4 Content Stockyard functions Stockyard machines The machine selection for capacity & blending or homogenizingThe machine selection for the storage of bulk materialsCASE: stockyard layout design for an import terminalSummaryDelwaidedok, Antwerp (Courtesy HeliHolland/Kees Vlot)
6 Stockyard functionsStorage: 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 propertiesHomogenizing: the standard deviation of the bulk materials is reduced while the average value remains the same.
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 tonsLarger 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 anoverhead 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 capacityEffective capacity ratio for a bucket wheel reclaimer relates to the used reclaiming methodLong-travel reclaiming methodSlewing bench reclaiming methodFor 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 wheelSlewing 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-meterDescriptionValueUnithsSlice height4.5[m]rbwRadius of bucket wheelΔxMax. chip thickness1ωssMinimum slewing speed0.145[rad/min]ρmBulk density coal0.8[t/m3]ωsmMaximum slewing speed0.58lbBoom length60asMaximum slewing acceleration/ deceleration0.5[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 speedWithout slewing speed adjustmentWith slewing speed adjustmentThe 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-meterDescriptionValueUnitltTotal pile’s length325[m]hSlice height4.5wPile’s width50ΔxMaximum chip thickness1Height of the pile18lbBoom length60ρmBulk density coal0.8[t/m3]rbwRadius of bucket wheelαAngle of repose38[°]ωssStart slewing speed0.25[rad/min]vtTravelling speed10[m/min]ωsmMaximum slewing speed0.58atTravel acceleration and deceleration0.15[m/min2]asMaximum slewing acceleration & deceleration0.5[rad/min2]yDistance 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 methodsNote: 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 pileStacker10,00030-60-Radial stacker8,000Ø120Side scraper reclaimer1,0000.7510-25AlongsideSingle boom portal scraper reclaimer2,20015-60Double boom portal scraper reclaimer4,400Bridge scraper reclaimer1,8000.95At the faceBridge bucket wheel reclaimerDrum reclaimer4,50020-50Bucket wheel reclaimer12,000
20 Blending or homogenizing machines Stacking is the starting point of the blending process. Generally there are four basic stacking methodsReclaimer machineStacking methodCone ShellChevronStrataWindrowSingle scraper reclaimer andPortal scraper reclaimer23-44-6Bridge scraper reclaimer-105-68-9Bridge bucket wheel reclaimer4-8Drum reclaimer9-107-8Bucket wheel reclaimer4-5Cone 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 archetypeCost calculationOperational 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 archetypesTwo layout archetypes
23 and the belt conveyor investment cost relates to its capacity Cost calculationSelection must be based on the archetype’s investment cost and performanceIt was assumed that the machine investment cost relates to its weightand the belt conveyor investment cost relates to its capacityStacker/reclaimers weight versus capacities as function of boom lengthTotal 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 increasesSome 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 ideaPrice 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 portThe port time is the sum of the waiting time and service timeThe ships waiting time relates to:Interarrival time distributionCarrier tonnage distributionThe ship (un)loader utilizationMean service rateMean arrival rateQueuing theory formulas or simulationIf 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: trainsInterarrival time distribution seaside and landside: NEDCarrier 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 landsideAverage seaside’s port time (Wss): 3 days and average landside’s port time (Wls): 0.5 dayBlending 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 meterNumber 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 conveyorsSimulation 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 unloadedLayoutMachineCs [kt/h]Cr [kt/h]AStacker/Reclaimer3.84.5BStacker3.6Reclaimer2.7
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 capacitiesInvestment cost of the stockyard machine(s):where for this case it was assumed that κsm was 8 [€/kg], machine fully installed at the stockyardInvestment cost for the belt conveyor(s):where Lbc is conveyor length (1,400 [m]) and κbc was according Figure slide 22 “upper limit”.LayoutMachineCs [kt/h]Cr [kt/h]w [kt]ICsm [M€]ICbc [M€]TIC(A) [M€]AStacker/Reclaimer3.84.59257.46.313.7BStacker3.64093.3516.1Reclaimer2.75064
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 ratioBlending 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
34 SummaryThree main stockyard functions: storage, blending and homogenizingMain characteristics of stockyard machines were presentedThe 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 materialsFor a specific case, the stockyard layout was designedFuture work: Design of the network of belt conveyors