the coal handbook: towards cleaner production || coal conveying

© Woodhead Publishing Limited, 2013

628

19 Coal conveying

G. L. JAMES, Calibre Minerva, Australia

DOI: 10.1533/9780857097309.3.628

Abstract : This chapter mainly discusses the design and operation of conventional trough belt conveyors in mining applications. There are also references to some of the emerging alternatives to troughed belts. The chapter looks at some of the important considerations in the design of large conveyor systems. Finally, integrated crushing and handling systems that receive material from haul trucks and feed the conveyor systems are also reviewed.

Key terms: coal, transport, troughed, belt, conveyor.

19.1 Introduction to belt conveyor technology

This chapter deals with conveying systems commonly employed for bulk

material transportation, and covers aspects of their design and some of the

key operational features.

The chapter is not intended to be a comprehensive text on the design

details of troughed belt conveyors, or a review of the alternative conveying

technologies, but covers details that are important to large conveyor designs

that are not commonly found in the standard texts. For more comprehen-

sive details on the design of conveyors, the reader is directed to Conveyor

Equipment Manufacturers Association (CEMA) (2005), DIN22101 (2000),

published papers and design manuals produced by the equipment supply

companies, and also to the specifi c mining company standards, specifi cations

and detail drawings.

A troughed belt conveyor consists of a wide belt typically running on

three idler rolls. The outer wing rollers are sloped upwards to form the

trough shape. The troughed belt then travels over the idler sets to trans-

port the load. A conventional troughed belt conveyor has the following

components:

Idlers. These are rollers with bearings that form a trough shape for the •

belting. The idler sets are typically spaced out between one and three

metres.

Coal conveying 629


Belting. The belting, which carries the load, rests on the idler rollers. •

Figure 19.1 shows the typical arrangement of the idlers supporting the

belt. The belt is pulled around in a loop with tension/power supplied by

drive pulley(s).

Drive. Figures 19.2 and 19.3 show the pulleys and drives used to move •

the belt.

Pulleys. The conveyor belt forms a loop. The carry side transports the •

load and the return side allows continuous cycling of the belt. The pul-

leys allow the belt to change direction at the loading and discharge ends,

as well as direction changes on the return side.

Transfer chute. This is where the material is loaded onto or discharged •

from the belt. See Fig. 19.4.

Conveyor take-up system. The take-up applies tension to the belt to •

limit the sag between the idlers and prevent slip at the drive pulley. The

take-up pulley moves to tension the belt. Take-up systems are typically

gravity, but can be winch, screw or hydraulic jack. The typical arrange-

ment has a pulley mounted on a trolley. The trolley is connected to a

gravity mass in a tower via a cable. See Fig. 19.5.

19.1 Belt supported by idlers.

630 The coal handbook


19.3 Conveyor drives.

19.2 Conveyor Drive Pulleys.

Coal conveying 631


19.5 Conveyor takeup.

19.4 Conveyor discharge chute.



19.1.1 Trends in conveyor design

Conventional troughed belts

The long-term trend for belt conveyors continues to be longer, faster, and

higher capacity. The highest capacity conveyors include the 40 000 tph ×

3200 mm wide belts on the Rheinbraun bucket-wheel excavators. The lon-

gest single fl ight conventional troughed conveyors include the 17 000 m

long 1000 tph conveyor for transporting limestone that crosses the bor-

der between India and Bangladesh. More recently, an Australian company,

Wesfarmers, commissioned a 20.3 kM 2500 tph × 1200 mm wide × 7.5 m/s

coal conveyor at Curragh North Queensland mine. This was designed by

Conveyor Dynamics Incorporated. The installed power is 4250 kW (4 ×

1000 kW and 1 × 250 kW). There are 2 × 1000 kW tripper drives located at

the mid position.

The use of the tripper drive concept is an extension of the underground

mine intermediate drive arrangements that have been used for many years.

These intermediate power injection designs have included piggyback

booster belts, powered rollers, and tripper drives. Torsten (1982) described

the mathematics of intermediate drive systems and how they could be used

to minimise the tensions around horizontal curves. Weigel (1982) described

a similar system used in a limestone mine. A more unusual idea, called the

Ozomin drive, used the return belt to drive a section of the carry belt. This

allowed the drive station to remain at the end of the conveyor. Some of the

power from the drive would be shifted to a point along the carry belt, via

the return belt.

The use of high speeds (for example, above 6 m/s), low energy rubbers and

intermediate drives will allow longer and higher capacity conveyors. There

are barriers emerging that will challenge this trend. These include noise, dust

emissions, belt pressures on idler rolls, and lubricant loss. Conveyor systems,

mines and populated areas are moving closer together, and environmental

standards are changing and becoming more rigorous. There are direct relation-

ships between belt speed, belt and idler roll surface geometry, noise, and dust

levels. Technology may allow, say, a 9 m/s belt, but night-time noise restrictions

at nearby homes may limit the speed to approximately half this value.

Non-conventional conveyors

In this context, non-conventional means non-troughed. An emerging tech-

nology in belt conveying is the Doppelmayr Ropecon system. This system

has applications in rough terrain regions and environmentally sensitive zones.

The conveyor can pass over these regions at a high level, as the conveyor is

supported by cables between pylons like a suspended cable bridge. The span

Coal conveying 633


between the pylons can be up to 1500 m. The conveyor is a box-type fl at belt

with fl exible vertical concertina side walls. The belt is supported by axles and

wheels that travel on the suspended cables. That means the items that require

maintenance, i.e. the wheels and bearings, travel around the system and back

to a convenient point where the work can be safely done. The longest length

to date is approx. 3500 m, and highest capacity approx. 3500 tph.

