquid phase density in order to determine the liquid phase mass, and to calculate the liquid phase volume above the liquid phase level and multiply it by the gas phase density in order to determine the gas phase mass. In order to determine the liquid phase mass, in this embodiment the volume located below the liquid phase level in the liquid gas tank is calculated and related to the previously determined liquid phase density, for example. Accordingly, to determine the gas phase mass, the volume located above the liquid phase level is calculated and related to the previously determined gas phase density, for example.As explained above, the volume determination can take into account the known volume and / or the known geometry of the LPG tank.

[0022] According to a further embodiment, the device can comprise a position sensor that detects a positional deviation of the LPG tank from a defined position, in particular an inclination of the LPG tank. The evaluation device can be designed to take measurement results from the position sensor into account when determining the liquid phase mass and the gas phase mass. This embodiment is based on the knowledge that changes in the position of the LPG tank, such as an inclination, can influence the determination of the liquid phase level and thus the determination of the liquid phase mass and the gas phase mass and consequently the total LPG mass. By taking into account corresponding measured values ​​from position sensors, this influence on the mass determination can be detected and computationally compensated by the evaluation device, so that the LPG mass is always accurately determined.

[0023] According to a further embodiment, the evaluation device can be configured to output the determined liquid phase mass and / or liquid phase density and / or gas phase mass and / or gas phase density and / or total mass of the liquefied gas in the liquefied gas tank to an operator, in particular on a display of the evaluation device or on a device separate from it, for example, a PC, laptop, tablet, or mobile phone. The temperature of the liquefied gas can also be output to the operator.

[0024] The evaluation device can further be configured to output the amount of liquefied gas filled or removed during a filling or withdrawal process to an operator, again, for example, as explained above. This enables transaction recording. For example, in real-time operation, a stock quantity difference can be used for transaction receipts. For this purpose, the fill level at the beginning and end of a transaction process, as well as any difference thereto, can be determined. All values ​​can be displayed electronically or as a paper-based receipt. A transaction process can also include a temporarily deactivated system.

[0025] According to a further embodiment, it can be provided that the evaluation device is designed to store a fill level of the LPG tank after a completed filling or removal process and to compare it with a fill level of the LPG tank before the start of the next filling or removal process and to determine any deviation in the fill level. In this way, loss of goods can be detected, in particular by securely storing a fill level before the device is switched off and comparing the fill level after the device is reactivated or even in real-time operation. If an inventory discrepancy is detected, a visible or covert message can be issued, if necessary in a non-editable log, in particular with stock and / or time information including the option of remote transmission. A non-qualified anomaly warning and / or a quantity indication can also be provided.

[0026] According to a further embodiment, the device can comprise a flow measuring device for measuring the amount of liquefied gas released when liquefied gas is withdrawn from the liquefied gas tank, wherein the flow measuring device is assigned a temperature sensor arranged outside the liquefied gas tank and a pressure sensor arranged outside the liquefied gas tank. The evaluation device can then be designed to compare the temperature sensor with the temperature of the liquefied gas inside the liquefied gas tank and / or to compare the pressure sensor with the tank pressure inside the liquefied gas tank. The aforementioned embodiment enables calibration and / or validation of the liquefied gas inventory measurement. In this case, a conventionally provided flow measuring device can be part of the device according to the invention, including the aforementioned relevant sensors.Calibration and / or validation can be performed against this system consisting of flow measuring device and sensors, or against an external reference, for example, a master meter. Calibration and / or validation can also include compensation for the volume and / or geometry of the LPG tank, in particular tank contour compensation, as well as the definition of high and low levels and individual measurements of individual sensors of the device. For example, the temperature sensor can be precisely calibrated based on the temperature determination using the vapor pressure in the LPG tank. If necessary, measurement uncertainties or warming factors can be added as temperature compensation valid from the time the product leaves the tank until it reaches the measuring point of the temperature sensor. The calibration can be performed during product withdrawal or filling, or while determining the LPG mass.The adjustment is possible in both directions, i.e. both an adjustment to the measured values ​​of the sensors of the flow measuring device and an adjustment of these sensors to values ​​determined by means of the device according to the invention.

