VOD (Ventilation on Demand) has been used at Xstrata’s Nickel Rim mine with great success. “The Nickel Rim mine project has enabled unique applications of technology with the goal of improving productivity and reliability. A key example of this can be found in the newly constructed surface exhaust fan installation where innovative approaches to ventilation technology include the use of variable frequency drives, multi-fan programmable logic control (PLC) and fan starting considerations¹.”

XPS Process Control (together with the mine’s Engineering and Operations team) has worked diligently in the design and commissioning of the Allen Bradley (Rockwell) control system and the surface fan controls optimisation, in a layered control application approach, specifically:

• Basic control loop standard
• Design and simulation
• Loop tuning of the whole control strategy (surface fans)
• Loop tuning of all AMS (air monitoring stations) underground
• Testing of surface fans interaction with AMS (air monitoring stations) under several different scenarios.

During July and August 2010, the whole control strategy was run in automatic and cascade control mode for several hours at a time on four occasions. The control strategy here is a basic to advanced, interconnected, regulatory strategy that has been programmed in the PLCs to co-ordinate surface fans exhaust and supply fans. Use of the Simsmart OMVOD system, during one of the tests, was for controlling a flow that could not be measured.

For the days tested, the exhaust fan rpm was observed to run up to 200 rpm slower, proving a realistic energy saving opportunity, or liberated capacity which can be used to drive further production, or increased productivity. The strategy was able to automatically recognise opportunities and adjust fan speed accordingly.

All the PID controllers have now been tuned and, following training and robustness testing, will shortly be ready to be used in their normal operating mode (auto and cascade) – a significant step to achieving ventilation on demand.

1. Wiltow and McCall, Engineering innovation at Xstrata’s Nickel Rim South surface exhaust fans, 13th Mine Ventilation Symposium, pages 545-552, Sudbury, June 13-16, 2010.