Other non-conventional conveyors include High Angle Conveyor

(HAC), Cable Belt, Pipe-types, Rail conveyor, Aerial ropeways, Sicon and

Aerobelt.

The HAC system uses an additional conveyor belt to create a sandwich.

The upper belt applies pressure to hold the material in place as it moves up

the steep incline.

Cable Belt conveyors use a cross-reinforced belt supported by cables on

each side. The belt is almost fl at, with a slight curve, so the supporting belt is

separated from the tension member. (A conventional trough conveyor has

the tension member within the belt.) The cables are supported by wheels

spaced out several metres apart. The longest length is 31 kM + 20 kM and

capacities around 4000 tph are located at a bauxite mine, Worsley Alumina

Pty Ltd Western Australia.

Pipe conveyors are similar to a conventional trough conveyor, except the

belt is wider so that it can wrap up into a circular or pipe shape. The idler

rollers, say six in a hexagonal pattern, hold the belt in the pipe shape. Pipe

conveyors can bend around smaller vertical and horizontal curves than con-

ventional troughed belt conveyors. Pipe conveyors are good for dusty mate-

rials and conveying in and around process plants. The longest lengths are

> 8 kM with capacities near 4000 tph.

The Rail conveyor is being developed at the University of Newcastle,

Australia. The system has a troughed belt, support carriages with wheels

that run on a railway track.

Aerial ropeways come in a couple of forms. There is the classic bucket

hanging from a rope (like the chairs on a ski lift). The bucket would hold

several cubic metres of material. Doppelmayr and others supply this type

of machine for low volumes over diffi cult or complex routes. Aerobelt con-

veyors are like conventional troughed belt conveyors, except the belt is sup-

ported by a cushion of air instead of idlers. There is an air plenum in the

shape of a trough with many holes to allow the air to leak out and form the

cushion. The longest length is near 800 m, and the speeds range up to 7 m/s.

The maximum capacity is near 400 tph.

The Sicon conveyor has the belt hanging like a teardrop-shaped pouch,

with the tension cables on the edge. These conveyors are good for dusty

materials and conveying in and around process plants. The highest capacity

is around 1000 tph and longest length 2.5 km.



19.2 Belt selection

Belt selection is critical to the reliability of the conveyor system.

19.2.1 Strength for tension

The technology of belting has been improving over time. Premature failures,

manufacturing, operating costs, and the need for stronger belts has forced the

change. A change to self-extinguishing fi re resistant belting in Germany in

the 1970s led to a series of early splice failures. The University of Hannover

developed a belt splice fatigue testing machine and ran a crash programme

to investigate and solve the problem. Flebbe (1988) describes the machine

fi rst being used at the University in 1975. Contitech had a similar machine –

see Alles (1982) for details of the machine and investigations of time strength

behaviour of belting. The University machine has been in operation since

1975. The research at the University with the support of the local belting

suppliers, such as Contitech and others, led to changes to the DIN standards

(Deutsches Institut Fur Normung E.V. the German national standard).

The approach adopted by DIN and Hannover University has been to

focus on the actual tensions across the belt width, and the fatigue strength

of the belt carcass or splice, the ratio giving the safety factor. The com-

mon, but perhaps less preferred, approach is to compare the highest aver-

age across the belt tension with the non-fatigued carcass ultimate strength.

This approach, although common, is not preferred because it masks the

actual situation. The work by Flebbe (1988) at Hannover University high-

lights a problem with using the ultimate belt strength as a reference for belt

safety factors. The reference discusses the test results of two belts ST6600

and ST7500 kN/m. At the time, companies were making claims as to which

had made the strongest belt in the world. At fi rst glance, the ST7500 belt

would appear to have been the stronger. However, the testing at Hannover

University established that the fatigue strengths were 50% and 38%,

respectively. So the ST6600 had a strength of 3300 kN/m after fatigue and

the ST7500 had a strength of 2850 kN/m. Pedro (2004 ) used Goodyear

dynamic splice test machine when reviewing a new splice assembly tech-

nique for steel cord belts. Pedro tested a ST1250 kN/m belt and an ST4500

kN/m belt on the Goodyear test-rig.

Hager (2000) gives an overview of the approach taken by DIN 22101.

19.2.2 Belt strength for impact and chute design

Conveyor systems are being built to handle larger volumes and at some

mines very coarse materials. This trend may be driven by:

Coal conveying 635


The move to the use of central processing hubs. The hubs may be old •

facilities that are no longer adjacent to the material being mined. So the

conveyor systems replace long-haul trucking.

A change in the types of materials and the associated crushing •

equipment.

A better knowledge and more confi dence in the design of transfers. •

Looking back to the 1970s, some of the early transfers had simple, large

open chute arrangements with low impact idler systems. The designs orig-

inated out of Germany, where the material was sticky lignite. The situa-

tion called for large open chutes that could handle some build-up, but still

allow the huge lumps to pass. These lumps originated from the very large

bucket-wheel excavators. The designs used suspended or garland idler sets.

Colijn (1973) describes how fi ve-roll suspended sets are used successfully

in the open mine pits at Rheinbraun in Germany. He provides a graph of

the impact force for various support arrangements. Precismeca (1998) has

similar curves for the impact loads on various idler support systems. As the

large lumps hit the belt, the suspended sets would change shape and reduce

the impact force. These arrangements fell out of fashion, due to the mainte-

nance of the links between the idler rolls, cost, and mass of the suspended

assembly. The large assemblies required lifting equipment to allow replace-

ment. Even then, the work was not easy.

