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    Belt conveyor network design using simulationT van Vianen*, J Ottjes and G Lodewijks

     Delft University of Technology, Delft, The Netherlands

    In this paper simulation is applied to design belt conveyor networks at dry bulk terminals. Stochastic variations in ship interarrival

    times, shiploads and equipment availabilities enforce the use of simulation. Parameters that affect belt conveyor network designs

    like the network connectivity, storage policy and stochastic distributions are evaluated in this paper. One of the main ndings is that 

    installing the maximum number of connections does not necessarily lead to better performances. Another nding is that redundancy

    of piles (a pile is in reach of two stockyard machines) is more ef cient than increasing the number of connections. In a case study,

    designs for belt conveyor networks were formulated and assessed using the simulation model developed.

     Journal of Simulation advance online publication, 13 February 2015; doi:10.1057/jos.2014.38

    Keywords: transport; queuing; simulation; stochastic processes; allocation and scheduling

    1. Introduction

    Dry bulk terminals are essential nodes in the supply chains for 

    coal and iron ore. These bulk materials are used for the world-

    wide production of energy and steel. To facilitate the expected

    growing cargo   ows, new dry bulk terminals will be built or 

    existing ones will be expanded. In the supply chains for these

    materials, bulk ships and cargo trains are generally used for 

    transport. The terminal operation is complex when both ships and

    trains have to be served at the same time to meet predened

    agreements (Robinson, 2007). This research focuses on the

    transport network at the terminals. Such networks have to

    facilitate all required transportation needs linking several sourcesand destinations and consist of belt conveyors and transfer points.

    In a transfer point, the material   ow is transferred between

    different belt conveyors.

    In this paper simulation is applied to determine the parameters

    that affect the design of belt conveyor networks and to assess

    such designs. In section 2, a literature review is presented about 

    dry bulk terminal design and in particular the network design.

    The simulation model developed is introduced in Section 3.

    In Section 4, the impact of terminal parameters on the network 

    design (like the network connectivity, the storage policy and the

    redundancy of stockyard machines) is investigated. Section 5

    demonstrates the integration of simulation for a belt conveyor 

    network design. Finally, conclusions are presented in Section 6.

    2. Literature review

    In Section 2.1, a literature review is presented for the design of 

    dry bulk terminals and in particular for belt conveyor networks.

    Due to the lack of a comprehensive design method, references

    published about pipeline networks were investigated to verify if 

    models presented can be applied for belt conveyor networks.

    In Section 2.2, these papers are reviewed. Section 2.3 presents an

    evaluation of this review and the selection for the modelling

    approach.

    2.1. Dry bulk terminal design

    Papers that discuss belt conveyor network designs were hardly

    found; possibly due to the protection of its substantial commercial

    value by industrial practitioners or consultation companies. Even in

    the most comprehensive design method for terminals, already

    introduced by the United Nations Conference on Trade and

    Development in 1985 (UNCTAD, 1985), there was no information

    found how belt conveyor networks should be designed.

    Many authors used simulation for the design of (parts of ) dry

    bulk terminals. In   Table 1, an overview is listed. Most of these

    references applied simulation for a specic case; these models

    cannot easily be applied for the design of belt conveyor networks.

    Two references discussed the network design in particular.

    Lodewijks et al   (2009) proposed several belt conveyor congura-

    tions for an export terminal. In this paper the following parameters

    were investigated that affect network design; direct transshipment 

    of materials, type of belt conveyor and using multiple shared or dedicated transport routes. Boschert and Hellmuth (2010)  applied

    the   ‘Simulation Tool for Conveying Systems’, developed by

    Siemens AG, to design conveying systems. Although the case

    studies presented look promising, the commercial programme is

    required to perform comparable studies.

    2.2. Pipeline network design

    On the design of pipeline networks for the transport of water,

    natural gas or hydrogen, a signicant amount of research has

    *Correspondence: T van Vianen, Delft University o f Technology, Department 

    of Marine and Transport Technology, Mekelweg 2, 2628 CD, Delft,The Netherlands.

