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First, the main factors causing the fiber dryer to catch fire
(1) caused by fiber drying process
The oxygen content in the gas stream is high, the drying temperature is high, and the fibers adhere to the pipe wall. Due to the long-term high temperature action, the carbonization is gradually pyrolyzed, and flammable materials are formed. Excessive drying of the fibers and the introduction of metallic foreign matter cause the air delivery system to collide and generate sparks.
(2) Dryer oil leakage
Due to design reasons or processing quality reasons, it is not suitable to use heat transfer oil to heat, but the heat transfer oil is misused. Because the steel can not withstand the "expansion" of the high temperature heat transfer oil, the weld seam is cracked, and the heat transfer oil higher than 2000 °C leaks from the crack. Contact with air "self-ignition" caught fire.
(3) The drying temperature is too high
Due to the failure of the dryer control or the operation, the inlet temperature of the dryer greatly exceeds 170 °C; or the heat transfer oil and steam valve are not closed in time after the fan stops, causing the temperature inside the machine to rise rapidly, and the high temperature ignites the adhesion. The fibers on the device ignite the fibers adhering to the drying tube to cause a fire.
(4) Other special reasons
Fires caused by special causes such as fiber blockage, electrical short circuit, and welding.
Second, the dryer safety protection measures
(1) Fixed point protection
Use an infrared spark detector at each hazardous point to control. Such detectors are typically equipped with sensitive components or other optoelectronic sensitive devices for the infrared source. Its sensitivity is faster than the transportation, burning and explosion speed of any material. It can send a fire alarm signal within 0.002~0. 003s, and push the actuator to control the fire extinguishing system to spray the fire extinguishing agent through the amplifier, and automatically cut off the fan power supply and close the valve. And a series of other operating systems, do not spread the fire source, the working principle is shown in Figure 1.
There are other ignition factors, such as the installation of metal detectors on the front of the dryer to prevent metal from entering the drying ducts; improved pulsed pipe drying to eliminate the adhesion of fibers to the pipe wall to reduce fire alarms. This series of comprehensive measures can be combined to minimize the risk of fire.
(2) Control drying temperature
The inlet temperature of the dryer should be below 1700 °C, the outlet temperature should be kept below 75 °C, the inlet and outlet temperature should not exceed the specified value, especially the inlet temperature should not exceed the specified temperature, and the production efficiency should be lower to ensure safety.
Figure 1 Schematic diagram of the working principle of the infrared spark detector fire extinguishing device
(3) Control the oxygen content of the drying medium
The burning of the material is caused by severe oxidation. Practice has proved that when the oxygen content in hot air exceeds 17%, it creates conditions for combustion. Therefore, as long as the oxygen content is less than 17%, it is not easy to ignite, and if it is reduced to a safe value of 13.3% or less, it is substantially impossible to burn.
A zirconia (Zr02) detector was used in each circulation system to control the oxygen content. When the oxygen concentration in the gas stream exceeds 17%, the output signal is amplified to control the valve operation of the inert gas (N2 or CO2) reservoir, and the inert gas is used to dilute the oxygen concentration in the circulating gas stream to less than 17%. Then it closes automatically. In this way, even if a spark occurs accidentally in the pipe, it does not cause the fiber to burn.
(4) Regularly clean dry pipes and dryers
It is necessary to scrape and clean the fibers, rubber, etc. adhering to the inner wall of the drying pipe and the fins of the dryer radiator. When scraping, care should be taken to protect the probes and nozzles of the automatic fire-extinguishing system. During the production time, electric welding and gas cutting operations cannot be carried out near the dryer, and the safety production awareness is improved, and the fire hazard is reduced to a minimum.
Third, the environmental protection of the dryer
Organic volatile compounds (such as tar, resin, sulphuric acid and hydrazine) contained in wood fibers are released when dried at high temperatures, causing air pollution. Enterprises also attach great importance to this issue, and there are two current solutions.
(1) The gas is trapped and burned at a high temperature (815 ° C), and a regenerative thermal oxidation treatment device can be installed on the automatic exhaust system. For inorganic particles that cannot be treated, a wet electrostatic precipitator can be used to precipitate before combustion. According to the installation trial, the total effective rate is 95% to 99%.
(2) Lower the drying temperature and lower the drying temperature below the hydrocarbon release point.
In addition, heating with boiler flue gas is environmentally friendly and energy efficient. Flue gas drying is divided into direct and indirect. Direct, simple, environmentally friendly, and low investment, but it will cause corrosion to the pipe of the dryer and affect the curing performance of the adhesive (the acidity of the flue gas contains CO2); the indirect type is safe for production because there is no Mars and smoke. Both sex and fiber quality are good.
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