Construction Materials Selection Properties and Applications of Building in modern asphalt production depend heavily on the efficiency and reliability of plant equipment. When Vulcan Materials undertook the modernization of its Peoria, Arizona asphalt plant, the company replaced a 1986-era CMI parallel-flow drum mixer with a new Maxam SOLO counterflow drum system. This upgrade, completed in under a week, addressed both production capacity and environmental performance goals at the facility located 1,000 feet above sea level. The Peoria plant, operated by veteran plant manager Edward Cox with 35 years of experience, required a system capable of 350 to 400 tons per hour while maintaining mix temperatures of 320 degrees Fahrenheit and processing aggregate with an average moisture content of 3.5 percent. The installation demonstrates how strategic equipment upgrades can extend the service life of existing plant infrastructure while improving both output and environmental compliance.
Counterflow Drum Technology Fundamentals
The decision to transition from a parallel-flow drum to a counterflow design represents a significant advancement in asphalt plant engineering. In a parallel-flow drum, aggregate and the burner flame travel in the same direction, which limits heat transfer efficiency and makes emissions control more challenging. Counterflow drums solve this by directing aggregate flow opposite to the burner flame, creating a more efficient heat exchange environment.
How Counterflow Design Improves Heat Transfer
The Maxam SOLO counterflow drum at the Peoria plant measures 8 feet 4 inches in diameter by 42 feet 6 inches in length, with a shell constructed of 3/8-inch INX50 steel. The counterflow configuration separates control of the exhaust stack temperature from control of the mix temperature, giving operators independent adjustment capability for each parameter. This separation is the key technical innovation that makes the SOLO system effective.
In traditional drum designs, the flight zones that create the material veil are typically 4 feet 8 inches to 5 feet long. The Maxam SOLO design uses flight zones that are only 2.5 feet long, achieved through shorter rows and staggered flight configurations. This tighter flight spacing creates more uniform veiling of aggregate across the entire cross section of the drum, allowing material to dry in a shorter distance as it travels through the drum.
The MAXAMizer Heat Recovery System
The MAXAMizer Heat Recovery System is mounted at the exhaust gas plenum of the drum and automatically maintains the stack temperature at the minimum acceptable level for the baghouse, typically 225 degrees Fahrenheit. With this system in operation, stack temperatures at the Peoria plant never exceed 250 degrees Fahrenheit. All excess heat that would normally escape through the stack is redirected into the material being processed.
This heat recovery technology delivers measurable benefits:
- Reduced air (CFM) and fuel (BTU) requirements for drying aggregate
- Production increases of up to 20 percent compared to conventional systems
- Fuel cost reductions of 5 to 10 percent per ton of asphalt produced
- Lower emissions from reduced fuel consumption
- Reduced thermal stress on baghouse bags, flights, and drum shell components
The system also prevents moisture condensation and buildup of mud on filter bags, which can cause bags to blind and require premature replacement. By maintaining temperatures always above the dew point automatically, the MAXAMizer protects the baghouse investment while improving overall plant efficiency.
Engineering Specifications of the Vulcan Upgrade
The conversion from the original 400-tph CMI parallel-flow drum to the Maxam SOLO counterflow system required careful engineering to ensure compatibility with existing plant infrastructure while delivering the desired performance improvements. The entire transformation took less than one week from shutdown to restart.
Drum and Structural Components
| Component | Specification |
|---|---|
| Drum shell | 8 ft 4 in diameter x 42 ft 6 in length, 3/8 in INX50 steel |
| Frame | Skid mount frame with supports to grade |
| Flighting system | Maxam Energy Efficient Flighting System with short, staggered flights |
| Tires | One-piece AISI 1045 forged steel, leaf spring mounting |
| Drive system | 125-hp wrap chain drive |
| Trunnions | Troo-Track self-aligning trunnions with rail car style bearings |
| Slinger conveyor | Reversible slinger conveyor with 7.5-hp drive |
| Ductwork | 3/16 in steel from drum to knockout box and to existing baghouse |
| Burner | Hauck StarJet 580 Extended Burner fired by waste oil |
Burner and Fuel System Design
The plant operates with a Hauck StarJet 580 Extended Burner running on waste oil, which provides significant operational cost advantages compared to natural gas or diesel fuel. The burner was specified alongside the MAXAMizer Heat Recovery System to maximize overall plant efficiency. During initial firing and commissioning, the system operated on Number 2 diesel oil before transitioning to waste oil for regular production. This fuel flexibility allows the plant to adapt to changing fuel markets and reduce operating costs.
Self-Aligning Trunnion System
One of the features that operator Edward Cox specifically highlighted after installation was the Troo-Track self-aligning trunnion system. Unlike conventional fixed trunnions that require periodic adjustment as the drum shell expands and contracts with temperature changes, the self-aligning design uses a leaf spring style mounting system that accommodates thermal expansion automatically. This eliminates the need for manual trunnion adjustments and reduces maintenance requirements significantly.
The one-piece AISI 1045 forged steel tires mounted on the leaf spring system can expand and contract without developing cracked or fractured welds, a common failure point on conventional drum installations. Cox noted that with the self-aligning trunnions, operators never have to worry about making adjustments because they are free-floating, minimizing wear and maintenance concerns.
