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FACULTY MECHANICAL, MARITIME AND MATERIALS ENGINEERING
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Specialization: Transport Engineering and Logistics Report number: 2014.TEL.7879
Title: Overview and Characteristics of Belt Conveyor Systems and Applications
Author: Maarten van Blijswijk
Title: Overzicht en beschrijving van bandtransporteur systemen en toepassingen
Assignment: literature Confidential: no
Supervisor: Dr.ir. Y. Pang Date: September 8, 2014
Delft University of Technology
FACULTY OF MECHANICAL, MARITIME AND MATERIALS ENGINEERING
Department of Marine and Transport Technology Mekelweg 2 2628 CD Delft the Netherlands Phone +31 (0)15-2782889 Fax +31 (0)15-2781397 www.mtt.tudelft.nl
Student: Maarten van Blijswijk Assignment type: Literature Assignment Supervisor: Dr. ir. Y.Pang Report number: 2014.TEL.7879
Specialization: TEL Confidential: No
Creditpoints (EC): 10
Subject: Overview and Characteristics of Belt Conveyor Systems and Applications
Belt conveyor systems find applications all over the world. The conventional troughed belt conveyors are the most commonly applied in various industrial production fields. The development of belt conveyor technology over the past decades has enabled the design and application of longer, faster and more efficient conveyors with higher capacity and less environmental impact.
This assignment is to provide an overview of the characteristics and applications of large-scale
conventional troughed belt conveyor systems based on worldwide literature sources. Both existing and the most recent under-construction projects will be surveyed. The research of this assignment should cover the following:
• An general overview of the configuration and application fields of belt conveyor systems; • The trend of development with respect to the scale of belt conveyor systems;
• The development in the efficiency of belt conveyors based on the Loss Factor of Transport and the DIN equivalent friction factor;
• The development of energy efficient belt conveyor systems with respect to the innovations of main conveyor components.
This report should be arranged in such a way that all data is structurally presented in graphs, tables, and lists with belonging descriptions and explanations in text.
The report should comply with the guidelines of the section. Details can be found on the website. The mentor,
Summary
This literature survey focusses on the overview and characteristics of belt conveyor systems and its applications. To further limit the analysis only single flight conveyors are taken into account, which are longer than 1000 meters. Furthermore they have to be of the troughed 3-roll type. A func-tional limitation is that projects of the 1970s and onward are included.
The belt conveyor is under continuous improvement, in the recent years most attention is given to the energy efficiency of belt conveyors. The result for the drive train is the use of variable speed motors, that use less energy when the required capacity is low. Besides this some first steps are taken in the field of energy recovery systems for the bulk material. The belts are produced with high strength materials such as aramid, both for the reinforcing carcass as the rubber covers. When looking at the idlers the material of the rollers is altered to give low friction resistance, the wing rollers are split into two pieces to lower the rotating inertia and load dependent garland idlers are used.
This focus on the energy efficiency can be seen from the analysis of belt conveyor systems of the last four decades. The length of the systems has increased, while the power remained constant; they have become more effi-cient. Furthermore the average belt speed has risen also, the recent belt con-veyor operate at higher speeds than the older ones. The maximum strength of the belts has increased over the course of the years, but not that dramatic. In the 1980s belts of 7000 mmN were used, the nowadays this is 7800 mmN . Although the overall trend is that the average belt strength is decreasing.
The transport efficiency of a belt conveyor system can be calculated using the DIN friction factor and the loss factor of transport. The difference between the two is that the second takes the mass of the load into account, the first the masses of idlers and belt too. Because of this difference the value of the loss factor of transport is a factor 2 higher that the DIN friction factor. The analysis shows that both efficiencies are decreasing in time. Thus the more recent belt conveyor systems are more energy efficient. The transport efficiency compared to the conveyor length is analysed too. The trend of this graph shows that a longer belt conveyor is more efficient.
Contents
Summary i
1 Introduction 1
2 Overview of troughed belt conveyor systems 4
2.1 Components of a belt conveyor . . . 4
2.2 Places of application . . . 5
2.3 Advantages and limitations of using belt conveyors . . . 7
3 Configurations of belt conveyor systems 9 3.1 Drive train configuration . . . 9
3.2 Belt . . . 13
3.3 Idlers . . . 17
3.4 Take-up system . . . 21
4 Innovation of components of belt conveyor systems 23 4.1 Drive train . . . 23
4.2 Belt . . . 27
4.3 Idlers . . . 31
4.4 Control and monitoring . . . 35
5 Development of the scale of belt conveyor systems 40 5.1 Belt conveyor data . . . 41
5.2 Analysis of data . . . 44
6 Transport efficiency of belt conveyor systems 56 6.1 DIN friction factor . . . 56
6.2 Loss factor of transport . . . 57
6.3 Calculated transport efficiency data . . . 58
6.4 Analysis of the transport efficiency . . . 58
7 Conclusion 63
Chapter 1
Introduction
The history of belt conveyors starts in 1795[1] with the introduction of leather belts. They were driven by horses or water power. This was the main problem of belt conveyors, when there are no horses or water power available, a conveyor will not work. It was in the second half of the 18th cen-tury that the next impulse occurred: with ongoing developments in steam engines the power problem could be solved. The next big leap in the ap-plication of belt conveyors came in 1942[2] with the introduction of steel cord conveyor belts by the Good-Year company. This resulted in stronger belts that lasted longer, making conveyor belt systems more attractive to customers. Nevertheless it took until the 1970s for the usage of belt con-veyors to sky rocket. This was induced by opening of remote mines, the transportation of the bulk material could only be done by conveyor belt.
This literature survey focusses on the overview and characteristics of belt conveyor systems and its applications. To further limit the analysis only single flight conveyors are taken into account, which are longer than 1000 meters. Furthermore they have to be of the (most common) troughed 3-roll type. A functional limitation is that projects of the 1970s and onward are included.
The report is started with a general overview of troughed belt conveyor systems in chapter 2. In this chapter the components of which a belt con-veyor is composed can be found. The main components are: the belt, idlers, drive train, take-up system and structure. After this the places of appli-cation of belt conveyors are explained and some attention is given to the ambient conditions in which conveyors have to operate. Belt conveyors are used in industrial areas with a focus around the handling of bulk materials. These areas can be all over the world, the Saharan heat or the Arctic cold. Concluding the first chapter the advantages and limitations are given. Belt conveyors are used because they perform better on the facets of conveyable materials, capacity, cost and additional functions. The main limitations
of belt conveyor systems are in the return on investment, sometimes it is cheaper to use available modes of transport.
In chapter 3 a detailed description of the main components can be found. The drive train of a belt conveyor system can be executed in the following ways: a single head or tail drive or a multiple drive. The multiple drive can be executed as a dual or tandem drive of using intermediate drives. Brakes and flywheels can be added to the drive train to alter the stopping characteristics. In the belting department there is the choice between steel cord and fabric belts. The first uses strands of steel wire as tension members, the second a woven textile fabric. Belt conveyor systems uses lots of idlers, in the carry line there is the choice between in-line, offset and garland idlers. The return idlers can be of the flat or Vee type. The take-up systems can be executed using a gravity, screw of winch system. The first is the preferred option because of its favourable characteristics.
