Owned by Gloucester Coal and operated by contractor Henry Walker Eltin under a TRM contract, the Stratford open pit operation is 95 km north of Newcastle and 100 km east of the Hunter Valley coalfields.
Developed in 1995, Stratford produces coking coal for the export market and thermal coal for domestic electricity production and export.
The new collector is being offered as a viable alternative to the widespread use of diesel as a collector agent in fine coal circuits.
The new collector’s introduction at Stratford came about as the mine’s CPP management team researched ways to increase the yield to coking coal.
The fines flotation circuit at Stratford, which includes two Jameson Cells, was installed as part of a coal preparation plant upgrade in 1997.
The project increased overall plant capacity from 550 tonnes/hour to 610 tonnes/hour with throughputs of up to 620 tonnes/hour available for favourable product.
With flotation accounting for almost 20% of all coking product, the new fines circuit gave Stratford a boost in production and encouraged further investigations as to how more output could be achieved.
“The Jameson Cells had given us an indication of the production output levels that were possible,” said Tony James, CPP superintendent at Stratford.
“The investment in the technology was in place and it was now up to us to make it work.”
James said Nalco were briefed late in 2001 and early the following year put a trial collector programme in place at the mine.
Twelve months later, the product has been accepted as an integral part of the Stratford fines circuit.
“Although the trial was spread over 12 months, at no time did we see it as a waste of resources,” said Tony James. “It might have been a long gestation period, but the results have more than justified the effort put into the trial by all parties.”
Throughout the trial period, collector additive amounts were varied in an effort to find the optimum production levels.
Ultimately, the mine made the decision to discard all product less than 38 microns and concentrate its efforts on the larger particle sizes.
“The amount of collector added could be varied to suit the type of feed and the output required,” said Tony James. “That level of accuracy and control is a real bonus for our overall production.”
Stratford also found the new collector could float the +125 micron coal that previous collector mediums used at the mine had been unable to achieve.
At Stratford, +125 micron coal has low ash content and can actually lower the overall product ash, allowing for increased tonnage from the dense medium circuit.
Since switching to the new collector, the average cake thickness off the end of the belt filter at the Stratford mine CHPP is 25-35 mm – a 100% increase over the previous 12-15 mm average.
Some of the benefits of the trial came from left field. The mine had been experiencing problems with the feed into the Jameson Cells, which was affecting the cells’ operation and performance.
A metallurgist with Nalco identified that the feed was splitting and one of the cells was receiving a disproportionate amount of feed, which was giving problems at the cell and downstream on the belt filter.
Various mechanical remedies as well as adjustments to the cell’s aeration rate and additives had been tried with limited success.
Tony James said that Nalco were able to solve the problem and optimise the operations of the two Jameson Cells. He added that the operators were given additional training by Nalco, which qualified them to maintain the optimum levels.
“The whole collector programme has been a huge win for us,” said Tony James. “We are seeing better fundamental operation of the flotation and associated equipment and the prep plant overall. And, with the removal of the diesel, working conditions inside the plant have improved markedly all of which are combining to give us a measurably better result where it counts in the production output tonnages.”