Bulk handling solutions provider Clyde Bergemann Power Group’s dense-phase pneumatic conveying system, installed at Unit 6 of national power utility Eskom’s Medupi power station, in Limpopo, has been exceeding its contractual capacity since commissioning started in December, Clyde Bergemann executive director Jeremy Kirsch tells Mining Weekly.

The contract, awarded to Clyde Bergemann in 2009, stipulates that the conveyor must be able to handle 168 t/h of fly ash; however, the conveyor has demonstrated an achieved rate of 210 t/h.

After pulverised fuel is burned, fabric filters catch the fly ash to separate it from the flue gas. The fly ash is fed from the hoppers into the pneumatic conveying system using a Clyde Dome valve.

The conveyor at Medupi uses compressed air to convey a dense plug of fly ash along a 430 m pipe to three of six 3000-t-capacity silos for storage.

Kirsch adds that, while the company drew on experience from its global sister companies, the bulk of the innovation and work that allowed Clyde Bergemann to achieve such high capacities took place at the company’s Johannesburg offices.

He believes that this accomplishment indicates the capacities that can be achieved through dense-phase pneumatic conveying in the mining industry.

“Not many projects of this scale exist,” states Kirsch, adding that he is also unaware of any existing projects that have the same operating requirements.

He explains that Clyde Bergemann had to pay particular attention to the coarse particles and soot in the fly ash, particularly during the boiler start-up, known as the oil ash mode, when it designed the system.

Clyde Bergemann also equipped the system with capacity-boosting capabilities, should these be required. Kirsch says this mode of operation is called the by-pass conveying mode and it uses the available air more consistently to achieve a higher output. When operated in this mode, the system can achieve throughput up to 25% higher than normal design operating capacities.

He highlights that dense-phase pneumatic conveying generally uses less air to transport one unit of material and achieves higher conveying rates with the size of pipeline that is used, compared with lean-phase pneumatic conveying systems, which move sparsely concentrated volumes of particles along a pipeline.

Kirsch notes that pneumatic technologies are not the only way of transporting fly ash, adding that mechanical and hydraulic methods can also be used.

He says Medupi’s Unit 6 is being commissioned and is supplying energy to the grid, which has subsequently provided Clyde Bergemann with the opportunity to put its products to the test.

The company is also installing identical conveyors for the remaining five units at Medupi.

Kirsch notes that Clyde Bergemann, prior to its project for Eskom, produced pneumatic conveyors to transport ore concentrate to smelters and fly ash away from furnaces in the mining industry.

Further, Clyde Bergemann has commissioned dense-pneumatic conveying systems in the transport of platinum and copper concentrate, such as a 120 t/h platinum concentrate conveyor at a smelter in Polokwane.

The company has also built dense-pneumatic conveying systems for the ferrochrome and aluminium industries when transporting off-gas dust.

Ash Conditioners
Clyde Bergemann also built a 350 t/h conditioner at Medupi to add water to the dry ash to prevent dust formation. Kirsch says this process allows for the ash to be transported along a conveyor belt from the silos to a permanent- storage location.

He notes that similar projects for transporting fly ash, but on a smaller scale, have been undertaken in the mining industry.

The conditioner, which had a contractual capacity requirement of 200 t/h, uses two parallel, counter-rotating shafts, fitted with mixing paddles to add 12% moisture to the ash. The moisture prevents the ash from blowing away when it is travelling along the multikilometre overland conveyor system.

Kirsch states that Clyde Bergemann’s work across the Zambia Copper Belt, as well as its involvement in several other projects, has provided the company with direct insight into the adverse effects of the economic downturn and the electricity crisis across the Southern Africa mining industry. However, he highlights that output and the prospects of the industry have been growing steadily.

Clyde Bergemann has, therefore, proven that it is prepared for the imminent uptick in the mining industry, which is bound to require a boost in the capacity of its systems, Kirsch concludes.