RockTron's Recycling Revolution

(Industrial Fules and Uses 8-2-2010) RockTron, an award-winning pioneer in recycling, has designed and built a new plant that can transform coal-fired power station waste, called fly ash or PFA (pulverised fuel ash), into highly valuable industrial eco-minerals. RockTron can recycle both fresh and stockpiled fly ash, reducing the need for costly and environmentally unfriendly long-term waste storage.Fly ash currently poses a huge global environmental problem, with an estimated 2bnt of fly ash currently stored in landfill sites and ash dumps worldwide, and over 100Mt in the UK alone. RockTron’s process is unique in that it can remove and recycle both fresh and stockpiled fly ash, and produces no waste or effluent. It thereby solves the problems of costly long term and large-scale coal ash waste storage by beneficiating 100% of the fresh coal ash as it arises, which will reduce the need for long term storage of fresh coal ash. It also enables the recovery, recycling and beneficiation of coal ash in containment ponds, landfills, quarries and other long term storage. The RockTron process does not need a working coal-fired power station to operate and process coal ash, as the process plants can be sited on legacy coal ash deposits as well, providing a constructive recycling solution to some of the highest risk coal ash sites in the world. RockTron’s new plant at Fiddler’s Ferry is the size of London’s Wembley Stadium and can recycle 800,000 tonnes of fly ash every year. In addition, the RockTron plant is a net energy contributor, returning more energy than it consumes.
 
RockTron’s Road to Success
 
RockTron’s story is testament to the resolve and drive of those who created and developed the technology. RockTron’s Founding Director, Philip Michael, first built a working prototype flotation cell to separate carbon from fly ash in Belgium in 1986. A fully operational plant was then built in Germany in 1989 and the first UK pilot plant in 1992. In 1999, Michael teamed up with Dr John Watt, and successful pilot trials for the company’s patented Fly Ash Beneficiation process followed shortly afterwards at Fiddler’s Ferry. Finally, in 2000, RockTron Limited, the foundation for today’s international group of companies was formed. The science was proven; the corporate infrastructure was in place. Yet despite the obvious commercial and environmental opportunities, and presentations given at the highest level throughout Europe, there were no takers for this new technology. Frustration reached its peak in 2002 when the dotcom bubble burst, preventing RockTron launching on the AIM market.
 
It was not until 2007 that Scottish and Southern Energy plc saw the potential of RockTron’s process and seized the initiative. In March of that year, the energy company formally announced its GBP30m funding of RockTron, enabling the company to build a demonstration plant at Gale Common in Yorkshire and a full-scale plant at Fiddler’s Ferry. By 2008, the first processed samples were being produced, and in September 2009, the plant came on line.RockTron New Eco-minerals.
 
RockTron’s 100% recycled products can be used as substitutes for fillers and extenders in a wide variety of industrial applications, namely: plastics, rubber and coatings. They cost less, have a lower carbon footprint and offer comparable or superior performance than their competitors. RockTron can help industries such as automotive, aviation, construction, medical and telecoms to cut their manufacturing costs, improve product performance and green their supply chain.
 
New Advanced Products
 
RockTron Advanced Products offer manufacturers new economic and environmental opportunities. These high performance eco-mineral fillers and extenders include hollow and solid alumino-silicate microspheres (<1 to 300 micron) and solid paramagnetic microspheres, designed to replace conventional and man-made inorganic fillers and extenders such as talc, GCC, glass fibres and glass microspheres. RockTron eco-minerals act as functional fillers in rubbers and plastics, and give improved physical properties including scratch and wear resistance for components and coatings, and even sound absorption.
 
RockTron’s fundamental advantage is that its products are naturally spherical. Their beneficiation process removes the surface alkali salts to enhance performance. Other attractive product attributes include a lower melt viscosity compared with many other inorganic fillers and also lower density. RockTron’s microspheres (Mohs hardness scale = 5-6) are glass and thus ensure low oil absorption, potentially reducing the amount of process oil or resin required compared to many other fillers. These spherical particles can also be coated to change their surface chemistry for use in paints, elastomers, thermoplastics, thermosets and other materials. For example, RockTron-filled plastic components in automotive applications help to reduce vehicle weight and overall vehicle CO2 emissions.
 
New Cementitious Products
 
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 that have many applications. The overall business objective is to process power station waste, PFA (Pulverised Fuel Ash or fly ash), 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 from PFA in order to produce an economically viable cementitious alternative with typically <5% Loss on Ignition (LOI).
 
