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WO1992005408A1 - Appareil de mesure du niveau inferieur et des fuites d'eau dans un reservoir - Google Patents

Appareil de mesure du niveau inferieur et des fuites d'eau dans un reservoir Download PDF

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Publication number
WO1992005408A1
WO1992005408A1 PCT/US1991/006868 US9106868W WO9205408A1 WO 1992005408 A1 WO1992005408 A1 WO 1992005408A1 US 9106868 W US9106868 W US 9106868W WO 9205408 A1 WO9205408 A1 WO 9205408A1
Authority
WO
WIPO (PCT)
Prior art keywords
tank
pressure
level
fluid
specified
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Ceased
Application number
PCT/US1991/006868
Other languages
English (en)
Inventor
Randy J. Longsdorf
Robert C. Hedtke
Richard L. Nelson
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Rosemount Inc
Original Assignee
Rosemount Inc
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Rosemount Inc filed Critical Rosemount Inc
Publication of WO1992005408A1 publication Critical patent/WO1992005408A1/fr
Anticipated expiration legal-status Critical
Ceased legal-status Critical Current

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Classifications

    • 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

Definitions

  • the present invention relates to a highly sensitive tank monitoring system capable of measuring an upper level of an impurity, such as water, settled at a bottom of a storage tank.
  • the invention is also capable of tank leak detection.
  • undesirable impurities such as water having higher specific gravities than the process liquid settle out and collect at the tank bottom, commonly known as a water bottom.
  • the water bottom is an accumulation of denser impurities, such as rain water that falls on a floating roof and leaks through a seal into the tank, injection water used to aid pumping of products from the ground to the tank, and sea water used for ballast by ocean going tankers transporting products. It is extremely important to know an upper water level for if water level reaches a tank outlet, which is typically only one to three feet above the tank bottom, any outflow of the process liquid would contain a high percentage of water.
  • water and other undesired dense liquids or solids can be corrosive to the tank bottom which shortens tank life and must be removed from time to time.
  • One method of measuring water level in a tank involves using two air bells, one disposed inside the other, each having an opening at different levels and communicating with a manometer, such as taught by U.S. Patent 4,084,435.
  • the drawback of this method is that the system must be inserted in the tank, and the bells need to be accurately positioned near the tank bottom, which may not always be a uniform surface.
  • HTG hydrostatic tank gauging
  • Many tanks have a hydrostatic tank gauging (HTG) system to measure the amount of process liquid in . the tank by mass, such as the Series 7500 manufactured by Rosemount Inc. of Eden Prairie, Minnesota.
  • HTG systems typically utilize two separate pressure transmitters at different elevations below a hydrostatic head created by the process liquid and separated a predetermined distance apart.
  • a first pressure transmitter measures hydrostatic pressure near the tank bottom, and a second pressure transmitter measures hydrostatic pressure at a known distance above the first pressure transmitter.
  • a mass of the process liquid is proportional to pressure measured by the lower transmitter multiplied by a horizontal tank area. Density is proportional to a difference between the two measured pressures divided by the height or distance between pressure taps for the two transmitters.
  • Level and volume can be calculated from mass and density calculations.
  • An instrument capable of accurately measuring water level at a tank bottom that can be easily converted to a highly accurate tank leak detector is desirable. Further, an instrument that is compatible with current HTG systems is desirable.
  • the present invention provides a simplified and highly accurate apparatus for determining an upper level of a denser impurity, such as water, settled at a bottom of a storage tank below a less dense process liquid.
  • the apparatus can automatically maintain an impurity upper level below a product outlet to avoid discharging t " ⁇ - ⁇ t impurity with the process liquid.
  • the apparatus can easily be converted to a leak detection system capable of automated control and is compatible with HTG systems.
  • a single low range differential pressure transmitter of conventional design has a high pressure port at a first level receiving a first hydrostatic head pressure created by both process liquid and denser impurity residing at and above the first level.
  • a low pressure port of the transmitter at substantially the first level receives a second hydrostatic head pressure from a purged column containing only process liquid.
  • the purged column opens into the tank at a level above an upper level of the impurity.
  • the differential transmitter senses differential pressure across the high and low pressure ports created by the denser impurity residing at and above the first level and provides a transmitter output representative of the impurity upper level with respect to the first level.
