Bulk materials handling systems supplier Techmatic, in partnership with one of the gold mines near Welkom, in the Free State, have completed what is believed to be South Africa’s longest dense phase pneumatic conveying system. The dense phase conveyor moves dry cement powder in batches over a distance of 3 000 m through a 65NB and 80NB conveying pipeline to the underground batching plant.

Traditionally, cement is transported underground in small rail car-mounted pressure vessels that are slung under the hoist cages to drop them to the required shaft level which, in this case, is about 1 500 m below the ground. From there, they are shunted to the underground cement batching plant, which is a further 1 500 m away from the shaft. The process from surface level to batching plant could take anything up to 48 hours to complete.

The gold mine contacted Techmatic in early 2010 to investigate an alternative method of moving the cement underground. On this basis, Techmatic supplied its dense phase conveying test rig to the mine to carry out the necessary testwork. Initial tests blocked the existing backfill pipeline, which was to be used as the conveying line. These blockages were traced back to the existing pipes having crusts of old backfill material on the inside. Over a period of 18 months, the mine cleaned the internals of the existing pipelines.

Once the pipes were clean, the system was tested and the dense phase conveying system is now successfully conveying cement at a feed rate of 0.6 t/h over the full distance.

Techmatic reports that the cost-saving implications were such that the mine decided to invest in purchasing the test rig in order to use the system on a full-time basis. The implications of being able to convey over that distance is that it frees up cage time, underground rail road usage time and space congestion. An added issue is that the empty vessels also need to be transported back to surface empty. The cement is fed to the batch plant on demand, taking roughly 20 minutes a batch instead of the typical 48 hours to reach the destination. The system can run when the shafts are evacuated for blasting.

“The use of dense phase conveying technology for this specific purpose has opened the possibility of implementing this at many other deep-level mines that are faced with similar challenges. In many instances, the cement batching plants are actually located deep underground directly below a town or below land not owned by the mine. In these cases, it is not possible to simply locate a cement silo vertically above the batch plant and drop the cement down a vertical shaft. The cost of sinking such a shaft is astronomical, compared with the dense phase conveying alternative,” reports Techmatic.

Hall 6 Stand K26