Every now and then it’s a good idea to kick back, find out where it all started, how we got to where we are today, and what’s on the horizon through emerging technology.
For example, we all know that asphalt serves as the foundation for modern road travel, but many may not realize its roots in road construction date back to the year 615 BC in ancient Babylon and its debut in America took place in 1870 as pavement in front of the Newark, NJ City Hall, according to the comprehensive historical report on the industry by the National Asphalt Pavement Association (NAPA).
The market really took off during the building and infrastructure boom that occurred in the decades that followed World War II as asphalt plants began to address the need to increase output, but also became sensitive to America’s growing attention to pollution control and the environment.
“When I first started, state-of-the-art was a batch plant that was dirty, that you could usually see three miles away,” the late Don Brock, founder of Astec Industries, commented in the NAPA historical report. “We’ve gradually progressed from there to cleaning them up with wet washers and baghouses to being invisible today. Today, we need to build a plant that you can’t see, you can’t hear, and you can’t smell.”
Today’s technological advancements have catapulted asphalt pavement production into a first class, highly efficient and cleaner process that suppresses noise, keeps emissions in line with local restrictions, makes greater use of recycled content than most other industries, and significantly saves costs—at least for those employing the latest available technologies and equipment.
Efficiency, Sustainability and Profitability
The biggest trends in new technology aimed at plant efficiency include efforts to increase mobility options, plant versatility to better meet individual customer requirements, increased use of reclaimed asphalt pavement (RAP) in mixtures, cost-effective material transfer and delivery—all while continuing to use the latest plant technology available to improve pavement performance.
Another recent development by Astec was its introduction of the more compact model BG 1800, part of the company’s BG series of modular batch plants with a design that eases set-up, relocation and upgrades as plant operations grow. With optional features, the BG1800 is capable of producing mixes containing a high level of RAP, which can be incorporated into mix via dryer drum or through mixer unit, and crafted for agencies and other customers that require flexibility to produce a variety of mix designs.
The BG 1800 modular and transportable batch type plant is rated to produce 120 tons per hour with 1800 kg batch sizes. Other plants in the BG series rate up to 240 tons per hour with up to 3200 kg batch sizes.
With another modular unit, Astec’s Voyager 140 raised the bar on portability and production in one compact continuous mix plant. Occupying a small and portable footprint, the Voyager 140 offers full-size plant features with components designed to maximize mix quality, while improving efficiency and sustainability.
“As a society and as an industry, we do not seem to fully recognize the synergy between practicing sustainability and our profitability,” Malcolm Swanson, product manager-asphalt equipment at Astec, wrote a while back in a white paper titled, Practicing Sustainability at Asphalt Plants.
“There are probably things done in the name of sustainability and climate change mitigation that do not meet the test of common sense or business sense; but as far as I have ever seen, such ideas are usually not good for sustainability either,” he added.
“If we run our business better, including being wise with our use of energy and materials, we will improve our profitability and at the same time we will operate in a more sustainable way.”
At the heart of the Voyager 140 is the decades-proven Double Barrel drum mixer with production capacity of 140 metric tons per hour and RAP mixing capability of 50%. Another highly portable plant, the Voyager 120, based upon the Unified drum design, can run up to 30% RAP. Both plants feature V-flights in the drum to provide greater uniformity of the aggregate veil during drying, resulting in better heat transfer, a reduction of fuel use and increased productivity.
The Voyager 140 and Voyager 120 feature a pulse jet baghouse to minimize impact on the environment. These baghouses offer the best available emissions control technology. Both the Voyager 120 and the Voyager 140 offer large plant features while maintaining a small plant footprint.
One of Astec’s most recent technological advances was its flagship Double Barrel XHR High RAP drum mixer. By combining components with decades of proven performance, but enhanced with state-of-the art design and material selection, recycle percentages of 70% are guaranteed. Also, known as the DBXHR, portable versions are available as well.
Today’s new, highly sophisticated and cost-effective equipment gives updated production facilities a huge competitive edge amid heightened environmental awareness and increased regulations across the country.
With pulse jet and other baghouse technology, plants can achieve greater efficiency and performance while meeting stringent emissions standards by removing particulates from the exhaust stream at levels greater than 99.95%, and lowering emissions to less than one quarter of EPA standards. The baghouses and cyclones capture the dust from the drying process for feeding back into the mix.
In some instances, blue smoke emissions may be directed to the burner for incineration. For further safety and efficiency, advanced blue smoke systems are able to capture and condense blue smoke from both silo tops and from truck loadout, while other systems control sound through the use of state-of-the-art sound suppression technology. Latest burner technologies may be retrofit into existing plants to improve both efficiency and emissions.
A critical component in the effort to drive efficiency and keep emissions in acceptable ranges at the asphalt plant comes down to implementation of a sophisticated control system that monitors exhaust gas temperatures at the baghouse inlet as the primary reference for control.
One such setup is Astec’s V-Pac stack temperature control system. As the exhaust gas temperature changes, the control system checks it against a set-point. If the temperature differs from the set-point, the control system automatically changes the speed of the drum, controlling temperature to the set-point.
The patented control technology can lower stack temperature on high RAP mixes, open graded mixes and stone matrix asphalt (SMA), and raise stack temperature on virgin mixes and low RAP mixes. It also allows the running of SMA and high RAP mixes back-to-back with virgin mixes without flight adjustments. Lowering the stack temperature saves drying costs. For every 50⁰F the stack may be reduced, there is a 3% fuel savings.
A variety of other new hardware and software control systems also are available and serve to boost asphalt plant productivity, accuracy and speed, while assuring consistent mix quality, including blending, burner, silo, and motor control technology.
In addition, a top-of-the-line truck management system, such as the WM2000, can support as many as six scales that can be any mix of platform, back weigh or weigh batcher. The Astec unit can be retrofitted to most facilities and supports accounting data transfer.
Eco-Friendly More Than Meets the Eye
As noted earlier in this article, about half a century ago, Astec founder Brock was in the forefront of the burgeoning environmental move taking place in America and envisioned building asphalt plants “that you can’t see, you can’t hear, and you can’t smell.”
That was just the beginning, and today the modern plant not only pleases the senses, but truly has achieved a level of environmental commitment and recyclability that is unmatched by most other major industries, creating asphalt pavement that is 100% recyclable at its end-of-life and at rebirth is just as durable, if not more so, than virgin material.
While the effort to boost the amount of RAP in new pavement is ongoing, much is happening at plant sites to build ever more efficiency into the utilization of recycled material in more cost-effective and environmentally friendly ways.
For example, the use of advanced storage silos onsite at asphalt plants can improve energy efficiency and reduce emissions through highly precise heating and sealing methods, improved insulation, close monitoring, and attentive operations management.
Today, new long-term silos enable storage of asphalt mix for multiple days to allow uninterrupted production and maximum equipment efficiency, while saving energy and reducing waste (see related article, “When to Add More Storage at Your Asphalt Plant”).
Plants that want to upgrade storage to meet high production requirements, but look to do so at lower cost, can install new high-efficiency short-term silo systems that range from 100-ton single units to 3,000-ton multiple silo systems with a wide variety of features.
Such innovative silo technology available today enable cleaner operation, more recycled material in the mix, quieter processes, and faster delivery of high-quality asphalt to pavement sites.
As Astec’s Swanson pointed to in his sustainability white paper, it’s also very important to recognize that there’s synergy between sustainable practices and profitability.
To put it another way, the wise use of energy and materials along with excellent business management will go a long way toward paving a better bottom line.