In high-temperature and complex industrial environments, thermocouples are key temperature measurement devices, and their performance directly affects the safety and stability of the production process. Especially in high-temperature and highly corrosive environments such as power plants, thermocouples are exposed to reducing atmospheres for a long time and are easily degraded by chemical corrosion, oxidation or mechanical wear. To address this problem, the WREKD2-04A thermocouple uses a ceramic protective tube to effectively solve the limitations of traditional metal protective tubes in reducing atmospheres, significantly extending the life of the equipment and ensuring measurement accuracy. The following will analyze the technical principles, application scenarios and actual effects.

I. Challenges of thermocouples in reducing atmospheres

Reducing atmosphere refers to a condition in which there are a large amount of reducing gases such as carbon monoxide (CO) and hydrogen (H₂) in the environment, and the oxygen content is extremely low or even completely absent. This environment places strict requirements on the stability and durability of thermocouples. Traditional thermocouples usually use stainless steel or nickel-based alloy metal protective tubes to wrap the hot electrode to isolate the external environment. However, in a reducing atmosphere, metal materials are prone to the following problems:

• Chemical corrosion: Reducing gases may react with metals at high temperatures, causing the oxide layer on the surface of the protective tube to peel off or the internal structure to deteriorate.

• Hydrogen permeation embrittlement: Hydrogen molecules penetrate into the metal lattice, causing the material to embrittle, reducing its mechanical strength and impact resistance.

• Thermal stress damage: Under high temperature conditions, the difference in thermal expansion coefficient between the metal protective tube and the hot electrode may cause local stress concentration and accelerate crack formation.

These problems not only shorten the service life of the thermocouple, but may also cause safety hazards due to measurement errors or equipment failure. Therefore, it is critical to choose a protective material that can resist the erosion of a reducing atmosphere.

II. Technical advantages of ceramic protective tubes

Ceramic materials have become the preferred solution for thermocouple protection in a reducing atmosphere due to their unique physical and chemical properties. The ceramic protection tube used in the WREKD2-04A armored thermocouple is mainly based on the following technical characteristics:

1. Chemical inertness and corrosion resistance

Ceramic materials (such as alumina, silicon nitride, etc.) have extremely high chemical stability at high temperatures and can effectively resist the erosion of reducing gases. For example, in an environment containing H₂, the ceramic surface is not easy to react with hydrogen molecules, avoiding the common hydrogen permeation problem of metal protection tubes. In addition, ceramics also show excellent corrosion resistance to acidic or alkaline gases (such as SO₂, NOx), allowing them to maintain structural integrity in complex working conditions.

2. High temperature tolerance

Thermocouples in power plants often need to work in high temperature environments of 800℃ to 1300℃. The temperature resistance of ceramic materials far exceeds that of metal materials, and their melting point is usually above 1600℃, and they can still maintain stable physical properties at high temperatures. This allows ceramic protection tubes to operate for a long time under extreme temperature conditions without frequent replacement.

3. Low thermal expansion coefficient

The thermal expansion coefficient of ceramics is significantly lower than that of metal materials. This feature reduces the risk of mechanical damage to the thermocouple due to thermal stress when the temperature changes suddenly, thereby improving the overall reliability of the equipment.

4. Surface smoothness and wear resistance

The ceramic surface has an extremely low friction coefficient and excellent wear resistance, which can effectively reduce the erosion and wear of particulate matter (such as fly ash in the flue gas of power plants) on the protective tube. This not only extends the life of the equipment, but also avoids the problem of thermocouple response hysteresis caused by surface roughness.

III. Application of ceramic protective tubes in reducing atmospheres in power plants

In actual applications in power plants, the WREKD2-04A thermocouple successfully solves the measurement problem under reducing atmosphere through the design of ceramic protective tubes. The following are its typical application scenarios and effects:

1. Boiler combustion monitoring

In coal-fired or gas-fired boilers, the combustion process is often accompanied by the generation of high-temperature reducing gases. Traditional metal protective tubes are prone to failure due to hydrogen permeation or corrosion in such environments, resulting in thermocouple measurement deviations. The ceramic protective tube can isolate external gases stably for a long time to ensure the accuracy of the thermocouple output signal. In addition, its high temperature resistance can adapt to the instantaneous temperature fluctuations in the boiler furnace, providing reliable data support for combustion control.

2. Desulfurization and denitrification system

In the flue gas desulfurization and denitrification systems of power plants, the flue gas usually contains corrosive gases such as H₂S and NH₃, and is in a high-temperature reducing environment. Ceramic protective tubes show excellent resistance to chemical erosion in such systems, effectively preventing the common cracking or perforation problems of metal protective tubes, thereby reducing equipment maintenance frequency and downtime costs.

3. High-temperature monitoring of steam turbines

In the high-temperature steam pipes of steam turbines, thermocouples need to withstand the combined effects of high-temperature water vapor and reducing gases for a long time. The high air tightness and moisture resistance of ceramic protective tubes can prevent water vapor from penetrating into the surface of the hot electrode, avoiding measurement errors caused by oxidation or scaling. At the same time, its low thermal conductivity characteristics help reduce heat loss and improve the response speed of thermocouples.

When looking for high-quality, reliable high temperature thermocouples, YOYIK is undoubtedly a choice worth considering. The company specializes in providing a variety of power equipment including steam turbine accessories, and has won wide acclaim for its high-quality products and services. For more information or inquiries, please contact the customer service below:
E-mail: sales@yoyik.com
Tel: +86-838-2226655
Whatsapp: +86-13618105229

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