US20130213818A1

US20130213818A1 - Apparatus and method for liquid level measurement in electrolytic cells

Info

Publication number: US20130213818A1
Application number: US13/726,988
Authority: US
Inventors: Mark Erik Nelson
Original assignee: SABIC Innovative Plastics IP BV
Current assignee: SABIC Global Technologies BV
Priority date: 2012-02-17
Filing date: 2012-12-26
Publication date: 2013-08-22
Also published as: WO2013122677A1; BR112014018043A8; EP2815215A1; KR20140126384A; CN104094089A; BR112014018043A2

Abstract

An apparatus and method for detecting a liquid level in an electrolytic cell are disclosed herein, the apparatus comprising a level tube in fluid contact with the electrolytic cell; a proximity sensor positioned to detect the presence or absence of liquid at a predetermined level in the level tube; and a control system responsive to the proximity sensor, wherein the control system is in communication with the liquid level sensor via a communication system. The proximity sensor detects the presence or absence of fluid in the level tube and sends a signal to the control system via the communication system; and the control system provides an indication of liquid level.

Description

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. Provisional Application Ser. No. 61/600,146 filed on Feb. 17, 20012, which is incorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

The subject matter disclosed herein relates to an apparatus and method for detecting a liquid level in an electrolytic cell.
Low or high liquid levels in electrolytic cells may result from non-equilibrium conditions present during shut-down and start-up, as well as from problematic cells having “fast running” diaphragms. A low liquid level in an electrolytic cell, coupled with a failure to detect the low liquid level in a timely manner, can result in a potentially hazardous situation. For example, when the electrolytic process is the chlor-alkali process, and the electrolytic cell is a diaphragm cell, a decrease in the liquid level below the low-low liquid level can result in exposure of the tops of the cathodes to the head space gases of the electrolytic cell, which comprise chlorine gas. When a portion of the surface of the cathode is exposed to the head space gases, the permeability of the diaphragm to hydrogen gas increases, and the potential exists for leakage of hydrogen gas into the head space comprising chlorine gas. When the amount of hydrogen gas in the head space is about 3 weight percent or more, there is a risk of an exothermic reaction of hydrogen with chlorine to form hydrogen chloride, i.e., a hydrogen fire caused by oxidation of hydrogen by chlorine. If the hydrogen concentration is high enough, detonation can also occur. Thus it is desirable to have an apparatus and method for detecting liquid level in an electrolytic cell wherein the liquid level can be continuously monitored from a remote location.
Liquid level can be measured in opaque electrolytic cells using a level gauge. The simplest and most reliable level gauge is a liquid sight monitor, also known as a direct reading level gauge, or sight glass. Under normal conditions, the electrolytic cells can be inspected by an operator at approximately 30-minute intervals. However, this inspection interval may be insufficient to catch “fast running” cells, in which the liquid level can decrease to a dangerously low level in less than 30 minutes.
Many methods for liquid level measurement other than direct visual observation are known. These include the use of float gauges, in which a float rests on the surface of the liquid, and is magnetically or optically coupled to a sensor; and the use of sensors that operate by measuring electrical resistance in the liquid. However, these methods are invasive, i.e., they require a float or a sensor to be in direct contact with the liquid. This is undesirable where the liquid in an electrolytic cell is corrosive. For example, the liquid in the anode half-cell in the chlor-alkali process contains chloride and dissolved chlorine gas, and is therefore highly corrosive. Moreover, the intense magnetic fields, arising from the application of high voltage, that are present during operation of electrolytic cells can interfere with the operation of these liquid level sensors. These harsh conditions can lead to malfunction of the sensors, and even render the sensors inoperable, which makes it difficult to know if the signals generated by the sensors are representative of the actual liquid level in an electrolytic cell. Moreover, the installation of these sensors requires modification of the electrolytic cell, as well as the down-time and capital investment necessary to make the modifications.
For at least these reasons, liquid level sensors in current use can be unreliable or lack cost-effectiveness under the operating conditions of electrolytic cells. It is therefore desirable to have an apparatus and method for detecting a liquid level in an electrolytic cell with improved reliability, particularly under severe operating conditions such as high magnetic fields and corrosive atmospheres. It would be a further advantage if installation does not require modification of existing electrolytic cells. It would be a still further advantage if the apparatus and methods are cost-effective.