The components described above have been under continuous improvement. Chapter 4 give the innovations of these components regarding the past years. Much attention is given to the energy efficient operation of the system. The drive train of belt conveyor systems have evolved from crude fixed speed sys-tems to the modern variable speed controlled type. The motor of the drive train can be electric or hydraulic, both have got pros and cons. The electric motors have got a higher efficiency, but need complicated starting arrange-ments. Hydraulic motors can be engaged from start without problems but need a complicated pipe network. Different energy recovery systems are be-ing installed on belt conveyors. Such as regenerative brakbe-ing on the modern variable speed drives and a ’waterwheel’ that is driven by the bulk mate-rial. The main developments in the belts focus around the use of aramid materials in the covers and carcass of the belt. This to increase the overall efficiency. In the idler section new materials improve the efficiency too. The rollers can be made from composite plastics. In the idler section there are some big leaps in the design, such as the additional wing roller and the ’in-telligent’ garland, which has load depended troughing angles. Concluding this chapter is the use of control and monitoring in belt conveyor systems. The power consumption can be reduced by using variable speed control, the speed of the belt is adjusted according to the capacity demand; the belt is always full. The monitoring of the belt and idlers is done using scanning equipment and RFID-sensors.
Chapter 5 gives the actual evaluation of dozens of belt conveyor systems of the past four decades. The results of this evaluation is that, over the years, the length has increased, whilst the power remained the same; belt conveyors have become more efficient. Another thing that has been derived from the data is that the speed of belt conveyors has increased over time and that the belt strength has decreased. The drive power set out against the length shows that the spread in data points is rather large, the overall trend is increasing, but apparently the belt conveyor length is not the decisive factor for the power. The belt safety factor has increased over the years, this can be explained by the use of the installed drive power, instead of the required drive power. Older belt conveyors are more overpowered than more recent examples. Compared to length and drive power the belt safety factor shows a decreasing nature, with a lower bound of almost 4. This is slightly lower than the current industry standard of 4,5 to 5, which can be also explained by the use of installed power.
In the last chapter the transport efficiency of the belt conveyor systems is evaluated. Two methods are used, the DIN friction factor and the loss factor of transport. The first is used to calculate the drive power of a belt conveyor in the design stage, the second to compare the efficiency of different modalities. The loss factor of transport is the true efficiency number, it takes only the mass of the material into account. The DIN factor uses the mass of the belt and idlers too in the equation. Both of the efficiencies show a decreasing trend over the years, which means that the recent belt conveyors are more efficient. The lower bound for the DIN factor is nearly 0,005 and for the loss factor of transport 0,001. The transport efficiency against conveyor belt length shows that longer belt conveyors are more efficient. It has to be noted that the spread of data points is quiet large, the length is not the decisive variable for the transport efficiency.
Chapter 2
Overview of troughed belt
conveyor systems
As a start point for the evaluation of troughed belt conveyor systems a general overview is given. First the components of which a belt conveyor is composed are given, followed by the different configurations of belt con-veyor systems. After which the places of application are stated. Finally the advantages and disadvantages of belt conveyors are elaborated.
2.1
Components of a belt conveyor
A conveyor belt system is composed of multiple different components., which can be divided into two groups: the main components and the sub compo-nents. This division is based on the importance for the operation of the conveyor. A conveyor will not work without the main components; these are essential for the operation. On the other hand, the sub components are not essential for the operation of the conveyor. A belt conveyor uses the following components: Main components • Belt; • Idlers; • Drive train; • Pulleys; • Take up system; • Structure. Sub components[3] • Loading chute; • Discharge chute; • Belt cleaner(s); • Weighing device; • Monitoring device(s); • Control device(s).
The main components (besides the structure) are shown in Figure 2.1[4].
Figure 2.1: Overview of the main components of a belt conveyor.
In the next chapter the different configurations of belt conveyors will be discussed, with the different options for the main components.
2.2
Places of application
Belt conveyor systems are used all over the world in different industrial areas. This section gives information about those areas and the limitations they put on the belt conveyor system. They are the preferred option for longer distance conveyance because of the lower costs of operation, energy and man power. The only downside is the higher initial investment.
Industrial areas
The main areas of application of troughed belt conveyors focus around the transportation of bulk materials. These bulk materials could be for example different types of ores, coal, wood chips or cement. Within the bulk material transport two subtypes of belt conveyor can be recognized, the short and long conveyor. Short belt conveyors are mostly used within a mine or at a transference point where the spacing between origin and destination of the bulk material is less than 1000 meters. The long belt conveyors are used in between the mine and transfer point of the bulk material and are in excess of 1000 meters in length. This literature survey focusses on the latter type.
The long haul belt conveyor systems come in two variants, the overland and the underground type. These two options impose different requirements upon the installed system. The overland conveyor systems are easier to reach, therefore the maintenance areas can be spread out over the distance of the conveyor. Underground conveyors have to run through a tunnel, digging such a tunnel is costly, therefore only the needed components are placed in the tunnel. The drive and take-up systems are placed on the outside. When the entire conveyor is underground, these systems have to be
made as small as possible. A challenge for the overland conveyor systems is the fact that it can be reached. It is open to locals and wildlife to see and investigate. To overcome this sufficient security measures have to be taken, such as putting the conveyor on stilts, or placing a cover over it. Another advantage of a cover is the containment of the dust particles produced by the movement of the material. Hereby reducing the environmental impact of the conveyor.
The characteristics of the conveyed bulk material gives additional require-ments to the installed belt conveyor system. These characteristics include density, lump size, adhesion/cohesion and dust production. The result of this is that identically looking and working belt conveyors are made from completely different parts. Only because one is transporting iron ore and the other wood chips.
Ambient conditions
The long overland belt conveyor systems are used in a multitude of places all over the world. They are used in the scorching heat of the Sahara and the bitter cold of northern Canada. This results in a great variation in the ambient conditions to which the belt conveyor is exposed. To work properly a conveyor has to be designed to cope with these conditions. For example a conveyor in Bangladesh has to work in the rain season, when meters of rain can come down and most of the land is flooded. The conveyor must be able to keep operating. Or when the outside temperature is -40◦C, the components used have to have a service interval comparable to those operating under normal conditions. Factoring in the ambient conditions in which the belt conveyor system is used is a key aspect of the design of the system. In Figure 2.2 [5],[6] two different ambient conditions can be found in which belt conveyor systems have to operate.
2.3
Advantages and limitations of using belt
con-veyors
Belt conveyor systems have some unique characteristics that make them into the best option for the conveyance of bulk materials over longer distances. This section gives these advantages, besides this the limitations are given too. Some additional boundary conditions have to be made, besides length of the system, to make this analysis valid. There has to be a sufficient throughput; when just one truck can move the daily yield of a mine it would be the preferred option. The investment in a belt conveyor system would be too high. The operational time of the system has to be in decades, to ensure a good return on investment. No manner of transportation (truck / train) is nearby that could be used. When a elaborate road or rail network is present it is cheaper to uses this in most cases. There are much more factors to take into account when deciding which way of transport to use. Especially the cost part can be very different for two projects. Therefore it can be stated that these considerations are valid when the belt conveyor is a valid option, after cost analysis.
