This page contains a Flash digital edition of a book.
Focus on Coal 


Recycling transforms fly ash into ‘eco-minerals’


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.


Philip Michael explica una innovadora tecnología de reciclaje que está transformando los residuos (cenizas volantes) de las centrales eléctricas a carbón en valiosos “ecominerales” ‘a escala industrial.


Philip Michael erklärt eine innovative Recycling-Technologie, mit der Kohlekraftwerksabfälle (Flugasche) in industriellem Umfang in wertvolle Ökomineralien verwandelt werden.


R


ockTron’s new plant at Fiddler’s Ferry in Widnes, Cheshire, UK (Fig. 1), can recycle 800 000 tonnes of fly ash a year. It is designed to process both fresh and stockpiled fly


ash, effectively solving the problems of large-scale waste storage and removal, site remediation and conservation of natural resources. Tis GGBS, or CEM I (Portland cement (PC)) substitution proposition, allows companies to cut their costs, increase their margins and maintain their bottom line. RockTron is currently negotiating new plants in the US, Malaysia and Russia. Essentially, RockTron uses a traditional mining technology, called ‘froth flotation’. Tis beneficiation process separates and washes the components that make up fly ash to produce new eco-minerals which have many applications (Fig. 2). Te overall objective was to process power station PFA waste from tip, lagoon and fresh arisings 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 <2 per cent 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 (typically 30 per cent solids). Star valves in the fly ash silo automatically control the solids rate. Te slurry is then pumped into a specially designed receiving vessel, the cenospheres removal tank. Te vessel’s design


Fig. 1. RockTron’s new plant at Fiddler’s Ferry in Widnes, Cheshire, UK.


www.engineerlive.com 43


Page 1  |  Page 2  |  Page 3  |  Page 4  |  Page 5  |  Page 6  |  Page 7  |  Page 8  |  Page 9  |  Page 10  |  Page 11  |  Page 12  |  Page 13  |  Page 14  |  Page 15  |  Page 16  |  Page 17  |  Page 18  |  Page 19  |  Page 20  |  Page 21  |  Page 22  |  Page 23  |  Page 24  |  Page 25  |  Page 26  |  Page 27  |  Page 28  |  Page 29  |  Page 30  |  Page 31  |  Page 32  |  Page 33  |  Page 34  |  Page 35  |  Page 36  |  Page 37  |  Page 38  |  Page 39  |  Page 40  |  Page 41  |  Page 42  |  Page 43  |  Page 44  |  Page 45  |  Page 46  |  Page 47  |  Page 48  |  Page 49  |  Page 50  |  Page 51  |  Page 52