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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4    Pulling in the Belt

The process for pulling in a tube belt needs to be coordinated between the OEM, belt manufacturer, service company and end-user. The pulling in procedure should be perfectly matched to the system.

The following factors need to be taken into account:

  • The forces required to pull in the belt should be calculated in advance and monitored during the pulling-in process.
  • Appropriate tools, machinery and auxiliary equipment matched to the demands of the system must be made available on-time (dozers, cable winches, crane, fork-lift truck, special pulling-in devices, connecting tools, splice shed, powered belt reeler, etc.).
  • The optimum timing for pulling in the belt needs to be coordinated with the customer (special measures may be required if it is particularly cold).

Before start to pull in, a preliminary installation meeting between all participants should be held on site. The following strategies are possible for pulling in the belt:

  • The entire tube belt can be pre-spliced next to the system (e.g. at the tail end or at the head end) and then drawn into the system.
  • Each section in turn can be drawn in or counter the conveying direction from one particular position or from multiple positions in the system in the top strand and/or bottom strand.
  • During the pulling-in of the belt, it is possible to use drive(s), dozer(s), cable winch(es) or a take-up device (either alone or in combination).

Fig. 14 shows the final strategy chosen for pulling in the belt.

The standard procedure for replacement of a tube belt involves the use of drives in order to reduce the very high pulling forces at the cable winch (dozer) or on the powered belt reeler. In this case the belt is pre-spliced and laid down next to the installation in order to reduce downtime. Drives are often not possible to use in a new installation. Here, the belt is pulled in sections that are connected one after the other. This also reduces the very high pulling force. The choice of the correct location in the system from which the belt can be pulled in is of paramount importance. Ideally, the system should have no curved sections and no elevations at this point. Figs. 15 and 16 show the special equipment used to pull in the belt.

The cone-shaped belt puller (clamp) allows the belt to be pulled in smoothly through the hexagonal idler stations in the system. The rolled-up tube belt is fixed form-locked in the pulling-in clamp between two steel cones. Here, the eye bolt of the inner cone must be able to rotate freely around its axis so that rotations on a pull rope that is not free of twisting can be compensated for.

In order to reduce the form forces of the tube conveyor at the start, packaging strapping (yellow) was wrapped around the first 5 m of the belt (0.5 m each). If necessary, further binding straps can be attached to the tube belt. In the area of the pulleys and/or the flat-to-troughed and troughed-to-flat transition zones, a conventional, flat puller (clamp) is used. Here, the pulley of the system must be protected against a tensioned pull rope with special pulley protection attachments. The pulling-in table with adjustable idlers seats and finger idlers has a very special design.

The process of pulling in the belt was performed in “creep mode” with a speed of vP = 4…5 m/min using a pulling dozer, a stationary dozer and a cable idler pulley system. A special beam with cable idler pulleys was used to pull in the belt at high elevations of the system. At the head of the system, the belt was pulled in with the aid of the already installed take-up. At the same time, a sliding additive was continuously fed in at the pulling-in table in the overlapping zone of the tube belt in order to reduce friction forces between the rubber belt edges of the overlap.

Fig. 17 shows the pulling in process at ground level and at an elevated point in the system.

During the process of pulling in the belt, the camber angle of the idlers was adjusted to ensure that the belt overlaps remained in the desired twelve o’clock position for the top strand and in the six o’clock position for the bottom strand. As a rule, there were around 16 idler seats on which the idlers need to be realigned. If the position of the overlap changed, it was necessary to turn back the tube belt. The low ambient temperatures resulted in high belt tensions and also caused additional difficulties due to snow and ice on the idlers and belt.

Special attention was paid to the technology used for splicing of the different sections. By using a special splice design, it is ensured that the same tube belt characteristics (such as optimal transverse stiffness, belt overlap, etc.) found in undisturbed sections of the belt are also provided at splices. All splicing work was supervised by an experienced ContiTech-supervisor on site.

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