CZ2006211A3 - Thermocouple probe with a casing for measuring temperature values in extreme conditions - Google Patents

Abstract

The thermocouple probe for measuring temperatures in extreme conditions with the housing, according to the invention, is that the outer sapphire sleeve (1) is formed by monocrystalline sapphire, which is defined as a co-valentine form of alumina corresponding to the crystallographic modification of corundum, where the atoms of the ideal crystalline grid are regularly arranged in formulas repeating in a given direction throughout the volume. The thermocouple probes of the invention are useful for measuring temperature at pressures above 1 MPa, and / or at temperatures above 800 degC and / or in strongly corrosive environments and / or moving solids with a Mohs scale hardness level, higher The thermocouple probe consists of an outer sapphire sleeve (1), at least one inner capillary (2) and at least one thermocouple (3) fixed by strengthening the first thermocouple probe head (4), from which the potential on the thermocouple corresponding to the measured temperature is subtracted.

Description

BACKGROUND OF THE INVENTION The present invention relates to a thermocouple probe for measuring temperatures in extreme conditions, in particular for measuring temperatures at pressures above 1 MPa, and / or at temperatures above 800 ° C and / or in highly corrosive environments and / or moving solids with hardness grades. Mohs scale greater than 5.

BACKGROUND OF THE INVENTION

High temperature can be measured in different ways, either directly or indirectly. At temperatures above 600 ° C, the indirect temperature measurement is carried out with a pyrometer. The advantage of this approach is contactless measurement, in which the measuring probe is not exposed to process conditions. However, this procedure cannot be applied if we want to know the temperature inside a confined object such as a glass melt stream or other closed process processes.

Directly the temperature can be measured by means of thermocouples immersed in the measured medium. There are several basic types of thermocouples - type S (Pt-PtRh10), type R (PtPtRh13), or type B (PtRh6 - PtRh30) are used preferably at temperatures above 1000 ° C. The W-Re thermocouple is used at temperatures above 1600 ° C. Conversely, at temperatures below 1000 ° C, a K-type (Ni-NiCr) thermocouple is used. Unprotected thermocouples very often suffer from conditions in the measurement area and their lifetime without a protective case would be very short. For example, platinum metals rapidly brittle and break in the presence of hydrogen. On the other hand, other metals are easily oxidized. Heavy metals present in some measurements form alloys with the thermocouples, and again damage the thermocouple.

The fact that the thermocouples themselves are easily damaged during the process means that they must practically always be protected by an external protective sleeve. The temperature is then measured by means of a so-called measuring probe, which consists of a housing protecting the thermocouple, a thermocouple and a thermocouple fastening over the thermowell head. The probe housing material must be mechanically and chemically resistant and must conduct heat quickly to minimize the response time of the entire probe.

The materials used as protective probe housings often differ. The simplest is to use metal alloys. Such a housing is inexpensive, has a high thermal conductivity and, above all, is flexible, which increases the resistance of the wells in an environment where mechanical impacts occur. However, metal housings have very low mechanical abrasion resistance, chemical corrosion resistance and are not usable at high temperatures.

Another material for the probe housings is ceramic. Ceramics are excellent in environments where metallic materials do not meet due to low heat resistance, ie above 1000 ° C, or do not meet due to corrosive environments. The most commonly used ceramic is corundum ceramic, which contains corundum form of alumina. The corundum content in ceramics may vary depending on the severity of the conditions. Corundum ceramics with the highest corundum content contain 99.7 wt. aluminum oxide. The advantage of ceramics with a high corundum content is abrasion resistance and high thermal and chemical resistance. The disadvantage compared to ceramics with a lower content of corundum is lower resistance to heat shocks and impacts, and last but not least the price. The cost can be reduced by reducing the alumina content, for example by adding silica. This, of course, also reduces the quality of protection.

Examples of other ceramics used are those containing zirconia or silicon carbide. These ceramics are more resistant to thermal shocks than corundum ceramics. Ceramics can also contain a number of other impurities that can modify their properties depending on the application.

