Asphalt Equals Climate Stewardship
BY Sandy Lender
Back in March, the Institute for Sustainable Infrastructure (ISI) announced that the L.A. Asphalt Plant No. 1 (AP1) replacement and modernization in an industrial district of Los Angeles, California, had received its Envision® Bronze award for sustainable infrastructure. While this is a laudable project on its own merits, AsphaltPro would like to share with the industry a few tips from the project to assist in other producers’ journeys toward net zero emissions and positive climate stewardship.
ISI stated in its March 10 press release: “To earn Envision Bronze, a project must demonstrate that it delivers a range of environmental, social, and economic benefits to the host and affected communities.”
Let’s look at how a plant from 1947, operated by the city of Los Angeles Bureau of Street Services (BSS), could produce between 100,000 and 200,000 tons of hot-mix asphalt (HMA) per year in an environmentally friendly manner. Specifically, how could a plant of that age introduce between 7.5 and 20% recycled asphalt pavement (RAP) without causing emissions troubles? The answer involves new technology, careful planning, and dust and emissions collection for re-use.
Map the Plan
For starters, the city worked closely with Partner Engineering & Science and brought in a full-service general contractor—Papich Construction Inc.—to demolish the old plant, remove old soil and detritus, bring in clean fill dirt, and build a new plant, alongside vendors such as Astec Industries of Chattanooga and Butler Justice Inc., of Long Beach, California. To get the new plant to fit on a roughly 2-acre site in an industrial area, the team had to create a detailed layout.
Eddie Van Zyl, sales director west integrated process solutions for Astec, told us the layout went through upwards of 20-plus revisions to ensure smooth traffic flow on the site for worker safety. “The biggest challenge on this project was to get all the equipment to function on a small site without being disrupted by truck traffic,” he explained. “We had to get all the pieces to work harmoniously with aggregate, RAP, and liquid asphalt deliveries taking place and not interfering with the hot-mix asphalt and Tac Oil pickup. Besides the asphalt plant, the site also houses Street Services personnel in the new administration building.”
The truck traffic continues night and day, he said. “And that’s the challenge. They’ve got to be very well coordinated.”
With the truck dump hopper and conveyors, the aggregate silos seen in the background of this picture cover about 200 feet of real estate on the AP1 site. All photos courtesy of City of L.A. BSS
The ISI release stated the “new AP1 will continuously produce asphalt at a rate of up to 400 tons per hour, up to 600k tons per year, and utilize up to 50% recycled asphalt product.”
“The plant can meet their capabilities,” Van Zyl said. “The logistics will be the bottleneck.”
Logistics will require over a hundred trucks per day to deliver aggregate to the 600-ton silos. That’s right: a 2-acre site won’t accommodate multiple large stockpiles of virgin aggregate, so Astec supplied five aggregate silos over the cold feed bins, totaling 3,000 tons of capacity.
“The silos are 26-feet in diameter,” Van Zyl said. “With the truck dump hopper and conveyors, they cover about 200 feet. The aggregate is unloaded into a 30-ton truck dump hopper. Minimal dust is created as the hopper sits well below grade. The conveyors are all covered with aluminum dust covers and all aggregate transition points have water mist dampeners. The RAP screen is completely covered so that any dust created is mitigated.”
Notice the LED lighting for the plant has covers to focus and direct it.
Collect Dust
Dust mitigation is one of the key factors that garnered the city’s Envision award. Under the category of air quality, the ISI stated: “As a project located in the South Coast Air Quality Management district, the project was required to meet stringent requirements to reduce particulate matter and other air pollutants. The new plant will be more efficient and provide significant improvements to air quality compacted to the previous plant that was designed in 1947.”
As Van Zyl mentioned, all conveyors and transfer points are covered. Astec supplied a 76,000-CFM pulse-jet baghouse for the project. Butler-Justice Inc. installed two insertable dust collectors along the RAP system to act as mini-baghouses at the Telsmith 4230 horizontal shaft impactor (HSI) and at the two 10-foot by 14-foot RAP bins.
“By utilizing material that would typically be sent to the landfill, this project is turning trash into a valuable material that is important for maintaining the city’s streets,” said Melissa Peneycad, ISI’s managing director. The award committee also noted that by using reclaimed aggregates from local resurfacing projects in the production of HMA, the city will avoid uncertainty in future mining and transportation costs.
To ensure the use of RAP is as environmentally friendly as possible, the project captures and re-uses its dust.
“By its very nature, the HSI will displace air, which causes dust to billow out,” Mike Butler of Butler-Justice said. “We collect the unruly dust created by the impactor and screen. The collector acts just like a vacuum cleaner; the 30 bags inside are like pillowcases. There are always 20 bags that are sucking particulate in. Every 10 seconds, a pulse goes off for a set of 10 of the bags. This is a constant rotation.
“We’re containing the unruly dust in the bag section. Then when the bag releases its dust cake onto the belt, the dust goes back into use.”
For the RAP material discussed here, special bags are required. “RAP wants to stick to bags,” Butler said. “But these bags balloon out when pulsed. The pores of the bag release the sticky dust.”
He explained that these small dust collectors—insertable baghouses—are gaining popularity with established plants where owners want additional dust control and want RAP dust to remain in the circuit. “In that 2-acre site, there’s not a lot of room for another stand-alone baghouse, plus conveyors and all the accoutrements that go with it.” He pointed out that capturing and storing RAP dust particulate could present additional environmental hoops for owners to jump through. Returning the dust to the system for immediate use makes sense. “We circumvent a problem we’d end up creating if we captured and stored the material,” Butler said. “Our whole job is to solve problems.”
On the far right of this picture, the blue box is one of the two insertable baghouses described in this article. Mike Butler explained these small dust collectors are gaining popularity with established plants where owners want additional dust control and want RAP dust to remain in the circuit. The RAP screen is completely covered so that any dust created is mitigated.
Collect Mist
A potential problem Astec proactively solved is that of fugitive emissions at loadout. The company supplied three 300-ton storage silos and beneath them is an enclosed loading zone and a blue smoke control system with a kick. Van Zyl described it:
“The 18,000-CFM blue smoke control system includes a Fiberbed mist collector. The system prevents odorous fugitive emissions from the mix storage silos during filling and load-out operations. The truck loading zone is completely enclosed. The enclosure is outfitted with u-shaped collectors at each silo gate to capture emissions as mix is discharged. The enclosure is also outfitted with auxiliary intakes at each end to prevent emissions from escaping when trucks exit the scale.”
The truck loading zone is completely enclosed and outfitted with u-shaped collectors at each silo gate to capture emissions as mix is discharged. You can also see here the auxiliary intake at this end, designed to prevent emissions from escaping when trucks exit the scale. To the side, notice the conveyors and transfer points are all covered carrying material to the 40-foot Double Barrel drum with V-Stack temperature control.
Collect an Award
When it’s all said and done, the AP1 in downtown Los Angeles is now designed to showcase how sustainable the asphalt industry can be. Right down to reducing light pollution.
“Lighting needs were designed based on local guidelines that encourages strategies that minimize light glare and trespass,” the ISI press release reported. “In addition to incorporating LEDs, lighting controls adjust to the project’s needs based on availability of daylight.”
With the latest technology in place, the plant “is expected to exceed regulatory requirements, permit requirements, and industry guidelines for energy efficiency and emissions control, and meet the current BACT condition set forth by the SCAQMD (Air Board).”
Whether you wish to meet new air quality standards in your county or wish to apply for your own green ratings certification for your operations, the steps BSS took for its site are a primer for getting started.