In Australia, in the 1960s, the iron ore and bauxite mines applied the

German designs, making changes to the chutes to accommodate the partic-

ular nature of the iron ore and bauxite. Iron ore, being abrasive and heavy,

forced a move to rock-box design. This minimised the quantity of wear

materials and lowered the impact on the belts. It was possible as the ore

was dry and free fl owing. At the bauxite mines the raw bauxite tended to be

small, less abrasive, and sticky during the wetter months.

So the chutes for most materials were kept large and open. The large open

simple chute designs worked well. When material is dumped crudely onto a

belt, the belt tracking is not that bad.

As the fl ows increased and the knowledge of the designers improved,

the designs slowly changed. The technology improvement had the support

of the mining companies and organisations that included: University of

Hannover Germany; University of Newcastle in NSW, Australia; Jenike and

Johanson, at the University of Wollongong, NSW, Australia; publications

by CEMA of the USA; the Mechanical Handling Engineers’ Association

in the UK; and others. These organisations have developed tests for fl ow

properties, behaviour, and wear, as well as the science of bin, hopper and

chute design.

In the 1970s, soft fl ow chutes were being used to improve the fl ows through

the transfers. These chutes were useful for granular non-sticky materials.



The benefi ts were reduced dust, degradation, and impact. Bringing the fl ow

up to the outgoing belt speed improved belt life. Coal companies in the

Hunter Valley of NSW, Australia and other areas used these chutes with

great success at this time. Colijn (1972) reviewed the equations that describe

the velocity of the upper and lower impact curved chutes. These designs

are known more recently as ‘hood and spoon’. Roberts (1981) looked at the

behaviour of the fl ow along fl at walls and around curved plates. These chute

designs and the associated equations were used successfully on the 13.1

km overland coal conveyor for Pt Kaltim Prima Coal, Indonesia. This con-

veyor was designed in 1989 and began operation early 1991. James (1992)

describes the use of chutes to accelerate the coal up to the outgoing con-

veyor belt speed. This conveyor has been through a series of upgrades since

1991. More recently, the chutes have been replaced by commercially avail-

able units from Tasman Warajay, Australia. These chutes consist of complex

3D shapes that control and direct the coal fl ow.

With the increasing use of soft fl ow chutes for large fl ows, the issues of

material stickiness, liner wear, and belt tracking began to re-emerge.

In recent times, there has been a trend towards conveying larger, heavier

lumps and below water table sticky materials. As the soft fl ow hood and

spoon arrangements tend to block or wear, there is a need to revisit the

chute designs. Sticky material demands simpler open chute designs. Open

chutes tend to be higher impact, so the open design requires belting and

loading points with good impact capability.

B ö ttcher (1978) published a paper on impact strengths as part of the

development of the 100 kM overland system in the western Sahara.

Manufacturers such as Contitech (see Alles (1988)) include the impact

strengths of various belt constructions. It is surprising how often the impact

strength is ignored by conveyor designers. The main focus has been on the

designs for tension.

A simple review of the major mining company standard drawings will

show that the typical transfer height is 5.5 m or more. With lumps weigh-

ing above 65 kg, the impact at the loading point can be high. James (2007)

described the move to design soft impact loading points for primary crushed

material. The method described is a departure from:

The rigid impact zones that aimed at providing a good skirt sealing and •

equipment that could withstand the high impact;

The soft fl ow ‘hood and spoon’ designs. •

19.2.3 Rubber power

Low energy rubber has been used in motorbike and car racing tyres, etc.

for many years. Without this technology, tyres overheat, lose grip, and fail.

Coal conveying 637


The application of low energy theory to conveyors goes back to the 1960s.

Work by Schwarz, Oszter, Behrands, Quass, Spaans, Jonkers, Funke, Hintz,

Hager, and many others investigated the topic to address the issue of the

resistance components such as idler seal drag, material fl exing, etc. For

example, Oszter (1980) showed that approx. 70% of the resistance of a long

conveyor was due to the imprint, i.e. the rolling resistance of the idler roll

on the belt cover. Hintz (1993) published similar results showing the high

contribution of the indentation resistance for a large range of belt cover

materials. Lodewijks (1995) provides a summary of a dozen or so authors

and their indentation loss equations. More recent work has been done by

Wheeler (2003) using a rubber viscoelastic test machine, tests of rollers on

a travelling belt loop, and fi nite element analysis of the contact zone. The

thesis also looks at the other loss components, including idler seal drag, belt

fl exure, etc.

The major belt suppliers all offer low energy belting.

19.3 Design of large conveyor systems

The drive is a key component in the conveyor package.

19.3.1 Large drive systems

Please refer to Fig. 19.6. This shows a base-mounted drive assembly. This

design was developed by James (2010) for the Worsley Alumina Pty Ltd

Marradong Bauxite project and has been used more recently on the Rio

Tinto Western Turner Syncline (WTS) project. The conveyor system on

WTS has a total length of approx. 25 km. of which the longest fl ight is almost

11 kM long. There are 9 × 1600 kW drives, as shown in Fig. 19.6.

In some respects, the arrangement is a move back to the past. In the 1960s,

base-mounted helical drives were used. These reducers used very large

through-hardened gears. The housings were large, with large volumes of oil.

