India's first Elevated, Triangulated Gallery Overland Conveyor System

Overland Conveyor System

India's first Elevated, Triangulated Gallery Overland Conveyor System

In 2010 the Adani Group broke ground on a new solid cargo handing port with the installation of a unique conveyor system that moves up to 6000 t/h to a rail loading silo approx. 4.75 kilometres from the port. These conveyors are supported by lightweight triangular galleries that do not include walkways and are maintained with a motorised trolley.
(ed. WoMaMarcel - 17/7/2014)
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High Speed Conveying

Operating SC-1A and SC-2A at 7.5 m/s reduced the capital expense of the system and reduced the belt tension in SC-1A allowing the conveyor to bend through tighter horizontal curves. However, operating these conveyors at high speeds reduces the life of their belts compared to identical belts running slower. This is because most belt wear occurs in the loading zone and, all else being equal, a high speed belt sees the loading zone more often than a low speed belt. Since SC-3 is much shorter than SC-1A and SC-2A we designed it to operate at 4 m/s to reduce the frequency of belt replacement on this conveyor.

Since the speed of SC-3 is 4 m/s instead of 7.5 m/s, the belt width of SC-3 is 2200 mm – far wider than the 1600 mm wide belts installed on SC-1A and SC-2A. In addition to the increased width, the weight of the SC-3 belt is 59 kg/m, almost 50% more than the weight of the SC-1A and SC-2A belts which weigh 42 kg/m. On SC-3 the linear weight of material on the belt is 476 kg/m whereas on SC-1A and SC-2A the increased speed reduced the linear weight of material on these belts to 264 kg/m. Reduced linear weight reduces the belt tension necessary to control sag, reduces the indentation losses, and reduces the tension required to lift the material. This reduces overall belt tension which improves belt tracking in the horizontal curves. The narrower belt also shortened the idler roll length from 816 to 594 mm reducing the weight and cost of the idlers.

The narrow belt reduced the width of the elevated gallery, cutting the weight, strength and space requirements for the gallery. These reductions reduce the capital investment.

However, the tolerances allowed for high speed conveyor components are substantially tighter than their equivalent low speed counterparts. In particular, to reduce vibration and noise and extend idler life, CDI recommends that idler TIR not exceed 0.4 mm at 7.5 m/s.

Only a handful of companies in the world can consistently manufacture idlers with 0. mm TIR. The typical welded end disk idler assembly usually fails to meet spec because the welding process warps the shell. Several leading edge manufacturers have approached the problem by designing press fit end disks. This is the approach Elecon chose when they designed a special idler roll just for Dahej (Fig. 3). The result was an idler with consist low TIR.

Tubular Triangular Gallery

The tubular triangular elevated conveyor gallery used at Dahej was not a new concept [3]. In his 2001 paper Stapples estimated that the tubular conveyor gallery is about 40% cheaper than the widely used box gallery style conveyor and recommended that all elevated overland conveyors adopt this design. However, the design of such galleries is not trivial.

Prior to working on the Dahej system, CDI designed two triangular gallery supported conveyors in Nigeria. CDI and Exclusive Technical Service (now part of Sandvik) collaborated on their first triangular gallery conveyor for the Dangote Cement plant in Nigeria [4]. Later, in 2009, CDI worked with Zigong Industrial Machinery in China to design and install a second triangular gallery conveyor at Dangote parallel to the first conveyor. In both of these cases CDI provided only GA drawings.

At Dahej, CDI was responsible for all detail design drawings of the conveyor gallery. This was the first time CDI created complete detail drawing of the triangular galleries. It was also PMC’s first time constructing triangular galleries. Our engineering teams needed to work closely to create a practical design.

Meeting the tight structural tolerances specified by CDI to minimize vibration on the high speed conveyor proved a significant challenge for PMC particularly in horizontal galleries. Precise alignment was further complicated by the introduction of camber. Each 36 m gallery was constructed from three 12 m modules. Precisely fabricated wedges were butt welded between these modules to create a single 36 m long cambered gallery. Ultimately PMC designed a jig system to control the conveyor alignment to within the straight and horizontally curved galleries. The jig controlled the belt centerline to within +/- 1 mm.

PMC fabricated all galleries and bents in a laydown yard at the port (Fig. 4). The gallery design could not accommodate training idlers and PMC engineers recognized that field adjustment of the idlers during commissioning would be difficult. To avoid belt training issues, the locations of the idlers were controlled to within 1 mm. In the horizontal curves a custom idler jig was used to position the idlers (Fig. 5). The work paid off as no idler adjustments were required during commissioning.

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