Protective housings, both metal and ceramic, can be covered with a protective material that increases their resistance to corrosion or mechanical abrasion. An example is stainless steel metal housings that are coated with silicon carbide. These probes are used in the temperature measurement process, for example, in fluidized bed boilers in which fuel or fly ash is moved. Very hard silicon carbide retards the abrasion of soft metal by moving powder. Similarly, ceramic sleeves coated with platinum are used in glass melting furnaces. Platinum prevents the direct reaction of the glass melt with the corundum well and thus increases the life of the well several times.

Despite all these possibilities, there are a number of manufacturing processes where the temperature measurement process is critical. In general, temperature measurement processes at high pressures, • 9

9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 • 9 99 99 99 99 99 at high temperatures above 1000 ° C, in environments with moving solid, very hard substances, or substances that are highly corrosive represent a serious problem.

Often the solutions used do not meet the requirements due to the short life span or the high price.

SUMMARY OF THE INVENTION

These problems are overcome by a thermocouple probe for measuring temperatures under extreme conditions with a housing according to the invention, which consists of a single crystal sapphire defined as a rhombohedral form of alumina corresponding to the crystallographic modification of corundum where the ideal crystal lattice atoms are regularly arranged in a pattern repeating in a given direction throughout the volume.

The sapphire can be tempered for at least 1 hour at temperatures above 1200 ° C.

The housing material comprises at least 90% by weight alumina and the remainder is other oxides selected from Group IV. to VII.B of the Periodic Table of the Elements, while maintaining the crystallographic modification of corundum.

The thermocouple probe consists of an outer sapphire capsule (1), at least one inner capillary (2) and at least one thermocouple (3) attached by means of reinforcing elements to the thermocouple probe head (4), from which the thermocouple potential corresponding to the measured temperature is read.

The sapphire sheath preferably has an outer diameter of 1 to 30 mm, preferably less than 16 mm, and a wall thickness of greater than 0.1 mm, preferably more than 1 mm.

The thermocouple probe of the invention is suitable for measuring temperatures at pressures above 1 MPa, and / or temperatures above 800 ° C and / or in a highly corrosive environment and / or in moving solids environments with a Mohs scale hardness greater than 5 .

The use of a thermocouple probe is particularly suitable for measuring the temperature of molten glass or in glass or porcelain furnaces or in furnaces for sintering or pressing ceramic at high temperature, or for measuring temperature in fluidized bed boilers. Also suitable for temperature measurement in pollutant removal processes.

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From the gaseous phase, such as ash removal, desulphurisation, nitrogen oxides removal and Claus process, or when measuring temperature during decomposition of solid samples prior to their elemental analysis or when measuring temperatures in metal melting furnaces or when measuring temperatures at Gasification of organic substances, in the production of ammonia or other chemical syntheses, at temperatures above 1000 ° C.

The use of monocrystalline sapphire as a construction material for the manufacture of thermocouple probe housings greatly extends their service life. The process of temperature measurement, especially under demanding operating conditions, ie at temperatures above 1000 ° C, at high pressure, or in the presence of corrosive compounds, will thus become significantly more reliable.

Sapphire is generally defined as optically transparent corundum, a variant of alumina. Monocrystalline sapphire is defined as the rhombohedral form of alumina, where the atoms of the ideal crystalline lattice are regularly arranged in a firmly repeating pattern. This pattern varies according to direction, but always repeats regularly throughout the volume of the material. The principal difference between monocrystalline sapphire and corundum ceramics is that in sapphire there is no grain boundary through which the sink corrosion is accelerated. Corundum ceramics is actually a polycrystalline, where the condition of uniformly repeating formula of atoms in all directions is not fulfilled, because each individual grain of the ceramics may be differently oriented.

