A new Technology for Steep Incline High Capacity Open Pit Conveying
A new conveyor design is set to help reduce conventional heavy-duty truck traffic and the resulting high operating costs in open pit mines. This article presents the design and the initial findings of the feasibility study on the Chevron-Megapipe conveyor for a 350 m-deep open pit mine and a mass flow of 5000 t/h.
Andrey Minkin, Peter Börsting, Norbert Becker
(ed. WoMaMarcel - 04/7/2016)
DirectDrive System with Single-Pulley Drive
As the name Directdrive implies, the drive power required for this application is transmitted to the drive pulley directly without a gearbox instead of using a multiple gearbox / drive system configuration. The main components in this drive configuration are a multi-pole, slow-running synchronous motor which is powered by a cyclo converter or a voltage source converter.
This technology is the first step in meeting the requirements of the global mining industry with regard to higher transport performance without increasing the complexity of the conveyor drive technology. A Directdrive can replace 2, 3, or 4 conventional drives, as required. The use of Directdrives in the raw material industry is nothing new. This technology has been used for decades in hoisting plants (e.g. mine winders) where a high degree of safety is a must for people and the material conveyed. Further applications include DirectDrives for bucket-chain excavators, draglines, mills, and pumps.
Around five years ago, Siemens and Thyssenkrupp recognized this trend, and together developed a Directdrive for high-performance, conventional belt conveyors on the basis of the “Bandberg Prosper” downhill belt conveyor, which they had built together already in 1985. This conveyor is an underground conveyor that is 3.8 km in length and rises around 800 meters, used at RAG Prosper-Haniel.
Thanks to the simple and robust mechanical structure, and the integration of the drive pulley and motor to the Directdrive in combination with state of the art converter technology and with the well proven control unit, a drive solution was created that facilitates cost-effective operation of large belt conveyors. It fulfils the demand of the mining industry to realize large conveyor capacities as center distances and angles of inclination become larger and larger. The reference list in Fig. 6 underlines this trend very clearly.
The Directdrive is also the ideal drive for the Chevron-Megapipe belt conveyor, the of which is intended for angles of inclination of 30° to 45°. Only one drive pulley can be used because of the ribbed conveyor belt. For this reason, the drive must provide the entire drive power – consisting of an acceleration component, the steady-state component, which is made up of the load, friction, and, in this case, a considerable elevating component – on just one driven pulley.
In the family of three phase induction motors, and particularly in slow-running and bearingless applications, the synchronous motor has established itself as a robust and reliable element. This is thanks to the simple and robust stator structure, comparable to the asynchronous motor. Unlike the asynchronous motor, which requires an air gap as small as possible, the synchronous motor is able to operate with a much larger air gap with no deterioration in the power factor or efficiency. With the asynchronous motor, the excitation power required in the rotor is induced by the stator winding via the air gap in the rotor; the level of excitation power required is among other also a function of the air gap. By contrast, in the synchronous motor, the excitation current is supplied directly in the rotor by means of slip rings; this current is equal to only a few percent of the stator current compared to asynchronous motors. In addition, the synchronous motor’s larger air gap reduces the stiffness requirements to be met by the mechanical components, in particular the pulley shaft.
The complete drive train (Fig. 7a), consists of the flange for the disk brake, the first bearing, the pulley, the second bearing, the rotor flange equipped with the rotor, and the stator. The “Belt Conveyor Technology Controller” control system developed specially for belt conveyors (Fig. 7b) facilitates jerk-free starting.