Asphalt Mixing Plant Dust Collection Control Treatment

Asphalt mixing plants will generate a lot of dust during the production process (such as raw material transportation, screening, mixing, drying, etc.), which not only pollutes the environment, but also may affect the health of operators. The following are the main equipment and methods for dust collection and control treatment of asphalt mixing plants.
 

I. Core equipment for asphalt mixing plant dust collection and treatment

1. Bag dust collector (most commonly used)
- Principle: Use filter bags to intercept dust. When dust-containing gas passes through the filter bags, the dust is blocked outside the bag and clean gas is discharged. Pulse cleaning (compressed air backwash) or mechanical vibration is used to remove dust on the surface of the filter bag.
- Features:
High dust removal efficiency (up to 99.9% or more), can handle fine dust (particle size ≤1μm).
Applicable to dust-generating points such as drying drums, batching bins, and mixing pots in asphalt mixing plants.
Pay attention to the material of the filter bag (such as high temperature resistance and oil resistance, PTFE or coated filter material can be selected to adapt to the viscosity and temperature of asphalt dust).
- Typical application: The dust concentration and temperature at the outlet of the drying drum are high (about 120-180℃), and the bag filter needs to be equipped with high-temperature resistant filter bags and insulation measures.

2. Electrostatic precipitator
- Principle: The dust is charged by a high-voltage electric field, and the charged dust is adsorbed on the plate and then removed by vibration.
- Features:
Small resistance, suitable for processing large air volume, low energy consumption.
It has high efficiency for treating dust with a particle size of 1-20μm, but poor effect for fine dust (<1μm).
If asphalt dust is oily or sticky, it may cause the plate to adhere, which needs to be cleaned regularly and has high maintenance costs.
- Applicable scenarios: Pretreatment of some large asphalt mixing plants, or combined with other equipment.

3. Wet dust collector (water washing method)
- Principle: Dust is captured by water through contact with dust-containing gas, forming sewage post-treatment. Common types include spray tower, Venturi dust collector, cyclone water film dust collector.
- Features:
The dust removal efficiency is high, and some harmful gases (such as VOCs in asphalt smoke) can be absorbed at the same time.
No filter bag is required, and maintenance is simple, but oily sewage will be produced, and a sewage treatment system (such as sedimentation tank, flotation tank) is required to avoid secondary pollution.
Anti-icing is required in winter, and the humidity of the exhaust gas may increase, affecting subsequent treatment.
- Applicable scenarios: For scenes where dust and asphalt smoke are mixed and discharged (such as mixing pots, asphalt unloading ports), dust and organic pollutants can be treated simultaneously.

4. Cyclone dust collector (pretreatment equipment)
- Principle: Use centrifugal force to separate dust, and large particles of dust are thrown to the wall and then settled.
- Features:
Simple structure, low resistance, low cost, suitable for removing coarse dust with a particle size > 10μm.
When used alone, the efficiency is low (about 50-80%), and it is often used as a pre-treatment of bag dust collectors to reduce the load of the main dust collector.
- Application: coarse dust emission points such as raw material silo feed port, screening machine, or used in series with other dust collectors.

5. Combined dust collection system
- Design: For example, "cyclone dust collector + bag dust collector" and "wet dust collector + electrostatic dust collector", combining the advantages of different equipment to improve the treatment efficiency of dust of various particle sizes, while adapting to the complex characteristics of asphalt dust (such as high temperature and viscosity).

II . Methods and processes for dust control and treatment

1. Source control and process optimization
- Enclosure and negative pressure ventilation:
The dust-generating points (such as raw material conveyor belts, screening machines, and mixing pots) are fully enclosed, and a negative pressure ventilation system is set up inside to suck the dust into the dust removal equipment to avoid unorganized emissions.
Breathing holes and dust collectors are set on the top of the raw material silo to prevent dust from overflowing during feeding.
- Wet dust suppression:
A spray system (water mist or dust suppressant) is set up at locations such as the raw material yard and feed port to increase the humidity of dust particles and reduce flying.
Note: The stone materials in the asphalt mixing plant need to be dried, and the amount of water should be controlled for wet dust suppression to avoid affecting the subsequent drying energy consumption.
- Low dust process improvement:
Adopt closed material transportation (such as screw conveyor, tubular belt) to reduce material drop and dust.
Optimize the design of screening equipment to reduce the amount of dust generated during the screening process.

2. Dust removal system design and operation management
- Matching of air volume and air pressure:
Design the pipeline system according to the air volume demand of the dust-generating point to ensure that the negative pressure at each point is balanced (such as the air volume at the outlet of the drying drum needs to be calculated according to the drum speed and material amount).
The pipeline wind speed is controlled at 15-25m/s to avoid dust deposition due to too low wind speed, or too high wind speed to increase resistance.
- Cleaning and maintenance automation:
The bag dust collector adopts PLC-controlled pulse cleaning, and automatically adjusts the cleaning frequency according to the dust concentration to avoid filter bag clogging.
Regularly check the damage of the filter bag, the cleanliness of the electrostatic precipitator plate, and the water level and water quality of the wet dust collector to ensure efficient operation of the equipment.

3. Dust recovery and resource utilization
- Treatment of collected dust:
The dust collected by the bag filter is mainly fine stone powder, which can be reused in production at a certain ratio (such as adding to the mineral powder bin), but the reuse amount needs to be controlled (usually ≤5%) to avoid affecting the performance of asphalt mixture.
The sludge produced by wet dust removal needs to be dehydrated and can be used as roadbed filler or building material raw material after drying.

4. Environmental protection and safety supporting measures
- Explosion-proof design:
Asphalt dust is a combustible dust. The dust removal system needs to be equipped with explosion-proof pressure relief devices (such as explosion relief plates), and electrical equipment should be explosion-proof to avoid static electricity accumulation.
- Emission monitoring:
Install a dust online monitor to monitor the emission concentration in real time (refer to the national standard GB 4915-2013 "Emission Standards for Air Pollutants in Cement Industry", particulate matter emission concentration ≤30mg/m³, and some areas are more stringent).
- Co-treatment of asphalt fume:
If the dust contains asphalt fume, activated carbon adsorption, photocatalytic oxidation or plasma treatment equipment can be added after the dust removal system to remove organic pollutants such as VOCs.

The combined application of the above equipment and methods can effectively control the dust pollution of the asphalt mixing plant, and at the same time realize the resource utilization of dust, taking into account both environmental protection and economic benefits.