    E-mail:  [email protected]

     Journal of Simu lation (2015), 1 – 9   © 2015 Operational Research Society Ltd. All rights reserved. 1747-7778/15

    www.palgrave-journals.com/jos/

    http://dx.doi.org/10.1057/jos.2014.38mailto:[email protected]://www.palgrave-journals.com/joshttp://www.palgrave-journals.com/josmailto:[email protected]://dx.doi.org/10.1057/jos.2014.38

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    been performed; see for an extensive review André et al   (2013).

    Similar to the dry bulk industry products are transported in a 

    continuous mode. A belt conveyor can be compared with a pipe

    and stockpiles with tanks. Some of the  rst authors that discusspipeline networks were Mah and Shacham (1978). These authors

    formulated the optimal network design as a constrained mini-

    mization problem based on the number of pipe sections, the

    length and diameter of the pipe sections, and cost coef cients that 

    are directly related to investment costs. This problem corresponds

    with the determination of the required transport capacity of belt 

    conveyors but gave no suggestions for network layouts. Further-

    more, a difference between dry bulk and tank terminals is that 

    generally at tank terminals, product dedicated or customer 

    dedicated pipelines are used between specic sources and

    destinations.

    André et al   (2013)  presented a methodology for the simulta-

    neous determination of the topology and the diameters of 

    hydrogen transport networks. These authors stated that with the

    choice made for a quadratic cost function and with head losses,

    losses of energy due to the internal wall friction of pipes, optimal

    networks are trees. This suggestion is a relevant one and can be

    translated to belt conveyor networks where the yard conveyors

    (that feed the stockyard machines) form the trunk and conveyors

    that connect the loading and unloading machines to these yard

    conveyors are branches. A difference between pipeline networks

    and a belt conveyor network is that the   rst networks are

    generally equipped with multi-sources (ie many hydrogen pro-

    duction plants) and the network ’s objective is to realize an

    optimal facility location/allocation problem. At dry bulk term-inals there are multiple transports required at the same time from 

    specic sources and to specic destinations using a limited

    number of belt conveyors.

    2.3. Evaluation and selection of modelling approach

    Design methods for belt conveyor networks were not found in

    literature, although several authors used simulation to assist 

    during the design process of dry bulk terminals. Several batches

    of materials must be transported simultaneously and on time

    while taking the stochastic arrival processes, equipment break-

    down behaviour and material   ows into account. Furthermore,

    dedicated transports have to be performed at the same time using

    a limited number of belt conveyors. A simulation model will bedeveloped to consider the stochastic processes mentioned.

    By varying characteristics in belt conveyor networks and by

    registering the corresponding performances, relevant insight will

    be acquired to design such networks.

    3. Simulation model

    This section introduces the simulation model that was developed

    for the design of belt conveyor networks. The advantage of this

    model is that not only the stochastic processes are considered but 

    also specic terminal operational procedures like the storage

    policy and particular network characteristics are taken intoaccount. The approach followed is mentioned in Section 3.1.

    Specic details of the simulation model are presented in Sections

    3.2 and 3.3; the verication of this model is discussed.

    3.1. The simulation-based approach

    For the development of the simulation model the process-

    interaction method introduced by   Zeigler   et al   (2000)   and

    Fishmann (2001)   was followed. The terminal was virtually

    broken down into relevant element classes each with their typical

    attributes resulting in an object-oriented data structure of the

    system. For all active element classes process descriptions, whichdescribe the functioning of each element as a function of time,

    were dened. In the simulation model all active elements act 

    parallel in time, synchronized by the sequencing mechanism of 

    the simulation software, in this case Delphi®, using the simula-

    tion application TOMAS (Veeke and Ottjes, 1999).

    3.2. Simulation model 

    The simulation model is applicable for both import and export 

    terminals but in this section the model will be explained for 

    Table 1   Review of references that applied simulation-integrated design of dry bulk terminals

     Author(s) Year Design Application

    Baunach et al    1985  Compare alternative berth and equipment congurations Coal terminal in Indonesia  El Sheikh et al    1987   Planning of future berth requirements Third-world port  Park and Noh   1987   Simulate future port capacity required Port of Mobile (US)Kondratowicz   1990   Simulation methodology for intermodal freight transportation terminals General

