Reliable availability of permeate process water, an additional 20% yield and an 85% reduction in membrane use are just three of the benefits for Austar, now that the RO plant is operating to its design specs.
The Austar underground coal mine in the Hunter Valley experiences above average water seepage and daily pumps 4.5 to 5 megalitres of high metals brackish water from the mine to a site storage dam.
Since its commissioning, the mine’s reverse osmosis (RO) plant has processed the site water but has not achieved yield to design specifications. The facility includes three separate processing units: Nos 1 & 2 for clean water recovery; and No 3 for tertiary processing of residual brine from units 1 & 2.
“The output of the plant varied,” said Allan Kerr, shift supervisor at Austar.
“Sometimes we would see good results, sometimes mediocre results and sometimes no result. With frustration levels rising and RO plant output falling, the decision was taken to get Nalco involved.”
Nalco was already working at the site, developing an antiscale program for mine water transfer equipment.
The brief was simple: a reliable and economic water supply of consistent quality suitable for CHPP and underground operations.
Communicating the problem
Austar already knew one of the problems – the short life span of a set of membranes within the RO trains.
They were changing out a set of membranes, on average, every three months, which pointed to inadequate pre-treatment and insufficient feed water scale inhibition treatments.
According to Alan Kerr, Nalco’s analysis of the RO plant and its performance identified operational and downstream areas which were also impacting on efficiency.
In practice, pre-treated water from the site storage dams is pumped to a coarse pre-filtration stage to remove particulate matter down to 5-10 microns. The water is then pumped to the RO filtration stage which incorporates DMI Green Sand media filters (to remove any residual iron and manganese) and cartridge filters (for polishing and removing any particles > 1 micron).
Between the media filters and the cartridge filters, Nalco’s PermaTreat® PC-504T Membrane antiscalant treatment is now introduced.
PermaTreat PC-504T was developed specifically as a calcium sulphate inhibitor for water with a CaSO4 Ipb/Ksp ratio of 2.8 to 7.0. It functions through a powerful threshold mechanism that retards the precipitation of calcium sulphate, increasing its relative solubility.
Compatible with all membrane types, it also exhibits strong inhibition properties against calcium carbonate and silica and is highly tolerant to the presence of iron.
Dosing of the antiscalant is managed by Nalco’s TRASAR® technology. Designed for real-time on-line monitoring of antiscalant concentration, the technology actively controls antiscalant dosing down to a level of 0.5ppm of product.
“Getting the RO plant operating as it was designed has been a direct benefit of the introduction of the PC504T,” Allan Kerr said.
“We are seeing tangible improvements to the operation, overall efficiency and output of the plant from a product that is both more effective and significantly cheaper than that used by the previous supplier.”
All three processing units are working closer to design specs with Unit 3 recovering around 20% more permeate from the brine processing cycle. Additionally, the plant has just achieved 14 months trouble-free operation from one set of membranes.
“The key to the success of this project has been Nalco’s commitment,” Kerr said. “Through their international network they found a product that was proven to work and combined it with the necessary technology to deliver the result we wanted.”