These drives required good support structures to maintain the alignment of

the couplings. As time passed and the required power became larger, the

cost of the support structures, reducers and installation became prohibitive.

These units were replaced by shaft-mounted bevel helical drives produced

by Flender (now Siemens) of Germany and many others. These units used

compact case-hardened gears. The small reducer and the shaft mounting

arrangement created a low-cost solution that was quick to fi t and did not

require stiff support structures. As these drives increased in size, additional

cooling systems were required. The old helical drives from the 1960s were

very large for the power transmitted. Heat was less of an issue. However, the

compact bevel helical case-hardened gear drives need fans, radiators, and

water- or air-cooled exchangers.


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Coal conveying 639


The ever-increasing drive sizes have forced the move back in time to the

arrangement shown in Fig. 19.6. The modern conveyors require drives that

are measured in megawatts. The reducer alone may weigh 30 tonnes. The

fl ywheel shown may weigh 7.5 tonnes with low-speed coupling of 3.5 tonnes.

These are very large components. If this equipment was shaft-mounted, the

entire assembly might weigh as much as 50 tonnes. The length might be sev-

eral metres. The shaft-mounted drive would be diffi cult to lift, and access

would become an issue.

The arrangement shown in Fig. 19.6 has extended couplings on both the

high and low speed sides of the reducer. The longer couplings solve the

alignment issue that forced designers to move to shaft-mounted drives. The

couplings allow large alignment errors.

The holdbacks, backstops or anti-runback systems are devices that pre-

vent a conveyor running backwards. The energy to cause the conveyor to run

backwards may come from the conveyed load, the elastic strain energy, ther-

mal transients, etc. The writer would use holdbacks on most conveyors even

though the material lift load is less than the system friction. Thermal tran-

sients can be large. The method of calculating the loads is described in James

(2007). This paper follows up on the work by Timtner (1996, 1998). Timtner

discusses the wind-up multiplier effect within a holdback and through the

drive system. He also looks at the effects of load sharing. It is common prac-

tice for holdbacks to be sized for the load from the lifted material. The work

by James (2007) strongly advised that the stalled drive should also be con-

sidered. The stalled drive may produce 250% to 300% of the motor full load

torque (MFLT). When this torque is multiplied by the wind-up effect, loads

of 10 × MFLT are possible. This load is seen by the drives, pulleys, structure,

etc. One way to limit these loads is to select holdbacks that slip momentarily

when the extreme loads are generated.

19.3.2 Low head drive arrangements

Please refer to Fig. 19.7. This shows a low head drive arrangement. This design

was developed by James (2010) for the Worsley Alumina Pty Ltd Marradong

Bauxite project and has been used more recently on the Rio Tinto WTS pro-

ject. Larger conveyors have larger powers and tensions. Larger conveyors

have bigger pulleys. The conveyor tensions have moved past 100 tonnes, and

the pulleys now weigh more than 25 tonnes each. The response to this trend

is the low head arrangement. This arrangement brings the heavy pulleys

and drives down to ground level. This provides improved access for mainte-

nance. Smaller cranes can be used to lift the components. The arrangement

shows access for a skid-loaded to clean up under the area. Light vehicles can

drive up a concrete ramp and be parked beside the drives.



19.3.3 Horizontal curves

The design of horizontal curves has been covered by Grimmer (1972, 1992).

More recently CEMA (2005) provided an update to the analysis of these

curves. The preferred method of bending a conveyor around a curve is

to use negative idler Camber and gravity. Some call this negative super-

elevation. Here, the idler set is sloped so that it is higher on the inside of

the horizontal curve. As the tensions rise, the belt moves towards the centre

of the curve. In doing so, it moves up the idler slope. The extra gravity from

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Coal conveying 641


the displaced belt resists the belt movement. If the design is correct, the

belt will fi nd a balance point with a reasonable belt drift. When the tension

reduces, the belt moves outwards to another balance point. As the belt is

moving sideways with variation in tension and load, consideration must be

given to the material edge clearance and idler set width.

The published methods also consider friction as a method to control the

belt movement. The friction is achieved by skewing and rotating the idler

rolls or sets. This is less preferred because:

The friction can vary with climatic conditions, rubber properties, and •

idler condition. There are many variables that make the prediction of

the friction factor problematic.

The extra friction drives up the tensions that fl ow back into belt •

movement.

Higher tensions mean more power, and bigger drives and belt. •

There are many load cases that must be accommodated. Friction may •

help in some cases and be a problem for others. For example, friction may

be benefi cial for, say, the high tension empty belt case. It may limit the

inward movement of the high tension empty belt (as it is being loaded).

However, the friction works against stability for the loaded belt low ten-

sion case. For example, during a braked stop when the tensions go low,

the loaded belt will be moved further out sideways due to this friction.

The accepted method to control the empty belt high tension case is by

side guide rollers.

19.3.4 Conveyor starting systems

There are many systems available, including:

Variable voltage variable frequency (VVVF). •

Wound rotor motors with step resistors, and liquid resistors. •

Fluid coupling, both static traction and scoop. •

Slipping clutch. For example, Baldor CST drives. •

Eddy current coupling. (These drives were used extensively at the lignite •

power stations in Victoria, Australia. Refer to Mitchell (1983).)

James (1992) describes the successful use of Voith scoop fl uid on cou-

plings on a 13.1 km overland coal conveyor located in Indonesia. The system

was found to be simple and robust. More recent projects have used VVVF

drives. Users such as Port Waratah Coal Services, Newcastle, NSW, Australia

use a large number of wound rotor motors with liquid resistance starters.