Conveyable materials
When using a belt conveyor material types that are damp, abrasive or sticky do not give the same problems as when using another type of conveyance. The lump sizes of the material is more limited compared to those other types, but conveyors can be made for the transportation of large lump sizes. As an effect the efficiency of the overall system will decrease slightly.
Capacity
Belt conveyors can be made as large as is needed (there are maximum di-mensions, but these are only practical limits). Thus for the high capacity needs of some applications it is very well suited. It can deliver this capacity on a continuous basis and thus eliminating the need of a large storage facility needed with discontinuous transport.
Structurally adaptable
The structure of a belt conveyor system is simple, it is composed of a number of steel brackets that are fixed to the ground. Since the belt conveyor system is lightweight the needed structure and supports are lighter and simpler compared to other types of transport. This makes crossing rivers, valleys and mountains less of a problem. And making the belt conveyor the desired choice for large scale cross-country transportation systems.
Additional functions
Besides conveyance of the bulk material other functions can be incorporated into the system. These could include: continuous weighing, sampling, spray-ing and scannspray-ing. In other types of transport a special facility is needed to perform these functions.
Cost
As stated before the cost of operation of belt conveyors is lower than any other manner of transport. For the distances covered by belt conveyor sys-tems the biggest competitors are trucks. In Table 2.1 [7] the cost of trucks is compared to belt conveyors.
Table 2.1: Comparison of the cost of truck and belt conveyor systems.
Although this table is from 1981 it shows that the cost of belt conveyor systems is lower than using trucks. When the assumption is made that the capital cost of both types evolved the same way these numbers are still valid. In most areas of the world the cost of manpower and energy has risen the past 30 years, the savings on these posts will be even higher for more recent developments.
Limitations
Besides the great advantages shown above there are some limitations to the use of belt conveyor systems too. When a belt conveyor is placed it is hard to move it, this is the main downside of having continuous transport. A belt conveyor has to do its work for multiple years, otherwise it is not economically feasible. The second limitation is based on the continuous transport too, there is no redundancy in the traditional single conveyor system. When a single component of the system fails, the entire system will fail. When using a discontinuous type of transport (like trucks) a single breakdown will not stop all trucks, the systems only operates at slightly lower capacity.
Chapter 3
Configurations of belt
conveyor systems
This chapter gives information about the different options in the configura-tion of belt conveyor systems. First the overall drive train configuraconfigura-tion will be discussed. This is followed by the choices in the selection of the main components, namely the belt, idlers and the take-up system. The other components are not shown since these standard are in most cases.
3.1
Drive train configuration
Without a drive train a belt conveyor system can not move any material. There are two different ways of executing the drive train, a single or multiple drive. These two types are elaborated in this section. Concluding some ancillary components of the drive are given.
Single drive
A single driven belt conveyor has got a only one drive train. This can be executed in two different ways, the head drive and tail drive. The head of a belt conveyor is where the material is offloaded, at the tail it is loaded.
Head drive
The head drive of a belt conveyor is situated at the unloading point of the belt. It powers the belt by pulling everything on the belt towards it. This type is shown in Figure 3.1 [8]. In most applications the head drive is the most efficient option. This is caused by the fact that the drive pulley pulls the belt at the spot where it is most heavy, just before unloading. This means that the maximal tension force in the belt is just before the drive pulley and that this maximal force is used to power the loaded belt directly. Thus reducing any additional losses when it would been driven elsewhere.
Figure 3.1: Conveyor belt head drive.
Tail drive
A tail driven belt conveyor has the drive train at the opposite end compared to the head driven example (or it runs in the opposite direction). For a conventional system this type of drive will not work. Since the needed tension just before the unload pulley stay the same and the maximal tension is at the drive pulley, the maximal tension has to be much higher to overcome the additional losses.
There are situations that a tail drive is the better solution, this is when the belt conveyor has to traverse large height differences. Especially when the drive motor becomes a drive generator the tail driven system is much better. This does not occur very often. But tail drives are applicable in another situation, it can be combined with a head drive to lower overall tension in this way. This is mostly used when the conveyor gets very long, or when it is used to transport bulk material two ways (coal one way, ash the other).
Multiple drive
The second method of belt conveyor drive is the multiple driven system. This type uses more than one drive pulley to power the belt. There are two options in this type of drive, the tandem drive and the use of intermediate drives. These two will be discussed in this section. Any combination of the four types (head, tail, tandem, intermediate) of drive can be possible, but
Tandem drive
When a single drive is not sufficient to drive the conveyor belt a tandem drive can be used (at head or tail). Most of tandem drives use only one motor to power the system, but it is also possible to install two complete systems. The difference between a single and tandem drive is shown in Figure 3.2 [9]. In this configuration the head (or tail) pulley is not the drive pulley, but two extra drive pulleys are installed. By doing so the degree of wrap increases which means that the drive can transmit more power. These systems are mostly used when single drive points are desirable, but the needed drive power becomes large. such as in long underground conveyor systems which have to lift the material out of the ground.
(a) Single drive pulley (b) Dual drive pulley
Figure 3.2: Comparison between single and dual drive
Intermediate drive
When the combination of head and/or tail drive still does not provide the lowest tensions in the belt (or practical limitations occur) intermedi-ate (booster) drives can be applied. An intermediintermedi-ate drive can be placed anywhere along the belt conveyor to give extra power.
There are three different types of intermediate drives, the belt-on-belt, rub-ber tire and fixed tripper drive, Figure 3.3[10] shows them.
• The belt-on-belt drive system uses an auxiliary belt underneath the main belt, due to the friction generated by the material lying on the main belt it can transfer its power;
• The rubber tire drive system is composed of two drives tires below and two non-powered tires on top of the belt. They are pressing the belt edges to provide friction for powering the belt conveyor;
• The fixed tripper is working the same way as the dual drive, which is shown in the previous paragraph, with one difference. The material has to be unloaded from the belt before the belt can be led through the drive.
Figure 3.3: Three methods of intermediate drives.
Ancillaries
The drive train of a belt conveyor can have ancillary equipment installed on it. This is done for one reason: to change the stopping characteristics of the belt when undergoing a non-powered stop with or without bulk material on the belt. This can be done by installing a brake or a flywheel. The installation of both is also an option, when the stopping time needs to be longer in one of the load cases, and shorter in another.
Brake
A brake is normally fitted to a belt conveyor system for one of the following three reasons:
• To reduce stopping time when the drive is out;
• Prevent an inclined conveyor from moving backwards after stop; • Prevent a declined conveyor from accelerating after stop.
There are multiple methods of braking a belt conveyor, all based upon the generation of friction. There are electromagnetic, electro-hydraulic and hy-draulic brake systems. The selection of the different type of brake depends
mainly upon the required braking torque. The hydraulic braking system is applied in most cases because it is capable of generating the highest braking torque. Figure 3.4 [11] shows a hydraulic disk brake.
Figure 3.4: Hydraulic disk brake on a coal conveyor.
