Hot Mix Asphalt Plant Pollution Control

Pollution control of hot mix asphalt plants requires comprehensive control measures targeting major pollution sources, including dust, exhaust gas (such as asphalt fumes and NOₓ), noise, wastewater and solid waste.
 

1. Dust Pollution Control
Dust primarily originates from the storage, crushing, screening, drying, mixing, and material handling of raw materials (sand, gravel, and mineral powder). Control measures include:
- Enclosed Storage and Transportation
Raw material and mineral powder silos should be enclosed to avoid open-air storage. Belt conveyors, screw conveyors, and other equipment should be equipped with enclosures to reduce material spillage and dust generation.
Unloading points (such as truck unloading into silos) should be equipped with enclosed discharge channels and localized exhaust ventilation to direct dust into the dust removal system.
 

- High-Efficiency Dust Removal Equipment
In the crushing/screening process, a cyclone dust collector and a pulse bag dust collector (secondary dust removal) should be installed to remove large dust particles and further purify fine dust (with an efficiency exceeding 99%). Dryer/Mixer: Exhaust ducts are installed at the dryer outlet and the top of the mixer, connected to large pulse bag filters to treat high-temperature, dusty exhaust gases (high-temperature-resistant filter bags are required).
Addressing Dust in the Plant Area: Mist cannons or sprinkler systems are installed around the material yard and on roads to regularly spray water to reduce dust. The hot mix asphalt plant floor is hardened and drainage ditches are installed to prevent accumulation of water and dust.

 

II. Exhaust Gas Control (Asphalt Fumes, VOCs, NOₓ, etc.)
- Asphalt Fume and VOC Control
Asphalt fumes are primarily generated during asphalt heating (in storage tanks and thermal oil furnaces) and mixing. They contain toxic substances such as polycyclic aromatic hydrocarbons and require the following treatment measures:
Enclosed Collection: Airtight collection hoods are installed at the asphalt storage tank breathing port and the asphalt addition port of the mixer, and piped into the purification system.
Purification Equipment: Utilize an electrostatic precipitator (efficiently removes tar particles from asphalt fume, with an efficiency exceeding 85%) and an activated carbon adsorption device (to treat residual VOCs); or high-temperature incineration (if integrated with a combustion system, waste heat can be used to decompose organic matter).
- Combustion Exhaust Gas (NOₓ, SO₂) Control
Drying drums are typically heated with diesel, natural gas, or biomass fuels, generating NOₓ and a small amount of SO₂ during the combustion process.
Low-NOx burners are preferred (reducing NOₓ generation by 30%-50%). If emission requirements are stringent, a selective non-catalytic reduction (SNCR) denitrification system (injecting ammonia/urea to reduce NOₓ) can be installed.
If high-sulfur fuel is used, a simple wet desulfurization system (such as an alkali spray) can be used to remove SO₂.

III. Noise Pollution Control
Noise sources include crushers, screens, fans, air compressors, mixing motors, pumps, etc. Control measures include:
- Equipment Selection and Vibration Reduction
Select low-noise equipment (such as low-noise fans and variable-frequency air compressors); install vibration damping pads and vibration dampers on the foundations of high-noise equipment (crushers and vibrating screens) to reduce vibration-induced noise.
- Sound Isolation and Silencing
Install fans and air compressors in separate soundproof rooms, using sound-insulating materials (such as soundproof panels) for the walls. Install impedance composite silencers at fan inlets and outlets to reduce airflow noise.
Plant tree green belts (width ≥ 10m) or install sound barriers (height 3-5m) around the factory area to attenuate outward-propagating noise.
- Reasonable Layout
Locate high-noise equipment (such as the crushing area) on the side of the factory area away from residential areas, maintaining a sufficient distance (typically ≥ 300m, depending on local standards) from sensitive areas (such as villages and schools).

 

IV. Wastewater Pollution Control
Wastewater primarily comes from equipment cleaning (such as mixing tanks and transport vehicles), site washing, and initial rainwater, and contains small amounts of oil and dust.
- Wastewater Collection and Reuse
Establish initial rainwater collection tanks and wastewater sedimentation tanks (tertiary sedimentation). Wastewater is then reused after sedimentation (e.g., for spraying to reduce dust and washing vehicles), achieving zero external discharge.
When cleaning equipment with high oil content (such as asphalt tanks), the floating oil is first separated in a grease trap before being processed in a sedimentation tank.

 

V. Solid Waste Pollution Control
Solid waste includes dust collected by the dust removal system, waste asphalt mixture, and waste oil (from equipment maintenance).
- Dust and Waste Mixture: Dust from dust removal can be reused in mix production (incorporated in proportion and subject to testing and compliance). Waste mix can be crushed and reused as base aggregate, avoiding landfill.
- Hazardous Waste Disposal: Waste engine oil, waste thermal oil, etc. are considered hazardous waste and must be stored in a dedicated, impermeable hazardous waste storage room and regularly handed over to a qualified organization for disposal.

 

VI. Comprehensive Management Measures
- Online Monitoring and Recordkeeping: Install online dust and NOₓ monitors at exhaust outlets, with data networked to the environmental protection department. Record equipment operation, reagent changes, and monitoring data.
- Regular Maintenance: Monthly inspect dust collector filter bags, electrostatic tar collector electrodes, and fan mufflers to ensure equipment efficiency. Quarterly calibrate monitoring instruments.
- Emergency Prevention and Control: Develop emergency response plans for dust leaks and excessive exhaust gas levels, and maintain backup adsorbents and spray equipment.
 

Through this combined approach of "equipment configuration + process control + end-of-pipe treatment," pollutant emissions from hot mix asphalt plants can meet the environmental protection requirements.