What was the purpose of steam lines on tank cars?

[Overmod]

You would need steam above 615psi, soaking for long enough to get all the liquid to temperature; I don't know how quickly convection would accelerate the heating above the 240 to 250-degree range, but I suspect it would be measurable.

A number that I don't think has been mentioned yet is the flash point, which is listed as 320 degrees F, at which point the vapor pressure is relatively slight.  Where the concern would be there is spills, as in disconnected hoses, around a flame source; a crew might not realize that flash ignition (producing prompt noxious gas) might occur at a temperature radically lower than that for sustained combustion of the liquid -- and that is saturation temp for only 75psi steam.

[Convicted One]

Overmod

d to get the bulk of the sulfur up to that autoignition temperature -- about 491F if anyone's not familiar.  That's way outside a pressure that would even accidentally be piped to car heating stations... assuming a process-heat system at a plant utilizing elemental sulfur would produce steam at that pressure

 I was just wondering in an "suppose all the holes in the swiss cheese happened to line up" sort of way. I'll acknowlege that it would be highly improbable.  You'd have to have a number of mistakes made, not the least of which being having someone totally incompetent do the plumbing.

 But, I have seen some fairly impressive results when automatic controls fail.

 Had a large, several hundred gallon, domestic water tank on the roof of one of our highrises, that had a dedicated air compressor connected to provide an air cushion above the water in the tank.

The pressure switch failed one weekend and the compressor ran continuously, until one of the most obnoxious lawyers you could imagine came in early in the morning to prep for a 9 AM trial,  And when he flushed the urinal, got what was likely the biggest "improbable" surprise of his life.   

 

 

[Overmod]

Convicted One

In fact, it would be possible to  blunder and use superheated  steam to heat sulfur above its autoignition temperature.  Of course in the absence of oxygen, it wouldn't ignite. But once you open that vent to drain the tank, whoaaa!

Probably not as much of an issue as you think.  The superheated steam is not sparged as in a fireless cooker; it is in closed pipes with a relatively low surface area, and any excess heat would begin to radiate increasingly well from the upper part of the car long before you got to the 832F at any tank vent areas needed to put sulfur in vapor phase.  Remember that there is very little added enthalpy per degree added in superheat; it is a pressure enhancer far more than a heat-content enhancer, and you can calculate the saturation pressure of the steam in long pipes needed to get the bulk of the sulfur up to that autoignition temperature -- about 491F if anyone's not familiar.  That's way outside a pressure that would even accidentally be piped to car heating stations... assuming a process-heat system at a plant utilizing elemental sulfur would produce steam at that pressure (let alone then superheat it further and circulate the steam fast enough to keep the superheat in the piping volume).

I would also at least suspect that some kind of gas blanketing is used when the tank is drained, which would minimize any oxidation well short of fire.  You do raise the interesting question of how hot you'd have to get sulfur to produce a critical-mixture explosion mixing with ambient air... I don't have the reference sources to assess that.  Erik?  Have your CRC rubber bible handy?

[Shadow the Cats owner]

Here at my work we have some tank cars that are heated also.  Why we haul some chemicals that require in transit heating to maintain certain tempatures to be usable at the final customer.  How it is done is via a diesel fired heater that is frame mounted on the tractor and we use quick connect fittings that pump hot coolant thru loops in the outer jacket of the trailer.  

[BaltACD]

Or if you heat the car and don't let it vent as it cools

[Convicted One]

SD70Dude

.  And if you switch them not long after they are loaded they can indeed be quite warm.

 

Being more familiar with the properties of sulphur now, after reading the above PDF...the melting point and the autoignition temperature are both lower than I would have guessed.

In fact, it woukd be possible to  blunder and use superheated  steam to heat sulpur above it's autoignition temperature.  Of course in the absence of oxygen, it wouldn't ignite. But once you open that vent to drain the tank, whoaaa!

 

I wonder if any bonehead has ever done that?

[BaltACD]

Tank cars are Private Owner cars, as such they ARE NOT subject to the Demurrage Rules that railroad owned cars are.  They nominally operate under 'trip leases' where the owner of the car is not the shipper and/or consignee of the car.  The trip lease specifies who pays what in the handling of the car at either/both the shipper/consignee facility and how long the car may remain at a facility for 'free'.

[SD70Dude]

Some tank cars (think sulphur and tar/asphalt) have permanent placards painted on them that say "HOT".  And if you switch them not long after they are loaded they can indeed be quite warm.

[Overmod]

tree68

 

Convicted One

I was surprised to see "24-48 hours" mentioned for the molten sulphur.

Likely governed by how long it's been off heat.

Perhaps also by the cost-effective length of piping and steam temperature provided.  If the operation can wait that time, they could economize on the likely reheating costs...

[tree68]

Convicted One

I was surprised to see "24-48 hours" mentioned for the molten sulphur.

Likely governed by how long it's been off heat.  I wouldn't be surprised to find the same type of number for asphalt.

[Overmod]

Lithonia Operator

But what about when the car is underway?

For a variety of reasons it's preferable to let some of these loads cool to the point they don't slosh or move in transport.  Part of the decision of how much insulation to apply to a car, and what type various parts of the insulation are, is overall economics.

Steam is generally used in preference to,say, Calrod-like electrical elements not only because of first cost but its high heat transfer at relatively low peak temperature.  Anyone who has suffered with any design of 'freeze plug' block heater understands heat-transfer concerns when excessive spot temperature degrades or cokes the material adjacent to the heating surface.  A sizable length of steam heating coil is easy to arrange, drain, and maintain, and providing process steam at the unloading point is not that difficult to support.

[Juniata Man]

Lots of products from chemicals to animal tallow must be heated in the car before they may be unloaded. Each product requires varying amounts of time on heat and this info is communicated to the consignee. I'll add that some products must be heated with hot water rather than steam because of the temperature difference between the two. Steam heat can damage some products as well as the interior lining of the car.

[Convicted One]

BaltACD

I don't know how long a car must be on steam for the contents to be flowable once it is at the consignees facility.

 

I was surprised to see "24-48 hours" mentioned for the molten sulphur.

[Convicted One]

Ulrich

What would be the purpose of steam lines on such a car, and what would be the source of the steam?

 

Molten Sulphur too. you might find this informative. (I didn't realize the Sulphur had such a low melting point.)  I've seen numerous molten sulphur transfer trains, but always just took it for granted that the originating source must have been "crucible like" furnaces.  Now seeing the lower temperature melt point, things make more sense

 

https://railroads.dot.gov/sites/fra.dot.gov/files/fra_net/4083/Molten%20Sulphur%20Rail%20Tank%20Car%20Loading%20and%20Unloading%20Operations_Final%20with%20Appendices.pdf

[BaltACD]

Lithonia Operator

But what about when the car is underway?

The car is not being unloaded while it is underway.  While underway the contents of the car will be cooling consistent with the temperature loss characteristics of the cargo.

I don't know how long a car must be on steam for the contents to be flowable once it is at the consignees facility.

[MMLDelete]

But what about when the car is underway?

[tree68]

Thick cargoes like asphalt.  

A facility that handles such commodities would have an appropriate source of steam.

The Susquehanna currently handles asphalt to a location between Binghampton and Syracuse.

[Ulrich]

In the January issue of RMC (page 21 top) there's an ad for a GATC  tank car... states that car complete with steam line inlet/outlet. Judging from the lettering on the car it is 1970s era. What would be the purpose of steam lines on such a car, and what would be the source of the steam?