In the process of fire refining bismuth, whether smelting or refining, flue gas dust are generated, wherein the compound of lead, arsenic, antimony, and zinc vapors containing volatiles. In order to protect the environment, in order to recover valuable elements, dust must be collected.
First, the characteristics of smoke and smoke
In the mixed smelting of bismuth, no large amount of dusty fumes will be produced in the reverberatory furnace or converter. In the igniting and arsenic refining process, a large amount of arsenic trioxide and trioxide will be produced in the process of arsenic removal and antimony oxidation. fumes of antimony, bismuth metallurgical dust collection, mainly two kinds of smoke on governance.
Tables 1 and 2 list the composition of the flue gas and soot produced by the reverberatory refining of the crucible and the refining of the refining pot; Table 3 lists the amount of flue gas, the dust content and the flue gas flow rate.
Table 1 Composition of reverberatory furnace and refining boiler flue gas (%)
Table 2 Resin furnace and refining pot soot composition (%)
Table 3 Flue gas parameters of reverberatory furnace and refining pot
The refining reverberatory furnace and the refining pot are periodically interrupted, so the amount of flue gas and dust content as well as the composition of the soot and the composition of the flue gas fluctuate greatly, which brings certain difficulties to dust collection.
According to the periodic production and flue gas characteristics, the metallurgical filter should adopt a filter bag dust collector. The separation of gas and dust by passing dusty flue gas through the fiber fabric is a feature of various bag filters.
The dust collecting mechanism of the bag filter is summarized in three main points:
(1) Screening action, when the dusty flue gas passes through the porous fiber filter medium, the dust particles are adsorbed on the medium by the blocking surface to form an additional filter layer, and the filter medium and the additional filter layer jointly bear the dust particles in the flue gas. effect. When the additional filter layer reaches a certain thickness and the flue gas passes through the difficulty, the negative pressure is increased, and the soot is swayed by the compressed air to cause the soot to settle into the dust collecting hopper by gravity.
(2) Collision, the dust particles are deposited by collision with the filter medium and the additional filter layer under the action of inertia or thermal action of gas molecules.
(3) Electrostatic action, depending on the electrostatic attraction between the dust particles and the charge of the fiber fabric.
Figure 1 shows the dust collection process of the dust from the reverberatory furnace through the bag filter:
Figure 1 bag filter dust collection flow chart
The flue gas temperature of the 10 m 2铋 reverberatory furnace is 1050 ~ 1150 ° C, the flue gas volume is 2700 ~ 4600 b m 2 / h, the dust content is 3 ~ 10 g / standard m 3 , after the dust is collected by the bag filter, the flue gas is purified. The dust content is less than 0.03 g/ m3 , and the dust collection efficiency is over 99%.
The bag filter is generally composed of a bag filter chamber, a filter bag and a skeleton, a dust removing device, a dust collecting bucket, an air inlet exhaust pipe, and a dust exhausting device. There are many types of filters, which are generally classified according to the method of cleaning. They can be divided into manual rapping, mechanical rapping, compressed air rapping, anti-blowing cycle cleaning, pulse blowing cleaning, gas ring moving. Backflushing and other methods.
Second, compressed air vibrating bag filter
Compressed air rapping is a type of mechanical rapping. The air pressure is generally 24.5 Pa. The pressure of the compressed air overlaps with the spring force of the spring to shake the filter bag to clean the dust particles deposited on the filter bag. Compared with mechanical rapping, compressed air rapping equipment has a small amount of maintenance and good cleaning effect, and is suitable for large smoke production.
The schematic diagram of the compressed air rapping device is shown in Figure 2.
Figure 2 Schematic diagram of the compressed air rapping device
1-spring; 2-compressed air inlet;
3-link; 4-filter bag holder;
5-filter bag; 6-piston;
7-vibrating cylinder
The compressed air vibrating bag filter is made of φ220×3000 mm bag, and the filtering area of ​​each bag is 2 m 2 . The cooled dust-containing flue gas first enters the filter bag, and the purified gas passes through the filter bag medium into the filter bag chamber due to the negative pressure generated by the exhaust fan suction, and then the exhaust pipe enters the chimney through the exhaust fan, and The soot is blocked in the filter bag, and after being ruffled, it falls into the dust collecting bucket and is periodically discharged.
The filter bag is made of polyester fiber woven "208" industrial polyester flannel, which is resistant to acid and alkali corrosion and can be used up to 170 °C.
Use a bag filter to collect dust. All equipment must be inspected and tested, the temperature of the filter bag chamber is controlled at 105-140 ° C, and the negative pressure is between 490.33 and 1471.00 Pa, which is often shaken and cleaned, and the damaged filter bag is replaced in time.
Third, the pulse blowing bag filter
The pulse jet bag filter is used to periodically blow the filter bag with compressed air to remove soot deposited outside the filter bag. When blowing, an instantaneous negative pressure is formed in the venturi tube region, and a large amount of surrounding gas is drawn into the filter bag, so that the dust particles attached to the outside of the filter bag fall into the dust collecting hopper. Its working principle is shown in Figure 3.
Figure 3 Pulse jet bag filter construction and working principle
1-venturi tube; 2-box;
3-filter bag and skeleton; 4-dusty flue gas inlet;
5-ash hopper; 6-ash ash valve;
7-pulse blowing pipe; 8-purifying gas outlet
Compressed air blowing time is 0.1 to 0.2 seconds, air pressure is 58.8 Pa, and the filter bag material is made of glass fiber fabric treated with graphite and silicone resin. The filter bag has a diameter of 120 mm, a length of 2000 to 2800 mm, and a temperature resistance of 250 °C.
The pulse spray filter bag is externally filtered to collect dust. The dusty flue gas first enters the filter box, and the dust particles are deposited outside the bag. Since the flue gas flows from the outside of the filter bag to the inside of the filter bag, there must be a support skeleton in the filter bag. In order to maintain the shape of the filter bag, the flue gas enters the bag after purification, and enters the chimney after being exhausted through the exhaust pipe and the exhaust fan.
The pulse jet bag filter is not convenient for checking and replacing the filter bag. Because the filter bag is small, the number is large, and the arrangement density is large, which hinders people from entering the filter bag room, so the upper extraction check method is adopted, and the inspection method is large. Uncovering and small cover. The large cover type air leakage rate is small, but the individual damaged filter bags cannot be treated until the dust concentration of the flue gas outlet is too high, so that the centralized replacement process is removed, so the dust removal efficiency is low; Dealing with individual broken bags, improving the efficiency, but the air leakage rate is as much as 30% to 50%.
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