Concrete Products

AUG 2015

Concrete Products covers the issues that attract producers of ready mixed and manufactured concrete focusing on equipment and material technology, market development and management topics.

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Page 37 of 59

36 • August 2015 Ahead of the Environmental Protection Agency's contentious Coal Combustion Residuals (CCR) management and disposal rulemaking, Lexington, S.C.-based proces- sor 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 win- dow, privately-held The SEFA Group topped CCR-processing and marketing peers in cap- ital 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 car- bon 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 ben- eficiation, 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 pow- der from high LOI ash. Underscoring the timeliness of a new thermal beneficiation method are market (low natural gas prices) and looming regulatory (EPA Clean Pow- er 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. Facili- ties 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. Raw feeds are subjected to heat and air-actuated chemical cycles that lower car- bon content from high single-digit or dou- ble-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 mois- ture content. "Water forms hydroxyl groups on the sur- face 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 dry- ing 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 mate- rials—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 con- tract. It has processed 600,000-plus tons of high (5 to 25 percent) LOI fly ash from more than 16 coal combustion units, netting pre- mium, concrete-grade powder of carbon pro- file 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., oper- ation, opened in 2012. With a production capacity of about 350,000 tons/year, assum- ing 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. Planning and engineering for a third STAR operation proceeded as favorable eco- nomics of the technology played out—and the EPA rulemaking languished. Continued on page 38 FEATURE BY DON MARSH Rising STAR SEFA Group's processing technology stabilizes fly ash supply chain as coal combustion levels cool Thomas Hendrix, president, founded The SEFA Group in 1976 after a long tenure with Universal Atlas Cement, with one of the post-war market leaders. Jimmy Knowles, vice president, Market De- velopment, was introduced to fy ash during high school and college summer stints in quality control with then-Atlanta market leader, (pre-Blue Circle) Williams Bros.

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