At the Glenlee site near Narellan on the southwestern outskirts of the Sydney Basin, Sada Coal Preparation Services is processing feed from the site’s tailings dams.
The fine coal product from this reprocessing is blended with coarse coking coal and ultimately exported to steel mill customers in Japan, South America and India.
Originally established in the late 1950s, the Glenlee coal preparation plant was, at one stage, considered the big facility of its kind in the southern hemisphere.
The original coal preparation plant closed in the early 1980s, and the site saw little action until 2002 when Sada commenced operations on a two-stage program.
Stage one involved processing tailings from a nearby coal mine, while stage two involved reprocessing tailings from old dams at Glenlee.
According to Sada’s manager, Peter Dunbier, the operation quickly reached a profitable status and consistently achieved the targeted sub-12% ash content in its output.
However, the move to stage two predicated problems in the float circuit at Glenlee.
“The introduction of material from the Glenlee tailings dams into the processing circuit exposed a problem with the existing flotation reagent. Sada could no longer achieve the required sub-12% ash content due to the inclusion of a high ash ultra fine particle size in the product.”
“Processing the old Glenlee tailings not only got off to a rocky start but became a testing time for all concerned,” said Peter Dunbier.
“What should have been a relatively smooth transition, we did expect some compatibility problems in the early stages became a period of protracted frustration as we experimented with collector and frother combinations, as well as other cell settings and plant modifications, to achieve target ash and yield.”
Because reagent supplier was not able to provide alternative products that would improve flotation efficiency over and above those currently in use, Nalco was invited to trial its flotation program at Glenlee in late 2005.
“The service and support from Nalco has been outstanding,” Dunbier said. “They are prepared to get involved and give any necessary assistance.”
The Glenlee trial included NALFLOTE 9843 frother and NALFLOTE 9836 collector, highly selective reagents developed to maximise the separation of coal from the associated ash constituents.
As a first step, the Sada team worked with Nalco to conduct a series of optimisation trials to gain familiarity with the cells and determine optimum reagent dose ranges, cell weir heights and inducted air levels.
With reference levels determined, the trial progressed to establishing the reagent levels required to produce a flotation product at the target ash level.
According to Dunbier, the trial made a difference within hours of initiation. “This has meant good results all round,” he said. “The ash content of the feed from the tailings dams can vary from 20% to 50% and change almost minute by minute but with the Nalco program in place we can consistently achieve our sub-12% ash content target. And the reagents also successfully remove the ultra-slimes from the feed to eliminate any impact on the processing circuit.”
Latest production figures show that Sada is processing some 1,200 tonnes per day, yielding 35% fine coal at 11% ash from a two-stage flotation process, an upgrade from the singlestage processing circuit initially used.
According to Dunbier, the change to the rougher and cleaner system was based on test results that showed refloating the primary froth product would produce a consistent sub-12% ash product, with little impact on yield – test results borne out at production levels.
Nalco Company is the provider of integrated water treatment and process improvement services, chemicals and equipment programs.
The company serves more than 70,000 customer locations in more than 130 countries.