03.03.2011 | Autor / Editor: S. Zamorano / Marcel Dröttboom
There are several options for conveying material over long distances, such as conventional conveyor belts and pipe conveyors amongst others. The main factors that influence the selection of the best option for each case include capital and operational cost, environmental impact, maintainability, reliability and safety.
The use of continuous systems is usually driven by their lower operational cost, as opposed to discontinuous systems such as trucks, which present relatively lower capital and larger operational costs. Having said that, it must be clarified that in high capacity systems (above 4000 t/h) the capital cost of a truck fleet can be higher than the cost of a conveying system.
The comparison of the different conveying systems presented in this article is based on the transport of bulk solids on a continuous basis over a distance larger than 1000 metres. These parameters correspond to systems generally accepted as ‘long distance’ in mining applications. The factor that changes the financial evaluations is that in many cases trucks are leased under agreements were their capital cost is diluted during the length of the contract.
In general, the longer the distance and the higher the capacity, the more likely it is that a continuous system will be the most effective option. A recent article compares transport cost between trucks, railway and conveyors in India  for 5 million tonnes per year and indicates conveying as the most suitable alternative. On the other side of the spectrum, on distances over 100 kilometres the large cost associated with railway loading and unloading is also diluted enough to make the railway option the most likely winner on the 100 to 1000 kilometre range. This can change if rivers or lakes allow the use of barges, which have even lower operating cost than trains.
On longer distances, marine transport is the clear frontrunner. Many large deposits with relatively low price per tonne commodities are deemed not feasible if they are too far from the water. On the other hand, lower yield, higher mining cost deposits can be feasible if they are relatively close to marine transport hubs. But the illustrations provided in the following sections are aimed at the different types of continuous transport systems and the factors that influence their selection. As with any multi-variable problem, there are no universal answers or infallible ‘rules of thumb’ but rather several key factors that change according with each particular project.
Hydraulic transport is not considered in this article as the key driving elements of this technology are the availability of water, the solids dewatering system and the disposal of used water. These types of systems constitute a ‘process operation’ and not a simple transport one; therefore, they are not discussed here. The commonly used continuous conveying systems over long distances are:
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