Energy-saving tips for dust control systems
Q: Our dust control system costs a lot of money to run. What can we do to minimize energy costs?
There are a number of things you can do to reduce the system’s operating costs without sacrificing dust control performance.
The dust control system’s operating costs typically are for the exhaust fan motor’s energy consumption and the filter-cleaning system’s compressed air usage. Much is written in our industry today about how to reduce the system’s static pressure by using new performance filter media that can provide a lower pressure drop across the filters. The fan energy needed to overcome pressure drop and move air and dust through the system can represent as much as 25 percent of your system’s total energy requirement, so reducing the pressure drop across your filters can save money year in and year out.
Other ways to reduce your dust control system’s operating costs can save even more money. Although they’ve been around a long time, they’re often ignored or forgotten. Here’s a checklist of these energy-saving tips:
Minimize fugitive dust emissions inside your plant by properly maintaining your processing and handling equipment. Seal all leaks by replacing gaskets, repairing damaged housings, covering open conveyors, and so on. This may not eliminate all dust emissions, but it will minimize the need for dust capture hoods. This, in turn, will mean that you can use a smaller dust control system. The smaller system will have lower energy costs and require a smaller makeup-air system because it needs less supply air to replace the smaller amount of exhausted air.
Use dust capture hoods on dust sources that you can’t eliminate. Industrial hygiene air sampling in plants has shown that well-designed local dust capture hoods can reduce the airborne dust concentration from dust sources by an average of 90 percent. Many existing dust control systems use canopy-type hoods with large hood sections and related ductwork, but these are usually ineffective. Such a hood requires excessive quantities of exhaust air because it’s too far away from the dust source. Yet bringing a canopy hood closer to the dust source typically doesn’t help, because this location can interfere with worker access to the production line and draw product as well as dust into the hood. Instead, a local dust capture hood must be properly designed so it can be installed very close to the dust source without interfering with workers or capturing product. This hood type also reduces the quantity of exhaust air required to control the dust. The capture hood has lower hood and ductwork fabrication costs and requires a smaller fan and dust collector, minimizing makeup-air needs and, of course, the dust control system’s operating costs.
Select a dust collector that will minimize energy usage. A dust collector that’s sized to operate at a pressure drop of 6 inches water column can have a lower purchase cost than a collector selected to operate at a pressure drop of 3 inches water column. Everything else being equal, the collector sized for the lower pressure drop is larger because it contains more filter media. For instance, the energy cost for a 6,000-cfm centrifugal exhaust fan operating 24/7 and serving a dust control system with a 12-inches-water-column system pressure drop can be about $3,300 less per year than for the same fan running in a system with a 15-inches-water-column system pressure drop. In this case, you’ll need to compare each collector’s initial purchase cost with its annual operating cost to make an intelligent buying decision. See the table below for more data on this comparison.
Check the dust control system for air leaks. Since a typical dust control system operates under negative pressure between 10 and 20 inches water column, it will always have air leaks. Even ductwork with continuous-weld seams, welded elbows, and other welded fittings won’t be perfect. System duct connections made in the field may not be airtight the first time around, either. In fact, depending on the system’s operating pressure and how the system was fabricated and installed, a typical installed system can leak 10 to 30 percent of the air moving through it. To stop the leakage, you need to check for and correct these air leaks when you install the system. Then, once the system is up and operating, regularly check for leaks. Fixing leaks in an effective dust control system that leaks 20 percent of its air volume will produce the same cost savings as using 20 percent less air, by allowing you to reduce the fan speed and makeup-air requirement. (One caution: When correcting a leak results in a lower fan speed, check with the fan manufacturer to ensure that your fan will still operate within the stable area of its performance curve. Otherwise, you may need to change the sizes of some ducts to maintain adequate dust-conveying velocities in the system.)
|Comparison of estimated annual operating costs for dust control systems with different total system pressure drops|
|Dust collector operating pressure drop
|System exhaust air quality (cfm)
||Total system pressure drop (inches wc)
||Estimated annual operating cost at $0.10/Kwh
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