Screens & Feeders

The case for conveyor-based haulage in the quarry industry

Two years. That?s the payback period for a conveyor system compared with trucks in a typical quarry operation, eg half a million tonnes per year, haul distance of one kilometre, zero per cent gradient (being kind to trucks!).

The economic benefits of conveyors versus trucks in quarry operations are well established, and given that many quarry operations in Australia are small proprietary and/or family-run businesses, the arguments are starting to look very compelling.

As we all know, the quarrying industry is highly competitive, whether you are a large multinational operator or a small private operation, with very thin margins for finished product rock.

Today, any operation looking at replacing its truck fleet needs to not only get quotes from competing truck suppliers, but also from conveyor system original equipment manufacturers (OEMs). The interesting thing about the quarrying industry is that it?s actually better suited to conveyor-based haulage than the mining industry.

The reason for this is that capital investment increases in direct proportion to distance with conveyors; the shorter the distance, the faster the payback time.

Take my opening example of a two-year payback on a 500,000-tonne operation with 1km haul roads. In round numbers, the cost of trucking material from pit to point of sale stockpile is 35 cents a tonne. For a conveyor, it?s just 12 cents a tonne.

Now, let?s go to the opposite extreme. Take that same amount of material over a 5km distance, which is pretty extreme for quarrying, then the payback jumps from two years to 16 years; the cost for trucking is 83 cents per tonne and the cost for conveying is 76 cents per tonne.

That?s still at zero per cent grade, remember. But if we take a more likely operation, an eight per cent gradient, moving one million tonnes over that 5km, you are talking about $1.45 a tonne for trucking versus 55 cents a tonne for conveying.

As soon as you add in any gradient, conveying becomes far more economically attractive than truck haulage. Let?s look at some of the reasons for this.

Conveyors are powered by electrical motors; trucks are diesel powered. Electric motors are more efficient than a diesel motor will ever be.
With a diesel motor, less than one per cent of the energy, in terms of fuel burnt, is actually used to turn the wheel; the rest of it is lost in drives, transmissions and emissions.

In contrast, an electric motor uses everything that it is given to power whatever it is moving ? in this case, a conveyor belt.
From an energy efficiency point of view, it is more effective to have an electric motor over a diesel motor any day of the year. And with a conveyor, you are not making an empty return trip back to the face.

Consider how much steel you move when you return from delivering the product or material with an empty truck. A truck?s tare weight is significant, and having to push that along a roadway, uphill, downhill, or along the flat ? loaded or empty ? is a very inefficient use of energy.

In addition to fuel, you have the humble tyre, that little round black thing underneath vehicles, which is becoming more expensive, and more difficult to obtain.

Another issue is people. Conveyors are controlled from a single point, a control room at the plant, or remote to the site, eg in a city office.
It doesn?t matter where it is, because that is the commercially available way of controlling conveyors today.

Trucks, however, are not yet commercially automated. You have to have a steering wheel attendant in every single one, and people, particularly in Australia, are not cheap.

So, apart from the person who has to be on the machine per shift, there is the absenteeism that goes with that as well, depending on how many vehicles you have to man up, along with all the support equipment, eg graders, water carts, dozers and so on.


Now let?s look at other environmental factors which will increasingly impact on costs.

First, let?s take water. In contrast to suppressing dust on haul roads associated with a quarry, conveying structures simply don?t need water for dust suppression, other than at transfer points. The fewer transfer points you have, the less water you use.

In round numbers, conveyors use 50 per cent less water than you would require for an equivalent trucking operation at a quarry. And that?s potentially a huge amount of water and it is our most precious resource.

Then there?s noise. First, it?s important to select good quality rollers beneath the conveyor belt. Cheap off the shelf rollers will do the job and carry the conveyor belt for a period of time, but they can be up to 20 dBL noisier. But with the right rollers, the noise is somewhere between 35 and 40 per cent less for a conveying operation than it is for a truck hauling operation ? a very important factor if you have a quarry close to built-up areas.

Another issue is dust. Even if you don?t fully encapsulate a conveyor, dust is 50 per cent less than an equivalent trucking operation.

And if you fully encapsulate the conveyor, which many operators are doing, even in Third World countries (though not widespread here in Australia yet), you can all but eliminate dust as an issue from a quarry operation.

A big argument against conveyors is that they are inflexible while trucks are 100 per cent flexible. My counter-argument is that ?flexibility? is just a word for ?bad planning?.

With conveyors, you must follow the quarry plan. Generally speaking, quarries are long-life assets, which in the majority of cases would suit good planning. If you don?t, you will come unstuck and everything will fall apart in terms of getting what you expect as performance out of the system.

With trucking, you can decide to go to any face at any point in the quarry, at any point of the day, because you can. That means the power is with the leader of a particular shift, normally a foreman or a supervisor, who?s in charge of manning up the machines and allocating people to those machines.

In a conveying operation, the power goes to the planning person, often someone in the head office, and a lot of operational people don?t like that. So, that is another issue to overcome; the inertia for no change is quite high because it affects the guys at the face.

The other issue with conveying versus a truck is that you can put any sized rock in a truck that you want, whereas with a conveyor, you must crush it first to fit it on the belt.

Of course, if the material you are digging is conveyable already ? eg in a sand and gravel operation ? it just needs to go through a scalper, screen or grizzly to remove the big stuff.

Over the past few decades, European quarries have been forced to be far more sensitive to multiple land-use needs. Quarrying using low noise idlers (Sandvik?s HM150 for example) under conveyors now form part of the urban landscape in harmony with those who need quarrying to live.

Doug Turnbull is a principal mining engineer with Sandvik Mining and Construction.

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