How does a furnace thermocouple work?

In industrial furnaces, armored thermocouples are often used as Furnace thermocouples. The thermocouple body has a metal sheath, which can directly measure the temperature of the medium. Or it can be placed in a protective tube as a temperature measurement core element. It has the advantages of bending, high-pressure resistance, fast thermal response time, sturdiness, and durability.

Armored thermocouples are usually used in conjunction with display instruments, paperless recorders and regulators. It can measure the temperature of liquid, vapor and gaseous media and solid surfaces in the range of 0-1600°C during various production processes.

Place the thermocouple core wire and inorganic mineral insulating material in a metal sleeve. The stretched solid assembly that can be wound becomes an MI Cable.

The armored thermocouple cable made of thermocouple wire as the core is welded to form the measuring end and assembled with the relevant junction box. The thermocouple is called the armored thermocouple. Furnace thermocouples can be manufactured into insulated, grounded, and exposed-end types as required.

Furnace thermocouple-Solution for coal chemical gasifier

The gasifier is the most representative device of the coal chemical industry. Sino-Inst is based on the special conditions of the TEXACO gasifier and the Shell gasifier. It shares the special structure and material selection of the gasifier thermocouple and other professional knowledge. Help users solve special problems The problem of temperature measurement in the occasion.

Accurate measurement and strict control of temperature are the key factors to ensure the normal operation of the process. It will directly affect whether the process is carried out under ideal conditions. It will even affect the service life, safety production and environmental protection of the overall equipment.

The temperature measurement conditions of TEXACO gasifiers and Shell gasifiers in the coal chemical industry are extremely specific due to the gasifier body structure, internal medium, reaction process, and operating conditions. Therefore, the choice of the corresponding Furnace thermocouple also highlights its special importance and complexity.

The author relies on many years of rich experience. The representative and typical working conditions of TEXACO gasifier and Shell gasifier. As well as the selection principles and precautions of the corresponding thermocouples, which I will discuss with you. It aims to provide reference guidance and suggestions for coal chemical users.

1.TEXACO gasifier

① Operating conditions of TEXACO gasifier

Representative sites of TEXACO gasifiers include Ningxia Coal Group’s 250kt/a methanol plant, Shenhua Baotou and Inner Mongolia Jiutai Energy’s coal-to-olefin project.

The above site adopts the TEXACO rapid cooling process and the whole waste boiler process, which is the most advanced energy-saving process in the world.

TEXACO gasifier has special working conditions such as high temperature, high pressure, coexistence of oxidizing and reducing atmospheres, strong scouring, and sudden changes in temperature and pressure.

The operating temperature of the combustion chamber is 1350-1500℃, and the operating pressure is 2.5-8.7 MPa.

The flame gas contains CO, H2, CO2, H2O, CH4, Ar, N2 and H2S and other components.

The melting point of coal ash is 1310-1370°C.

The shell of the combustion chamber and the lining refractory bricks are likely to shear each other due to the different coefficients of thermal expansion.

The most important thing is that the scouring and abrasion in the gasifier is extremely serious, so the measuring point of the thermometer must be located 15-25mm away from the inner wall of the furnace wall.

However, it is difficult to ensure uniformity in the furnace wall during the masonry process. Coupled with the existence of scouring and wear in the furnace. The furnace wall will be inevitably thinned gradually during the production process.

②The performance requirements of TEXACO gasifier for Furnace thermocouple:

Due to the special working conditions of the above-mentioned TEXACO furnace, the temperature sensor must be able to withstand a high temperature of 1600°C and a high pressure of 8.7MPa.

It can resist the double corrosion of oxidizing and reducing gas at the same time.

It has an adjustable insertion length and a follow-up structure. When the inner lining changes in thickness and torsion and shear, corresponding structural changes can be made.

③Temperature measurement solution for TEXACO gasifier

In response to these requirements, the Furnace thermocouple is designed with special materials and structure. It satisfies the harsh requirements of the gasifier operating conditions for the temperature sensor. It is a kind of thermocouple special for gasifiers with adjustable anti-vibration, erosion resistance, anti-oxidation, and multi-stage leakage resistance.

First of all, the main structure of the Furnace thermocouple adopts the design concept of adjustable anti-vibration.

When the thickness of the gasifier wall lining changes, the Furnace thermocouple can be adjusted within the range of ±120mm through the shrinkable threaded sleeve. In order to achieve the measurement, the element is always maintained in the best position.

When the furnace shell and the inner lining are sheared, the universal rotating ball can be used to make the probe rotate with the inclination. And under the action of the limit guide tube and the correction damping spring.

Keep the probe always in the correct position in the center of the wall bushing. It prevents the thermocouple of the gasification furnace from being broken when the furnace wall is deformed.

Multi-stage leak-proof structure design. When the thermowell is damaged, it can prevent convection between the inside of the furnace and the outside through the sleeve. Safety hazards caused by high temperature conduction or even leakage in the furnace. Reflect safety awareness and environmental protection concepts.

Secondly, the Furnace thermocouple protection tube material adopts imported silicon carbide material made by pressureless sintering of sub-micron silicon carbide powder. The material has the dual characteristics of ceramic and metal and can be used reliably even at high temperatures exceeding 1750°C.