Places where the crystallographic grid of corundum is broken or even completely broken, as in the case of ceramics, albeit sintered, are the point of entry of corrosion and abrasion. Monocrystalline sapphire combines the chemical and mechanical resistance of said form of alumina and the homogeneity of the material making maximum use of a solid and uninterrupted bond within the single crystal. Even though poor quality sapphire may locally cause crystallographic lattice defects or even twins, the number of sites accessible to corrosive substances is orders of magnitude lower compared to polycrystalline materials. The sapphire is therefore preferably applicable to said temperature measurement application in very corrosive environments.

Corundum ceramics are typically prepared by sintering small corundum (alumina) crystals. Monocrystalline sapphire is prepared by gradual melt crystallization. Methods of production of single crystal sapphire can be divided into two groups:

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(a) profile sapphire cultivation methods:

The most common method of profile sapphire cultivation is the Edge-Defined Film-Fed Growth (EFG) method discovered in the 1960s. The method consists in drawing the sapphire melt over a die of the desired geometric shape. The sapphire melt flows through a capillary tube into a die of, for example, a circular shape, where it is mounted on an oriented nucleus and solidifies just above the die in a high temperature gradient onto a single crystalline material. Another method is the Štěpán method, which was implemented in the 1950s in the then Soviet Union. Here, the growth of the profile sapphire single crystals is realized not by dragging through the die but by means of geometric baffles. In both cases, single crystal growth can be monitored by a camera on the monitor and controlled automatically.

(b) Bulk sapphire cultivation methods:

The most used method is Kyropoulus, where the crystal is cultivated on a cooled oriented nucleus. The crystal grows below the sapphire melt level. To improve the homogeneity of the material growth takes place in a vacuum (10 ^-4 mbar) and tungsten crucibles. With this method, sapphire single crystals weighing up to several kg can be obtained depending on the size of the crucible in which the cultivation takes place. Less used is the horizontal Bridgeman method, where the crucible with the melt passes through a temperature gradient in the horizontal direction. The crystals prepared by this method are not suitable for special optical applications due to their lower homogeneity.

The functionality of the material is not determined by its method of preparation, but by the homogeneity of the material and the achievement of an ideal crystallographic structure of corundum throughout its volume of the shell. The entire single crystal growth process must be optimized as is known in the art. In addition to optimum conditions for crystallization, tempering of the single crystal may also be advantageously used, where at temperatures above 1200 ° C the stress in the crystal lattice is relaxed after a certain period of time. Likewise, crystallization additives or compositions may also be advantageously used. Typically, titanium or chromium (ruby) containing materials are added to the alumina melt, but the list of ingredients is not limited by these elements. The crystallographic structure of corundum in the form of a single crystal with an alumina content of more than 90% by weight is decisive.

The single-crystal sapphire protective housing must be designed to meet the effective measurement requirements of the prior art.

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Measurements must be fast and accurate (ie maximum heat transfer to the thermocouple), but long-term protection of the thermocouple must be ensured (well wall thickness). A typical arrangement will include an outer sapphire sheath having an outer diameter of 3 to 20 mm and a wall thickness of 0.2 to 8 mm. At least one thermocouple branch will be routed through the capillary to avoid short circuits. The capillary can be simple - then the second branch is guided outside the capillary. Alternatively, the thermocouple may be guided through a multiple capillary. The interior of the well may comprise one or more thermocouples, additionally located at different distances from the end of the well. The thermocouples are then led to the head where they can be connected to the measuring electronics via the transmitter. The design of the temperature measuring probe is, of course, adapted to the particular application as exemplified in the examples and may be further customized by one skilled in the art. An example of such a probe is shown in Figure 1.

The single crystal sapphire sheath is preferably used in the above-mentioned environments where the solutions used do not satisfy due to insufficient durability, high cost or, for example, slow response due to excessive wall thickness of the sheath.

