Dust Control and Suppression

Dust emissions are a major problem not only for employees but also for neighbours and the areas around the dust source. ...
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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.

 

What are the sources of dust?

  • 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

  • Agg-Net; New Techniques for dust suppression and Control [https://www.agg-net.com/resources/articles/environment-restoration/new-techniques-for-dust-suppression-and-control]
  • Benedict, Mark; (1996)revised 2016; Methods for Dust Control; Department of ecology state of Washington; publication number 96-433
  • Bigu J, Grenier MG [1989]. Reduction of airborne radioactive dust by means of a charged water spray. AIHA J 50:336-345.
  • Brown CE, Schrenk HH [1938]. Control of dust from blasting by a spray of water mist. Pittsburgh, PA: U.S. Department of the Interior, RI 3388.
  • Chander S, Alaboyun AR, Aplan FF [1991]. On the mechanism of capture of coal dust particles by sprays. In: Proceedings of the Third Symposium on Respirable Dust in the Mineral Industries (Pittsburgh, PA, October 17-19, 1990). Littleton, CO: Society for Mining, Metallurgy, and Exploration, Inc
  • Colinet JF, Spencer ER, Jankowski RA [1997]. Status of dust control technology on U.S. longwalls. In: Ramani RV, ed. Proceedings of the Sixth International Mine Ventilation Congress. Littleton, CO: Society for Mining, Metallurgy, and Exploration, Inc., pp. 345-351.
  • Courtney WG, Cheng L [1977]. Control of respirable dust by improved water sprays. In: Respirable Dust Control – Proceedings of Technology Transfer Seminars, Pittsburgh, PA, and St. Louis, MO, IC 8753, pp. 92-108. NTIS No. PB 272 910.
  • Hu Q, Polat H, Chander S [1992]. Effect of surfactants in dust control by water sprays. In: Proceedings of the Symposium on Emerging Process Technologies for a Cleaner Environment. Littleton, CO: Society for Mining, Metallurgy, and Exploration, Inc., pp. 269-276.
  • Jayaraman NI, Jankowski RA [1988]. Atomization of water sprays for quartz dust control. Appl Ind Hyg 3:327-331.
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  • Meets EJ, Neethling AF [1987]. Some experiences in the use of wetting agents to suppress dust at Sigma colliery. J Mine Vent Soc S Afr Oct:126-133.
  • Kost JA, Shirey GA, Ford CT [1980]. In-mine tests for wetting agent effectiveness. Bituminous Coal Research, Inc. U.S. Bureau of Mines contract No. J0295041. NTIS No. PB82­ 183344/XAB
  • MRDE [1981]. Methods of reducing dust formation and improving dust suppression on longwall faces: final report on ECSC research project 7256-12/003/08. Mining Research and Development Establishment (U.K.).
  • Mukherjee SK, Singh MM [1984]. New techniques for spraying dust. Coal Age June:54-56.
  • Seibel RJ [1976]. Dust control at a transfer point using foam and water sprays. Pittsburgh, PA: U.S. Department of the Interior, Bureau of Mines, TPR 97. NTIS No. PB-255-440.
  • Tien JC, Kim J [1997]. Respirable dust control using surfactants. Appl Occ Env Hyg 12(12): 957-963.
  • NIOSH [2003]. Handbook for dust control in mining. By Kissell FN. Pittsburgh, PA: U.S. Department of Health and Human Services, Centers for Disease Control and Prevention, National Institute for Occupational Safety and Health, NIOSH Information Circular 9465, DHHS, (NIOSH) Publication No. 2003–147.