All Systems Go At Shardlow

New integrated process control system helps Shardlow sand and gravel quarry realize its full potential. Robert Barksfield, contracts manager for Batching & Blending Systems, explains how the new system is helping to achieve operational benefits

In 1993 Hanson’s sand and gravel quarry at Shardlow, near Derby, was praised for its innovative design, which included new measures to remove lignite

The quarry produces sand in two grades and naturally rounded aggregate in various sizes, mainly for use in the construction trade but with large quantities of the material being supplied to Hanson Premix plants in the area.

While the plant itself has proven to be more than capable of the task of producing around 1 million tonnes a year, the existing process control system was becoming less able to meet day-to-day requirements. Also, it did not provide for the level of reporting and data that Hanson required to help achieve optimum plant performance and to monitor output grades.

Regarded as ‘state of the art’ at the time of its installation, the control system had in more recent years begun to display many problems associated with legacy equipment. The original GEM80 PLC system was of a design that was around 27 years old and limited back-up or support was available. Parts were either difficult to obtain or unavailable, with the prospect of lengthy downtime in the event of system failure.

The system itself was centralized but lacked any database or data-output facilities and was not truly integrated with either the Checkmark lorry load-out control or the hydrolig controls run from separate panels.

The requirement was to find a new process control system capable of integrating all functions and providing operational and management data for forecasting and analysing trends.

Shardlow’s processing operation is relatively straightforward; trucks supply a reception hopper that feeds a surge pile via a conveyor. The surge pile recovery conveyor discharges into a splitter hopper that feeds dual conveying lines supplying the initial processing operations.

Each line is processed through an initial screening stage, which rejects any +150mm material, selects the –150mm +40mm fraction for crushing and passes the –40mm for lignite removal.

The –40mm material goes to the de-ligniting station where lignite and any other low-density materials are floated off using twin vertical tanks. The material is then washed and graded for either secondary crushing or transfer to final screening and storage.

Crushed material and re-crushed product is kept on a separate line to the other materials in order that a range of natural gravels can be produced.

The sand plant takes fluidized –5mm material and wash water to grade into either concrete sand or building sand. Gravel is output to final screening and then to storage hoppers, which discharge directly into trucks via the Checkmark system, as required.

The challenge for Batching & Blending Systems was not only to design an appropriate system to encompass the wide range of processes, but also to meet deadlines with a project timeline that was measured in weeks rather than months.

The new system was designed in the four weeks prior to the Easter shutdown and installed and commissioned during the week-long shutdown period. At the time of installation, additional weighers were installed on several conveying lines to improve the level of information capture.

The new process control system is based on an Allen-Bradley SLC500 PLC with remote input/output modules being used in the Checkmark and hydrolig panels to link these back to form one overall plant control system. The Allen Bradley SLC500 was selected because of its exemplary back-up. With 1.6 million of these PLCs in use worldwide there is likely be a readily available spares supply network for many years to come.

The resulting system is now fully operational and already proving its value in use through improved information capture and feedback. Having a more integrated approach has also reduced control duplication and achieved a number time savings in control terms.

As before, the plant is controlled by a single operator from within the main control office, which also houses CCTV monitors. With just two initial screens, the new system is more intuitive in use as well as being able to show key information at a glance.

Brian Partner, the system operator, explained: ‘I took to the new system very quickly as it’s really easy to see what’s happening and then go into logical sequences to sort out any issues. I tend to view the CCTV monitors less as the new system has a much better level of information. It is also reassuring to be able to run daily reports that detail all activity.’

Looking to the future at Shardlow, additional database and reporting functions will be used in more depth to look at overall site efficiency and to assist in further extraction plans.