BRIEF DESCRIPTION OF THE INVENTION

An embodiment is an apparatus for detecting a liquid level in an electrolytic cell, the apparatus comprising a level tube in fluid contact with the electrolytic cell; a proximity sensor positioned to detect the presence or absence of liquid at a predetermined level in the level tube; and a control system responsive to the proximity sensor, wherein the control system is in communication with the liquid level sensor via a communication system.
Another embodiment is an apparatus for detecting a brine level in a chlor-alkali electrolytic cell, the apparatus comprising a level tube in fluid contact with the chlor-alkali electrolytic cell; a capacitive proximity sensor adjustably mounted on the level tube to detect the presence or absence of brine at a predetermined position on the level tube; a support for positioning and mounting the capacitive proximity sensor on the level tube; and a digital control system responsive to the capacitive proximity sensor, wherein the digital control system is in communication with the capacitive proximity sensor.
Another embodiment is a method for maintaining a target liquid level in an electrolytic cell, the method comprising providing an apparatus comprising a level tube in fluid contact with an electrolytic cell, a proximity sensor positioned on the level tube at a target liquid level to detect the presence or absence of a liquid, and a control system responsive to the proximity sensor, wherein the control system is in communication with the proximity sensor via a communication system, and indicates the presence or absence of the liquid at the target liquid level on the level tube in response to a signal from the proximity sensor; and adjusting the liquid level in the electrolytic cell to the target liquid level in response to the signal.
Another embodiment is a method for maintaining a target brine level in a chlor-alkali electrolytic cell, the method comprising providing an apparatus comprising a level tube in fluid contact with the chlor-alkali electrolytic cell, a capacitive proximity sensor adjustably mounted on the level tube to detect the presence or absence of brine at the target brine level on the level tube, a support for positioning and mounting the capacitive proximity sensor on the level tube, and a digital control system responsive to the capacitive proximity sensor, wherein the digital control system is in communication with the capacitive proximity sensor and indicates the presence or absence of the brine at the target brine level on the level tube in response to a signal from the capacitive proximity sensor; and adjusting the brine level in the chlor-alkali electrolytic cell to the target brine level in response to the signal.
These and other advantages and features will become more apparent from the following description taken in conjunction with the drawing.

BRIEF DESCRIPTION OF THE DRAWING

The foregoing and other features and advantages are apparent from the following detailed description, claims, and examples, taken in conjunction with the accompanying Figure, which is not limiting, and in which:

The Figure is a schematic diagram of an apparatus for detecting liquid level in an electrolytic cell comprising a level tube in fluid contact with the electrolytic cell and a proximity sensor.

