Project manager John Menasce of TWP says, “This advanced workshop will be used for benchmarking others for the next 20 to 30 years. It has been designed to accommodate full maintenance activities of a fleet of 50 trackless vehicles, including six 30 tonne dump trucks and six LHDs.

“The workshop is well illuminated and safe and is equipped to conduct diesel fuel dispensing, a lubrication service with pipe ranges throughout the workshop and used lubricant storage and safe disposal, mechanical and hydraulic repairs, fabrication repairs, a component exchange, tyre storage and handling, basic fitting, basic electrical repairs, mechanical and hydraulic repairs, a vehicle washing bay at the entrance to the drainage collection dams and electrical distribution boards. Lifting requirements are provided by electric overhead travelling cranes and remotely operated workshop cranes, including height to lift LHD buckets over vehicles.

“The new facility has some very interesting features, such as underground, brick-built tiled workshop offices with computer communications, a training room, kitchen, tearooms, toilet and change room facilities and a First Aid room. There’s also a tracked/trackless transfer bay, diesel storage and distribution, with piped feed from surface, 400 metres down vertical shaft, full cable racking throughout and floor drainage to a common collection point

Trackless vehicle ramp

Trackless Vehicle Ramp
and oil lubrication

ISO 14000
“One of the design features we are most proud of is the oil separation control system in the No 3 Shaft underground workshop, that ensures that ISO 14000 standards will be diligently maintained underground,” says Menasce.

“Separating oil from the workshop wash down water is a necessary requirement to maintain the hygiene of the underground workshop, prevent pollution of the mine service water dam below the workshop environment and fulfil the objectives of Assmang’s ISO 14000 standards. Our control methodology will mechanically separate the wash down water from any mineral oil mixed with it, before this water is returned to the underground dam for reuse.”

There are two areas of oil collection and oil pollution responsibility. Total Oil SA will take responsibility for all oil and fuel spillage from its bulk supplies and dispensing units underground and this will be contained in separate areas for specific management. Assmang workshop wash down areas, wash bays and fuel and lubricant top up bays will be the responsibility of the mine.

The wash water dams comprise one settling dam with ramped access from both sides to allow a small front-end loader or LHD to clean fines off the bottom of the dam and a second settling dam where the oil skimming action takes place. This dam will be fed from the settling dam by a weir. A floating oil skimmer in this dam skims off a mixture of oil and water and passes it through the oil-water separator back to the clarified water dam below this dam.

Typical service bay

Typical service bay
with administration offices.

A third dam holds clarified water fed from the second dam via the oil-water separator plant clean water outlet. Should this device fail for any reason, or there is an abnormal amount of water flow, a submerged overflow pipe will allow gravity feed of water from the second dam to percolate Trackless vehicle ramp and oil lubrication ranges. into this third dam. By taking in the water below the floating oil level, any floating pollutants in the second settling dam are held back in that dam.

A fourth dam is gravity fed directly from the clarified water dam by a submerged pipe and it acts as a final hold point should any pollutants have escaped the previous separation process. This dam will discharge into the mine service water system via by a submerged pipe. In the event of massive flooding beyond the capability of the oil separation system for the workshop drainage system — estimated at 150 litres/minute max flow — all dams will have overflow weirs allowing water to flow from one dam to another.

All wash down water is guided via a system of open V drains to a central point feeding the first settling dam where the heavy fines will be allowed to settle to the bottom of the dam.

The construction of the dam is such that the settled fines can be cleaned out by a skid steer loader, or other small front end loader driving through the dam, and scraping the settled fines off the concrete bottom with its bucket. The dam’s dirt holding capacity is about five days of wash down water and fines or 100,000 litres/day of water, including 5% solids. Dirt capacity is estimated over five working days as 25 m3 of settled silt.

Flow of water the through the dam system averages 70 litres/minute with maximum water flow of 36,000 litres over a four hour period (or 150 litres per minute maximum).

Settled water from the dam passes over a weir into a second settling dam where the oil is skimmed off using a floating skimmer. This skimmer is manually adjustable to cope with the depth of oil lying on the top of the water and pumps a mixture of oil and wash water into the main tank of the skimmer.

Next Phase
The next phase of the oil separation process is a tank containing a plate-pack separator which separates the tank into two areas: Pre-pack area (oil and water mix) and post-pack area (oil skimmed off and sludge separated).

The plate pack separator consists of a series of submerged corrugated plates mounted on an incline. The incoming liquid flows longitudinally over the corrugations and cascades downwards working its way between the plates as it does so. The heavier fines and sludge are washed down the valleys of the corrugations and settle out at the bottom of the tank via some vertical channels at the ends of the corrugated valleys. At the same time, the lighter oil droplets coalesce in the apexes of the corrugated plates of the separator and rise up the incline, where they eventually rise to the surface of the tank through some vertical channels fitted at the one end of the plates.

Oil that has now collected at the top of the tank is skimmed by an adjustable weir and flows by gravity into an internal oil tank above the plate pack separator. The oil is separately drained from this tank by the workshop maintenance staff into a suitable container for correct disposal.

Diesel receiving tanks

Diesel receiving tanks.

Clean water (at a maximum flow of 150 l/min) exiting the post pack chamber now flows into a second chamber where it is passed through a media bed coalescing filter before being discharged into the clarified water dam. This filter cartridge can be replaced at intervals by the workshop maintenance staff and the dirty filter removed and disposed of in the correct manner.

A second set of oil skimming weirs in this clarified water tank takes care of any oil that may have escaped from the plate pack separator and the first set of skimming weirs.

The clean water exiting from this chamber is passed back to the third dam (clarified water) where it then flows into the fourth dam and out to the mine service dam for eventual reuse.