Coal Storage and Transportation

James M. Ekmann , Patrick H. Le , in Encyclopedia of Energy, 2004

1.1.1 Loading and Unloading Railcars

Typical coal railcars can carry 80 to 125 tons per car and the average load is 100 to 110 tons. Two types of railcars are in service: the solid bottom gondola and the hopper car.

A rotary dump system can handle gondola and hopper cars, whereas the undertrack pit can handle only hopper cars with bottom-opening doors.

The selection of the unloading method requires an evaluation of several trade-offs, such as the following: (1) gondola cars are the least expensive, need minimal maintenance, and can be completely unloaded with minimum coal hang-up but do require an expensive rotary dumper with the capability to accurately position the cars; and (2) hoppers (or bottom-dump cars) are more expensive and require more maintenance than the gondolas, due to the gate mechanism, but they can be unloaded more quickly on a relatively inexpensive track hopper. In addition, hopper cars are more difficult to unload under freezing conditions.

In addition to loading and unloading the coal, the issue of windage losses is frequently overlooked. Windage losses, i.e., coal blown out by wind from open-top cars, cause economic loss and environmental concern. One solution is a lid system, such as a flip-top lid, to control windblown loss, reduce dust, and prevent additional moisture from penetrating the coal, thus reducing the potential for freezing. Frozen coal is a troublesome problem related to unloading coal because the exposed top surface, the size plates of the car, and the surfaces of the sloped hoppers could be frozen. Several methods to thaw the cars are available, ranging from bonfires and oil-burning pans to sophisticated sheds. Treating the car sides and bottoms of the cars with oil can minimize freezing and ease the coal unloading process.

In terms of loading systems, three types of trackage are commonly used for unit trains. These are (1) the loop or balloon track, (2) the single track that is situated above and below the loading station, and (3) the parallel tracks that allow loading on both tracks. The loading system consists of locomotive, car haul, tripper conveyor, and hydraulic ram. The locomotive moves the cars in one pass under the loading station. The car-haul system moves two strings of cars in opposite directions on parallel tracks under two loading stations. The tripper conveyor system moves two-way loading chutes over two stationary parallel strings of cars. The hydraulic ram system moves the cars into loading position, after the locomotive has been removed.

In terms of unloading systems, there are two major types: the rotary dump and the undertrack pit. The rotary dump system handles the rollover type of car (hopper or gondola design) and the undertrack pit handles bottom-up cars.

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A CONTRIBUTION TO BALLAST MECHANICS

Karl Klugar , in Railroad Track Mechanics and Technology, 1978

Test Procedure

A stress was built up in the rails by heating, in order to test their buckling under high temperatures. To avoid longitudinal movement of the track, the ends of the test sections were fixed by loading them with locomotives and hopper cars. The rails were heated by heating units ( Fig. 19) to a temperature of 80°C, measured with thermo-probes and fixed thermometers. The temperature of 80° was maintained for one hour to assure its uniform distribution along the entire section.

Fig. 19. Rail Heating

Extreme overheating of the rails was avoided, first because the testing temperature was already far above maximal rail temperature and second, because we did not want to damage the rubber shim plates (Fig. 20).

Fig. 20. Chronological Development of Rail Temperature in Section I

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Railway Engineering

William W. Hay , in Encyclopedia of Physical Science and Technology (Third Edition), 2003

VII.B Car Design

The conventional car consists of a steel center sill running the length of the car, to which are attached transverse members or floor beams to hold the car body. The car assembly is supported at each end of four-wheeled car trucks and connected to the car body by a center plate on the trucks and a center pin, fitting into the plate from the car body, that permits the cars to swivel on curves. The coupling devices and shock-absorbing draft gear are mounted at the ends of the center sill. The train line, air brake equipment, and brake rigging are mounted under the car body or, with some hopper car designs, at the end of the car body under the slope of the hopper.

Particular attention has been given to improving the safety and strength of cars carrying hazardous materials in a derailment. Strong outer shells and end shields and so-called shelf couplers to guard against coupler puncture in the event of derailment are among these improvements.

