@Rob Leese posted:

A recent discussion on the sources of water for steam locomotives sent my mind to a related question pertaining to water. Some boiler systems are referred to as “closed loop” systems where steam vapor is recovered downstream from its work purpose and returned as condensate to the boiler.  I maintained such a system at a hospital where steam was used to heat water and sterilize surgical instruments.
I realize that most or maybe all American steam locomotives exhausted steam vapor into the smokebox to enhance draft, yet I have found examples of closed loop design in foreign steam locos.
It is an interesting thought to be able to operate a steamer on condensate with a minimum of makeup water.  Was this ever attempted?

Yes. The South African Railways had a class of 4-8-4s set-up as condensing locomotives, where the exhaust steam was captured, sent through cooling coils/radiators on the tender and returned to the tender as water.

Fascinating! :-)

As I recall Jack those South African condensing locomotives ran fairly late in steam too?  Into the 80's?

Interesting article and pictures of the massive tenders here:

SAR Condensing Tenders

I think Lear tried a condensing car where the condenser was on the roof. (?) The ACE 3000 locomotive had a condenser

Dan Weinhold

@sleepmac posted:

I think Lear tried a condensing car where the condenser was on the roof. (?) The ACE 3000 locomotive had a condenser

What "ACE 300 locomotive" was THAT????

Dan Weinhold

I think the ACE 3000 was Rowland's effort.

https://locomotive.fandom.com/wiki/ACE_3000

Dan Weinhold

@sleepmac posted:

I think the ACE 3000 was Rowland's effort.

https://locomotive.fandom.com/wiki/ACE_3000

Dan Weinhold

It was ONLY a "proposal", that was never fully designed nor built. In fact, an EMD SW1500 switcher could start and pull more than it could.

HW, I know you're right. Funding ran out, and that was "all she wrote".

Dan Weinhold

Interesting. Since closed loops were common on stationary boilers, why was it not used in steam locomotives. I understand the exhaust improved draft but would not that have been solvable? There must have been reasons. Just wondering and Google was not my friend.

@Caldwell posted:

Interesting. Since closed loops were common on stationary boilers, why was it not used in steam locomotives.

Increased maintenance, plus water was generally in great supply.

I understand the exhaust improved draft but would not that have been solvable?

No, notarially.

There must have been reasons. Just wondering and Google was not my friend.

Extremely high maintenance for condensing steam locomotives, thus NOT used on the North American Continent, where water was pretty much easily obtainable.

@Caldwell posted:

Interesting. Since closed loops were common on stationary boilers, why was it not used in steam locomotives. I understand the exhaust improved draft but would not that have been solvable? There must have been reasons. Just wondering and Google was not my friend.

To add to what has already been stated, stationary boilers are not subjected to the stresses of non-stationary boilers.  Movement of any kind leads to challenges, especially in the joints.

There is also an element of cleanliness that can be obtained in stationary environments over that of a rail locomotive which is subjected to the elements.

As a young engineer in the 1970s I worked on a project to develop a steam-powered automobile with low emissions. To extract maximum efficiency (fuel economy), the system operated at high steam pressure (1200 psi), high temperature (1200 deg-F), and included a feedwater heater and condenser (closed cycle with no makeup water). Ultimately, this advanced system proved to be impractical because the thermal efficiency was not sufficient to minimize the use of fuel and therefore it had high emissions even with a well-designed boiler. Steam locomotive efficiency would have benefited from a closed system. Exhausting steam up the stack and bringing in more cold water to replace it was a waste of energy. Most likely, the condensing system on a steam locomotive would have been large, heavy, and maintenance-intensive.

MELGAR

Thanks for the replies. My experience is with stationary boilers. I understand the movement part and suspect that is why safety appliances like low water cutoffs would not work. Looking at the size of later steam engines, I wonder if a boiler that size were in a building they  would just go with a water wall boiler.

Thanks again,

Another factor is the type of engine being powered.  A steam turbine, for example, is better suited for a closed loop system than a reciprocating engine owing, as mentioned above, to the greater number of moving parts and their movement cycles... 

Mitch

@Hot Water posted:

It was ONLY a "proposal", that was never fully designed nor built. In fact, an EMD SW1500 switcher could start and pull more than it could.

How do we know that an SW1500 could start and pull more if the ACE3000 was never built?  The specs on paper I’ve read are 70,000-100,000 lbs of tractive effort and 3000 DBHP.

there's a lot of issues with going to a condensing mode in a steam locomotive.