DETAILED DESCRIPTION OF THE INVENTION

The inventors hereof have developed an apparatus and method for detecting a liquid level in an electrolytic cell. Accordingly, a level tube is placed in fluid contact with the electrolytic cell to detect the level of the liquid in the cell. The level tube is fitted with a proximity sensor positioned to detect the presence or absence of liquid at a predetermined level in the level tube. A communication system links the proximity sensor to a control system responsive to the proximity sensor. The control system can be used to alert the operator when the fluid level of the electrochemical cell is not within the desired range, or to perform other actions.
Thus, a method for detecting a high or low liquid level in an electrolytic cell comprises use of an apparatus comprising a level tube in fluid contact with an electrolytic cell, a proximity sensor positioned on the level tube to detect the presence or absence of liquid, and a control system responsive to the proximity sensor, wherein the control system is in communication with the proximity sensor via a communication system; and wherein the proximity sensor detects the presence or absence of fluid in the level tube and sends a signal to the control system via the communication system. The control system can then provide an indication of liquid level in response to the signal from the proximity sensor. In a method for maintaining a target liquid level in an electrolytic cell, the liquid level in the electrolytic cell is adjusted to the target level in response to the signal from the proximity sensor to the control system.
Advantageously, the apparatus and methods are reliable under severe operating conditions such as high magnetic fields and corrosive environments. Moreover the apparatus and methods do not require modification of existing electrolytic cells, are cost-effective , and do not require process down-time or large capital investment to implement.
The terms “a” and “an” do not denote a limitation of quantity, but rather the presence of at least one of the referenced item. The term “or” means “and/or.” The open-ended transitional phrase “comprising” encompasses the intermediate transitional phrase “consisting essentially of” and the close-ended phrase “consisting of” Claims reciting one of these three transitional phrases, or with an alternate transitional phrase such as “containing” or “including” can be written with any other transitional phrase unless clearly precluded by the context or art. Recitation of ranges of values are merely intended to serve as a shorthand method of referring individually to each separate value falling within the range, unless otherwise indicated herein, and each separate value is incorporated into the specification as if it were individually recited herein. The endpoints of all ranges are included within the range and independently combinable. Reference throughout the specification to “another embodiment,” “an embodiment,” “some embodiments,” and so forth, means that a particular element (e.g., feature, structure, property, and/or characteristic) described in connection with the embodiment is included in at least one embodiment described herein, and can or cannot be present in other embodiments. In addition, it is to be understood that the described element(s) can be combined in any suitable manner in the various embodiments.
The Figure is a schematic diagram of an apparatus 1 for detecting liquid level (the position of the liquid-gas interface) in an electrolytic cell 11 comprising a level tube in fluid contact with a liquid contained in the electrolytic cell 11 and a proximity sensor 3. In particular, in the Figure, electrolytic cell 11 contains liquid 12 exhibiting a liquid level 8 in electrolytic cell 11. Liquid 12 can be any liquid in the cell. In an embodiment, it is an electrolyte, for example a solution of water in which ions are dissolved. In an embodiment, the liquid is a solution of sodium chloride in water (brine). The liquid level 8 in the cell can vary depending upon process conditions. The liquid level can be adjusted, for example by increasing or decreasing the flow of liquid into or out of the electrolytic cell. Level tube 2 (also known as a direct reading level gauge, or sight glass) is in fluid contact with the liquid 12 in the electrolytic cell so that the liquid level 8 in the level tube 2 is representative of the liquid level 8 in the electrolytic cell. Proximity sensor 3 is positioned adjacent the level tube 2 so as to detect liquid level 8 in the level tube. Measurement zone 5 represents the area in which the proximity sensor detects the presence or absence of liquid. A variety of means can be used to position the proximity sensor 3. For example, the proximity sensor can be imbedded in or attached to a support 7 as shown in the Figure, which is held in place by a clamp, or an elastomeric O-ring 6 as shown in the Figure. In an embodiment, the position of the proximity sensor is fixed, for example by an adhesive. In other embodiments the position of the proximity sensor is adjustable along the vertical axis of the level tube. Liquid level 9 represents a low liquid level, and liquid level 10 represents for example a critical liquid level, at which there is an increase risk of a hazardous condition. The proximity sensor can comprise at least one display light, which is indicative of the presence or absence of liquid at the position of the proximity sensor. The proximity sensor 3 is in communication with a communication bus, for example via electrical connection 4.
The electrolytic cell can be any chemical reactor that utilizes direct current electricity to induce the simultaneous oxidation and reduction of charged chemical components of an electrolyte (ions or a solution containing ions) to produce oxidized and reduced products in a process called electrolysis. The electrolyte can be a solution of an inorganic salt in a solvent, for example water. The electrolyte can also be a molten inorganic salt or oxide. Examples of electrolytes are aluminum, lithium, sodium, potassium, magnesium, calcium, copper, zinc, and lead salts and/or oxides, which are used in the production of the corresponding high purity metals. Specific examples of an electrolyte are bauxite, which is used in the production of aluminum, and sodium chloride, which is used in the simultaneous production of chlorine gas and sodium hydroxide. In electrolysis, an electric voltage is applied to the electrolyte via an anode and a cathode. The oxidation takes place in a half-cell comprising the anode, and the reduction takes place in a half-cell comprising the cathode. For example, in the chlor-alkali process, the electrolyte is a solution of sodium chloride in water (brine). The chloride ions are oxidized to chlorine gas in the half-cell comprising the anode, and water is reduced to hydrogen gas and hydroxide ion in the half-cell comprising the cathode. The brine that bathes the anode, and in which oxidation takes place, is called the anolyte, and the caustic solution which bathes the cathode, and in which reduction takes place, is called the catholyte. In the diaphragm cell process, the two half-cells are separated by a permeable diaphragm, which can be made of asbestos or a ceramic material, which allows migration of sodium ions from the anode half-cell to the cathode half-cells, but not the back-migration of hydroxide ions. Thus in some embodiments, the electrolytic cell is a chlor-alkali electrolytic diaphragm cell, and the liquid is brine. A schematic diagram of an example of a chlor-alkali electrolytic diaphragm cell is provided in the Figure.
