CASE STUDY RECYCLING TRANSFORMS FLY ASH
INTO ECO-MINERALS Philip Michael, co-founder and Technical Director of RockTron Ltd
Philip Michael explains an innovative recycling technology, which is transforming coal-fired power station waste (fly ash) into valuable ‘eco-minerals’ on an industrial scale.
RockTron’s new plant at Fiddler’s Ferry in Widnes, Cheshire, UK, has the capacity to recycle up to 800,000 tonnes of fly ash a year. It is designed to process both fresh and stockpiled fly ash, effectively solving the current problems of large-scale waste storage and removal, making long-term fly ash site remediation possible and, through the recovery of useful eco- minerals, enables the conservation of virgin natural resources. For example, in the concrete sector the partial substitution of traditional CEM I (Ordinary Portland Cement) with RockTron Alpha allows concrete companies to cut their costs, increase their competitiveness and maintain their bottom line. Although RockTron’s award-winning technology was first successfully tested over 20 years ago, it took two decades to gain the financial support that they have today. In 1986, RockTron built a working prototype of their flotation cell to separate carbon from fly ash in Belgium. A fully operational plant was then built in Germany in 1989 and the first UK pilot plant followed in 1992. Vital studies and patents ensued throughout the 90’s but the real catalyst for the RockTron launch came when I and Dr John Watt joined forces in 1999.
The determination and drive of our team was unrelenting. In 1999 successful pilot trials for fly ash beneficiation were completed at Fiddler’s Ferry Power Station in Cheshire, using run-of-station fly ash and stockpiled material from adjacent ash lagoons.
2000 saw the formation of RockTron Limited, the foundation for today’s international group of companies. Subsequently, RockTron’s Research arm was established in 2001. The science was proven; the corporate infrastructure was now in place. Yet despite the obvious commercial opportunities and presentations given at the highest level throughout Europe, there were no financial takers. Frustrations reached their peak in 2002 when the dot com bubble burst, preventing RockTron from launching on the AIM market. Then, in 2006, one company saw the full potential of RockTron’s innovative process and seized the initiative. In March 2007, Scottish and Southern Energy plc
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formally announced their funding of RockTron to build a demonstration plant at Gale Common in Yorkshire and a full-scale commercial plant at Fiddler’s Ferry. By 2008, the first processed samples were being produced. RockTron’s fly ash beneficiation process uses a traditional mining technology, called ‘froth flotation’. This separates and washes the components that make up fly ash to produce new eco-minerals which have many applications. The overall business objective is to process power station PFA (Pulverised Fuel Ash or fly ash) waste from tip, lagoon and fresh arisings in order to produce economically viable products with no waste or effluent. Historically, BS 3892 and BS EN 450 - the British and European Standards stipulating the use of fly ash as a cement substitute - emphasise the key measures of particle size and carbon content. While dry classification and/or selective removal has been successfully employed for the past 20 years, power stations producing fly ash with a high carbon content had no alternative but to stockpile their waste. So RockTron set out to remove the carbon content in order to produce an economically viable cementitious alternative with typically <5% Loss on Ignition (LOI).
Stage One - Feed. RockTron’s plant can accept feed from either stockpiled, lagoon or fresh ash from a power station’s precipitators. Fresh ash from electrostatic precipitators is sluiced with recycled process water into a pump suction tank, where the pulp density is automatically controlled for optimum pumping to the plant. The slurry is then pumped into a specially designed receiving vessel - the cenospheres removal tank. The vessel’s design allows gentle agitation and
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