During the period from 2010 – 2020, US electricity generation from coal-fired power units declined by 51%.1 The result has been a dramatic tightening of the supply of freshly generated production fly ash for use as a supplementary cementitious material (SCM) in several important markets throughout the US. Further declines in coal generating capacity have been announced industry-wide, as existing coal units are retired or converted to natural gas. Longer term, the fast-improving economics of renewable power and the global emphasis on fighting climate change is expected to dramatically reshape the electrical generation industry. For the cement and concrete industries, decarbonization will mean a stepwise reduction in CO2 emissions through a multifaceted approach of clinker substitution, energy efficiency improvements, process changes and technological adaptation.
Fly ash has played and will play even a bigger role in the decarbonization efforts of the cement industry, and especially Titan America. Titan America was an early adopter in the fly ash beneficiation and marketing space. In 1997, Titan America formed its first fly ash processing joint venture with Separation Technologies (ST) at the Roxboro Steam Plant, located outside of Durham, North Carolina, USA.
For Titan America - the ST electrostatic separation equipment made the industrial scale recycling effort and beneficial use of fly ash possible. The ST electrostatic beneficiation process works as follows - the raw unprocessed fly ash is fed into the ST separator at a continuous basis, at a feed rate of up to 40 tons per hour. The mineral rich particles and the residual coal char particles collide with each other at high speed, transferring electrostatic charge in the process. The mineral fraction and carbon fraction, now charged opposite to each other, are attracted to opposing electrodes within the separator. The particles are conveyed out of the separator by the action of a belt inside the separator that sweeps the electrodes at high speed. A schematic drawing of the ST separator is shown in Figure 1. The small gap, high voltage field, counter current flow, vigorous particle-particle agitation and self-cleaning action of the belt on the electrodes are the critical features of the ST separator. By controlling various process parameters, the ST process produces consistently low LOI (loss on ignition) fly ash at carbon contents set anywhere between 1.5 and 4.5% from feed fly ashes ranging in LOI from 5% to over 25%. The process is entirely dry, requires no additional materials other than the fly ash and produces no waste water or combustion-related air emissions. The recovered materials consist of fly ash reduced in carbon content and controlled to levels suitable for use as a pozzolanic admixture in concrete (ProAsh®), and a high carbon fraction (EcoTherm®) useful as fuel or cement kiln raw-mix additive that brings fuel value while displacing virgin materials. Utilization of both product streams provides a 100% solution to fly ash disposal.
After a successful second joint venture at Brandon Shores generating facility in 1999, Titan America acquired ST in 2002 and began a phase of rapid expansion of the ST fly ash beneficiation and marketing footprint in the east coast of the USA. By 2008, ST had installed 13 fly ash separator systems in North America, and marketing the high-quality fly ash product, ProAsh®, to both internal and external ready-mix concrete customers. However, during the period from 2010 – 2020 US electricity generation from coal-fired power units declined by 51%.1 The resulting shortage in fly ash availability during peak construction seasons led to a steady decline in fly ash substitution rates in ready-mix concrete, replaced with slag cement at times. In some markets previously served by ST, the discretionary use of fly ash has been almost eliminated for lack of supply.
Fly ash remains a desirable key ingredient in many ready-mix concrete designs due to its concrete durability and workability benefits. With new sources of fresh fly ash unavailable, Titan America looked for opportunities to recycle fly ash from landfills and impoundments where low quality and / or excess fly ash was disposed of in previous years. In partnership with Talen Energy, ST identified the Brunner Island generating facility as a potential source of reclaimed fly ash. For Talen Energy and ST, the Brunner Island fly ash harvesting project was a natural fit. ST has been a reliable processor and marketer of the freshly generated fly ash at the Brunner Island station since 2006. In total, ST has processed and marketed five million tons of ProAsh over its 21 years of onsite operation at Talen Energy facilities. However, fresh fly ash generation has slowed in recent years as the utility had mostly converted the station to fire on natural gas. At the same time, the utility was able to make harvested fly ash available to ST as a feedstock. After multiple rounds of sampling and pilot testing, ST commissioned its first industrial scale fly ash drying and electrostatic separation plant to reclaim fly ash from surrounding coal ash impoundment basins in 2020 at the Brunner Island generating facility.
The landfill fly ash processing facility combines ST’s novel drying and particle sizing system with ST’s long proven electrostatic separation process for removing unburned carbon from fly ash. The drying process consists of a coarse screening process to reject bottom ash, followed by a thermal flash drying process and a particle size segregation stage to achieve an ASTM fineness compliant feed fly ash. The feed fly ash, now dried but still containing an elevated carbon level, is fed to the existing ST electrostatic separation equipment at high feed rate of up to 40 tons per hour. The resulting product is high quality, low LOI ProAsh®, for use in concrete construction. Multiple studies by ST have confirmed the reclaimed fly ash product meets all ASTM C618 specifications and concrete testing has confirmed that the performance is equivalent to conventional ProAsh.
In addition to conveying numerous concrete performance benefits, the use of ProAsh® in concrete dramatically reduces the carbon intensity of the final concrete product by reducing the cement required in the concrete mixture. This is because the manufacture of Portland cement is itself a carbon intensive process - one ton of Portland cement results in emissions of approximately one ton of CO2. Therefore, each ton of fly ash recycled into concrete results in approximately 0.9 tons of avoided carbon emissions. Because the fly ash is recycled from a decades old landfill, the CO2 emissions that were originally generated as a result of burning coal from electricity occurred many years ago – thus there is no new increase in CO2 emissions to generate the fly ash. In fact, the CO2 emissions generated as a result of removing the fly ash from the landfill, drying it and processing it to ProAsh® represent only about 6% of the emissions from manufacturing an equivalent amount of Portland cement. Recovering and recycling fly ash from historic landfills has other environmental benefits, including preventing future fly ash landfill failures in environmentally sensitive areas, mitigating potential groundwater contamination and reclaiming landfill space for future use.
“Fly ash pond and landfill reclamation represents the future of the supplementary cementitious materials industry,” says Tom Cerullo, President of Separation Technologies. “ST is proud to announce this important milestone in our 25th year of history developing industry leading solutions for the construction material and power generation sectors. This advancement now can be widely deployed as part of Titan Group’s commitment to sustainable business practices, CO2 reduction, and the development of environmentally responsible products.”
For Titan America, the successful installation and operation of the fly ash drying system at Brunner Island represents an important milestone in a broader strategy of decarbonizing its operations while simultaneously investing for future growth.
“This breakthrough achievement represents Titan America’s commitment to the reduction of CO2 through innovation as we plan to deploy this technology across the power generation and construction material sectors,” says Bill Zarkalis, Chief Executive Officer of Titan America. “By harnessing the power of this technology, ST is utilizing a revolutionary beneficiation process that is capable of converting reclaimed ash from basins in an efficient manner. The result is a high-grade, low carbon construction product and a fuel-rich product for power generation and cement manufacturing.”
ST and Titan America foresee a bright future for the landfill fly ash processing technology. Current and future projects include utilities who are looking to eliminate environmental liability from their existing fly ash disposal sites at a minimum cost, and in full compliance with environmental laws.
In addition to utility customers, ST believes that a cement plant also provides an advantageous location for a fly ash drying and electrostatic beneficiation process, which would offer the advantage of using waste heat recovery as a method of drying the wet fly ash. Cement users would also be able to directly consume both products of the ST separation process. The ProAsh® product would be used for the manufacture of blended cement, while realizing a significant offset in the carbon intensity of their operations. The carbon rich EcoTherm® would be utilized by the host cement plant as an alternative fuel and a mineral additive for the cement kiln.
