Pneumatic level measurement system and method for measurement of powder material in a container.

Field of the invention

[0001]The invention relates to a pneumatic level measurement system and method for measuring the level of a powder material in a container. More specifically, the invention relates to a pneumatic level measurement system and method for measuring the level of alumina oxide or aluminum fluoride in a silo or hopper in an aluminum smelting cell or a connected airslide, silo or hopper to an aluminum smelting cell and in the vicinity of a strong magnetic field. The invention may also be utilized for level measurement in other areas, material and environments as well as other powder material containers as well as other powder material transport systems.

Background of the invention

[0002]During the process of aluminum smelting, aluminum is extracted from alumina oxide, known as alumina. To extract aluminum an electrolysis process known as the Hall-Heroult process is the major production form. Said process is driven by electrical current in an electrolysis cell used to contain a molten bath of cryolite and dissolved alumina. When alumina dissolves in cryolite the melting temperature of alumina is drastically decreased to a temperature of 940-980 °C. Carbon anodes are immersed into the electrolyte cell carrying electrical current which then flows into the molten cryolite containing dissolved alumina. As the electrical current can be 300 500 kA, a minor change in the electrical resistance through the molten cryolite and alumina bath, will result in a huge change in the effect. This increase in resistance in the reduction cell is caused by gas bubbles forming under the anode. This anode effect is sensed and then controlled by a pot controller. To regulate the anode effect and thereby the electrical resistance of the bath, containers known as hoppers or silos containing aluminums fluoride is situated in a superstructure above the bathe and the aluminums fluoride is dispensed into the molten cryolite and alumina bath to regulate the resistance. Said superstructure also contains hoppers or silos containing alumina oxide.

[0003] Due to limitations of technical means and on-site conditions such as the strong currents, high electrical potential and strong magnetic fields from the direct current through the electrolyte cell and the high temperature from the process, it is troublesome and complicated to measure the level of alumina or aluminums fluoride in the containers of the superstructure. Dust from the powder material also makes radar measurement form a distance inaccurate. One of the common process for measuring the level of aluminums fluoride or alumina in the containers of the superstructure is to use tuning force switches. [0004] Other means for measurements of the level of powder material in an aluminum an electrolysis process is disclosed in documents CN 107560691 A, where a conical shaped metal pressure sensor 2 comprising three strain gauges is lowered down in an alumina silo. When the sensor 2 is lowered down through the level surface 5 of the alumina, the pressure sensor 2 emits an electrical signal output [0027] to a logical controller and the length of cable 3 connected to the pressure sensor 2 determines the level of alumina in the silo. Other means for measuring a content in an container is disclosed in application KR 2012/0035754 A, which discloses a device comprises a container 30, a gas discharge unit 50 and a gas feeding unit and method for measuring the level of a container and to measure a level change by detecting a pressure change of gas according to a level change. Patent application WO 00/58015 A1 discloses a level measuring device for a powder sprayer unit containing an inductive proximity sensor 22. Documents EP 0525303 A1 discloses a powder level indicator 21 that is arranged in a powder chamber 20, which is designed as a pneumatic height monitor with a pressure pipe 22 and a membrane 23 in the cross section of this pipe at its lower free end. In the case of pneumatic filling level monitoring, the membrane 23 at the end of the pressure pipe 22 detects the filling level according to the weight of the powder acting on it.

[0005]The above-mentioned solution is adapted for use with the lager bulk alumina silos situated a distance away from the electrolyte cells and away from the magnetic fields and the heat, and it is therefore constructed after different principles and solves a different problem then the invention disclosed herein. As the solution includes electronics inside the container it is unlikely that the solution would be accurate in the containers in relation to the superstructure, or placed above the melt bath, of a typical Hall-Heroult cell due to the previous disclosed on-site conditions caused by the magnetic fields and the heat.

[0006]If the electrolysis process runs out of alumina or aluminums fluoride the process may become be undersaturated, which may lead to increased power consumption and a higher degree of unwanted waste gas.

[0007]It is therefore an aim of the present invention to overcome the shortcomings of the disclosed prior art and to provide an alternative to the prior art. To achieve this objective a device and method according to the independent claims is provided.

Summary of the invention

[0008]The invention is set forth and characterized in the main claims, while the dependent claims describe other characteristics of the invention.

[0009] It is thus provided a system for measurement of the level of powder material in at least one container, wherein the system is comprises at least one conduit for fluid transportation, and at least one pneumatic pressure device, for building up pressure and forcing a fluid through said conduit, and at least one pressure sensor device for measuring the pressure inside said conduit. The conduit has at least a first end connected to the pneumatic pressure device and at least a second end ending inside the container with an opening at the second end at a predetermined distance above a lower bottom of the container.