Flywheel
A flywheel is used to elongate the stopping time of the belt conveyor during a non-powered stop. A flywheel is essentially a very big mass that is rotated with the belt conveyor. When the power is cut of the inertia of the flywheel generates a forward motion that drives the belt for some time. The flywheel stores energy from the drive of the conveyor and returns it into the belt when the motor is turned of.
3.2
Belt
Another essential part of a belt conveyor system is the belt. This component keeps the bulk material that is being transported in the system. There are two main options in belts, the steel cord (Figure 3.5a) and fabric belt (Figure 3.5b). Besides this there are many subcategories in these two main types. This section uses information from suppliers of belt conveyors[12][13].
(a) Layers of a steel cord belt. (b) Layers of a fabric belt.
Steel cord belt
The first category of belt material is the steel cord belt. The name comes from the steel strands that are used to strengthen the belt. First the carcass of the belt will be evaluated, after that the cover material, followed by the splicing of the belts. The last part is about subclasses in steel cord belts. The steel cord belts are available in widths up to 6000 mm wide, the length is infinite when combining multiple sections.
Carcass
The carcass is the tension member of the belt. This gives the belt the strength to operated under the tension needed in belt conveyor systems. As said before this tension member is made of strands of steel wire in steel cord belts. The belt strength of steel cord belts is solely depended on the strength of the used steel wires. It can be anywhere in the range of 500 − 10.000mmN . This is the amount of force a certain width of belt can hold. The carcass of the belt is held in place by the cover material.
Cover material
The cover material has to fulfil three functions in a belt. It has to keep the tension members is place, has to provide a surface from the bulk material to rest on and it has to provide protection to the tension members. The cover material is always made of a type of rubber. It has the advantages of flexibility, durability and workability (easy to manipulated). The choice of cover material has to be taken not too lightly, it leads to the highest contribution to the total resistance of the belt conveyor. This resistance component is depended upon the hardness of the rubber, very soft rubber result in more resistance.
Splicing
Even the smallest conveyor belts have got a connection in the belt, the splice.
Figure 3.6: Four step splice for a steel cord belt.
When the length of the conveyor in-creases, the number of splices follow. Such a splice is the weakest spot in the belt, because the steel tension wires are interrupted. The solution for this is to use a stepped splicing method for the connection of the two sections of belt. A four step splice is shown in Figure 3.6. The process of splicing begins with the freeing of the steel cords, after which the cords are placed in the pre-described order. When everything is in place the rubber cover is vulcanized in place for a
Subclasses
Within the class of steel cord belts there are multiple subclasses of belts suited for a special application. An overview of the special types of belts is shown in Table 3.1.
Table 3.1: Special types of belt material from Contitech.
Fabric belt
The second category of belt material is the fabric belt. The name comes from the woven fabric material that is used to strengthen the belt. First the carcass of the belt will be evaluated, after that the cover material, followed by the splicing of the belts. The last part is about subclasses in fabric belts. The standard width of a fabric belt is approximately 3200 mm, but wider belts can be made up to 5600 mm. The main advantage of fabric belts is the lower weight and thickness.
Carcass
As the name indicates the tension member of fabric belts is a mesh of woven fabrics. This fabric is made from a durable plastic such as polyester or poly-amide. The number of plies dictates the eventual maximum tensile strength of the belt and is in the range of 200 − 3.000mmN . The higher tensile strengths are reached by using 5 or 6 plies of textile. Again the cover material is used to keep the fabric plies in place.
Cover material
For the selection of the cover material the same considerations apply as given for the steel cord belt. The only difference is that the cover does not have to provide corrosion protection.
Splicing
Just as steel cord belts, the fabric counterpart can be made in all lengths.
Figure 3.7: Two stage splice for a fabric belt.
To make the longer belts splicing is used too. Only the method of splicing is dif-ferent for fabric belts. The initial step is the same, the different plies of fabric is freed from its rubber surroundings. After that the different plies are cut to size to be layered into a splice in which each following ply of fabric overlaps the previous one. This can be seen in Fig-ure 3.7. In this figFig-ure a 3-ply belt is connected using two stages. It is self-evident that the number of stages
in-creases with the number of plies. When the layering of the plies is done the open cover is healed by vulcanizing the carcass in place with rubber. For the fabric belts the splices are the weakest spots in the belt, just as with steel cord belts.
Subclasses
For the fabric belts there are also subclasses of belts. Table 3.2 gives an overview of these special types.
3.3
Idlers
The belt of a belt conveyor system runs on a track of idlers. In the idlers a division is made between the carry- and return idlers, the first supports the belt that has got bulk material on it, the second only the empty belt. The idlers give the belt the needed support for the conveyance of the material. The different types of idlers are made in the same way, a (steel) frame supports a roller on which the belt runs. Such a roller is shown in Figure 3.8 [14], where the main features are noted.
Figure 3.8: Cross section of a roller with most important features.
The overall design of a roller is a shaft over which a roller is able to freely move. This roller can be made from a material such as steel or aluminium. To improve lifespan of the component the two parts are fixed with heavy duty bearings and multiple seals to keep the inners of the assembly clean.
Carry idlers
As noted before the carry idlers have to support the belt with bulk material on it. Therefore the spacing in between the idlers has to be low to prevent excessive belt sag. There are three main types of carry idlers, namely the in-line, offset and garland idler. All the idlers given in this section are from the troughed type. This is one of the additional functions of the idlers, shaping the belt into the desired shape.
In-line idler
The in-line idler is the most common type of idler. Figure 3.9a [14] shows the schematic overview of the in-line idler. The origin of the name of this type of idler can be seen in this figure, the axis of rotation of the three rollers lay on the same line. In Figure 3.9b [14] a redering of such an idler is given. The main reason for the use of in-line idlers is cost. They are the cheapest option and therefore the most widespread. The direction of belt motion does not matter for this type of idler since it is symmetrical.
(a) Schematic overview of an in-line idler.
(b) Rendering of an in-line idler.
Figure 3.9: The in-line idler.
Offset idler
The offset idler is a special type of idler which has some distinct differences compared to the in-line idler. The main difference is that the axis of rotation of the rollers does not lay on the same line. This explains the name, the rollers are place offset of each other. This can be seen in a schematic overview in Figure 3.10a [14]. Figure 3.10b [14] gives a rendering of an offset idler.
(a) Schematic overview of an offset idler.
(b) Rendering of an offset idler.
Figure 3.10: The offset idler.
There are two main reasons for using offset idlers:
No idler gap Because the offset nature of the idler allow the rollers to overlap the belt is supported over the full width. This is a big advantage for thin lightweight belts that are prone to pinching.
Low height The height of the idlers is lower because of the offset lay-out. This is why they are used in the underground mining industry, where tunnel height is the limiting factor.
There are two downsides to using offset idlers. Firstly the belt has to hit the centre roller first. This means that the direction of belt movement matters. The second limitation is that offset idlers cannot be loaded as much as in-line idlers. Thus resulting in an lower idler spacing.
Garland idler
The garland idler is a special type of in-line idler, and is shown in Figure 3.11 [15]. Here can be seen that the garland idler is composed of a ’chain’ of rollers, with a flexible link as connection. The ends of the garland idler are connected to the frame.
