At a large coal loading facility:
1. can more than one car be filled at a time?
2. how long does it take to fill one car?
3. does the loco have to move up one car at a time as they are filled? If so, how does the Engineer gauge how far to pull forward each time?
4. does filling the train fall to a switcher and yard assigned crew, or is the road crew/loco responsible to fill their own train?
5. all told, how long does it take to fill a 115 car unit train?
Once at the receiving power plant:
1. who, what, & where controls and activates the "dump doors" (insert proper name here) and are they mechanically locked en route?
2. do they dump on a "bridge" where the coal falls through the rails/ties to a conveyer funnel below the tracks?
3. do they dump one car at a time?
Any other info or related questions are appreciated.
Thanks.
nodyAt a large coal loading facility: 1. can more than one car be filled at a time? Unit train loaders load one car at a time in continuous motion in a train. Old-style tipples load more than car at once, but are much slower overall. 2. how long does it take to fill one car? Between 60-180 seconds, or about 4,000-8,000 tons per hour. 3. does the loco have to move up one car at a time as they are filled? If so, how does the Engineer gauge how far to pull forward each time? Most unit train loadouts are set-up to load the train in continuous motion. The engineer sets a speed on a creep control similar to an auto "cruise control" and the operator informs him by radio to dial it up or down slightly. The creep control maintains a constant speed by throttling the locomotives up or down (actually, they vary field excitation and the engine throttle postion remains constant.) If the operator needs to have the train stop or back up, he informs the engineer by radio. Through experience the engineer has a very good idea of the correct initial speed on the creep control. 4. does filling the train fall to a switcher and yard assigned crew, or is the road crew/loco responsible to fill their own train?In the old days, switchers were sometimes used but not commonly, and only on mines where there wasn't enough room or the right topography for gravity loading. The mine run train would spot empties into receiving tracks, mine personnel would roll the cars individually through the tipple, then roll them again into departure tracks, where the mine run train would collect them. The unit train era is entirely different because the idea is to get the cars into and out of the mine as quickly as possible to cut down on car-hire expense. Some mines have separate crews assigned to the mine usually provided by a third-party rail contractor. Those crews accept the inbound empties from a road crew, load the train, then release the outbound loaded train to a road crew. This is the most common practice in the Powder River Basin. At other mines, the road crew arrives, loads the train, and returns the train to their original crew-change location, assuming they haven't run out of hours in the meantime and need to be recrewed. This is the common practice everywhere in the Rocky Mountain states other than the PRB. 5. all told, how long does it take to fill a 115 car unit train? From arrival to departure, between 2-3 hours at most mines. The standard PRB train now is 135 cars, with some 150s. The standard Colorado or Utah train is 105 cars. I don't know what the Gallup-area mines are doing now, probably 135 car. Once at the receiving power plant: 1. who, what, & where controls and activates the "dump doors" (insert proper name here) and are they mechanically locked en route?Rotary-dump cars of course have no doors. Rapid-discharge cars have electrical-over-pneumatic door controls and are opened and closed automatically as they pass through the dumper pit. A "shoe" is "ungagged" by a human. The shoe then contacts a rail, creating an electrical current to open the doors. The contact rail is of course located at the proper location. No human touches the doors. The old-style manual door locks are knocked open by a human using a sledge and the door falls open by gravity. When the car is empty the door is closed and locked by a human, with lots of whacks to beat on the locks if they're bent. Lots of personal injuries happen here. 2. do they dump on a "bridge" where the coal falls through the rails/ties to a conveyer funnel below the tracks?Some of the older rapid-discharge dumpers used a bridge in open air. Recent designs are enclosed for dust control and dump into a pit. Rotary-dump cars dump into a pit. Some old manual-door dumping sites used trestles, but the preponderance of them are over a pit. The pit is protected by a "grizzly", a set of steel bars to prevent oversize chunks or foreign matter from falling into the pit. Some pits where freezing coal may be an issue have either thaw sheds before the car gets to the dumper or a mechanical coal breakers to break apart the large chunks inside the pit. Most rapid-discharge dumper pits today have a throughput rate of 4,000-8,000 tons per hour, the rate depending upon the width and speed of the conveyor belts, and whether the coal pile at the end of the belts can accept coal at that rate. Rotary dumpers (single) are good for 4,000 tons per hour, tandem for 6,000 tons per hour. 3. do they dump one car at a time? Most rotary dumpers are single-car, that is, only one car is overturned at a time. There are some tandem (two-cars at a time) rotary dumpers but they are not common. Rapid-discharge and rotary-dump trainsets usually dump as a solid train in continuous motion but there are some locations that require the train to be broken into pieces and run through the dumper in cuts because the plant footprint isn't big enough to accept a loop or a continuous train shuttled through. Most rotary dumpers that dump the whole train without breaking it into pieces use a mechanical indexer to advance the train, either rack-and-pinion or cable. The cable ones aren't very good because the cable stretches and the indexer becomes inaccurate until the slack is taken up. Rotary dumpers where the train has to be broken up usually use a switch engine because the train has to be horsed around anyway between the inbound and outbound tracks, and indexers are very expensive. Manual-door cars dump one at a time. Any other info or related questions are appreciated. There are also older rotary dumpers at rail-to-water and steel mills that were set up to dump one car at a time, using either a kickback trestle to roll the empty out by gravity, or a gravity receiving yard. The cars were hauled into the dumper by either a car puller or an "electric mule," a small electric locomotive that ran on a narrow-gauge track adjacent to the regular track. Thanks.