The conventional three-piece truck includes two side frames set over the journal boxes that provide bearings for the axles. Each frame also contains a nest of springs. The side frames are connected transversely by the truck bolster, which holds the center plate and side bearings. The center pin attached to the car body bolster fits into the center plate.

Not all cars follow this basic design. Four-wheeled cars with single-axle trucks have been introduced in trailer-on-flatcar service (piggyback), and tank cars and hopper cars have been designed with no center sills. The car body rests on stub end sills over the trucks and longitudinal strength is obtained through the car body.

Other trailer-on-flatcar units have been designed to operate in 10-car units for hauling highway trailers, and another design stacks container boxes two tiers high on one car. Covered rack cars carry automobiles on two or three levels, protected from the elements and vandalism.

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MARINE TRANSPORTATION NEEDS FOR U.S. ENERGY SUPPLY

Bruce A. McAllister , in Energy and Sea Power, 1981

Transportation of Domestic Coal Production

Two-thirds of U.S. coal production is transported by rail. Highway vehicles and barges each account for about 11 to 13% of loadings. About 12% of production is consumed near the mine mouth by industry or power-generating plants, and about 1% is moved from the mines by slurry pipelines or other means.

Railroads haul coal almost exclusively in open-top hopper cars. Newly produced cars have a capacity of 100 tons. However, older and smaller cars continue to be used. As a result, the average coal load per car in 1975 was 84.3 tons. Recently, there has been a growing trend in the use of unit trains which are wholly dedicated to the movement of a single commodity from a single origin to a single destination, ideally on a continuous basis. A unit train transporting coal consists of 100 hopper cars carrying 100 tons each for a total of 10,000 tons. The trains move directly from origin to destination in line haul service, bypassing intermediate yards. This reduces transportation costs per ton by permitting rapid turnaround, dependable schedule, and a more efficient use of fuel.

Coal traffic in the east originates from smaller mines and moves shorter distances. For these and other reasons, unit trains are not employed as often as in the west. In 1974, 36% of the coal originating in the east moved by unit train as compared to 61% for western coal. Overall, the use of coal-efficient unit trains has grown from 32% in 1971 to 46% in 1976.

Railroads generally load coal at or close to the mine, often after a short truck movement. In most cases the railroads deliver the coal directly to the ultimate domestic consumer or port in the case of export coal. On occasion, railroads will transship coal to a water carrier for further movement to a domestic user or port.

The waterway system of the United States consists of 26,000 miles of commercially navigable waterways; the shipping lanes of the Great Lakes and coastal trade routes; and, in excess of 200 commercial inland and coastal harbors and ports. The inland waterway system is maintained by the Corps of Engineers. Coal transshipped from railways moves by barge to the ultimate domestic user or port. Significant coastal movements of coal by ocean-going vessels occurs primarily in the Great Lakes and on occasion between the Gulf and Florida.

As noted previously, many coal movements, especially in the eastern region, require truck haulage from the mines to rail or barge tipples. At the present time, the highway system supporting these truck movements is in poor shape and is operating near capacity.

Only one coal slurry pipeline is currently in operation. The Black Mesa pipeline moves coal as slurry a distance of 273 miles from Arizona to southern Nevada. Four million tons of coal a year is now moved along this pipeline, and the system has been operating successfully for a period of eight years. The technical problems associated with moving coal as slurry appear resolved.

Overall, the transportation system is more than adequate to move current coal production for domestic consumption. However, as domestic demand rises and projected coal production is realized, a number of problems will require resolution.

Additional equipment as well as system improvements are required to maintain the flow of coal by rail. Assuming railroads have good prospects of carrying additional coal traffic at adequate rates, it is generally agreed that the necessary capital to effect the required expansion and improvements will be available.

The highway infrastructure, particularly in the east, requires significant improvement. Given the current condition of the roads and large projected increases in coal production for domestic purposes, coal road maintenance is a serious concern. Cost estimates to improve the coal roads range from $4 billion at minimum repair standards to $20 billion for full improvement.

