Quarrying
A new approach
Tarmac’s 480tph lignite removal plant at its Snabe Quarry in Scotland is showing how a new approach can bring significant advantages
As a result of the small island that we live on everyone working in the quarrying sector in the UK is aware of the growing requirement to tackle materials that would not have previously been considered for processing. As we approach the time when the majority of clean and easily processed material has been exhausted the attention turns to how we can effectively process these ‘difficult’ materials to allow for the production of high quality sand and aggregates.
The contamination of sand and gravel deposits with lignite and the development of processing systems to deal with this contamination is evidence that there is increasing pressure to process materials that were previously overlooked. Lignite in itself can be a very useful commodity being a soft brown fuel, the characteristics of which put it somewhere between coal and peat. In Greece over 50 per cent of electricity comes from lignite fuelled power plants. In Germany deposits of lignite are concentrated around the Cologne area and stocks are believed to be over 50 billion tonnes. These are currently being exploited and generate some 25 per cent of the electricity produced by Germany.
Tried & tested system
However, when lignite is present in deposits of sand and gravel it presents a significant problem for companies such as Tarmac as it will compromise the final quality of the sand and aggregate products. In seeking to process this material effectively the specification of a system that is tried and tested in the effective removal of this lignite material is key.
One such company that has considerable experience in the design of such processing systems is CDE Ireland. The area surrounding Lough Neagh in Northern Ireland is another where there are significant lignite deposits and the proximity of these deposits to the company’s headquarters in Cookstown, County Tyrone has meant that CDE has developed significant experience with local quarry operators in the effective removal of lignite from sand and gravel deposits to ensure the production of clean, high quality building materials. “We are very familiar with the problems posed by lignite and have been asked the question about effective removal by several local operators over many years,” explains Dermot Murphy, CDE’s technical manager for all lignite removal plants. “This experience has helped us to develop a lignite removal system that we believe to be the most effective available for operators faced with this issue.”
A long history
The site of Tarmac’s 480tph lignite removal plant is its Snabe Quarry in South Ayrshire, Scotland. As a company Tarmac has a long history of supplying a wide range of building materials to the UK market. Its product portfolio is extensive and includes crushed rock, sand and gravel, armour stone, horticultural sand,
38 Solids & Bulk Handling • March 2010
slag products agricultural lime and rail ballast. The responsibility for the plant at the Snabe Quarry lies with Tarmac’s area manager, David Chalmers.
Performance guarantees
When dealing with a plant to process lignite contaminated feed material it is usually the case that quarry operators will be seeking guarantees regarding the extent to which the lignite can be removed. This is a result of the detrimental effect that any significant volume of lignite in the final products will have on their commercial viability. This requirement also significantly limits the options available to companies such as Tarmac as there are a limited number of suppliers of equipment that will agree to performance guarantees for the plant. The CDE plant at Snabe Quarry has been custom built to specifically tackle the individual characteristics of the feed material at the site. The plant’s performance is measured by a set of pre-defined production requirements including final levels of lignite in the sand and aggregate products.
The plant currently in operation at Snabe Quarry has a capacity of 480tph and is producing two commercial sand products – a concrete sand and a building sand – as well as a 5-10mm and 10-20mm aggregate product. The plant includes a wide range of equipment from the CDE portfolio including its Prograde screens, numerous feed, stockpile and transfer conveyors in various configurations and its CFCU system for the washing of the lignite contaminated sand product.
The processing system
The location of the plant in relation to the material to be processed was the first issue at the Snabe Quarry. This required the development of a unique feed system where raw feed is first delivered to a 34m inclined transfer conveyor. From here material is discharged to a stockpile area where two vibrating
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