The advantages of the use of garland idlers are:
Flexibility The design of the garland idler allows movement of the belt.
Replacement Since all the rollers are fixed in two places it is easier to replace the rollers.
Impact resistance Because of the flexibility in the system the garland idlers are more resistant to impact.
And the limitations are:
Flexibility Because the rollers are not fixed to the frame the idler will swing in the direction of belt motion.
Replacement Since all the rollers are in a chain they have to be replaced as a set. Also when only one is damaged.
Excess wear The belt slides a little bit on the rollers because they are not fixed. This results in a higher wear rate for the rollers and the belt.
Investment Garland idlers require a higher initial investment and have a higher maintenance budget.
Return idlers
The return idlers of a belt conveyor system can be of one of two types, the Vee and the flat idlers. These two types can be found in Figure3.12 [14]. Since the load on the return idlers is much lower compared to the carry idlers (there is no bulk material on the belt), the idler spacing can be much larger. The difference can be ad much as a factor three.
Figure 3.12: A selection of return idler options.
Flat idler
The flat return idler is the easiest way of producing an idler. It is used primarily in fixed, shorter and straight (no horizontal bends) belt conveyors. They are the preferred option for the low cost and the efficient operation.
Vee idler
The Vee return idler is used when the conveyor belt does not fall into the category of fixed, short and straight conveyors. This group contains nearly all long haul belt conveyor systems. They all use Vee idlers because they have belt aligning properties. When the belt runs along the Vee idlers it keeps itself in the middle of the rollers. The downside is that the energy consumption of these idlers is higher.
Loaded return idlers
A special type of return idlers is used in belt conveyors where the returning belt is loaded with bulk material. In this case the return idlers are of the types shown in the previous paragraph. The dual carriage belt conveyor systems are used for certain coal fed applications, the carry side is loaded with coal, the return side with ash.
3.4
Take-up system
A take-up system of a belt conveyor has got three main purposes: • Allow elongation of the belt;
• Prevent excessive belt sag by provide minimum tension;
• Provide minimum tension to ensure sufficient friction on drive pulley. Different options for the take-up system are available namely gravity, screw and winch. These types are discussed in this section.
Gravity
A gravity take-up system uses a block of material (most of the time concrete) and a system of pulleys to provide the tension to the belt. This can be seen in Figure 3.13 [8].
The advantages of the use of this type of take-up system are: • Simplicity;
• Can follow the differences in belt tension without delay; • Gravity is free, it does not cost any energy.
The main downside of using a gravity take-up system is that it requires a lot of space. There has to be several meters of room present in most cases to be able to install such a take-up system.
Screw
The screw type take-up system works by changing the length of the belt by using a thread and nut. The main advantage of this type is that it requires less space, but it is more complicated, it handles changes in belt tension with large delays and it costs energy to change the belt tension. An example of a screw take-up system is shown in Figure 3.14 [8].
Winch
A winch take-up system works similar to the screw, the belt is elongated using a winch and a steel cable. Just like the screw take-up it requires little room, but is more complicated than gravity systems. It does cost energy to change belt tension and fluctuations in belt tension are handled with a delay (not as much as with a screw take-up system). A winch take-up can be seen in Figure 3.15 [8].
Figure 3.13: Gravity take-up system
Figure 3.14: Screw take-up system
Figure 3.15: Winch take-up system
Variable length conveyors
A special type of take-up system is needed for variable length belt conveyors. These are mainly used in the mining industry at the extraction and storage points of the bulk materials. This kind of belt conveyor seldom uses a gravity system since the required travel would be to big. The take-up system has to be able to change the tension in the belt and has store the excess belt material when the conveyor is made shorter. Figure 3.16[16] shows the schematic overview of a retractable belt conveyor, with take-up system (green box).
Figure 3.16: Schematic overview of a retractable belt conveyor take-up sys-tem.
Chapter 4
Innovation of components of
belt conveyor systems
Over the years the different components of a belt conveyor system have undergone changes. There are improvements of existing systems and the introduction of new ones. This chapter gives an overview of the main inno-vations in belt conveyor components of the recent years. There is a section on the drive train, belt and idlers. After that the development in the control and monitoring of belt conveyor systems is given.
4.1
Drive train
Over the years the drive train of belt conveyors has undergone some changes. The fixed speed conventional drive systems are still used, but for many operations the modern drive systems are more in demand, because the speed of the belt can be adapted. These conventional and modern drive system can be found in Figure 4.1 [17].
The two conventional drive systems are pretty similar looking at the com-ponents used, with one major difference. The first uses a resistance starter, while the second operates without starter. This is possible because it uses a hydraulic coupling between the motor and gearbox. During starting the motor and belt conveyor are not moving; everything needs to started up. Es-pecially when the belt is loaded the required initial torque is too high for the engine, it will fry when attempting to start-up caused by overheating. This can be solved by bypassing the largest part of the electrical energy through a resistor; the motor will receive less power and will not overheat. When the belt picks up speed the resistor is de-powered to provide the maximal power to the motor and belt. The second type does not overheat because of the hydraulic coupling. In this coupling the motor moves an enclosed body of fluid by using a rotor. In the same encasing another rotor is present which is
attached to the gearbox shaft. When the fluid is moved by the drive rotor, it automatically starts-up the driven rotor. At first slowly and when the required torque decreases more swiftly. This is the exact task of the resistor during start-ups and is therefore not needed.
Besides the conventional systems there are modern drive systems shown too in the figure. They use transformers and Variable Frequency Converters (VFC) to provide the starting up of the motors and for the control of belt speed. The main difference between the two types shown is that one uses an asynchronous motor, whilst the other uses a synchronous motor. The difference between the two is that the synchronous motor is able to generate a very large torque from start-up. Therefore the use of a gearbox is not needed.
Conventional drive systems Modern drive systems fixed speed speed controlled
Asynchronous motor, Asynchronous motor, Synchronous motor,
Resistance starter Hydraulic coupling Frequency converter Gearless drive
SRM: Slip Ring Motor
VFC: Variable Frequency Converter
Figure 4.1: Basic configurations of conventional and modern drive systems.
As can be seen in the Figure 4.1 the most essential part of the drive train is the motor, all the types makes use of them. There are two main choices in the motor department, the common electric motor, or the hydraulic motor.
Electric motor
Electric motors are graded according to the rules set up by the International Electro-technical Commission. The main point of grading is the efficiency of the motors, which can be found in Table 4.1[18]:
Table 4.1: Efficiency grades with required efficiency for 200−375 kW motors.
Grade Description Efficiency [%] IE1 Standard Efficiency 94,00
IE2 High Efficiency 95,00 IE3 Premium Efficiency 95,80 IE4 Super Premium Efficiency -IE5 Ultra Premium Efficiency
-The last two grades are not yet on the market for large scale operations, but for low power applications different manufacturers have got IE5 compliant motors. For example ABB with their SynRM2-line[19]. The use of a higher
efficiency motor is beneficial to the entire system efficiency, for a motor in the range of 200 − 375 kW the motor efficiency can be increased with nearly 2% by selecting a Premium Efficiency motor.