The level tube comprises a vertical tube that can be opaque, translucent, or transparent, generally constructed of glass or plastic, positioned outside of the electrolytic cell. The level tube is in fluid communication with the electrolytic cell so that the liquid level in the level tube is the same as the liquid level in the electrolytic cell. With reference to the Figure, the level tube 2 is in fluid contact with the liquid 12 at the side of the electrolytic cell. The level tube connects to the electrolytic cell at a point near the tops of the cathodes and anodes. The dimensions of the level tube can vary widely depending on the requirements of the application, manufacturing considerations, desired visibility of the liquid in the tube, and like considerations. For example, the level tube can have an inside diameter of about 0.2 to about 2 inches, specifically about 0.25 to about 1 inch. The level tube can extend in a vertical direction about 6 to about 30 inches, specifically about 10 to about 20 inches above the tops of the cathodes and anodes.
Although an operator can determine the liquid level in the tank simply by viewing the liquid level in the level tube at various time intervals when the level tube is transparent, as described above, such monitoring is prone to error, and may still not provide adequate warning of a low- or high-level condition if the condition occurs between views. Accordingly, continuous automated monitoring of liquid level, optionally at a remote location, is provided. Continuous automated monitoring of liquid level also allows automated process control for shutting down the electrolytic cell in an emergency situation or for adjusting the liquid level in electrolytic cells.
The inventors hereof have found that continuous monitoring can be provided where the liquid level is detected with a proximity sensor positioned adjacent to the level tube. In an embodiment, the proximity sensor is located on, and in contact with, an outside surface of the level tube. Proximity sensors detect the presence of nearby objects without any physical contact with the object. In the apparatus and method for detecting a liquid level in electrolytic cells, the proximity sensor detects the presence or absence of liquid at its position on the level tube, without coming into physical contact with the liquid. The proximity sensor can send a signal indicating either the presence or absence of liquid at its position on the level tube to the control system via a communication system.
There are many types of proximity sensors, which operate using various types of electromagnetic radiation or acoustic waves to detect target objects. Types of proximity sensors include, but are not limited to, capacitive sensors, eddy-current sensors, inductive sensors, magnetic sensors, optical sensors, infrared sensors, and ultrasound sensors. Any of the foregoing can be used. The proximity sensor can be in a “barrel” (cylindrical) shape or “flat” (planar) shape. Flat proximity sensors can have the advantage of a lower weight than barrel proximity sensors, thereby imposing less stress on the level tube on which it is mounted. The proximity sensor can have a local display. The local display can be a LED or a LCD. A local display advantageously allows an operator to readily determine the operational status of the sensor while visually confirming the liquid level.
In some embodiments, the proximity sensor is a capacitive sensor. The capacitive sensor can have fixed or adjustable capacitance. In some embodiments, the capacitive sensor has adjustable capacitance. When the capacitance is adjustable, the capacitance can be optimized for rapid detection of the presence or absence of liquid at the position of the capacitive sensor on the level tube. When the capacitance is fixed, the capacitance should be such that it is suitable for detection of the presence of absence of liquid. The capacitive sensor should be unaffected by any build-up of solid residue on the inside of the level tube at the measurement position. Exemplary capacitive sensors that can be used are available from Lion Precision of St. Paul, Minn., Dwyer Instruments, Inc. of Michigan City, Ind. and others.
As stated above, the proximity sensor can be associated with the level tube by a variety of means that provide the desired degree of adjustability or fixedness. For example, as shown in the Figure, the proximity sensor rests on an elastomeric O-ring (6 in the Figure) around the level tube and is reversibly affixed to the level tube by way of a support (7 in the Figure). The proximity sensor is readily detached from the support and removed from the level tube. The position of the O-ring is readily adjustable by sliding along the vertical axis of the level tube. Thus, the position of the proximity sensor along the vertical axis of the level tube can be easily adjusted. The electrical connection to the proximity sensor can be fixed or adjustable and/or detachable. In an embodiment, the electrical connection is flexible so that the proximity sensor can be removed from the level tube for inspection and repair without disconnecting the electrical connection. Thus adjusting the position of the proximity sensor on the level tube and maintenance of the proximity sensor can be done without interrupting the normal operation of the electrolytic cell.
In a method of detecting the liquid level of an electrolytic cell, a target liquid level is determined, for example, the liquid level that provides a good balance of productivity, efficiency, and safety. The target liquid level depends on the type of electrolytic process and the type of electrolytic cell being used. The target liquid level can be identified with reference to any point within the electrolytic cell, for example the top of the cell, or the vertical distance measured from the top of the cathodes and anodes. When the electrolytic process is the chlor-alkali process, and a diaphragm cell such as the one schematically depicted in the Figure is used, the liquid level detected is that of the anolyte, i.e. the brine bathing the anode. The target liquid level can be about 4 to about 12 inches, specifically about 5 to about 10 inches, and more specifically about 6 to about 8 inches, above the top of the cathode.
In some embodiments, a single proximity sensor is used to provide an indication of a low liquid level relative to the target liquid level. When the liquid level represents a low liquid level, the liquid level can be 0 to about 70%, specifically 0 to about 60%, more specifically 0 to about 50% of the target liquid level. The liquid level can be 0 to about 6 inches, specifically 0 to about 5 inches, and more specifically 0 to about 4 inches, above the top of the cathode in the electrolytic cell. In some embodiments, a single proximity sensor is used to provide an indication of a high liquid level relative to the target liquid level, for example the top of the cell. When the liquid level represents a high liquid level, the liquid level can be about 70 to about 95%, specifically about 70 to about 90%, more specifically about 80 to about 90% of the target liquid level. The high liquid level can be about 6 to about 3 inches, specifically 6 to about 4 inches, and more specifically 6 to about 5 inches below the top of the electrolytic cell.
