A Brief Discussion on Key Technologies for Dust Control in Concrete Mixing Plants

With China's continuous urbanization, ready-mix concrete has rapidly developed and been widely used in large and medium-sized cities across the country, leading to the rapid development of concrete mixing plants (buildings). Currently, there are numerous concrete mixing plant manufacturers in China, with a series of products. However, the technical levels vary greatly, with only some products approaching international advanced levels. Some technologies have even surpassed imported concrete mixing plants. Some products boast advantages such as high automation, high production capacity, high weighing accuracy, low investment, good mixing quality, the ability to achieve multi-bin, multi-mix design, uninterrupted continuous production, and a high degree of domestication of the mainframe and its main components. However, China's concrete mixing plants (buildings) still suffer from shortcomings such as low overall technology content, low popularization rate, large regional differences, low intelligence level, and poor environmental performance.

The pollution from concrete mixing plants mainly comes from three aspects:

Firstly, dust pollution; secondly, noise pollution; and thirdly, wastewater pollution.

Many ready-mix concrete companies, in order to save investment, have not prioritized pollution control measures, which is the main reason for the low environmental performance of mixing plants in China.

On the other hand, the insufficient control力度 from the government and relevant industry authorities on environmental protection is another important reason for the low environmental performance. With social progress, the requirements for urban environmental protection in China's large and medium-sized cities are becoming increasingly stringent. For ready-mix concrete mixing plants on the urban fringe, dust control will be the mainstream direction for future development.

Dust Control: Dust control should be implemented throughout the material transportation process.

1. Enclosed Material Yard: Due to the backward technical level of China's building materials industry, crushed stones are not washed, resulting in high dust content and easy dust generation during storage and transportation. The sand has an even higher dust content. Introducing enclosed aggregate yards to urban ready-mix concrete mixing plant aggregate storage yards, using new hollow bricks for the walls, not only prevents dust from discharging into the surrounding environment during aggregate unloading, but also effectively reduces noise pollution from engineering vehicles.

2. Fully Enclosed Plant: The mainframe is fully sealed, and the aggregate feeding conveyor belt is also enclosed with color-coated steel sheets, reducing the probability of dust entering the atmosphere during aggregate transportation. In the sealing design, we should strive to improve the sealing degree. After installing a dust collector, the dust concentration discharged from the mainframe is already very low. With the addition of the enclosure, the concentration of atmospheric dust discharged into the surrounding environment can be controlled to an even lower level.

Partial Enclosure: At the junction of the upper and lower systems in the aggregate transportation process, dust is easily discharged into the atmosphere. This area has many moving parts, making sealing difficult. In our technical solution, we are exploring some expandable sealing structures that achieve good sealing while allowing the moving parts to move freely.

3. Mainframe Dust Removal: Traditional mainframe dust removal only involves traditional dust collectors, with the dust pipes of the mixer cover, cement metering bin, and fly ash metering bin connected to the dust collector. While this has some dust removal effect, it is not ideal. Our technical solution considers the characteristics of large instantaneous pressure changes and high humidity in the mainframe airflow. We have developed a negative pressure dust collector (with dehumidification function) to alleviate the instantaneous pressure increase during material feeding and filter out moisture, preventing the clogging of the dust filter element.

4. Cement Silo Dust Removal (Powder Dust Removal): Traditional dust removal methods use a top bag dust collector on the silo, which is generally effective. Our technical solution replaces the bag dust collector with an airflow back-blowing dust collector and adds a tubular dust collector for further filtration of the airflow after passing through the dust collector.

5. Mainframe Water Spraying Method: Traditional water spraying methods in the mainframe cannot effectively suppress dust. Our solution is to add a pressure pump and improve the nozzle structure to create a water curtain during water spraying, suppressing dust generated during mainframe material feeding.

6. Material Process Research: We conduct experimental research on the feeding sequence and cross-feeding methods of sand, stone, cement, and water to obtain an optimal feeding process, effectively reducing dust emissions.

Through the research of the above technical solutions, the dust emissions of urban ready-mix concrete mixing plants can meet the requirements of the national standard GB10172-2005 "Concrete Mixing Plants (Buildings)".