  • Means for calculating receives the transmitter output and connects to a device capable of receiving and storing specific gravity data of the process liquid and the impurity.
  • the means for calculating calculates the upper impurity level from specific gravity data and the transmitter output in a known manner. Common head effects from the process liquid across the transmitter cancel allowing a low range differential pressure transmitter having a higher accuracy to be used.
  • a valve is interposed between the purged column and the tank for selectively isolating pressure in the purged column from the tank, permitting the apparatus to accurately detect tank leaks.
  • a portion of the purged column extends upward opening to the tank at a point above liquid in the tank.
  • a fixed reference level is established in the purged column equal in height to total liquid in the tank. Any subsequent changes in the height of the tank liquid generates a proportional change in differential pressure across the differential pressure transmitter.
  • the transmitter output is not an absolute measurement of volume of leakage, but is proportional to level changes. After a predetermined time period since closing the valve, a start reading of the transmitter is established.
  • the invention is compatible with conventional hydrostatic systems since the transmitter can be connected to previously installed tank flanges used in conventional hydrostatic tank gauging systems.
  • the invention is non-intrusive, meaning the entire apparatus can reside exterior to the tank, but, if desired, the apparatus can be placed interior to the tank.
  • Figure 1 is a schematic representation of a water bottom measurement system of the present invention illustrating the principles of determining water level in a tank.
  • Figure 2 is a schematic representation of a second form of the invention which includes an ability to convert the water bottom measurement system to a leak detection system.
  • a liquid storage tank indicated generally at 10 contains liquids of two different specific gravities or densities, including a lighter or less dense than water process liquid 12, and a denser impurity or water 14 residing below process liquid 12, which can include sediment.
  • tank 10 has a bottom section 16 for collecting water impurities, commonly known as a water bottom.
  • Water bottom measurement system 20 connects to tank 10 and can reside inside tank 10, or outside tank 10 as shown in FIG. 1.
  • Purged column 22 taps into tank 10 at port 24 residing above water level 26, which is an interface between process liquid 12 and water 14, and ideally, below outlet port 28 at level 30 and therefore always below upper tank level 32 in tank 10. Purged column 22 extends downward to purge valve 34 which can be automatically controlled by controller 36 via control line 38 to purge column liquid 40 of any contaminants such as water 14 prior to any measurements.
  • Differential pressure transmitter 42 such as Model 3051C manufactured by Rosemount Inc. of Eden Prairie, Minnesota has a high pressure port 44 connecting via passageway 46 to port 48 of tank 10 at a point very near tank bottom 16 sensing a pressure head P 1 created by both higher specific gravity water 14 and lower specific gravity process liquid 12.
  • Low pressure port 50 opens via passageway 52 to purged column 22 at substantially the same elevation as high pressure port 44 and senses pressure head P 2 , serving as a reference pressure, created by only lower specific gravity process liquid 12 in purged column 22 and tank 10 since purged column 22 bypasses water level 26.
  • Differential pressure sensor 54 in transmitter 42 senses differential pressure P ⁇ -P 2 between high and low pressure ports 44 and 50, respectively, generated by a presence of higher specific gravity water 14 above port 48.
  • Transmitter 42 generates a transmitter output signal on line 56 proportional to differential pressure, for example, a DC current in a range of 4-20 A or a digital output, which routes to receiver 58 in electrical circuit 60 which can comprise logic circuits or a microprocessor based system. Since high pressure and low pressure ports 44 and 50, respectively, are at substantially the same level, common head effects due to process liquid 12 cancel, hence, a low-range differential transmitter having a high sensitivity can be used to measure small pressure differences due to denser water 14.
  • Specific gravity data 62 comprised of stort ⁇ suitable look-up tables, measured specific gravity, entered specific gravity, or the like, provides density or specific gravity data of water 14, as well as of process liquid 12, to calculator 64 in electrical circuit 60.
  • Calculator 64 calculates water level 26 from specific gravity data 62 and the transmitter output signal provided on line 56 in a known manner.
  • Computation storage 66 stores calculations from calculator 64 and provides output 68, where output 68 is representative of water level 26. If no water 14 resides above port 48, then both pressures 2 and P 2 are created by only process liquid 12 and are equal, therefore, differential pressure P i - 2 is zero and computation storage 66 generates output 68 correspondingly.
  • Output 68 can be used, for example, to drive a recorder, or, to sound an alarm when water level 26 exceeds a predetermined level.
