How to Deal with Exhaust Gas in Dryer Production
The exhaust gas from the dryer has a large blowing rate, large moisture and a high emission point and high dust concentration, it is easy to form dew with a high dew point, and has a wide 
range of pollution. All of that mentioned above are dust removing difficulties. The exhaust gas from the dryer is related to technological conditions of each factory. Some factories have a changeable production with drying multiple materials, frequently shut-up and shut-down, and fluctuation range is large. Besides, sulphur oxides in exhaust gas will corrode the metal structure parts by using coal as heat source, which makes it more difficult to select the dryer.
1.Cyclone Dust Removal Technology
Cyclone dust removal technology, which is suitable for the air of high dust concentration, has the characteristics of low cost, easy to operate and can deal with high-temperature gas. The operating principle is that on effect of the draught fan, the air flow which contains dust gets into the volute of the cleaner along with the tangential direction from the inlet in a higher speed, it rotates spirally from top to bottom, and the dust particle is threw to the outer wall under the impact of the centrifugal force, and rotate down along the wall, it turns to axis with the shrink of the conicalness, then gets bace in force of the bottom resistance, spirally rotates and expels from barrel from bottom to top along with the axis. Dust particle in the outer wall drop into the bucket along the wall drove by the gravity and air flow downwards. Due to the cyclone dust collectors working depends on dust particle inertance to separate, collection efficiency is proportional to grain diameter, large grain size will have a better clean effect, and bad effect with the small grain size. In general, remove the dust more than 20 micrometers, the collection efficiency is 70%～90%.
2.Bag Dust Removal Technology
Everybody knows that bag dust removal technology is stable, efficient, easy to maintain and reliable running, its collection efficiency could be 99% to deal with the dusty gas of 0.1 micrometer. There is no need to consider the problem of that the emission concentration is out of limits with selecting bag dust cleaner when use the exhaust gas dust removal equipment of the drying equipment.
Anti-condensation glass fiber dust remover of the dryer is an ideal dust removal purigying equipment at present. The equipment is controlled by the computer, it can clean the dust regularly and install the temperature detection displayer and overtemperature alarm device. It can prevent dew formation of the filter-bag with CW300—FcA anti-condensation glass fiber filter-bage, and the filter-bag can not be burned out. Mineral waste residue of 3×24 m diameter changes the two-stage dust removing process into one-stage LFEF7×358—HSY／H anti-condensation bag cleaner. According to the test result determined by the environmental protection department, exhausted air quantity is 42621m3/h, dust concentration in inlet is 69620mg/ m3, dust concentration in outlet is 147mg/ m3, and this can reach the National Emission Standard. It not only improves the output, but also recycles the dried materials, economic benefit every year can be about 700000RMB, at the same time, it gets social benefits obviously. But it has the disadvantages of using large area and high investment. With the development and wide use of filter-bag membrane technology, the disadvantages can be overcome.
3.High Voltage Electrostatic Precipitation Technology
High voltage electrostatic precipitation technology, change the alternating current of 50Hz, 220V to direct current of 100kw or more, make direct current to negative pole to form the uneven high voltage, gas ionization produce a lot of anions and electrons, which make the charge dust tend to the opposite pole on effect of electric field force. In general, positive pole is dust collection pole, which finishes the cleaning process depends on dropping into ash bucket and discharge. High voltage electrostatic dust collector efficient low resistivity can be widely used in the dust pollution situation of building materials, metallurgy and chemical industry. It has a good dust extraction effect with high concentration dust, and it applies to cleaning dust of exhaust gas of dryers and can satisfy the dryer equipments with different air quantity.
4.Wet Process Dust Removal Technology
Wet process dust removal technology, draught fan brings dusty gas into the bottom of dust removal tower through air pipe. The section is large, and flow speed is low, coarse particle dust settled in air flow first and fine dust goes up with air flow, droplets sprayed and dust air flow move in reverse direction. Dust is wet and the weight is on the increase, it drops to muddy water by overcoming the lift force of air flow in the force of gravity, then it goes to settling pond through the bottom pipeline, and dust is removed. Muddy water to be clear water through 2～3 level circulation and sediment, it will not result in secondary pollution by forcing into dust removal tower with pump and use recycled. Positive pressure of this technology is used for drying clay and various of materials. Recycled material is easy to mixed with other matters and wear the fan blade heavily, so it can not be used. Apply wet process dust removal technology to clay dryer of 2.2×12m diameter, emission concentration can satisfy national emission standard, that is, 132mg/m3. Clean settling pond once every year, wet soil can be as material, store it after drying. The dust removal system has good economic benefit and social benefits with high efficiency, low resistance, no secondary pollution, flexible process, stable running, low power consumption, low cost, non-condensing and good adaptability.