Some of the big miners in Australia use wound rotor motors with step resis-

tors on larger drives. They will also use VVVF drives on specifi c conveyors.

The writer has not used slipping clutch systems. However, it is understood

that slipping clutch systems, by Baldor for example, also have good end-user

support.

19.3.5 Dynamics of starting and stopping

General

The dynamic behaviour occurs when the conveyor is running, starting or

stopping.

Running dynamic behaviour, including belt fl ap and structural reso-

nance, will not be discussed in detail. Belt fl ap occurs when the roll or belt

passing frequency is in sync with the belt stringfl ap frequency. Normally,

the consequences are not signifi cant. An interesting phenomenon that has

been observed is classic fl ap vibration on the carry side causing the mate-

rial to migrate. The even material load moves, to become discrete masses

equal to the idler frame pitch and causing considerable vibration and spill-

age. The vibration can be explained by string theory with distributed con-

centrated masses.

Starting dynamic behaviour is infl uenced by the drive start system. The

starting cases can be smooth and carefully controlled by the drive system.

The starting method can be by VVVF, fl uid coupling, wound rotor motors,

slipping clutches, etc. A fl ywheel, although not normally used for this purpose,

can also extend the starting time and smooth out the dynamic behaviour.

Funke (1974) looked at the basic equations that describe the dynamic

behaviour of conveyor belts. Nordell (1984) and Funke (1987) also address

the issue. Lodewijks (2002) provides a historical overview of two decades

of dynamic analysis work going back to Oehmen (1959) and Dumonteil

(1967).

Harrison (1984) described the shape of the ‘S’ curve starting method.

Refer to an example in Fig. 19.8. This curve minimises the dynamic response.

In simple terms, there is no acceleration at the beginning or end of the start

cycle, and maximum acceleration at the middle of the cycle. The starting

cases are interesting but less challenging than the unplanned stopping cases.

The normal planned stopping events can also have a controlled ramp down

of the speed. The unplanned events, such as loss of supply power, or detec-

tion of, say, belt rip will cause immediate loss of power and a large step

reduction in the tension applied by the drive system.

The stopping dynamics will be discussed in more detail below.

CEMA (2005, Chapter 16, p. 498) looks at the analysis of the transient

system and asks the question: ‘When is Dynamic Analysis Required?’ It

Coal conveying 643


provides a basic check list. In short, the list includes existing conveyors that

have problems, new conveyors greater than 1 mile (1609 m) long, conveyors

with high lift or high regeneration, multiple drives, conveyors greater than

8000 tph or 1000 fpm (5.1 m/s), etc.

Stopping dynamics

James (2000) described a simple method to approximate transient dynamic

tensions in belt conveyors when they are stopping. These tensions can be sig-

nifi cantly higher than those predicted by conventional methods. High tran-

sient tensions are often the primary cause of equipment failure. The effect

of these rules on various take-up systems is also discussed. The rules assume

that the conveyors are a simple spring, and the tensions adjust at high speed.

The rules are not a substitute for full dynamic analysis methods (i.e. actual

forces may be higher than predicted by this method).

Conveyor analysis methods published by CEMA, DIN and ISO do not

consider the dynamic response of the elastic conveyor during starts and

stops. They are generally called static methods of analysis, where the belt is

considered to be a rigid body. A number of practitioners, including the writer,

have developed sophisticated dynamic programs that take into account the

elastic behaviour of the belt and other dynamic properties. Although the

theory has been in the public domain since the 1960s, the programs are not

commonly available or used. The majority of conveyors are not designed

using the dynamic analysis methods. The experts with the tools are often

called in when there is a problem in the fi eld, or when a designer consid-

ers the conveyor to be ‘big’. This is a dangerous approach. The potential for

catastrophic failure is ever-present. Some try to cover dynamic loads with

00

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Time (seconds)

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19.8 Typical ‘S’ start curve with a pre-tension zone at the start.



simple tension multipliers. This approach is not recommended. Ultimately,

if there is a problem it may be expensive to solve. There may be overload

due to high tensions or spillage from low tensions. Sag snap is when the belt

quickly goes from low tension to high tension, or high to low sag. Under the

right conditions, material can be thrown off the belt.

James (2000) discusses in simple terms the possible dynamic effects.

The paper encourages designers to move from the simple static methods

to full dynamic analysis using sophisticated dynamic tools. The reference

describes a simple method that gives the approximate tensions during a

stop. The paper noted that this method is not a substitute for full dynamic

analysis methods. The paper includes a few simple rules, which are based

on conservation of the average belt tension and its relationship with take-

up travel. The rules will often give higher tensions at non-drive pulleys

than predicted by the static methods. This depends on the actual conveyor

arrangement. The rules may still under-predict the tensions. Although the

average tension and take-up movement is conserved, the conveyor in the

fi eld may have a zone of low tension, which is compensated by a zone of

high tension elsewhere.

Equipment

The key equipment required to control the stopping dynamics are brakes

and fl ywheels. The loss of power during a non-planned stop sends tension

waves around the conveyor. These waves travel approximately at the speed

of sound. The conveyor tensions move from the running state to the stopped

state. In simple terms, the conveyor is a spring mass system, and the loss of

power is the step forcing function.

Flywheels add inertia to the drives. They convert the sharp step function

into a longer ramp. It is interesting to note that the extra inertia generally

has little effect on the full conveyor stopping time. However, the extra iner-

tia has a large effect on the tensions around the conveyor and the associated

take-up movement.