The furnace side problem is simple so let's start there. Without the blast of steam from the cylinders going up the stack to act as an ejector, there is no draft.  To replace this source of draft a fan is used.  A locomotive style boiler is induced draft as opposed to forced draft.  I.e. The fan or ejector is pulling air through the coal bed and the firebox volume is under negative pressure.  A forced draft boiler like most small stationary units or a scotch-marine style boiler has a fan upstream of the flame and the fuel pressure is raised to deal with the positive pressure combustion volume.  Forced draft works just fine for fuels that flow easily like oil or natural gas/propane.  Forced draft only for coal on grates just doesn't work well for all kinds of reasons.  Therefore the fan on the SAR units was in the smoke box, making them induced draft boilers.  In stationary coal fired applications there is a device of some kind to collect the flyash before it goes out the stack.  This has never been a requirement in steam locomotives and would be prohibitive due to its physical size.  ( collection devices would be an ash precipitator or baghouse.  A precipitator works like a giant bug zapper to collect the ash particles into large enough clumps to handle)  Since there is no flyash collection device in a steam locomotive all that ash passes through the fan - and beats it up.  Maintenance requirements of the fan are very high.  This can be somewhat mitigated with wear protection materials, but it won't go away.  Also the energy to turn that fan isn't free.  It needs to be driven by something and I believe the SAR locomotive fans were driven by small turbine.  The steam driving the turbine would also need condensed and take away from steam available to drive the pistons - aka a parasitic loss.  full size power plants are always working to reduce these losses.

As to the condensing itself, setting up the condensation system requires a good understand of the steam tables.  The big question is: how do you turn exhaust steam back into water?  The answer is the right combination of temperature, surface area, and pressure.  Temperature and pressure are key.  The lower the pressure, the lower the temperature needed to get the steam to condense back into water. To accomplish a lower pressure the condenser section is kept under vacuum.  Near perfect vacuum - like outer space - is roughly -31" Hg(mercury). A big power plant will consider -30 " hg to generally be max achievable, and keep the condensers on the turbine around at 27" Hg vacuum and less.  There are actually interlocks to prevent operating above 25" for a number of equipment safety reasons.  A quick look at the controls for a running unit at my facility reveals 28.9" Hg vacuum this morning, which is great.  Cooling is the next problem.  At a stationary plant water is used to cool the condenser.  On a locomotive that's not an option.  You need to use air cooled condenser tubes.  So lots of small diameter tubes and air being pulled across them.  These means more fans to move the air, so more turbines, and more parasitic losses.  Also more parts to maintain and by the way, the way that vacuum is attained is usually by an ejector, which for this application is much more efficient that a vacuum pump, but does require some steam to be thrown away.  Also, any air in leakage drops the efficiency of the condenser, so you are always looking for even the smallest vacuum leaks.  There is a whole industry that uses helium to detect vacuum leaks at the big plants. 

So why bother with all the headache - well in the case of the SAR it was exactly what you would think.  Clean water was hard to find.  There are still losses even with condensing locomotive but it stretched out the distances between refills by factors of 2 to 3 time the non-condensing distance ( maybe more) . In a stationary plant the make-up amount is very small because there is space and incentive to optimize everything.  Also at the much higher operating pressure and temperatures the water cleanliness requirements go up dramatically.  Usually power plant make up water is treated through a reverse osmosis membrane process which is very expensive. 

I hope this helps shed some light on the subject without going too far down the rabbit hole.  Exhaust fans get beat up, and condensing steam back into useful water requires complicated equipment not well suited for a locomotive.

"notarially"?...

notarially

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no·tar·i·al

  (nō-târ′ē-əl)

adj.

1. Of or relating to a notary public.

2. Executed or drawn up by a notary public.

North America was indeed a friendly place to use steam locomotives, or steam engines in general. Water, water almost everywhere, and much of it was not overly mineral-bound. Large areas had water soft enough that you could suck it right out of the river, if you chose. Good points were made above about how much easier were the lives of stationary or marine steam engines. A ship is essentially a stationary platform, as far as many engine stresses are concerned.

A locomotive, however, is an absolute nightmare for a  steam power plant. High speeds, high-frequency vibrations, low-frequency impacts (the train dynamics), unavoidable imbalances (drivers and rods), no protection from the weather, extreme temperature variations, both seasonally and operationally, a terrible lubrication scenario.  There is also, you know, hitting things. These locomotives should have never worked. No cozy engine room or car body here.

The ATSF, especially, was one of the best candidates for a condensing loco, and I think that they were seriously discussed. The Santa Fe, and I guess the SP, had to have water trains to fill tanks so that other trains could come along and use the water. Expensive. The EMD FT's must have looked like salvation.

Steam locos already had blowers to force a draft while waiting on the terminal ready tracks to keep the fire at a decent level, while getting up and maintaining pressure. So, I suppose that it was usable on the road if a condensing loco was desired.

@D500 posted:

...Steam locos already had blowers to force a draft while waiting on the terminal ready tracks to keep the fire at a decent level, while getting up and maintaining pressure. So, I suppose that it was usable on the road if a condensing loco was desired.

The blower on a steam locomotive is a STEAM blower. It is a ring of steam jets placed concentric with the exhaust nozzle. It is not a fan in the sense that we normally think of a “blower.”

@dkdkrd posted:

"notarially"?...

notarially

Also found in: Thesaurus, Legal, Encyclopedia.

no·tar·i·al

  (nō-târ′ē-əl)

adj.

1. Of or relating to a notary public.

2. Executed or drawn up by a notary public.

I'm guessing "no, not really".

The South African Ry's condensing 4-8-4's were employed across the the Great Karoo Desert - very arid, hot and limited rainfall.