Independent Research
 
Independent research into RockTron’s products carried out by ARTIS (Avon Rubber), Queens University Belfast (polymers) and Kirton Concrete over the past 12 months have yielded impressive results. It has been found that RockTron’s Advanced Products used in a silica passenger tyre compound demonstrate increased tan δ at 0ºC (which predicts improved tyre wet grip) and reduced tan δ at 70ºC (which predicts reduced tyre rolling resistance). Meanwhile, researchers have found that RockTron’s cementitious products have a substitution capability of up to 35%, whereas most traditional fly ash cement substitutes typically can only replace 20-30% of the cement. Using RockTron’s substitutes can therefore cut costs and significantly reduce the amount of CO2 emissions linked to cement and concrete production, which is one of the largest contributors to man-made global warming after transport and energy generation.
 
In recognition of RockTron’s spectacular achievement, the company has been awarded IChemE’s (Institution of Chemical Engineers) most prestigious International Innovation and Excellence Award, the new IChemE Nicklin Medal for the most outstanding entry across all eleven categories. In doing so, they beat 48 other shortlisted entrants, including BP, Dow, Anglo American and GlaxoSmithKline, plus many internationally renowned universities.
 
Superior Performance in Concrete

  • What is so remarkable about RockTron’s beneficiation process is that, unlike other fly ash processes, it:
  • Removes and recovers hollow glass cenospheres – improving concrete density and reducing the possibility of gas entrainment
  • Removes the surface alkaline salts – exposing free silica to make the material more reactive with other materials, such as lime from the cement when used in concrete
  • Reduces the LOI to typically less than 5%, as demonstrated by the work at Kirton Concrete, which showed that strength development in concrete using a 50% substitution of Alpha with 1% LOI was equivalent to that obtained using a 30% substitution of Alpha with 7% LOI.

 
Cutting Carbon Emissions
 
Such is the potential of RockTron’s new process that it could help cut man-made CO2 emissions by up to 2%, enabling the UK government to meet its commitment to cut carbon emissions by at least 26% by 2020 and 80% by 2050. This is because every tonne of traditionally produced cement currently produces approximately 0.82 tonnes of CO2 (which amounts to more than 5% of annual man-made CO2 globally). A further environmental benefit of recycling fly ash is the reduced demand for materials that would otherwise need quarrying, and also the substitution of materials that would be energy-intensive to create.
 
Beneficiation Process
 
RockTron’s new technology is radical because power stations producing fly ash with a high carbon content have traditionally employed dry classification and / or selective removal which leaves no alternative but to stockpile the resulting waste. But the RockTron process removes the carbon content using Froth Flotation, which is explained below.
 
Stage One – Feed. RockTron’s plant can accept feed from either stockpiled, lagoon or fresh ash from a power station’s precipitators. Either fresh ash from electrostatic precipitators or stockpiled ash 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 cenosphere removal tank. The vessel’s design allows gentle agitation and physical separation of the cenospheres under gravity. The resulting CenTron™ product has particular applications in the automotive and aerospace industries.
 
Stage Two – Flotation circuit. The remaining slurry is then pumped into the flotation circuit, the central hub of the plant where pulp density is established and mixed with reagents to ensure product quality. The whole circuit is fully automated and insensitive to widely fluctuating changes in head grade. The culmination of these processes causes the carbon to float off. A cleaner circuit cleans it to increase the overall grade with a target of >90%. The carbon is then dewatered on a horizontal belt filter and, if required, flash dried. In filter cake form the carbon is ideal for reuse by the power station.
 
Stage Three – Magnetite removal. Following carbon removal, the remaining feed comprises alumino-silicate particles and spherical magnetic particles in the form of Fe3O4-Al2O3-SiO2. This spherical magnetic component may be recovered, dewatered and dispatched. Removal of the magnetite is discretionary. The remaining slurry is eventually separated into the RockTron Alpha and Delta products for the cementitious market.
 
Stage four – classification. The remaining alumino-silicates are then pumped into high efficiency hydrocyclones (used in the clay industry) and classified into two particle size groups resulting in the fine 5-9µm (d50) Alpha particles and the coarser 60-80µm (d50) Delta particles. Delta is then dewatered and stored in bulk. Alpha is dewatered to <0.5% moisture and stored in silos.
 
The Future of RockTron
 
These new superior, environmentally and economically efficient products offer exciting new applications for a vast range of industries. RockTron is currently negotiating new plants across the world, namely in Asia, Poland, Russia and the US. RockTron Asia is launching in October at the International Greentech & Eco-Products Exhibition & Conference Malaysia 2010 (www.igem.com.my) two years ahead of schedule due to unprecedented demand. This new company is confident that RockTron’s new Advanced Product range, supported by results from further independent research expected later this year, will open up huge export potential in Malaysia, China, Korea, Singapore and Japan, re-affirming RockTron’s position as a key player in the fly ash recycling market. 
 
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