Hydraulic motor
Instead of using an electric motor hydraulic powering of the drive system is an option too. In operation it is similar to the gearless drive system shown in Figure 4.1, it does not use a gearbox and couplings, since it is a low speed, high torque motor. The advantage of the hydraulic motor is that it can operate in driving and braking mode, in the forward and reverse direction. Excessive belt tensions can be avoided by setting a maximum pressure for the hydraulic pump. When the tension in the belt becomes too high the motor automatically slows the belt down. But the hydraulic motor has downsides too, the total efficiency is lower compared to the electric motor. The hydraulic pressure has to be generated by an electric motor and the hydraulic system has some losses in it too. Because the hydraulic motor is fed using hydraulic pipelines the use in a multiple drive system becomes complicated, long hydraulic pipes do not carry the pressure very well; the loss in efficiency only increases.
Energy recovery systems
All the energy that is put into the system has to be put to good use, to keep the costs as low as possible. One of the most wasteful parts of the operation of belt conveyor systems is the slowing down of the conveyor; power has been put into the system that is converted into heat by the brakes. To overcome this problem the use of energy recovery systems is the solution, these are put in many different applications of electric motors. The energy recovery systems of a belt conveyor works by changing the frequency of the electric motor such that it starts to deliver power instead of using it. The power that is delivered comes from slowing the belt. This is known as regenerative braking and can be installed on all the modern drive systems, since these have got VFCs installed to them.
The second energy recovery system is based upon the recouping of energy lost when the bulk material leaves the belt. At the loading point the bulk material has to be accelerated to the belt speed, this requires energy. The bulk material holds this kinetic energy during the ride on the conveyor belt. But when it reaches the end all this kinetic energy is lost when the bulk material hits the ground. This problem is solved by the ”Solid State Material Driven Turbine” (SSMDT)[20] and a prototype of this system can be found in Figure 4.2a, a Discrete Element Method analysis of the turbine can be found in Figure 4.2b.
(a) Prototype of a simple SSMDT. (b) DEM-analysis of a SSMDT.
Figure 4.2: Solid State Material Driven Turbine (SSMDT).
It works the same way as a waterwheel, it captures the forward energy of the bulk material and converts it into rotational energy. This rotational energy can be used for additional drive of the belt, or to generate electrical energy. The prototype reached an energy saving of 14, 3% during testing. This result can not be compared to full-scale belt conveyor systems, but it shows the potential of this system.
4.2
Belt
The belt of belt conveyor systems still looks and operates the same as four decades ago. The changes in belts have taken place in the carcass and the cover material of the belt. They are aimed at increasing the efficiency of the total belt conveyor and thereby achieve energy savings.
Carcass
Most long overland belt conveyor systems make use of steel cord belts. These belts are heavier than comparable textile reinforced belts, but are in most cases the only option for numerous reasons. The added weight of the belt needs to be rotated which costs energy. The reduction of the weight of the belt is a viable option to reduce the energy consumption of the belt.
With the application of other carcass materials such as aramid the total belt can be lighter. Aramid is a man-made synthetic fibre that is known for their high strength, heat-resistance and low weight. It has got the same breaking strength as steel at only one fifth of the weight. Table 4.2[21] gives a comparison between aramid and steel used as reinforcement for a coal conveyor system. As can be seen the aramid belt weighs considerably less than the steel belt. This results in a energy saving of 10%.
The different methods of fabricating the aramid reinforcement can be seen in Figure 4.3 [22]. There are two options, the first is to use aramid cords, similar to the steel cords. The second option is to make the aramid fibres into a fabric. For the cord type the maximum belt strength is 2000mmN , the fabric version can be delivered in 2500mmN . This shows a limitation of aramid reinforced belts, for the very high stress applications they are not (yet) suited.
Figure 4.3: Different methods of using aramid reinforcement.
Figure 4.3 shows a difficulty using aramid belts, the splicing can become problematic for the fabric type. This is solved by using another method of splicing, shown in Figure 4.4[23]. The ends of the two pieces of belt are cut into fingers, long triangular segments. The segments of one belt fit neatly into the segments of the other. When everything is in place the belt covers are re-applied by vulcanizing the rubber in place.
Cover
As described in the previous chapter the cover material is made from a rubber compound. The additives to that compound determine for a large part the special characteristics compared to ’normal’ rubber. The rubber cover material is worth investigating because it is the biggest contributor to the total power consumption of the belt. This can be seen in Figure 4.5 [24]. 50 to 70% of the total resistance of a long conveyor belt is caused by the roll-over resistance (or indentation resistance). This resistance occurs when the belt hits an idler, the soft material is made into a hump just before the idler. This results in a small loss for each idler and there are many idlers in a belt conveyor system. Thus lowering the roll-over loss is the first step in energy efficient operation of the belt.
Figure 4.5: Breakdown of power consumption of a belt conveyor.
Figure 4.6: A pile of Sulfron pel-lets of 6 mm.
One of the methods of lowering the roll-over resistance is the addition of Sulfron [25] to the rubber compound. Sulfron is a modified aramid, which is produced in pellets (Figure 4.6[25]). During the manufacturing of the rubber compound the Sulfron is added to the mix and re-acts sub-sequentially with other parti-cles in the compound. The resulting compound has a lower friction coeffi-cient and improved hysteresis proper-ties. Hysteresis can be best explained by a spring, the strength of the spring decreases as it is stretched out more of-ten. This reduction in strength is know as the hysteresis loss and can be seen
as the ’memory’ of the spring. When these two characteristics of the rub-ber are taken into account the result is a more efficient compound, which performance does not decrease as much as normal rubber over time.
The calculated power saving for an example project can be found in Ta-ble4.3[22]. The power saving is based upon the old steel cord belts with normal rubber covers and the new rubber type and carcass type shown in the table. The carcass is made of the Twaron aramid fibre. The rubber needs some more explanation, NR stands for Natural Rubber, BR means Butadiene-Rubber and 2.0phr Sulfron 3001 is the amount of Sulfron added to the mix in parts per hundredth rubber. Thus 2.0 phr Sulfron means that per 100 g of rubber 2 g of Sulfron has been added.
Table 4.3: Energy savings for the Optimum belt conveyors.
By changing the material of both the carcass and the cover the power savings are 40% for a fully loaded belt and 50-60% for the empty belt. These results can be improved even more when the lower tensions in the belt are taken into account which lead to a lower belt class. The lower tensions are caused by the lower power consumption of the belt.
Table 4.4[22] gives the different savings when changing from the old belt to the new one. Also stated is the payback time of the installation. This ranges from 2 to 4 months and is very short, when taking into account that normal investments take multiple years to reach the payback point.
4.3
Idlers
On first sight the idlers of belt conveyor systems are the same as they where years ago. They function in exactly the same way as they used to do. This is partly correct; a lot of effort has been made to further optimize the existing design since this was easier and cheaper than designing from scratch. Some of these optimization attempts are given in this section. Besides this some other innovative designs for (parts of) idlers are shown too.