There are potential bottlenecks within the current lock and dam system of our inland waterways which could adversely affect future water movement of coal. These areas are currently under study by the Corps of Engineers for possible expansion of capacity. There appear to be no major constraints on the ability of the barge industry to handle future increases in domestic or export coal shipments. However, the future level of waterway user charges will bear heavily on the economics of this mode of transportation.

The efficient movement of coal requires serious consideration of the expansion of coal slurry pipelines. In addition to the Black Mesa pipeline, seven other pipelines are now contemplated–six in the west and one in the east. Four of the six western pipelines could be built without federal eminent domain legislation.

However, only one western company would have a firm water supply. The eastern pipeline does not have water supply problems, but federal eminent domain legislation would be required before it could be built. For the third time, Congress is considering eminent domain legislation which would clear the way for development of a slurry pipeline network. However, whether a specific coal slurry project is economically efficient will depend on location and adequacy of rail facilities already in place.

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THE DEVELOPMENT OF ANALYTICAL MODELS FOR RAILROAD TRACK DYNAMICS

D.R. Ahlbeck , ... R.H. Prause , in Railroad Track Mechanics and Technology, 1978

Recent Track Measurements

Track dynamic response measurements were made on high-speed tangent track under both summer and winter ambient conditions during a recent AAR Track Train Dynamics Program task. Although the task was aimed primarily at the measurement of dynamic track gauge, tie plate loads and rail vertical and lateral absolute deflections were also measured. This provided an additional opportunity to compare actual measurements with computed values from the analytical track models.

The track at the measurement site consisted of 133 lb/yd (66 kg/m) continuous welded rail on 8 × 14-in. l:40-cant tie plates, a processed phosphate-ore ballast with at least a 24-in. depth, and a subgrade of uniform fill material (probably crushed lava rock and sand). Estimated track parameters used to calculate the track stiffness (eqs. 2 through 7) are given in Table 2. From these parameters, the individual and overall stiffnesses of the track structure are calculated from linear theory, and are listed in Table 3.

Table 2. Estimated Values of Track Parameters

Parameter Numerical Values
Rail weight 133 lb/yd 66 kg/m
Flexural rigidity, EI 24.9(10) 8 lb-in2 7.15(10) 8 MN-m2
Tie spacing, l t 23 in. 58.4 cm
Tie tamped area, At 360 in.2 2323 cm2
Tie width, w 9 in. 22.9 cm
Ballast depth, h 24 in. 61.0 cm
Ballast modulus, Eb 30,000 lb/in.2 207 MN/m2
to 40,000 lb/in.2 276 MN/m2
Subgrade modulus, KO 150 lb/in.2 1.03 MN/m2
to 500 lb/in2 3.45 MN/m2
Ballast densit, ρb 2200 lb/ft3 35,200 kg/m3
Subgrade density, ρs 2500 lb/ft3 40,000 kg/m3

Table 3. Calculation of Track Stiffness and Deflections Under Load

Calculated Parameter Numerical Values
kb (ballast stiffness) 944,000 lb/in 165 MN/m
to 1,260,000 lb/in 220 MN/m
ks (subgrade stiffness) 229,000 lb/in 40 MN/m
to 762,000 lb/in 133 MN/m
kbs (combined stiffness) 184,000 lb/in 32 MN/m
to 475,000 lb/in 83 MN/m
Kt (assumed tie stiffness) 1(10)6 lb/in 175 MN/m
K (track modulus, per rail) 3,650 lb/in 25 MN/m/m
to 8,350 lb/in 58 MN/m/m
β (inverse characteristic length) .0246 in−1 .97 m−1
to .0303 in−1 1.2 m−1
Kr (track stiffness to point load, per rail) 297,000 lb/in 52 MN/m
to 551,000 lb/in 97 MN/m
λ (influence coefficient) * 0.13
to -0.01 (uplift)
y (total vertical deflection) * .125 in 3.2 mm
to .059 in 1.5 mm
(*)
Based on a 33,000-pound wheel load and a 72-inch axle spacing (100T car)

