Green filters, fan motor VFDs handle dust efficiently
January 22, 2013
Because an industrial dust collector is designed to clean a factory’s environment of dust and fumes, it is inherently green. But a properly designed dust collection system can contribute to sustainability in many other ways as well.
Because an industrial dust collector is designed to rid a factory environment of dust and fumes, it is inherently green. But a properly designed dust collection system can contribute to sustainability in many other ways as well.
For years many plants have dealt with welding fumes and other airborne contaminants by exhausting them outside. The new U.S. Environmental Protection Agency (EPA) National Emission Standards for Hazardous Air Pollutants (NESHAP) Rule 6X, which went into effect in 2011, changes that (see http://www.epa.gov/ttn/atw/6x/6xpg.html).
The regulation applies to all manufacturing processes using materials that contain a minimum of 0.1 percent cadmium, lead, nickel, or chromium materials that contain 1 percent manganese (which is true of most welding applications). Simply stated, in a 20-minute test period, there can be no more than three minutes of visible emissions (zero opacity) originating from these types of processes. The regulation spells out the monitoring and test methods required for compliance and outlines control techniques that may be used.
One corrective strategy you can use to eliminate visible emissions is a dust and fume collector with high-efficiency cartridge filtration. The regulation identifies cartridge filtration as an acceptable control device.
If you opt to recirculate the filtered air downstream of the dust collector rather than exhaust it outside, that indoor air still must comply with Occupational Safety and Health Administration (OSHA) permissible exposure limits (PEL). OSHA has established PELS for hundreds of dusts, based on an 8-hour time-weighted average exposure (www.osha.gov/SLTC/pel).
How do you know if your people are adequately protected by a dust collector that complies with OSHA and EPA emission thresholds? The equipment supplier should provide a written guarantee stating the maximum emissions rate for the equipment over an 8-hour time-weighted average.
Although a small car is greener than a big gas guzzler, the analogy does not hold true when it comes to dust collection equipment. A dust collector must be properly sized to run dependably and efficiently at the required airflow.
If a collector is undersized, a host of problems can result: The operating pressure drop may be too high; filters may be overloaded and require frequent changeout; and larger maintenance problems may surface. If any of these occur, operating costs and energy usage can actually be higher for a smaller unit than for a large one.
Heavy-duty construction is likely to result in longer life. This is particularly true of a dust collector equipped with explosion-protection devices, as is now required for combustible dust applications.
Vessel strength is an important factor in determining which type of explosion-protection technology is required and how the equipment should be sized. A heavy-duty collector, constructed of thick-gauge metal and with a high pressure rating, might enable you to use a simpler and less costly explosion-protection system to comply with National Fire Protection Association (NFPA) standards.
Field experience has also shown that such collectors are far more likely to survive a combustible dust explosion, whereas a lighter-weight model may not, and then would have to be scrapped, generating waste.
Dust collectors that are manufactured using environmentally friendly paint finishes and construction materials contribute to sustainability. Energy-efficient components in the system also make it a greener machine. Ask your dust collection supplier to provide a sustainability report or other documented evidence of its green manufacturing initiatives. Also ask whether energy-efficient or NEMA Premium™ efficiency components are offered as standard or optional.
No matter how maintenance-friendly a collector may be, the less service it needs, the better—especially in hazardous dust applications. Extended-life cartridge filters reduce filter changeout frequency. This minimizes worker exposure to dust, saves on maintenance and disposal costs, and reduces landfill impact.
A misconception exists that the more media a filter contains, the longer it will last. Actually, the amount of media contained in a filter is not as important as the amount of usable media surface area. Many filters have media packed so tightly into the cartridge that most of it is not available for filtering.
New open-pleat designs expand capacity utilization of the media with less media area per filter (see Figure 1). This design improves airflow through the filter, which reduces pressure drop and saves energy. Open-pleat filters also respond well to pulse-cleaning and use less compressed air than some other filter designs, saving more energy and lasting longer, which in turn lowers replacement and disposal costs.
Sometimes filters are described as "removing 99.9 percent of contaminants" of a certain particle size. Others may be labeled as having filter efficiency as a minimum efficiency reporting value (MERV), a numerical value given to filters to identify their filtering abilities.
Although these measures are useful for comparing different filters, the EPA and OSHA don't recognize percentage efficiency claims or MERV. The criterion they look at is whether emissions are at or below required thresholds. The best way to make sure the filter you're considering buying is in compliance is to ask the filter manufacturer for a written guarantee of emissions performance, stated as grains per cubic foot.
Though PLCs are popular for use with many manufacturing processes, they are not well-suited to controlling pulse-cleaning of dust collector filter cartridges. Pulse-cleaning relies on very brief (150 milliseconds or so), high-energy bursts of compressed air to blow dirt off the filter surfaces. Typically, a PLC's valve opens too slowly for proper pulsing to occur. To optimize cleaning and ensure reliable and efficient dust collector operation, use a timer board designed for filter pulsing. It can be used independently or tied into your PLC.
When choosing a cartridge dust collector filter, consider calculating total cost of ownership to help you make the most economical and sustainable choice (see Figure 2). Similar to life-cycle costing, total cost of ownership is a step-by-step evaluation of the four main components of filter cost—energy, consumables, maintenance, and disposal.
To choose the most economical and sustainable filter, it is best to do a total cost of ownership calculation that takes all these components into account. A filter with a lower initial price may end up costing you thousands of dollars a year more in energy and operating expenses.
Another misconception is that a mechanical fan damper reduces a collector's energy consumption. Actually, a damper has only minimal impact on energy use. A variable-frequency drive (VFD) controls fan speed far more effectively.
This electrical control is highly efficient in maintaining the desired airflow through the collector, and energy use is greatly decreased, with a typical return on investment of less than one year. By helping reduce the spike in overall energy consumption, a VFD may also lower your utility rate as well.
Energy waste from industrial electric motors is a widespread problem. NEMA Premium efficiency fan motors are designed to improve energy performance and meet or exceed requirements of the Energy Independence and Security Act of 2007 (EISA) (see Figure 3).
Designed for cooler operation and more efficient performance, a Premium efficiency motor can pay for itself in reduced electrical power use. Many electric utilities offer rebates and incentives that can add even more savings. You can use Premium motors with VFDs for optimal fan speed control and energy savings.
If you follow these 10 steps, you'll be on your way to a more efficient operation that is green, clean, and lean.