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**Stockyard layout (re)design**

Delft University of Technology Faculty 3ME, Transport Engineering & Logistics G. Lodewijks, T.A. van Vianen and J.A. Ottjes

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**Export Terminal Saldanha Bay SA**

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**Bulk terminal simulation**

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**Content Stockyard functions Stockyard machines**

The machine selection for capacity & blending or homogenizing The machine selection for the storage of bulk materials CASE: stockyard layout design for an import terminal Summary Delwaidedok, Antwerp (Courtesy HeliHolland/Kees Vlot)

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1. Stockyard functions

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Stockyard functions Storage: large batches are supplied to piles and smaller batches are transported from the stockyard. Blending: mixing of at least two different bulk materials to achieve a blend with a new average level of bulk properties Homogenizing: the standard deviation of the bulk materials is reduced while the average value remains the same.

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2. Stockyard machines

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**Stockyard machines - Overview (1)**

Handling coal using wheel loaders and mobile feed bunker (Courtesy N.M. Heilig BV) Stacking of coal using a stacker (Courtesy ThyssenKrupp) Circular storage (Courtesy HeliHolland/ Kees Vlot) Relatively small terminals use wheel loaders and mobile feed bunkers, e.g. Dutch terminals with annual throughput less than 4 million tons Larger terminals use stackers to stack bulk materials in piles at longitudinal lanes (picture left under) Circular storage systems are also used. Advantages are a compact design, simultaneously endless stacking and reclaiming and well suited for roofed storage. Disadvantages are the higher investment costs and limited storage size. Picture right under shows a circular open storage near a coal-fired power plant in Amsterdam.

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**Stockyard machines - Overview (2)**

Bucket wheel reclaimer (Courtesy FAM) At many dry bulk terminals, bucket wheel reclaimers or bucket wheel stacker/reclaimers are installed. A wheel with attached buckets is used as reclaiming mechanism. Bucket wheel stacker/reclaimers combine the two functions stacking and reclaiming into a single unit. Left under picture shows such a machine during stacking of coal and right under shows the reclaiming of coal. Bucket wheel stacker/reclaimer, left: stacking, right: reclaiming (Courtesy ThyssenKrupp)

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**Stockyard machines - Overview (3)**

Double sided bridge scraper reclaimer (Courtesy ThyssenKrupp) At many dry bulk terminals, bucket wheel reclaimers or bucket wheel stacker/reclaimers are installed. A wheel with attached buckets is used as reclaiming mechanism. Bucket wheel stacker/reclaimers combine the two functions stacking and reclaiming into a single unit. Left under picture shows such a machine during stacking of coal and right under shows the reclaiming of coal. Reclaiming with a side scraper and stacking with an overhead belt conveyor (Courtesy Taim Weser)

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**3. The machine selection for capacity & blending or homogenizing**

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**Stockyard machines - Effective capacity ratio (1)**

During terminal (re)design, the effective capacity ratio is essential to prevent selecting a machine with insufficient capacity Effective capacity ratio for a bucket wheel reclaimer relates to the used reclaiming method Long-travel reclaiming method Slewing bench reclaiming method For many stockyard machines the effective capacity ratio was found in many references. However, for bucket wheel reclaimers many different values were found, varying from 0.5 until Because of this large variation and to determine the parameters which determine this ratio, this ratio was analytically determined. Long-travel: bucket wheel is inserted in the pile and the machine travels alongside the pile. Capacity relates predominantly to travelling speed and maximum digging capacity of bucket wheel Slewing bench: boom rotates and the machine steps small distances (~ 1 meter) forwards. The capacity per slew motion will be determined

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**Slewing reclaiming method A) top view and B) lateral view**

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**Maximum slewing acceleration/ deceleration**

Nominal reclaiming capacity: Para-meter Description Value Unit hs Slice height 4.5 [m] rbw Radius of bucket wheel Δx Max. chip thickness 1 ωss Minimum slewing speed 0.145 [rad/min] ρm Bulk density coal 0.8 [t/m3] ωsm Maximum slewing speed 0.58 lb Boom length 60 as Maximum slewing acceleration/ deceleration 0.5 [rad/min2]

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Reclaiming capacity for the slewing bench reclaiming method relates to (i) slice cross-sectional area, (ii) the slewing speed and (iii) bulk density of the reclaimed material. The reclaim capacity can be kept stable with an increase of the slewing speed Without slewing speed adjustment With slewing speed adjustment The slice cross-sectional area reduces when the slewing angle θ increases. To compensate this reduction, the slewing speed can be increased.