[0027] The evaluation device can further be configured to stop the filling process of the LPG tank when a predetermined maximum liquid phase level is reached. This reliably prevents overfilling of the LPG tank. It can also reliably prevent a tanker equipped with the LPG tank from exceeding a permissible maximum weight.

[0028] According to a further embodiment, the evaluation device can be designed to control a withdrawal rate when withdrawing liquefied gas from the liquefied gas tank depending on the liquid phase level. For example, undesirable vortex formation can be avoided in this way. For example, the speed can be reduced as the fill level decreases, for example by reducing the delivery rate of a withdrawal pump or by controlling one or more valves in the pump and / or measuring section accordingly. In this way, it is also possible to reliably detect cavitation when the vapor pressure is reached, in particular in combination with a flow measuring device. The tank pressure can be regulated and / or the withdrawal rate adjusted in order to avoid undesired cavitation. This can be done in the manner explained above. By avoiding orBy reducing cavitation, potentially serious pump damage and measurement errors in a flow measuring device can be avoided. The invention also relates to a liquefied gas tank comprising a device according to the invention. The liquefied gas tank can, for example, be a double-walled liquefied gas tank, in particular a cryogenic liquefied gas tank. However, it can also be a single-walled low-temperature or normal-temperature liquefied gas tank.

[0029] The invention also relates to a tank vehicle comprising a liquid gas tank according to the invention with a device according to the invention.

[0030] The invention also relates to a method for determining the liquefied gas mass contained in a liquefied gas tank using a device according to the invention and / or a liquefied gas tank according to the invention and / or a tank vehicle according to the invention. In the method, the steps for which the device, in particular the evaluation device, is designed can be carried out.

[0031] An exemplary embodiment of the invention is explained in more detail below with reference to a drawing. The single figure schematically shows a liquid gas tank according to the invention with a device according to the invention.

[0032] The liquefied gas tank 10 shown in the figure can be a single-walled or double-walled liquefied gas tank 10. It can be, for example, a cryogenic liquefied gas tank 10 for a cryogenic liquefied gas. The liquefied gas tank 10 can be mobile, for example, installed on a tank vehicle. However, it can also be a stationary liquefied gas tank 10. The liquefied gas tank 10 contains a liquefied gas that exists partly in the liquid phase and partly in the gaseous phase. The liquid phase of the liquefied gas is located below the liquid phase level 12, and the gaseous phase is above the liquid phase level 12. The volume and geometry of the liquefied gas tank 10 are known, as is the type of liquefied gas it contains.In the example shown, the LPG tank 10 is equipped with a position sensor 14 that detects a deviation of the LPG tank 10 from a defined normal position, for example, an inclination of the LPG tank 10. The detection data of the position sensor 14 are transmitted to an evaluation device 16 of the device according to the invention via a data connection (not shown in detail). The evaluation device 16 takes into account any positional deviation of the LPG tank 10 detected by the position sensor 14 when determining the LPG mass contained in the LPG tank 10, in particular when considering the volume and geometry of the LPG tank 10.

[0033] In the example shown, the LPG tank 10 can be filled with LPG either via a first filling line 18 connected to the underside of the LPG tank 10 or via a second filling line 20 connected to the top of the LPG tank 10. A first filling valve 22 is arranged in the first filling line 18, and a second filling valve 24 is arranged in the second filling line 20. The filling valves 22, 24 can be controlled by the evaluation device 16, so that by opening and closing the filling valves 22 and 24, the LPG tank 10 can be filled either from the underside or the top. This can influence the tank pressure prevailing in the LPG tank 10, since filling from the top leads to a drop in the tank pressure, and filling from the bottom leads to an increase in the tank pressure.Also connected to the second filling line 20 downstream of the second filling valve 24 is a pressure relief valve 26, which, in turn, can be used to relieve pressure in the LPG tank 10 under the control of the evaluation device 16, for example, to adjust the vapor pressure in the LPG tank 10 or when undesirable pressure peaks occur. The evaluation device 16 controls the filling valves 22, 24 and the pressure relief valve 26 via control lines 28, 30. The evaluation device 16 also controls a pump 32 via the control line 28, which can be used to discharge the LPG tank 10. For this purpose, the pump 32 is connected to the underside of the LPG tank 10 via a discharge line 34, in which an isolation valve 36 is arranged.Downstream of the pump 32, the discharge line 34 leads to a flow meter 38, which measures the amount of liquefied gas discharged in a conventional manner when the liquefied gas tank 10 is discharged. The liquefied gas is discharged via a discharge valve 40.