1. can more than one car be filled at a time? Unit train loaders load one car at a time in continuous motion in a train. Old-style tipples load more than car at once, but are much slower overall.
2. how long does it take to fill one car? Between 60-180 seconds, or about 4,000-8,000 tons per hour.
3. does the loco have to move up one car at a time as they are filled? If so, how does the Engineer gauge how far to pull forward each time? Most unit train loadouts are set-up to load the train in continuous motion. The engineer sets a speed on a creep control similar to an auto "cruise control" and the operator informs him by radio to dial it up or down slightly. The creep control maintains a constant speed by throttling the locomotives up or down (actually, they vary field excitation and the engine throttle postion remains constant.) If the operator needs to have the train stop or back up, he informs the engineer by radio. Through experience the engineer has a very good idea of the correct initial speed on the creep control.
In the old days, switchers were sometimes used but not commonly, and only on mines where there wasn't enough room or the right topography for gravity loading. The mine run train would spot empties into receiving tracks, mine personnel would roll the cars individually through the tipple, then roll them again into departure tracks, where the mine run train would collect them.
The unit train era is entirely different because the idea is to get the cars into and out of the mine as quickly as possible to cut down on car-hire expense. Some mines have separate crews assigned to the mine usually provided by a third-party rail contractor. Those crews accept the inbound empties from a road crew, load the train, then release the outbound loaded train to a road crew. This is the most common practice in the Powder River Basin. At other mines, the road crew arrives, loads the train, and returns the train to their original crew-change location, assuming they haven't run out of hours in the meantime and need to be recrewed. This is the common practice everywhere in the Rocky Mountain states other than the PRB.
From arrival to departure, between 2-3 hours at most mines. The standard PRB train now is 135 cars, with some 150s. The standard Colorado or Utah train is 105 cars. I don't know what the Gallup-area mines are doing now, probably 135 car.
Rotary-dump cars of course have no doors. Rapid-discharge cars have electrical-over-pneumatic door controls and are opened and closed automatically as they pass through the dumper pit. A "shoe" is "ungagged" by a human. The shoe then contacts a rail, creating an electrical current to open the doors. The contact rail is of course located at the proper location. No human touches the doors. The old-style manual door locks are knocked open by a human using a sledge and the door falls open by gravity. When the car is empty the door is closed and locked by a human, with lots of whacks to beat on the locks if they're bent. Lots of personal injuries happen here.
Some of the older rapid-discharge dumpers used a bridge in open air. Recent designs are enclosed for dust control and dump into a pit. Rotary-dump cars dump into a pit. Some old manual-door dumping sites used trestles, but the preponderance of them are over a pit. The pit is protected by a "grizzly", a set of steel bars to prevent oversize chunks or foreign matter from falling into the pit. Some pits where freezing coal may be an issue have either thaw sheds before the car gets to the dumper or a mechanical coal breakers to break apart the large chunks inside the pit. Most rapid-discharge dumper pits today have a throughput rate of 4,000-8,000 tons per hour, the rate depending upon the width and speed of the conveyor belts, and whether the coal pile at the end of the belts can accept coal at that rate. Rotary dumpers (single) are good for 4,000 tons per hour, tandem for 6,000 tons per hour.