Operational Performance and Production Results
Since the Maxam SOLO drum was fired up, the Peoria plant has demonstrated consistent operational performance at approximately 90 percent of its rated capacity. The plant operates year-round, six days per week, serving a diverse customer base that ranges from residential mix requirements to DOT Superpave designs.
Production Capacity and Mix Flexibility
The 320-tph Maxam drum system meets the plant’s production needs while providing operational flexibility for a grocery store style operation that stops and starts throughout the day. The Peoria plant produces three to four different mix designs daily, requiring a system that can transition between mix types with minimal wasted product and minimal disruption. The counterflow drum design enables these rapid transitions because its independent temperature control zones can stabilize more quickly than parallel-flow designs when mix parameters change.
The plant does not process reclaimed asphalt pavement (RAP) in its mix designs because Arizona Department of Transportation specifications do not require RAP content in projects. While the SOLO drum technology offers advantages for RAP processing through its ability to directly heat RAP without superheating virgin aggregate or producing blue smoke, this capability was not a deciding factor for the Peoria installation.
Emissions Performance
Shortly after installing the new drum system, the plant conducted a stack test for emissions compliance. The results showed output well below that of the previous parallel-flow drum system. This emissions reduction comes from two sources:
- Reduced fuel consumption: The MAXAMizer Heat Recovery System captures exhaust heat that would otherwise be wasted, lowering the total fuel required per ton of asphalt produced.
- Lower combustion temperatures: More efficient heat transfer means the burner can achieve target mix temperatures with less intense combustion, reducing NOx and particulate formation.
The reduced emissions benefit the surrounding community and help the plant maintain compliance with increasingly stringent air quality regulations in Arizona. This environmental performance aligns with the broader industry trend toward cleaner asphalt production methods.
Retrofit Considerations for Plant Operators
The Vulcan Materials Peoria project offers several lessons for plant operators considering similar upgrades. The decision to retrofit an existing plant rather than build a completely new facility required careful evaluation of compatibility between new and existing components.
Key Evaluation Criteria for Drum Upgrades
When evaluating a counterflow drum retrofit, operators should consider these factors based on the Vulcan experience:
- Production requirements: The new system must match or exceed existing capacity while accommodating future demand growth. Vulcan targeted 350 to 400 tph to match their market position.
- Aggregate characteristics: Moisture content, gradation, and abrasiveness all affect drum design. The Peoria plant processes aggregate at 3.5 percent average moisture, a moderate level that the SOLO drum handles efficiently.
- Existing infrastructure compatibility: The new drum must connect to existing baghouses, silos, and conveyor systems. Vulcan’s new drum was designed to work with the existing 46,000-cfm baghouse.
- Fuel availability and cost: Waste oil, natural gas, and diesel each have different burner requirements. Vulcan selected waste oil for its cost advantages.
- Elevation and climate: The Peoria plant sits at 1,000 feet above sea level, which affects combustion efficiency and burner sizing.
Installation and Commissioning Timeline
The conversion at the Peoria plant took less than one week from shutdown to production. This rapid turnaround minimized revenue loss during the upgrade period. Key steps included removal of the old CMI parallel-flow drum, installation of the new skid-mounted SOLO drum frame, connection of the 3/16-inch ductwork from the new drum to the knockout box and from the knockout box to the existing baghouse, installation of the Hauck StarJet 580 burner and waste oil fuel system, and commissioning and stack testing.
Maintenance Advantages
The new drum system offers several maintenance advantages over the older parallel-flow design. The closely spaced flights are easy to maintain and produce a uniform veil during mixing that helps produce consistent mix quality. The electrical system required to operate the new drum is simple and straightforward, reducing the complexity of troubleshooting and repairs. The self-aligning trunnions eliminate a routine maintenance task that operators of conventional drums must perform regularly.
The lower stack temperatures maintained by the MAXAMizer system also extend the service life of baghouse bags by reducing thermal stress. The automatic temperature control prevents the moisture condensation that can cause mud buildup on filter bags, a problem that often leads to premature bag replacement in conventional systems. These maintenance savings compound the fuel and production efficiency gains of the counterflow design.
For operators considering similar plant upgrades, Advanced Construction Materials Fiber Reinforced Polymers Mass Timber represents an evolving area of materials science, but in asphalt production the fundamental engineering decisions revolve around drum technology, burner selection, and heat recovery. The Choosing Roofing Materials a Complete Guide to Materials approach to evaluating options by weighing cost against performance applies equally to asphalt plant equipment decisions. Understanding thermal dynamics through systems like Phase Change Materials can inform better heat recovery design in industrial applications.
The Vulcan Materials Peoria plant upgrade demonstrates that a well-planned drum replacement can extend the productive life of an existing asphalt plant by decades while simultaneously improving production capacity, reducing operating costs, and lowering emissions. The Maxam SOLO counterflow drum with MAXAMizer Heat Recovery System addressed all of the operator’s objectives without requiring major modifications to the existing plant layout, proving that sometimes the most effective solution is to upgrade the heart of the plant while keeping the supporting infrastructure intact.