BoydInstead of the complications of a rotary dump system, why don't they just vacuum the coal out of hopper cars at their destination?
Two reasons not so far mentioned:
1) Trituration. Coal grinds up against itself (this is where the 'coal dust fines' come from) and it is likely (to me) that any vacuum system going to a storage pile and not directly to bunkers/grinders/burners is going to cause considerable breakage and fines above what a simple gravity dump and conveying/loading would.
2) There's no such thing as a 'vacuum' system -- it's an induced-wind system. The amount of air that has to be moved to levitate a gon-full of coal against its own weight in the 'short time' comparable to a train advance plus rotary dump, without passing the coal through the inducing fan with the air that levitates it, is going to be considerable ... as is the power needed to accelerate the airflow at the start of extraction, or to keep the fan speed up between cars.
In addition, something has to move the vacuum nozzle around (like those old leaf collection 'elephant trunks'), prevent the levitation equivalent of bridging, deal with the situation when a slug of air gets pulled between two slugs of coal load, and so forth. I see no big savings here, and unless you have the aspirin concession for the unloading facility you're unlikely to want to use that approach.
Why do they have heating coils in them simple you try pumping out liquid that thinks it is a solid at 50 degrees when the temp is 0 outside it becomes peanut butter in the hoses. You add a little heat to the product and it flows right out of the tank car. Sulphar is actually solid unless it is heated above 220 degrees IIRC sorry been a while since I read the MSDS on pure elemental Sulphar for the melting point. It is pumped in liquid turns into a block of rock basically reheated into liquid and is pumped out of the cars.
Yes, Johnny, cars for stuff like molasses, corn syrup, asphalt, and such usually are insulated, and have steam coils in them. I'm not sure about the physics here, but I remember one time when we had a corn-syrup tank car with a defective system in it...what basically happened is that the steam in the coils cooked the load, solidifying it. Somebody had to buy that load and the car containing it. (Think about the "Fireless Cooker" technology--a little steam with a bit of pressure can work for a long time!)
Carl
Railroader Emeritus (practiced railroading for 46 years--and in 2010 I finally got it right!)
CAACSCOCOM--I don't want to behave improperly, so I just won't behave at all. (SM)
DeggestyWhile on the subject of speed in delivery, do tank cars that carry molasses have heaters in them (especially useful in January delivery)?
Don't know about molasses specifically, however 'molton sulphur' gets connected to steam sources at destination to ensure that the sulphur remains in liquid form for unloading. Suspect similar procedures may be employed for molasses in January (and most of the rest of the year).
Never too old to have a happy childhood!
While on the subject of speed in delivery, do tank cars that carry molasses have heaters in them (especially useful in January delivery)?
Johnny
Boyd Instead of the complications of a rotary dump system,,,, why don't they just vacuum the coal out of hopper cars at their destination?
Instead of the complications of a rotary dump system,,,, why don't they just vacuum the coal out of hopper cars at their destination?
Potentially, balancing the costs of a rotary dump facility against a vacuum sustem effect the decision of which system to be implemented. The rotary dump offers a higher volume of product movement in a shorter time. The vacuum system would require much more time, and a more complicated process (ie; it becomes a pretty expensive system to implement).
A pnematic OTR tanker is unloaded by an on-board blower ('trucker' pays for fuel,and unloading time, and also any equipment maintenance issues, if they should arise). It depends on the 'flow rate' of the product transported, as to the amount of time utilized in the unload. Generally, those 'loads' are gravity loaded while the truck is 'scaled' to gain its capacity.
Unloading from a railcar or other bulk source can be very 'trying' for the driver, as the load needs to be ' road legal'; not to mention time consuming, [ all sorts of 'variables', come into play,] in this scenario,in order to go to delivery. And at deliver, the driver may unload by 'b;owing off' the product into a silo type storage facility, or in a lot of cases with deliver of types of plastic pellets, he may have to "Box' the load off [ ie; into whatever system a plant may use to get its raw materials to the end use point... gaylord-type cardboad boxes, or metal type hopper boxes] This kind of unload become an industrial ballet; driver, employees of the receiver, containers, forklift(s), and physical location...stressful.
Time it takes to unload. 1-2 minutes for a rotary car dumper to unload a car compared t0 1 hour to vacucum out a car. We use pressure to force off our liquid tanks they can unload 5K gallons in less than 45 mins time. If the customer wants gravity unload we are talking 2 hours. On our plastic hoppers we can unload them with 15 psi we can unload 24 tons in less than 40 mins but then we areate the load before we open the valves.
Modeling the "Fargo Area Rapid Transit" in O scale 3 rail.
Our community is FREE to join. To participate you must either login or register for an account.