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| The newest STAR facility and load-out occupy 6.5 acres of Santee Cooper Power’s 408-acre Winyah Generating Station, the principal power source for nearby Myrtle Beach, S.C. The reactor has direct feed of dry ash from the adjacent generating station. |
SEFA GROUP’S PROCESSING TECHNOLOGY STABILIZES FLY ASH SUPPLY CHAIN AS COAL COMBUSTION LEVELS COOL
By Don Marsh
Ahead of the Environmental Protection Agency’s contentious Coal Combustion Residuals (CCR) management and disposal rulemaking, Lexington, S.C.-based processor and marketer The SEFA Group mastered a thermal beneficiation technology suiting the best of both worlds in what became a final rule governing electric utilities’ ash stock: More recycling, less disposal.
Concrete and cement interests will long recall the 2009–2014 rulemaking for the cloud it brought to ASTM C618-grade fly ash market prospects. During that window, privately-held The SEFA Group topped CCR-processing and marketing peers in capital outlays and contracts (> $75 million) by building first, second and, effective April 2015, third generation versions of its Staged Turbulent Air Reactor (STAR). Consistent with EPA’s favorable take on stepped up CCR recycling rates, STAR yields high quality Class F or Class C ash from conventional or substandard raw feeds, respectively: low carbon content or loss on ignition (LOI) fly ash directly from generation; and, impounded, high LOI (5–30 percent carbon, depending on station combustion efficiency) pond ash from previous operations. The reactor and its new treatment methodology are similar to older thermal processes common in ash beneficiation, but limited in their potential for handling low-grade feeds.
EPA’s final rule (note sidebar, page 38) changes ash handling and storage economics from power station pond to landfill. Through energy efficiency and effective chemical transformation, the STAR process improves the math of extracting concrete-grade powder from high LOI ash. Underscoring the timeliness of a new thermal beneficiation method are market (low natural gas prices) and looming regulatory (EPA Clean Power Plan) forces that have lowered utilities’ annual coal consumption. U.S. mine output has dropped below 1 billion tons for the first time in two decades.
The SEFA Group engineers, fabricates and erects the fittingly named STAR. Facilities combine raw feed preheating chamber; pneumatic transfer channels for raw feeds and finished powder; vertical, multi-zone reactor vessel; plus, finished powder silos and load out. Ashes’ LOI determines capacity: As carbon levels increase, throughput decreases.
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| Dewatering of pond ash (above), fed separately or concurrently with dry ash, begins in sheltered storage and continues in pre-heating chambers (below) that draw high temperature air from the reactor, which runs on raw feed carbon combustion. Ash particles meet air and water streams at ring headers placed along the reactor vessel. STAR technology can process bituminous and sub-bituminous coal fly ashes, Class F and Class C, respectively, and run various blends to meet concrete customers’ specific performance requirements. |
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Raw feeds are subjected to heat and air-actuated chemical cycles that lower carbon content from high single-digit or double-digit percentages to less than 1 percent. In the case of pond ash—high on the EPA CCR rulemaking radar—the STAR process imparts or restores cementitious value to material often bearing 25-30 percent moisture content.
“Water forms hydroxyl groups on the surface of high LOI ash stored in ponds, which lowers the strength activity of the material,” explains SEFA Group Vice President, Market Development Jimmy Knowles. “Simply drying the ash does not restore its pozzolanic value. STAR equipment optimizes or restores the reactive alumina silica chemistry in ashes by driving off the hydroxyl groups through a calcining phase. The process is similar to heat treatment converting kaolin or clay to supplementary cementitious materials—metakaolin or calcined clay.”
EQUIPMENT EVOLUTION
STAR debuted in 2008 at the South Carolina Electric & Gas McMeekin Station, near The SEFA Group’s headquarters on the outskirts of Columbia, capital city. STAR I is company owned and operated under long-term contract. It has processed 600,000-plus tons of high (5 to 25 percent) LOI fly ash from more than 16 coal combustion units, netting premium, concrete-grade powder of carbon profile well below ASTM C618 thresholds.
Ash quality and process efficiency observed in the premier reactor propelled Houston-based NRG Energy to enlist The SEFA Group for a turnkey Morgantown, Md., operation, opened in 2012. With a production capacity of about 350,000 tons/year, assuming raw feed averaging 9 percent LOI, the STAR II facility serves an adjacent coal-fired generating station, while also processing CCR from NRG’s Chalk Point, Md., power plant. The marketability of Morgantown ash has enabled the utility to defer disposal infrastructure investment at Chalk Point, from which most CCR is now trucked to STAR II.
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| The Staged Turbulent Air Reactor has its own stack with integral continual emission monitoring system to ensure permit compliance. The SEFA Group builds each STAR operation as a stand-alone facility that can operate independently of the host utility. |
Planning and engineering for a third STAR operation proceeded as favorable economics of the technology played out—and the EPA rulemaking languished.
