During the production process of asphalt mixing plant, a large amount of dust, asphalt smoke and trace VOCs pollutants will be produced in the processes of aggregate drying, screening and mixing, which have the characteristics of high flue gas temperature, high moisture content, strong dust viscosity and mixed particle size.With the continuous tightening of environmental emission standards, traditional extensive dust removal equipment can no longer meet the ultra-low emission requirements, scientific selection of dust removal equipment, directly determine the mixing plant environmental protection standards, production stability, operation and maintenance costs and equipment service life.This paper combines the working condition characteristics of asphalt mixing plant, the performance of mainstream dust removal equipment, core selection parameters and landing application scenarios, systematically combs the selection ideas and key points of dust removal equipment, and provides professional reference for equipment configuration and upgrading of mixing plant.

I. Core characteristics of dust removal conditions of asphalt mixing plant
The core premise of selection is to match the site conditions. The flue gas dust conditions of asphalt mixing plant are different from ordinary industrial dust. The special attributes directly determine the boundary of equipment selection. The core characteristics mainly include four points:
Second, the dust composition is complex and viscous.Dust contains fine particles of aggregate, mineral powder and asphalt light components. Asphalt oil and gas are easy to adhere to the surface of dust removal parts at high temperature, which is easy to cause filter material blockage and hardening. Ordinary dust removal equipment is easy to have the problem of rapid attenuation of dust removal efficiency.
Fourth, strict emission requirements.At present, the particulate matter emission limit of asphalt mixing plant in mainstream areas in China is ≤10mg/Nm³, and stricter standards shall be implemented in key environmental protection areas, and the dual requirements of online monitoring and non-organized dust control shall be met.
Second, asphalt mixing plant mainstream dust removal equipment comparative analysis
1. Cyclone dust collector (primary pretreatment)
However, this equipment has very low removal efficiency for PM10 and PM2.5 fine dust, which cannot meet the environmental protection emission requirements alone. It is only suitable for pre-treatment and cannot be used as a main dust removal equipment alone. It is often combined with a bag filter to form a multi-stage dust removal system.
2. Bag filter (core fine dust removal)
According to the dust cleaning method, it can be divided into pulse bag filter and offline dust cleaning bag filter, among which offline dust cleaning equipment is more suitable for asphalt high viscosity dust working condition, which can effectively avoid the paste bag problem caused by incomplete dust cleaning.The disadvantage is that there is filter loss, which needs to be replaced regularly, and the initial equipment investment is higher than that of cyclone dust collector.
Electrostatic precipitator uses high-voltage electric field to adsorb dust, dust removal efficiency can reach 98%~99.5%, suitable for high concentration, large flue gas volume conditions, but the equipment investment cost is high, the structure is complex, the operation and maintenance technology threshold is high, the adaptability to asphalt viscous dust is poor, electrode scaling, abnormal discharge and other problems are easy to occur, currently only in large-scale mixing station pilot application, the popularity rate is low.
Three, dust removal equipment core selection key parameters
Combined with the operating conditions and equipment performance, the selection should be accurately matched around the five core parameters of air volume, filter material, filtration wind speed, temperature adaptation and emission standard, so as to avoid problems such as excessive environmental protection, high energy consumption and frequent failures caused by inconsistent parameters.
1. Processing air volume and allowance configuration processing
Air volume is the basis for selection, which shall be calculated comprehensively in combination with mixing plant capacity, exhaust gas volume of drying drum and total air collection volume of mixing cylinder, and shall not be selected solely according to equipment nameplate parameters.Conventional selection needs to reserve 10%~15% air volume margin to deal with unexpected situations such as high aggregate moisture content, increased production load, equipment aging and air volume attenuation.Too small air volume will lead to dust escape and excessive emission; too large air volume will increase equipment investment, fan energy consumption and filter material loss, resulting in waste of resources.
2. Filter material precise selection
Filter material is the core consumable of bag filter, which directly determines the dust removal efficiency and service life. It is necessary to select the appropriate material according to the flue gas temperature, dust viscosity and corrosivity.There are two kinds of filter materials commonly used in asphalt mixing plant: one is Nomex filter bag, temperature resistance 180~200℃, short-term instantaneous temperature resistance up to 220℃, excellent wet heat resistance, anti-adhesion performance, suitable for most conventional mixing station conditions, the highest cost performance; the other is Nomex high temperature filter bag, temperature resistance 200~250℃, short-term temperature resistance 280℃, filtration accuracy up to 0.1μm, extremely high removal rate of PM2.5, suitable for mixing stations in high temperature, high load and environmental control areas.It is forbidden to use ordinary filter bags at room temperature to avoid coking at high temperature and rapid damage.
