Permitting Tips: Dust
PERMITTING GUIDE PERMITTING TIPS 20 P roducers looking to reduce dust in their operations have numerous options from which to choose. These options range from operational practices to the use of dry collection systems, says Mark Kestner, Ph.D., president of Mendham, N.J.-based National Environmental Service Co. Typically, aggregates producers begin with low- or no-cost options and work through the spectrum of dust control measures based on conditions specific to each site and the area in which it operates. There are two outstanding operational prac-tices to reduce dust, Kestner says. These are choke-feeding crushers and avoiding interrup-tions to process flow, both of which are good for production and good for dust control. The more rock you run through a crusher, the less air that passes through it and the less dust that is generated. Conversely, interruptions in pro-cess flow allow machinery, particularly crushers, to windmill and generate more dust. The next series of dust-reduction strategies involve engineering controls. One common practice is source enclosure. Examples include making sure the transfer points and crusher discharges are properly enclosed and covered. Good engineering is designed to contain emis-sions, he notes. These procedures will help to ratchet your emission rate down. Other engineering controls involve landscap-ing and screening. One reason in-pit crushing has gotten very popular is because people can't see you, he explains. If you can't move into the pit, you can shelter the plant from view with a berm, screens, or vegetation anything to keep (the public) from seeing you. The third category of dust controls includes spray systems. The guideline here is to make sure you use high pressure around 200 pounds per square inch so that you are able to get the atomization and the power to knock dust and penetrate the material flow, Kestner says. You're trying to do two things: you're trying to knock down air-borne dust and add just a small amount of material to the process to help prevent emissions from downstream operations. Typically, a pump is sized so that it doesn't add more than half a percent by weight to the process. For example, a 20-gallon-per-minute pump should be suitable for a process flow of 1,000 tons per hour. Dry collection is what Kestner describes as a dust-reduction strategy of last resort. He says that a lot of states are implementing tougher standards and operations may not be able to eliminate as much dust as necessary by using wet suppression. Dry collection may be the only op-tion if the material is reactive, such as cement. Less than 5 percent of the operations Kestner sees use dry collection but that can depend on the area, particularly in restrictive districts and in states such as New Mexico, Arizona, and Cali-fornia where dry collection may be more widely employed. Fortunately, he notes that only 5 to 10 percent of capital costs of a new aggregate plant are invested in pollution controls, while in other industries such as power generation of foundries, that same figure may be 30 to 40 percent. Plants should develop dust control plans that first rely on control measures that cost the least, such as operating practices and engineering controls, in order to reduce their reliance on more expensive wet suppression and dry collection systems, Kestner explains. AM BITE THE DUST According to the Aggregates Manager Permitting Survey, more than of permits recently received by respondents contained restrictions related to air and emissions. Dial Down the Dust Particulate emissions can be lowered through the use of the right operational practices, engineering controls, and equipment. by Therese Dunphy, Editor-in-Chief 48%