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Power station ash for new cut price fillers

By Chris Smith
Posted 9 September 2009
A new reprocessing technology that extracts high performance fillers from the waste ash produced by coal-fired power stations could slash the cost of manufacturing performance polymer compounds, according to process developer RockTron.

The UK-based company - set up with £35m (€39.8m) of backing from a group of private and commercial investors, with a significant stake held by UK-based power station operator Scottish and Southern Energy – is running its first commercial scale reprocessing unit alongside the Fiddlers Ferry power station at Widnes in the north-west of England.

This first installation has the capacity to handle 200 tonnes an hour of pulverised fuel ash (PFA) waste, from which it extracts a range of products including cenospheres (alumino-silicate hollow glass spheres), solid alumino-silicate microspheres, carbon and magnetite.

These recovered products have been used in bulk applications - the carbon as a fuel and the remaining materials as low cost fillers in cement production. The intention now is to market some of the materials as high performance fillers.

“What we have is patented and exclusively licensed processes that take waste and separate it into useful minerals,” says Godfrey Short, director of business development at RockTron Advanced Products.

Short says RockTron’s “PFA Beneficiation” process is highly efficient and produces no unusable waste. And there is no shortage of raw material; there is an estimated 15m tonnes of PFA stockpiled on the Fiddler’s Ferry site alone and this is being topped up at the rate of 500,000 tonnes a year.

RockTron expects to be able to supply microspheres – which make up around 80 wt% of PFA - at a substantial cost saving over traditional alternatives. In part, this is because the raw material is a waste product that would otherwise incur a landfill tax.

“We start with a negative raw material cost because it costs the power station to dispose of this stuff,” says Short. “That means we are looking at hundreds of Euros a tonne [for our microspheres] rather than thousands of Euros.”

Tests carried out at the Polymer Processing Centre at Queens University in Belfast on PA6,6 and PBT compounds have shown that the RockTron MinTron microspheres compare well with commercial alternatives in terms of their effect on rheology, tensile and flexural modulus, elongation at break and impact performance, according to Short.

These early trials were carried out using an off-the-shelf coupling agent; Short expects even better results using an optimised system.

The most noticeable drawback for the RockTron product is the colour – the glass spheres are quite dark which will initially restrict use to coloured applications. However, Short says the company is working on a process technology to coat the surface of the MinTron microspheres with titanium dioxide.

The current technology in use at Fiddler’s Field classifies the microspheres in two sizes: seven microns – the most suitable for plastics applications – and 70 microns.

While the immediate focus of the RockTron team is to develop higher added value applications for the MinTron microsphere products, Short believes some of the other PFA waste products could also provide unique benefits that could be exploited by the polymer industry.

The magnetite component, for instance, has a spherical particle shape that Short says has much less impact on the flow properties of plastic compounds than current ground magnetite products, opening up opportunities in EMI and RFI shielding to incorporate higher loadings.

Short says that the company is also looking at ways to extract and make use of the sub-micron sized fraction in the microsphere produts, which amounts to around 26,000 tonnes a year from the existing plant. “One of our longer term objectives is to find a way to get this [sub-micron fraction] so we have a true nano-material,” he says.

With the European filler market for thermoplastics estimated to amount to around 1.5m tonnes a year, and with a substantial cost advantage over current products, Short believes RockTron has a real opportunity to replace existing fillers and develop new applications that would be too costly using current microsphere fillers. “This is potentially a disrupting technology,” he says.


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