Recent examples of designs by the writer place the fl ywheel between

two oil lubricated bearings FAG LOE or SKF SNOL housings. As an initial

reference point, the diameter is limited by the rules specifi ed by Factory

Mutual Datasheet 13–6.

Brakes can serve a couple of functions. They can inject a value of tension

say at the tail pulley to ‘hold up’ the tensions. Typically, the tensions near

the tail of the conveyor may drop during a stop. Brakes can also be used at

the drives to control the run-on time of the non-full belt cases. For exam-

ple, with large fl ywheels, the empty belt may run on for more than 100 s.

Proportional brake systems can be used to bring all load cases to a stop in

a constant time.

Coal conveying 645


Another tool that can be exploited is the take-up system. James (1994,

2000) describes the use of winch take-up systems. On stopping these sys-

tems lock in the tensions. The winch system cannot adjust quickly. So, as

the tensions equalise at the speed of sound, they are seen by the pulleys.

Provided the equipment can handle the loads, and effects such as ‘sag snap’

are not present, these take-up systems may be a viable solution. Note, some

may consider the winch systems as adding complexity.

19.3.6 Discrete element modelling of chutes

The discrete element modelling DEM method is a computer simulation of

discrete particles fl owing through a chute. CEMA (2005, Chapter 16) pro-

vides a brief overview of the discrete element method. Wypych (2010) goes

into the subject in more detail, noting that there is often a lack of validation

of the model. A number software packages are available in the market, and

companies are offering consulting services. As with any software, the output

depends to a large extent on the quality of the inputs. There will also be a

difference in the algorithms used and the complexity of the particle model,

for example, the stickiness, elasticity and damping behaviour. So how valid

are the inputs and outputs, and are the particles behaving correctly? Are the

simulations fi ctitious animations, or is there a scientifi c basis?

Wypych has taken a scientifi c approach to the validation process, develop-

ing a series of tests and calibration techniques. With this in place the DEM

outputs are compared with material fl ow physical scale chute models. The

work shows close alignment between the methods. The work is ongoing.

19.3.7 Noise

Noise from conveying typically becomes an issue when the system is adja-

cent to local domestic residences. Noise limits at night are more restrictive

than daytime limits. An example may be a port adjacent to a nearby town.

Often the towns spread over time and the space between the old port and

the homes gets smaller. Similarly the activity at the port and its function

may increase over time. So over the years issues such as odour, dust and

noise emerge. Also the community expectations and environmental stan-

dards change as the data of the environmental effects become known. This

knowledge fl ows into the design of new and old facilities.

Brown (2004) discusses the defi ciencies in understanding of the issue in

some parts of the industry. This lack of knowledge can mean that once a

noise issue is identifi ed, there may be a limited number of practical and

cost-effective noise management strategies that can be applied. A key input

to the noise level is the belt velocity. Noise is generated at the belt/idler



interface primarily by the idler surface profi le velocity. A better understand-

ing of the noise source would prompt the designer to consider lower belt

speeds, larger idler roll diameters and/or better quality idler rolls.

Brown (2004) proposes a parameter called the Maximum Instantaneous

Slope (MIS) that can be used as a practical basis to predict the noise levels

from the equipment.

Various low noise idlers are available for the suppliers. These include:

Machined and electronically balanced steel rollers. The machining •

improves the MIS value.

Aluminium rollers with polyurethane ends. The aluminium tubing can •

have better MIS values than the un-machined steel tubing.

PVC shells and nylon glass composite ends. •

The reader is encouraged to investigate issues such as actual noise perfor-

mance, shell wear, roll life, bearing life, grease retention, seal design, rolling

drag, carry back adhesion, cost, availability, mass for replacement, standardi-

sation, fi re rating, corrosion resistance, etc.

19.4 Integrated crushing systems

Integrated systems move the truck dump point closer to the coal face by

using conveyors.

19.4.1 General

With the shortage of truck tyres, and the cost and availability of labour,

trucks and fuel, integrated crushing systems are becoming more popular.

In a world where there are penalties for production of CO 2 , the move

to integrated crushing systems is probably inevitable. Integrated systems

have been used sporadically with great success for a number of decades,

e.g. the design of the in-pit crushing plant for Bougainville Copper in

the 1980s (not erected). At that time, companies such as Mountain States

Engineers, Krupp, MAN, and others had built crawler transportable or

walking type crushing and or conveying structures. Krupp had a range

of out-of-the-catalogue crawler transporters, ranging from 240 t to 1200

t with a centred load. PHB-Weserh ü tte supplied mobile crushing units

to Worsley Alumina Pty Ltd, Western Australia in 1981, and a number of

other locations.

James (2010) gave details of a recent project where the ROM hopper

for the haul trucks was moved. This is a fi xed installation. The project study

originally planned to have the ROM approximately 1000 m outside the pit.

Coal conveying 647


During the detailed design phase, the ROM was moved into the pit area.

This reduced the annual truck travel by 250 000 km. This is about six times

around the world. So, getting the ROM near the mining activity has major

energy and cost benefi ts.

Chasing the mining activity with mobile or moveable semi-mobile mod-

ular systems is even better. Strzodka (1993) investigated the economics of

in-pit crushing systems, and discussed the use of semi-mobile crushing sys-

tems. The work concluded that there were savings between 30% and 60%

in favour of the in-pit crushing system. The example was of a 15 mtpa mine

in Mexico.

