How are tank cars unloaded?

[Murphy Siding]

     The short answer,  I'm sure, is that somebody turns the faucet.  What about unit trains of ethanol and such?  Is there a squad of faucet turners at the destination point?

[tomikawaTT]

The valve (faucets are only found in lavatories) is located at the lowest point in the tank.  There is also a vent valve at the top - on top of the dome, if there is one.

Where tank cars are unloaded en masse they unload at long racks.  A crew hooks up the hoses and opens the valves, sequentially from front to as many cars as the rack will hold, or as many as can be connected and started before the first one is drained and ready to close up and disconnect.  Then they return to the first car, close the valves, remove and stow the hoses and sign off the paperwork - there is ALWAYS paperwork to sign off.

If the tanks are in a unit train either the rack is as long as the train or, more probably, the train pulls forward until the first load is opposite the first rack connection and the dance begins again...

Chuck

[nbrodar]

 Not all tanks are unloaded from the bottom.   Many hazardous materials are top unloaded.   This is a safety measure against having the bottom valves damaged during a derailment.

Some locations have hose spots to unload an entire cut of cars en mass.  Some locations only have a few spots, so any extra cars will have to jockeyed about to get unloaded.

Nick

[Bob-Fryml]

GATX, the tank car people, have a system called "TankTrain."  It consists of a series of individual tank cars that are semi-permanently coupled together.  At the top of each tank car end, a product flow hose connects one tank car to its adjacent one or ones.  The idea here is that a customer needs to attach only one hose to the TankTrain in order to add or drain product to/from all the cars.  The system is designed for liquid shipments.

Adding product seems like a no-brainer.  Start pumping the liquid into the first car and when that one fills the excess product will spill over into the second car and eventually to the third, fourth, fifth, and however many cars constitute a TankTrain set.

To get product out, though, it would seem to require a compressed gas that would have to be injected into the one end of the TankTrain set while the opposite end drains the entire set of cars.  Injecting that gas under pressure strikes me as very energy intensive and could therefore negate the convenience of having only one hose connection for unloading.

Also there's the issue of minimizing product spills during derailments.  Unless the TankTrain is hauling fresh water, I should think it would require some kind of shutoff valve attached to each end of the product flow hoses.

I've closely observed a lot of freight trains in recent decades, but I can't recall seeing any more than a very small number of TankTrain cars.  Does anyone know if they're being used anymore?

For further information Google "TankTrain".

[Paul_D_North_Jr]

As of a couple years ago, there were 2 or 3 TankTrain routes in Canada - Sarnia comes to mind as a town that was common to them. Look on RailPictures.net and search there for photos of the TankTrain - there's a fellow who has done some really nice photos of them, esp. in winter. There were also 1 or 2 routes in California, but with refinery closings and corporate changes, I don't know if any of those are still running or not. - Paul North.

[PNWRMNM]

Murphy,

There are three basic answers.

Case 1 - Nonpressure car with bottom outlet, applies to most nonhazardous materials, flammable liquids, some corrosives, and some other materials.  Typical car specification 111A100W.  This is your basic attach hose to bottom outlet.  These cars have a vacuum breaker valve so that the material will continue to flow and to protect the car from being crushed by atmospheric pressure.  Think about this, can you drink all of your favorite beverage from a can or bottle without letting air in?

Case 2 - Nonpressure car with no bottom outlet AND pressure cars.  These cars all have liquid lines that reach to the bottom of the tank and a vapor valve.  The vapor valve is used to introduce pressurized vapor into the tank to force the liquid out the liquid line.  What the vapor is depends on the product.  In most cases it is the vapor of the product itself.  LPG is an example.  The receiving tank has a vapor pump that withdraws vapor from the receiving tank, compresses it and sends it to the tank car.  This creates a pressure differential with causes the liquid to move in an attempt to equalize the pressure.  It takes only a few pounds per square inch of differental to move the product.  To the best of my knowledge most products are unloaded using their own vapors.  Tomato paste is a food grade product so nitrogen gas is used to create the pressure differential.  Nitrogen is used to prevent bacterial growth in this case.  Nitrogen is relatively cheap and nonreactive so if other than product vapors are used to unload, I would expect nitrogen to be the gas of choice.

Case 3 is Tank Train.  It works like case 2, that is pressure differential, except that you have several/many interconnected cars.  For a product that readily vaporizes, like gasoline or ethanol. I would expect them to use product vapors.  For crude oil, which does not vaporize much, I suspect they use nitrogen.

