Copper Concentrator - SAG& Ball Mill Case Study

The Problem

Our client experienced a significant water and debris contamination event in theFixedBearing circuit of the SAG Mill.  The mill was immediately shut downto avoid bearing damage and the contaminated oil was removed and new then oil introduced.  Even so, there was concern that the circuits still had potentially harmful debris and moisture present. 

The lubricant removed was very dirty and saturated with water to 5000ppm, a level of contamination that high would normally mean disposal/total loss, at a cost of $20,000.

Lost production downtime at this mill is circa $1,000 per minute of downtime as the two mills run in series potentially affecting other operations.

BioKem’s mobile VDOPS, on site and operational within hours of arrival, and conforming to all site requirements.

 The Challenge

The rapid response solution was to firstly remove residual water and particulate contamination in the in-service SAG fixed bearing lube tank followed by cleaning and polishing of the bulk contaminated oil.  All tasks were completed in an urgent timeframe to mitigate any potential damage to the gearbox and trunnions.

Working with ISO 460 oil requiredraising the temperature from operating temp of 47°C to >70°C to lower the viscosity to a workable 100cSt or less.

Filtration was to be conducted on in-service oil by way of kidney bypass to the required standard in a reasonable timeframe.  Access restrictions added to the complexity of the job.

Solution

After initial contact and a phone consultation, BioKem mobilised the 50GPM Vacuum Dehydration Oil Purification System (VDOPS) asset and engineering team to the remote site in Queensland immediately.  Site inductions, JSEA and documentation were completed and BioKem were on site with all equipment within 30 hours.

The Mobile VDOPS is equipped with 2 x 32 kW heaters, capable of heating 100L/min of this gear oil to 80°C, and drawing over 20” Hg of vacuum, for the most efficient moisture dehydration and viscosity adjustments, without risk of damaging the oil further.

The VDOPS is capable of moisture removal and dissolved gases to below 50ppm, and ISO 4406 cleanliness to 13/12/10, with a β1000, 2.5 micron filtration.Equipped with 4m, 6m, and 12m hoses, we can access the most challenging locations. With 8 drain points and a pressurised flushing system, we ensure no cross contamination from previous jobs between different tanks and lubricants.

Fitted with 2” Camlocks, Plugs & Caps for quick installation and adhering to a ‘NO SPILL’ policy.

To keep downtime and revenue losses to a minimum, BioKem has developed operational procedures and reporting systems, that maximiseefficiency and professionalism, setting the industry standard.

In this case BioKem’s VDOPS not only purified the contaminated oil, but also polished other in-service oil whilst the asset was available, offsetting the cost of having BioKem onsite for the event and saving the customer money.

Purification Tasks

1.      SAG Mill Fixed Bearing Tank                                  6,000 L

2.      SAG Mill Floating Bearing Tank                              4,500 L

3.      Outside Bulk Tank                                                   5,000 L

4.      Polishing SAG Mill Floating Tank                           4,500 L

5.      Ball Mill Floating Bearing Tank                              4,500 L

       Total Oil Purification Completed                         24,500 L

1. SAG Mill Fixed Bearing Circuit Tank 6000L

Starting ISO:                            21/21/17 (out of spec)

After Purification ISO:     16/15/12

Water Content:               Not tested at start

Water Content after:      <50ppm

VDOPS Purifying Time:  26.9 Hrs

Comment: Client had sensibly drained the contaminated oil and deployed a small centrifuge that helped.  VDOPS further reduced the moisture and significant larger debris was captured as shown. 

2. SAG Mill Floating Bearing Circuit Tank 4500L

Comment:  Filtration was commenced on this oil however the oil did not respond normally.  It had a very dark appearance and smelled ‘burnt’.  A sample was taken and this oil displayed a ‘cake of fines’. 

Action:  Client was advised to go offline drain this tank as this contamination will cause significant wear.

A cake of fines is a very high concentration of silt size particles and/or additive pack ingredients that build up on the patch membrane obscuring all other contaminants.  If the additive package breaks down in this way and drops out of solution it is no longer performing its intended function.  The oil that was removed was dehydrated and left to be filtered over the next two weeks with depth filter media to remove these sub-micron contaminants.  Afterwards an additive pack will be needed to restore this oil.

3.     Outside Bulk Tank 5000L

Operating outside and beyond ISO 4406 spec

Starting ISO:                            23/22/17 (out of spec)

After Purification ISO:     21/17/15

Water Content:               5000ppm (out of spec!)

Water Content after:      100ppm

VDOPS Purifying Time:   20.3 Hrs

Comments: A huge 25L of water was removed and lubricant could then be returned to service.  The image shows the VDOPS collection chamber extracting water from the emulsified oil. No free water was present.

Summary

In total 24,500L of oil was purified to better than target specification in 114.2 Hrs.

The outcome was returning the plant to operation with a minimum of downtime and without discarding any lubricant resources and associated costs.  The client was so impressed with our response service and professionalism; they have requested a regular 90 day service agreement to manage the oil cleanliness.

Job#	Vol	ISO 4406 Start*	ISO 4406 Finish*	Hrs	Note
1  SAG Mill Fixed	6,000L	20.19.16	16.15.12	26.9	Excellent improvement in ISO4406
2  SAG Mill Floating	4,500L	-	-	33.5	Clean, however sub-micron ‘cake of fines’ still present
3  Bulk Tank	5,000L	23.22.17	20.19.16	20.3	Highly emulsified oil, 25L of water removed
4  SAG Mill Floating Polish	4,500L	20.19.16	-	12.3	Low level fines residue – visually OK
5  Ball Mill Floating	4,500L	23.22.17	Await result	21.2	Oil was dry, however anticipate significant improvement in cleanliness.
TOTAL	24,500L	-	-	114.2

Photo Essay

Comparison of SAG Floating oil contaminated with ‘cake of fines’ (Left) darker pigment compared to SAG Fixed in-service oil after VDOPS has cleaned it (Right).

Zero Spill Policy & Procedures

Advantage of pre-filtering the oil before the high value glass fibre filter is subjected to this level of contamination!

Graph of how the ISO 4406 cleanliness will saw tooth with the proposed deep filtration cycle over a rolling 90 days.  The redline is the upper allowable limit.

Redundant Technology was onsite, deemed unsuitable and mothballed