Roller materials
As described in the previous section the rollers of the idlers are generally made from steel or aluminium. But there are new developments in the application of different plastics as roller material. For example Flexco of-fers rollers in High-density Polyethylene (HDPE) for some years and Nylon (Figure 4.7[26]) just recently. Both of these composite materials offer the following benefits compared to metal rollers:
• Corrosion- and abrasion-resistant;
• Lower dynamic coefficient of friction, up to 30% less power needed; • Lower noise production, ±10 dB lower;
• Lightweight.
The HDPE rollers are resistant to most solvents and acids, therefore they are the preferred choice when handling such liquids. Even the handling of sulphuric acid is not a problem with HDPE, there metal counterparts would not last very long since the acid increases the corrosion rate of steel.
(a) Stack of Nylon rollers. (b) Installed Nylon rollers.
Additional wing roller
One of the benefits of using 3-roll troughed idlers is the self aligning proper-ties. When the belt is not laying square on the rollers this is automatically fixed due to the geometry of the rollers and belt. The downside is that the rollers have to be larger than the belt to accommodate this movement. And longer rollers give more mass that is rotated and that results in more power consumed by the rollers.
A solution for this phenomenon is the use of an idler with an additional wing roller[27], which can be seen in Figure 4.8. The normal idler is shown on the right, the additional wing roller is shown on the left. As can be see the rollers are separated into two parts, the blue is always in contact with the belt, whilst the red rollers only come into contact when the belt is not aligned properly. This ensures the most efficient operation since the rotating mass is kept as low as possible.
Figure 4.8: Normal idler and idler with the additional wing roller (red).
This method of using an additional wing roller can be applied on every type of idler with self aligning properties (Vee- or trough-shaped). Since the Vee-shaped idlers are used in the return line, all the idlers can be made a little more efficient. There are no indications (yet) on the energy saving percentages for the total belt conveyor, only a worked-out example[27].
The energy saving per idler is 6, 422 kW h on a yearly basis. The belt conveyor system used for the analysis is 1000 meter long and runs at 5ms. This is the reduction of energy of the wing roller design compared to the normal design. There is not mentioned what the total energy use of one of the designs is, therefore the stated reduction can be 1%, 10% or even 50%. This makes is very hard to give a thorough analysis of the to be expected energy saving. Even better would have been that the energy saving percentage for the total belt conveyor system was stated.
Impact idler
A special type of idlers is known as impact idlers. These are heavy duty, robust designs of normal idlers that are built to endure the impact of the bulk material at the loading point. These type of idlers are essential to the reduction of belt wear at the loading point, since the idlers have to take the strain, not the belt. The spacing between the impact idlers is generally very small, to ensure that they take most of the impact. But the idler system is far from prefect: since the idler uses rollers there are gaps in between the different idlers. Over these gaps the belt is unsupported and vulnerable to rips, tears and impact damage.
The solution is to used a slider bed type of construction, as manufactured by Richwood Industries. Their set-up can be found in Figure 4.9 [28]. Instead of using multiple rollers it is composed of a bed of Ultra High Molecular Weight rubber segments. These are placed head to tail in a steel frame such that there is a continuous bed on which the belt can rest. When multiple of these frames are placed side by side along the loading area of the bulk material an impact zone is created without any gaps.
Figure 4.9: Richwood Combi-Pact Impact Saddle.
There is one main drawback of using this system instead of traditional im-pact idlers. The energy consumption for each segment is considerably higher that the traditional one. This is the side effect of wanting a large impact area. In traditional impact idlers the belt-idler friction is reduced by using bearings. The impact saddle does not use any rotating parts and the contact area between belt and saddle is much larger. A detailed cost analysis has to be made to determine the type of impact device.
Intelligent garland
Figure 4.10: The intelligent garland. The advantage of using a garland
idler is that it is flexible because it is suspended in the frame. The next leap forward in the design of the garland idler is the so called intelli-gent garland, which can be found in Figure 4.10[29]. The design uses a spring to adjust the troughing angle according to the load, which can be seen in Figure 4.11 [29]. A normal garland frame is used on which a bracket is fixed that holds a spring. When the mass flow is small (left part) the force on the spring is also
small. This results in a short spring and a low troughing angle. On the other hand when the mass flow is high, the load on the spring is large and the spring becomes longer. This longer spring enables higher troughing an-gles. This load depended geometry of the intelligent garland has got some advantages over normal garlands:
• Reduction of power consumption, up to 13%; • Uniform load distribution on all garlands; • Increased idler life time;
• Reduced frame vibrations; • Impact dampening.
The reduction in power consumption is caused by the lower troughing angle when the belt is empty. The forces on the idler are four times higher for a troughing angle of 30◦ than for an angle of 10◦. And the forces on the idlers lead to the roll-over resistance which is the biggest contribution to the power consumption of a belt conveyor.
4.4
Control and monitoring
The most recent changes in belt conveyor systems have taken place in the area of control and monitoring. In the early days this was not possible be-cause of the lack of adequate technologies. If there was any equipment for the control and monitoring it was of the centralized type. The data was gathered in one place and handled nearby. But as time progressed tech-nologies became available to gather data remotely. As a result a distributed control and monitoring system is not a problem any more. This section gives information about some of the most widespread methods of control and monitoring that have been introduced in the recent years.
Variable speed control
As shown in the section about the drive train of belt conveyor systems the modern drive systems are able to control the speed at which the belt runs. This is inherent to the nature of the system as it uses a Variable Frequency Converter (VFC).
A belt conveyor systems has a capacity that it can handle, this is based upon calculations taking into account the (near) maximum demand of the conveyor. This maximum demand of the system only rarely occurs, the belt conveyor runs most of the time at a lower load factor. This is where the variable speed control come into play. When the belt is fully loaded the belt speed is maximal, but when the needed capacity is lower the belt speed decreases accordingly. This has got the following advantages:
• Less wear on all components because the belt makes less circulations; • Lower take-up movement, resulting in lower belt tensions;
• Less degradation of material on the belt because it is filled with ma-terial;
• Reduction in energy use [30] [31].
The reduction in energy use is shown in Figure 4.12[31]. The Overland 1 belt conveyor system is 4220 meter long, has a capacity of 4000 ht with a belt speed of 2,86 ms. In this graph the blue dashed line represents the required drive power against the capacity for the constant speed operation. The pink continuous line is the relation for the variable speed operation. Both concepts use the same power when the belt conveyor system is running at full capacity, which makes sense. All the running gear remains the same, only the control part changes. The differences become bigger when the capacity decreases. At 2500 ht the difference between the two is nearly 175 kW, which is a energy saving of almost 18%. The actual saving will not be as high as 18%, but could still reach 10% in some cases in which the belt is most of the time under loaded.
Figure 4.12: Comparison of power usage (blue line is constant speed, pink variable).
The use of variable speed control requires some detailed information of the state of the system. Both the belt speed and de actual supply of bulk material onto the belt have to be known for proper operation of the system. Figure 4.13[32] shows a tachometer for the measurement of belt speed and a scale for the measurement of the material flow from Siemens.
(a) Belt tachometer. (b) Belt scale.
