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Waste plant overhauls sorting facility

26 April 2009

Cawleys in Luton, UK is a waste recycling company. Its business is to collect commercial waste and sort it to high grade material for recycling. The recycled material income offsets the cost of the landfill, which is required for the small amount that is left over after sorting.

The company has just accepted a new sorting facility designed and installed by OKLM Recycling Technology, with DB Controls of Doncaster being subcontracted for automation, motor control and SCADA – for which they used COPA-DATA’s zenon.

The recycling company built its first Waste Reclamation Factory was constructed in Luton in the 1970s. Since then the site has been developed and now houses a 40,000ft² materials recycling facility which enables them to reclaim and recycle as much material as possible.
The new OKLM reclamation facility takes material delivered in skips through a process of automatic and manual separation to sort out the main recovered recycling material types of card, polythene, paper, film, plastic, metal, timber and hardcore. The plant has many conveyors that transport the waste from stage to stage – at each step valuable recyclable material is removed until the final stage has residual material that can only go to landfill.
The separation uses various technologies, such as infra-red, magnetic, and sorting by blowers in a large rotating drum. Sorting operations are undertaken in two shifts.

The plant has to run at all times, with care being taken of safe working for operators and also to protect the machinery. This second aspect is of significance as the inverter-driven motors have to be able to cope with a wide range of loads as different material is moved by the conveyors. They have sufficient power to do much damage to the plant if left unsupervised, especially when an abnormal item finds its way onto the conveyor system, or build up of material causes a blockage.

Supervising operations…
The whole motorised conveyor system is powered by a MCC (Motor Control Centre) – designed and developed by DB Controls. The plant control room is fitted with the zenon SCADA system that communicates with various points within the MCC and also across the plant. The primary function of the SCADA is to provide safe and reliable plant operation.

As with many SCADA systems colour is used to draw the attention of the operator to any problems, and also to provide an indication of how long a problem has occurred. An example of this is monitoring of the load of each drive; where this is measured as being above 80 per cent for several minutes the colour of that area changes to red and the operator has to take action. Experience and common sense shows that such a load condition is likely to be a jammed or partially jammed conveyor, probably caused by an abnormal item on the conveyor or a build up of waste material.

To quickly check the source of the problem CCTV cameras are installed in many locations around the plant. The displays of material input and dispatch are shown on dedicated CCTV monitors in the control room. The internal CCTV cameras that monitor the plant are called up as and when needed by the operator using the SCADA display. A video window opens in the SCADA screen and a high resolution colour display allows the operator to quickly see the problem and then call a mobile operator over voice R/T, to clear the problem – keeping the plant running and protecting plant machinery.

In a similar way all key components in the plant are constantly monitored and kept running. Situations that do not require immediate attention are notified by a colour change to orange – drawing the operator’s attention to that part of the plant. When the screen shows all green, then all is well. All alarms are stored in an alarm list within zenon in chronological order.

The MCC has high technology inverter drives that allow the conveyors to run at the correct speed even though the loading may be continuously changing. Although the drive parameters were set at commissioning these can be displayed and changed directly in a zenon SCADA pop-up window – the window resembling the “hard” interface of the inverter itself. This avoids time-consuming trips to the plant floor where the MCC is positioned – the ease of use also encourages the supervisor to tune the plant to a new state should there be a significant change in the material being handled. In a similar way the status of all of the main devices within the MCC can be displayed on the central SCADA screen.

SCADA – MCC – CCTV integration…
System Integration was undertaken by DB Controls Ltd on behalf of OKLM, the main contractor. The zenon SCADA communicates with a Schneider Electric M340 controller that is at the heart of a Prisma Plus MCC (Motor Control Centre), using the standard zenon driver; the protocol being Modbus TCP/IP. The devices within the MCC each have an active web page that is accessed through zenon to open up windows on the SCADA display that show device parameters and status – using a standard zenon HTML picture.

The facility requires visual checking when an alarm is raised, this is provided by CCTV that is directly interfaced to zenon and appears as full colour video using the zenon video picture template – allowing very fast visual diagnosis of an abnormal situation.

DB Controls technical director, Graham Allmendinger, concluded: “We fully utilised the complex objects and objects structure within zenon, this allowed us to develop and test each major control element and then re-deploy instances of them as many times as was required in the project. This has significantly assisted us to produce a close to perfect solution prior to installation and commissioning. The system is fully accessible remotely at DB Control’s engineering office; this has also eased the tuning and resolution of residual teething problems.”


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