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.
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.
The site of Tarmac’s 480tph lignite removal plant is 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, slag products agricultural lime and rail ballast. The responsibility for the plant at the Snabe Quarry lies with Tarmac’s area manager, David Chalmers.
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.