carnej1The railroad industry doesn't seem to agree with you about LNG/CNG fuel as they are pressing ahead to develop the technology given Natural Gas's current price advantages vs. diesel.
I was talking strictly about external-combustion locomotives.
There have been various efforts to develop CNG locomotives for quite some time (remember RailPower's CINGL development?) but only recently (with the gas glut from fracking) has the economics come together. LNG is technically more complex in some respects (here is a Railway Age article that's a good introduction to the subject), and some recent technical advances have made it far more practical. But these largely remain systems with IC engines (combustion turbines or piston engines) and comparatively few even use or propose Rankine-cycle bottoming even though there are comparatively mature systems to do that.
Your point about burning 'much more efficiently' is accurate and correct... and it probably is fair to add that NG fueling can produce "cleaner" exhaust than diesel, with considerably less fancy (and expensive, and economy-reducing, etc.) aftertreatment systems. Clean air was at one time the significant salient advantage for natural-gas locomotives, IIRC.
,
Here is a link to a good article that describes the basic Oxford Catalysts approach.
Note that there are other approaches that utilize both catalytic decomposition of H2O2 to 'direct steam' and the use of ;combustion' fuel/H2O2 to produce steam. A key differentiation is that the Oxford Catalysts team understood early that modulating the average number of steam molecules generated per fuel-molecule oxidation can control the temperature in the catalyst bed and hence the expected service life of the catalyst in a commercial machine such as a practicable locomotive.
In case you wonder why this is 'the best idea you never heard of', the principal issue was, and probably always will be, the ease of producing TATP from even moderately concentrated hydrogen peroxide, combined with the relative ease of diversion in any really practical-scale implementation of direct-steam technology on American railroads. Believe me, I am unhappy about this.
Methanol as a carrier fuel is useful in other contexts, of course, and its use is not limited to direct steam applications. One of the things I have been waiting for is an inexpensive reforming technology, and here it appears to be...
ndbprrWell the reality is steam is totaly impractical. Energy Is lost converting water to steam and more energy is lost converting steam to power. Internal combustion eliminates the steam step making it more efficient on the power side and the exhaust polution side. Steam can't win in any way.
Well yeah, we know all that, but this is just fun speculation. No harm in that.
Kind of like speculation on "what if General Robert E. Lee had an atomic bomb at Gettysburg?"
"Gen'ral Lee, we're losin' sir! What're we gonna do?"
"NUKE 'EM!"
The Rankine (steam power) cycle, with some tweaks such as a feedwater heater, is pretty close to a Carnot cycle. The Carnot cycle is the theoretical highest efficiency -- subject to a limit on the "hot side" temperature and the "cold side" temperature of the thermodynamic cycle.
The Brayton (gas turbine) cycle is also a pretty close approximation to a Carnot cycle. One key difference with the Rankine cycle is that there is no phase change -- the raising steam from water you talk about. This means that considerable mechanical shaft power from the turbine has to be recycled into running the compressor, to boost the air working fluid in pressure so that heat can be transferred to it at a higher temperature than heat is rejected at the turbine exhaust.
Gas turbine engines live or die on the mechanical/aerodynamic efficiencies of turbines and compressors. This also explains why gas turbine efficiency drops off so dramatically at part load -- as you drop the RPM's on the turbine and compressor, their efficiency as well as pressure ratio drops off.
The steam engine (Rankine cycle) only needs to move a much denser fluid -- liquid water -- from atmospheric pressure in the tender up to boiler pressure. This needs much, much less mechanical power than a gas turbine compressor, whether the water is "injected" into the boiler using a mechanical pump or using a steam-ejector pump (the common type of steam locomotive "injector"). The "supercritical" steam cycles used in some of the latest electric power plants is sorta halfway between a Rankine (phase change) and a Brayton (air -- no phase change) cycle. There is more pumping work, but not nearly as much as with a gas turbine.
OK, what limits the efficiency. The Carnot efficiency, and the Rankine cycle achieves that in a rough round-number approximation, requires as high a boiler temperature as possible, and it requires as low a cylinder exhaust temperature as possible.
So what are the limits on the boiler temperature. Largely, the boiler pressure. Owing to the phase change, boiling adds heat at the constant boiling temperature for that boiling pressure. I came up with a way to remotely measure the pressure in those unclad boilers at these Gas and Steam shows or Thresherees -- I point my remote-sensing infrared temperature gauge, read the temperature, and then look up the boiler pressure on a chart.
What is the limit on the exhaust steam temperature? It is the exhaust pressure.
In a non-condensing steam locomotive cycle, the exhaust pressure can be no lower than atmospheric pressure, hence the exhaust temperature can be no lower than the atmospheric boiling temperature of 212 deg-F. If you ran a steam locomotive at the high altitudes of the Andes Mountains, the ambient boiling temperature is lower and hence the Rankine and Carnot efficiencies could be higher. In practice, however, you always have some exhaust back pressure, so the heat rejection temperature of the steam locomotive is that much higher.
