Infrared dryer

Infrared dryer Infrared dryers are widely used in the pre-drying process of continuous pad dyeing and chemical finishing. This equipment uses radiant heat transfer for drying. It d…

Infrared dryer

Infrared dryers are widely used in the pre-drying process of continuous pad dyeing and chemical finishing. This equipment uses radiant heat transfer for drying. It does not require other substances as a medium, that is, it can enter the interior through the surface of the fabric, causing the internal and external temperatures of the fabric to rise rapidly at the same time, and the fabric can be dried in a very short time. In this way, uneven drying will not cause dye “migration”, and uneven distribution of surface resin and finishing agents will not affect product quality.
Infrared ray is a kind of electromagnetic wave just like visible light. Its wavelength range is 0.76~1000μm, especially the infrared heat effect in the wavelength range of 0.76~40μm, which is often called heat ray. In the research and application of infrared heating drying technology, infrared rays are divided into near infrared rays (λ is 0.76~3μm), mid-infrared rays (λ is 3~30μm) and far infrared rays (λ>30μm). Infrared drying technology uses infrared rays with a wavelength of 1 to 15 μm.
When infrared radiation reaches the surface of an object, part of its total radiation energy is reflected on the surface of the object, and the rest of the radiation energy is injected into the interior of the object, part of which is absorbed by the object, and the other part passes through the object. It can be seen that the thermal efficiency of infrared heating drying depends on the absorption rate of infrared rays by the object to be dried, and this absorption rate is related to the type of object, surface condition, and wavelength of infrared rays.
At present, infrared dryers in dyeing and finishing plants can be divided into electric heating and gas heating according to their heat sources.
(1) Electric heating infrared dryer: as shown in Figure 5-40. Its infrared radiator is an electric quartz tube type infrared radiator (Figure 5-41). The quartz tube is placed outside the electric heating wire, placed on the asbestos pad, then put on the brass sleeve, and clamped with a clamp. There are three axial long grooves on the sleeve to increase elasticity. The radiator is clamped in the spring clip of the frame by sleeves at both ends. In addition to being used to fix the heating wire and reduce oxidation corrosion of the heating wire, the quartz tube also plays a role in transmitting infrared rays and reducing convective heat loss.

The characteristics of quartz tubes used as radiating elements are good insulation and heat resistance. And it can transmit almost all the infrared rays with λ<4μm radiated by the electric heating wire, and absorb almost all the infrared rays with λ≥4μm (Figure 5-42). After extraction, the temperature of the quartz tube increases and it is radiated twice. The wavelength characteristics are shown in Figure 5-43.

The outer diameter of commonly used quartz tubes is 12~13mm, the wall thickness is 1.5~2mm, the length is 1~1.5m, and it is equipped with 2 ~2.5kW electric heating wire. Quartz tubes cannot withstand mechanical impact and should be used with great care. Heating wire is the main component that converts electrical power into thermal power. Its temperature is related to the current passing through it, heating wire material, diameter, winding outer diameter, pitch, etc. Generally, the temperature of the electric heating wire is controlled by adjusting the voltage to obtain the required radiation wavelength and radiation power.
Using silicon carbide tubes instead of quartz tubes is not only cheap, but also the infrared radiation spectrum of silicon carbide tubes is very uniform in the 3-16μm band, without peaks, and has different radiation characteristics from quartz tubes.
During the process of drying, coloring and fixing the fabric, it mainly relies on absorbing mid-infrared rays with a λ of 4 to 5 μm, and the corresponding temperature of the radiator surface is 550°C. The structure of the far-infrared electric heating tube that generates this type of infrared ray is shown in Figure 5-44. Its biggest advantage is that it consumes less power and can save 30.5% of electricity compared to ordinary electric heating infrared radiators.

(2) Gas-type infrared dryer: The gas-type infrared dryer currently used in printing and dyeing factories is a gas infrared radiator. Coal gas contains combustible gases (H2, CO, CH4, C3H3, C4H10, H2S, etc.), auxiliary gas (O2), non-gas (N 2, CO2, H2O), etc.
In terms of its structure, gas infrared radiators can be divided into metal mesh infrared radiators (Figure 5-45) and porous ceramic plate-covered metal mesh infrared radiators (Figure 5-46).

①The working process of the metal mesh radiator is that when the gas with a certain pressure is pressed into the ejector A of the burner through the nozzle, The high-speed fluid in the gas ejector causes the pressure in hole A to drop, automatically inhaling air from hole B of the burner. The mixed gas of gas and air gradually obtains a uniform speed and concentration along the ejector, continues to move forward, and burns The air flow baffle on the inner wall of the burner is impacted and then sprayed into the entire internal space of the burner. It burns between the inner mesh and the surface mesh, causing the temperature of the surface mesh, radiant mesh, and inner mesh to rise sharply. The red-hot surface mesh, radiant mesh, and inner mesh and their high-temperature smoke all emit infrared rays. Under normal circumstances, a qualified radiator, under standard gas pressure, should burn steadily without flames, be red inside and outside, and have uniform brightness and no noise after being ignited. Since the expansion coefficient of iron-chromium-aluminum is very large, in order to prevent the radiation net from deforming when it is red, it is stamped into a corrugated shape in advance.
②In the infrared radiator covered with a metal mesh outside the porous ceramic plate, the mixture of gas and air is sprayed from the gap between the air flow baffle and the radiator shell to the porous ceramic plate, and the mixed gas is sprayed between the porous ceramic plate and the metal mesh. Combustion produces infrared radiation.

Under normal use, the temperature of the metal mesh of the gas infrared radiator is between 800 and 1000°C, and the infrared radiation with a wavelength of 2 to 6 μmMainly external radiation, radiation within this wavelength range accounts for 70% of all radiated energy.



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Author: clsrich