[0034] Downstream of the pump 32, several sensors are arranged on the discharge line 34: a measuring section temperature sensor 42, a measuring section density sensor 44, and a measuring section pressure sensor 46. These measure the temperature, density, and pressure of the liquefied gas discharged via the discharge line 34 as measurement parameters for the flow measuring device 38. The measurement results of the sensors 42, 44, and 46 are transmitted to the evaluation device 16 via a data line 48. The measured values ​​of the flow measuring device 38 are also transmitted to the evaluation device 16 via a data line 50. In this way, the evaluation device 16 receives information about the discharged quantity of liquefied gas from the flow measuring device 38. It should be noted that the measuring section density sensor 44 can only determine the density for certain liquefied gases, such as LPG.For a majority of liquefied gases, no usable density measurement data are available via the measuring section density sensor 44.

[0035] The device further comprises a first pressure sensor 52, which in the example shown is a differential pressure sensor 52. The first pressure sensor 52 is connected to the underside of the LPG tank 10 via a first differential line 54 and to the top of the LPG tank 10 via a second differential line 56. Located in the second differential line 56 is a first multiplexer valve 58, which can be opened or closed by the evaluation device 16 via a control line 60. In the open state, the pressures at the top and bottom of the LPG tank 10 are therefore present at the first pressure sensor 52. The first pressure sensor 52, designed as a differential pressure sensor 52, uses this to determine the geodetic pressure of the LPG contained in the LPG tank 10. The determined geodetic pressure is also applied to the evaluation device 16 via the data line 50.

[0036] The device further comprises a second pressure sensor 62, which is also connected to the top of the LPG tank 10 and measures the tank pressure inside the LPG tank 10. The measurement results of the second pressure sensor 62 are transmitted to the evaluation device 16 via a data line 64.

[0037] The function of the device according to the invention is explained below. To determine the liquefied gas mass contained in the liquefied gas tank 10, the first pressure sensor 52 measures the geodetic pressure of the liquefied gas contained in the liquefied gas tank 10 and transmits the measurement results to the evaluation device 16 via the data line 50. For example, by controlling the pressure relief valve 26 or the first and second filling valves 22, 24, the evaluation device 16 sets the vapor pressure of the liquefied gas contained therein in the liquefied gas tank 10. This vapor pressure is measured as the current tank pressure by the second pressure sensor 62, and the measured vapor pressure is transmitted to the evaluation device 16 via the data line 64. For example, based on vapor pressure curves previously stored for the liquefied gas, the evaluation device 16 determines the temperature of the liquefied gas inside the liquefied gas tank.The determination of the vapor pressure and thus the temperature of the liquid gas in the liquid gas tank 10 can, for example, take place before and / or after a filling or unloading process.

[0038] During filling or discharging of liquefied gas, the pressure in the liquefied gas tank 10 changes regularly. This changed pressure is measured as the tank pressure by the second pressure sensor 62 and transmitted to the evaluation device 16 via the data line 64. From the measured tank pressure and the previously determined temperature of the liquefied gas, the evaluation device 16 determines the liquid phase density and the gas phase density of the liquefied gas in the liquefied gas tank 10, for example based on previously stored data. From the geodetic pressure of the liquefied gas measured by the first pressure sensor 52 and the determined liquid phase density and gas phase density of the liquefied gas, the evaluation device 16 determines the height of the liquid phase level 12 in the liquefied gas tank 10, taking into account the known volume and geometry of the liquefied gas tank 10, and if necessary, taking into account positional deviations detected by the position sensor 14.From the height of the liquid phase level 12, the evaluation device 16 then further determines the liquid phase mass and the gas phase mass of the liquefied gas contained in the liquefied gas tank 10. From this, the evaluation device 16 can determine the total mass of the liquefied gas contained in the liquefied gas tank 10 by summing the values. The data determined by the evaluation device 16, in particular regarding temperature, density, liquid phase level, liquid phase mass, gas phase mass, and total mass, can be output in full or selectively, for example, on a display for an operator. Such a display can be located on the tank vehicle itself. However, it can also be output via mobile data transmission, for example, to a PC, laptop, tablet, or smartphone.