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**Stockyard machines - Effective capacity ratio (2)**

The effective capacity ratio was calculated for bucket wheel reclaimers for the long-travel and the slewing-bench reclaiming method. Para-meter Description Value Unit lt Total pile’s length 325 [m] h Slice height 4.5 w Pile’s width 50 Δx Maximum chip thickness 1 Height of the pile 18 lb Boom length 60 ρm Bulk density coal 0.8 [t/m3] rbw Radius of bucket wheel α Angle of repose 38 [°] ωss Start slewing speed 0.25 [rad/min] vt Travelling speed 10 [m/min] ωsm Maximum slewing speed 0.58 at Travel acceleration and deceleration 0.15 [m/min2] as Maximum slewing acceleration & deceleration 0.5 [rad/min2] y Distance centerline machine to pile

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The effective capacity ratio was for the long-travel reclaiming method 75% and for the slewing bench reclaiming method 45% Reclaiming capacity during a time interval of 40 hours for two reclaiming methods Note: these ratios are not general but were derived using specific input parameters

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**Reclaiming efficiency versus the pile's length for the long-travel reclaiming method**

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**Stockyard machines Main Characteristics Machine type**

Maximum capacity [t/h] Effective capacity ratio [-] Stockpile width [m] Reclaiming method to the pile Stacker 10,000 30-60 - Radial stacker 8,000 Ø120 Side scraper reclaimer 1,000 0.75 10-25 Alongside Single boom portal scraper reclaimer 2,200 15-60 Double boom portal scraper reclaimer 4,400 Bridge scraper reclaimer 1,800 0.95 At the face Bridge bucket wheel reclaimer Drum reclaimer 4,500 20-50 Bucket wheel reclaimer 12,000

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**Blending or homogenizing machines**

Stacking is the starting point of the blending process. Generally there are four basic stacking methods Reclaimer machine Stacking method Cone Shell Chevron Strata Windrow Single scraper reclaimer and Portal scraper reclaimer 2 3-4 4-6 Bridge scraper reclaimer - 10 5-6 8-9 Bridge bucket wheel reclaimer 4-8 Drum reclaimer 9-10 7-8 Bucket wheel reclaimer 4-5 Cone shell and chevron can be realized using a luffable boom stacker, strata and windrow stacking requires a luffable and slewable stacker. Depending on the required bed blending efficiency ratio, the reclaimer must be selected. Blending is good to very good: 7-10, moderate to good: 4-6. High blending ratios (ε: 7-10) can be realized using reclaiming the pile from the face; the bridge reclaimers and the drum reclaimer.

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**4. The machine selection for the storage of bulk materials**

Selection of archetype Cost calculation Operational performance

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**Selection of archetype**

Multi-purpose machine (stacker/reclaimer) or two single-purpose machines (stacker and reclaimer) For the storage of bulk materials, two main options exist. Installing a stacker and reclaimer or use the combined stacker/reclaimer. An archetype contains two stockyard lanes and a terminal area can has been build up by a multiple of archetypes Two layout archetypes

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**and the belt conveyor investment cost relates to its capacity**

Cost calculation Selection must be based on the archetype’s investment cost and performance It was assumed that the machine investment cost relates to its weight and the belt conveyor investment cost relates to its capacity Stacker/reclaimers weight versus capacities as function of boom length Total investment cost per archetype is the sum of the investment cost for the stockyard machine(s) and belt conveyor system(s) From 75 operating rail-mounted stockyard machines the machines weight, boom length and installed capacities were gathered. Because this data comes from many manufactures, there was a lot of variation in the data. Although it appears that the machine weight increases when the capacity and the boom length increases Some quotations for the price per meter for belt conveyor systems were received. The price varies per country and manufacturer. Belt conveyor suppliers do not like to share this (for them) confidential data. Thus this picture gives just an idea Price per meter for belt conveyors versus its transport capacity

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**Operational performance**

The performance at dry bulk terminals is generally expressed in the total time that ships and trains spend in the port The port time is the sum of the waiting time and service time The ships waiting time relates to: Interarrival time distribution Carrier tonnage distribution The ship (un)loader utilization Mean service rate Mean arrival rate Queuing theory formulas or simulation If the interarrival time or carrier tonnage distributions can be represented with general distributions then the Queuing theory formulas can be used. However, real-world data of carrier tonnages cannot be represented with a general distribution and then simulation is required.