Typical force and deflection traces are shown in Fig. 12 for heavy 100-ton (LC3) and 125-ton (LC4) covered hopper cars, and 6-axle radio-controlled diesel units, at a train speed near 50 miles per hour. In Fig. 13 a group of empty 100-ton covered hopper cars are shown near 60 miles per hour. Both of these recordings were made under winter ambient (frozen ballast) conditions. To check the comparison between the measured and computed deflection shapes, the idealized deflection curves were plotted, based on two identical cars coupled together: two loaded 125-ton cars (P = 39,200 lb), and two empty 100-ton cars (P = 8,000 lb). Points from typical measured deflection curves were then plotted over these linear, idealized curves (in reality, a time-variation compared with an ideal spatial variation). Results of these plots are shown in Fig. 14. It is immediately apparent from this plot that track modulus (K) exhibits a nonlinear, "hardening" spring rate quite similar to an elastomeric pad in compression. While the deflection under maximum wheel load (purposely matched by choice of a track modulus of 5500 lb/in/in, or 38 MN/m/m) agrees well in magnitude and shape, the deflection under light wheel load is actually three times greater than calculated. The slight increase in deflection from a 39,000-lb. wheel load (LC4 car) over the 33,000-lb. wheel load (LC3 car) is indicative of the very high tangent stiffness under load.

Fig. 12. Tie Plate Vertical Load and Rail Vertical Deflection Under Heavy Freight Cars and Locomotives of Unit Train (Train Speed 50 mph, 80 kph)

Fig. 13. Tie Plate Vertical Load and Rail Vertical Deflection Under Empty and Lightly-Loaded Freight Cars (Train Speed 60 mph, 97 kph)

Fig. 14. Comparison of Idealized (Linear Beam on Elastic Foundation) and Measured Rail Deflection Shapes Under Wheel Loads of Coupled Cars

To pursue this further, representative data points were plotted for a range of wheel loads under both summer and winter conditions. Ranges of tie plate vertical loads and corresponding vertical absolute rail deflections are shown in Fig. 15. From an average value of locomotive-induced tie plate loads (assumed to be 33,000-pound vertical wheel loads, and limited to lower-speed recordings), the instrumented tie plate was found to support about 33 percent of the wheel load in summer, about 48 percent in winter. Tangent stiffness values under maximum static wheel loads (per rail) were calculated from these tie plate-to-wheel load ratios, assuming (for the locomotives) a negligible influence from adjacent wheels. Choosing nominal, linear stiffness values from these curves (rail deflection under heavy wheel load), "secant" values of 290,000 lb/in (51 MN/m) for summer, and 425,000 lb/in (74 MN/m) for winter are calculated, which fall reasonably close to the calculated values of Table 3. The tangent stiffness, however, for small oscillations about the static load, is seen to be roughly twice the calculated stiffness.

Fig. 15. Tie Plate Load Versus Rail Vertical Deflection Downward From Rest Position, 133 lb/yd Rail

It is apparent from the deflection traces of Figs. 12 and 13 that the track structure is highly damped under vertical load. Even the high impact load of a flat wheel on one diesel unit (Fig. 12) is very quickly damped. Oscillation frequencies of 20 to 25 Hz were observed, as well as higher-frequency oscillations of 88 to 100 Hz under impact loads, with higher static wheel loads. Under light cars (6000 to 9000-pound wheel loads), impact oscillations of 50 to 70 Hz were observed.

Experimental measurements of rail lateral stiffness were also conducted by applying a lateral force to the rail in increments of 1000 pounds up to 10,000 pounds maximum, simultaneously with a 33,000–pound vertical wheel load. A patch of Teflon tape and a witch's brew of Molykote and EP grease were applied under the wheel to reduce lateral frictional hysteresis. Under these conditions, a lateral stiffness of 330,000 lb/in (58 MN/m) was measured at the rail head, reasonably linear up to this load level. Lateral oscillations in dynamic gauge were noted in recordings, particularly at rail temperatures near or above the "laying" temperature, ranging from 20 Hz under heavy wheel loads (particularly locomotives), down to 15 Hz under the light wheel load of a caboose. Absolute lateral oscillations near 10 Hz were occasionally seen under impact loading.