    King et al    1993   Planning and de-bottlenecking studies Power plant in China  Weiss et al    1999   Optimize receiving, storage, blending and shiploading facilities GeneralDahal et al    2003   Design and operation, including equipment replacement and operational scheduling Iron ore terminal in UK Sanchez et al    2005   Determination number of berths Power plant MexicoOttjes  et al    2007   Improving operational control GeneralLodewijks  et al    2009   Network design layouts and belt conveyor types (bi-way or single-way) Iron ore terminal India Boschert and Hellmuth   2010   Design and optimization of belt conveyor systems Stockyard at a steel factoryCassettari  et al    2011   Determination grab unloader and storage capacities Coal power plant  

    2   Journal of Simulation

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    import terminals. Ships deliver bulk materials and trains pick upmaterial in small portions. Figure 1 shows an arbitrary terminal

    layout with the main element classes; ships and trains with their 

    generators, piles of bulk materials at stockyard lanes (L1–L4),

    belt conveyors and stockyard machines, in this case stacker-

    reclaimers. Stacker-reclaimers combine the two functions of 

    stacking and reclaiming into a single unit. Consequently, only

    one of the two functions can be fullled at a time.

    Bulk handling activities are called jobs. A job can be a 

    trainload or a (part of the) shipload. The job material is stored

    temporarily in a pile at the stockyard. Piles stored at the middle

    lanes (L2 and L3) are in reach of two stacker-reclaimers. These

    piles can be stacked and/or reclaimed together or separately at thesame time. In Figure 1  two generators are shown; one for ships

    and one for trains. In the ship generator, the ship arrivals and

    shiploads are determined using historical data or are sampled out 

    of analytical distributions. In the train generator the pile’s storage

    time is determined using the storage time distribution and trains

    are generated to pick up the pile’s material within its storage time.

    To express the network connectivity, the indicator (τ ) [ − ] was

    introduced. This indicator expresses the ratio between the number 

    of installed and the maximum number of connections. A connec-

    tion is formed by a transfer point. For example, the routing

    exibility (τ ) is   7 / 12 for the network shown in  Figure 1  because

    this network is equipped with seven transfer points while the

    maximum number is 12.

    3.3. Veri cation

    Verication of the simulation model is required to check the

    correct translation of the conceptual model into computer code

    and to determine if the simulation model performs as intended.

    Simulation results for a simplied network (as shown in

    Figure 2a ) were compared with analytical results using queuing

    theory. For the incoming (Qin) as well as the outgoing material

    ow (Qout ) it was assumed that the interarrival times werenegative exponential distributed. Furthermore, it was assumed

    that there was no variation in job size (called in queuing theory:

    deterministic (D)) and both incoming and outgoing job sizes were

    assumed as 100 kilotons [kt]. To each stacker-reclaimer three

    grades were assigned. For example, at the lanes within the reach

    of stacker-reclaimer 1 only material with grades A, B or C is

    stored. When these conditions are considered, the terminal layout 

    of Figure 2a  can be represented by two individual M/D/1-queuing

    systems, as shown in Figure 2b.

    The relation for the job waiting time as function of the service

    time and the stockyard machines utilization was derived from an

    M/G/1-queuing system. This relation was formulated by Tijms andKalvelagen (1994) and is expressed algebraically in Equation (1).

    Wt   ¼1

    21 + c2 B

      ρSR1 -  ρSR

    1

     μ(1)

    where   Wt   is the average job waiting time, expressed in the

    inverse of the service rate [ μ], cB [ − ] is the variation coef cient 

    for the service times (for the M/D/1-queuing system this

    coef cient is 0) and   ρsr 

      [− ] is the average utilization for the

    stacker-reclaimers.

    For the simulation results the average ship and train port times

    were determined at the end of each simulation run (displayed as a 

    single dot in the graphs that show the results) as function of the

    machine utilization. To achieve an accuracy of ± 5% at least 8000ships have to be generated per simulation run.

    Figure 3 shows the results for the verication study. From this

    gure it can be concluded that the simulation results of the

    simplied network correspond with the analytical results for the

    M/D/1-queuing system. For more complicated networks and

    more realistic input data (that takes the real-world ship interarrival

    times and shiploads into account) the tracing function of TOMAS

    was used to follow the unloading process of several ships. Results

    of this analysis have shown suf cient reasons to consider that the

    simulation model performs as intended.

