Dust Control Handbook for Industrial Minerals Mining and Processing

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CHAPTER 2: WET SPRAY SYSTEMSProbably the oldest and most often used method of dust control at mineral processing operationsis the use of wet spray systems. In essence, as the fines are wetted each dust particle's weightincreases, thus decreasing its ability to become airborne. As groups of particles become heavier,it becomes more difficult for the surrounding air to carry them off. The keys to effective wetspray dust control are proper application of moisture, careful nozzle location, controlling dropletsize, choosing the best spray pattern and spray nozzle type, and proper maintenance ofequipment.In the vast majority of cases for mineral processing operations, the wet spray system used is awater spray system. Although the use of water sprays is a very simple technique, there are anumber of factors that should be evaluated to determine the most effective design for a particularapplication. The following two methods are used to control dust using wet sprays at mineralprocessing operations.Airborne dust prevention, achieved by direct spraying of the ore to prevent dust frombecoming airborne.Airborne dust suppression, which involves knocking down dust already airborne byspraying the dust cloud and causing the particles to collide, agglomerate, and fall outfrom the air.Most operations will use a combination of both of these methods in the overall dust control plan.PRINCIPLES OF WET SPRAY SYSTEMSTo use wet sprays effectively, it must be remembered that each ore type and application point isa unique situation and needs to be evaluated separately to achieve the optimal design. Forexample, wet sprays cannot be used with all ores, especially those that have higherconcentrations of clay or shale. These minerals tend to cause screens to blind and chutes to clog,even at low moisture percentages. Also, water cannot be used at all times throughout the year invarious climates where low temperatures may cause freezing.Water ApplicationWhen water is used to control dust, it has only a limited residual effect due to evaporation, andwill need to be reapplied at various points throughout the process to remain effective. Overapplicationin the amount/volume of moisture can be a problem in all operations and may impactthe equipment as well as the total process and transportability of the final product if shipped inbulk. In most cases, a properly designed spray system using finely atomized water sprays willnot exceed 0.1 percent moisture application [USBM 1987]; however, systems that addressprevention over larger areas with larger droplet sprays may add up to 1.5 percent moisture to theprocess.Wet Spray Systems 61
The vast majority of dust particles created during crushing are not released into the air, but stayattached to the surface of the broken material. Therefore, adequate wetting is extremelyimportant because it ensures that the dust particles stay attached to the broken material.Uniformity of wetting is also an important issue for an effective system. By far the best dustreductions can be achieved by spraying the ore with water and then mechanically mixing the oreand water together to achieve a uniformity of wetting.Ideally, the spray system should be automated so that sprays are only activated when ore isactually being processed. For dust knockdown, or suppression, a delay timer may beincorporated into some applications to allow the spray system to operate for a short time periodafter a dust-producing event.Nozzle LocationDue to the unique characteristics of each application, there are no hard and fast rules forspecifically locating spray nozzles in dust control applications; however, the followingguidelines will contribute to spray system efficiency.For wet dust prevention systems, nozzles should be located upstream of the transfer pointwhere dust emissions, in most cases, are being created [Blazek 2003].Care should be taken to locate nozzles for the best mixing of material and water[Blazek 2003].For airborne dust prevention, the nozzles should be located at an optimum target distancefrom the material—far enough to provide the coverage required but close enough so thatair currents do not carry the droplets away from their intended target [Blazek 2003].Droplet size also needs to be considered when setting the correct target distance.For airborne dust suppression, nozzles should be located to provide maximum time forthe water droplets to interact with the airborne dust.Figure 2.1 illustrates a common dust control application at a conveyor dump point into a bin.this dust suppression application, spray nozzles are positioned in a manner which allows thespray patterns of the individual nozzles to properly interact with the dust particles and at adistance where the droplets will not be carried off by air currents.InFigure 2.1. Common dust control application illustrating nozzle positioning [SSCO 2003].62 Wet Spray Systems
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Report of Investigations 9689Dust C
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FUNDAMENTALS OF DUSTCOLLECTION SYST
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Minimizing Field Fits and Welds ...
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Recommendations for Proper Wet Dril
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CONTROL TECHNOLOGIES FOR FILLING 50
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Effective Filtration ..............
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ILLUSTRATIONSFigure 1.1. Relationsh
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Figure 3.2. The air and water flow
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Figure 9.5. Problem created by heat
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UNIT OF MEASURE ABBREVIATIONSUSED I
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Robert J. Franta, Quotation Enginee
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silica. Quartz is the most common s
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DUST CONTROL HANDBOOK FOR INDUSTRIA
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CHAPTER 1: FUNDAMENTALS OFDUST COLL
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The shape of particles affects how
Page 40 and 41: EXHAUST SYSTEMS DESIGNAll exhaust s
Page 42 and 43: stripping, which allows workers to
Page 44 and 45: When using the air quantities in Ta
Page 46 and 47: X = distance in feet from the face
Page 48 and 49: Checklist for Hood EffectivenessThe
Page 50 and 51: A major disadvantage of the high-ve
Page 52 and 53: A common misconception when designi
Page 54 and 55: Avoiding Mitered Elbows Greater Tha
Page 56 and 57: Figure 1.13. Depiction of the horiz
Page 58 and 59: Figure 1.14. Typical design of grav
Page 60 and 61: Baghouse CollectorsBaghouse dust co
Page 62 and 63: Table 1.2. Emission factors for cru
Page 64 and 65: Figure 1.17. Typical design of a me
Page 66 and 67: Reverse Jet (Pulse Jet) CollectorsR
Page 68 and 69: Figure 1.20. Cartridge collector wi
Page 70 and 71: Wet scrubbers are particularly adva
Page 72 and 73: Electrostatic precipitators normall
Page 74 and 75: may be related to specific applicat
Page 76 and 77: times. When considering the depth o
Page 78 and 79: Figure 1.25. Demonstration of how a
Page 80 and 81: Figure 1.26. A typical fan performa
Page 82 and 83: Fan TypesThere are two basic types
Page 84 and 85: Figure 1.30. Typical centrifugal fa
Page 86 and 87: Figure 1.32. Typical roof ventilato
Page 89: DUST CONTROL HANDBOOK FOR INDUSTRIA
Page 93 and 94: Table 2.1. Particle/droplet size in
Page 95 and 96: Air Atomizing NozzlesAir atomizing
Page 97 and 98: Hydraulic Flat Fan NozzlesFigure 2.
