High Angle Conveying
The Cost and Value of High Angle Conveying – 2012
Snap Lake and Victor Project
The indirect costs are real and significant. Such costs motivated DeBeers Canada, more than twenty years ago, to incorporate sandwich belt high angle conveyors into the planning of the recovery facilities of their two premier diamond mines, at Snap Lake, Northwest Territories, and at Victor Project, Northern Ontario, Canada.
Fig. 8 illustrates how the two Snake conveyors define the size of the recovery facilities, each conveying to the opposite side of the building. Conversely one can extrapolate how much larger the building would be if conventional conveying angles were use to achieve the required material lifts to the various crushing and screening stages of the recovery functions. Located in Canada’s Northwest Territories, near Yellow knife the facilities are routinely subjected, in winter, to frigid temperatures below minus 40 °C. This requires heating the large facilities throughout the winter at a great expense in natural gas. That expense is minimised as is the environmental footprint because of the shorter elevating distances possible with high angle conveyors that are suitable for the handling requirements.
The story at the DeBeers Victor Project is similar and represents a continuation of confidence in the sandwich belt high angle conveying systems. The Victor project is located in Northern Ontario, west of James Bay in the region of Attawapiskat. Like Snap Lake the climate is frigid in the winter and the facilities must be continuously heated. The arrangement at Victor is somewhat different than Snap Lake with twin Snake Conveyors (one for coarse pebble ore and the other for granular ore) travelling in the same direction from the secondary screen, at one end of the building, to the next screening and crushing stages at the other end. A third Snake unit, running in the perpendicular direction, transfers coarse pebble ore back to a crusher feeding conveyor. This unit in affect defines the width of the building.
The building is shorter and narrower because of the high angle conveyors, minimising the environmental foot print, the building costs and the fuel costs to heat the facilities in winter.
Snake Ship Loader at the Port of Adelaide, Australia
The indirect costs are also real and significant at the Port of Adelaide, NSW, Australia. There the savings are in dock costs. Fig. 10 shows the Snake Ship Loader manoeuvring easily within a narrow dock space. The height required to load the Panamax class ships could not be accomplished with the low angle of the conventional ship loaders. Extensive additional dock construction would be required with the conventional systems.
What is the Best Angle?
The best elevating profile depends largely on site and functional requirements. In general, the best solution is the most direct path from loading point A to discharge point B. The present study however reveals economic comparisons that would prompt a combination conventional conveyor along the ground to an elevating sandwich belt conveyor, even when ample space exists for a conventional conveyor solution. This can be a sandwich belt conveyor with a long approaching bottom belt. In general, loading point A and discharge point B will be located for the best use of space. The total investment comparison reveals large differences, at the very high lifts, between the conventional and the sandwich belt conveyors but not among the sandwich belt systems. At the highest lift, a 60 degree DSI Snake profile has approximately 10 percent higher investment than the 90 degree (vertical) DSI Snake. A 45 degree profile has approximately 18 percent higher investment.
Operational considerations might warrant the higher investment in a 60 degree system, or even a 45 degree system. Such considerations are (1) System clean-up and (2) System access.
Sandwich belt systems at any angle can be designed spillage free. Minor material carry back can occur due to none perfect belt scraping and even the occasional leakage, due to poor belt alignment and other aggravations. The magnitude of the accumulation is far less important than its nature and consequence. At a vertical system such carry back does not have a clear path away from the equipment and tends to accumulate progressively on the rolling equipment. Periodic cleanup is required, typically by high pressure wash-down. Wash-down water at the outer parts of the wing rolls has contaminated the bearings and caused frequent premature bearing failures requiring high rates of roll replacement. No such phenomenon has occurred at sandwich belt conveyors of any incline less than vertical. Any carry back tends to fall away clear of the rolling equipment and build up is not progressive towards the bottom.
Access to the equipment is important in any case. Many specifications require access by stairway (vertical ladders are not allowed). The maximum stairway slope, according to architectural standards, is 50 degrees. At higher angles step ladders (51 to 70 degrees) or ladders (71 to 90 degrees) must be used, with safety lines or safety cages and landings. The cost of stair towers can sometimes approach the cost of the sandwich conveyor systems.
In view of the modest premium shown in Fig. 5 and consideration 1 (material carry back), it is this writer’s opinion that the 60 degree DSI Snake solution with access by ladders and landings will prove very economical and most reliable. Furthermore, if a stairway is required then the additional premium show in Fig. 5 may be warranted making the preferred conveying angle less than 50 degrees.
Many cases of limited space will warrant vertical systems. It is not our intent to discourage these as the cited problems can be resolved by conscientious design and clean-up procedure.
Complete rationalisation of the sandwich belt conveyor technology in the conventional conveyor technology was achieved in the period 1979 to 1982. Many successful sandwich belt steep and vertical conveyors have been built in compliance with that rationalisation and have demonstrated the performance characteristics of conventional conveyors. The DSI Snake is the only high volume sandwich belt system to utilise all and only conventional conveyor equipment and componentry. Material hugging pressure is induced by exploiting the inherent belt tensions on an engineered alternately curving (snaking) profile. An investment comparison shows great savings when conveying to high silos with DSI Snake sandwich belt conveyors at various angles from 45° to 90° (vertical). To date, sandwich belt conveyors have not been widely recognised as mainstream technology despite the many successful systems and the demonstrated economies. There is no basis for reluctance in the wide use of sandwich belt conveyor systems. Such systems should be embraced as mainstream technology and exploited to lower the costs of silo loading and other applications.
This article has focused on the cost of elevating materials to silos. High angle conveying is equally advantageous in elevating to other covered storage systems such as storage barns and domes. Dome type structures for covered storage have gained prominence and use. The DSI Snake profile is ideal for continuously elevating materials to the top of such domes sharing a compatible curving geometry. Enroute to discharge, at the top of the Dome, a DSI Snake system will impart a gentle distribution of structural loads onto the Dome structure. The combination will be an aesthetically pleasing, uncluttered system.
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