With the advent of Australia’s mining “˜boom’, the slurry pipelines sector has received a welcome boost to its level of investment and construction activity, most of which has been particularly notable in Western Australia.
According to industry expert Phil Venton, Venton and Associates Pty Ltd, mineral slurry pipeline systems operate at similar pressures to those used in oil and gas pipeline systems; they are required to deliver the same level of reliability as these systems and they experience many of the same operating and maintenance problems – however, because they deal with minerals, not oil and gas, there is limited information transfer between mineral slurry pipeline designers and operators and those who design and operate oil and gas pipelines.
Australia has a strong history in the global slurry pipelines sector, having the world’s first iron concentrate pipeline, the 2 MMt/a Tasmanian Savage River magnetite slurry line, which has been in operation over 40 years, and the world’s longest single pump station slurry pipeline being the Century copper concentrate line in Northern Queensland.
Other major operating slurry pipeline systems include the Whyalla magnetite slurry line and the recently commissioned CITIC Cape Preston 30 km, 24 MMt/a magnetite line.
Australia also plays host to the world’s first successful beach sand bypassing system, being the Nerang River Entrance Sand Bypassing system in Queensland.
Offshore Australia, significant slurry pipeline systems are also operated in New Zealand (ironsands), Papua New Guinea (copper and pyrites concentrates and nickel ore), while several iron concentrate pipelines either exist or are planned.
Australia’s mines and some thermal power stations also operate innovative high-concentrate mineral tailing pipeline disposal systems that introduce significant efficiencies to these operations.
Besides Extension Hill, the other Western Australian project planning a 90 km slurry line is the Grange South Downs magnetite project in the southwest of Western Australia.
The attraction of slurry
“Slurry transport’s attractive characteristics, in addition to cost, are that it is silent, dustless, noiseless and, once installed, leaves the land able to be reused for cropping and it does not inhibit crossing at any point,” says Matt Duxbury, Manager – Infrastructure Services at Asia Iron Australia.
Mr Duxbury, who has significant industry experience in the Australian, and in particular Western Australian slurry pipelines sector, says that slurry pipelines are also used to transport mineral concentrates where it is cheaper, has less environmental and community impact and safer than road or rail.
“In most cases the concentrate is able to be slurred without further size reduction. If further grinding is necessary to be able to slurry transport, it simply adds cost,” he says.
According to Mr Duxbury, construction of slurry pipelines is very much the same as nigh pressure gas pipelines; where they differ, however, is if the slurry pipeline is lined. “Industry-accepted lining material for slurry concentrate pipelines is high density polyethylene (HDPE). The decision whether to use a liner or not is a big subject of its own, but is determined by internal corrosion assessment,” says Mr Duxbury.
“HDPE adds significant additional processes to installation. The HDPE is typically either extruded on site or welded into 600-1,000 m sections and drawn under tension into the pipeline. The tension reduces the diameter, allowing the pull, with HDPE’s natural memory for its shape snapping it back to the original diameter once tension is released. Each section has to be fitted with bolted flanges to tie off the HDPE. Century and Cape Preston are lined, Whyalla is not, Extension hill plans not to line, while South Downs plans to be line lined.”
Mr Duxbury says that the actual installation logistics and process for internal bare steel slurry and gas pipelines is identical, however the difference comes about because of the dangerous nature of gas compared to most concentrates. “Slurry pipelines can generally be considered industrial water pipelines, with a high level of entrained solids,” he says.
Mr Duxbury notes that capital required for slurry lines is impacted by demand for return water lines.
“Concentrates are generally either low value, high volume commodities, such as magnetite iron ore of bauxite, or relatively high value, low concentrate ores, such as copper that requires further processing. Slurried concentrate transport is generally in the millions of tonnes per annum, with pipeline capacities increasing all the time, i.e. 30 MMt/a.
“Capital for slurry is impacted by the need, in most cases now, for the water to be recovered and reused, so return water lines are now generally needed, certainly in Australia. However, even with a return water line, slurry pipelines are generally of the same order of capital cost as a rail, if the terrain is benign and cheaper, if the terrain is mountainous, such as the South Americas. If a rail line is already proximate to the project, rail may win out. The big advantage for slurry pipeline transport is that the operating cost is the order of one-tenth to one-fifteenth of rail,” Mr Duxbury.
However, Mr Duxbury notes that given the number of factors involved in the decision-making process, each project and its situation can have a different result.
“I’ll use Extension Hill Magnetite Project to give an indication of the parameters for a slurry transport system. Inlet pressure is 23 MPa (at this time a single pump station is planned), pipeline diameter is 500 mm, inlet wall thickness is 15 mm, telescoping down over the length, pipeline is 280 km, and transporting 1,300 dry weigh concentrate per hour for an annual throughput of 10 MMt/a.
“Filtering at the port produces a 9 per cent by weight concentrate paste and the 91 per cent decant water is pumped back the 280 km to the mine site, at 670 m3 per hour. This also is a high-pressure line with inlet pressure of 9 Mpa,” says Mr Duxbury.