Modern Residue Transport and Dump Systems for Power Plants

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Glatt Ingenieurtechnik GmbH

EDL Anlagenbau Gesellschaft mbH

Pörner Ingenieurgesellschaft mbH

Overland Residue Transport

Continuous overland transport can be facilitated by troughed and curved or by tube conveyors. With the Medupi power station straight pairs of troughed conveyors are used to bridge the rather short distance between power plant and ash dump. The ash dump is built layer by layer by a crawler mounted spreader linked to the overland conveyor by extendable and shiftable conveyors (Fig. 5).The double line conveyor system offers a very high reliability. In case of an emergency the overland conveyors, equipped with a shuttling head, may dump onto an emergency stockpile.

Longer distances may often not be bridged by straight lined conveyors any more. In these cases horizontally curved or tube conveyors may be installed to avoid additional transfer towers with all the resulting requirements for power supply, dedusting units, with wear in the transfer chutes etc. [2]. The longest distances covered by a single flight troughed belt conveyor reach around 20 km.

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Whereas troughed conveyors for the removal of residues from power plants have to be covered very well and protected against side winds tube conveyors enclose the residue completely in a tube formed by the rubber belt. Moreover, tube conveyors can negotiate much tighter horizontal and vertical curves than troughed belts and can, therefore, be adopted very well to the terrain.

Of paramount importance for the proper operation of a tube conveyor is the correct position of the belt overlap, in particular when conveying wet or very fine grained material such as ash and other residues. This position depends on a number of factors such as

• belt tension,

• radius of horizontal curves,

• specific weight and position of the tension members within the belt,

• specific weight of the material transported,

• filling degree of the tube cross section,

• friction between idlers and belt, and

• lateral stiffness of the belt.

Since some of these factors may vary during the operation of the conveyor the area of the overlap may move even with a well-adjusted belt. To avoid adverse effects of such a twisting an automatic adjustment system was developed (Fig. 6). The overlap position is permanently monitored by a set of ultrasonic sensors. Based on their measurements a set of electromechanically operated idlers of special spherical shape always turns the belt back into its correct position.

Nowadays, a tube conveyor may already be operated safely within a wide range of ambient conditions without the need for any cover. Nevertheless, for the system in Russia with ambient temperatures down to -40 °C and large amounts of snow in winter time it was recommended to put the whole system into a gallery. Special measures were adopted to make the system fit and reliable even under the most adverse conditions. This includes but is certainly not limited to substantial reserves in the installed drive capacity, special procedures in case of a power failure etc.

Furthermore, in the Maritsa project special attention had to be paid to the reduction of noise emissions in a stretch nearby a residential area. Compared to the standard steel idlers used in such conveyors the noise emissions could be reduced by more than 50 % by installing special plastic idlers (Fig. 7). In addition the respective stretch was completely enclosed with noise insulating conveyor covers.

Fig. 8 shows the power consumption measured after 6 months of operation. With the lifting height being small compared to the horizontal length of the conveyor the empty belt consumes about 82 % of the belt loaded with an average capacity of around 700 t/h. Reason for this very typical characteristic of a tube conveyor is the stiffness of the belt causing additional loads to the idlers to hold the belt tubular shape.

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