Hytec’s hydraulic systems advance drum reclaimer technology
One of five drum reclaimers supplied by Thyssenkrupp Industrial Solutions to South Africa’s new-build power stations.
These dual drum reclaimers reclaim coal down the one side of the stockpile while the stacker is adding coal behind.
Five drum reclaimers were recently supplied by Thyssenkrupp Industrial Solutions to the new-build power stations in South Africa: two for Medupi and three for Kusile. Hytec was chosen to develop and supply hydraulic solutions for the rake operation systems; heel adjustment mechanisms; and a new conveyer belt adjustment system of these state-of-the-art reclaimers.
The fully automated dual drum reclaimers feed blended coal into common bunkers, from where coal is fed to all six units at the respective power stations. “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,” explains Klaus Marggraff, Hytec Systems Sales Manager. The rake’s role is to initiate and control material flow without causing avalanches.
“The reciprocating movement of the rakes is achieved using a single through rod cylinder with a 2 m stroke on each rake,” Klaus continues. 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 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. Speed control and direction change is achieved via a proportional control valve, with an input signal coming directly from the system’s main controller.
The heel adjustment mechanism is driven from the same power pack used for the rake and is also centrally controlled by the drum reclaimer’s master controller.
In order to control the coal feed flow into the drum reclaimer, the rake angle has to be adjusted to match the inclination angle of the stockpile at the point where the surface material can flow freely. “Wet coal, for example, is sticky, so it needs a steeper rake angle, while dry coal will flow at lower inclinations,” Klaus says. The rake angle adjustment is done via a mechanical pulley system.
In addition to the rake angle, these systems incorporate an adjustable heel that sits below the rake and just above the drum for additional fine flow adjustment. This regulates the amount of coal being picked up by the drum’s buckets and dropped onto the belt inside.
The third hydraulic system is a hydraulically operated conveyor belt tensioning system – the first ever application of continuous belt tensioning to be used on drum reclaimer belts in South Africa.
This solution replaces the need for manual tensioning and straightening, and dramatically reduces downtime. “The new hydraulic system enables the ideal belt tension to be continuously maintained, using two parallel cylinders on either side of the belt, which are connected to the shaft of the idler pulley. Integrated position transducers on the cylinder rods are used to ensure belt adjustments on either side are within 3.0 mm to ensure that the belt always runs true.”
Tension is achieved by maintaining the hydraulic pressure that produces the exact belt tension required. The system also gives an early warning to belt tears, overloading or other problems.
The cylinder stroke of 1.5 m provides excellent adjustment flexibility and makes it very easy to slacken the belt, should a splice be required, for example. “The cylinders are driven by a small 2.2 kW power pack. It’s a very elegant use of hydraulics that increases reliability, uptime and belt service life compared to a manually adjusted pulley,” Marggraff concludes.