Welkom Industrial Controls (WIC) was approached by Powertech IST after an investigation had established that there was potential saving to be made by automatically controlling the three Demag air compressors at Harmony’s Unisel mine. The mine requires a minimum of two compressors running at almost 100% during peak mining hours, but during the hours from 6 to 8pm this could be reduced to save energy during a peak billing period. For maximum effect, this would require one of the compressors to be switched off and the other to cut back during these times.
Automated operation and new instrumentation required
Due to a machine needing to be stopped and started outside of standard working hours, it was required that this be done automatically. For this to be done unmanned and safely, a complete instrumentation and PLC upgrade was proposed. The 4 MW machines would also require an upgrade of the medium voltage switchgear. This was done by Actom Medium Voltage division with WIC contributing to aspects of the design to ensure the safe unmanned operation of the equipment.
The Schneider Quantum PLC was selected as it had proven itself in similar upgrades in the past, of which WIC had implemented an impressive seventeen times. New Fisher pneumatic high speed blow off valves were installed on each of the compressors because of their ability to open fully in less than 2 seconds, which was considered crucial to the safety of the machines.
Along with this, new vibration, pressure, temperature and proximity sensors were installed on all machines to monitor every crucial operating aspect. WIC’s chief engineer was tasked with building the anti-surge control functionality into the PLC, which the high speed Quantum CPU handled with ease. Also, a complete new instrument-air backbone had to be installed to accommodate much of the new pneumatic instrumentation. A master PLC controller was installed to accommodate the master set-point, auxiliary air compressor and the cooling water pump control.
For successful compressor cut back, it was necessary for underground air usage to be reduced. To achieve this, Auma electric actuated valves were installed at all production levels with only a small bypass left open to ensure that mining safety regulations were not compromised. Every level was equipped with a Yokogawa multivariable flowmeter in order to determine the air usage or wastage on each level. A master flowmeter was also installed on the main air column to ensue flow stays balanced to within the 2% allowed fault.
Scada system functionality extended for system control
A Wonderware InTouch with a Historian Server was implemented for the system control. WIC then developed an embedded active X object within the scada system to schedule the operation of the compressors. This allows the user to predetermine which machine would cut back or switch off at any time of day, scheduled for more than a year in advance. All historical data is available at the click of a button. With all the critical parameters logged, operators are able to diagnose and analyse all types of system conditions and faults. From the first month of measurement and verification, the project has achieved more than 100% of the target savings that the customer originally required.
For more information contact Llewellyn Coveney-Winter, Welkom Industrial Controls, +27 (0)57 357 5724, [email protected], www.wic.co.za
© Technews Publishing (Pty) Ltd | All Rights Reserved
printer friendly version