Most rotary dumpers are single-car, that is, only one car is overturned at a time. There are some tandem (two-cars at a time) rotary dumpers but they are not common. Rapid-discharge and rotary-dump trainsets usually dump as a solid train in continuous motion but there are some locations that require the train to be broken into pieces and run through the dumper in cuts because the plant footprint isn't big enough to accept a loop or a continuous train shuttled through. Most rotary dumpers that dump the whole train without breaking it into pieces use a mechanical indexer to advance the train, either rack-and-pinion or cable. The cable ones aren't very good because the cable stretches and the indexer becomes inaccurate until the slack is taken up. Rotary dumpers where the train has to be broken up usually use a switch engine because the train has to be horsed around anyway between the inbound and outbound tracks, and indexers are very expensive. Manual-door cars dump one at a time.
There are also older rotary dumpers at rail-to-water and steel mills that were set up to dump one car at a time, using either a kickback trestle to roll the empty out by gravity, or a gravity receiving yard. The cars were hauled into the dumper by either a car puller or an "electric mule," a small electric locomotive that ran on a narrow-gauge track adjacent to the regular track.
RWM
I don't know if I am allowed to name a company, but a certain video company has published an excellent DVD on the operations of Powder River Basin. It shows the mining, the loading of coal trains and the train movements in the area. IMHO it is an informative video.
Jared
Thank you RWM . Very thorough and clear. I know coal is a big if not the biggest customer for the class I's. The unit train seems like the ultimate in efficiency, and it is interesting to hear how little "down time" there is for the cars and road locos/crews.
I know yards by definition are way stations, but it is always a little disappointing to see how little ever seems to be going on in most yards, during the day when I have time to stop and watch. I'm sure I'm not the first guy to lament this.
I've always been fascinated by coal trains and feeding our hungry power plants. People who think we can get by without coal are just plain ignorant. Without trains hauling coal, there would be very little electricity, and most of us would die. Take that "climate change" morons!
nodyThank you RWM . Very thorough and clear. I know coal is a big if not the biggest customer for the class I's. The unit train seems like the ultimate in efficiency, and it is interesting to hear how little "down time" there is for the cars and road locos/crews. I know yards by definition are way stations, but it is always a little disappointing to see how little ever seems to be going on in most yards, during the day when I have time to stop and watch. I'm sure I'm not the first guy to lament this. I've always been fascinated by coal trains and feeding our hungry power plants. People who think we can get by without coal are just plain ignorant. Without trains hauling coal, there would be very little electricity, and most of us would die. Take that "climate change" morons!
Intermodal surpassed coal as the largest revenue generator/profit source several years ago, but coal is very important. However, even if coal all vanished tomorrow, it would not be the end of railroading, though it would be the end of a few subdivisions both in the east and the west. Coal isn't carrying the burden for other commodities anywhere except on the subdivisions that are almost nothing but coal. At present, coal supplies 48.2% of U.S. electricity, nuclear 19.3%, natural gas 21.6%, oil 1.1%, hydro 6.5%, and other sources (mostly biomass, but also wind, geothermal, and solar) about 3.2%. See http://www.eia.doe.gov/cneaf/electricity/epm/epm_sum.html
Glad to help and share my knowledge, and as always, anyone who can in turn sharpen my knowledge I greatly appreciate.
I do not want to discuss pros and cons of climate change in this forum, however. I think it's fair to discuss how legislation or public opinion affects railroads or might affect railroads in the future, but whether that legislation or public opinion is something we like or think is a good idea is I think best removed in its entirety from this railroad forum to a political forum. At the railroads, we all have our own politics. Some of us are climate-change morons and some of us are climate-change-ain't-real, but we're usually gentlemen about it and don't force our politics, religion, or belief systems upon each other
Railway ManThe standard PRB train now is 135 cars, with some 150s. The standard Colorado or Utah train is 105 cars. I don't know what the Gallup-area mines are doing now, probably 135 car. RWM
Thanks to Chris / CopCarSS for my avatar.
A power plant near me gets in +/-100 car trains. Their dumper will handle 10-12 car groups, which they switch in with a switch engine. The cars are bottom dumped and the coal travels by way of a couple of conveyors to the storage yard, where bulldozers keep the dump point clear.
I hesitate to call the dumping shed a warming shed (I've never been in it) - it's not very long and open on both ends while they're working. They do have a car shaker, however, which can be felt in nearby buildings.
Larry Resident Microferroequinologist (at least at my house) Everyone goes home; Safety begins with you My Opinion. Standard Disclaimers Apply. No Expiration Date Come ride the rails with me! There's one thing about humility - the moment you think you've got it, you've lost it...