  • Calculator 64 can initiate controller 36 to open drain valve 70 automatically via control line 72, where valve 70 connects to drain port 74 opening to water 14 in tank 10, to reduce water level 26 by draining water 14 and any other sludge residing at bottom section 16, ensuring water level 26 remains below outlet port 28.
  • Controller 36 also controls valve 76 via control line 78, where valve 76 connects to tank outlet port 28 to selectively dispense process liquid 12.
  • Mass calculations of water 14 and process liquid 12 can also be calculated by calculator 64 by multiplying known horizontal area of water 14 and process liquid 12 as a function of vertical elevation in tank 10.
  • pressure transmitter 42 should be connected to tank 10 via passageway 46 as close to tank bottom section 16 as possible, and valves 34 and 70 should reside at substantially the same level.
  • Passageways 46 and 52, and purged column 22 should comprise the same material as tank 10 and be insulated, and should be attached to tank 10 opposite the sun, which is the north side in the northern hemisphere.
  • FIG. 2 a second preferred embodiment of the invention is shown capable of measuring both height of water level 26 and tank leakage.
  • measurement system 80 similar to measurement system 20 described in the first preferred embodiment, connects to tank 10.
  • High pressure port 44 of transmitter 42 opens to port 48 of tank 10 via passageway 46 and two-way valve 82.
  • Low pressure port 50 of differential pressure transmitter 42 opens to purged column 86 via passageway 52 and two-way valve 84.
  • Purged column 86 extends downwardly to purge valve 34, which can be automatically controlled by controller 36 via control line 38 as previously explained, and upwardly to passageway 88, which opens to tank 10 at port 89 above liquid level 32 thus exposing column liquid 40 to same vapor pressure as process liquid 12.
  • Purged column 86 also opens to passageway 90 which connects to passageway 92 via valve 94.
  • Passageway 92 opens to port 24 of tank 10 at a point above water level 26 and, ideally, below output port 28 whereby only lower specific gravity process liquid 12 is drawn into purged column 86 when purging purged column 86 prior to any measurements.
  • measurement system 80 measures water level 26 as described in the previously described first preferred embodiment.
  • valve 94 is selectively closed, for example by controller 36 via control line 96, communication of pressure between purged column 86 and tank 10 via passageways 90 and 92 is discor inued, and measurement system 80 serves as a tank leak detector.
  • Reference liquid 40 comprising process liquid 12 remains at a constant level 98 corresponding to level 100 while any chang .
  • valve 94 When valve 94 is selectively opened, for example by controller 36 via control line 96, communication of pressure between purged column 86 and tank 10 is resumed and shortly thereafter a second reading is established by transmitter 42 corresponding to liquid level 32.
  • Calculator 64 calculates an absolute change in liquid level 32 during the predetermined time period utilizing the change in transmitter output signal on line 56 between the start reading and the second reading and specific gravity data 62, and computation storage 66 provides output 68 representative of tank leakage. Since the time period between the start reading and the second reading is substantially short, errors due temperature errors and drifting of transmitter 42 are reduced substantially. If tank 10 has a horizontal surface area uniform in the vertical direction, such as a cylinder positioned on end, volume of leakage can be calculated by multiplying level change of liquid level 32 by surface area.
  • Differential pressure transmitter 42 can be a very sensitive low-range transmitter since common head effects cancel and only small changes in differential pressure are encountered when measuring ref rence level 98 and tank leakage, thereby providing highly accurate leak measurements.
  • Two-way valve 82 interposes between high pressure port 44 and port 48, connecting to passageway 102 which opens to low pressure port 50.
  • Two-way valve 84 interposes between low pressure port 50 and reference column 86, connecting to passageway 104 which opens to high pressure port 44.
  • valve 84 now directs lower specific gravity reference column liquid 40 via passageway 104 to high pressure port 44 of differenticl pressure transmitter 42 and discontinues pressure communication to low pressure port 50.
  • valves 82 and 84 By switching valves 82 and 84 to their alternate positions, communication of pressure heads P ⁇ j ⁇ and P 2 to high p ⁇ assure port 44 and low pressure port 50, respectively, are interchanged.
  • This provides calculator 64 an ability to average differential pressure measurements of sensor 54, as represented by transmitter signal on line 56, eliminating any errors due to zero shifts in differential pressure sensor 54.
  • Plumbing internal to differential transmitter 42 such as a valved manifold, can also permit pressures P A and P 2 to route to opposite pressure ports in a similar manner.
  • the invention disclosed is compatible with existing HTG systems, including those that have been previously installed.