Mac

[Paul_D_North_Jr]

Here's the link to the TankTrain photo I had in mind:

 http://www.railpictures.net/viewphoto.php?id=133704 

But, to find it I also had to search RP.net for ''Ultramar''.

Mac, thanks for that very comprehensive answer.    I've seen glimpses of those operations form time to time - I installed many sets of 'spill protection pans' at loading and unloading spots in the 1980's, as well as general track maintenance and repair at such places - but never troubled myself to ask or look into those kinds of questions.  And as you know, asking too many unnecessary questions not related to the task at hand is usually discouraged, and getting any photo in those kind of places can be tough, so it's hard to depict any other way. 

- Paul North. 

[samfp1943]

Here is a link as Bob suggested: http://www.alaskarails.org/fp/TankTrain.html

When the term 'Tank Train'  was mentioned, my reaction was, 'Sure!'  'The SP's famous move over the mountains into California.'   I was not aware that others had similar equipment moves as well. Poto's from the link show the GATX equipment and descripotives, as well as equipment from Alaska RR and CN RR in Canada.

[samfp1943]

To Mac: 

"...Case 1 - Nonpressure car with bottom outlet, applies to most nonhazardous materials, flammable liquids, some corrosives, and some other materials.  Typical car specification 111A100W.  This is your basic attach hose to bottom outlet.  These cars have a vacuum breaker valve so that the material will continue to flow and to protect the car from being crushed by atmospheric pressure.  Think about this, can you drink all of your favorite beverage from a can or bottle without letting air in?..."

Found this illustration to a graphic real life depiction of what you are indicating here...(Note that the affected cars are connected at the bottom by hose).  

 Here is the link:  http://www.youtube.com/watch?v=Zz95_VvTxZM

[ericsp]

As far as I know, the Coast Line Oil Cans are still running.

There are and have been a few other Tank Trains besides those in CA and CA (California and Canada).

Burlington, VT; Rutland, VT

http://www.rrpicturearchives.net/showPicture.aspx?id=803627 

http://www.rrpicturearchives.net/showPicture.aspx?id=867180 

http://www.rrpicturearchives.net/showPicture.aspx?id=867179 

http://www.rrpicturearchives.net/showPicture.aspx?id=867177 

http://www.rrpicturearchives.net/showPicture.aspx?id=867178 

http://www.rrpicturearchives.net/showPicture.aspx?id=689008 

http://www.rrpicturearchives.net/showPicture.aspx?id=867168 

http://www.rrpicturearchives.net/showPicture.aspx?id=689004 

http://www.rrpicturearchives.net/showPicture.aspx?id=867171 

http://www.rrpicturearchives.net/showPicture.aspx?id=867169 

http://www.rrpicturearchives.net/showPicture.aspx?id=867170 

Durand, MI; Bay City, MI

http://www.rrpicturearchives.net/showPicture.aspx?id=163205 

http://www.rrpicturearchives.net/showPicture.aspx?id=163201 

http://www.rrpicturearchives.net/showPicture.aspx?id=175251 

http://www.rrpicturearchives.net/showPicture.aspx?id=175234 

East Camden, AR

http://www.rrpicturearchives.net/showPicture.aspx?id=510565 

East Deerfield, MA

http://www.rrpicturearchives.net/showPicture.aspx?id=344808 

Greenwood, SC

http://www.rrpicturearchives.net/showPicture.aspx?id=71149 

http://www.rrpicturearchives.net/showPicture.aspx?id=71150 

Hammond, IN

http://www.rrpicturearchives.net/showPicture.aspx?id=1905443 

http://www.rrpicturearchives.net/showPicture.aspx?id=1833079 

http://www.rrpicturearchives.net/showPicture.aspx?id=1970799 

Olean, NY

http://www.rrpicturearchives.net/showPicture.aspx?id=1123600 

Tucson, AZ

http://www.rrpicturearchives.net/showPicture.aspx?id=245896 Contrary to the photographer's comment, this is not a tankcar from the Oil Cans.

