1. Stockyard layout (re)design
Delft University of Technology
Faculty 3ME, Transport Engineering & Logistics
G. Lodewijks, T.A. van Vianen and J.A. Ottjes

2. Export Terminal Saldanha Bay SA2

3. Bulk terminal simulation

4. 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)

5. 1. Stockyard functions

6. 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.

7. 2. Stockyard machines

8. 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.

9. 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)

10. 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)

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

12. 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

13. Slewing reclaiming method A) top view and B) lateral view

14. 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]

15. 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.

16. 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

17. 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

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

19. 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

20. 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.

21. 4. The machine selection for the storage of bulk materials
Selection of archetype
Cost calculation
Operational performance

22. 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

23. 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

24. 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.

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

26. 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

27. 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]

28. 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

29. 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

30. 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

31. 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

32. Step 5:
Final layout.

33. 6. Summary

34. 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

35. Questions?