3. Reasonable control of filtering wind speed
Filter wind speed is a key index affecting dust removal effect. Asphalt flue gas contains viscous dust. Too high wind speed will cause dust to quickly penetrate filter bags and paste bags to be blocked. Too low wind speed will cause large equipment volume and increased investment.The net filtration wind speed of conventional asphalt mixing plant should be controlled at 0.8~1.2m/min, and the high humidity and high viscosity conditions should be reduced to 0.6~0.8m/min, giving priority to ensuring dust removal stability and sacrificing the volume advantage of some equipment.
4. Temperature and anti-condensation design
According to the characteristics of high humidity and temperature fluctuation of flue gas in mixing station, it is necessary to check the anti-condensation and high temperature resistance design of equipment during type selection.The equipment shell shall be equipped with insulation layer to avoid dew condensation of flue gas in low temperature environment; the filter material, bag cage and sealing parts shall be fully adapted to high temperature conditions; the bag cage shall be preferably made of organic silicon anti-corrosion treatment material to resist flue gas corrosion and prolong service life.
5. Match local environmental emission standards
Before type selection, it is necessary to clarify the national standards and local special standards implemented in the project location, confirm the emission limits of particulate matter, asphalt smoke and VOCs, and adapt to the installation requirements of online monitoring equipment.Conventional areas can meet the emission of 10mg/Nm³. High-precision dust removal equipment shall be selected for key environmental protection areas, scenic spots and Urban area stations, and ultra-low emission upgrading space shall be reserved to avoid environmental protection rectification risks.

IV. Different scenario selection schemes and optimization strategies
1. Small and medium-sized conventional mixing plant (capacity below 1000 tons/hour)
Priority is given to the two-stage dust removal system of "cyclone dust collector + pulse bag dust collector", which has the best cost performance.The front cyclone dust collector intercepts large particles of dust and reduces the rear load; the main equipment selects Metas filter bag pulse bag dust collector, controls the filtration wind speed of 0.8~1.0m/min, meets the conventional environmental protection emission requirements, simple operation and maintenance, low consumable cost, and adapts to normal production conditions.
2. Large high-load mixing plant (capacity of more than 1000 tons/hour)
It is recommended to use offline dust cleaning bag dust removal system, with Nomex high temperature filter bag, equipped with automatic intelligent dust cleaning, temperature sensing monitoring, over-temperature alarm function.Under high production capacity conditions, flue gas volume is large, temperature fluctuation is frequent, dust concentration is high, offline ash cleaning mode can realize separate shutdown ash cleaning, thoroughly remove viscous dust, avoid continuous paste bag, ensure continuous and stable operation of equipment for 24 hours, and adapt to high-intensity production requirements.
3. Mixing station in Urban area and strictly controlled environmental protection area
On the basis of two-stage dust removal, optimize equipment sealing and gas collection system, complete with closed gas collection hood and pipeline negative pressure collection device to eliminate non-organized dust emission.Select high-precision high-temperature filter material, strictly control filter wind speed, reserve VOCs auxiliary treatment interface, meet ultra-low emission and normal environmental protection supervision requirements, and adapt to strict supervision scenarios.
V. Common mistakes and precautions in type selection
First, do not only focus on price light adaptation.In order to control the cost, some stations select low-cost and low-equipped equipment, which has problems such as poor high temperature resistance of filter materials, insufficient air volume margin, weak ash cleaning system, etc., which is easy to cause paste bags and excessive emissions in the short term, and the long-term operation and maintenance cost far exceeds the equipment price difference.
Third, ignore the system compatibility.Dust removal equipment shall be matched with fan, pipeline and gas collection system. The wind pressure and air volume of fan are insufficient, and the pipeline resistance is too large. Even if the host equipment meets the standard, the dust removal effect is not good and the dust escapes.
Fourth, belittle operation and maintenance adaptability.The selection shall take into account the convenience of operation and maintenance in the later stage, and the equipment with modular design, easy replacement of filter material and intelligent monitoring shall be preferred to reduce the difficulty and cost of maintenance and consumable replacement in the later stage.
VI. Conclusion
The core of the selection of dust removal equipment for asphalt mixing plant is the adaptation of working conditions, accurate parameters, system matching and long-term stability.Abandoning the single price-centered selection thinking, combining the mixing plant capacity, flue gas conditions, environmental protection standards, operation and maintenance requirements, adopting the multi-stage dust removal system of "pre-pretreatment + back-end fine dust removal", accurately matching the core parameters such as filter material, wind speed, air volume, etc., in order to give consideration to environmental protection standards, stable production and controllable costs.Scientific selection can not only help the mixing plant avoid environmental risks, but also effectively reduce the equipment failure rate and operation and maintenance costs, and realize the two-way improvement of production efficiency and environmental protection benefits.