With the rotating batcher system, Gallagher reduced the number of conveyors on top of the silos from four to one. There are only two batchers to service the five silos. The single transfer conveyor pivots around the middle silo and rides on a curved rail to provide a radial feed to the other four silos. “Not only has this change resulted in reduced noise, but it was less expensive initially, is less expensive to maintain, and requires less horsepower,” Trost says.
Another key area for noise reduction was the Double Barrel dryer/mixing drum. “The Astec Double Barrel plant is typically chain driven,” Trost says. “The chains on the drum drive create noise. We went to Astec and asked them to consider building this plant with a trunnion drive system. They were cautious, but agreed to try it out. The results have been very good. Not only is the drive much quieter, but it requires less maintenance and housekeeping is improved with no chain lubricant residue.”
The drum burner was another loud area of the old plant.
“We had sound walls strategically located to try to dampen the sound from the burner area,” Trost says. “With the new plant we went with Astec’s Phoenix model, a totally enclosed burner. The blower that provides air for combustion for the burner is powered by a variable speed drive.
The drive only runs the blower at the speed required for the amount of heat you need from the burner, whereas the old plant burner blower ran at full speed all the time. This burner runs so quiet it’s often difficult to determine if it is running or not.”
A variable speed drive system for the exhaust fan was also chosen to reduce noise. The exhaust fan only runs the speed necessary to provide the amount of air needed for the system.
In most older plants, the exhaust fan runs at full speed and the volume of air is controlled with a damper. The new system runs quieter and eliminates a separate damper and associated moving parts and maintenance requirements, according to Trost.
Other typical sources of noise with HMA plants include the plant air compressor and the positive displacement blower for conveying fines removed from the bag house. “You have to blow the fines from the bag house up into the storage silo. These blowers tend to be very loud when they operate,” Trost says. “Both our plant air compressor and the fines transfer blower at the new plant were placed inside sound enclosures engineered to drastically reduce the noise while allowing cooling for reliable operation.”
For simplicity and reliability, Gallagher also worked with Astec to minimize the number of augers required to move fines in the plant. Other than the bag house hopper auger, the plant has two augers.
In 2010, Gallagher’s Joliet plant received the National Asphalt Paving Association’s Ecological Award. The Joliet plant has several feature designed to be environmentally friendly. “We did some very extensive landscaping between the road and the new plant,” Trost says. “We put up a berm where the new plant is located so a lot of the plant is out of view of the public and the noise associated with truck loading is screened from the neighbors.”
Another enhancement is the paint scheme selected for the new plant. “We used neutral, beige tones to blend the plant with its surroundings,” Trost says. “We also paved the area around the plant to keep dust from the truck and loader traffic down.”
Ultimately, Gallagher found success in its efforts taken to build a plant with such enhancements. “The project was a big undertaking, but putting in the extra effort up front to spec out the things we wanted to make this a flexible, productive, efficient, reliable and environmentally friendly facility and HMA plant definitely paid off,” Trost says.