Thermocouple

Abstract

The utility model relates to the technical field of temperature measuring instruments, in particular to a thermocouple, which consists of a junction box, a protective tube and a temperature measuring element, the protective tube comprises a protective head, an outer protective tube arranged at the upper end of the protective head, an inner protective tube sleeved in the outer protective tube, a flange arranged at the upper end of the outer protective tube and a boss connected with the flange, and ceramic fibers are filled between the inner protective tube and the outer protective tube. According to the thermocouple, the temperature measuring element is protected through the structure of the inner and outer protection tubes and the ceramic fibers filled between the inner and outer protection tubes, so that the thermocouple can stably operate in a high-temperature and high-scouring environment.

Description

TECHNICAL FIELD

[0001] The utility model relates to temperature measuring instrument technical field especially relates to a thermocouple. BACKGROUND

[0002] At present, although temperature measuring instruments are various in kinds and principles are different, the most used is still thermocouple, and the thermocouple is a contact type temperature measuring primary instrument, and is widely applied in petroleum, chemical industry and other fields.

[0003] Ethylene is the core of petrochemical industry, and ethylene cracking furnace is the core equipment of ethylene production device, mainly for processing natural gas, refinery gas, crude oil and naphtha and other various raw materials into cracking gas, and providing for other ethylene devices, and finally processing into ethylene, propylene and various by-products.In the cracking reaction of ethylene cracking furnace, cracking temperature is the most important process variable, which not only affects the cracking reaction, but also determines the mechanical limit of the furnace.Unlike conventional use scenarios, when measuring the temperature of ethylene cracking furnace, there is not only high-temperature oxidation and high-temperature corrosion, but also high-temperature erosion and wear of flowing medium.

[0004] Therefore, in order to ensure that the accurate cracking temperature is measured, it is necessary to design a thermocouple specially for the cracking reaction of ethylene cracking furnace. CONTENT OF THE UTILITY MODEL

[0005] In order to overcome the shortcomings in the prior art, the utility model aims at providing a thermocouple with good stability and accurate measurement.

[0006] Technical scheme: a thermocouple is composed of a junction box, a protection tube and a temperature measuring element, the protection tube includes a protection head, an outer protection tube arranged at the upper end of the protection head, an inner protection tube sleeved in the outer protection tube, a flange arranged at the upper end of the outer protection tube and a boss connected with the flange, and the inner protection tube and the outer protection tube are filled with ceramic fibers.

[0007] As a further preferred scheme, the protection head is made of Cr25Ni35Nb material, and the outer protection tube is made of Inconel 800H material.

[0008] As a further preferred scheme, the end of the protection tube is a half vertebral body structure.

[0009] The utility model has the following advantages:

[0010] The thermocouple protects the temperature measuring element through the structure of the inner and outer protection tubes and the ceramic fibers filled between the inner and outer protection tubes, so that the temperature measuring element can stably operate in a high-temperature and high-washing environment.

[0011] In addition, the protective head, which is the part of the protective tube that contacts the medium at the bottom, is made of Cr25Ni35Nb material, while the outer protective tube is made of Inconel 800H. This arrangement can maximize the erosion resistance and corrosion resistance of the protective tube. Attached Figure Description

[0012] Fig. 1 This is a three-dimensional structural diagram of the present invention.

[0013] Fig. 2 This is a cross-sectional view of the protective tube of this utility model.

[0014] Among them: 1-junction box, 2-protective tube, 21-protective head, 22-outer protective tube, 23-inner protective tube, 24-flange, 25-bore, 26-ceramic fiber, 3-temperature sensing element. Detailed Implementation

[0015] The technical solution will be further described below with reference to specific embodiments. It should be noted that the terms "up," "down," "left," and "right" used herein refer only to the position of the illustrated structure in the corresponding drawings. The component numbers used herein, such as "first," "second," etc., are merely for distinguishing the described objects and have no sequential or technical meaning. Furthermore, terms such as "connection" and "linkage," unless otherwise specified, include both direct and indirect connections.

[0016] like Figs. 1-2 The thermocouple shown is a thermocouple specifically used in ethylene cracking furnaces. It is basically composed of three parts: junction box 1, protective tube 2, and temperature sensing element 3. The electrodes of the temperature sensing element 3 are composed of two conductors with different compositions, preferably a combination of nickel-chromium-nickel-silicon or nickel-chromium-silicon-nickel-silicon. The temperature measuring range can reach -40 to 1200℃. The protective tube 2 includes a protective head 21, an outer protective tube 22 set above the protective head 21, an inner protective tube 23 sleeved inside the outer protective tube 22, a flange 24 set at the upper end of the outer protective tube 22, and a boss 25 connected to the flange 24. Ceramic fiber 26 is filled between the inner protective tube 23 and the outer protective tube 22.