If you have a condensing cycle as in a steam power plant, you can exhaust to lower temperature -- the temperature at which you can cool your condenser -- and a correspondingly lower condenser inlet pressure, which may need compound expansion to realize in practice. Can you use a condenser on a steam locomotive? Apart from there only be a few examples -- the South African Railways Class 25C being the most notable, the question is, to what temperature can you cool your condenser?
The condenser temperature makes a big, big difference on the Rankine efficiency, and power plants like to use a (cold) body of water such as a lake or river. A steam locomotive can only reject heat to the ambient air temperature, which may be higher. But not only that, air is a much poorer heat transfer medium than cool water, so getting even close to the ambient air temperature with a condensing tender requires either very large cooling coils taking up space and weight, or very powerful cooling fans, that are a "parasitic" power load that lowers overall efficiency.
OK, what limits you on the hot side? Basically boiler pressure, and there are a variety of reason why steam locomotives never went to higher-than-300 PSI water-tube boilers, although the Jawn Henry ran 600 PSI in a water-tube boiler, and to the extent that the Jawn Henry had operational problems and was scrapped, I am told they didn't have to do with the water tube boiler.
What else can you do? Superheat, you can use very high levels of superheat. When you do that, you are no longer close to a Carnot cycle -- you have to use very high hot-side temperatures in relation to an equivalent Carnot cycle. But many practical cycles -- gas turbines, gasoline and Diesel car and truck and loco engines, use very high hot-side temps to squeeze out more efficiency.
But what is the limit in a steam locomotive, could you not use "insane" levels of superheat, and Chapelon advocated very high superheat? For one thing, there is cylinder lubrication, but Wardale wrote about cooled cylinder liners to circumvent this.
Here is the situation. In intermittent internal combustion (gasoline, Diesel piston engines), you can get very high combustion temperature spikes -- for very short times, and you cool the cylinder wall with radiator cooling water, the piston by oil splash. A modern Diesel locomotive has a very large radiator, but that radiator is just maintaining cooler cylinder temp than combustion temp and represents a parasitic loss -- there was talk of "adiabatic" engines with ceramic pistons to boost efficiency. That radiator cooling is nothing like the main thermodynamic cycle heat flow passing through a steam condenser.
In continuous internal combustion (gas turbines) you can't get quite the same combustion temperatures as in with intermittent combustion in piston combustion chambers. But there are "tricks" -- mainly exotic metals for the turbine blades to withstand the temps along with compressor "bleed air" to cool the turbine blades -- this is also a parasitic loss that you try to minimize.
Now, in a steam engine, which is external combustion, you have to transmit combustion heat across a tube wall, of either a boiler or a superheater. Even if you have the cylinder lube problem under control with cylinder cooling per Wardale, you have to prevent your superheater tube from burning up or melting, and the question is how high can you (economically) go, but modern power plants are using some exotic allows to push this limit -- would you use them in a steam locomotive that already gives up half the efficiency by rejecting heat to ambient air, whether in a condensing or a non-condensing cycle, in relation to the steam power plant using cool river water.
As to whether steam not being able to win, what doesn't win is external combustion, where the hot-side heat transfer has to take place across a metal surface -- in the internal combustion schemes, the heat transfer is by combustion in the actual working fluid, and you can apply cooling to the back side of metal surfaces as needed.
So why do you need external combustion? To burn coal or other solid fuels, including biomass such as waste wood or fuel crops such as switch grass or perhaps solid waste. The steam locomotive is all about burning solid fuels -- if you are burning liquid or gas fuel, you may as well use a gas turbine or a piston engine.
If you are going with external combustion, there are alternatives to the Rankine cycle -- external combustion closed-circuit (usually helium working fluid) gas turbine, Stirling engine, supercritical (highly compressed) CO2, and so on. I went to a talk at the "U" given by engineers from Argonne Lab under US Navy contract to test the supercritical CO2 engine -- as a possible replacement for the steam powerplant in atomic subs, where you have a condensing cycle, but you use little or not superheat because the hot-side temp limit is where nuclear fuel pellets start to melt.
Your ever-eager Forum participant raised his hand during the Q&A and asked, "I see in your supercritical CO2 engine 3 heat exchangers -- these would be the feedwater heater, boiler, and condenser in a steam engine? The thing is that water is a really effective heat transfer medium, both as a liquid and in phase change between liquid and gas? How is pressurized CO2 on that score." At that point, the guys from Argonne labs all looked down at their shoes, and the one guy said, "Yeah, there is that bit about heat exchangers -- what we are gaining in theoretical efficiency with CO2 we appear to be giving up in heat exchanger losses . . ."
So no, there is nothing impractical about steam, especially if the "design requirement" is external combustion to use solid fuel, nuclear fuel, or even solar heat. The steam power cycle is probably as good as it gets with external combustion, as the Navy kinda found out by giving a bunch of money to study this to the Argonne Labs people. Given that you don't have a supply of river water, L.D. Porta was arguing until the time of his passing that a (refined) Stephenson steam locomotive is as good as it gets to derive traction from solid fuel -- coal or biomass.
If there is a requirement for external combustion, and that requirement comes from the need to use solid fuel, and the conversion of solid into liquid fuel can be an inefficient process in its own right, not only can steam win, it is still the only game in town.
