RU1784906C - Solid electrolyte dip pick-up - Google Patents

Description

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(21) 4868W25

(22) 09/25/90

() 12/30/92. Bull. IT 8

(71) All-Union Research Institute of Analytical Instrument Making

(72) R.S. Stankevich, L.V. Melnik, E.V. Tseshkovsky and P. B. Karev

(56) Prospectus from Corning Glass. / / Glass Furnace, Oxygen Sensors and Monitors. Corning, N-Y. U.S.A., 14830.

USSR copyright certificate No. 1562828, cl. G 01 N27 / 30.1989. (SUBMERSIBLE SOLID ELECTROLYTE. SENSOR.

(57) Use: control of the oxygen content in the exhaust gases of furnaces in a wide range of concentrations, control of the carbon potential of the atmosphere of heat treatment furnaces. SUMMARY OF THE INVENTION: The sensor comprises a removable sensing element and a screen made of heat-resistant material to protect the ceramic cell from abrasion. The sensing element comprises a metal mandrel with an insulating gasket and a collector ring to which the collector of the inner electrode is connected, and the collector of the outer electrode is connected to the metal mandrel. For galvanic contact with a replaceable assembly (sensing element), the sensor also comprises a collector ring installed in the insulating gasket. The junction of the sensor with the sensor and the junction of ceramics with metal are continuously cooled by water. 1 ill.

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The invention relates to the field of analysis of hot gases, in particular, control of the carbon potential of the atmosphere of heat treatment furnaces of mechanical engineering products, measurement of oxygen content in the exhaust gases of glass melting furnaces, as well as in the production of ceramics, brick, etc.

A submersible electrochemical sensor based on ion-conductive ceramics is known for detecting and incorporating glassmaking furnaces in flue gas control systems, manufactured by Corning Glass, USA.

The sensor contains a ceramic sensor element made of zirconia stabilized with yttrium oxide, made in the form of a tube closed on one side with platinum electrodes on the inside and outside of the closed part, a thermocouple, a protective tube, a sensor head having its own forced air cooling system, in which a fitting for supplying a reference gas (air) to the internal electrode and contacts of down conductors.

The sensor is designed to operate at gas mixture temperatures

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up to 1 ° C ° C. The ion-conducting ceramic tube has a immersion length of up to 600 mm, etc. itself acts as a holder for the sensing element. This makes it possible to transfer the fastener assembly of the sensitive ceramic element to metal ones. parts that are required to have a high degree of tightness to separate the reference and, if not, the probe into the outside of the furnace and the trace is in the low temperature zone. However, the temperature of the head located near the furnace wall may exceed 150 ° C, which leads to oxidation of the contacts and loss of signal and increases the likelihood of depressurization of the ceramic and metal attachment site. This circumstance necessitates the forced cooling of the head with air to a temperature below

150 ° c. . ,. . / ....

A disadvantage of the sensor is the low mechanical strength of the long ceramic tube. When monitoring oxygen in glass melting furnaces in low pressure zones, the sensing element should protrude from the refractory wall to a length of about: 160 mm (6 inches) with a masonry thickness of 600-1000 mm, which requires the use of sensors with a immersion length of 1000 mm. When monitoring the carbon potential in medium- and high-capacity heat treatment furnaces, immersion of the sensor to a depth of 800-1000 mm is required. .

The Corning Glass sensor has a maximum working length. 600 mm which limits its scope. In the working position, the ceramic tube is

.console beam clamped at one end. Static loads arising under the influence of own

the mass of the tube, NaTruck1; bm: vibrations cause the destruction of ceramics. In this case, especially the sky G при is attractive, the horizontal arrangement of the sensor. Fluctuations in the temperature of the tube, especially when it is introduced into and removed from the furnace, contribute to its operation. In order to avoid a shock, the sensor is installed in the furnace with a speed of not more than 25 mm / min, which only reduces, but does not exclude the possibility of its destruction. .

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In order to increase the mechanical strength and increase the immersion part, it is more favorable to provide a ceramic sensor holder made of metal.

Closest to the present invention is an immersion sensor containing a sensing element in the form of a ceramic cell made of ion-conducting material with internal and external electrodes, a holder of the sensing element made of heat-resistant conductive material.