    Ship

    generator

    Interarrival time

    distribution

    Shipload

    distribution

    Bulk ship Cargo trainStacker-

    reclaimer

    Pile SR1

    SR2

    SR3

    Train

    generator

    Storage time

    distribution

    Belt conveyor Transfer station Pile

    Stockyard

    lane

    (un)loader Control signals

    L1

    L2

    L3

    L4

    Figure 1   Schematic representation of the simulation model (description follows in text).

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    4. Assessment of design parameters

    In this section the following parameters that affect the network 

    design will be investigated; the network connectivity, the storage

    policy and the stochastic processes. The network connectivity (τ )

    was already introduced in the previous section and expressed the

    number of transfer points installed  versus the maximum number.

    The storage policy and stochastic processes will be further 

    explained in Section 4.1. Simulation experiments are shown in

    Section 4.2

    4.1. Storage strategy and stochastic processes

    For the storage policy, two different strategies were introduced by

    Leech (2010); the cargo assembly mode (CAM) and Identity

    Preserved (ID). For CAM, materials are stored in piles based on

    their grade and for the ID-storage policy segregated piles are

    formed for individual clients. The CAM storage policy is

    generally applied at export terminals, where materials from a 

    limited number of mines are stored, or at single-user import 

    terminals. When the ID-storage policy is applied several piles can

    contain the same grade but the pile owners are different. The

    ID-storage policy is generally applied at stevedoring import 

    terminals where customers’ materials have to be stored individu-

    ally to prevent mixing and to realize tracking and tracing of material. The potential downside of the latter storage policy is

    that it demands a greater level of network   exibility and

    operational planning.

    For the stochastic processes, several distribution types were

    proposed. For the ship interarrival time distribution   UNCTAD

    (1985) and Bugaric and Petrovic (2007) stated that the arrivals of 

    bulk ships are best approximated by a Poisson arrival process.

    The ship interarrival times can then be represented by a negative

    exponential distribution (NED). Altiok claimed that at specialized

    dry bulk terminals (eg, single user terminals) the interarrival

    times show less variation. An Erlang-2 distribution can better be

    applied for these terminals (Altiok, 2000).

    For the ship service time distribution two references proposed

    an Erlang-2 distribution,  UNCTAD (1985) and   Jagerman and

    Altiok (2003). However, these distribution types do not corre-

    spond with measured data from three dry bulk terminals. This

    analysis has shown that the shipload varies signicantly and a  t 

    with analytical distributions cannot be made. Empirical shipload

    data can better be used as input to comply with real-world

    operation.

    There was no reference found that discussed the stochastic

    variations of material stored at stockyards. To get an impression,

    real-world data that contain storage times of 8500 piles during

    19 years of operation for a specic terminal was analysed. The

    average pile’s storage time was 0.2 year. A  χ2

    method was usedto   t the storage time distribution with analytical distributions.

    Results of this  t show a match with the NED. This distribution

    was implemented in the simulation model but using empirical

    data is also possible.

    For the belt conveyor network, the conveyor breakdown

    behaviour must be considered as well. A transportation route

    consists of multiple belt conveyors in series, if one belt conveyor 

    fails the entire route fails. According to   van Beek (2009), the

    system reliability can be approximated by multiplying the

    availability of the individual components. Historical operational

     

    Qin+ Qout

    SR1

    M/D/1

    SR2

    M/D/1

    A   B C

    D   E FQout

    (M/D) 100 [kt]

    B

    C

    Qin 

    (M/D) 100 [kt]

    A

    E

    F

    D

    a b

    SR1

    SR2Qin+ Qout

    Figure 2   Verication of the simulation model for a simplied network layout (a), which can be represented by two individualM/D/1-queuing systems (b).

    0.0

    0.2

    0.4

    0.6

    0.8

    1.0

    1.2

    1.4

    1.6

    0.3 0.4 0.5 0.6 0.7 0.8 0.9

       W   t   [   1   /  µ   ]

    sr [-]

    M/D/1

    Simulation Results

    Figure 3   Verication of the simulation model; comparison

    between analytical results (M/D/1) and simulation results for thesimplied network layout as shown in Figure 2a .