[0017] In addition, the thermocouple protection tube 2, manufactured under high temperature, corrosion, and erosion conditions, requires not only the airtightness, mechanical strength, stability, and thermal conductivity required of ordinary thermocouples, but also the following:

[0018] (1) High temperature resistance: It can be used at the upper limit of thermocouple temperature measurement without deterioration or deformation, and has good oxidation resistance at high temperature.

[0019] (2) Thermal strength: It does not soften at the operating temperature of the thermocouple.

[0020] (3) Corrosion resistance: When the thermocouple protection tube 2 must be immersed in the medium, it should have corrosion resistance to the medium.

[0021] (4) Certain temperature change resistance performance, comprehensive performance of thermal shock resistance, high thermal conductivity, thermal expansion

[0022] Therefore, in the comparison analysis of metal materials, non-metallic materials and composite materials, the following conclusions are drawn:

[0023] (1) The main metal materials that can withstand high temperature (above 1100°C) are Cr28, Cr25Ni20, Cr25Ni35Nb, Inconel 800H, GH3030, and GH3039.

[0024] (2) Most non-metallic materials can meet the general high-temperature oxidation and high-temperature corrosion environment due to their good high-temperature resistance, thermal conductivity, high strength, high hardness, low density, small thermal expansion coefficient, and good oxidation resistance and wear resistance, but they have poor resistance and are not suitable for ethylene cracking furnace environment.

[0025] (3) Metal ceramics combine the wear resistance, high temperature resistance and oxidation resistance of ceramic materials with the high strength of metal materials, but have poor thermal shock resistance and are still not suitable for ethylene cracking furnace environment.

[0026] (4) The technology of composite coating is not mature at present and is not considered for the time being.

[0027] After calculation and derivation, it is found that Inconel 800H is the material with the slowest corrosion rate, and Cr25Ni35Nb (a high-temperature alloy with high chromium and nickel content) is only second to Inconel 800H (a high-temperature corrosion-resistant alloy belonging to iron-based nickel-chromium alloy), but Cr25Ni35Nb is the material with the strongest erosion resistance. Therefore, we consider using the two metals together, using Cr25Ni35Nb as the part of the protection tube that contacts the medium at the bottom, i.e. the protection head 21 is made of Cr25Ni35Nb material, which is the part where the temperature sensing element senses the temperature. The outer protection tube 22 is made of Inconel 800H material, the inner protection tube 23 is made of 316 stainless steel, the flange 24 and the boss 25 are made of 304 stainless steel, and ceramic fiber 26 is filled between the inner and outer protection tubes as a heat insulation material.

[0028] In a specific embodiment, the thermocouple is formed according to four welding processes of different high-temperature-resistant materials, mainly including welding of the protective head 21 (Cr25Ni35Nb) and the inner protective tube 23 (316 stainless steel), welding of the protective head 21 (Cr25Ni35Nb) and the outer protective tube 22 (Inconel 800H), welding of the outer protective tube 22 (Inconel 800H) and the flange 24 (304 stainless steel), and welding of the flange 24 (304 stainless steel) and the boss 25 (304 stainless steel)

[0029] In addition, the junction box 1 is provided with terminals for external wiring of the thermocouple, and the terminals inside the box are waterproof and dustproof, and in some cases, explosion-proof. Experiments show that the temperature at the junction box is lower than that at other parts during work, so when designing the junction box, we choose ADC12 cast aluminum material, and the surface is sprayed with polyurethane coating.

[0030] In order to better adapt to the erosion of the medium to the temperature measuring element 3 and the protective tube 2, the end of the protective tube is designed as a semi-elliptical structure to reduce the erosion of the fluid and better protect the temperature measuring element 3.

[0031] The above-described embodiments only express the preferred embodiments of the present application, and the description is more specific and detailed, but it should not be understood as limiting the scope of the present application. It should be noted that for ordinary skilled persons in the art, without departing from the concept of the present application, a number of modifications, improvements and substitutions can be made, which all belong to the protection scope of the present application. Therefore, the protection scope of the present application should be subject to the appended claims.

Claims

1. A thermocouple consisting of a terminal box (1), a protection tube (2) and a temperature measuring element (3), characterized in that, The protection tube (2) comprises a protection head (21), an outer protection tube (22) arranged at the upper end of the protection head (21), an inner protection tube (23) sleeved in the outer protection tube (22), a flange (24) arranged at the upper end of the outer protection tube (22), and a boss (25) connected with the flange (24), and ceramic fibers (26) are filled between the inner protection tube (23) and the outer protection tube (22).

2. The thermocouple of claim 1, wherein, The protection head (21) is made of Cr25Ni35Nb material, and the outer protection tube (22) is made of Inconel 800H material.

3. The thermocouple of claim 1, wherein, The junction box is externally sprayed with a polyurethane coating.

4. The thermocouple of claim 1, wherein, The protection tube (2) is in a half-vertebral structure at the end.

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