Page 99 and 100: for dust knockdown or suppression,
Page 101 and 102: Nozzle MaintenanceFigure 2.14. Typi
Page 103 and 104: Accidental DamageInadvertent harm t
Page 105 and 106: NDT Educational Resource Center, Io
Page 107 and 108: 78 Wet Spray SystemsDUST CONTROL HA
Page 109 and 110: contains a piston which delivers ha
Page 111 and 112: produce an increase in the penetrat
Page 113 and 114: Dry DrillingDry drilling is accompl
Page 115 and 116: Circular ShroudIn contrast to the u
Page 117 and 118: The collector airflow has a more su
Page 119 and 120: Air-Blocking ShelfThe air-blocking
Page 121 and 122: dust emissions from mast lowering,
Page 123 and 124: This simple procedure of creating a
Page 125 and 126: Figure 3.15. Air ring seal used to
Page 127 and 128: Figure 3.17. Illustrations showing
Page 129 and 130: unsubstantiated due to the inconsis
Page 131 and 132: safety considerations may preclude
Page 133 and 134: Figure 3.22. A filtration unit, loc
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Page 137 and 138: USBM [1995]. The reduction of airbo
Page 139 and 140: 110 Drilling and BlastingDUST CONTR
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Wet Control MethodsPREVENTION AND S
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Figure 4.2. Examples of compressive
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Figure 4.5. Illustration of a dry (
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Figure 4.6. Illustration of a dry (
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Wet dust control methods for crushi
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Work Practices to Minimize Dust Exp
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Some specialty grinding operations
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should be frequently inspected for
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Open screen decks slowly to allow i
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CHAPTER 5: CONVEYING AND TRANSPORTT
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Figure 5.3. Basic depiction of mate
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that the material falls before land
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Figure 5.10. Skirtboard used within
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CarrybackMaterial that sticks or cl
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CONVEYOR DESIGN AND MAINTENANCE ISS
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Figure 5.15. Conveyor transfer encl
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High-volume, high-pressure sprays s
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Figure 5.19. Depiction of a bucket
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Figure 5.21. Depiction of two types
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Figure 5.25. Venturi eductor utiliz
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CHAPTER 6: BAGGINGThis chapter disc
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caused during manufacturing, includ
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Overall PerforationsThe use of over
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Figure 6.5. Open-top bag being load
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Bagging operators should be aware t
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Figure 6.8. Exhaust hood to capture
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In the original design, a single no
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The OASIS is a relatively simple de
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Figure 6.13. Bag storage shelves sh
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Figure 6.14. Bag and belt cleaner d
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other industrial application using
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The robotic arm automatic palletize
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For many years, this plastic wrappi
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warehouse location until a later ti
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used successfully to perform this c
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CHAPTER 7: BULK LOADINGDuring the b
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Figure 7.2. Loading spout discharge
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Cascading Loading SpoutFigure 7.5 i
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a seal at the entry and exit points
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REFERENCESBiere G, Swinderman RT, M
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200 Bulk LoadingDUST CONTROL HANDBO
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many years, as well as some new and
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Figure 8.2. Air spray manifold desi
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Figure 8.3. Test subject wearing po
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Spills of product material are a co
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epetitive dust leaks should not sim
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Effective Upward Airflow PatternThe
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Figure 8.8. Open-structure design c
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manually removing the bags and plac
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Figure 8.12. Increase in worker’s
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In other cases, an operation may wa
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Cecala AB, O'Brien AD, Pollock DE,
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224 Controls for Secondary SourcesD
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where C o = outside respirable dust
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minimal improvement in the cab's ai
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RECOMMENDATIONS FOR FILTRATION/PRES
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Effective FiltrationFigure 9.4. Res
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average decay times were between 16
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Figure 9.6. Filtration unit showing
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This table highlights a number of c
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NIOSH [2001b]. Technology news 486:
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upon the wind velocity (or disturba
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Maximum size is the largest particl
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Figure 10.4. Use of end-dumping wit
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conditions. Performance of each of
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A water truck, used to apply water
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Surfactants work by reducing the su
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which differed for the various site
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Figure 10.9. Self-tarping dump truc
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percent [Fryrear and Skidmore 1985]
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Figure 10.12. The armoring process
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A current method of stockpile forma
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Figure 10.15. Demonstration of how
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Chekan GJ, Cecala AB, Colinet JF [2
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Midwest Research Institute [1981].
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GLOSSARYAbrader. An implement used
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Carryback. Material that sticks or
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End-dumping. A process of spreading
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Open structure building design. A p
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Table bushing. A bushing used to se
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Delivering on the Nation’s promis
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