The temperature measurement process using a thermocouple probe with a sapphire sheath finds application, for example, in the glass or porcelain industry (temperature measurement of glass melts, temperature in furnaces with corrosive compounds), in the metallurgical industry (metal melting furnaces), fluidized-bed boilers), in chemical plants (production of synthesis gas, ammonia, inorganic acids, etc.), in flue gas removal plants (desulphurisation, Claus process, etc.), in high-temperature furnaces with a temperature above 1500 ° C often connected by compression (sintering) ceramics) or instrumentation (for example, when measuring the temperature of solid sample decomposition for elemental analysis).

These enumerated applications may be supplemented by a number of other examples by one of ordinary skill in the art, which is not intended to limit the scope of this patent. In general, sapphire wells find application in temperature measurement processes at high pressures, high temperatures above 1000 ° C, in environments with moving solid, very hard substances, or substances that are highly corrosive.

A specific measurement procedure with a sapphire well is given in the examples.

Overview of pictures

Figure 1 shows a thermocouple probe

DETAILED DESCRIPTION OF THE INVENTION

Example 1

The sapphire sheath 1 was produced by melt drawing by the EFG method. Its diameter was 16 mm and length 800 mm. The inside diameter of the sleeve 1 was 4 mm. At the end, the sleeve 7 was sealed with a seal of 20 mm in length. The sleeve 1 was additionally mechanically protected at the end of the head 4 by means of a protective ceramic tube of ceramic type C799 (corundum 99.7%) and fixed in the measuring aluminum head 4 with the terminal block. A sapphire capillary 2 having an outer diameter of 2 mm was inserted into the sapphire capsule 1 shown in FIG. One branch of type B thermocouple 3 was led through the center of the capillary 2. The connection of the two branches was placed at the bottom of the sapphire sheath 7. This probe was used for measurements in the following cases.

Example 2

The sapphire sheath 1 was extracted from the corundum melt containing 0.8% Cr (ruby) by the EFG method in the C orientation. The sheath I was 10 mm outer and 5 mm inner and a total length of 700 mm. At one end, the sleeve 1 was sealed with sapphire melt. Housing 1 was covered with a 1 mm thick corundum layer of corundum. The end of the housing 1 was directly fastened by the sleeve in the aluminum head 4. Two thermocouples 3 of type S were fastened from the terminal block in the housing 1, one ended directly at the seal, the other 100 mm from the end. Thermocouples 3 were fed in two sapphire double capillaries 2, grown by the EGF method. This probe was used for measurements in the following cases.

Example 3

The sapphire probe with the thermocouple of Example 1 was tested to measure the temperature in a soda-glass glass fiber at 1150 ° C. The probe was immersed 15 cm below the melt level and was tested for 100 days. The material loss was a maximum of 1.3 mm per tube diameter. By extrapolating to the diameter of the tube, it can be predicted that the life of the sapphire probe under the given conditions is about 2.5 years.

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Degussit AL23 ceramics, which are corundum ceramics with a very close to 100% purity and a density close to that of corundum (corundum = 3.98 g / cm3, AL23 to 3.95 g / cm3), were tested at the same site. The ceramic probe construction was double-walled, with a total wall thickness corresponding to sapphire. The ceramics lasted 4 months under identical conditions. Then the ceramics were completely etched, the remaining parts at the surface were cut off and the thermocouples were mechanically interrupted.

A platinum probe consisting of a 16 mm diameter ceramic tube coated with 80 g of platinum was placed in the same location. The platinum sink was broken after about five years of operation when the thermocouple was shorted.

Example 4

The probe of Example 2 was tested in a glass furnace with 500 kg of melt at approximately 1190 ° C. The probe was placed above the melt with an end ca 15 cm from the furnace wall. The melt contained over 20% PbO. Lead oxide tends to evaporate and penetrate through the ceramic protection of commonly used ceramic probes. PbO settles on the ceramic tubes at the cooler point of contact with the furnace wall, where the thermocouple is destroyed over a relatively short period of time. The lead penetration of lead sapphire is of the order of magnitude less than that of ceramics commonly used for sensor production (C799 ceramics). The failure of the ceramic probe corresponding to the example of Example 2 occurred after 75 days, while the sapphire probe had a lifetime of more than 3 years.