Roberts (1985) looked at the components that make up the capital and

operating costs of conveyors and other transport systems. The cost param-

eters would have changed, but the methodology is still relevant today.

Constructing a series of graphs for operating and capital costs for various

capacities and distances allows the methods and designs to be compared.

For a conveyor, the optimum solution is normally narrow and fast.

19.4.2 Mobile and semi-mobile systems

The movement of large digging, crushing and conveying machines was not

new to German and American designers. The Germans have been build-

ing large digging and transporting systems since the 1800s. The power

station in the Latrobe Valley, Victoria, Australia, used bucket-wheel exca-

vator and track-shiftable conveyor technology to move overburden

and lignite. The Heritage Victoria National Trust Database notes that

LubeckerMaschinenbauGesellschaft (LMG), Lubeck, Germany, supplied

the fi rst dredger to Morwell open-cut. It began operation in 1955. The

machine weighed 750 tonnes. The design of this machine originated in the

German coal mines in the 1930s. The fi rst German bucket chain excavators

were used at Yallourn in 1928.

Haddock (2002) notes that a French contractor, Alphonse Couvreux, used

a bucket chain excavator in 1859 on the Ardennes railway. In the period

1863–1868, seven Couvreux machines excavated 8 million yards of earth in

the construction of the Suez Canal.

Haddock (2002) also notes that the American engineers were good at

moving huge machines on crawlers. This reference describes stripping

shovels as the ‘kings of the mobile machine world’. The early machines dat-

ing back to 1899 were mounted on rails. The book includes the details of

many outstanding machines built in the twentieth century. One of the most

impressive was the Marion 6360 stripping shovel, built in 1965. Mounted on

an eight crawler undercarriage, the machine had a 180 cubic yard bucket. It

weighed in at 15 000 t and had an operating radius of 220 ft.



In summary, the world’s engineers have moved huge items of equipment

and there is now a real need to just do it!

It is interesting to ponder the question of why the systems have not been

used more widely. One would speculate that in open pit mines the mine

planners are reluctant to give up the fl exibility of trucks. Conveyor systems

quarantine parts of the pit, require extra planning, and reduce fl exibility.

As we move forward, economic and environmental issues will challenge

this view.

Considering the history of moving large equipment, moving ROM hop-

pers, jaw and gyratory crushers, sizers, apron feeders, electrical rooms, etc. is

not a problem.

Kahrger (1987) described a new mobile conveying system to link in-pit

crushers to the process plant. Track-shiftable and crawler-mounted bridge

systems are also available. Caterpillar manufactures ‘out of the brochure’

crawler assemblies. Placing the typical conveyor truss/bridge on crawlers is

not diffi cult.

Pagels (2008) describes the mobile crawler-mounted conveyors, stack-

ers and reclaimers that have been used in heap leach operations for many

years. Neagle (1983) described the moveable face conveyors used at the

Loy Yang power station located in Latrobe Valley, Victoria Australia.

Mitchell (1983) provided a 20-year history and a detailed tabulation of

the 150–2440 kw drive-heads used at Morwell, Yallourn and Loy Yang

lignite power stations Latrobe Valley, Victoria, Australia. The belt widths

ranged from 1220 to 2000 mm, mass 35 to 400 t, and belts speeds from

4.85 to 5.3 m/s.

If we think about the reluctance of mine planners and the need for fl exi-

bility, it is also interesting to note that the writer had patents issued in 1988

for the invention of a mobile elevator conveyor. This could be described as

the missing link. The unit is described in James (1985). The mobile machine

overcomes the issue of the large earth ramps and fi xed conveyors that could

upset the mine plan. The strategy would be to have crawler-mounted or

track-shiftable conveyors running along the benches, and the mobile eleva-

tor unit would then lift the material out of the pit.

The machine has a fl exible boom to support a steep-angle conveyor. A

number of steep-angle conveyors are possible. The bench height targeted at

the time was 55 m. The USA patent number 4765461 describes the machine

as follows – refer to Fig. 19.9:

‘A mobile elevator conveyor, comprising a main support structure (10)

mounted on tracks (11), for mobility along an upper level (14) when in

use, an elevating conveyor (13) supported on a boom (12) adapted to be

extended from a retracted position within the main frame to an extended

position outwardly of said main frame. The boom supporting the conveyor

is formed from a plurality of boom segments (22), and is adapted, during

Coal conveying 649


extension and retraction, to pass over an outwardly and downwardly curv-

ing guide frame (29) mounted on said main support structure. The boom

segments are hingedly connected at their lower edges such that the boom

structure bends downwardly along its bottom chord at the hinges (23)

between the boom segments as it moves over the guide frame, and down to

a lower level (15). The interaction of the boom segments is such that bend-

ing in the opposite direction is resisted so as to form a rigid boom structure.

A collecting conveyor (38) extends along the length of the main support

structure and receives material from said elevating conveyor and conveys it

to a discharge point.

19.4.3 Modular components

With the use of 3D design, large fabrication shops, transport systems, and

large cranes, it is possible to build (and disassemble) the ROM hopper in

large modular units. Figure 19.10 shows a typical ROM station with apron

feeder and sizer. Figure 19.11 shows a module of the ROM hopper. This

unit weighs about 250 t. A typical mine may run the ROM stationing one

location for several years. At the appropriate time, a second unit could be

built in a new position. Then the old unit can be taken out of service, dis-

assembled, and overhauled to be ready for the next task. Under the right

circumstances, the schedule may allow one unit to be used. The move may

take say 2–3 weeks.