A plurality of proximity sensors can be positioned at various locations on the level tube. In some embodiments, two proximity sensors are positioned on the level tube. In this configuration, the first proximity sensor can detect a first liquid level, and the second proximity sensor can detect a second liquid level below the first liquid level. The two proximity sensors can be used to provide indications of two liquid levels, for example the first proximity sensor can be used to provide a low liquid level indication, and the second proximity sensor can be used to provide a low-low liquid level indication. Indications of low liquid level and low-low liquid level are indications that action should be taken by an operator to increase the liquid level to the target liquid level, for example, by increasing the flow rate of the liquid into the electrolytic cell. The second proximity sensor, which provides a low-low liquid level indication, can serve as a back-up to the first proximity sensor, which provides a low liquid level indication.
When the first liquid level represents a low liquid level, the first liquid level can be about 40 to about 80%, specifically about 50 to about 70%, of the target liquid level. When the second liquid level represents a low-low liquid level, the second liquid level can be 0 to about 40%, specifically about 20 to about 40%, and more specifically about 30 to about 40%, of the target liquid level. The first liquid level can be about 2 to about 6 inches, specifically about 3 to about 5 inches, and more specifically about 3.5 to about 4.5 inches above the top of the cathode in the electrolytic cell. The second liquid level can be 0 to about 4 inches, specifically about 1 to about 3 inches, and more specifically about 2 to about 3 inches, above the top of the cathode in the electrolytic cell.
A reduction in liquid level in the electrolytic cell below the low-low level described above is a potentially hazardous condition. For example, when the electrolytic process is the chlor-alkali process, and the electrolytic cell is a diaphragm cell, such as the one schematically depicted in the Figure, a further decrease in the liquid level below the low-low liquid level can result in exposure of the tops of the cathodes to the gases in the head space of the electrolytic cell, which comprise chlorine gas. When the surface of the cathode is exposed to the head space atmosphere, the permeability of the diaphragm to hydrogen gas increases, and the potential exists for leakage of hydrogen gas into the head space comprising chlorine gas. When the amount of hydrogen gas in the head space is about 3 weight percent or more, there is a risk of reaction of hydrogen with chlorine to form hydrogen chloride, i.e. a hydrogen fire fueled by oxidation of hydrogen by chlorine. If the hydrogen concentration is high enough, detonation can also occur. Thus, in some embodiments, a proximity sensor can be positioned on the level tube at a liquid level at a liquid level of 0 to about 2 inches, specifically 0 to about 1 inch, and more specifically, 0 to about 0.5 inch, above the top of the cathode in the electrolytic cell. When a signal is received from a proximity cell so positioned on the level tube indicating the absence of liquid, immediate steps can be taken to reduce the risk of a hazard such as a hydrogen fire or detonation. These steps include turning off the electric power to the diaphragm cells and purging the head space of the diaphragm cells with nitrogen, another inert gas, or steam. A control system can be designed so that when a signal from a proximity sensor so positioned is received, controls which can shut off electrical power to the diaphragm cell, and which can purge the head space of the diaphragm cell with an inert gas or steam, are automatically actuated. The design of such control systems are within the ability of the skilled person in the art.
A first and second proximity sensor can also be used to provide indications of high and low liquid levels. For example, a first liquid level, detected by the first proximity sensor, can be a high liquid level, and a second liquid level, detected by the second proximity sensor, can be a low liquid level, each relative to a target liquid level determined by the top of the cathode in the electrolytic cell. When the first liquid level represents a high liquid level, the first liquid level can be about 110 to about 150%, specifically about 110 to about 140%, and more specifically about 110 to about 130%, of the target liquid level. The first liquid level can be about 7 to about 12 inches, specifically about 7 to about 11 inches, and more specifically about 7 to about 10 inches, above the top of the cathode in the electrolytic cell. When the second liquid level represents a low liquid level, the second liquid level can be 0 to about 40%, specifically about 20 to about 40%, and more specifically about 30 to about 40%, of the target liquid level. The second liquid level can be 0 to about 4 inches, specifically about 1 to about 3 inches, and more specifically about 2 to about 3 inches, above the top of the cathode in the electrolytic cell.
The configuration with two or more proximity sensors also allows for redundancy. For example, if the first proximity switch fails, the second proximity switch can provide a backup signal for low liquid level. Various methods for providing redundancy in liquid level detection, such as providing a plurality of proximity sensors for each electrolytic cell and/or a plurality of communication pathways for each proximity sensor will be readily apparent to the skilled person in the art.
The proximity sensor is in communication with a control system via a communication system. The communication system can be a direct electric wire connection or wireless, including infrared. The communication system can be based on an industrial computer network protocol, for example an industrial Ethernet or a fieldbus. Fieldbus is the name for a family of industrial computer network protocols standardized under International Electrotechnical Commission (IEC) Standard 61158. Fieldbus computer network protocols include Foundation Fieldbus H1, ControlNet, Profibus (process fieldbus), P-Net, Foundation Fieldbus HSE (High Speed Ethernet), WorldFIP, and Interbus. Computer network protocols related to fieldbus include AS-Interface (Actuator Sensor Interface, or AS-I), CAN bus (controller area network), Interbus, LonWorks, Modbus, Bitbus, CompoNet, SafetyBUS p, Sercos interface, and RAPIEnet. Industrial Ethernet network protocols include EtherCAT, EtherNet/IP, Ethernet Powerlink, BACnet, Profinet IO, Profinet IRT, SafetyNET p, Sercos III, TTEthernet, Varan, and RAPIEnet.
In some embodiments, the communication system can be fieldbus, Profibus, industrial Ethernet, or AS-Interface (Actuator Sensor Interface, or AS-i), more specifically an AS-Interface. AS-Interface is designed for networking simple field input/output devices, including binary On/Off devices, in discrete manufacturing and process applications using a single 2-conductor cable. Binary On/Off devices that can be networked with AS-Interface include actuators, sensors, rotary encoders, analog inputs and outputs, push buttons, and valve position sensors. The communication procedure in an AS-Interface is a master-slave method, by which the master initiates data exchange with a slave and requires the slave to respond within its defined maximum time. Thus, the AS-Interface comprises a network master, a plurality of network slaves, which are signal input and output modules, a power supply, which powers the network slaves, and which enables communication with the network master, and wiring infrastructure, comprising 2-conductor cables. AS-Interface is well-suited as a communication system for proximity sensors.
The control system can be a digital control system (DCS). Examples of digital control systems are microcontrollers, application-specific integrated circuits, programmable logic controllers (PLC, programmable controller), microcomputers, and mainframe computers. Microcomputers include, for example, workstations, personal computers (PC), portable computers, laptop computers, and tablet computers.