Example 5

The temperature measurement probe of Example 2 was tested together with a two-shell ceramic probe in a heavy metal-doped potassium glass furnace. The environment is extremely aggressive. The double-shell ceramic probe was made of C799 ceramic with a purity higher than 99.6% Al2O3. Both ceramic shells were etched and completely dissolved within 35 days. The sapphire probe of Example 2 with a wall thickness of 2.5 mm and a diameter of 10 mm lasted for 6 months.

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Example 6

The temperature measuring probe described in Example 1 was used to measure the temperature of the fluidized bed combustion of coal at the places where fly ash was collected at 300 ° C. At the same location, a probe with a 24 mm diameter outer casing of heat-resistant steel coated with a silicon carbide layer and an inner case with a 16 mm diameter of corundum ceramic was used. The service life of the steel probe at a given location is about 1 year, when the housing is ground. The sapphire probe does not show visible signs of damage during this period. In addition, the sapphire probe responds twice as fast to temperature changes, ie the measured temperature stabilization time is half that of the original probe.

Example 7

A thermocouple B protected by a sapphire sheath having an outer diameter of 8 mm and an inner diameter of 5 mm was used to measure the temperature in the Claus process for desulfurization of petroleum products at 1350 ° C. Probe lifetime exceeded 6 months.

Industrial applicability

The invention can be used to measure temperature under industrial conditions for temperature measurement at pressures above 1 MPa, and / or at temperatures above 800 ° C and / or in a highly corrosive environment and / or in environments with moving solids with a degree of hardness of the Mohs scale, higher than 5.

Claims (12)

Thermocouple probe for measuring temperatures under extreme conditions with a housing, characterized in that the housing is formed of a single crystal sapphire defined as a rhombohedral form of alumina corresponding to the crystallographic modification of corundum, where the atoms of ideal crystalline lattice are regularly arranged in a repeating pattern in a given direction throughout the volume. A thermocouple probe according to claim 1, characterized in that the sapphire for the housing is tempered for at least 1 hour at temperatures above 1200 ° C. 3. The thermocouple probe of claim 1 wherein the housing material comprises at least 90% by weight alumina and the remainder is oxides selected from Group IV. However, the crystalline modification of corundum is retained by the periodic system of elements, preferably titanium or chromium oxides. The thermocouple probe according to claim 1, characterized in that it comprises an outer sapphire housing (1), at least one inner capillary (2) and at least one thermocouple (3) attached by means of reinforcing elements to the thermocouple probe head (4) from which it is read. potential on the thermocouple corresponding to the measured temperature. Thermocouple probe according to claim 1, characterized in that the sapphire sheath has an outer diameter of 1 to 30 mm, preferably less than 16 mm and a wall thickness of greater than 0.1 mm, preferably more than 1 mm. Use of a thermocouple probe according to claims 1 to 5 for measuring temperature at pressures above 1 MPa, and / or at temperatures above 800 ° C and / or in a highly corrosive environment and / or in moving solids environments with a degree of hardness of the Mohs scale , greater than 5. Use according to one of Claims 1 to 5, characterized in that the temperature measurement is carried out in a molten glass or in glass or porcelain furnaces or in furnaces for sintering or pressing ceramic at high temperature. 11 ···· ·· ·· ·· ·· Use according to one of Claims 1 to 5, characterized in that the temperature measurement takes place in fluidized bed boilers. Use according to claims 1 to 5, characterized in that the temperature measurement takes place in processes for removing pollutants from the gas phase, such as ash separation, desulfurization, nitrogen oxides removal and Claus process. Use according to claims 1 to 5, characterized in that the temperature measurement takes place during the decomposition of solid samples prior to their elemental analysis. Use according to claims 1 to 5, characterized in that the temperature measurement takes place in metal-melting furnaces. Use according to claims 1 to 5, characterized in that the temperature measurement takes place in the gasification of organic substances, in the production of ammonia or other chemical syntheses at temperatures above 800 ° C.