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SA Instrumentation & Control Buyers' Guide

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Breaking rocks intelligently: instrumentation and control trends in quarrying
July 2008, Maintenance, Test & Measurement, Calibration

If, like me, you thought that instrumentation and control in quarrying was low tech with just a bit of conveyor interlocking then you are in for a surprise. This industry has evolved to the point where systems are highly integrated and technologies like wireless, GPS, laser and radar technology are becoming par for the course.

At its simplest, quarrying is the breaking of big rocks into smaller rocks, but that belies the challenges involved.

Control and monitoring aid efficiency

Huge quantities of aggregates are moved in quarrying operations – often by conveyor. Without rapid response to abnormal process conditions, when things go wrong conveyor and drive systems can become buried under tonnes of material. In the past valuable production time was lost in digging out plant after such occurrences.

Modern systems which monitor drive motor current and conveyor mass flow are able to respond quickly enough to prevent this and the result is higher output and more efficient production requiring less operations personnel.

In earlier plants, crash stops required clearing of the crusher prior to restarting and size adjustment was a labour intensive affair requiring up to two days of lost production while screen decks, meshes and crusher liners were changed. Metso’s Nordberg crushers make provision for the operator to empty the crusher cone prior to restarting if it has been stopped when fully loaded. This feature can significantly improve system uptime and overall operating efficiency. The hydraulic systems can be controlled from a control room to adjust the crusher while it is in operation. Sandvik’s Hydrocone units offer controlled adjustment of the crushing to yield a particular aggregate size. The company’s ASRi (automated setting regulation) is an intelligent system that continuously and automatically adjusts the crusher setting in accordance with the composition of the raw material to maintain the required aggregate size.

Just as PLC sequence control and monitoring have improved efficiencies under abnormal plant conditions, so scada-based recipe control has improved blending operations – many quarry products are blends of differing aggregates where recipe handling systems have improved cost control, product consistency and logistics. Intelligent scheduling and routing enhance asset utilisation since conveyor systems can be used for multiple aggregates with automation ensuring that the correct aggregate charges are consistently routed to the required stockpiles or discharge points.

The introduction of modern automation systems often facilitates the introduction of continuous working, enabling production to continue during tea breaks, lunch breaks and shift changes. In turn this means lower production costs per tonne and improved asset utilisation.

Scada systems provide operations and management a clear overview of plant, production rates and key performance indicators (KPIs) as well as drawing prompt attention to stoppages and alarm conditions.

The combination of such intelligent automation with variable speed drives help to ensure that belts are fully and uniformly loaded to save energy and prevent unnecessary wear.

The challenge of mobility

As one area of a site is quarried out it often makes economic sense to move the crushing and screening plant closer to new operational areas of a quarry.

One way in which plant mobility can be facilitated is by using intelligent field-located motor starters like Rockwell’s ArmorStart Distributed Motor Controllers, which are networked using a fieldbus such as DeviceNet. Each starter is self-contained in its own enclosure and the network makes it possible to remotely stop and start drives, monitor motor speed, current draw, run hours, trip and diagnostic status without requiring huge quantities of control cabling. It has been estimated that this distributed approach to motor control combined with networked monitoring and control can offer savings of up to 20% over centralised MCCs.

A case study on the application of wireless instrument transmitters in a copper mining application where leach pads for heap leaching require moving every seven months has shown the successful implementation of wireless transmission of instrument signals in an environment that is similar to quarrying. Mantos Blancos is an open pit copper mining complex and chose to trial Honeywell’s line of XYR 5000 transmitters. Honeywell’s wireless solution made possible significant operational gains and the 'no wires' approach resulted in considerably lower installation costs than conventional wired instrumentation.

Condition monitoring

Employing preventative condition monitoring can reduce unplanned downtime in quarrying plant and equipment. Condition monitoring uses a range of techniques, including acoustic, vibration and tribology, to identify impending equipment failures. This allows problems to be corrected during planned maintenance work rather than at breakdown.

