For emissions control, Mountain Enterprises added a Terex® RA320S Roto-Aire baghouse. Two 125-hp. motors powering a 542 fan generates 68,000-cfm air flow, while 16,992 square feet of cloth offers a low 4.1-to-1 air-to-cloth ratio for efficient particulate capture. The baghouse does not rely on air compressors, so there are fewer moving parts to minimize maintenance.
Rounding out the new components purchased for the Hazard plant are two 30,000-gallon vertical AC tanks to reduce the plant’s footprint, an upgrade to the most recent Terex plant controls package and a complete RAP run-around system. A closed-loop crushing circuit that allows oversized material not passing the screen deck to be properly resized, the RAP crushing system is a critical component that allows Mountain Enterprises to control mix costs. “Running 10 percent RAP saves us approximately 1.5 percent liquid asphalt per ton in a mix calling for 5.5 percent AC,” explains Graves.
By melding the existing components with the new, some would be concerned about how well all the components would work together. However, according to Graves that has not been a problem. “All the plant components are working well together, and it’s a great plant for making mix,” he says. In addition to its staple mixes, Mountain Enterprises is also mixing polymer-modified designs with the plant.
A tight fit
Prior to the new and existing plant components coming together in Hazard, the only real concern that Graves and Wisdom had was how to fit everything on the small site. That’s where Terex Roadbuilding stepped in to provide assistance.
“It really was not the size of the Hazard location but its shape and elevation,” explains Tim Franck, design engineer for Terex Roadbuilding. “We also had to design the new plant around the existing batch plant, so it was definitely a challenge for us.” The perimeter of the site was surrounded by three major obstacles — the four-lane State Highway 15, a service road and a right-of-way restriction. This created a triangular footprint for the plant.
According to Franck, it was a team effort to get the plant layout to fit the lot size so material would flow freely and the design would leave access for future plant maintenance. After laying out the initial design electronically, Franck and O’Neal took the plans to Hazard. “The four of us (Franck, O’Neal, Wisdom and Graves) went to the site and used spray paint to map out the location of all the components,” says Franck. “We had to make several runs at it before we could make it work.”
The major challenge to getting the layout right revolved around the silos and RAP run-around system. Wisdom wanted the trucks to enter and exit Highway 15 from a traffic light at the south end of the lot. However, this limited silo position options, and the final site selection required some creative engineering. “Typically, the bottom of the silos and slat conveyors are on the same level, but with this installation the silos had to be positioned about 2 ft. below the drag slat, which required us to shorten the slat,” explains Franck.
While it was critical to install the RAP run-around system, the crushing circuit’s footprint posed a problem with the extremely tight plant site. Franck was forced to elevate the crusher and shorten the conveyor from the RAP bin to the screen in order to leave access for maintenance. “It’s remarkable that they were able to fit everything on this site,” marvels Graves.
With installation complete and initial reports positive, the last hurdle for Mountain Enterprises was the stack tests. Again, the plant impressed both Wisdom and Graves. “The EPA (Environmental Protection Agency) representatives were amazed at how clean the plant runs, and even I cannot tell if the plant is operating just by looking at it,” says Wisdom.
For the EPA Opacity or Method 5 (visual) inspection, which allows up to 20 percent opacity, the Hazard asphalt plant passed with a perfect score of zero. A total of three emissions tests were run on the new plant setup, and the baghouse stack test averaged 0.019, less than half of the federal 0.04 maximum allowable.