Murphy SidingRailway ManThe standard PRB train now is 135 cars, with some 150s. The standard Colorado or Utah train is 105 cars. I don't know what the Gallup-area mines are doing now, probably 135 car. RWM What determines the number of cars used? I thought maybe the route profile, but the PRB trains of 135 or 150 cars take the same route. Is there a signifigance in the cars being in increments of 15?
If the route can take it, whether the plant can take a train of that length. Most cannot. I believe all the mines in the Southern PRB are 150-capable now.
The transportation rate is paying in large part for the slot the train uses. The slot cost is the same whether the train is one car long or 150 cars long. Thus there's significant economic incentive for the coal customer to accept the longest train possible.
Note that just because a line can take one 150-car trainset doesn't mean it can take more than one 150-car trainset. Only one train has to fit in the siding at a meet. Few subdivisions or lines have 100% uniform siding lengths. As long as there are a few long sidings, more than one long train can be run, so long as you can arrange your meet events to always occur at those locations (which is not very easy to do with regularity). There is always an upper limit to how many long trains you can run on a short-siding subdivision and exceeding that number is ugly. Not that people don't try and push the limit every day.
Your question appeared specific to bottom discharge of hoppers. In warmer (above freezing) climates you just use a lever and twist the locking mechanism on both sides. In the north it is a totaly different matter. The mines flood the cars with water to control dust. My personal and probably wrong opinion is they are trying to sell the customer some water at coal prices. Having seen steel mills trying to unoload the stuff it is a wonder the cars ever survive the trip. Some will be beaten to death by a vibrator hung in a bracket if equipped. Others will be heated with massive torchs - that's why the sides are all rusty. if all else fails get the bucket from the overhead crane on the ore bridge that feeds the blast furnace conveyer and beat the cr** out of the car from any side you can and then drop it in the car to break up the ice. I've even seen crews get one up to about twenty miles an hour and cut it loose to let it ram the bumper on the end of the track. None of it is pretty and most of it is ineffective. That's why ore docks had thawing sheds for the iron ore because they had the same problems only colder (usually). Never volunteer to unload coal in a steel mill or anywhere else in the winter.
Natural iron ore (as opposed to taconite pellets) has a high moisture content, which is why it freezes up in winter. Consequently, the mines (and DMIR) had to shut down in the winter.
The coal may have been sprayed with water in an attempt to keep the dust under control.
Don't forget the plain old weather. A load of coal leaving PRB or the coalfields of Appalachia may depart in a rain storm, only to arrive at their northern destination in below freezing weather. Or get snowed on and encounter a thaw and another freeze.
One story from the Blizzard of '77 concerned a bunch of hoppers that got loaded with snow in Buffalo, NY, with the intent that they would have melted out by the time they got south for loading. A cold snap ensured that they arrived at their destination still fully loaded, much to everyone's chagrin.
ndbprrYour question appeared specific to bottom discharge of hoppers. In warmer (above freezing) climates you just use a lever and twist the locking mechanism on both sides. In the north it is a totaly different matter. The mines flood the cars with water to control dust. My personal and probably wrong opinion is they are trying to sell the customer some water at coal prices. Having seen steel mills trying to unoload the stuff it is a wonder the cars ever survive the trip. Some will be beaten to death by a vibrator hung in a bracket if equipped. Others will be heated with massive torchs - that's why the sides are all rusty. if all else fails get the bucket from the overhead crane on the ore bridge that feeds the blast furnace conveyer and beat the cr** out of the car from any side you can and then drop it in the car to break up the ice. I've even seen crews get one up to about twenty miles an hour and cut it loose to let it ram the bumper on the end of the track. None of it is pretty and most of it is ineffective. That's why ore docks had thawing sheds for the iron ore because they had the same problems only colder (usually). Never volunteer to unload coal in a steel mill or anywhere else in the winter.
Each carload is both weighed and sampled at the coal mine when loaded. Each carload is both weighed and sampled at the power plant when unloaded. The coal mine has specific quality requirements it guarantees including BTU, ash, ash fusion temperature, sodium, mercury, size, amount of tramp iron, and moisture content. The coal mine might want to sell the power plant some extra water but the power plant ain't buying. Power plants will reject coal if it's specs change between coal mine and power plant and have the contractual right to do so. They get very angry at the railroad when trains are delayed in winter and snow accumulates on the coal. I recall being in the COO's office one morning the day after we'd had a big coal train derailment due to poor train handling. The morning paper showed in splendid color a big, excellent photograph of our wrecked train -- and the snow-covered coal loads of the cars that didn't derail. The COO said to me, "The power plant just called and said we might as well wreck those cars too because we're not taking them now."