The disadvantage of the sensor is its low temperature stability. The ceramic junction with a heat-resistant metal holder (cermet unit) is located in a high temperature zone (up to 1200 ° C in heat treatment furnaces, up to 1 ° C in glass melting furnaces). Ceramics and metals have a significant difference in thermal expansion coefficients (TCR), and TCR with a different temperature is of a different nature. C: as the temperature rises, the difference in TCR of metals and ceramics increases. Thus, for zirconium dioxide, TCR in the temperature range from 70 to 1000 ° C varies little and has a value of 7.7, 1 / ° C. For high-temperature nickel-based alloys, TCR with a temperature change of 20 to 1000 ° C is (15-17) -10-6, 1 / ° C and 1.5 times higher than TCR in the temperature range of 20-200 ° C. With a difference in the TCR values and their different temperature variations in the ceramic-metal assembly, forces inevitably arise that destroy the layer of high-temperature adhesive and, as a result, lead to depressurization of the assembly. As the temperature rises above 900 ° C, the rupture forces increase, which makes the sensor unsuitable for operation at high temperatures. As a result of loss of tightness, the analyzed mixture enters the comparative electrode, which reduces the accuracy characteristics (a drop of accuracy, sensitivity, stability) and ultimately leads to the destruction of the sensitive element. This phenomenon is also facilitated by the preload of the nozzle for supplying the reference gas to the internal electrode in order to ensure contact, since the force is subjectively regulated and works on the detachment of the element. from the holder 51784906

l The absence of a protective pipe reduces reliability, because ceramic cheek is exposed to particulate matter from the atmospheres analyzed.

A disadvantage of the sensor is that its durability is limited by the service life of the ceramic cell and its mount to the metal holder. The ceramic cell and the attachment unit are subject to faster wear than other structural elements of the sensor due to the above reasons. Construct10

the cell element is carried out by means of a tube connected to a sub-lead fitting. Water is discharged through another nozzle. Both pieces are mounted on the non-immersed part of the protective tube.

The introduction of water into the sealed cavity allows maintaining the temperature of the junction of the ceramic with the metal mandrel of the sensing element at a level of up to 100-150 ° C depending on the flow rate of the cooler (on average about 0 4 m3 / s). At

with the immersed part of the sensor, 15 such temperature values

non-integral, which makes it impossible to remove the sensitive element and leads to the need to replace the sensor as a whole. This significantly affects the reliability indicators, reducing the service life of the sensor by 3-4 times.

The purpose of the invention is to increase the upper limit of operating temperatures, stability of readings and increase the service life of a submersible solid-state sensor.

This goal is achieved in that between the protective tube and the holder of the sensing element of the immersed solid-state electrolyte sensor, a sealed cavity filled with running water is formed by means of the hollow-tip sleeve sensors mounted on the ends of the protective pipe of the flange and the internal head baffle having internal and external threads for mounting the removable sensitive element and screen of heat-resistant material, in the non-immersible part of the protective pipe are two fittings, one of which is connected to Formation in a sealed tube cavity for supplying water to the place of the removable fastening element is sensitive, while the second serves for dewatering.

The essence of the invention lies in the fact that the node connecting the ceramic cell to the holder of the sensing element through an intermediate metal mandrel is subjected to forced cooling by water, for which a tight cavity is formed between the holder and the protective pipe with the help of the flange and the sleeve with a hollow tip installed in the ends of the protective pipe. Cold water supply to mounting point

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cell element is implemented | using a tube connected to the inlet fitting. Water is discharged through another nozzle. Both fittings are mounted on the non-immersed part of the protective tube.

The introduction of water into the sealed cavity allows maintaining the temperature of the junction of the ceramic with the metal mandrel of the sensing element at a level of up to 100-150 ° C depending on the flow rate of the cooler (on average about 0 4 m3 / s). At

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The TCR of the materials of the assembly practically does not change and are close to each other (discrepancy up to 25%), which greatly simplifies the manufacturing technology

0 of this unit, reduces the requirements for bonding material, increases the mechanical and temperature stability of the sensor in a practically unlimited temperature range from above.

The cooling of the ceramic / metal junction allows the sensor element to be removable. This increases the overall life of the sensor. Screen sensitive

The element 0 is also removable, which facilitates the fastening of the sensitive element and protects the sensitive element from the abrasive action of the analyzed medium.

e In the drawing pbkaean submersible electrolyte sensor.

Ceramic cell 1 of the sensor element of the sensor is closed on one side of the pipe 0 KU of ion-conducting ceramic material. Electrodes 2 and 3 are located on the inner and outer sides of cell 1. Cell 1 is reinforced with glue in a metal mandrel 4,

5 on the outside of which the thread is applied. The mandrel k is connected to the holder 5 via a sleeve 6 with a hollow tip having internal and external threads. In this case, the mandrel 4

0 is screwed into the hollow tip of the sleeve 6.