[0010]In an embodiment of the invention the at least one container is located in an area with a magnetic field and the at least one pneumatic pressure device is located a distance away from the at least one container, wherein the distance equals at least a distance corresponding to said magnetic field being substantially reduced.

[0011]In another embodiment of the invention the conduit fluidly connects the at least one pneumatic pressure device and the at least a second end ending inside the container with an opening at the second end at a predetermined distance above a lower bottom of the container, and wherein the sensor device is located between the at least one pneumatic pressure device and the at least a second end of the conduit, and where the sensor device is in fluid communication with the inside of said conduit to measure the pressure within said conduit.

[0012]In yet another embodiment of the invention the system further comprises means to measuring a powder material in at least two containers, wherein said means comprises the at least one conduit having at least a third end after the conduit is split by a junction in the conduit, wherein the at least third end is ending inside at least the second container with an opening at the at least third end at a predetermined distance above a lower bottom of the at least second container.

[0013]In yet another embodiment of the invention the system further comprises means to measuring a powder material in at least two containers, the system further comprises a conduit selection device, wherein the conduit selection device divides the at least one conduit into at least a first conduit branch and a second conduit branches, wherein the first conduit branch ends in an open conduit end, ending inside a first container with the opening at a predetermined distance above a lower bottom of said container, and wherein the second conduit branch ends in an open conduit end inside a second container with the opening at a predetermined distance above a lower bottom of said container, wherein the conduit selection device may selectively open or close the fluid communication to said at least two branches and the pneumatic pressure device.

[0014]In yet another embodiment of the invention the system further comprises a control unit, for selectable controlling time intervals for when the at least one pneumatic pressure device is to push a fluid through at least one conduit. [0015]In yet another embodiment of the invention the control unit further controls the conduit selection device to control if the fluid from the pressure device is sent to a first conduit branch and/or at least a second conduit branch.

[0016]In yet another embodiment of the invention the fluid is air or an inert gas.

[0017]In yet another embodiment of the invention the pneumatic pressure device is any one of; a pump, a fan, a compressor or an instrument air device.

[0018]In yet another embodiment of the invention the at least one container is a hopper or silo in an aluminum smelting cell and the powder material is alumina or aluminums fluoride.

[0019]It is also provided a method for measuring the level of powder material in at least one container with a pneumatic measurement system as disclosed comprising the steps of activating the at least one pressure device thereby introducing fluid under pressure in and through the conduit, and register by the pressure sensor the pressure in said conduit. If the pressure increases above a predetermined pressure level, this will determine that the level surface of the powder material is at or above the predetermined height level Lcr. Otherwise, if the pressure does not increase above a predetermined pressure level, this will determine that the level surface of powder material is lower than the predetermined height level Lcr.

Brief description of the figures

[0020] These and other characteristics of the invention will become clear from the following description of a preferential form of embodiment, given as a non-restrictive example, with reference to the attached schematic drawings.

Figure 1 is a view of an embodiment of the systems according to the invention with a close to full container of material.

Figure 2 is a view of an embodiment of the systems according to the invention with a close to empty container of material.

Figure 3 is a view of an embodiment of the systems according to the invention with two containers.

Figure 4 is a view of an embodiment of the systems according to the invention with two containers and a selection device.

Figure 5 is a view of an embodiment of the systems according to the invention with multiple branches and containers.

Figure 6 is a view of an embodiment of the systems according to the invention with five containers and a selection device. Figure 7 is a view of an embodiment of the systems according to the invention with two containers and two pressure sensors.

Detailed description of the invention

[0021] The following description will use terms such as “horizontal”, “vertical”, “lateral”, “back and forth”, “up and down”, ’’upper”, “lower”, “inner”, “outer”, “forward”, “rear”, etc. These terms generally refer to the views and orientations as shown in the drawings and that are associated with a normal use of the invention. The terms are used for the reader’s convenience only and shall not be limiting. Like numerals on different drawings describe the same feature. For numerals consisting of a number and a letter, a usage of numerals without a letter refers to any of the numerals with a letter: “16” may stand for any of the numerals “16a” to “16e” in the drawing or to a figure only containing “16”.

[0022] A basic principle of the invention is the ability of monitoring volume parameters, inside or within containers (for example hoppers, silos, tanks, reservoir, etc.).