Landscapes

  • Physics & Mathematics (AREA)
  • Fluid Mechanics (AREA)
  • General Physics & Mathematics (AREA)
  • Measurement Of Levels Of Liquids Or Fluent Solid Materials (AREA)

Abstract

Un émetteur de pression différentielle (42) est utilisé pour mesurer le niveau d'eau de décantation (14) se trouvant sous un fluide de traitement (12) et au fond d'un réservoir (10). L'émetteur de pression (42) mesure une différence de pression entre un soutirage de pression (48) du réservoir situé sous un niveau supérieur de l'eau de décantation de densité plus élevée et un second soutirage de pression (24) d'une colonne de référence (22, 86, 88) contenant uniquement un fluide de traitement d'une densité inférieure et débouchant dans le réservoir (10) à un niveau (26) situé au-dessus de l'eau de décantation. La pression différentielle est une fonction de la densité de l'eau (14) et de la charge d'eau (14). En utilisant les données de pression différentielle et de densité, on peut déterminer la hauteur de l'eau (14) se trouvant dans le réservoir (10). La colonne de référence (22, 86, 88) peut être purgée pour éliminer de l'eau ou d'autres impuretés éventuelles. Une partie de la colonne de référence (22, 86, 88) s'étend au moins sur une hauteur aussi importante que le fluide plus léger (12), à l'intérieur du réservoir (10). La colonne de référence peut être une colonne séparée (86, 88) que l'on peut isoler du réservoir (10) en la fermant pour permettre à l'émetteur différentiel (42) de détecter les changements de pression différentielle dus à des changements de niveau du fluide dans le réservoir (10).
PCT/US1991/006868 1990-09-26 1991-09-20 Appareil de mesure du niveau inferieur et des fuites d'eau dans un reservoir Ceased WO1992005408A1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
US58826490A 1990-09-26 1990-09-26
US588,264 1990-09-26

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WO1992005408A1 true WO1992005408A1 (fr) 1992-04-02

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CN (1) CN1061660A (fr)
WO (1) WO1992005408A1 (fr)

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5379638A (en) * 1992-02-04 1995-01-10 Robert Bosch Gmbh Method and device for detecting the fluid level in a tank
CN104035453A (zh) * 2014-05-29 2014-09-10 中冶南方工程技术有限公司 一种煤气柜底部油沟油水界面高度检测方法及其装置
CN107764361A (zh) * 2017-09-13 2018-03-06 美核电气（济南）股份有限公司 用于核电站差压测量的吹扫系统及方法
EP3396333A4 (fr) * 2016-01-27 2019-01-30 Mitsubishi Heavy Industries, Ltd. Dispositif de détection de niveau de liquide d'appareil de distribution de liquide, procédé de détection de niveau de liquide pour appareil de distribution de liquide et appareil de distribution de liquide équipé dudit dispositif de détection de niveau de liquide

Families Citing this family (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN100392362C (zh) * 2006-06-30 2008-06-04 中国科学院合肥物质科学研究院 一种密封油罐液位变送器
DE102017110112A1 (de) * 2017-05-10 2018-11-15 Grohe Ag Verfahren zum Detektieren einer Leckage in einer Flüssigkeitsleitung sowie Wasserzähler mit einer Steuerung zur Durchführung des Verfahrens

Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB1075908A (en) * 1924-12-25 1967-07-19 Deutsche Erdoel Ag Means for determining the level of the interface between a fluid and a displacement liquid in underground reservoirs
US3371534A (en) * 1966-05-10 1968-03-05 Foxboro Co Level sensing apparatus
US4638656A (en) * 1984-10-17 1987-01-27 The Foxboro Company Apparatus and method for calibrating span of pressure measuring instruments
US4643025A (en) * 1985-06-03 1987-02-17 Stone Gerald P System for measuring liquid level in a pressurized vessel
US4765945A (en) * 1985-11-25 1988-08-23 Kraftwerk Union Aktiengesellschaft Method and apparatus for measuring the filling level in a reactor pressure vessel of a boiling-water reactor

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB1075908A (en) * 1924-12-25 1967-07-19 Deutsche Erdoel Ag Means for determining the level of the interface between a fluid and a displacement liquid in underground reservoirs
US3371534A (en) * 1966-05-10 1968-03-05 Foxboro Co Level sensing apparatus
US4638656A (en) * 1984-10-17 1987-01-27 The Foxboro Company Apparatus and method for calibrating span of pressure measuring instruments
US4643025A (en) * 1985-06-03 1987-02-17 Stone Gerald P System for measuring liquid level in a pressurized vessel
US4765945A (en) * 1985-11-25 1988-08-23 Kraftwerk Union Aktiengesellschaft Method and apparatus for measuring the filling level in a reactor pressure vessel of a boiling-water reactor

Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5379638A (en) * 1992-02-04 1995-01-10 Robert Bosch Gmbh Method and device for detecting the fluid level in a tank
CN104035453A (zh) * 2014-05-29 2014-09-10 中冶南方工程技术有限公司 一种煤气柜底部油沟油水界面高度检测方法及其装置
EP3396333A4 (fr) * 2016-01-27 2019-01-30 Mitsubishi Heavy Industries, Ltd. Dispositif de détection de niveau de liquide d'appareil de distribution de liquide, procédé de détection de niveau de liquide pour appareil de distribution de liquide et appareil de distribution de liquide équipé dudit dispositif de détection de niveau de liquide
CN107764361A (zh) * 2017-09-13 2018-03-06 美核电气（济南）股份有限公司 用于核电站差压测量的吹扫系统及方法
CN107764361B (zh) * 2017-09-13 2024-04-30 美核电气（济南）股份有限公司 用于核电站差压测量的吹扫系统及方法

Also Published As

Publication number Publication date
CN1061660A (zh) 1992-06-03

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