coaltrans asia 2003

7/30/2019 Coaltrans Asia 2003

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The use of In-Pit crushing and conveying methods to

significantly reduce transportation costs by truck

Detlev L. Schröder

ThyssenKrupp Foerdertechnik GmbH / Essen / Germany

Open-pit mining is where overburden is removed in order to recover the coal or other minerals

which are underneath.

The final coal or mineral production is a dependent on the amount of overburden to be removed

and the depth of the overburden determines the amount to be handled.

In the majority of the open-pit mines around the world, the ratio between overburden and coal or

mineral turns out to be unfavourable for the coal or mineral, i.e. for one single unit of coal or mineral,

several units of overburden have to be removed. As a result, in most cases, the planning and

operation of an open pit are primarily determined by the removal, transport, and dumping of the

overburden. Over the years, both continuous and discontinuous working methods have been

employed in open pits.

Operations in coal, mineral, or overburden can be split into continuous and discontinuous mining,

transport, and dumping. The application of continuous mining, transport and spreading equipmentdepends on the geological and climatic conditions prevailing in a specific mine. The main criterion to

select the most suitable mining method is the material to be dug. The mechanical properties of the

material, i.e. compressive and tensile strength, (toughness), moisture content, abrasiveness, etc.,

have to be considered. The most important property influencing the selection of the digging method is

the compressive strength.

It should also be noted that the geological structure of the material may complicate the use of a

particular mining method. For instance, it is often unprofitable to dig soft material with embedded

boulders or hard interseams using bucketwheel excavators, since the non-homogenous material

causes frequent interruptions to the continuous operation.

On the other hand, it is also obvious that it is not profitable to dig homogenous material withdiscontinuously working excavators, since this type of material is best dug by continuously working

excavators.

Selecting the best methods of transport and dumping is not necessarily affected by the same

factors as for the digging operation. The main criteria here is cost efficiency.

Feasibility studies have been prepared to determine the proper working method and equipment for

a specific open-pit mine.

ThyssenKrupp has built the first In-Pit crusher in 1956. This crusher was for lime stone and fully

mobile, mounted on crawlers.

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The technology for In-Pit crushing, continuous hauling and spreading the overburden has become

more and more important for open pit mining projects, due to their excellent performance.

For high outputs, In-Pit crushers have been engineered to rest on pontoons to save investment

costs. These In-Pit crushers are called semi-mobile because they can be relocated from time to time,

according to the progress of the open-pit mine.

Figure 1 : Large Semi-Mobile In-Pit Crusher for

overburden in a coal mine

The blasted material is dug by a shovel, loaded

onto trucks and then transported to the crusher,

with the distance to be travelled by truck being kept

as short as possible. The crushing plants are

located at the deepest possible point of the open-

cast mine. Therefore, heavy trucks loaded with

overburden have to travel downwards - not upwards

- to feed the crushing plants and then, empty, travel

back upwards to be re-loaded.

Due to this mode of operation, the number of

heavy trucks can be cut to a minimum, since the

transport of overburden is carried out close to the

place of mining and material transfer, i.e. near to

the loading shovels and the crushing plants. This

arrangement also results in cost savings, with lower fuel consumption and less wear.

Depending on the progress in the mine, the crusher and the downstream belt conveyor system

have to follow the mining face accordingly. There is no need to adapt the size of the crusher to the

capacity of the shovel, as the required production figure for the open-cast mine decides the size of the

crusher.

ThyssenKrupp Fördertechnik has built the largest In-Pit crushing system in the world, which has a

throughput of up to 10,000 tons per hour.

Figure 2: Large Semi-Mobile In-Pit

Crusher in a copper mine fed by two apron

feeders

In order to obtain this high throughput,

the crusher is equipped with two apron

feeder conveyors.

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Again, depending on progress in the mine, the continuous mining and transporting systems have to

follow the mining or dumping faces and, to achieve this, ThyssenKrupp Fördertechnik have developed

heavy-load transport crawlers, which are being used throughout the world.

Figure 3: Transport Crawler for loads of

200 t and 750 t

The series of transport crawlers

engineered by ThyssenKrupp

Fördertechnik can carry loads from 200

to 1,200 tons.

Heavy, semi-mobile crushing plants are designed in such a manner that they can be relocated by 2

or 3 partial transports to keep the sizes of the transport crawlers at an optimum level.

The first large In-Pit crushing, continuous haulage and spreading system with high capacity for

overburden was commissioned in 1984 in the open-pit mine Mae Moh of the Thai Electricity

Commission EGAT in Northern Thailand.

Figure 4: In-Pit Crusher at Mae Moh

Mine

The development of In-Pit crushers for open pit mines with very high outputs in a profitable working

manner was a dynamic and progressive process, finally culminating in ThyssenKrupp Fördertechnik’s

In-Pit crushing systems with a capacity of up to 10,000 tons per hour of ore and weathered rock.