[0039] Based on the acquired data, the evaluation device 16 can, as explained above, determine, output, and further process transaction data during the filling or emptying of the liquefied gas tank 10. Based on the recording and determination of the above-mentioned data, for example the tank pressure, which occurs, for example, at regular intervals or continuously during a filling or discharging process, the evaluation device 16 can control the above-explained valves 22, 24, 26, 36, 40 and the pump 32. For example, the evaluation device 16 can stop a filling process if it detects an impermissibly high tank pressure. It is also possible, in the manner explained above, for the evaluation device 16 to save a current status of the acquired data before switching off the device and, after reactivating the device, to compare the newly acquired data with the stored data.In this way, a loss of goods can be detected and further processed, for example reported, in the manner explained above.

[0040] As also explained above, by opening the first multiplexer valve 58, the pressure at the top of the liquid gas tank 10 is applied to the first pressure sensor 52. The figure shows that the first pressure sensor 52 is also connected to the discharge line 34 via a first multiplexer line 66 downstream of the flow measuring device 38 and upstream of the discharge valve 54, and is also connected to the discharge line 34 via a second multiplexer line 68 upstream of the flow measuring device 38 and downstream of the pump 32. Located in the first multiplexer line 66 is a second multiplexer valve 70, which is usually closed during the differential pressure measurement by the first pressure sensor 52 described above. The evaluation device 16 can also control the second multiplexer valve 70 via the control line 60.By closing the first multiplexer valve 58 and opening the second multiplexer valve 70, the first pressure sensor 52 records the pressure in the discharge line 34 downstream of the flow measuring device 38. This measured value can be fed to the flow measuring device 38 via the second multiplexer line 68. In this way, a differential pressure flow measurement can be performed. It is also possible to compare the temperature of the liquid gas, determined based on the vapor pressure in the liquid gas tank 10, with measured values ​​from the measuring section temperature sensor 42. Furthermore, it is also possible to automatically compare the second pressure sensor 62 with the measuring section pressure sensor 46, if necessary also by controlling the isolation valve 36. Thus, if necessary, solely the feedback of the measuring chain to the measuring section pressure sensor 46 is sufficient to calibrate the second pressure sensor 62 and the measuring section temperature sensor 42. List of reference symbols.

[0041] 10 LPG tank

[0042] 12 liquid phase mirrors

[0043] 14 Position sensor

[0044] 16 Evaluation device

[0045] 18, 20 filling lines

[0046] 22, 24 filling valves

[0047] 26 Pressure relief valve

[0048] 28, 30 control lines

[0049] 32 Pump

[0050] 34 Discharge line

[0051] 36 Isolation valve

[0052] 38 Flow measuring device

[0053] 40 Discharge valve

[0054] 42, 44, 46 sensors

[0055] 48, 50 data lines

[0056] 52, 62 pressure sensors

[0057] 54, 56 differential lines

[0058] 58, 70 Multiplexer valves

[0059] 60 control cable

[0060] 64 data lines

[0061] 66, 68 multiplexer lines

Claims

Claims 1. Device for determining the mass of liquefied gas contained in a liquefied gas tank (10), characterized in that the device comprises a first pressure sensor (52) which is designed to measure the geodetic pressure of liquefied gas contained in the liquefied gas tank (10), and in that the device comprises an evaluation device (16) which is designed to determine the height of the liquid phase level (12) of the liquefied gas in the liquefied gas tank (10) from the measured geodetic pressure and from the liquid phase density and the gas phase density of the liquefied gas in the liquefied gas tank (10), and to determine the liquid phase mass and the gas phase mass of the liquefied gas in the liquefied gas tank (10) from the determined height of the liquid phase level (12).

2. Device according to claim 1, characterized in that the first pressure sensor (52) is arranged outside the liquid gas tank (10).

