Dust removal device of the hottest asphalt mixer

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Asphalt mixer dust removal device

Abstract: the analysis of asphalt mixing will pay more attention to the source of pollution caused by the consumer experience machine, briefly describe the classification of the dust remover, and after analyzing its economic and technical performance, such as dust removal efficiency, economic cost, etc., introduce the design, manufacturing and use effect of the asphalt mixer dust removal system

asphalt mixer is an important equipment in the construction of asphalt pavement, which is mainly used for the generation of asphalt mixture for large and medium-sized maintenance of highway asphalt pavement. The traditional asphalt mixing mechanism has the advantages of simple construction, less investment, low power consumption and low dust removal effect. The asphalt concrete mixing equipment produces a large amount of smoke and dust in the processes of drying, screening, transportation and mixing of hot aggregate, mainly the dust generated by the stone system, which causes great pollution to the surrounding environment when used. It is imperative to reform the dedusting technology of asphalt mixer

1. Main causes of mixer pollution:

(1) composition of mixer system

asphalt mixer is mainly composed of asphalt oil system, mineral powder system, stone (including stone chips) system, mixing system, storage system and control system. The raw materials used in the asphalt mixer are: asphalt oil

material, mineral powder (sand) and stone, and the finished product is asphalt mixture

(2) pollution of the mixer

the production process of the asphalt mixer is to add the processed stones to the drum dryer through the material handling device, heat them to 140 ℃ ~ 180 ℃, then send them to the asphalt mixer, and mix them with a certain proportion of heated asphalt to form an asphalt mixture for paving. The traditional asphalt mixer generally does not have a dust removal system, but the asphalt mixer produces a large amount of smoke and dust in the processes of drying, screening, transportation and mixing of hot aggregate, mainly the dust produced by the stone system. The dust produced by shilao is directly discharged from the smoke exhaust outlet, and its dust emission concentration is far greater than the national emission standard, which not only endangers the health of workers, but also seriously affects the surrounding environment. May 2003 Longyan city environment! The smoke and dust detection results of the temporary testing center: its average smoke and dust emission concentration reaches 3558.1mg per cubic meter,

the smoke and dust emission is 103.4kg/h, which is 23.5 times higher than the national standard

2. Design basis of dust removal device:

(1) selection of dust collector type

the causes of dust pollution produced by the mixer are analyzed. The selection of dust collector of the mixer should also start with reducing dust emission. At present, there are mainly two types of dust collectors commonly used in asphalt concrete mixing equipment and with good dust removal effect: wet dust collector and bag dust collector

wet dust collector is a dust removal equipment that uses liquid, liquid film or liquid droplets to collect dust and purify dust by virtue of the contact between liquid and dust and flue gas. Wet dust collectors rely on inertial collision, interception and diffusion, as well as condensation effect and other mechanisms to separate smoke and dust. This kind of dust remover is characterized by mainly using water as the dust removal medium, also known as washing dust removal. Wet dust collector has the advantages of simple structure, low cost and high dust removal efficiency, and the dust removal efficiency can generally reach more than 95%. It is stable in medium and small asphalt mixers

bag filter is a kind of purification equipment that uses organic or inorganic fibers as filter bags to filter out the dust in the gas. It is an efficient dust collector, which can collect more than 0.3mm

dust, and the dust removal efficiency can reach 95% ~ 99%. The dust concentration of the discharged flue gas can reach less than 100 mg per cubic meter, or even meet the requirements of higher standards. However, the investment (cost) of bag filter is high, and the operation and maintenance costs are high. It is generally used in large asphalt mixing plants

based on the comprehensive analysis and comparison of the working principle, dust removal effect, investment cost, operation cost, maintenance cost of the above two kinds of dust collectors, as well as the actual utilization rate and transformation cost of our asphalt mixing equipment (see Table 1) and economic considerations, the cost of purchasing the dust remover produced by the manufacturer is high. It is decided to design a simple wet dust collector to transform the asphalt mixer according to the working principle of the wet dust collector, and the transformation cost is controlled within 100000 yuan

