Residuals Removal at Maritza E1

Tube Conveyor Systems

Residuals Removal at Maritza E1

Design, Installation and Commissioning of a Tube Belt Conveyor
With the reconstruction of the power station Maritza East 1, the residual materials disposal system has also been reorganized. This project was contracted to Takraf in 2006. The heart of the residual material transportation system is a 4.5 km tube conveyor that follows the course of an old railway line and was realized in cooperation with ContiTech.
(ed. WoMaMarcel - 09/12/2014)
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3    Design of the Tube Belt

Takraf ordered an approximately 9.1 km long tube belt from ContiTech Conveyor Belt Group for the new Maritza tube conveyor system in Bulgaria. ContiTech also helped during the planning, installation and commissioning of the system. They have supplied more than 120 tube belts worldwide since 1987 and enjoy a high level of trust and confidence both from OEMs and from many plant operators.

In comparison to a conventional troughed overland conveyor belt, which can be operated at maximum conveyor speeds of vF = 8.0…8.5 m/s, the maximum conveyor speed of a tube conveyor system is limited to around vF = 6.5 m/s. Furthermore, the conveyor cross-section of a troughed conveyor belt of equal width is around 3 times larger. However, a tube conveyor belt offers decisive advantages over a troughed conveyor belt, and in some cases these advantages make the use of a tube conveyor belt actually indispensable. A summary of the advantages and disadvantages of a tube conveyor system is outlined in Fig. 10.

During the selection and design of a tube conveyor and the tube belt itself, many factors need to be taken into account, such as the radii of curved sections, the significantly increased running resistance caused by the high form forces and additional friction forces in the belt overlaps, the shape of the overlap zone, and so on. This is why a new tube con­veyor and the tube belt are often jointly designed by a OEM and a conveyor belt manufacturer. The new Maritza tube conveyor uses a high speed tube belt “HS-Rollgurt 1500 S-K2 7T:6S Conti Extra” with a width of 1500 mm and a nominal breaking strength of kN = 1500 N/mm. Figs. 9, 11 and 12 present the special features and requirements associated with a tube belt.

The highest friction forces in the conveyor system occur during the initial hours (days) when the tube belt is first taken into operation (i.e. empty) (exception: conditions when the belt is first pulled in). The design of a tube belt should always be based on a “normal operating state” (i.e. after the running-in period), while the choice of suitable drives should always take into account both possible operating states (i.e. during commissioning and after the running-in period).

If a tube belt is designed, selection of the optimal transverse stiffness and overlap design is essential. Fig. 11 shows a different behaviour of a tube belt between idler panels: good (left) and unsuccessful designs of the tube belt (middle and right). Fig. 12 shows a different behaviour of a tube belt under tension in a horizontal curve: sufficient (left) and non-sufficient (right) transverse stiffness.

Once the tube belt design has been decided upon, the forming forces and overlapping zone are tested with the aid of a test sample (Fig. 13). Various operating factors such as the ambient temperature, temperature of the material, and the minimum radius for curved sections need to be taken into account here. Optimized transverse stiffness should maintain the tubular shape in curves to provide sufficient tube cross sectional area for the material and not cause very high running resistances resulting in high power demand.

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