Mining Recovery demands require new technology

Tag: valve disc

For many years, new technology was not employed in the valve equipment used in the mining industry, and has only recently been introduced, owing to increasing demands to improve recoveries, says valves specialist Ragon Industries director Hendrik Ras.

Ras comments that it is essential that valve technology keep pace with developments in the bus system and other control-system demands, as, previously, valves were not fully aligned to the levels of control now being demanded by mining operators.

Traditionally, valves have been manufactured specifically for the transport of slurries.

Therefore, a premium has been paid for solutions that ensure unencumbered pipeline operations, so as to reduce wear. Inner linings have traditionally also been soft, given the industry’s aversion to buying expensive hard linings. Attention has also been given to correct line sizes, as a decrease in line size could cause blockages in the pipeline.

But a valve that is line size, says Ras, either needed to be made of rubber, or rubber inserts had to be pinched to close it off. This causes high thrusts, and large actuators are needed to operate it automatically, as the area of the pipe and the pressure in the line need to be added together to calculate the thrust in closing a valve.

When pressures are low in the line, the flow needs to open the valve, and if the pinch effect is removed, deterioration, inherent characteristics or the memory of different rubbers could keep the valve closed and cause blockages.

Ras argues that this process causes the plant to be unstable from a control perspective, which, in turn, causes inefficient recovery. This translates into increased use of chemicals, the wearing out of pipes, the short lifespan of pumps, and valves failing, owing to a severe demand from a distributed control system or programmable logic controller.

Mines currently spend millions on sophisticated instrumentation and control systems in the hope of increasing recovery. However, field-final instruments are often excluded from the equation, leaving com- panies to try to correct the control of a valve through sophisticated valve positioners. In these instances, Ras claims, companies will succeed only if the control is not critical, and more often than not, they fail.

Ragon believes it has a solution, despite offering valves that are 10% of the weight of competitors’ products, which has the added benefit of reducing rigging and pipe stresses.

Ras says that, while pinch valves and diaphragm valves are generally associated with slurries, his company is deploying butterfly valves.

The design offers 90� valves that provide advantageous linear-control characteristics, owing to their unorthodox liner design. The valve shaft is designed to go through the disc, and this, coupled with a square drive, decreases the backlash between the actuator and the disc, he says. Further, the valve is guided at the top and the bottom, so it can withstand water hammer better, and is safer. The valve disc is also hardened to stand up to the most severe slurries applications, he notes.

Ras claims that the solution has increased control stability, and has had the added benefit of increases recoveries and, ultimately, profit. Further, he asserts, the valves’ class six shut-offs could change the face of the mining industry, where stable control and recovery play a main role in relation to a mine’s profitability.

Ras acknowledges that the solution is, at times, more expensive, but that these costs are more than compensated for by its life-cycle benefits. He maintains that it can also make marginal operations economically viable.

The company also exports its products into the rest of Africa, South America, and Aus-tralia. It has opened a branch dealing specifically with African operations, and there are plans to set up a facility based possibly in Zambia. Its raw pro- ducts, which are sourced from Europe and China, are first modified to conform to the company’s specifications, and then imported, he says.

Ras, who is currently the company’s sole shareholder, founded Ragon in March 1997. Frans van der Merwe manages the local opera- tion. Its Ragon Africa branch is 70% owned by Ras, with Mark Mulenga, a Zambian national, holding the 30% balance of the shares.