(2) operation parameters of the simple wet dust collector

the main parameters that the simple wet dust collector must meet in order to achieve the predetermined dust removal effect are as follows:

liquid (droplet) coverage ≥ 98%; Smoke emission ≤ 27kg per cubic meter: smoke emission concentration ≤ L50 mg per cubic meter

3. The simple wet dedusting device is mainly composed of circulating sedimentation tank, centrifugal clean water pump, water spray gun head, dedusting bucket, smoke and dust separation bucket, various connecting pipes and seals. See Gang L for its structure

(1) the design of water spray gun head is the key to whether the simple wet dust removal device can meet the dust removal requirements. According to the atomization characteristics of pressure nozzle and the influence theory of atomization pressure and nozzle aperture on atomization characteristics. When the water pressure is ≥ 2MPa, when the nozzle aperture is 6inin, a water film with an included angle of more than 90 degrees is formed by spraying, and the water flow velocity is greater than 10m/S; When the nozzle aperture is less than 3inm, the water is completely atomized. Considering the processing technology and the atomization effect of water, the porous water gun head made of A3 steel with an inner diameter of 50 film and an outer diameter of 57mm is selected (because the water pump outlet pressure is not large, the material strength of the water spray gun head used is far greater than the actual required strength, so it is not necessary to calculate and check the strength). The diameter of the main outlet hole of the water spray gun head is 6mm. On the circle with a diameter of 30mm, eight auxiliary water holes are set uniformly, and the center line forms a 45 degree angle with the center line of the main outlet hole. When the working water pressure is 2MPa, the volume of sprayed water contacting with dust is moderate, and the atomization effect is ideal, which meets the requirements of liquid coverage ≥ 98%, and the dust removal ability is very strong

(the bottom of the box should be higher than the ground 2) dust removal water source

in order to ensure that the working water pressure of the water spray gun head can meet the design requirements, a set of s65-50-160 centrifugal clean water pump (rotating speed 2900r/min, lift 50m, flow 30m 3/h, motor power 7.5kw) is selected as the dust removal water source, and the water inlet pipe of the pump is installed at one end of the Zhici sedimentation tank of the water ditch (this can ensure that the water pump absorbs clean water), The water pipe of the water pump is connected with the water spray gun head through a pipe. Through hydraulic test, the water pump can ensure to provide sufficient pressure water source for the spray gun head (working water pressure ≥ 2MPa)

(3) dedusting bucket

as a dedusting container, it is necessary to ensure that there is enough space for the smoke and water to fully contact, and that the water of the main nozzle can completely collide with the barrel wall to produce splashing water droplets. The dedusting bucket is welded with 5mm thick steel plate into a cylindrical bucket with a diameter of 600mm and a height of 700mm. In order to facilitate the installation of water spray gun head and other components, the upper cover is fastened with bolts and dense gaskets. The top of the dust discharge pipe is made of 5mm thick steel plate

into a 300mm diameter conical baffle (the top of the cone is upward), and the conical baffle is welded with the dust discharge pipe of the induced draft fan. It is used to slow down the flow rate of smoke and dust, change the flow direction of smoke and dust, and prevent water from entering the smoke exhaust pipe. The big end (with a diameter of 50ram) of the water spray gun head is connected with the water outlet pipe of the water pump with a pipe. The end of the water spray hole enters about 400mm above the conical top of the conical baffle from the barrel cover. The diameter of the dust discharge pipe is 200mm, and four uniformly distributed 50mm dust discharge holes are set on the circle 100mm below the connection between the dust discharge pipe and the conical baffle. A hemispherical bucket made of 5mm thick steel plate is set under the dust discharge pipe (the diameter direction of the hemispherical bucket is upward, which is used to change the flow direction of smoke and dust, causing the smoke and dust in the bucket to flow around). The smoke and dust mixture discharged by the exhaust pipe of the asphalt mixer will fall into the hemispherical bucket after being washed by the mist water sprayed by the water spray gun head, and an outlet with a diameter of 200mm is set on one side of the hemispherical bucket. The dust cement mixture after dust removal flows into the dust separation barrel through the connecting pipe from the outlet. Through experiments, the liquid (water droplets) coverage in the barrel is ≥ 98%, meeting the dust removal requirements