The control system is in communication with the proximity sensor, and is responsive to the proximity sensor. In particular, the proximity sensor generates a signal, for example an electric signal, which is indicative of the presence or absence of liquid at its position on the level tube. This signal is transmitted via the communication system to the control system. The control system can be in communication with a plurality of proximity sensors positioned to detect the liquid levels in a plurality of electrolytic cells via the communication system. Based on signals received from the plurality of proximity sensors via the communication system, the control system can indicate the presence or absence of liquid as well as the identity and location of the electrolytic cell for each proximity sensor. In this way, the liquid level in a plurality of electrolytic cells can be monitored from a remote location. The control system can be programmed to issue an alarm as a function of electrolytic cell location when the liquid level drops out of the range of the proximity sensor. The alarm can be a light alarm, an auditory alarm, or a combination thereof. The alarm can also be in the form of an electronic signal to a receiver such as a pager.
The control system can be programmed to transform signals form the proximity sensors to a numerical or graphical display of liquid level for each electrolytic cell being monitored. The control system can also be programmed to store and to display the liquid levels as a function of time. The programming can be done using commercially available software, for example, LabVIEW, available from National Instruments Corporation of Austin, Tex. LabVIEW is a graphical programming environment that uses graphical icons including graphical wires to generate programs in a format resembling a flowchart.
Methods for detecting liquid level in an electrolytic cell and for maintaining a target liquid level in an electrolytic cell are readily apparent from the foregoing description. Thus a method for detecting liquid level in an electrolytic cell comprises providing an apparatus comprising a level tube in fluid contact with an electrolytic cell, a proximity sensor positioned on the level tube below a target liquid level to detect the presence or absence of liquid, and a control system responsive to the proximity sensor, wherein the control system is in communication with the proximity sensor via a communication system; wherein the proximity sensor detects the presence or absence of fluid in the level tube and sends a signal to the control system via the communication system; and the control system provides an indication of liquid level in response to the signal from the proximity sensor. Moreover, a method for maintaining a target liquid level in an electrolytic cell comprises providing an apparatus comprising a level tube in fluid contact with an electrolytic cell, a proximity sensor positioned on the level tube below the target liquid level to detect the presence or absence of liquid, and a control system responsive to the proximity sensor, wherein the control system is in communication with the liquid level sensor via a communication system, and provides an indication of liquid level in response to a signal from the proximity sensor; and adjusting the liquid level in the electrolytic cell to the target level in response to the signal. Either of the foregoing methods can further comprise determining a target level for the liquid level, and determining the presence or absence of liquid relative to the target level. Adjusting the liquid level can be performed by the control system or a human operator.
In another embodiment, a method for maintaining a target liquid level in an chlor-alkali electrolytic diaphragm cell comprises providing an apparatus comprising a level tube in fluid contact with the chlor-alkali electrolytic cell, a capacitive proximity sensor adjustably mounted on the level tube to detect the presence or absence of a brine at a predetermined position on the level tube, a support for positioning and mounting the capacitive proximity sensor on the level tube, and a digital control system responsive to the capacitive proximity sensor, wherein the digital control system is in communication with the capacitive proximity sensor and indicates the presence or absence of the brine at the predetermined position on the level tube in response to a signal from the proximity sensor; and adjusting the brine level in the chlor-alkali electrolytic cell to the target level in response to the signal. For example, a method for maintaining a target liquid level in a chlor-alkali electrolytic diaphragm cell comprises detecting with a capacitive proximity sensor the presence or absence of a brine at a predetermined position on a level tube in fluid contact with the chlor-alkali electrolytic cell, sending a signal from the capacitive proximity sensor to a digital control system in communication with the capacitive proximity sensor indicating the presence or absence of the brine at the predetermined position on the level tube; generating a signal from the control system indicating the presence or absence of the liquid at the predetermined position on the level tube; and adjusting the brine level in the chlor-alkali electrolytic cell to the target level in response to the signal from the control system.
The apparatus for detecting a liquid level in an electrolytic cell can also be used to monitor inspection rounds made by an operator of the electrolytic cell. Operators can make inspection rounds at fixed intervals of time, for example at 30-minute intervals, to determine liquid levels by visual inspection of level tubes. When proximity sensors are positioned on the level tubes, the operator can inspect the proximity sensor at the same time. The operator can temporarily adjust the position of the proximity sensor above the actual liquid level to generate a signal for the absence of liquid, and then replace it to its original position. In this way, an inspection log based on brief indications of the absence of liquid at fixed time intervals can be generated by the digital control system.
The control system can also be programmed to automatically adjust the fluid level in the electrolysis cell in response to indications of low or high fluid levels detected by the proximity sensors. In this method, the valves and/or pumps that control the flow of liquid in and out of the electrolytic cell are actuated valves and pumps, capable of being turned on and off, and adjusted, based on signals received from the control system via a control bus. Apparatus and methods for setting up automatic control of liquid level in an electrolytic cell will be apparent to the skilled person in the art based on the description of the apparatus and methods herein.
While the invention has been described in detail in connection with only a limited number of embodiments, it should be readily understood that the invention is not limited to such disclosed embodiments. Rather, the invention can be modified to incorporate any number of variations, alterations, substitutions, or equivalent arrangements not heretofore described, but which are commensurate with the spirit and scope of the invention. Additionally, while various embodiments of the invention have been described, it is to be understood that aspects of the invention may include only some of the described embodiments. Accordingly, the invention is not to be seen as limited by the foregoing description, but is only limited by the scope of the appended claims.