Companies like Corus Northern Engineering Services provide condition monitoring as an outsourced service. On a recent routine inspection visit one of their service engineers detected abnormal acoustic signals on the primary crusher at a client’s lime quarry. Further investigation revealed that the main bearings were failing and these were replaced during a scheduled shutdown. When the equipment was stripped the inner raceway of the bearing was found to be damaged and showed signs of significant wear.

SKF’s Copperhead system provides continuous fault detection for crushers, conveyors, mills and vibrating screens using combined vibration and temperature sensors and special transmitters which embody multiple vibration analysis algorithms. For vibrating screens such systems can detect a multitude of mechanical and operational faults including gear faults, bearing faults, lubrication faults, overloading and bottoming out. For crushers the system is also able to detect rotor imbalance.

Laser, radar and nuclear measurement

Laser technology can be applied in quarrying for both surveying (for instance Measurement Devices (MDL) Quarryman Pro) and for aggregate level detection in silos (for instance K-TEK’s LM80 laser transmitter).

The Quarryman Pro is a reflectorless rock profile and 3D laser scanning system used by major surface mine and quarry operators around the world. The system facilitates high-speed 3D rock profiling for determining rock-face geometry and blast-hole burdens. The company claims that a large Irish aggregate quarry which started using Quarryman systems reported benefits which included 150% extra production hours, a 20% increase in crusher throughput and a 20% saving in explosives.

Many manufacturers of ultrasonic and laser level systems have developed radar level measurement options which have proved reliable in the dusty environment of cement and aggregate storage. The Siemens Sitrans LR460 is a 4-wire 24 GHz radar level transmitter with high signal-to-noise ratio and advanced signal processing for continuous monitoring of solids up to 100 m, and is ideal for level measurement in extremely dusty environments.

One of the challenges faced in quarrying is the accurate measurement of mass flow of aggregates over conveyors. Vega Ohmart nucleonic system can be easily mounted around a conveyor, screw or chain feeder, or even a gravity chute with no intermediate machinery or additional space needed. Since there are no moving parts this solution is well-suited to the quarrying environment with its ever-present abrasive particles.

GPS and LEO for heavy equipment

GPS (global positioning satellite) technology has proved to be a boon for users of heavy equipment. Many Caterpillar machines are now offered with GPS interfaces which can be used in quarrying. Heavy equipment fitted with Caterpillar’s computer aided earthmoving system (CAES) performs earthmoving work in accordance with CAD design files which represent the mapped work area. As the machine moves an on-board display shows the operator in realtime and to centimetre accuracy what cuts he needs to make, without requiring the prior setting up of survey stakes. The system includes geo-fencing to indicate no-go areas and incorporates on-board mapping so that terrain profile and radio signal coverage is accurately mapped as the equipment works.

Caterpillar’s Product Link provides two-way information flow between machine on-board systems and users’ desktop computers for data such as machine location, machine health information, service meter hour readings, fuel level and consumption. The on-board GPS, ECM and other vehicle-mounted systems link to a data module which uses VHF radio to communicate via ORBCOMM’s network of low-earth orbiting (LEO) satellites, offering a potential worldwide solution to these data communications.

Always knowing the location of a particular item of equipment has secondary benefits – on large sites it means that field service teams can easily find the equipment and can efficiently plan service routes between multiple heavy equipment assets.

Watch this space

In January 2008 Rio Tinto announced a ground-breaking programme to develop a world-leading system to automate its Pilbara iron ore operations in Western Australia. The company has formed an alliance with Komatsu to develop and deploy advanced autonomous haulage solutions and is building a Remote Operations Centre (ROC) in Perth, 1300 km from Pilbara. CEO Tom Albanese says that remote control 'intelligent' trains, drills and trucks will be operational within Rio Tinto Iron Ore during 2008.

About the author

Andrew Ashton has electrical, mechanical and business qualifications and has been active in automation and process control since the early 1980s. Since 1991 he has headed up a company that has developed formulation management systems for the food, pharmaceutical and chemical manufacturing industries and manufacturing solutions involving the integration of various communication technologies and databases. Developed systems address issues around traceability, systems integration, manufacturing efficiency and effectiveness. Andrew is features editor for SA Instrumentation and Control and editor of Motion Control in Southern Africa.

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