The improvements were implemented on eight agitator assemblies in AC1 which enabled an extended operating campaign.
The agitator assemblies were removed during a major shutdown in June 2017 and replaced with a trial modified agitator blade assembly design that had been developed with the use of computational fluid dynamics (CFD) and paint modelling.
The design incorporates a ‘swept’ impellor blade geometry with a weld-on blade connection and wear resistant chromium oxide coating. The configuration helps reduce turbulence caused by the presence of blade bases and bolting while minimizing erosion on the back of the blades and on top of the disc, to which the blade attach.
“We (Lihir engineering and reliability team) developed the current impeller design progressively over several years, combining the learnings of numerous trials to get to this point as we learnt more about the process and agitator flow dynamics,” said senior mechanical reliability engineer, Andrew Petrik.
He said inspections conducted in June this year proved that the agitator blade design had been successful and the long term goal of safely achieving 12-month operating campaigns on autoclaves 1-3 was now a reality.
“The benefits associated with improved autoclaves agitation are extensive. In addition to the longer operating campaigns are increased production, there will also be reduced maintenance costs and reduced scale build-up inside the vessels meaning less descale time during shut downs,” he said.
Mechanical engineer, Clayton Benson, said with these improvements and extensions of AC1-3 operating campaigns from nine to 12 months, operating campaigns are now standardized across all four autoclaves which simplifies the long term planning and process on site.
At Lihir, gold is present in the orebody primarily as auriferous pyrite, a gold-bearing variety of pyrite – hence the ore is refractory. This means the ore must go through a leach process to recover gold. Additionally, the sulphur grade ore deposit in Lihir is relatively high, thus the bulk of this sulphur must be oxidized before the leach process takes place.
The autoclaves in Lihir play a key role in providing the oxidizing environment. Without oxidation, very low gold recoveries are achievable through the leach process.
In maintaining the autoclaves, site mechanical engineers constantly identify and investigate problems and initiate and implement improvements to help autoclaves in safely delivering great results.
(Local Lihirian process technician, Orim Yetua, doing his field checks at the autoclave area in the process plant in Lihir)