Raymond Brown Aggregates latest IBA processing plant operation for Viridor is a total success.


Having been successfully selected by Viridor Oxfordshire Ltd to recover and process bottom ash from its new Energy from Waste facility (EfW) in Ardley, Oxfordshire, Raymond Brown Aggregates (RBA) has invested over £2 million in the overall project, which includes a bespoke design IBA (Incinerator Bottom Ash) processing plant. The contract with Viridor Oxfordshire Ltd (VOL) will run for 15 years, with RBA processing approximately 75,000 tonnes of IBA annually.

The new plant was constructed and installed under contract by DUO Manufacturing (Division of DUO plc) over a period of three months, with testing and commissioning successfully completed in September 2014. The first batch of Oxfordshire IBA has now been processed and marketed with excellent results and product quality.

Several challenges had to be overcome, as the IBA processing building at Ardley was already designed and approved under the overall site planning permission. This meant RBA and DUO had to work closely to ensure that the available area was maximised and utilised in the best possible way to ensure a practical and safe layout.

The EfW receives a constant flow of Oxfordshire household waste alongside a small amount of commercial waste and burns, approximately 300,000 tonnes of waste annually which provides a residue of around 23% - 25% IBA. The new processing plant is rated for 100,000 tonnes per annum.

This is the second IBA processing facility that is operated by RBA, with the first located in Hampshire. Technical advances and experience have allowed the recovery of <5mm non ferrous metals to be included in the new plant design.

Lee Thompson – Operations Director RBA, commented, “We are delighted with the plant, it’s our own design, which is based on our experience, and significant research and development. We went to DUO and asked if they could meet our processing design requirements. Their positive response and successful IBA plant upgrade carried out for RBA in 2011 gave us the confidence that they had the expertise to deliver. There were several significant hurdles to overcome; the project teams for both RBA and DUO deserve huge credit for achieving very tough deadlines."

The process operation.
The IBA is discharged from the EfW into a holding bay. This is then picked up by loading shovel and taken outside and put into individual storage areas. At this point the material is still warm, with a pH value of around 13 (alkaline). The material then remains in storage and goes through a 6-12 week ageing process. During this process the IBA stabilises and the pH reduces prior to processing.

This ‘aged’ material is then is then taken to the plant by loading shovel and fed into the main feed hopper. The material is then delivered to the main trommel screen by conveyor belt. The trommel has round apertures of 65mm, splitting the feed into +65mm and -65mm. The +65mm material is discharged at the end of the trommel and collected by a conveyor belt and sent for hand sorting. The sorting involves recovering all metals for recycling, the residue is generally masonry, and ceramics which are sent for crushing and reintroduced to the IBAA. (incinerator Bottom Ash Aggregate).

The -65mm material drops through the trommel and is then delivered by conveyor belt to the Binder ‘flip flow’ screen, passing under a high powered magnet along the way to recover the first cut of ferrous metal. Here the Binder machine is the true nucleus of the operation, separating the material into three fractions, a -5mm fraction, a 5mm-16mm fraction, and a 16mm-65mm fraction. The three way separation ensures a more single size fraction that allows optimum presentation over the eddy current separators.
All three fractions are delivered to the respective eddy current separators by conveyor belt, each conveyor has a built in magnetic head drum to remove the smaller ferrous metals. The remaining inert and non ferrous materials are passed over the eddy current separators, where any non ferrous metals are recovered.

Lee Thompson added, “After significant research in Italy, we decided to change our eddy current separators from eccentric to concentric. With the eccentric concept, you can achieve greater drum and head speeds. The general rule of thumb is with any ECS the faster you go the better the throw, resulting in more efficient separation.

All the recovered ferrous and non ferrous metals are stockpiled and sold on for recycling to both UK and European markets.

The resulting inert IBA fractions (free of metals) are then blended back together to make IBAA. The IBAA is used as a sub base equivalent, offering significant product performance and commercial advantage over its primary aggregate counterpart, as well as being a sustainable resource.

This secondary aggregate consists of fused clinker, ceramics, glass, stone and concrete and has been widely used in construction for nearly 20 years, with over seven million tonnes used to date in the UK.

Here at the Viridor - Ardley site RBA are processing a waste material with considerable success!