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    data of the utilization of belt conveyors at an export terminal

    during 1 year of operation has shown a variation of the tech-

    nical availability between 0.9 and 0.97. In this research, a 

    technical availability of 0.97 will be used for each belt conveyor.

    In accordance to Tewari  et al   (1991)  and  van Beek (2009)  the

    (negative) exponential distribution is implemented in the simula-

    tion model to describe the probability density function of a 

    failure. This distribution type corresponds with real-world opera-

    tion; usually the failure time is relatively small (eg, fuse out due

    to overloading) and a single time exceptional long (eg, the belt is

    demolished).

    In the simulation model, the active job’s handling time will be

    extended with the repair time of the broken conveyor. This

    corresponds with reality, changing a route is not regularly

    performed due to the short downtime and relatively long start-up

    times of another route.

    4.2. Simulation experiments

    A network layout as shown in Figure 1 is used to investigate thestorage policy on the network design. The simulation model was

    applied to determine for several scenario’s the sum of the average

    ship and train port times. The input parameters used are listed in

    Table 2.

    Two network congurations are shown in   Figure 4   for the

    CAM-storage policy. The allocation of grades to the stacker-

    reclaimers is different for both scenarios. In Figure 4a  each grade

    is assigned to a single machine and in   Figure 4b each grade is

    assigned to two machines. This distribution of grades across

    multiple machines corresponds to the stockpile duplication

    proposed by   Leech (2012)   and introduces a stacker-reclaimer 

    redundancy.

    Figure 5 shows the sum of the average ship and train port times

    versus   the annual throughput (Q) for both layouts as shown in

    Figure 4. Another layout with a fully equipped network (τ =1)

    was assessed. This layout is not displayed separately in this paper 

    but can easily be derived by combining the network conguration

    from  Figure 6b   with the stockyard layout of   Figure 4a . From 

    Figure 5  it can be concluded that stacker-reclaimer redundancy

    realizes a larger reduction of the sum of the average ship and train

    port times than a fully equipped network.

    For the assessment of the ID-storage policy, the network 

    congurations as shown in Figure 1 and 6 are used. The network 

    connectivity varies from τ =7/12 (Figure 1) until τ =1 (Figure 6b).

    0

    30

    60

    90

    120

    150

    10 12 14 16 18 20

       W  s   h   i  p  +   W   t  r  a   i  n

       [   h   ]

    Q [Mt/y]

    Fig. 4A, CAM, τ=7/12

    CAM, τ=1

    Fig. 4B, CAM, τ=7/12, SR-redundancy

    Figure 5   The sum of the average ship and train port times versusthe annual throughput for the CAM-storage policy.

    (CAM, τ=7/12)

    SR1

    SR2

    SR3

    A

    BC

    DE

    F

    (CAM, τ=7/12, stacker-reclaimer redundancy)

    SR1

    SR2

    SR3

    BA

    C D

    E F

    A B

    a b

    Figure 4   CAM-storage policy with different grade allocation procedures; (a) each grade is assigned to a single stacker-reclaimer and

    (b) each grade is assigned to two stacker-reclaimers.

    Table 2   Input parameters for the simulation model

    Parameter Value Parameter Value

    Ship interarrival time distribution NED SR-capacities [kt/h] 2.5Shipload distribution Historical data* Average pile’s storage time [h] 500Storage time distribution NED Average shipload [kt] 101Belt conveyor technical availability [− ] 0.97 Trainload 4

    *Based on data of 898 visited ships at a dry bulk terminal.

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    Figure 7 shows the results determined. As expected, the average

    port times decrease when the network connectivity increases.

    However, the reduction of the port times is limited when the

    network connectivity was increased from  ¾ until the maximum 

    value of 1. For this case, a fully equipped network does not 

    bring that much improvement anymore compared to a less

    extended belt conveyor network.

    The impact of the stochastic distributions on the network 

    design was investigated by evaluating the layout of  Figure 1 with

    different stochastic distributions. The   rst series (Figure 1, ID,

    τ = 7/12, M/G (Hist. data)) was already shown in  Figure 7. For 

    the same layout, the Erlang-2 distribution was used to represent the ship interarrival times and shiploads were sampled uniformly

    between 50 and 150 [kt]. The results are shown in   Figure 8.