[0023] During the process of aluminum smelting containers 1 containing the powder material 2 is situated above a bath cell 17. The containers are normally equipped with dispensing means (not shown) at the bottom 11 to gradually dispense the powder material into the bath 17 of an electrolysis process. During this process the powder material 2 is dispensed from the container 1 and the powder material will eventually run out if it is not filled up again with powder material. The invention relates to a system and method for register if the material 2 in the containing 1 is below or above a predetermined level Lcr.

[0024] In figure 1 an embodiment of the pneumatic measurement system is illustrated. The container 1, which is also known as a hopper or silo, any of which would be known to a person skilled in the art, holds the powder material 2. The surface level 3 of the powder material 2 is in figure 1 is close to the top of the container 1 at top filling level Lfull and above the opening 7 of the second end of a conduit 4, indicating that the container is not close to running out of the powder material. The conduit 4 has a first end 5 in fluid connection to a pneumatic pressure device 9. The pneumatic pressure device 9 may be any one of; a pump, a fan, a compressor or an instrument air device capable of supplying an increased air or fluid pressure into the conduit 4. The conduit 4 may be one of the following, but not limited to, a longitudinal rigid or flexible pipe, tube or hose. The conduit 4 may be of any suitable material such as, but not limited to, stainless steel, steel, copper, rubber, Teflon, plastic or other suitable hose, tube or pipe material. In fluid communication with both the pneumatic pressure device 8 and the conduit 4 is a pressure sensor 8. The pressure sensor may be any device such as a pressure instrument or gauge capable of sensing the air or fluid pressure inside the conduit 4. The sensor can be an analog gauge type sensor or an electric switch or transducer type which converts an applied pressure into a measurable electrical signal.

[0025] In figure 2 the surface level 3 of the material 2 is below the opening 7 of the second end 6 of the conduit 4. The height of the opening 7 above the bottom 11 of the container 1 represents a predetermined critical surface level Lcr for the contained material 2. The bottom level Le indicates the level of which the container 1 is empty.

[0026] If the pneumatic pressure device 9 is activated in the situation illustrated in fig.

1, the material 2 in the container 1 will block the opening 7 of the second end 6 of the conduit 4, and the pressure will increase inside the conduit 4. The pressure sensor device 8 will register that there is an increase in pressure and a user or control system 10 will know that the material level inside the container is at least the critical level Lcr or higher. In this way the system described herein is used to measure the amount of powder material in an absolute way i.e. either the amount is at a certain level or higher, or the amount of material is under that level.

[0027] If the pneumatic pressure device 9 is activated in the situation illustrated in fig.

2, the opening 7 of the second end 6 of the conduit 4 will be open to the surroundings, and the pressure inside the conduit 4 will not increase above a predetermined level.

The pressure sensor device 8 will not indicate any increase and a user or control system 10 will know that the material level inside the container is below the critical level Lcr. This will indicate that more alumina or aluminums fluoride material must be added to the containers of the smelting proses to avoid undersaturation.

[0028]Figure 3 illustrates an example of the system in use with two containers la, lb of powder material 2a, 2b. It should be noted that the system can be used to measure the level in any number of containers. In the illustrated example, the conduit 4 has an third end 18 after the conduit 4 is split by a junction 19 in the conduit 4, wherein the third 18 end is ending inside at least the second container lb with an opening 7b at the third end 18 at a predetermined distance Lcr above a lower bottom of the second container lb. The split in the conduit 4 by the junction 19 in figure 3 is illustrated by a T-junction. The junction can be any type of conduit or tube junction that splits or divides a conduit, tube or pipe into multiple branches, in this example two branches 13, 14. In this illustrated example the surface level 3b of the material in container lb is lower that the critical level Lcr and the surface level 3a of the material in container la is higher that the critical level Lcr. In this situation there will be no resistance in the opening 7b of the third end 18 of the conduit 4, and there would be no significant increase in pressure registered by the pressure sensor 8 when activating the pneumatic pressure device 9. In this configuration an operator or control unit 10 would know only that the level in one container 1 is below a critical level Lcr, but not which one. This configuration is a simple and inexpensive way of checking multiple container.

[0029] In the example of figure 3 the pressure sensor 8 is receiving the conduit 4 in one end of pressure sensor 8 and the conduit 4 is exiting the pressure sensor 8 in another end. In figure 1 and 2 the pressure sensor 8 is connected to the conduit in a T- type junction 20. In other examples (not shown) the pressure sensor 8 can be integral parts of the pneumatic pressure device 9. These different variations are merely examples of some of the possible variations and should not be seen as limiting embodiments.