BKDOU/DOBKU

http://www.rrpicturearchives.net/showPicture.aspx?id=384720 

http://www.rrpicturearchives.net/showPicture.aspx?id=1881497 

http://www.rrpicturearchives.net/showPicture.aspx?id=1867457 

http://www.rrpicturearchives.net/showPicture.aspx?id=1867459 

http://www.rrpicturearchives.net/showPicture.aspx?id=1867460 

OWPDO/ODOWP

http://www.rrpicturearchives.net/showPicture.aspx?id=637284 

http://www.rrpicturearchives.net/showPicture.aspx?id=100273 

I know I have also seen photographs of Tank Trains hauling sulfuric acid in New York (from about 30 years ago) and a single Quaker State Tank Train in Fullerton, CA. 

[Paul_D_North_Jr]

Wow  !  Thanks for all those links, ericsp, and the research and time to compile and post them.    I had no idea there had been/ still are so many of those operations.  I happen to think it's an idea and equipment that's underutilized, but that's just me . . .  

- Paul North. 

[Murphy Siding]

     With all the equipment and advances in design, in order to dump coal cars faster, it seems that , in comparison, a unit train of tank cars must take forever to unload.

[Paul_D_North_Jr]

Murphy Siding

       The short answer,  I'm sure, is that somebody turns the faucet.  What about unit trains of ethanol and such?  Is there a squad of faucet turners at the destination point? 

No - it's a squad of ''hose handlers'' instead.    Here's a recent photo from an unidentified facility that unloads around 100 tank cars a day.  I'm told there are 4 guys needed to do that at this location.  As you'll see, they - or at least this one anyway - use flexible metal hoses with a 2-handled red 'quick disconnect' at the tank car end - one is barely visible under the near tank car in the shadows at the lower right.  The other end connects to the white manifold pipeline in the foreground.  From the photo, I'd presume they drain by gravity - I don't see any visible connections or lines to pressurize them to drain faster, etc.

 

- Paul North. 

[BFBX]

Wonder how long it takes 30,000 gallons plus gravity fed in those hoses. Tough on turn around time.

[BaltACD]

Ethanol trains in my area have about 48 hour turnaround time - load to empty.

[Rader Sidetrack]

Sometimes the tankcar unloading process is just a towable pump on a trailer that transfers the product directly into a truck.

Image linked from: http://www.rbtsi.com/Pumps-PE400.asp

The photo is from an equipment manufacturer, but I have seen a similar arrangement at an ethanol transloading point on the Yadkin Valley Railroad in North Carolina.

[Paul_D_North_Jr]

BFBX

Wonder how long it takes 30,000 gallons plus gravity fed in those hoses. Tough on turn around time.

The facility in the photo posted can gravity-empty those 80 cars in 8 - 10 hours.  That's effectively 8 to 10 cars per hour, or 6 to 8 minutes each,  but that's unloading most of them simultaneously at a much slower rate, I'm sure.  In any event, they often 'turn' a train daily, which is governed more by how often the serving railroad wants to show up, than by the actual unloading rate.   

From the GATX Tank train website, at: http://www.gatx.com/wps/wcm/connect/GATX/GATX_SITE/Home/Rail/Rail+North+America/Products/Equipment+Types/Tank/Tank+Train/  

"The GATX TankTrain™ System can be loaded or unloaded at a rate of 3,000 gallons per minute. A five-car string loads in just 90 minutes, while a 90-car train takes less than five hours." 

To unload a single car through a 4" or 6" hose by gravity alone would take a little fluid mechanics and physics math to figure out.  A wild guess tonight would be 500 gals. per minute average, or about an hour for 30,000 gals.   

- Paul North. 

[BroadwayLion]

What is being transported? Many tank cars have heaters in them to heat the contents so that it will flow.

Each material has its own handling characteristics.

Certain cars and/or commodities require cars to be steam cleaned before their next trip.

Kindly take care of the equipment when cleaning.

[CSSHEGEWISCH]

Without being absolutely certain, it looks like that tank car was an empty which imploded when the vapor inside the sealed tank condensed.

[Semper Vaporo]

Watch it happen!

watch?v=Ehci9vrvfw

[John WR]

Thanks for the illustration.  It sure shows how important admitting air can be.  It reminds me of a simple experiment in physics.  You take a gallon can with a screw top, put a little water in it and boil the water until the can is filled with steam.  Then take the can off the fire and screw on the top.  You can run cold water over it or just let it stand and watch the slow collapse as it implodes.  

[Semper Vaporo]

WHOOPS!  posted to the wrong thread!  Sorry about that.