    A reduced variability of the ship arrival processes enables

    installing a less extended belt conveyor network still guarantee-

    ing the predened performance.

    5. Network design: a case study

    To demonstrate the application of simulation during the design

    process of belt conveyor networks a case study was formulated.

    A terminal operator planned to redesign a part of its belt conveyor 

    network. Within this part, shown with the hatch lled rectangle in

    Figure 9, many connections between different belt conveyors can

    be made. The rst step was to implement Layout 2011, which is a 

    combination of  Figures 9 and 10a , into the simulation model to

    determine the initial performance. Besides, the possible connec-

    tions for Layout 2011 were investigated. Two alternative designs

    will be formulated and assessed in this case study. These designs

    must comply with the requirement that at least the same

    connections must be possible as it was in the original layout.

    More details from the formulation of both alternative designs are

    listed below.For the   rst design (as shown in   Figure 10b) an extra 

    requirement was formulated that even a comparable simultaneity

    of the transport activities should be realized as in the current 

    layout. This means that the number of routes that can be used at 

    the same time may not be reduced. To reduce the number of 

    transfer points, dedicated belt conveyors are proposed between

    the stacker-reclaimers (SR1: 210, SR2: 220 and SR3:230) and

    loading machines. The consequence was that all quay conveyors

    (numbers 10, 20 and 30 in  Figure 10b) need to be connected

    to the three stacker-reclaimers via the four cross-conveyors

    SR1

    SR2

    SR3

    (ID, τ=¾)   ba (ID, τ=1)

    SR1

    SR2

    SR3

    Figure 6   ID-storage policy applied at two layouts each with different values for the network connectivity (τ ).

    0

    30

    60

    90

    120

    150

    10 12 14 16 18 20

       W  s   h   i  p  +   W   t  r  a   i  n

       [   h   ]

    Q [Mt/y]

    Fig.1, ID, τ=7/12

    Fig.6A, ID, τ=¾

    Fig.6B, ID, τ=1

    Figure 7   The sum of the average ship and train port time   versusthe annual throughput for different network layouts.

    0

    30

    60

    90

    120

    150

    10 12 14 16 18 20

       W  s   h   i  p  +   W   t  r  a   i  n

       [   h   ]

    Q [Mt/y]

    Fig.1, ID, τ=7/12, M/G (Hist.data)

    Fig.1, ID, τ=7/12, E2/G (50-150 [kt])

    Figure 8   ID-storage policy applied for network layout as shownin Figure 1 with different stochastic distributions.

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    (100, 110, 120 and 130) while one or two of them are active with

    reclaiming. Using dedicated belt conveyors reduced the total

    number of belt conveyors in the terminal from 51 to 45. Two

    extra transfer points are needed to realize all connections resulting

    in an increase of the network connectivity (τ ) from 0.9 to 0.94.

    Advantages of this design are the expected decrease of the

    disturbance time, thanks to the reduction of belt conveyors, and

    the decrease of the transportation power because the material

    does not need to be fed up as frequent as in the existing layout.

    For the formulation of the second design (as shown in

    Figure 10c) it was allowed that some routes, which are hardly

    used simultaneously based on historical operational data, cannot 

    be performed at the same time anymore. The transport of 

    materials to the second barge loader (belt conveyor 520 in

    Figure 10c) cannot be performed at the same time anymore when

    material is transported to the iron ore railcar loader (135) or to the

    blending silo’s (114). This concession was justied by the fact that at the terminal three barge loaders are installed and loading of 

    three barges at the same time did hardly happen. Moreover, a 

    relatively small amount of material (11% of coal) is fed to the

    blending silos so the probability is limited that this conicting

    situation will occur. Design 2 applies further the fundamentals of 

    the  rst design; all quay conveyors need to be connected to the

    cross-conveyors and dedicated belt conveyors are proposed for 

    the transport to the loading machines. In Design 2 less transfer 

    points are then needed resulting in a decrease of the network 

    connectivity (τ ) to 0.83.

    For the terminal layout of  Figure 9 combined with one of the

    network layouts as shown in Figure 10, the average port times for 

    ships and landside jobs (trains, barges, coastal ships and exports

    to the coal-red power plant) were determined using the simula-

    tion model as function of the annual throughput. The input 

    parameters as listed in   Table 2  were used and the results are

    shown in Figure 11. From this  gure, it can be concluded that the

    average port times will be reduced when both designs will be

    applied in comparison to the existing layout, which is

    Layout 2011.

