Western Railroad Discussion > Inert gas in a tank car

The ethanol cars that shuttle between the midwest and California are traveling empty 1/2 the time. Having contained a flammable, would the interior of the car still contain explosive gas after unloading? Are the cars ventilated prior to the return deadhead? Is an inert gas used to prevent ignition as is done aboard some aircraft?

John Gezelius
Tustin, CA

As a former tankship operator I can assure you that the environment inside an empty ethanol tank car is extremely volatile. And no the railroads are not required to inert the empty tankers.

The only vent to my knowledge on your standard tank car while traveling is an safety/over pressure valve up top.


Jeff

Is ethanol "vapor" volatile? I know gasoline's is, but without better information I don't know that a similar issue exists with corn juice, even if there is residual amount of product in the car after unloading.

Just because something burns does not mean that it, or its vapor, explodes.



Edited 1 time(s). Last edit at 05/28/13 17:08 by toledopatch.

Google "ethanol vapor".

From watching Ethanol Tank Car unloaded while I waited to switch them- The Air in the tank truck is displaced into the tank car while the Ethanol is being transloaded. The Fumes are very strong even though it was being contained.

Posted from Android

Yes residual ethanol, liquid or vapor, is flammable/explosive depending on amount of EtOH present, % oxygen present, and temperature, primarily. That said obviously at the very least ordinary air displaces EtOH as it's unloaded, and presumably the unloading process is as efficient as possible, nobody makes money on residual ethanol hauled back to the plant (although the shipper can win on outgoing loads that might not require quite so many gallons to fill*). IMHO the residue would be so small that if there was a wreck in which such cars were breached with an ignition source present a few 'poofs' and maybe even brief fires might occur, but a major disaster, even if many cars were involved, is hard to imagine.

*Assuming what's left in the car is indeed EtOH with no more H2O than the specs allow. EtOH is hygroscopic, that is it absorbs water from air and other sources, and that, obviously I hope, can be bad news for contamination, good news for reducing hazards. It is one of the main reasons pipelining EtOH has been such a difficult proposition. Not only does water contaminate the product it causes corrosion in pipes and pumps. We never complained too much about residual coal in empties we loaded, so long as it wasn't so much as to affect overall specs. We occasionally got cars that had been used for copper concentrates, however, and those at the very least had to be cleaned by the railroad at the loadout before loading, at worst rejected entirely. The most interesting contaminate we ever had was a stoned naked hippie and his crumpled-up bicycle; he was lucky he wasn't buried in 100 tons of coal......hopefully that will never be a problem with an empty EtOH tank!



Edited 2 time(s). Last edit at 05/28/13 21:06 by lowwater.

Uh...it's NOT "corn juice"...it's a form of alcohol, and when mixed with oxygen it IS very volatile...

Those of us of a certain age remember ethanol mixed with gas in dragsters...wheee doggie...!!!

toledopatch Wrote:
-------------------------------------------------------
> Is ethanol "vapor" volatile? I know gasoline's is,
> but without better information I don't know that a
> similar issue exists with corn juice, even if
> there is residual amount of product in the car
> after unloading.
>
> Just because something burns does not mean that
> it, or its vapor, explodes.

At the risk of being too much of a stickler for terminology, being volatile means that a substance can turn to vapor. Even water is volatile--slightly so at room temperature, allowing a wet surface to dry gradually, and more so as the temperature approaches 100°C, where liquid water will completely volatilize to steam. Volatility is necessary (but not sufficient) for forming an explosive mixture; water is volatile, but it lacks another important property that would make its vapor explosive.

The property that really is at issue concerning residual ethanol vapors is whether the vapors, once formed, are combustible. And as was well described above, each combustible fuel generally has a range of fuel/oxygen mixtures that are explosive at a particular temperature. Internal combustion engines precisely meter the amount of fuel and air to achieve an optimally explosive mixture.

One factor in volatility is the boiling point. As I recall, ethanol boils at about 78°C. Thus ethanol is more volatile than water (which boils at 100°C); at a given temperature, ethanol will vaporize more readily than water will. A separate, independent fact is that ethanol vapors are combustible, whereas water vapor is not. Another comparison would be that gasoline is more volatile than diesel fuel; at a given temperature, the smaller gasoline molecules will more readily turn to vapor than the larger diesel fuel molecules will. But of course gasoline and diesel fuel vapors are both highly combustible.

And I'll concede being somewhat flip in referring to ethanol as corn juice, though for the purpose of comparing it to various petroleum products I don't think that's really "wrong," either.

What I want to know, and am challenging an embedded assumption about in the initial posting to this thread, is whether a residual amount of ethanol in a tank car would be sufficiently volatile AND combustible to create an explosion hazard. It's well known that an empty gasoline tank is more explosive than a full one, but can that also be said of ethanol -- even ethanol that has been cut with gasoline as a denaturant? I'm skeptical. A loaded ethanol tank will certainly boil and explode in a fireball if heated without pressure relief (BLEVE), but would an "empty"? And if not, then what is the value of purging the car as suggested in the initial post?



Edited 1 time(s). Last edit at 05/28/13 20:58 by toledopatch.

I'm interested to know too. I've spotted hundreds of Ethanol cars, yet know little about the contents aside from reading what my hazmat says on the work orders.

Posted from Android

Where do you think we get popcorn from?...

Safeway...???

Different grades of coal do constitute contamination of other grades. When I set up a mini unit train shuttle for petroleum coke on SFe between Santa Fe Springs and Long Beach, CA, the railroad and coke buyer insisted on thoroughly cleaning all the traditional coal hoppers put into the cycle before commencing the program, to avoid any impurity contamination from the equipment's prior use. Likewise, I can confirm the problems of ethanol in pipeline or other fuel handling systems.. the dang stuff does like to hang onto water, which leads to corrosion and engine fouling problems.

Steve Donaldson
Pacific Grove, CA

SteveD Wrote:
-------------------------------------------------------
> Different grades of coal do constitute
> contamination of other grades. When I set up a
> mini unit train shuttle for petroleum coke on SFe
> between Santa Fe Springs and Long Beach, CA, the
> railroad and coke buyer insisted on thoroughly
> cleaning all the traditional coal hoppers put into
> the cycle before commencing the program, to avoid
> any impurity contamination from the equipment's
> prior use. Likewise, I can confirm the problems
> of ethanol in pipeline or other fuel handling
> systems.. the dang stuff does like to hang onto
> water, which leads to corrosion and engine fouling
> problems.

Absolutely, re pet coke. We were loading high-grade coking coal through Kaiser at San Pedro and they loaded pet coke too. Mixing them, even a little, was a major no-no. On the other hand a little marginal coking coal from the North Fork (Colorado) or Sunnyside (Utah) stuck in the cars wasn't a huge problem. And vice versa, the pet coke buyers didn't want any coal mixed in. Especially in some applications, the volatile matter in coal mixed with coke, regardless of the source, could be downright dangerous.