A radiant tube refers to a pipe extending in a straight line from the center to all directions. Refers to the non-central pipeline (or main pipe), which transports the material of the main pipe to a designated or non-designated address. The radiant tube is widely used in heating furnaces and is the main heating element of the heating furnace. The currently used radiant tubes are mainly divided into two categories: gas radiant tubes and electric heating radiant tubes. Among them, the thermal efficiency of the gas radiant tube is about twice as high as that of the electric heating radiant tube.
Among them, the Gas-Fired Radiant Tube is a commonly used heating device in industrial kilns, and the main heat transfer method is radiation. The application of gas-fired radiant tube heating devices in industrial kilns can reduce the infrastructure and operating costs of the kiln, improve production efficiency, and extend the life of the kiln. The combustion atmosphere and combustion products of the gas radiant tube do not directly contact the heated workpiece, which greatly improves the quality of the product, and is widely used in the field of metal heat treatment and industrial drying.
The basic components of the radiant tube are the tube body and the burner. High-efficiency radiant tubes often have waste heat recovery devices.
The key component of the radiant tube is the tube body, which radiates the heat released by fuel combustion to the heated material. Because the surface of the tube is in direct contact with the combustion flame and high-temperature flue gas, the working environment is harsh. For the radiant tube of metallic materials, the material will fail due to local burning and oxidation for a long time; if it is along the length of the tube There is a large temperature difference, the tube body needs to withstand a large thermal stress, which will directly affect the length of the tube body’s life; coupled with the impact of the air flow during combustion, it will also produce a certain amount of vibration.
Therefore, the material of the radiant tube needs to meet the following conditions:
1) High temperature resistance
2) High surface blackness
3) Large thermal conductivity
4) High structural strength and good air tightness
5) Under the highest working temperature and self-load, the oxidation resistance is good, and it can withstand high enough high temperature creep and destruction strength
6) Small thermal expansion coefficient
7) Low cost
Most of the radiant tube materials used in China are heat-resistant steel, and the temperature range of use is around 900～1000℃. The processing method is usually made by rolling, extruding steel pipe or centrifugal casting. Theoretically, the maximum use temperature of various heat-resistant steels will vary with the use conditions and controllable atmosphere. In the actual production process, a reasonable radiant tube material should be selected according to the process conditions of the furnace temperature, furnace atmosphere, and the type of materials to be heated.
Gas Radiant Tube material table and temperature：
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The core device of the radiant tube heating technology is a gas burner. The radiant tube burns and heats the incoming fuel through the burner. The power of the burner controls the wall temperature distribution, thereby affecting the power, thermal efficiency and life of the radiant tube. In order to meet the process requirements, the burner needs to have the following characteristics:
1) The combustion flame has good stability, and it can burn stably under a low excess air coefficient
2) In the case of frequent switching, no flashback or serious carbon deposits will occur
3) In the process of gas flow adjustment, the air coefficient remains relatively stable
4) The surface temperature of the burner and the fixed device is less than 100℃, the distribution is relatively uniform, and the local overheating is minimized as much as possible
5) Easy to repair and replace
Parallel flow and swirling flow combustion nozzles are commonly used radiant tube combustion nozzles. With the development of combustion technology, the forms of burners used in conjunction with radiant tubes have gradually been innovated, such as low NOX burners, high temperature air combustion burners and regenerative burners, which have achieved good results during use. Soviet-made TPHY and TYD radiant tubes are more advanced forms of radiant tube combustion. In the entire device of the gas radiant tube, an important component to improve the thermal efficiency of the gas radiant tube is the waste heat recovery device. There is no radiant tube provided with a flue gas waste heat recovery device, which results in large exhaust loss and low thermal efficiency. A waste heat recovery device is installed at the exhaust end of the radiant tube to preheat the fuel or combustion air, which reduces the exhaust temperature and reduces environmental pollution while improving efficiency.
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