    The minor difference in port times between design 1 and

    design 2 is remarkable. Although the belt conveyor network of 

    design 2 is less redundant, the higher network connectivity does

    not bring a signicant reduction of the average port times for 

    design 1. Apparently, the conicting situations when material

    must be transported to the second barge loader, the iron ore rail

    car loader and the blending silos at the same time are rare.In conclusion, for the redesign of the belt conveyor network 

    design 2 is proposed because a comparable reduction of the

    average port times will be realized as for design 1 but the network 

    can be carried out simpler and cheaper.

    6. Conclusions

    Belt conveyor networks have to facilitate transport activities

    to meet the contractual agreements for the terminal’s seaside

    SR5

    SR6

    SR3

    SR4

    Figure 10

    SR1

    SR2

    QCV1 QCV2 QCV3

    L1

    L7

    L2

    L3

    L4

    L5

    L6

    Figure 9   The investigated terminal layout with the redesign object (shown with the hatch lled rectangle).

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    and landside. Due to the lack of comprehensive models that 

    can support the belt conveyor network design and to take the

    stochastic processes into account, a simulation model was

    developed. To be in line with the terminal operation, empirical

    data can be used as input. Nevertheless, analytical distri-

    butions can also be selected to represent the stochastic

    variations. The simulation model was applied to determine the

    consequence of parameters like the network connectivity,

    storage policies and stochastic processes on the design of belt 

    conveyor networks. The stacker-reclaimer redundancy, a pilestored at the stockyard is in reach of two stockyard machines,

    results in a larger reduction of the average ship port time

    (which is the objective for terminal operators) than an

    increase of the number of connections. Another  nding was that 

    installing the maximum number of connections does not 

    lead directly to better performances. The stochastic variations

    should be considered as well during belt conveyor network 

    design. An increase of the variation requires more active

    transport routes at the same time and more connections are

    needed to realize the performance predened. In a case study,

    Layout 2011 (τ: 0.9) Design 1 (τ: 0.94) Design 2 (τ: 0.83)

    135

    240 240

    20

    30

    10

    210

    220

    230

           5        1        0

           5        2        0

    410

            1        1        4

            1        4        4

            1       5        4

    240

    420

    712

    135

            1        3        0

            1        2        0

            1        1        0

            1        0        0

            1        1        1

    1001

            1        3        1

    1341000

    340

    330

    210

    220

    230

    135

    20

    30

    10

            1        3        0

            1        2        0

            1        1        0

            1        0        0

    210

    220

    230

            1        1        1

           5        1        0

           5        2        0

    410

            1        1        4

            1        1        1

            1        2        1

            1        3        1

            1        4        4

            1       5        4

    134

    340

    420

    712

    330

    Belt conveyor

            1        1        4

    10

    20

    connection

            1        3        0

            1        2        0

            1        1        1

    712

           5        1        0

           5        2        0

    410

    420

            1        1        3

            1        2        2

            1        3        2

            1        3        6

            1        4        4

            1       5        4

    330

    134

            1        3        3

            1        2        3

    340

    131121

    Transfer point

    30

    a b c

    Figure 10   Different network congurations for the redesign object; existing layout in 2011 (a) and two designs (b–c).

    60

    75

    90

    105

    120

    25 30 35 40

       W  s   h   i  p  +

       W   l  a  n   d  s   i   d  e   j  o   b   [   h   ]

    Q [Mt/y]

    Layout 2011 (τ=0.9)

    Design 1 (τ=0.94)

    Design 2 (τ=0.83)

    Figure 11   The sum of the average port times for ships andlandside jobs (trains, barges, etc) for the existing layout and newdesigns.

    8   Journal of Simulation

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    the simulation model was applied to formulate and to assess belt 

    conveyor networks for the replacement of a part of an existing

    network.

     Acknowledgements—The authors acknowledge the terminal operator whoprovided operational data of the ship arrival and storage processes and for giving valuable feedback during this research.

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     Received 25 February 2014;

    accepted 29 October 2014 after one revision

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