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**5. Case: stockyard layout design for an import terminal**

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Main requirements: Import terminal with an annual throughput of 37 [Mt/y], 21% bypass (no storage and handling by stockyard machines) Required stockyard area: 92 [ha] Seaside: bulk carriers, landside: trains Interarrival time distribution seaside and landside: NED Carrier tonnage distribution: based on historical data (avg. 101 [kt]) Train tonnage distribution : uniform distributed between 2 and 4 [kt] Stockyard machine efficiency: 0.55 [-] 4 unloaders at seaside and 4 loaders at landside Average seaside’s port time (Wss): 3 days and average landside’s port time (Wls): 0.5 day Blending of coal: 1.7 [Mt/y] 28 different grades of bulk materials must be stored separately

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Step 1: Determine the number of stockyard lanes (nl) and dimension the stockyard lanes (length Ll and width w). Assume a machine’s boom length (lb) of 60 meter and use 10 meter as distance from the machine’s centerline to the stockyard lane (p). Assume that the lane’s length (Ll) must be in the range between 1,000 and 1,500 meter Number of stockyard lanes must be an even number to realize complete archetypes. Calculate the number of archetypes using the following equation: An outcome is nl = 14, Ll = 1,315 [m] and w = 50 [m]

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Step 2: Determine the required machine capacity based on Wss ≤ 3 days and Wls ≤ 0.5 day for both archetypes. Layout B with 7x archetype (II) Layout A with 7x archetype (I) Layout consists of 4 unloaders, 4 loaders and 7 archetypes. Two different archetypes will be investigated thus two main layouts are possible. Assumption: the four unloaders and the four loaders can be connected to the yard conveyors Simulation is needed because: (i) not each archetype has its own specific unloader and loader (these must be shared) and (ii) carrier tonnage distribution and train tonnage distribution are not the same and besides these distributions cannot be represented with a general distribution type

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**Step 2: results of the simulation study**

Stacker/reclaimer: the jobs were totally serviced, thus if a train arrives to get a specific grade but the appropriate stacker/reclaimer was busy stacking the material from a bulk carrier, the train had to wait till the bulk carrier was totally unloaded Layout Machine Cs [kt/h] Cr [kt/h] A Stacker/Reclaimer 3.8 4.5 B Stacker 3.6 Reclaimer 2.7

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**Calculate the total investment cost per archetype. **

Step 3: Calculate the total investment cost per archetype. Calculate the stockyard machine’s weight (w) based on the determined stacking and reclaiming capacities Investment cost of the stockyard machine(s): where for this case it was assumed that κsm was 8 [€/kg], machine fully installed at the stockyard Investment cost for the belt conveyor(s): where Lbc is conveyor length (1,400 [m]) and κbc was according Figure slide 22 “upper limit”. Layout Machine Cs [kt/h] Cr [kt/h] w [kt] ICsm [M€] ICbc [M€] TIC(A) [M€] A Stacker/Reclaimer 3.8 4.5 925 7.4 6.3 13.7 B Stacker 3.6 409 3.3 5 16.1 Reclaimer 2.7 506 4

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**Design the blending bed with associated machine types. **

Step 4: Design the blending bed with associated machine types. Future: high-quality coal will probably become scarce thus install stacker and reclaimer combination which is able to realize the highest bed blending ratio Blending bed dimensions: assume coal-fired power plant’s own storage of 5 days and use two blending beds for simultaneously stacking and reclaiming. Thus bed dimensions is 24 [kt]. Use two blending beds for simultaneously stacking and reclaiming. Use double-sided bridge scraper reclaimer with span of 30 meter. Then total blending .bed of 500 [m] is required

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Step 5: Final layout.

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6. Summary

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Summary Three main stockyard functions: storage, blending and homogenizing Main characteristics of stockyard machines were presented The effective capacity ratio for bucket wheel reclaimers differs per reclaiming method; a method has been provided. Different combinations of stacking methods and reclaimers result in specific bed blending effect ratios. A selection procedure was introduced to select single-purpose or multi-purpose machines for the storage of bulk materials For a specific case, the stockyard layout was designed Future work: Design of the network of belt conveyors

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