Two more illustrations. The Geneva Steel taconite trains when SP got the contract from UP were reloaded with Utah and Colorado coal for midwestern utilities. The cars were cleaned at Provo, Utah, when made empty of pellets and at Stevens Point, Wisconsin, when made empty of coal. Coal plants that found ONE repeat ONE taconite pellet on their tramp iron trap would immediately call to complain, and when Geneva found coal dust in the bottom of their loads, they'd call to complain too.
The second illustration concerns a carload of coal on the D&RGW that lost its waybill after being loaded. It showed up at CILCO Wood River, Illinois, along with 104 of its brethern in a coal train. Wood River couldn't match the car number to the waybill, so they cut it out of the train and refused to empty it. Samples were taken and it appeared the coal came from the same mine all the other cars in that train had loaded it, of course. But without an ironclad guarantee of the coal's provenance CILCO refused to take it, even for free, because they wouldn't take the risk the coal wouldn't slag their boiler tubes or cause them to go out of compliance on their air quals. Finally the car was sent back to SP East St. Louis and it sat there for awhile while people argued about what to do with it. The coal desk offered this carload of free coal, with free transportation, to every one of its coal customers in the Midwest, and every one of them refused it. It was looking as if the coal would be going to the landfill but finally Geneva Steel agreed to take it. The car was hauled back to Utah and made empty and released back to us. Later we asked Geneva Steel what they'd done with the free coal, and they replied "We gave it to employees. Our coke-oven department wouldn't touch the stuff."
Railway ManLater we asked Geneva Steel what they'd done with the free coal, and they replied "We gave it to employees. Our coke-oven department wouldn't touch the stuff."
Hopefully not in their Christmas stockings!
Interesting stuff RWM, keep it coming. Thanks.
An ethylene glycol and water solution sprayed on coal is very effective at keeping wet coal from freezing into a solid block. The chemical doesn't keep the water from freezing. Rather, it weakens the crystaline bond of the ice enough so that a car shaker can break up the frozen coal and allow a fairly complete discharge.
The coal company I worked for used the chemical any time the loads might be moving into areas where sub-freezing temperatures would be expected. I don't recall the rate of application of the product, but it wasn't much-maybe a few gallons per carload. As for cost, it was a pretty good hedge against the possibility of a big demurrage bill for cars that couldn't be unloaded and released back to the railroad.
"We have met the enemy and he is us." Pogo Possum "We have met the anemone... and he is Russ." Bucky Katt "Prediction is very difficult, especially if it's about the future." Niels Bohr, Nobel laureate in physics
RWM -
Funny stories ! As a colleague of mine once said, though: "Too true to be funny !"
We couldn't invent this stuff. That's why life on and around the railroad is so interesting.
It also says a lot about our institutions, the people that staff them, and their tolerance for risk and aggravation. The iron ore & coal round trip idea sounds good in theory - business-school / MBA type stuff - until you have to cope with these picky little details, the weather, the guys out at the plants, random chance events, and the effects of Murphy's Law on all of them. Then maybe itis not so good, at least not until you have a chance to work out these bugs.
John G. Kneiling used to advocate more frequent uses of such trip routing - "like a tramp steamer on an iron ocean" he often wrote. The load contamination that you describe would definitely be a challenge to overcome with such an operation. However, I recall he also viewed the then-existing hopper car designs as a bunch of bad compromises mainly intended to have a lowest common denominator car that could survive the kinds of frozen-coal abuses so well described by ndbprr above. Instead, John advocated a smoother-side design, with rounded corners to avoid just this kind of problem. He also recommended preventing the frozen-coal problem by applying low-temperature heating resistance tape to the sides of the cars, and then covering it / them with spray-on insulation (urethane of some kind, I recall). That was a radical idea back in the day of mainly loose-car railroading and only a few unit coal trains - Detriot Edison's circa 1967 aluminum cars and locos were the 1st all-owned by the power co., as I recall. But now such fleet arrangements (the cars, not the loco ownership) are common-place, and with special cars even now being segregated and equipped for electronically-controlled braking ("ECB"), it might be more feasible to try that idea again.