(4) smoke and dust separation barrel

the smoke and dust separation barrel is welded with 5mm thick copper plate. One side of the barrel is provided with an inlet with a diameter of 200mm, which is connected with the outlet of the dust removal barrel through a pipe. The smoke and dust water after dust removal enters the smoke and dust separation barrel from this inlet. The top of the barrel is provided with a smoke exhaust hole with a diameter of 150mm, which is connected with the cigarette merchant with bolts. The separated smoke enters the cigarette merchant through this hole and is discharged into the atmosphere. A 100mm diameter row hole is opened at the lower part of the barrel, and the separated dust and water are mixed into the pipeline through this hole and then flow into the secondary sedimentation tank. The smoke separation bucket uses the flow direction of the mixture of smoke and dust water to separate the dust water mixture that quickly flows into the bucket, so that it cannot be discharged into the atmosphere by the smoke merchant with the smoke. The dust water mixture falls to the lower part of the bucket due to gravity and sudden change of flow direction, and flows into the first sedimentation tank of the circulating sedimentation tank through the pipe through the discharge hole at the lower part of the bucket, so as to achieve the effect of dust removal

(5) circulating sedimentation tank

in order to ensure sufficient water for dust removal, the circulating sedimentation tank must have sufficient volume. The circulating sedimentation tank can be made of bricks, with a length of about 1.2m, a width of about 6 m and a height of about 1.5m (if the site allows, the tank can be larger). A partition wall is built along the length of the pool to separate a 0.6m wide called ditch (the water in the return ditch is the clean water flowing into after sedimentation). A 0.5m wide and 0.6m high water inlet is opened on the upper part of the partition wall away from the pump end to make the clean water in the stable pool enter the return ditch, so as to form circulating water to provide water source for the pump. Three partition walls are set along the width of the pool, and one 0.5m is set at the upper part of each partition wall × For the 0.6m water outlet, the water outlet should be arranged in a staggered manner, as close to the side wall of the pool as possible. The size of the separated pool varies, and the water dust mixture enters the pool (the first sedimentation pool) at the maximum, and then decreases in turn. The amount of dust deposited in the first sedimentation tank is about 70%, the amount of dust deposited in the secondary sedimentation tank is about 25%, the amount of dust deposited in the third sedimentation tank is about 4.5%, and the amount of dust deposited in the stable pool is about 0.5%. After stabilization, the clean water flows into the return ditch water supply pump from the water inlet called the ditch for reuse. The partition wall in the water must be set to facilitate the deposition of dust and meet the requirements of circulating water (fill the pool with clean water before use)

4. Use effect of dust collector:

after the simple wet dust collector is processed according to the design drawings, the total cost is about 95000 yuan. It is installed on slhb-14 asphalt mixing and construction atmosphere equipment, and the dust removal effect is very good. Clean up the

deposited dust in the sedimentation tank regularly, which will not cause secondary pollution. In November 2003, Longyan Environmental Monitoring Center tested again, and the concentration of smoke and dust discharged into the atmosphere after treatment by the system reached 45.5mg per cubic meter, and the smoke and dust emission was 23.6kg/h

after five years of use, the improved asphalt mixer has generated more than 30000 tons of asphalt mixture, and the dust removal effect has achieved good results. The smoke and dust emission has reached the emission standard GB16297-1996 stipulated by the national environmental protection department. Since 2004, this technology has been transformed and used on Asphalt Mixers in six branches of our city, and achieved good results, which has been affirmed by the masses and maintenance workers. Practice has proved that the dust removal system is simple in structure, easy to manufacture, easy to disassemble, low in cost and good in dust removal effect. It is a rare supporting facility for semi mobile asphalt mixer

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