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Trade Efficiency and Security

Darren J. Prokop , in Global Supply Chain Security and Management, 2017

Containerization

The shipping container highlights the market efficiency and security trade-off. The modern version of the shipping container grew popular because it avoided costly and laborious repetition when cargo had to be loaded and unloaded when moving from one mode of transport to another, say from a truck to an ocean vessel. Today, it is just a matter of moving the whole container with its cargo inside. 2 Of course, with the cargo locked inside the container at its source, and not retrieved until the container is opened at its destination, it would appear that security is enhanced as well. After all, more steps of loading and unloading increases the risk of cargo damage, theft, and smuggling. However, as the container moves from one point along the supply chain to another, and from one mode of transport to another, the movers are dependent on the honesty and accuracy of the shipping documents accompanying the container. These documents note cargo contents and weight among other things. Before containerization, a carrier knew what was being placed in the truck trailer, the rail hopper car, or the cargo hold simply by observing the cargo loading process. Today, a container vessel captain only really knows how many containers he is carrying; the contents are less tangible in his mind. Therefore, a trade-off remains to the extent that speed is precluded by the time necessary to complete and verify all necessary documentation. Inaccurate declarations of cargo contents and cargo weight are still a security and safety issue.

While it is not possible to guarantee complete accuracy of documentation across the millions of cargo containers moving in, within, and out of the United States, mitigation of the problem is possible. Physical inspection is possible at multiple steps, but this would amount to the same thing as unloading and reloading in the era before containerization. For international transport the container must pass through the screening and/or inspection processes of Customs and Border Protection (CBP). Accuracy of documents are necessary in order to determine tariffs and duties. Also, if the container is held in a foreign port within the Container Security Initiative (CSI) program there is the added layer of security upon departure for the United States. For surface transport the C-TPAT program incentivizes shippers and carriers to be accurate.

As to cargo weight, the challenge has been where the weighing of the laden containers should take place: at origin or at port of entry. Inaccurate weights can create safety issues for carriers and crews. Some recent incidents include the MSC Napoli in the English Channel in 2007. The hull collapsed when faced with a strong storm. The captain intentionally beached the vessel to prevent further damage. Out of the 660 containers which were transported, 137 (or about 21%) were found to be over their declared weight by a range of 3–20   metric tons. The Deneb in the Port of Algeciras in 2011 suffered a similar fate. The ship nearly capsized on its starboard side because 1 out of every 10 containers had declared weights significantly below their actual weight. Sixteen out of 168 containers being, on average, four times overweight was enough to cause the accident. The UK Marine Accident Investigation Branch, following up on a collapse of stacks of containers on the P&O Nedlloyd Genoa in 2006, reported: "[I]ncorrect weight can result in stack overload and the application of excessive compression and racking forces on containers and their lashings. Although there are no financial gains to be made by the shipper who declares less than actual weight, the industry acknowledges that over-weight containers are a problem. However, as yet this has not justified a requirement for compulsory weighing of containers prior to loading." 3

The incidents noted above did indeed prompt a multiyear study of the problem by the International Maritime Organization (IMO). In response, the IMO decided that the onus for accurate weighing would be on the shipper. The Safety of Life at Sea (SOLAS) convention as of July 1, 2016 requires container weight verification be provided to the carrier on a document and this will be a condition for vessel loading. Shippers will have two options in order to comply. The first is to drive the container over a weighbridge and subtract the weight of the truck, chassis, and fuel. The second option is to weigh each cargo item (including packaging, pallets, and securing material). The sum of these items' weights is to be added to the weight of the empty container. If a container is found to be in noncompliance, the vessel may leave with container held at the port for either return to the shipper or to the proper authorities. Unlike CSI, the carrier is the intermediary simply passing the document along. It does not bear an onus to insure that the shippers comply. Of course, it is the carrier who takes on the operational risk against safety when weights are not accurate.

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