Technological mining solutions company TAKRAF India in August outlined the design features and challenges overcome in designing an overland conveyor – “a lifeline” for Indian aluminium producer Utkal Alumina International’s Utkal plant, which conveys bauxite ore from mine to plant
The successful completion of the roughly 19-km-long overland conveyor system marked yet another TAKRAF development milestone.
The contract with Utkal Alumina International called for an overland conveyor system to transport bauxite from the mines to a new 4.5-million-ton-a-year alumina plant. This also included the longest single-flight conveyor system to be installed to date within Indian territory.
The bauxite for Utkal Alumina is sourced entirely from the Baphlimali mines, some 16 km from the plant site in the village of Doragurha. Prior to being conveyed overland to the processing plant, the bauxite is crushed to a size of –150 mm, with the fixed crushing package having been provided in 2012 by a sister company, the then Bateman India.
Conveying Ore to the Plant
The scope of the overland conveyor project covered design, basic and detailed engineering, procurement and fabrication, right through to erection, which included civil and structural work, commissioning, performance guarantee test runs and handover of the 2 850 t/h conveyor system. An intermediate transfer point and unloading station, including silos and buildings, were also supplied with complete electrical and instrumentation systems.
The system design brief called for the primary crushed bauxite ore of size –150 mm to be fed from the mine end junction house, through a chute to an overland conveyor of 14.5 km. This overland conveyor, ending at an intermediate junction house, in turn feeds an overland conveyor of 13.6 km. The latter, shorter conveyor ends at a plant end junction house, feeding a 500 t material surge hopper using a two-way chute.
The overland system comprises 2 000 and 4 000 tensile strength steel cord conveyor belting, with a minimum belt safety factor at a steady state of >5.5, supported on a series of underslung-type idlers. These, in turn, are supported on a structural system made up of ground modules and gantries, with the overland conveyors routed partly along the ground and partly along an elevated portion.
Advanced Design and Engineeering
The execution of the project represented a groupwide effort, drawing on the global expertise of TAKRAF Group. Industry-leading software was used to maximise routing, equipment use and specifications. The conveyor design was supported by horizontal curve analysis and dynamic analysis to optimise the long-distance conveyor power and belt tensions. Global procurement was also followed to optimise costs but simultaneously source the most advanced and reliable components.
Initially, two technologies were considered, overland trough-belt conveying and cable belt, with the client selecting the former, owing to its many advantages in such inhospitable and remote terrain. In addition, almost all the components and spares for trough belts are available in India, with a very small percentage of imported components.
Designing for Complex Terrain
In its final configuration, the system’s two conveyors traverse a highly undulating and complex terrain. Dropping in total by 250 m over its course from material loading to discharge, the conveyor system passes through 11 branch rivers, the Ratachuan river, one forest stretch of nearly 470 m in length, a high voltage line crossing, 37 road crossings, a paddy field adjacent to the plant boundary with a stretch of about 2.5 km, eight hills and several villages. The elevated structures were provided with cage ladders spaced at about 150 m, and pile foundations were provided for the river crossing and one of the downhill crossings.
As a result of the topography, the conveyors were designed with head and tail drives, and multiple, very tight compound horizontal and vertical curves. In total, the conveyor system features ten right hand curves, four left hand curves and horizontal curve radii of 2 500 m across all locations but one: a critical zone on the shorter conveyor where the horizontal curve is 1 800 m.
This portion of the conveyor passes over a hill and through the plant boundary. The longer conveyor has a ground module and a graded portion. The overland gallery on both conveyors together features 403 straight sections, 154 right hand curves and 61 left hand curves, with a maximum gallery length or support interval of 49.5 m and standard gantry length of 27 m.
With an installed power of 6 × 850 kW and 2 × 850 kW, the conveyor system features six drives at the tail end and four at the head end on the longer conveyor, while the shorter conveyor has two drives at the head end only.
Each conveyor features a fail-safe hydraulic disc brake at the tail end. A take-up winch with capstan brake arrangement has been provided at the head end of both conveyors.
The intermediate transfer point between the two conveyors is located in hilly terrain so the conveyor drive and take-up areas are mounted on a portal steel structure. These lightweight but high-strength structures provide the design flexibility to accommodate the terrain. Advanced material flowability testing was used in the design to minimise risks such as environmental pollution and spillage, accelerated belt wear and blockages. To facilitate maintenance, approach roads and a mine road were made available all along the conveyor length, with the cage ladders provided on the elevated structures enabling ease of access.
Erection of the conveyor system was complicated by the requirement to minimise disturbance of the various villages through which the conveyor system passes, as well as the need to blast and excavate a suitable route.
With major equipment used for erection of the elevated structures, TAKRAF India placed particular focus on safety, strictly conforming both to TAKRAF’s global promise of Zero Harm and to the client’s safety protocols.
Performance guarantee testing was carried out over nearly one week, with the system consistently achieving its present capacity of 1 500 t/h. The successful completion of this project is testament to TAKRAF’s ability to employ its long-standing experience in designing conveyors to meet new challenges.