Belt wear analysis
The belt of a belt conveyor system is the hardest to replace component. The preferred option is to repair it whilst it is in place, before it suffers too much damage. There is only one problem, the belt of a belt conveyor can be very long (in excess of 30 km) and it is not feasible to check every centimetre of it by hand. This is where the belt wear monitoring systems come into play. A division into two types of systems can be made, the in- and outside monitoring ones. As the name indicates, the inside monitoring systems look inside the belt to check the carcass, the outside type looks at the state of the top- or bottom cover.
Figure 4.14: DiMI image of belt with damage.
Carcass monitoring
The monitoring of the steel cord carcass is done by a Digital Mag-netic Imaging (DiMI) system. Such a system is shown in Figure 4.15[33]. It works by magnetizing the steel cords in the belt, which are passed by an array of sensors that read the magnetic radiation of the belt. An example of the image that this sys-tem produces can be found in Fig-ure 4.14[33]. All the damaged cords show on this image as an black or white dot (depending on the
polar-ity). The black dot of the cord end shown in this figure begins in the splice, where the white begin can be found. With this image the state of the belt can be monitored and the affected parts can be repaired.
Cover monitoring
The cover of a belt conveyor is the part that is subject to the most wear. Therefore the monitoring of the cover has to be performed on a continuous basis. This is done using cameras that scan the empty belt. All the pictures are then analysed using specialized image processing software. In Figure 4.16 [34] a single video frame is given of a splice which shows early signs of de-lamination. When multiple of these images are collected and processed a keogram is made showing the belt state. Such a keogram can be found in Figure 4.17 [34]
Figure 4.16: A single video frame showing a de-laminating belt splice.
RFID-monitoring
One of the newest methods of belt conveyor system monitoring is by using Radio-Frequency Identification (RFID) technology. RFID technology can be used to monitor all the different aspects of the belt conveyor, but are specifically interesting when it comes to monitoring of the idlers. As said before the idlers are an essential part of the smooth operation of the belt conveyor. When they are not operating as supposed to, the system will use more energy. This requires for frequent checking of all the idlers, in some cases tens of thousands. This monitoring of the idlers can be done remotely by RFID technology.
The system uses a RFID sensor in each idler roller to monitor its state. The sensor performs the actual measurement, the RFID tag the communication. The sensor monitors the vibrations and temperature in the roller, when there is a problem one or both will differ from the normal operating baseline and a message is send for control, repair or replacement. Figure 4.18a[35] shows the idler roller with the embedded RFID sensor. All the sensors in the system need to be powered. The use of battery power is not an option because all the batteries have to be replaced when they are out of power. A solution is shown in Figure 4.18b[35], it proposes a local power generation method that powers each RFID sensor individually.
(a) RFID sensor embedded in idler
roller. (b) Power generating sensor node.
Figure 4.18: RFID-technology in conveyor belt monitoring.
The data collection is done by the RFID sensors, but still has to be sent to the central monitoring system. There are multiple options for this, for example decentralized collection points that gather data from a section of the belt conveyor and forward it to the monitoring system. But the RFID sensors them self can be incorporated in the path towards the monitoring system. The sensors are equipped with a RFID transceiver, the type that can sent information and receive it. This type of system is less vulnerable to breakdowns, when one of the RFID sensors stop working the network automatically routes the data flow around it.
Chapter 5
Development of the scale of
belt conveyor systems
This chapter will give an overview of the developments of belt conveyor systems over the years. First the data for the evaluation is given. After that an analysis is performed on the different aspects of these conveyor belts.
5.1
Belt conveyor data
The developments in the scale of belt conveyor systems is evaluated using the characteristics of several dozens of actual systems. These can be found in Appendix A (page 68), in Tables 2 and 4. To give an idea of the projects used, some are given in detail next. The following belt conveyor systems are elaborated: the longest, highest capacity, most powerful, fastest and strongest belt. The conveyors shown are not necessary the world leaders in their category, but they are leader in the database.
The longest single flight - Lafarge Surma
The Lafarge Surma belt conveyor system begins in the limestone mine of Meghalaya, India and ends at the cement plant in Noarai Chhatak, Bangladesh. It is constructed in 2006 and used to transport 1.2 million tons of material per year. It is a curved conveyor system with vertical and horizontal curves to fit in the landscape.
Year 2006 Material Limestone Length 16.833 m Capacity 800 ht Power 1.890 kW Belt speed 4 ms Lift 59 m Belt class 2.500 mmN Belt width 800 mm
Drive configuration: 1x tail drive of 630 kW + 2x head drive of 630 kW.
When looking at belt conveyor length over the entire industry there are multiple systems that surpass the Lafarge Surma belt conveyor. The Bod-dington Bauxite Mine in Western Australia is composed of two flights, one of 20 km and one of 31 km. This is said to be the record belt conveyor system and the runner up concerning length. These belt conveyor systems have not been added to the belt conveyor database because of insufficient data on them.
Highest capacity - Bingham Canyon
Bingham Canyon is a copper mine near Salt Lake City in Utah, USA. It is operational since 1903 and is part of the largest and most up-to-date integrated copper operation in the world. With a capacity of 9100 ton per hour it is by far the highest throughput system when looking at tonnage (volume is a different story). Combined with the length of 5300 m this is the longest high tonnage overland conveyor in the USA.
Year 1988 Material Copper Length 5.300 m Capacity 9100 ht Power 4.480 kW Belt speed 4,7 ms Lift -27 m Belt class 3.000 mmN Belt width 1.829 mm
Drive configuration: 2x tail drive of 1.120 kW + 2x head drive of 1.120 kW.
Most powerful - Henderson PC2
The Henderson PC2 belt conveyor is the second belt of the three-flight Henderson conveyor system. It is located in Colorado, USA around 150 km west of Denver at an elevation of 3000 m. The total length of the three conveyors is 24 km and is used to transport molybdenum ore and is curved with 11 vertical and 9 horizontal curves.
Year 1999 Material Molybdenum Length 16.825 m Capacity 2.270 ht Power 8.200 kW Belt speed 4,5 ms Lift 475 m Belt class 5.400 mmN Belt width 1200 mm
Fastest - Adani Group SC-1A
In 2013 the Adani group commissioned two belt conveyors to haul coal from the Dajeh Port (Bharuch district, west India) to a stockpile. Besides the high transport speed this belt conveyor system has got another unusual feature. The structure is made from ultra lightweight elevated, triangulated galleries, weighing only 209 kgm. They do not include walkways and are therefore maintained using a motorized trolley.
Year 2013 Material Coal Length 1.600 m Capacity 6.000 ht Power 1.000 kW Belt speed 7,5 ms Lift -6,7 m Belt class 1.000 mmN Belt width 1.600 mm
Drive configuration: 2x head drive of 500 kW.
Strongest belt - Selby South
The Selby Coalfield in Great-Britain is were the Selby south belt can be found. It is part of a system of one cable belt, one long overland belt conveyor and six underground belt conveyors. This system is used to mine for coal since 1983, but the coalfield is operational since the early 1950s. This conveyor has the strongest belt because the maximum belt speed in 8,2 ms, since this speed is not often reached the average speed is shown.
Year 1983 Material Coal Length 12.232 m Capacity 2.500 ht Power 5.050 kW Belt speed 4,2 ms Lift -805 m Belt class 6.950 mmN Belt width 1.300 mm
