Modern Residue Transport and Dump Systems for Power Plants

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Glatt Ingenieurtechnik GmbH

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Modern Residue Removal Systems

For the new plants alternative solutions had to be found meeting the requirements for an environmentally friendly, economic and reliable removal of the residues (Table 1).

The majority of those requirements is well addressed by continuously operating conveying and dumping systems. They usually consist of:

• in-plant conveyors (troughed, screw, drag chain type etc.),

• overland conveyors (troughed or tube), and

• dump conveyors with mobile spreaders (Fig. 3).

In addition, certain auxiliary equipment such as magnetic separators, metal detectors, dust suppression systems, weigh scales is required. The advantages of belt conveyor systems include:

• high capacity,

• rather wet and sticky material can be safely conveyed,

• low operating cost, as well as

• low emissions.

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So, residue removal systems in particular of large power plants, but not limited to those are increasingly equipped with conveyor systems and mobile dump spreaders. While the systems for the Enel OGK-5 power plant in Russia and Medupi in South Africa will both operate conveying systems directly connecting power plant and residue dump for Maritsa Iztok-1 three options were investigated for the 8.8 km distance between plant and residue dump[1]:

• A 4.5 km long tube conveyor with a truck loading station at the end of the conveyor and truck transport over the remaining 4.3 km with the option of later replacement of the truck transport by a second tube conveyor.

• A 8.8 km long tube conveyor in a single flight.

• A two flight solution with one flight of 4.5 km and the other one of 4.3 km with emergency truck discharge/feed at the transfer point between the flights.

The spreading of the residues at the dump side was planned right from the beginning based on trucks and wheel loaders. The residue transport of the new plant had to replace the rail transport of the old boilers, preferably using the same routing as the existing rail tracks. Particular attention was paid to a low emission solution since the transport route had to pass a village. Next to those constraints the investment costs and the reliability of the system was of utmost importance.

Finally, the first option was chosen with the village being passed by tube conveyor, completely enclosed in that section, and truck transport for the distance from behind the village to the dump. The option caused the lowest initial investment. The truck fleet still necessary could be used in an emergency for the whole distance, of course with reduced capacity. The option for a second conveyor flight covering the remaining distance to the dump was left open for the future.

The system has to handle in average:

• fly ash (48 %),

• bottom (wet) ash (7 %), and

• gypsum (45 %).

The moisture content and density of the material can vary. The system must be suitable for transporting a mixture of the three materials as well as each of the materials separately if necessary. Moreover, experience shows that significant deviations in the characteristics of each material may occur depending on the feed material quality as well as on the operating conditions of the boiler and silos.

The varying density of the feed material required special attention when feeding the tube conveyor. In addition to a normal weigh scale a measuring device for the volumetric flow was installed after the last feeding point of the open troughed belt conveyor residue collecting system. A PLC controls the speed of the feeding conveyor BC-1C as well as the feed opening of the last silos to avoid any overloading of the tube conveyor. Furthermore, a shuttling head pulley of BC-1C allows dumping all the residues on the conveyor onto an emergency stockpile at any point in time. From there the residues can be easily fed back onto the belt via emergency hopper.

Emergency considerations were also the driver for a bypass installed at the end of the long tube conveyor. Regularly, the residue is fed via shuttling conveyor, two truck loading conveyors and respective telescopic chutes onto the 24 t trucks. In case of an emergency the whole volume of material on the 4.5 km long tube conveyor can be dumped onto an emergency stockpile inside the truck loading station (Fig. 4).

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