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Improved spray scavenging of particulates via acoustical excitation of drop oscillations.
Atlanta, GA: U.S. Department of Health and Human Services, Public Health Service, Centers for Disease Control and Prevention, National Institute for Occupational Safety and Health, R01-OH-009546, 2012 Oct; :1-28
In spite of significant efforts that have been made to protect the respiratory health of mine workers, exposure to coal dust, silica dust, diesel particulate matter and other suspended particles continues to threaten the pulmonary health of the mining work force. This is true in both surface mining and underground mines. Within the mining work force illnesses that continue to be common are silicosis and coal workers' pneumoconiosis (CWP or black lung disease). Of greatest threat to respiratory health are particles that are approximately one micron in diameter. Particles which are much larger than this size range tend to be captured in the oropharyngeal area of the human respiratory system. However, significant alveolar deposition occurs for particles ranging in diameter from O.Olum to 10um (EPA, 1999). Water sprays are used in many aspects of mining in an attempt to reduce the level of particulate matter in the air that is breathed by the mining work force. Sprays are used to wet the gallery walls where cutting occurs, as well as to wet recently cut rock and coal. Additionally, sprays are employed in wet scrubbers that are used in the cabs of mining vehicles. Wet scrubbers are also used on the sides of continuous mining machines where air is pulled from the cutting region, directed through the scrubbers and then returned at the rear of the continuous mining machine in the vicinity of the operator. Unfortunately, while water sprays can be very effective at removing relatively large and very small particles from air, for particles precisely in the 0.01 to 10 um range that are most dangerous to respiratory health, water sprays are relatively ineffective. Because a large installed base of water spraying nozzles and affiliated equipment already exists, the focus of the proposed work was to improve the efficacy of such sprays, rather than to develop a completely different method for lowering dust levels in mines. Specifically, the use of ultrasonic excitation of the spray was proposed as a means for improving the ability of sprays to scavenge particulate matter from the air. In this work, an ultrasonic standing wave was generated between an ultrasonic transducer and a reflector. This standing wave field forms 'accretion disks' in the air. These are regions where the air flow collects and anything that is suspended in the air is concentrated. A spray was directed through this standing wave field, along one axis, and a particle-laden air stream was directed through the standing wave field along a perpendicular axis. In the accretion disks, the particles and the spray drops were concentrated and brought into close proximity with each other. The spray drops grew and fell to the floor, removing particles with them. In short, a small scrubber was developed, where ultrasonics were used to increase the ability of the spray to remove particles. Improvements of nearly 150% were attained.
Exposure-levels; Coal-dust; Silica-dusts; Mining-industry; Mineral-dusts; Underground-mining; Underground-miners; Miners; Humans; Men; Diesel-emissions; Diesel-exhausts; Particulates; Particulate-dust; Silicosis; Pneumoconiosis; Black-lung; Respiratory-irritants; Respiration; Respirable-dust; Respiratory-system-disorders; Pulmonary-disorders; Pulmonary-function; Pulmonary-system; Pulmonary-system-disorders; Sprays; Wet-scrubbers; Air-contamination; Airborne-dusts; Airborne-particles; Dust-exposure; Dusts; Dust-particles
Prof. John R. Saylor, Department of Mechanical Engineering, 229 Fluor Daniel EIB, Clemson University, Clemson, SC 29634-0921
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National Institute for Occupational Safety and Health
Page last reviewed: April 12, 2019
Content source: National Institute for Occupational Safety and Health Education and Information Division