Dust Control and Suppression
Why is Dust a Problem?
Dust can contain soil, ash, soot, salts, pollen and spores, and a host of other materials depending on the location and activity causing the dust. For example, dust from construction sites, industrial areas, agricultural operations, or roadways might contain pesticides, heavy metals, asbestos, bacteria, fungi, and a variety of other contaminants. Dust particles are very small and easily inhaled. Even short-term exposure to dust can cause respiratory problems and allergic reactions.
- Rural areas
- Waste cleanup sites
- Industrial facilities
- Land clearing
- Construction activities
- Demolition activities
- Storage piles
- Masonry
- Landscaping
- Paved and unpaved roads
- Transportation and track out
- Activities on vacant land
- Equipment yards
- Agricultural field operations
- Parking lots or feed lots
What are the methods to break them down?
The three basic types of dust-control system currently used in minerals extraction and processing operations are:
- dust collection
- wet dust suppression
- airborne dust capture
Dust-collection systems use ventilation principles to capture the dust-filled airstream and carry it away through ductwork to the collector.
Wet dust-suppression techniques use water sprays to wet the fugitive material so that it generates less dust.
Airborne-capture systems also use water sprays but in this case, the airborne dust particles are sprayed with atomized water. When the dust particles
When the dust particles collide with the water droplets they agglomerate and rapidly settle out due to their increased size. Moreover for increase the performance, chemical surfactants may be added to the water to reduce surface tension, thereby reducing droplet size. These additives also improve the ability of water to wet and to agglomerate finer particles.
N.B: Too much water can cause operational problems, while too little water means ineffective dust control.
High-pressure sprays
One way to improve sprays is to raise water pressure. This raises the efficiency per unit use of water, as shown in the graph. Airborne capture performance of four types of spray nozzles. Jayaraman and Jankowski [1988] tested the airborne capture of both conventional and high-pressure sprays at a full-scale model continuous miner face. A conventional spray system on the miner (0.689 N/mm^2, 1,2 l/s) gave 30% respirable dust reduction. A high-pressure system (17,24 N/mm^2, 0,19 l/s) gave the same reduction, but with much less water. The two systems operating together (1,4 l/s) gave 59% dust reduction. The dual system would be the choice for underground use, providing both airborne capture and sufficient wetting of the broken material. A marked disadvantage of high-pressure sprays is that they entrain large volumes of air, often leading to more dispersal of dust than is captured. Because of this secondary dispersal, their application is limited to enclosed or semi-enclosed spaces, such as under the boom of a continuous mining machine.
It’s possible to increase the performance of the system?
- Foam. For dust control, foam works better than water. It provides dust reductions of 20% to 60% compared to water. Foam also can produce similar results at lower water use, that is, the amount of water needed to make the foam is less than the equivalent water spray. Seibel [1976] compared high-expansion foam to water sprays at a belt transfer point. Compared to water, the foam averaged an additional 30% dust reduction. Mukherjee and Singh [1984] found that foam released from a longwall shearer drum cut the dust an additional 50% compared to conventional water sprays on the drum. Also, the system used one-half the water of the conventional sprays.
- Wetting agents (surfactants). Wetting agents receive a disproportionate amount of attention, perhaps because they seem to offer an easy fix to dust problems. Most interest has been in coal mining because of the hydrophobic nature of coal. The effectiveness of wetting agents has been the subject of considerable research over the years, without much of a definitive answer on how well they work. Various studies have shown a respirable dust control effectiveness compared to plain water, averaging about 25% and ranging from zero [MRDE 1981; Chander et al. 1991] to 25%-30% [Kost et al. 1980] to more than 40% [Meets and Neethling 1987]. It seems that wetting agent effectiveness depends on the type of wetting agent, type of coal, dust particle size, dust concentration, water pH, and water mineralogy [Hu et al. 1992; Kim and Tien 1994; Tien and Kim 1997]. However, no general formula or methodology has emerged that would allow a mine operator to select a wetting agent appropriate for its specific coal (or rock) type. The only alternative is to try out a prospective wetting agent and discontinue its use if there is no clear benefit. However, given that the average effectiveness of a wetting agent is 25%, about the same as the accuracy of dust sampling methods
REFERENCES
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