Geo Robson & Co is contributing its expertise in handling alternative fuels for cement manufacture to a new facility at the Tunstead Works of Buxton Lime Industries in the UK.

The Sheffield-based company has been given responsibility by BLI's owner the Tarmac Group for the handling aspects of a system that will add up to 20 per cent of tyre chips to the Tunstead cement kiln's calciner, which until now has been entirely coal-fired.

Robson's £1.6m turnkey contract includes the design, manufacture, installation and commissioning of the tyre chip handling stage of the process, along with all associated civil structures: a hard-standing apron for vehicles; a 20m x 20m area with an anti-tipping frame onto which the tyre chips are delivered; and an adjacent storage building with sufficient capacity for a 500 -tonne back-up supply.

Delivered chips - which have a nominal size of 50mm x 50mm - are taken by a bucket loader into storage or transferred directly to the calciner feeding system, depending on production requirements at the time.

Instead of a conventional steep-sided silo, the feed route to the calciner begins with an 88cu m capacity push-floor unit purpose-designed by Robson. The unit has two hydraulically operated frames in its base that oscillate constantly, dispensing chips into the delivery conveyor and overcoming their natural tendency to stick together and bridge across the storage bin.

Chips are raised to the top of the calciner 50 metres above ground level by a 160m-long troughed belt conveyor inclined at an angle of 17 degrees. At the head end they pass through a screw conveyor and belt weigher, which feeds a constant flow of chips at a pre-set rate into the calciner.

The weighing system has extensive fire suppression facilities, with a double flap valve to prevent hot gases escaping from the calciner and a fire detection system above the screw conveyor that triggers a water spray in the event of an emergency.

Delivery rate of the system is up to 15tph of tyre chips to the weigher and 2-5tph into the calciner. The design also allows as far as is practicable for other waste material fuels that may be used in the future.

Robson started work on site in March 2006 and the system will be operational by August.

It is in most respects, similar to the tyre chip handling facilities that the company has already supplied to the Lafarge Cement plant in Hope, Derbyshire and Cemex Cement in Rugby, except that Tunstead favours weighing at the head rather than the tail end of the belt conveyor so that chips can de delivered into the calciner with enhanced response times.

Robson also supplied handling systems to the Ketton Works of Castle Cement and Lafarge Cement's Westbury works, both of which burn whole tyres, and is currently installing facilities for introducing a bio-mass material as an alternative fuel at one of the UK's biggest power stations.

Burning tyre chips in cement kilns is one very productive way of disposing of the 400,000 tonnes of worn-out tyres that the UK discards every year. It is also an efficient way to generate energy, providing a heating value of 6,000 kcal/kg, which is 20% greater than coal.