Vulcan upgrades Arizona plant

When you've been an asphalt plant operator for 35 years, running a plant that produces quality mix without a lot of maintenance downtime is about all it takes to keep you happy. For Edward Cox, operator of Vulcan Materials' Peoria plant in Arizona, the recent drum upgrade has been keeping the veteran asphalt producer happy ever since the new Maxam SOLO drum was fired up last summer.

The folks at the Vulcan operation basically wanted to upgrade the 1986 400-tph CMI parallel-flow drum mixer with a new counterflow system, with the following general parameters:

• 350- to 400-tph production capability
• Maintain a 320 degree F mix temperature
• Equip with a heavy oil (waste oil) burner
• Efficiently process aggregate containing an average moisture content of 3.5 percent
• Operate efficiently at the site's location, which is 1,000 feet above sea level
• Be compatible with the plant's existing 46,000-cfm baghouse

The solution
Vulcan's research and analysis led to a new Maxam SOLO counterflow drum shell with frame extension. The SOLO technology separates the control of the exhaust stack temperature from the control of the mix temperature, and provides a means to directly heat RAP without superheating the virgin aggregate and without producing blue smoke.

For the Vulcan installation, the RAP advantage did not play a critical role in the selection process, because the plant has no request for RAP mix designs.

The drum is equipped with Maxam's MAXAMizer Heat Recovery System, where the stack temperature is automatically maintained at the minimum acceptable level for the baghouse (typically 225 degrees F). With the MAXAMizer Heat Recovery Unit mounted at the exhaust gas plenum of the drum, stack temperatures never exceed 250 degrees.

All the excess heat that normally escapes the stack goes right into the material, and the technology's resulting low stack temperature means air (CFM) and fuel (BTU) requirements are reduced, increasing production by up to 20 percent and reducing fuel costs by as much as five to 10 percent per ton. Less fuel consumption also results in low emissions, and the lower temperatures mean less stress on the bags, flights and drum shell.

The system ensures the lowest possible baghouse temperature, but always above dew point and maintaining that temperature is automatically controlled. The MAXAMizer Heat Recovery System prevents moisture condensation and build-up of mud on the filter bags, which can cause them to blind and require replacement.

The Vulcan replacement
According to Cox, the conversion at the plant took less than a week, and the transformation included:

• An 8-foot 4-inch diameter by 42-foot 6-inch long SOLO counterflow drum shell constructed of 3/8-inch INX50 steel
• A skid mount frame with supports to grade
• Maxam Energy Efficient Flighting System - using short flights that allow more staggers, which in turn provide a more uniform veil across the entire drum cross section
• One-piece AISI 1045 forged steel tires - leaf spring style mounting system allows for expansion and contraction without cracked or fractured welds
• MAXAMizer Heat Recovery System firing #2 oil (diesel)
• Burner/material discharge housing with high temperature seals
• Exhaust housing with high temperature seal
• 125-hp wrap chain drive
• Maxam's exclusive Troo-Track Self-Aligning Trunnions
• Reversible slinger conveyor with 7.5-hp drive
• Dust injection screw
• Thrust roller with rail car style bearing and structural support
• 9' x 9' knockout box, tip valve, discharge chute and structural to grade
• 3/16-inch-thick ductwork from new drum to knockout box and from knockout box to existing baghouse
• A Hauck StarJet 580 Extended Burner fired by waste oil

The SOLO advantage
According to Ron Murphy, general manager for Maxam, the primary benefit of the SOLO technology is that it provides more drying in a shorter veiling environment due to the staggered, closely configured drum flights. For the Vulcan installation, the design was well suited considering the low moisture content of the aggregate being processed, and the installation of a shorter drum allowed the producer to retrofit its existing plant without any significant modifications.