1. moisture absorption of dust
Hygroscopicity and deliquescence dusts such as CaO, Na2CO3, NaHCO3, NaCI, etc. are easily absorbed on the surface of the filter bag, or become viscous liquid after deliquescence, resulting in difficulty in cleaning, excessive pressure loss, and even forcing the bag filter to stop operation. In this case, general precautions for handling hygroscopicity and deliquescent dust are listed below.
(1) Use a lint-free, lint-free filter cloth. Such as the use of carpet filter. It should be surface treated. The selection principle is:
a. The chemical fiber is superior to the glass fiber, and the expanded glass fiber is superior to the ordinary glass fiber; the fine, short, and crimped fibers are superior to the coarse, long, and smooth fibers;
b. Felt is better than fabrics. Needle-punching is used in the felt to strengthen the inter-compatibility between fibers. The satin fabric is the best in the fabric, and the brushing on the fabric surface is also a measure to improve the wear resistance.
c. Surface coating, calendering, and other post-treatments can also improve wear resistance. For glass fiber filters, silicone oil, graphite, and PTFE resins can improve wear resistance and folding resistance.
(2 )should use the offline cleaning operation system. During the stoppage time, the dust on the surface of the filter bag is fully removed.
(3 )Bag filter should not be started continuously regardless of whether the dust source facility is operating or not. The bag filter should only be operated when the dust source facility is started. When dust is deposited on the filter cloth, moisture-containing air should not be passed through.
Exhaust gas of many dryers and sintering kilns is mostly high-temperature and high-humidity gas. When the bag filter stops running, the temperature drops and the humidity increases, which is easy to absorb moisture. For this purpose, a small hot air generator should be installed on the dust removal equipment. In this way, when the operation of the dust source device is stopped, hot air can be fed to maintain the internal temperature of the bag filter as it is.
Using the pre-coating method, that is, when dealing with local dust collection with a low concentration of dust, a layer of other powder may be pre-coated on the filter cloth, that is, only other powders may be supplied to the pipe, and after a period of operation, A layer of dust is attached to the filter cloth to collect the wet dust that needs to be collected.
2. Dust-laden gas containing tar mist
It is difficult to treat the gas containing only tar mist with a bag filter, but the gas can be filtered when the oil mist is not large but contains a considerable amount of dust. For example, in an asphalt concrete plant, the smoke from stone dryers is the main source, and dust from conveyors and other exhaust gases enters the bag filter. At the mixer and unloading the finished material. The tar mist generated by the heated asphalt concrete also enters the bag filter. In this case, the amount of dust accumulated on the filter cloth far exceeds the amount of oil mist, so that the trouble of oil mist adhesion can be prevented and the stable operation of the bag filter can be ensured.
In the production of electrodes, molded carbon products, and the like, a tar mist is also generated in the process of mixing the powder with the thermal adhesive. At this time, if dust is mainly generated during handling and pulverization, only a part of tar mist may be mixed with a bag filter. However, if the coke flue gas contained in the tail tar burner contains more tar, a suitable amount of coke powder should be added before the flue gas enters the precipitator to adsorb the coke.
If the gas contains only a small amount of oil mist, it can be treated separately. That is, adding a suitable amount of powder as a filter aid on the pipe, the bag filter can be used. After the added dust absorbs tar mist, it should be returned to the manufacturing process as much as possible.
3. high dust concentration gas
For handling gas with high dust concentration, cyclone dust collectors or gravity dust collectors can be installed as pre-dust, but this will increase the resistance of the system and increase power consumption. Therefore, when the dust or the finished product does not need to be classified, most of the dust collectors are used directly.
Not all baghouses can handle gases with high dust concentrations. Only a bag filter with a wide spacing between filter bags and a continuous cleaning device equipped with a filter outside the bag is suitable for handling gases with a high dust concentration.
When dealing with high dust content, the structure of the bag filter should be as far as possible to directly fall into the ash hopper or add some baffles to reduce the amount of dust attached to the filter bag; to prevent the friction damage of the filter cloth, should not The high-speed movement of dust directly hit the filter cloth.
The shape of the baghouse inlet and inlet baffles is shown in the figure. The latter is a part of the middle of the box as a pre-dust collector, and doubles as a power sedimentation chamber for dust and a diversion chamber for inlet gas.
The baghouse dust collector used for the pneumatic conveying device to collect dust has a cylindrical shape although it has a smaller amount of air to be handled, a higher concentration of dust, and a pressure-resistant box. Enterprises with conditions may replace the bag filter with plastic dust collectors.
The inlet of the cylindrical box is made tangentially to make it have a separating effect, and many rotary counter-blowing bag dust collectors are in this form. The hopper part is sometimes made in the form of a cyclone. For baghouse dust collectors for pneumatic conveying systems, because of the large amount of powder, the ash hopper volume and the diameter of the ash discharge port must be designed to be larger, and the capacity of the dust evacuation device must also have enough room to avoid the accumulation of powder in the ash hopper. material.
