Diamond Mine – Decline Underground Conveyor System for ore extraction

SK Technologies was awarded the contract for the design, manufacturing and installation of a fully automated underground decline conveyor system at a diamond mine in the Free State Province of South Africa. Our scope was to build and supply all the MCC’s and PLC equipment to achieve this.

This decline conveyor belt system consisted of 10 conveyor belts. The first conveyor was horizontal and  received ore from the crushers situated on the 490 Level. The 9 subsequent conveyors which transported the ore to surface for onward transportation to the processing plant stockpiles were inclined at 12° The total power requirement on the conveyors alone for this project was 974KW.

The MCC’s that was manufactured conformed to Type 2 Coordination at 525VAC. As SK Technologies is a official channel partner for ABB, all switchgear that was used including the Soft Starters, the PST type, was from ABB.

The automation platform was done by using the Phoenix Contact Inline controllers of PLC’s and their Visu+ SCADA Package. There was a central containerized control room on surface level by which one operator could operate the entire conveyor system. The link between all 10 MCC’s PLC’s and the SCADA PC was done via a fibre optic network installation running Profinet, which included the Phoenix Contact fibre switches installed in each of the MCC’s. This fibre installation was done completely by SK Technologies.

We are faced with the problem that in the event of failures or emergencies, there was no way for the operator above to contact personal below( bear in mind this was a dormant mine brought back to life). The solution we came up with was to in addition to the PLC’s and SCADA on the fibre optic network, to also install a VOIP telephone system for the operator to be able to communicate to the relevant personal down below. This worked extremely well.

The belts was designed to meet the following performance criteria:

  • Maximum tonnage rates = 400 t.p.h.
  • Conveyor belt speeds = 1.5 to 1.6 m/s standard.
  • Brocken rock density = 1.8 – 2.0
  • Broken lump size = 300mm during the development phase and 160mm for production
  • Operating temperatures = 20-30 deg.C
  • Relative humidity = 75-85%

The following safety devices had to be fitted to each of the ten conveyors:

  • Pull-key switches and trip wires.
  • Belt rip detection
  • Belt slip protection
  • Lock out type Isolator stations complete with emergency stop button and start/stop buttons at each drive
  • Start-up warning sirens
  • Blocked chute detection and warning system
  • Safety Sensors for Gates
  • Dual Misalignment Unit
  • Tail End Slip Sensor
  • Dust Suppression
  • Fire Detection
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