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Figure 5 : In-Pit crusher at Syncrude Mine

The largest double roll crusher currently in

operation is in an oilsand open-pit mine at Fort

McMurray at Syncrude Canada Ltd. This was

supplied by ThyssenKrupp Fördertechnik and has

a capacity of 5,500 t/h.

In 1997, two more double roll In-Pit crushers

from ThyssenKrupp Fördertechnik, each with a

capacity of 7,500 t/h for oilsand, were installed at

the Syncrude open-pit mine.

As mentioned before the main amount of material to be handled in the mine is always the

overburden and overburden needs to be deposited again either on an outside dump or inside the mine

behind the mining area.

Figure 6 shows a typically very large open-pit mine with a continuous round-the-pit haulage

system.

Figure 6: Continuous round-the-pit haulage

system.

The overburden or the waste material has to be

spread outside the opening of the mine, which

requires a high dump operation from the spreader.

As the material is transported from near the

bottom of the mine to the top and is also dumped

up high by the spreader, this is the most

expensive operation.

Figure 7: Spreader in high dump operation

outside the open-pit mine.

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When the coal or mineral has been excavated and hauled out of the mine, the big hole created can

be refilled with the waste from the excavating side of the mine. The spreader is then used for In-Pit

mine dumping - mainly in low dump operation. However, even in this phase, the overburden has to be

hauled to a higher level, mainly due to the swell factor of the excavated waste material.

Figure 8: Spreader in low dump operation in the

open-pit mine.

Figures 9 and 10 show the large open pit mines of Chuquicamata and Escondida in Chile. These

are circular copper ore mines where the copper is covered by a very hard material

Figure 9: Chuquicamata mine - Chile

Before installation of the conveyor the waste

material was transported along the circular ramps:

a very expensive operation.Conveyor line

Figure 10: In-Pit crushing continuous haulage

and spreading system at Escondida mine/Chile

ThyssenKrupp Fördertechnik has supplied in

the last decades In-Pit crushing continuous

haulage and spreading systems for both of these

mines, which have drastically reduced the costs of operation.

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The main reason for installing In-Pit crushing systems (IPC-systems) is, in all cases, economy.

It is the conveyor which makes the continuously operating mining equipment economical. While

the investment cost of a belt conveyor system is higher than the cost of a truck fleet, the lower

operating costs very soon compensate for this higher initial investment.

The next figure illustrates the cost advantageous of the belt conveyor.

Conveyors as key element of continuosly operating systems

Wear and Spearparts :

Tyres : yearly cost in relation to investment cost : approx. 5 – 1 0 %

Belts : yearly cost in relation to investment cost : approx. 1 - 2 %

Operators wages : trucks have approx. three times higher costs

Energy requirement :Truck 85 sht :

•Payload : = 77 t

•Weight of truck : = 58 t

•Service weight : 2 x 58 t + 77 t : = 193 t

( to be moved empty and full in both directions )

•relation of service weight to payload : 193 / 77 : = 2.5

Conveyor B 1800 mm :

•material weight per m : = 620 kg

( trough 40 °, angle 10 °, s.g.1.6 t/m³ )•mass of rotating and moved parts : = 154 kg

( empty belt, medium quality )

•total mass in operation : 620 + 154 : = 774 kg/m

•relation of total masses to payload : 774 / 620 : = 1.25

Figure 11 : Conveyors within a continuously operating system

Expenditure for maintenance costs and wages, as well as the lower energy costs, are decisive for

the selection of a belt conveyor system.

An 85 t truck has a payload of 77 t and a dead weight of approx. 58 t. One cycle means that the

truck has to transport twice its dead weight of 58 t and once its pay load of 77 t., a total of 193 t. The

ratio of pay load to dead load is 193 to 77 = 2.5.

When using a belt conveyor system, 1 m. of belt transports 620 kg of material. The mass rotating

and moving parts, belt, idlers, pulleys, amount to 154 kg per meter, giving the ratio 744 kg to 620 kg =

1.25.

A comparison of the moving parts shows that, for a truck, more dead load has to be transported

than for a belt conveyor system. A further consideration is that the truck tyres have considerably

higher rolling resistance than those created on the belt conveyor system. Rolling resistances, even on

well serviced roads, are seldom lower than 2 %. If roads are badly maintained and climatic conditions

are unfavorable, the rolling resistance quickly increases to 4 - 5 %, i.e. in relation to a lifting height of

100 m., the material has to be lifted by an additional 5 m.

This proves the considerably lower energy requirement of belt conveyors compared to truck

operation.

