Implementation and Tuning
When the coding was completed, Minnovex engineers brought the expert system back to the Kemess mine, installed it on a PC, and began the coarse tuning process. At first, they ran the expert system connected to the DCS in an advisory mode while operators and supervisors viewed and commented on its responses to the changing mill conditions.
The initial version required relatively few changes. In only three days everyone was happy with its performance and the first line was put under its control while operators continued to closely monitor its decisions.
After two more days, the second line was put under control of the MET expert system and, after another day of monitoring, the MET expert was allowed to control both lines.
A key to the fast implementation was the way that Minnovex obtained input from the operators and explained how the system was simply implementing decisions that they would have made on their own. The operators bought into the expert system so they rarely interrupt its operation.
Semi autogenous grinding (SAG) mills grind rock from 6 inches down to ½ in.
With the mill running under the control of the expert system, we noticed significant increases in throughput almost immediately. The main difference is that the expert system implements the control strategy on a much more consistent basis. It monitors instrument readings continually and adjusts operating parameters every couple of minutes, avoiding drift and keeping the mill running at a heavy load. The expert system can also monitor many more points simultaneously and reacts to changes much faster than an operator, which helps to avoid upsets that sometimes caused downtime in the past. For example, if the load on the SAG mill increases too much, the expert system will quickly decrease the density and feed to bring conditions back into line.Extra Revenues Realized
When Northgate first put the lines under the control of the expert system, operators kept a watch on the system and made notes on areas that might be improved. Minnovex’s engineers came back a few weeks later and spent several days in a fine-tuning process that provided even further throughput gains. Northgate has since taken over administration of the system and it has remained stable and easy to maintain. Another benefit of this whole effort has been that Northgate’s operators are now more knowledgeable about controlling mill processes and better prepared to help drive future improvements.
Before Northgate installed the expert system, the company’s two mill lines were producing an average of 49,500 tons/day. The mills are now running at 51,500 to 52,000 tons/day, a nearly 5% improvement, which generates an extra $7 million in revenues per year. Based on its success Northgate is planning to use a similar systems to control flotation cells, which accept the output of the ball mills and separate the minerals from the crushed rock. Finally the company is in the process of installing new flotation cells using vision technology to monitor the size of the bubbles and speed of the froth. With the expert system controlling the process based on this and other process data, Northgate expects to achieve gains similar in magnitude to those that achieved on the mill lines.
Greg Rasmussen is Mill Superintendent at Kemess Mines in Vancouver, British Columbia, Canada (copper/gold). His mining experience streches across numerous minerals and several mines throughout British Columbia.