Its thermal conductivity is equivalent to stainless steel, 5 times that of alumina. Hardness is one of the high-performance materials second only to diamond. Ultra-fine crystals smaller than 10μm have been tested by helium gas leak detection.

The porosity is almost 0, which can effectively prevent H2 and CO from damaging the Furnace thermocouple wire through the pores on the tube wall. Ultra-high hardness and density make it have ideal wear resistance and long-term resistance to material erosion. It can work in oxidizing and reducing atmospheres and corrosive environments of strong acids and alkalis even at ultra-high temperatures.

Gasifier temperature measurement solution

2.Shell gasifier

At present, more than ten sets of Shell gasifiers have been introduced in China. Representative sites are Henan Kaixiang Methanol Project, Yunwei Group’s synthetic ammonia and Guangxi Liuhua coal gasification plants.

①Shell gasifier operating conditions characteristics

Conditions to ensure the normal operation of Shell gasifiers:

Neither can cause damage to the over-temperature of the vaporizer. It is necessary to consume the lowest amount of oxygen as much as possible. To achieve complete carbon conversion, temperature control is essential.

However, the structural characteristics of the Shell gasifier determines that the temperature of the gasifier cannot be directly measured. It can only be controlled by indirect methods.

An “annular space” is formed between the inner membrane wall of the gasification furnace and the outer shell. Hot syngas cannot escape into the “annular space”, causing the shell to overheat. Calculating the temperature in the furnace by measuring the temperature of the water wall in the “annular space” is the characteristic of Shell gasification furnace temperature measurement.

The temperature in the “annular space” is collected at multiple points, and each temperature measurement point is the key to understanding whether the gasifier is operating normally. If there is any abnormality, find and analyze the cause immediately. And deal with it in time, otherwise it will cause major damage to the gasifier.

②Shell gasifier performance requirements for Furnace thermocouples

Because the pulverized coal of Shell gasifier is 4MPa. It is combusted with O2 and steam in a gasifier at around 1500°C. And when it was sent to the coal burner, it was already under a pressure of 2MPa. Therefore, the thermometer is required to have a pressure resistance of not less than 2MPa. It also has emergency measures in case of overpressure, and can withstand a high temperature of 1500°C.

Because the Shell gasifier is composite equipment that integrates dynamic and static equipment, as well as combustion, reaction, heat exchange, and quenching processes. Therefore, it is required that the thermocouple used must be easy to install and remove, and easy to replace. Because of its complex structure and many control points, a multi-point thermocouple must be used.

③Shell gasifier temperature measurement solution

The design solution of the special Furnace thermocouple for the multi-point core-pulling and leak-proof Shell gasifier has solved the on-site requirements.

a. Multi-point thermocouples of different lengths (up to 6m) are used to measure the temperature of different control points in one fell swoop, using 3-point or 4-point thermocouples.

b. According to the characteristics of on-site installation, 4in (1in=25.4mm) No. 600 flange mounting parts are used. This part and the temperature measurement body are separable structures. The flange installation and fixing can be completed first. Then the temperature measurement body Installation with flange.

This solution allows the bulky flange to be installed at one time. In daily maintenance, only the main part needs to be replaced, which is convenient and quick. Closely combined with this structure is the independent replaceability of the core elements. Each measuring element is a detachable individual. If any one fails, it can be taken out and replaced separately. The maintenance cost and the quantity and expense of spare parts are reduced.

c. Due to the large amount of HCl in the medium in the furnace. Incoloy and Inconel alloys are often used in equipment manufacturing. In order to maintain a high resistance to high temperature and corrosion, the selection of Furnace thermocouple protection tube materials must all use Inconel600 alloy. Keep temperature measurement components , The material consistency of the mounting flange and the sealing sleeve.

d. The thermometer must have a multi-stage leak-proof sealing structure design. That is, each element must have a double-stage leak-proof device. When any temperature measuring element is damaged, due to the existence of leak-proof, the “annular space” The high temperature and high pressure airflow will not leak. It also guarantees the safety and environmental protection on-site requirements.

Furnace thermocouple installation instructions

3.Furnace thermocouple installation instructions

①After the gasifier is shut down, consider the decompression effect of refractory materials and pressure vessels and the problems of thermal expansion and contraction. The pressure relief and replacement process of the gasifier is carried out slowly, and the furnace pressure should be basically reduced to atmospheric pressure and completely replaced.

After that, while the molten slag has not completely solidified, the gasifier thermocouple is drawn out of the furnace.

If the slag is solidified, the thermocouple ceramic sleeve cannot be pulled out, only the metal part at the back can be pulled out. The ceramic sleeve is usually driven into the furnace with a special tool.

②When installing a new gasifier thermocouple, put the assembled gasifier thermocouple on a special bracket. The bracket is placed on the wheeled trolley so that the gasifier thermocouple is exactly aligned with the gasifier thermocouple.

The equipment takes over in the middle. Slowly push the gasifier thermocouple into the furnace, about 10mm every 5 minutes. Protect the thermocouple from thermal shock.

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