 

Well. I do have something to say here too... the collapse is often NOT "slow".  Once the stress reaches a certain point the vessal will start to collapse and once over the starting point, it occurs very rapidly.

[John WR]

Semper Vaporo

the collapse is often NOT "slow".

I didn't intend to suggest that a tank car which is drained without allowing air to enter would collapse slowly.  Rather, in the experiment I describe if the steam filled can is allowed to cool slowly the collapse will be slow because it takes the steam a while to condense.  When a tank car is incorrectly drained the vacuum is produced very quickly so I would expect the collapse to be fairly quick.  

I am surprised that no fail safe system to prevent such a collapse has been found.  Tank cars have been around for a pretty long time now so the problem must not be new.  

[PNWRMNM]

Most nonpressure cars equipped with bottom outlets have a "vacuum breaker" valve for exactly that reason.

Mac

[John WR]

Since pressure relief valves are commonly used even on hot water heaters it did seem to me that relieving the vacuum inside a tank car should not be difficult.  After all, the problem is excess pressure in the atmosphere.  

[Paul_D_North_Jr]

Ironeagle2006

Well I can unload 6k gallons of product in a tank trailer
in less than 30 mins with 10 psi of air pressure in my trailer and that is hauling corn syrup. 

  What diameter outlet or hose ? 

The 10 psi would greatly speed up the process, too.  The average pressure of the syrup in an 8 ft. diameter (guess) tank from gravity only would be on the order of 2 psi*, so with the 10 psi added that's 6 times greater. 

*Assuming corn syrup has roughly the same density as water - 62.4 lbs. per cubic foot / 144 sq. inches per square foot = 0.43 psi per foot of depth, so under gravity only (no air pressure added) the pressure at the outlet would vary from about 3.5 psi when the 8 ft. diam. / high tank is full to 0 when it is empty.  No idea on the viscosity or 'flowability' of the corn syrup, or at what temperature, etc. 

- Paul North. 

[Paul_D_North_Jr]

Sparing everyone the math, and ignoring friction, 'head losses', 'edge', orifice, or 'inlet control' effects, etc.:

A 6" diam. outlet has an area of about 0.20 sq. ft.

A 10 ft. diam. tank at half-full (5 ft.) of water at normal temps. will discharge at about 18 ft./ sec. (per Bernoulli's equation).

With various measurement unit conversions, that works out to about 1,600 gals. per minute, if I've done the basic math right this late at night.

So to unload that 30,000 gal. tank car through a single outlet would take about 20 mins., more or less.

Details and refinements, etc. are invited.

- Paul North.     

[edblysard]

The first photo is the result of a plant worker steam cleaning a tank car, exiting the car and closing the manway hatch, without opening the tank car drain and safety valve.

The video is from Brazil, it is a training tape made for plant workers showing what happens when a non-pressure differential tank car is drained without opening the safety valve.

All US tank cars that carry pressurized gas and liquids have what Mac says, a vacuum breaker valve, which is a one way valve that allows outside air to enter the car.

[Rader Sidetrack]

Paul_D_North_Jr

Assuming corn syrup has roughly the same density as water  ...

High Fructose Corn Syrup (HFCS) is actually quite a bit more dense than water. Not all HFCS in commercial use is exactly the same, but generally it is of similar density to honey.  Roughly, water is 8 lbs per gallon, honey is 12 lbs per gal. A typical HFCS product is about 11.5 lb per gallon.

(I am also a beekeeper, and honey, sugar, and substitutes are hot topics on beekeeping forums. )

[Murphy Siding]

Ironeagle2006

Stuff I haul every now and then I might get 2 loads a month has the consistency of 90W Gear Oil when Cold.  Compared to the Acid I haul it is a Very and I mean VERY Stable load inside those Smooth Bore Tankers.  We use a Standard 4 Inch line to Drain the trailer and no more than 10 PSI otherwise the relief Valve will pop and then you got a Problem.  WPG is right around 12 how we haul so much to the Factory is Simple they do not have a Direct Rail Unload Point at their Factory.  However my Boss has a Trans Shipment Point less than 20 miles away.  So we load up and go with a FULL and I mean FULL tanker load and get it over there when they call for one.  Best part is getting the Free Stuff from this Plant every Now and then like Cookies and such. 

   Well,  I'm just a little concerded, that you're hauling truckloads of gear oil and acid to a cookie factory, but I guess that everybody has their own secret ingredients that make the cookies taste good.