The protective tube 7 is connected to the holder 5 through the flange 8 and the sleeve 6 by welding, which creates

an airtight cavity 9 into which water is supplied to cool the sensor. The sensor element is covered by a screen 10, which is connected to the sleeve 7 by means of an internal thread

1784906

6. Through the holder 5, a thermocouple tl is introduced into the ceramic cell 1. In the non-immersed part of the sensor, two fittings are mounted on the protective pipe by welding. The nozzle 12 serves to supply water through the tube 13 to the cavity 9, and the nozzle 14 serves to drain the water.

A connector 16 is attached to the head 15 for connecting a secondary device to which the cold junctions of the thermocouple 17 and the current output 18 of the solid-electrolyte sensor are connected. A nozzle 19 is located in the head 15 for supplying a reference gas (air) through a tube 20 into the internal cavity of the solid-electrolyte sensor.

In order to remove potentials from the electrodes of the removable sensing element, insulating strips 21 are mounted on the sleeve 6 and the mandrel 4, on which the collector rings 22 are attached, to one of which a current lead 18 is connected, and to the other a lead 23 from the inner electrode 2. Terminal 24 from the outer electrode 2 is welded to a mandrel, through which it is connected via a thread to a protective tube

The sensor operates as follows.

From the inside, the solid-electrolyte cell is washed by the reference gas (air), and from the outside, by the analyzed gas. As a result of the difference in the partial pressures of oxygen on both sides of the ceramic, an electromotive sid (E1C) occurs on the surface of the cell. The sensor EMF with a constant oxygen content in the reference gas and a constant temperature value is determined by the oxygen concentration in the analyzed gas. The stability of metrological tests is achieved by strict separation of the reference and working gases. The supply of cooling water into the cavity leads to a decrease in temperature at the junction of the ion-conducting ceramic material tube with the metal mandrel, which despite the different KTPs at the mandrel and the tube, due to the location of the contact in an area with a temperature of 200 ° C, dramatically reduces the possibility of depressurization and thereby increases the reliability and stability of metrological characteristics.

The threaded connections on the sleeve with the hollow tip are located around

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areas significantly reduced (200 ° C) compared with the working area of the ceramic cell temperature, therefore, are not subject to wear when located inside the furnace space.

The least reliable assembly in the sensor is a ceramic cell, which, with rapid temperature changes, is prone to cracking. Therefore, the sensor element is removable, fixed in the hollow tip of the sleeve with thread on the mandrel and can be replaced with a new one.

The service life of the sensor as a whole is increased by 3-4 times.

The implementation of the proposed invention allows to solve the problem of monitoring the oxygen content in gas mixtures in a wide range of oxygen concentrations and a wide temperature range from 650 to, without the use of complex hot gas sampling systems and sample preparation, which allows the use of a sensor to monitor the carbon potential in furnaces heat treatment, determination of oxygen content in the flue gases of glass melting furnaces and other industries.

The use of an easily replaceable sensitive element extends the life of the product as a whole and reduces the cost of operation.

The economic effect of using the sensor is achieved by improving the quality of metal products during cementation, improving the quality of glass and saving fuel.

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Claims (1)

The claims Immersion solid electrolyte sensor containing a sensitive element in the form of a ceramic cell made of ion-conductive material with internal and external electrodes, down conductors, a holder of conductive material connected to a ceramic cell, a protective tube, a sensor head, characterized in that the purpose of increasing the upper limit of operating temperatures, stability of readings and increasing the term 5 of the service, between the protective tube and the holder there is formed a sealed cavity filled with running water with the help of the flange and the inner partition mounted at the ends of the protective tube 5 ki of the sensor head and sleeve with a hollow tip having internal and external threads for mounting a removable sensitive element and a screen made of heat-resistant material, and in the non-immersed part of the protective pipe HS i / 9 .9, 7 .5 p 21 U 1 & S Editor Compiled by R. Stankevich Tehred M. Morgenthal Order 4362 Circulation VNIIIPI of the State Committee for Inventions and Discover at the State Committee for Science and Technology of the USSR 113035, Moscow, Zh-35, Rauska nab., 4/5 there are two fittings, one of which is connected to a tube installed in the sealed cavity for supplying water to the attachment point of the removable sensing element, and the second is used to drain the water. 23 112 Proofreader S. Baker Subscription