MechChem Africa

Following the recent commissioning of two ThyssenKrupp drum reclaimers at the Medupi Power station and the delivery of a further three to Kusile, MechChem Africa talks to Klaus Marggraff, systems sales manager for Hytec, about the novel hydraulic being used to advance the performance of ThyssenKrupp SA’s specialist technology.

TKISSA drum recalimer hytec hydraulicsThyssenKrupp Industrial Solutions SA has now completed the delivery of five drum reclaimers to the new-build power stations in South Africa, two to Medupi and three to Kusile. “Hytec developed and supplied the hydraulic systems for these machines: the system to operate the rakes; the heel adjustment mechanism that sits underneath the rakes; and a new conveyer belt adjustment system,” begins Marggraff.

These are dual drum Reclaimers, which means that they can reclaim coal down the one side of the stockpile while the stacker is adding coal behind. Then, when at the end of the pile, the front rake is switched off and the rear rake is activated for reclaiming in the opposite direction. Marggraff adds that the machines are fully automated. “There is an operator on each reclaimer, but his role is to respond to safety issues and unusual events. The routine reclamation process proceeds under full automatic control,” he says.

Coal stacking and reclamation at power stations is essential for blending purposes, so that the pulverised coal that enters the boiler has relatively consistent calorific value. This is to prevent excessive temperature, pressure and power fluctuations.

The ThyssenKrupp drum reclaimers are used to feed blended coal into common bunkers, from where coal is fed to all six units at the respective power stations.

Describing the role of the rakes on the reclaimers, Marggraff says: “The rakes oscillate across the stockpile so that a steady stream of coal flows down the pile, into the drum and onto the conveyor inside the drum. The rake’s role is to initiate material flow without causing avalanches, which could cause the system to overload.

“The reciprocating movement of the rakes is achieved using a single through rod cylinder with a 2.0 m stroke on each rake,” he informs MechChem Africa. Cylinders with a 160 mm bore and a 120 mm rod are used at an operating pressure of around 160 bar, with the through rod cylinder design ensuring that speed in either direction can be easily maintained.

“The rake system is driven by a 90 kW hydraulic power pack, with an electric motor driving a variable displacement Rexroth A11 swash-plate hydraulic pump capable of producing a maximum flow rate of 370 ℓ/min,” Marggraff says.

“Speed control and direction change is achieved via a proportional control valve, with an input signal coming directly from the system’s main controller,” he adds.

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