Causes of dust precipitation in large-scale aggregate production line and treatment measures

The process links of the sand and gravel processing system include crushing, screening, transportation and storage. Sand and gravel will generate a large amount of dust during the production process, which not only directly affects the normal operation of operators, but also seriously pollutes the environment. This article analyzes the causes of dust generation and prevention measures for a large sand and gravel processing system of a limestone mine project.

1. Sand and gravel production process and dust source

1.1 Process flow of sand and gravel processing system

A limestone mine project in Anhui Province mainly includes crushing, screening, sand making workshops, semi-finished products yard, 4.75～31.5mm mixed material yard, ≤4.75mm finished sand yard, ≤6.00mm stone chip yard and belt type Conveyor etc.

1.2 Source of dust

The ore processing adopts the whole dry production process. Sand and gravel processing mainly produces different degrees of dust in the processes of crushing, screening, sand making, transportation, and various storage yards. The main components of dust are fine particles of dust and stone, without special pollutants. Dust emissions are basically unorganized emissions, with large amounts of dust produced in the links of crushing, screening and material transfer.

2. Influencing factors of dust generated by sand and gravel processing system

2.1 Material moisture content

If the ore has high water content, the amount of dust produced is small. The material contains internal water and external water. The internal water is the water that exists naturally during the formation of the ore; the external water is the water attached to the ore particles by the external environmental water. Due to the influence of geological conditions and climate, the water content of the raw ore is generally not high, so the size of the external water will have a significant impact on the dust. Although the sand and gravel processing system is produced by dry process, there is a lot of rain in the area where the system is located, and some production points have external water infiltration, and external water management needs to be strengthened.

2.2 Belt running speed

The belt running speed is too slow to reach the specified processing capacity, and it will cause the backlog of ore on the yard; too fast speed will easily cause the belt to run off and cause a large amount of ore to fall, which will increase the dust pollution in the crushing and screening workshop. During a certain period, the greater the output of ore passing through the chute to the lower belt, the greater the impact on the belt, more dust particles, and more serious belt damage. Therefore, the belt running speed should be controlled as much as possible.

2.3 Chute drop

During the falling process of the ore, the collision of dust particles at the chute and the friction between the particles and the chute will produce a large amount of dust. A large amount of small particles staying in the air for a long time will increase the pollution of the dust at the transfer point. The drop at the reprinting point should be minimized.

2.4 Reprinting point form

At the transfer point, the ore particles deviate from the original orbit and will naturally settle in the air in a short time. Smaller dust particles will stay in the air for a long time, causing pollution, while the fine particles on the belt will adhere to the larger particles and become dust.

2.5 Dust particle size

The schematic diagram of different dust falling is shown in Figure 2 and Figure 3. From Figure 2 and Figure 3, it can be seen that due to the drop of the transfer point and the vibration of the belt, the coarse particle dust departs from the original running track, enters the air and becomes dust, but the amount of dust is extremely small and will naturally settle in a short time .

Small particles of dust will leave their own trajectory and adhere to particles with relatively large diameters and enter the air. Small-diameter particles stay in the air for a long time, even if they have settled down, they will become secondary pollution under the next ore impact.

3. Comprehensive dust control plan

3.1 Crushing workshop

1) Equipped with a bag filter for negative pressure dust collection at the discharge port of the crusher, and the well is tightly sealed with a fully enclosed guide trough.

2) Equipped with a dust suppressor to suppress the dust generated by material crushing. Adopt the double-electron-layer nano-film with good stability and mix it with the material in the crushing cavity. In the process of continuous wrapping, adsorption, agglomeration, and sedimentation, the nanomembrane comprehensively suppresses a large amount of dust generated, most of the dust will disappear, and the nanomembrane will continue to be effective for a certain period of time.

3) Equipped with dual-fluid cloud dust seal to spray dry mist, so that the dust at the unloading port of the mobile trolley will agglomerate and settle in the dry mist.

3.2 Screening workshop

Due to the large height difference between the vibrating screen surface and the receiving belt conveyor (3~7m), the impact force generated during the fall of the material makes the materials collide with each other, forming secondary dust. It is necessary to install a fully enclosed guide trough for sealing, and configure a bag filter. The collected stone powder is sent to the ash storage tank through the silo pump under the bag filter. The cloud dust seal is configured to capture and reunite the dust generated by the vibration and collision of the material, and strengthen the follow-up effect.

3.3 Belt adapter

The transfer point of the processing system belt conveyor is equipped with a cloud dust seal spraying dry mist with a diameter of 5-100μm, which can effectively capture dust of this type and deal with the problem of ultrafine particle diffusion; a fully enclosed guide trough is used to seal the transfer point to ensure dust removal effect.

3.4 Storage Yard

Fog cannons are arranged around the storage yard for fixed-point jet dust removal, and the lower corridor of the storage yard is equipped with cloud dust seals and guide troughs for dust suppression.

4. Integrated dust collection system

Use the static pressure and dynamic pressure of compressed air to convey materials with high concentration and high efficiency. The conveying system consists of 5 parts, namely gas source, conveying, pipeline, ash storage and control. Each pump of fly ash is a working cycle, and each cycle is divided into 4 stages

Through understanding the source of system dust and the influencing factors of dust precipitation, this case proposes a comprehensive dust prevention and control plan for the crushing workshop, screening workshop, belt adapter and storage yard, and has achieved good dust prevention and environmental protection effects. Welcome to leave a message to discuss the problems you encounter.