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Looking at this calculation, it is clear that the most economic IPC system will be a continuously

operating system without any trucks - unfortunately, a situation which can rarely be achieved because

of restraints caused by the material deposit and the mining operation itself. Fully mobile crushing

plants which follow directly behind the shovel can only operate if it is possible to have long straight

mining faces with mobile face conveyors. Last year, a large fully mobile crusher went into operation in

the Goonyella mine in Australia – and in another two years’ time, a system with three fully mobile

crushing plants operating on one face conveyor will commence operation in Uzbekistan’s Angrenskij

mine. ThyssenKrupp have recently signed the order for the Angrenskij system and two drawings

illustrating the system are shown below:

Figure 12 : Schematic drawing of operation of fully mobile crushing plants in Uzbekistan

The crusher itself is patented and will look like the one in the picture below :

Figure 13 : Fully mobile crushing double roll crushing plant

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There are not many geological structures in Indonesian ore and coal mines which can give long

straight mining faces. In most cases, the coal mines operate steep seams of between 30 and 90

degrees inclination, which are mined in the direction of strike. Ore mines, such as Freeport Indonesia,

are normally deepened and widened in all directions.

Figure 14 : Development of the Grassberg mine of Freeport Indonesia

In these conditions, it is mainly semi-mobile crushing plants which can be used.

The following is an example cost calculation, which has been based on a typical situation in

Indonesia. The following picture has been specially created to illustrate a typical coal mine in

Kalimantan.

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RL – 100m

RL – 160m

OverburdenCrushers

Outside dump

Coal Crushers

Stockpile /Loading station

Figure 16 : Exemplary coal mine with In-Pit Crushing systems for coal and overburden

The mine currently operates two main seams and multiple smaller ones in between. It started at the

outcrop and, over the past few years, has been developed in the strike direction and deepened at the

same time. The overburden is deposited at an outside dump and the coal is transported to a stockpile

and loading facility which is close by. In the future, the main mining operation will commence in a

northerly direction and an In-Pit dump will be developed. Two possible applications for In-pit-Crushing

systems are shown in this picture.

On the one side is the overburden dump, which is fed by two large semi-mobile crushing plants at

the east side of the pit. On the other side there are two coal crushing plants which load onto a ramp

conveyor system leading to the stockpile / loading area.

A typical crusher for this application is shown in fig. 4 and a typical stockpile / loading facility would

look as follows :

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Stock ile for 200 000 t

Truckloadin silo

Figure 16 : Typical stockpile and truck loading facility

This coal handling system will be able to handle approx. 20 million tonnes of coal per year, which

is large both for Indonesia and worldwide.

Figure 17 : Equipment and basic data for cost calculation

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The table in figure 17 gives an overview of the equipment and the figures which are used to

produce a cost calculation :

Figure 18 : Split up of costs for IPC and truck transport systems

The big difference in the total handling costs mainly result from the low costs for the conveyor

transport, as explained above.

Overall, the difference in operating costs is high enough to give a payback period of approx. 2

years.

Figure 19 : Net present cost cashflow curve for IPC and truck systems

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CONCLUSION

The larger and deeper open-pit mines are, the more profitable is the technology of continuous

haulage mining systems.

For hard material, mixed mining and haulage systems were developed in the 1960s, i.e. blasting

the material, excavating it with shovels and then loading it into the hopper of a crusher which sizes the

material down sufficiently to suit the connected belt-conveyor, forming the continuous haulage system.

Thus the ”IN-PIT CRUSHING, CONTINUOUS HAULAGE, AND SPREADING SYSTEMS ” have

been developed.

This technology has been developed from starting capacities achieved 25 years ago of 300 to 700

t/h, and is operating successfully, with major benefits for the user. The biggest In-Pit crushing system

in the world, comprising an In-Pit crusher with a capacity of up to 10,000 t/h, was built by

ThyssenKrupp Fördertechnik.

The major advantages of In-Pit crushing continuous haulage systems against non-continuous truck

transport are:

♦ lower investment cost for very high capacities

♦ powered by electric energy instead of fuel

♦ shorter haulage distance due to steeper ramps of the haulage route out of the mine

♦ lower consumption of spare parts

♦ longer lifetime, up to 50 - 60 years of operation

♦ lower maintenance cost

♦ highly reduced road preparation

♦ less auxiliary equipment♦ fewer movements during operation

♦ major environmental advantages due to

• electrically driven motors versus burned fuel

• prevention of dust on the haulage route

• in total less consumption of energy and consumables

ThyssenKrupp Fördertechnik's In-Pit crushing, continuous haulage and spreading systems for very

large open-pit mines with high outputs are, in the long run, superior to all other known technologies in

respect of profitability and environmental aspects.

ThyssenKrupp Fördertechnik’s In-Pit crushing continuous haulage and spreading systems inIndonesia, China, Chile, Brazil, USA, Canada, South Africa, Zaire, Thailand, Australia, Europe etc.

prove that this technology is suitable for large open-pit mines and operates at high performance levels

with a very long service life under any climatic conditions.

THE IN-PIT CRUSHING, CONTINUOUS HAULAGE, AND SPREADING SYSTEMS ARE THE

SUPERIOR TECHNOLOGY FOR LARGE OPEN PIT MINES WITH HIGH OUTPUTS.

coaltrans asia 2003

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