3. Device according to one of claims 1 or 2, characterized in that the first pressure sensor (52) is a differential pressure sensor (52) which measures a pressure difference between a line (56) connected to an upper side of the liquid gas tank (10) and a line (54) connected to an underside of the liquid gas tank (10).

4. Device according to one of the preceding claims, characterized in that the device comprises a second pressure sensor (62) which is designed to measure the tank pressure in the liquid gas tank (10), and in that the evaluation device (16) is designed to determine from the measured tank pressure and the temperature of the liquid gas the To determine the liquid phase density and the gas phase density of the liquefied gas in the liquefied gas tank (10).

5. Device according to claim 4, characterized in that the second pressure sensor (62) is arranged outside the liquid gas tank (10).

6. Device according to one of claims 4 or 5, characterized in that the temperature of the liquid gas taken into account by the evaluation device (16) is calculated from the vapor pressure inside the liquid gas tank (10) measured by the second pressure sensor (62).

7. Device according to claim 6, characterized in that the evaluation device (16) is designed to adjust the vapor pressure inside the liquid gas tank (10) by controlling a pressure relief valve (26) connected to the liquid gas tank (10) and / or by controlling a first filling valve (22) arranged in a first filling line (18) connected to an underside of the liquid gas tank (10) and / or a second filling valve (24) arranged in a second filling line (20) connected to an upper side of the liquid gas tank (10).

8. Device according to claim 7, characterized in that the evaluation device (16) is designed to regulate the tank pressure inside the liquid gas tank (10) to a desired value during filling or emptying of the liquid gas tank (10) by controlling the pressure relief valve (26) and / or the first and second filling valves (22, 24).

9. Device according to one of the preceding claims, characterized in that the evaluation device (16) is designed to determine the liquid phase mass which is located below the to calculate the liquid gas volume located above the liquid phase level (12) and to multiply it by the liquid phase density, and to determine the gas phase mass, to calculate the liquid gas volume located above the liquid phase level (12) and to multiply it by the gas phase density.

10. Device according to one of the preceding claims, characterized in that it comprises a position sensor (14) which detects a positional deviation of the liquid gas tank (10) from a defined position, in particular an inclination of the liquid gas tank (10), and in that the evaluation device (16) is designed to take into account measurement results of the position sensor (14) when determining the liquid phase mass and the gas phase mass.

11. Device according to one of the preceding claims, characterized in that the evaluation device (16) is designed to output the determined liquid phase mass and / or liquid phase density and / or gas phase mass and / or gas phase density and / or total mass of the liquid gas in the liquid gas tank (10) to an operator.

12. Device according to one of the preceding claims, characterized in that the evaluation device (16) is designed to output the amount of liquid gas filled or removed during a filling or removal process to an operator.

13. Device according to one of the preceding claims, characterized in that the evaluation device (16) is designed to store a filling level of the liquid gas tank (10) after a completed filling or removal process and to compare it with a filling level of the liquid gas tank (10) before starting the next filling or removal process and to determine any deviation in the filling level.

14. Device according to one of the preceding claims, characterized in that the device comprises a flow measuring device (38) for measuring the amount of liquid gas delivered when liquid gas is withdrawn from the liquid gas tank (10), wherein the flow measuring device (38) is assigned a temperature sensor (42) arranged outside the liquid gas tank (10) and a pressure sensor (46) arranged outside the liquid gas tank (10), and in that the evaluation device (16) is designed to compare the temperature sensor (42) with the temperature of the liquid gas and / or to compare the pressure sensor (46) with the tank pressure inside the liquid gas tank (10).

15. Device according to one of the preceding claims, characterized in that the evaluation device (16) is designed to stop a filling process of the liquid gas tank (10) when a predetermined maximum liquid phase level (12) is reached.

16. Device according to one of the preceding claims, characterized in that the evaluation device (16) is designed to control a withdrawal speed when withdrawing liquid gas from the liquid gas tank (10) depending on the liquid phase level (12), in particular in such a way that vortex formation and / or cavitation during the withdrawal of the liquid gas is reduced or avoided.

17. Liquid gas tank (10) comprising a device according to one of the preceding claims.

18. Liquid gas tank (10) according to claim 17, characterized in that the liquid gas tank (10) is a double-walled liquid gas tank (10).