Claims

What is claimed is:

1. An apparatus for detecting a liquid level in an electrolytic cell, the apparatus comprising

a level tube in fluid contact with the electrolytic cell;

a proximity sensor positioned to detect the presence or absence of liquid at a predetermined level in the level tube; and

a control system responsive to the proximity sensor, wherein the control system is in communication with the proximity sensor via a communication system.

2. The apparatus of claim 1, wherein the position of the proximity sensor is adjustable along the vertical axis of the level tube.

3. The apparatus of claim 1, wherein the proximity sensor is a capacitive proximity sensor.

4. The apparatus of claim 5, wherein the capacitive proximity sensor has a fixed capacitance for detecting the presence or absence of liquid in the level tube.

5. The apparatus of claim 5, wherein the capacitive proximity sensor has an adjustable capacitance tunable to a value effective to detect the presence or absence of liquid in the level tube.

6. The apparatus of claim 5, wherein the capacitive proximity sensor has a flat configuration and an adjustable capacitance.

7. The apparatus of claim 1, wherein the communication system is a digital communication bus.

8. The apparatus of claim 1, wherein the control system issues a signal to an operator in response to a signal from the proximity sensor.

9. The apparatus of claim 1, wherein the liquid is an electrolyte.

10. The apparatus of claim 1, wherein the electrolytic cell is a chlor-alkali electrolysis diaphragm cell.

11. The apparatus of claim 10, wherein the liquid is brine.

12. The apparatus of claim 1, wherein the proximity sensor detects a low liquid level, and wherein the low liquid level is 0 to about 70 percent of a target liquid level.

13. The apparatus of claim 12, wherein a target liquid level is about 6 to about 8 inches above the top of a cathode in the electrolytic cell; and wherein the low liquid level is 0 to about 4 inches above the top of the cathode in the electrolytic cell.

14. The apparatus of claim 1, comprising a first proximity sensor and a second proximity sensor, wherein the first proximity sensor detects a first liquid level, and the second proximity sensor detects a second liquid level below the first liquid level.

15. The apparatus of claim 14, wherein the first liquid level represents a low liquid level and the second liquid level represents a low-low liquid level, and wherein the first liquid level is about 40 to about 80 percent of a target liquid level, and the second liquid level is 0 to about 40 percent of the target liquid level.

16. The apparatus of claim 14, wherein a target liquid level is about 6 to about 8 inches above the top of a cathode in the electrolytic cell; wherein the first liquid level represents a low liquid level and the second liquid level represents a low-low liquid level; and

wherein the first liquid level is about 3 to about 5 inches above the top of the cathode in the electrolytic cell, and the second liquid level is about 2 to about 3 inches above the top of the cathode in the electrolytic cell.

17. The apparatus of claim 14, wherein the first liquid level represents a high liquid level and the second liquid level represents a low liquid level, and wherein the first liquid level is about 110 to about 130 percent of a target liquid level, and the second liquid level is 0 to about 40 percent of the target liquid level.

18. The apparatus of claim 14, wherein a target liquid level is about 6 to about 8 inches above the top of a cathode in the electrolytic cell; wherein the first liquid level represents a high liquid level and the second liquid level represents a low liquid level; and

wherein the first liquid level is about 7 to about 10 inches above the top of the cathode in the electrolytic cell, and the second liquid level is about 2 to about 3 inches above the top of the cathode in the electrolytic cell.