36a

37 12’

1312

22

25a

14a

25b

1550

36b35a

22a

35

232629 21a 141617 18

47112134a3446

20 38d 37 36 36f 38a 4849 19 28 10 17 38 48 38b 39 39’

19.9 Mobile elevator conveyor.


19.1

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od

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ize

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Coal conveying 651


19.5 References Alles R. (1982) Stressing of Rubber Conveyor Belts and Its Mathematical Treatment.

Bulk Solids Handling , March 1982.

Alles R. (1988) Conveyor Belt System Design Manual. Contitech, Hannover.

B ö ttcher G. (1978) Measures Concerning the Slitting Protection of Conveyor Belts

with Steel Cables. pp. 357–359 SonderdruckAusBergbau, August 1978.

Brown S. (2004) Conveyor Noise Specifi cation and Control. Proc. of Acoustics 2004

QLD Australia

CEMA.(2005) 6th Edition Belt Conveyors for Bulk Materials. Conveyor

Manufacturers Association, USA.

Colijn H. and Conners P. (1972) Belt Conveyor Transfer Points. AIME Transactions

Volume 252, 1972.

ROM bin grizzly beams, for detailsrefer to DRG 02006-DR-ST-0014.00102006-DR-ST-0014.004 Rock box module

for details refer02006-DR-ST-0014.0

1.5T SWL monorail beams

Upper ROM bin modulefor details referto 02006-DR-ST-0009

19.11 A 250 t module for the ROM hopper.



DIN 22101 (August 2000). Belt Conveyors for Loose Bulk Materials- Basis for Calculation and Dimensioning. DeutschesInstitut Fur Normung E.V. the

German National Standard.

Dumonteil P (1967) ‘Outline of a theory of the start-up of the conveyor belt’, Mineral Industry Review , 1967.

Flebbe H. (1988) Dynamic Splice Strength – Design Criterion for Conveyor Belts.


Funke H. and Dr-Ing (1974) The Dynamic Stress of Conveyor Belt Systems During Start-up and Shutdown . Braunkohle, March 1974.

Funke H. and Dr-Ing (1987). Experimental and Theoretical Investigations for the

Design of a Long-distance Belt Conveyor System. Braunkohle October 1987.

Gallagher D. (2000) Technology in Motion for the International Rubber Conference

Melbourne, Australia.

Grimmer K and Beumer B (1972) Design and Operation of Curve Going Conveyors with Standard Belts. F ö rdern and Heben, March 1972.

Grimmer K. and Kessler F (1992) The Design of Belt Conveyors with Horizontal

Curves. Bulk Solids Handling , October 1992.

Haddock K. (2002) The Earth Mover Encyclopedia: The Complete Guide to Heavy Equipment of the World . MBI Publishing Company, St Paul USA.

Hager M. and Simonsen H. (2000) Calculation and Design of Belt Conveyors for

Bulk Material. Braunkohle. May/June 2000

Harrison A. (1984) Minimising Transient Stress in Conveyor Belts. IEAUST

Mechanical Transactions.

Hintz A. (1993) ‘Infl uence of the Belt Structure on the Energy Consumption of Belt

conveyor Systems’, Doctoral thesis University of Hannover Germany.

James G (1992a) A Non-destructive Test for Belt Splices. How Good Are Your

Splices? Bulk Solids Handling , Vol 12, Number 4.

James G. (1992b) Design of a 13.1 Kilometer Overland Conveyor. Bulk Solids Handling , Vol 12, Number 4.

James G. (1994) A Review of Conveyor Take-up Design. IEUST International

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James G. (2000) Simple Rules to Approximate Transient Tensions in Belt Conveyors.

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James G. (2007a) Handling Primary Crushed Ore. IIR Conference Brisbane .

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Material Handling IBC ASIA Singapore 2010.

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Open Pit Mines & Quarries/ Conveyor Belt Technology book 1986.

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Lodewijks G. (1995) Rolling Resistance of Conveyor Belts. Bulk Solids Handling ,

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Coal conveying 653


Mitchell D. (1983) The Development of Movable Conveyor Drive Heads. International

Conference on Bulk Materials Storage, Handling and Transportation.,

Newcastle Australia August 1983.

Neagle J. (1983) Some Design Aspects of a Movable Open Cut Face Conveyor. Bulk Solids Handling , November 1983.

Nordell L. and Ciozda Z. (1984a) The Analysis of Starting and Stopping High Strength. High Capacity Belts Using Modern Engineering Tools . SME-AIME

Annual Meeting 1984.

Nordell L. and Ciozda Z. (1984b) Transient Belt Stresses During Starting and

Stopping: Elastic Response Simulated by Finite Element Methods. Bulk Solids Handling , March 1984.

Oehmen (1959) The starting Behaviour of Conveyor Belt Systems, Dissertation,

Hannover University of Technology, Hannover, Germany, 1959.

Oszter Z.F. (1980) Large Capacity Belt Conveyors, Motion Resistance Evaluation

Mining Engineering.

Precismeca (1998) Idler Design Manual Catalogue #101F.Precismeca Canada circa

1998

Roberts A.W., Harrison A. and Hayes J. (1985) Economic Factors Relating to the

Design of Belt Conveyors for Long Distance Transportation of Bulk Solids.

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Roberts A. W. and Scott O. J. (1981) Flow of Bulk Solids Through Transfer Chutes

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