Dust Control Handbook for Industrial Minerals Mining and Processing

CHAPTER 4: CRUSHING, MILLING, AND SCREENINGMineral crushing, milling, and screening operations can be major sources of airborne dust due tothe inherent nature of size reduction and segregation processes. Control of dust generated bythese operations can be achieved with proper analysis of the sources, identification of appropriatecontrol technologies, and consistent application and maintenance of selected controls.Worker exposure may be managed through engineering controls to suppress or enclose the dustsources—as described below—or by isolating the worker from the dust source, as discussed inChapter 9—Operator Booths, Control Rooms, and Enclosed Cabs. Administrative controls suchas operating procedures, work practices, and worker training are also commonly applied tosupplement engineering controls. Until feasible engineering and administrative controls areinstalled, or when they do not achieve the desired level of exposure reduction, and duringmaintenance, repair, and other unusual operating conditions, personal protective equipment mayalso be necessary.As with any process component, installation of the selected dust controls, even if they areappropriate, will not guarantee continuing effective performance. The performance of installeddust control systems, which often represent large capital expenditures, should be periodicallyevaluated, maintained, and, when necessary, modified to maximize performance. For example,the effectiveness of dust control systems installed to protect worker health can only bedemonstrated by collecting personal air samples for comparison to the occupational exposurelimit for the substances in question.Different mineral processing equipment generates different amounts of dust emissions. Relativedust emission rate ratios (setting the primary crusher emission rate as the baseline) for commonmineral processing equipment are presented in Table 4.1. This ranking is based on EPAestimatedparticulate emissions for crushed stone operations, and is presented only to illustratethe relative magnitude of the various dust sources [EPA 2003]. It can be seen that emissionsincrease as the size of the material processed decreases, as one would expect.Table 4.1. Relative emission rate ratios of crushing and screening equipmentEquipmentRelative Emission Rate RatioPrimary crusher 1Secondary crusher (No data, tertiary crusher rate would be an upper limit)Tertiary crusher (dry) 51Tertiary crusher (wet) 2Screen (dry) 214Screen (wet) 12Crushing, Milling, and Screening 111