19. Tank vehicle comprising a liquefied gas tank (10) according to one of claims 17 or 18.

20. A method for determining the mass of liquefied gas contained in a liquefied gas tank, comprising the steps of: • Measuring the geodetic pressure of liquefied gas contained in the liquefied gas tank (10), • Determining the height of the liquid phase level (12) of the liquefied gas in the liquefied gas tank (10) from the measured geodetic pressure and from the liquid phase density and the gas phase density of the liquefied gas in the liquefied gas tank (10), • Determining the liquid phase mass and the gas phase mass of the liquid gas in the liquid gas tank (10) from the determined height of the liquid phase level (12).

21. The method according to claim 20, characterized in that the tank pressure in the liquefied gas tank (10) is further measured, and in that the liquid phase density and the gas phase density of the liquefied gas in the liquefied gas tank (10) are determined from the measured tank pressure and the temperature of the liquefied gas.

22. Method according to claim 21, characterized in that the temperature of the liquid gas taken into account by the evaluation device (16) is calculated from the vapor pressure inside the liquid gas tank (10) measured by the second pressure sensor (62).

23. Method according to claim 22, characterized in that the vapor pressure inside the liquid gas tank (10) is adjusted by controlling a pressure relief valve (26) connected to the liquid gas tank (10) and / or by controlling a first filling valve (22) arranged in a first filling line (18) connected to a bottom side of the liquid gas tank (10) and / or a second filling valve (24) arranged in a second filling line (20) connected to a top side of the liquid gas tank (10).

24. Method according to claim 23, characterized in that by controlling the pressure relief valve (26) and / or the first and second filling valve (22, 24), the tank pressure inside the liquid gas tank (10) is regulated to a desired value during filling or emptying of the liquid gas tank (10).

25. Method according to one of claims 20 to 24, characterized in that for determining the liquid phase mass, the sample located below the The liquid gas volume located below the liquid phase level (12) is calculated and multiplied by the liquid phase density, and to determine the gas phase mass, the liquid gas volume located above the liquid phase level (12) is calculated and multiplied by the gas phase density.

26. Method according to one of claims 20 to 25, characterized in that a positional deviation of the liquid gas tank (10) from a defined position, in particular an inclination of the liquid gas tank (10), is detected by a position sensor (14), and that measurement results of the position sensor (14) are taken into account in the determination of the liquid phase mass and the gas phase mass.

27. Method according to one of claims 20 to 26, characterized in that the determined liquid phase mass and / or liquid phase density and / or Gas phase mass and / or gas phase density and / or total mass of the liquid gas in the liquid gas tank (10) is output to an operator.

28. Method according to one of claims 20 to 27, characterized in that the quantity of liquid gas filled or removed during a filling or removal process is dispensed to an operator.

29. Method according to one of claims 20 to 28, characterized in that a filling level of the liquid gas tank (10) is stored after a completed filling or removal process and compared with a filling level of the liquid gas tank (10) before the start of the next filling or removal process and any deviation in the filling level is determined.

30. Method according to one of claims 20 to 29, characterized in that the amount of liquefied gas delivered when liquefied gas is withdrawn from the liquefied gas tank (10) is measured with a flow measuring device (38), wherein the flow measuring device (38) is assigned a temperature sensor (42) arranged outside the liquefied gas tank (10) and a pressure sensor (46) arranged outside the liquefied gas tank (10), and that the temperature sensor (42) is calibrated with the temperature of the liquefied gas and / or the pressure sensor (46) is calibrated with the tank pressure inside the liquefied gas tank (10).

31. Method according to one of claims 20 to 30, characterized in that when a predetermined maximum liquid phase level (12) is reached, a filling process of the liquid gas tank (10) is stopped.

32. Method according to one of claims 20 to 31, characterized in that a withdrawal speed during withdrawal of liquefied gas from the liquefied gas tank (10) is controlled as a function of the liquid phase level (12), in particular in such a way that vortex formation and / or cavitation during the withdrawal of the liquefied gas is reduced or avoided.

33. Method according to one of claims 20 to 32, characterized in that it is carried out with a device according to one of claims 1 to 16 and / or a liquid gas tank according to one of claims 17 or 18 and / or a tank vehicle according to claim 19.

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