Anyway, thanks for sharing - those rank right up there with F. H. Howard's "Night Roundhouse Foreman" stories from about 20 years ago !
Also, nice job on your dissertation above on the loading-unloading process and rates and cautions, etc. to respond to the original post. That's a heck of a lot of information collected at 1 place - I think it took me about 20 years to learn or see or experience all of that. Has to be worth at least a half-day seminar !
- Paul North.
Paul, thanks, but I will never be a tenth as clever as F. H. Howard!
Reloads like you say are great in theory, tough in practice. The Geneva move was an unusual and propitious combination of market opportunities that leveraged spare railroad and Rocky Mountain coal mine capacity that happened to be available for a brief period of time while the PRB mines ratched up capacity, the power plants worked to adapt their boilers to the slagging characteristics of PRB coal, while Geneva used up its own window of opportunity of high steel prices against a mill in which most of the elements were attaining obsolescence simultaneously and air attainment rules had not yet been implemented, and there was a glut of cheap steel cars on the market as everyone transitioned to aluminum, cars which themselves were all rapidly approaching their scrapping date.
The big problem with reloading is the loss of car cycle time. Generally the out-of-circuit mileage and the cost and time for car cleaning drives the idea onto the nearest shoals.
I think John, bless him, was full of really bad mechanical ideas.
While there are many stories about efforts to empty hoppers cars with frozen coal-I have a few myself-I doubt that the condition is so common as to require a "radical solution". The problem doesn't stem from the moisture in the coal structure and it usually takes a combination of weather events to get the condition. Water from rain or snow melt will percolate down through coal in an open storage pile or loaded in a car. There are methods of getting the dryer coal out of an open storage pile, but water from heavy rain or snow melt on loaded cars that are subsequently subject to freezing temperatures might set up a problem. However it takes more than a light rain and a day or two of sub freezing temperatures and at that it is extremely unlikely that the entire load will freeze into one solid block. A little frozen coal on the sides or bottom of a gon isn't that much of a problem. When the car is turned over, most of the coal is going to fall out.
Standard hopper cars are more susceptible to problems as water will settle into the hoppers and if that part of the load freezes, the openings are plugged. With that, no amount of shakening, hammering, chipping or anything else but heat is going to get the job done. I was once at a power plant where the drill on the pole rig was tried and failed to break open the plug.
Aside from the use of anti-freeze to prevent the condition, thaw sheds with gas or electric can work. I was at one owned by American Electric Power at a rail to barge terminal on the Ohio down near Cairo. Maybe 5 to 10 carlengths long, it used electric for radiant heat.
By the way, just about every facility for unloading standard hoppers has and routinely uses a car shaker. Most coal is not sufficiently fluid to just completely drop out of the car without a little help.
jeaton [snip] Standard hopper cars are more susceptible to problems as water will settle into the hoppers and if that part of the load freezes, the openings are plugged. With that, no amount of shakening, hammering, chipping or anything else but heat is going to get the job done. I was once at a power plant where the drill on the pole rig was tried and failed to break open the plug. Aside from the use of anti-freeze to prevent the condition, thaw sheds with gas or electric can work. I was at one owned by American Electric Power at a rail to barge terminal on the Ohio down near Cairo. Maybe 5 to 10 carlengths long, it used electric for radiant heat. [snip]
Aside from the use of anti-freeze to prevent the condition, thaw sheds with gas or electric can work. I was at one owned by American Electric Power at a rail to barge terminal on the Ohio down near Cairo. Maybe 5 to 10 carlengths long, it used electric for radiant heat. [snip]
I've done work at something like 10 or 12 power plants and steel mills here in the NorthEast US that received coal or coke (or ore or pellets) in hopper cars of some kind, and as I recall all had thaw sheds of one sort or another to cope with the problem. No two were alike, either. Some just had heaters on the track - and those varied, too - others had them on side walls, some had roofs, others were open-air at the top, etc. They sure used a lot of energy when running.
From an engineering standpoint, the key consideration is to make the thaw shed long enough so that the average "dwell time" of the incoming cars in that heat is long enough to thaw the coal load as much as is needed - as jeaton notes, only enough to be able to dump (most of) it. That depends on how fast the dumping operation - whether a rotary car-dumper or through the bottom hoppers, etc. - is typically going. The faster it goes in terms of cars per hour or minutes per car, then the longer the thaw shed needs to be. Most of the ones I saw were in the 200 to 300 ft. range, which would be 4 to 6 car-lengths.
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