[0030]Figure 4 illustrates an example of the system in use with two containers la, lb of powder material 2a, 2b. It should be obvious that the system in accordance with any embodiment of the invention may be used on any number of containers, and the numbers illustrated herein is for illustrative purposes only and should not be limiting. In the figure the system further comprises a conduit selection device 12. The conduit selection device 12 is a device with means for selectively directing a fluid current to any one of multiple different outputs. Said means for selectively directing a fluid can be valve arrangements or actuators controlling gates or ports. The conduit selection device 19 in figure 4 divides the at least one conduit 4 into at least a first conduit branch 13 and a second conduit branches 14, wherein the first conduit branch 13 ends in an open conduit end, in this example the second end 6 of the conduit, ending inside a first container las with the opening 7a at a predetermined distance Lcr above a lower bottom 11 of the container la, and wherein the second conduit branch 14 ends in an open conduit end, in this example the third end 18 of the conduit, inside a second container lb with the opening 7a at a predetermined distance Lcr above a lower bottom 11 of the container lb. The conduit selection device 12 may selectively open or close the fluid communication to said at least two branches 13, 14 and the pneumatic pressure device 8.

[0031] Figure 4 also illustrates the system with a control unit 10. The control unit 10 may be a computer device or any device with computational and/or controlling means to send and receive signals to and from the pressure sensor 8 and/or the pneumatic pressure device 9 and/or the conduit selection device 12. The control unit 10 has the means and capabilities to read the sensor 8 by receiving sensor signals and to control both the conduit selection device and the pneumatic pressure device. Furthermore, the control unit 10 may comprise timing means for selectable to activate and deactivate the pneumatic pressure device 9 within predetermined time intervals to preformed level measurements at determined intervals. The timing means can also be set to decide when the control unit 10 will control the conduit selection device 12 to change which conduit branch to be in open communication with the pressure device 8 and sensor 8. Furthermore, the control unit 10 may comprise signaling means to signal by sound or light if the system indicates that at least one of the containers are below a critical level Lcr.

[0032]In figure 4 the pressure sensor 8 is illustrated by a pressure transducer sign, and the pneumatic pressure device is illustrated by a compressor sign.

[0033] In figure 5 the system is illustrated in a typical embodiment above a bath 17 of the aluminum oven for the containers to dispense the material into. In this example there is a smaller container 15 typically intended for aluminums fluoride as the powder material 2, and five lager containers 16a-16e typically intended for alumina as the powder material. The illustrated system comprises a control system 10 to control and monitor the functions, at least one conduit 4 for fluid transportation in fluid communication with at least one pneumatic pressure device 9, for building up pressure and pushing a fluid through said conduit 4 when activated or turned on, and at least one pressure sensor device in fluid communication with the conduit 4 and pneumatic pressure device 9, for measuring the pressure inside said conduit 4. The conduit is further connected to, and in fluid communication with, a conduit selection device 12, that selectively open and closes the fluid communication between a first conduit branch 4a, a second conduit branch 4b and the conduit 4. The first conduit branch 4a is divide into five conduit brace ends 18a- 18b ending in five containers 16a- 16b, respectively, a predetermined distance Lcr above the bottom 11 of each container 16a- 16b. Each branch end comprises an opening (not shown). The conduit branch 4b in figure 5 ends in conduit brace end 6 in container 15, with the opening a predetermined distance Lcr above the bottom 11 of said container 15. By adding one or multiple additional containers to be checked by one device, the conduit must be divided into one more or multiple additional branches. Also, multiple individual devices may be used on respective containers throughout a smelting facility, i.e. one device per container.

[0034] The system illustrates in figure 5 can measure if the level in the smaller container 15 separately from the other five container 16a- 126b, by having the fluid communication to the first conduit branches 4a closed and the fluid communication to the second branch conduit 4b open, by selectively opening or closing valves or gates in the conduit selection device 12. If the fluid communication between the first conduit branches 4a and the pneumatic pressure device 9 is open and the fluid communication between the second conduit branches 4b and the pneumatic pressure device 9 is closed, the system will be able to monitor the level of material in all five containers 16a- 16b simultaneous, excluding the container 15 from the reading. [0035]In figure 6 the system is illustrated in a typical example above a bath 17 of the aluminum oven for the containers to dispense the material into. In this example there is five containers 16a-16e. The illustrated system comprises a control system 10 to control and monitor the functions, at least one conduit 4 for fluid transportation in fluid communication with at least one pneumatic pressure device 9, for building up pressure and forcing a fluid through said conduit 4 when activated or turned on, and at least one pressure sensor device 8 in fluid communication with the conduit 4 and pneumatic pressure device 9, for measuring the pressure inside said conduit 4. The conduit 4 is further connected to, and in fluid communication with, a conduit selection device 12, that selectively open and closes the fluid communication between any of the five conduit branches 4a-4e and the conduit 4. In a non-illustrated, example pressure sensors may be respectively fitted to each conduit branches 4a-4e to measure the pressure in each conduit branches 4a-4e respectively. The illustrated example allows for the system to measuring the powder material in all five containers 16a-16e individually by selecting which branch to have an open fluid communication with by actuating the conduit selection device 12. If the conduit selection device 12 selectively opens up conduit 4a and selectively closes conduits 4b-4e, and pressure is reassessed and forced through the conduit system, the pressure will increase and be sense by the pressure sensor. This will determine that the amount of material in container 16a is above the critical height level Lcr. If the conduit selection device 12 selectively opens up conduit 4c and selectively closes conduits 4a, 4c-4e, and pressure is reassessed and forced through the conduit system, the pressure will not increase as the end 18c is above the material inside the container 16c. This will determine that the amount of material in container 16c is under the critical height level Lcr.

