New conveying systems for big UK cement site

A Robson Handling Technology product story

Edited by the Engineeringtalk editorial team Nov 16, 2001

Bulk handling specialist Geo Robson and Co has helped Rugby Cement to fine-tune the clay conveying system at its new plant in Rugby, UK, based on the country's largest semi-wet process kiln

Bulk handling specialist Geo Robson and Co has helped Rugby Cement to fine-tune the clay conveying system at its new plant in Rugby, UK.

Based on a semi-wet process kiln - the country's largest, and the first to be built since the 1980s - the single production line has replaced six wet kilns and came on stream in mid-1999.

The plant is on course to achieve its planned 3,800tpd output this summer, but optimising such a large-scale process revealed a number of teething troubles.

Although Robson was not involved with the original installation, the company was called in to make modifications to crushing and weighing facilities in the clay preparation section.

As first built the handling line used the principle of 'weigh, then crush' with a weigh feeder at the point where clay was picked up from the storage hoppers, and two crushers downstream to reduce the lump clay to <50mm and then to the <30mm granule size required for milling.Three problems came to light when the system went into service.

Uneven distribution of uncrushed material on the belt of the metering conveyor caused inaccuracies in batch weights.

Larger fragments spilled over from the open troughed belt conveyors before they reached crusher one.

Material was already at the target <30mm when it reached crusher two.

Although this effectively made it redundant, the crusher had to continue to run (incurring unnecessary energy costs) because it provided the link with the conveyor feeding the raw mill.

Rugby Cement's engineers decided that the solution was to reverse the sequence of operations, so that clay is crushed before it is weighed.

This was done by relocating the crushing operation at the start of the handling sequence beneath the storage hoppers, in the position previously occupied by the weigh conveyor.

Crusher two was also removed and replaced with new weighing facilities immediately before the clay passes onto the raw mill feed conveyor.

Robson successfully tendered for the modifications, and implemented them during a three-week break in production for work on the plant's crusher/dryer.

Although existing equipment was utilised where possible, the company designed and built a drag scraper conveyor, a surge hopper, and chutes to maintain the continuity of the system.

It also supplied a new proprietary crusher and weigh feeder.

The drag scraper conveyor has been built to a swan-necked design so that it could be accommodated in the existing pit below the storage hoppers, where it extracts clay at a maximum rate of 110 tph.

The material then passes via an existing recovery conveyor into the new Bedeschi double roll crusher.

Material transition at the point previously occupied by crusher one is provided by a new chute system, and the former crusher two position is now occupied by the weigh station.

This consists of a 5m3 capacity surge hopper supplying a Clyde Richard Simon constant rate weigh feeder with a +/-1% accuracy.

To complete the handling route, a discharge chute delivers the weighed material onto the raw mill feed conveyor.

Robson has guarded against the tendency of the clay to stick by installing blockage detectors in all the chutes, and lining the sloping surfaces of the chutes and the surge hopper with flow-promoting polyethylene.

In addition to its work in the clay preparation area, Robson manufactured and installed two 800mm wide troughed belt conveyors - part of a new system to supply imported clinker to the plant's three cement mills.

Other cement industry contracts in the last two years have included work in the UK for Blue Circle and Castle Cement, and a project for Blue Circle's Egyptian subsidiary, the Alexandria Portland Cement Company.