The facility entered the commercial phase earlier this year at the Santee Cooper Power Winyah Generating Station in Georgetown, S.C. It replaces a 10-year old thermal beneficiation line that averaged 200,000–250,000 tons/year of concrete-grade fly ash. To justify equipment replacement and boost output closer in line with market demand in the Carolinas and neighboring states, SEFA Group engineers looked beyond fly ash for raw feed, determining their reactor could be tooled to process the station’s impounded pond ash.
Based on 6.5 acres leased from the state-owned Santee Cooper, STAR III opened with 450,000 tons’ annual processing capacity, netting up to 300,000 tons of ASTM C618-grade product. “The Winyah STAR reduces what had been a much longer residence time to a little as 7 to 10 seconds, and lowers the carbon content of fly ash from 5–25 percent to an average of 0.2 percent,” notes Knowles. “The reactor handles 18 to 50 tons per hour, depending on raw feed LOI, and recovers about 70 percent of the carbon’s Btu value.”
The Winyah reactor is equipped with four lines, which can receive separate fine and coarse raw feeds. The reactor taps feed ashes’ recoverable Btu to a point where, following start up fueling, the beneficiation process is self-sustaining and exothermic: No fuel is required for continuous treatment, while excess heat can be drawn from the reactor for raw feed drying or sold to outside users. As ash rises through the refractory-lined steel vessel, air is injected at various locations to process the ash in stages to augment carbon removal or passivation. In extreme instances, a single piece of carbon char breaks into hundreds of spherical, pozzolanic particles.
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| Electric utilities are subject to increasingly stringent emissions controls and, potentially, forthcoming rules capping greenhouse gas emissions levels. For now, Santee Cooper maintains customary levels of coal and limestone (below, foreground), the latter used in scrubbers. Regardless of Winyah Station operating status, The SEFA Group has a 20-year lease for the STAR III facility, coupled with 11 million tons of pond ash “reserves.” |
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In a 2015 World of Coal Ash presentation, Knowles and colleagues John Castleman, P.E., and William Fedorka, P.E., offer further STAR III insight, describing the technology as “Specifically designed and operated to reduce the heterogeneity of fly ash by eliminating or lowering the amount of unburned carbon and other contaminants, including unburned organics from alternative fuels. The plant operates at temperatures that are high enough to burn off residual organics comingled in the fly ash, including coal char particles. [It] can also be operated to reduce some types of agglomerates, improving particle size distribution, as well as to blend various coal fly ashes in order to reduce variations in ash chemistry or to optimize the performance of coal ash for particular ash utilization opportunities/markets.”
SUSTAINED STREAM
Much like a cement or aggregate producer assessing limestone or granite reserves for mill or quarry development, The SEFA Group sited STAR III amid an abundant low-grade CCR impoundment, ultimately bound by the EPA final rule. “If the generating station shut down tomorrow, we would have enough raw feed for 20 years. That’s what was needed to justify our investment at Winyah,” says President Thomas Hendrix.
STAR III was financed through $40 million in S.C. Jobs Economic Development Authority bonds, he adds. It brings SEFA Group’s payroll past 200, including an engineering and construction department, plus fleet of 70 tankers. Additional STAR installations and contracts are certain, as utility operators confront compliance with new ash storage, disposal and landfill operation guidelines, and sweeping changes across the power generation business disrupt the supply chain of a widely accepted pozzolanic powder.
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| SEFA Group operated a thermal beneficiation facility at the Winyah Generating Station for a decade prior to building the more efficient and versatile STAR III line. Ramp up of the latter saw a 15,000-ton concrete storage dome join an existing silo. A company fleet serves three STAR plants, plus four Carolinas and Tennessee generating stations from which The SEFA Group distributes fly ash requiring less processing. With 15-plus years in thermal beneficiation, yielding more than 5 million tons of marketable powder, the company is promoting the STAR technology at Georgetown, S.C., as a unique, proven solution for pond ash management and new source of ASTM C618-grade fly ash. |
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FINAL COAL COMBUSTION RESIDUALS RULE
The U.S. Environmental Protection Agency published the final rule regulating Coal Combustion Residuals (CCR) on April 17, 2015. It regulates new and existing CCR landfills and surface impoundments (i.e. ponds) at electric-generating stations as non-hazardous solid waste units under Resource and Recovery Act Subtitle D. These new rules provide similar protections to those for municipal solid waste landfills with their focus on protecting human health and the environment by addressing groundwater, structural integrity of impoundments, and specific requirements for using liners for all new CCR units. Groundwater monitoring is required for all continuing or closed CCR units; closure requirements include a 30-year monitoring period. These rules will increase costs related to disposal of coal ash moving forward, and extend the long-term liability associated with the risks of storing coal ash on the utility’s property. — from “Reclaiming and Recycling Coal Fly Ash for Beneficial Reuse with the STAR Process,” a 2015 World of Coal Ash presentation by The SEFA Group’s Jimmy Knowles, John Castleman, P.E. and William Fedorka, P.E.