19. An apparatus for detecting a brine level in a chlor-alkali electrolytic cell, the apparatus comprising

a level tube in fluid contact with the chlor-alkali electrolytic cell;

a capacitive proximity sensor adjustably mounted on the level tube to detect the presence or absence of brine at a predetermined position on the level tube;

a support for positioning and mounting the capacitive proximity sensor on the level tube; and

a digital control system responsive to the capacitive proximity sensor, wherein the digital control system is in communication with the capacitive proximity sensor.

20. A method for maintaining a target liquid level in an electrolytic cell, the method comprising

providing an apparatus comprising

a level tube in fluid contact with an electrolytic cell,

a proximity sensor positioned on the level tube at a target liquid level to detect the presence or absence of a liquid, and

a control system responsive to the proximity sensor, wherein the control system is in communication with the proximity sensor via a communication system, and indicates the presence or absence of the liquid at the target liquid level on the level tube in response to a signal from the proximity sensor; and

adjusting the liquid level in the electrolytic cell to the target liquid level in response to the signal.

21. The method of claim 20, the method further comprising

detecting with the proximity sensor the presence or absence of the liquid at the target liquid level on a level tube;

sending a signal from the proximity sensor to the control system in communication with the proximity sensor indicating the presence or absence of the liquid at the target liquid level on the level tube;

generating a signal from the control system indicating the presence or absence of the liquid at the target liquid level on the level tube; and

adjusting the liquid level in the electrolytic cell to the target liquid level in response to the signal from the control system.

22. The method of claim 20, wherein the proximity sensor comprises a display.

23. The method of claim 20, wherein the proximity sensor is a capacitive proximity sensor.

24. The method of claim 23, wherein the capacitive proximity sensor has a fixed capacitance for detecting the presence or absence of liquid in the level tube.

25. The method of claim 23, wherein the capacitive proximity sensor has an adjustable capacitance tunable to a value effective to detect the presence or absence of liquid in the level tube.

26. The method of claim 23, wherein the capacitive proximity sensor has a flat configuration and an adjustable capacitance.

27. The method of claim 20, wherein the communication system is a digital communication bus.

28. The method of claim 20, wherein the control system issues a signal to an operator when the liquid is present or absent at the target liquid level on the level tube.

29. The method of claim 20, wherein the liquid is an electrolyte.

30. The method of claim 20, wherein the proximity sensor detects a low liquid level, and wherein the low liquid level is 0 to about 70% of the target liquid level.

31. The method of claim 30, wherein the target liquid level is about 6 to about 8 inches above the top of a cathode in the electrolytic cell; and wherein the low liquid level is 0 to about 4 inches above the top of the cathode in the electrolytic cell.

32. The method of claim 20, wherein the apparatus comprises a first proximity sensor and a second proximity sensor, wherein the first proximity sensor detects a first liquid level, and the second proximity sensor detects a second liquid level below the first liquid level.

33. The method of claim 32, wherein the first liquid level represents a low liquid level and the second liquid level represents a low-low liquid level, and wherein the first liquid level is about 40 to about 80 percent of the target liquid level, and the second liquid level is 0 to about 40 percent of the target liquid level.

34. The method of claim 32, wherein the target liquid level is about 6 to about 8 inches above the top of a cathode in the electrolytic cell; wherein the first liquid level represents a low liquid level and the second liquid level represents a low-low liquid level; and

35. The method of claim 32, wherein the first liquid level represents a high liquid level and the second liquid level represents a low liquid level, and wherein the first liquid level is about 110 to about 130 percent of the target liquid level, and the second liquid level is 0 to about 40 percent of the target liquid level.

36. The method of claim 32, wherein the target liquid level is about 6 to about 8 inches above the top of a cathode in the electrolytic cell; wherein the first liquid level represents a high liquid level and the second liquid level represents a low liquid level; and

37. A method for maintaining a target brine level in a chlor-alkali electrolytic cell, the method comprising

providing an apparatus comprising

a level tube in fluid contact with the chlor-alkali electrolytic cell,

a capacitive proximity sensor adjustably mounted on the level tube to detect the presence or absence of brine at the target brine level on the level tube,

a support for positioning and mounting the capacitive proximity sensor on the level tube, and

a digital control system responsive to the capacitive proximity sensor, wherein the digital control system is in communication with the capacitive proximity sensor and indicates the presence or absence of the brine at the target brine level on the level tube in response to a signal from the capacitive proximity sensor; and

adjusting the brine level in the chlor-alkali electrolytic cell to the target brine level in response to the signal.

38. The method of claim 37, further comprising

detecting with a capacitive proximity sensor the presence or absence of brine at the target brine level;

sending a signal from the capacitive proximity sensor to the digital control system indicating the presence or absence of the brine at the target brine level on the level tube;

generating a signal from the digital control system indicating the presence or absence of the brine at the target brine level on the level tube; and

adjusting the brine level in the chlor-alkali electrolytic cell to the target brine level in response to the signal from the digital control system.