[0036] Figure 7 illustrates the system comprises a control system 10 to control and monitor the functions, at least one conduit 4 for fluid transportation in fluid communication with at least one pneumatic pressure device 9, for building up pressure and forcing a fluid through said conduits 4, 4a, 4b when activated or turned on. The conduits 4, 4a, 4b is further connected to, and in fluid communication with, a conduit selection device 12, that selectively open and closes the fluid communication between any of two conduit branches 4a or 4b and the conduit 4. The two pressure sensor devices 8a and 8b in fluid communication with respective conduits 4a and 4c and pneumatic pressure device 9, measures the pressure inside respective conduits 4a, 4b. When multiple sensors 8, 8a, 8b are respectively fitted to conduit branches 4, the pressure in each branch may be monitored separately and continuously.

[0037] Although shown as different elements in the figures, the pneumatic pressure device 9, the pressure sensor 8 and the conduit selection device 12 may also be one single unit or device with multiple means. The distance from the containers and to the hardware i.e. the pneumatic pressure device 9, the pressure sensor 8, the conduit selection device 12 and the control unit must be such a distance that any magnetic field close to the containers and smelt ovens will be reduced. The amount of reduction necessary, and thereby the distance, depends on the sensitivity of the devices and units. Most preferably the fluid of the system is air or other types of suitable gaseous fluids. The amount of air or fluid and the pressure produced by the pneumatic pressure device 9 must not blow the content of the containers 1, 15, 16 out of the containers 1, 15, 16. The activation pneumatic pressure device 9, and thereby releasing pressurized air into the conduits 4, 13, 14, may be done by opening a valve (not shown), turning on the electricity of the system or sending control signals from the control unit.

[0038] The method for measuring the level of powder material in at least one container with a pneumatic measurement system as disclosed herein comprising the steps of first activating the at least one pressure device 9 thereby introducing fluid, preferably a gasses fluid under pressure in and through the at least one conduit 4, 13,

14. After the fluid is introduced the pressure sensor 8 is used to register and read the pressure inside the at least one conduit 4, 13, 14. If the pressure increases above a predetermined level, it is determined that the level surface 3 of the powder material 2 in the at least one container 1, 15, 16 is above the predetermined critical level Lcr. Other vise, if the pressure does not increase above a predetermined level, it is determined that the level surface 3 of powder material 2 in the at least one container 1 ,

15, 16 is lower the predetermined critical level Lcr. The predetermined level for the pressure to increase above might be any level higher than an atmospheric pressure or a reference level set by the ambient surroundings.

[0039] Any numbers of containers 1 may be situated above the bath cell 17, however it is common with anything from one to six baths cells 17. The containers are normally part of a construction known as a superstructure (not shows). It should be obvious that the system could be used for other configurations for melting and producing aluminum, any of which would be known to a person skilled in the art. The type and layout of the facility should not be limiting, as the system can be readily adapted within the scope of the claims. Having described preferred embodiments of the invention it will be apparent to those skilled in the art that other embodiments incorporating the concept may be used. These and other examples of the invention illustrated above are intended by way of example only and the actual scope of the invention is to be determined from the following claims. Reference numerals

1 Container

2 Powder material

3 Surface level of powder material in container

4 Conduit, tube or pipe

5 First end of conduit

6 Second end of conduit

7 Opening in the second end

8 Pressure sensor

9 Pneumatic pressure device

10 Control unit

11 Bottom of the container

12 Conduit selection device

13 First branch

14 Second Branch

15 Aluminums fluoride hopper

16 Alumina hoppers

17 Bath smelt cell

18 Third end of conduit

19 Junction or split in conduit

20 Junction for pressure sensor