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The primary target for improving dustsuppression at TCL was the mobilecrushing unit. The company uses oneof the largest tractor rippers in theCaribbean to extract raw limestone,and the quarried stone is trucked to animpactor with a capacity of 530 tonnesper hour, which crushes the rock to anaverage size of 25 mm.To control the airborne dust generatedfrom crushing and transporting,TCL selected a DustBoss ® DB-60, theheavyweight design from Dust ControlTechnology. The DB-60 uses a seriesof 30 specially-designed brass nozzlesto atomize water droplets to theoptimum size for maximum particleattraction and coverage area, thenlaunches them with a powerful 25 hpfan. In contrast to most suppressionequipment suppliers, the companyoffers a wide range of nozzles fordifferent applications, selecting theoptimum spray pattern and droplet sizeto suit the specific type of dust beingaddressed.The ducted fan delivers 30,000 cubicfeet (about 850 cubic meters) of airflow per minute through the barrel,giving it a throw of more than 200 feet(60+ meters). It can also be equippedwith a 10 hp booster pump to increasewater pressure up to as much as 150psi from a 2-inch supply hose. TheDB-60 has an adjustable elevationfrom 0-50°, and the oscillating headdelivers 40° of motion. The workhorsedesign can cover nearly half an acre(.2 hectares) from a single location, andthe wheeled carriage-mounted mobileunit can be easily located wherever it’sneeded most on a given day.The unit’s suppression efficiency derivesfrom its ability to balance a numberof critical properties that tend to workagainst one another, such as dropletsize, spray pattern, air flow, range, andvelocity. “If spray nozzles create largedroplets, they can be thrown a longerdistance than small ones, giving a unitmore range,” explains DCT CEO EdwinPeterson. “Unfortunately, large dropshave a lower capture rate and morespace in between, makingthem less efficient overall.“The optimum condition iswhen the water droplets areapproximately the same sizeas airborne particulates,producing the greatestattraction between the two,”says Peterson. Given theaverage dust particle sizesinvolved in most quarryingand crushing operations,testing and experience haveshown that droplets 50-200microns in size typicallydeliver the highest efficiencyin most situations.“Similarly, a high velocityair flow allows an atomizedspray to be thrown farther,so a powerful fan deliversan advantage,” Petersoncontinues. “But the higher thevelocity, the smaller the dropstend to become. Even thoughsmall drops produce goodcapture and surface wetting,there is a point at whichsuppression efficiency falls offin the attempt to reach greaterair speed and distance,” headds. “Maximum particlecontrol is the result ofconsidering all the goals andtradeoffs, ultimately producinga design that balances each componentin relation to the others.”The results at TCL have been excellent,and the versatility of the dust controldesign allows crews to quickly adjustpositioning, throw angle and oscillationto accommodate specific worksitesand weather conditions. Crews run theDB-60 whenever the mobile crusher isoperating, blanketing material piles,storage areas, or truck paths to best suitthe day’s work load and wind conditions.The unit is easily set up by one person,and can run all day unattended.As the regulatory landscape in Trinidadalso continues to evolve, with new andemerging legislation likely to dictate aCONTROLLING THE DUSTThere are many opportunities for disturbedmaterial to take to the air in the quarryingprocess while it is being blasted, crushed,screened, transported, and stored. Technologycontinues to develop to provide more efficientcontrol of the dust but it really all boils down tosome basic principles.“There are only three ways that you can managedust,” says Dust Control Technology presidentEdwin Peterson. “It can be contained, collected,or suppressed.”While it certainly isn’t practical to containan entire quarry, parts of the process can beenclosed quite easily. Collection may be thebest solution in some situations through useof electrostatic precipitators, suction systems,cyclones, and filters. The third approach,suppression, puts tiny water particles in theatmosphere and these attract the dust, whichthen drops to the ground.Using a mobile dust control unit in addition tothe dust suppression system with manifold oncrushing equipment like jaw crushers, couldbe a winning combination for ultimate dustcontainment.need for improved dust control in manyindustries, effective suppression hasbecome an important element of TCL’sprocess. The Draft Air Pollution Rulesof Trinidad and Tobago, as well as theregion’s Occupational Health and SafetyAct, already have applicable sections,and TCL is working to stay ahead ofminimum requirements and demonstrateenvironmental leadership. The companyis certified as fully compliant withISO 14001: 2004, the most widelyrecognized set of environmentalmanagement standards in the world.For more information on Dust controlTechnology, call 800.707.2204,e-mail info@dustboss.com, or visitwww.dustboss.com ■Today’s aggregate & mining solutions | volume 3, number 1 23