If GM "killed the electric car", what am I doing standing next to an EV-1, a half a block from the WSOR tracks?
Firelock76 ndbprrWell the reality is steam is totaly impractical. Energy Is lost converting water to steam and more energy is lost converting steam to power. Internal combustion eliminates the steam step making it more efficient on the power side and the exhaust polution side. Steam can't win in any way. Well yeah, we know all that, but this is just fun speculation. No harm in that. Kind of like speculation on "what if General Robert E. Lee had an atomic bomb at Gettysburg?" "Gen'ral Lee, we're losin' sir! What're we gonna do?" "NUKE 'EM!"
This nothing like speculating on "what if General Lee" had an atomic bomb. This is like speculating on "what if China develops their missile tech to the point that our Carrier Battle Group Navy is rendered obsolete -- what do we do now?"
It may not be in 10 years, in may not be in our lifetimes, and it may not be in a 100 years, but at some point, we are going to run out of economic oil. You live-steam hobbyists, you people exhibiting steam traction engines at shows, all of you operating steam locomotive railroad excursions, all of you arm-chair engineers speculatin' away on trains.com, keep doing what you are doing, because there may come a time when knowing how to build, maintain, and operate steam locomotives will become essential.
Paul Milenkovic Firelock76 ndbprrWell the reality is steam is totaly impractical. Energy Is lost converting water to steam and more energy is lost converting steam to power. Internal combustion eliminates the steam step making it more efficient on the power side and the exhaust polution side. Steam can't win in any way. Well yeah, we know all that, but this is just fun speculation. No harm in that. Kind of like speculation on "what if General Robert E. Lee had an atomic bomb at Gettysburg?" "Gen'ral Lee, we're losin' sir! What're we gonna do?" "NUKE 'EM!" This nothing like speculating on "what if General Lee" had an atomic bomb. This is like speculating on "what if China develops their missile tech to the point that our Carrier Battle Group Navy is rendered obsolete -- what do we do now?" It may not be in 10 years, in may not be in our lifetimes, and it may not be in a 100 years, but at some point, we are going to run out of economic oil. You live-steam hobbyists, you people exhibiting steam traction engines at shows, all of you operating steam locomotive railroad excursions, all of you arm-chair engineers speculatin' away on trains.com, keep doing what you are doing, because there may come a time when knowing how to build, maintain, and operate steam locomotives will become essential.
But at what point are we going to run out of economic natural gas? Hint: a LOT longer than the oil reserves..
The one scenario where I could imagine some type of steam technology being used for railroad traction would be utilizing solid biomass fuel but it's hard to picture that taking the place of fossil fuels.
As far as Rankine cycle bottoming although the railroad industry doesn't seemed to be focused on it there is at least one company offering a system based on essentially 0ff-the-shelf technology.
Voith turbo, knows to some US railfans as the company that provided the Hydraulic transmission system for Espee's Alco built Diesel Hydraulic locomotives, is trying to market such a system:
http://resource.voith.com/vt/publications/downloads/1971_e_g_2161_e_steamtrac_rail_2012-08_screen.pdf
"I Often Dream of Trains"-From the Album of the Same Name by Robyn Hitchcock
Paul Milenkovic It may not be in 10 years, in may not be in our lifetimes, and it may not be in a 100 years, but at some point, we are going to run out of economic oil ... there may come a time when knowing how to build, maintain, and operate steam locomotives will become essential.
It may not be in 10 years, in may not be in our lifetimes, and it may not be in a 100 years, but at some point, we are going to run out of economic oil ... there may come a time when knowing how to build, maintain, and operate steam locomotives will become essential.
You did not read the references for Oxford Catalysts very carefully. ;-}
It is not difficult to determine the marginal cost for a barrel of syndiesel (or equivalent) prepared via Fischer-Tropsch either from gasified coal or natural gas. It is not difficult to determine the marginal-price range for great extension of the various biodiesel processes -- specifically including algae, which is the only generation technique that does not need to follow Malthusian proportions.
In brief, we are never going to 'run out of oil' as long as there is a cost-effective demand for it, even if as a carrier fuel. There are too many advantages, including the ease of distribution and storage.
It probably won't, except for political or witch-hunt reasons. Some of the 'biomass' contenders, notably the torrefied fuels, are primarily intended to work as additives for reasonably clean coal combustion -- economics (including, if you must, 'welfare economics') will determine the operant proportion of biomass above that which produces all the desired effects from the 'additive' components.
I am working on a multifuel system that is essentially a throwback to the very early days of oil firing on locomotives. This uses a GPCS-compatible bed of mixed coal and biofuel, providing baseline output, with some combination of liquid and gas fuel (as needed) through separate burners... which can use the firebed as assistance for continued atomization, flameholding, or maintenance of a zone of gas over transition temperature, and (among other things) eliminate any tendency for sooting or smoking even up to high secondary-fuel mass flow.
Voith is not the only company with fairly-well-advanced Rankine cycle bottoming; BMW had a well-defined one at automobile scale years ago. (Notably, this followed the precedent of their fuel-cell system in being sized for the ancillary loads normally driven off a vehicle IC engine, and not being designed to substitute for the wide-range high-vanity-cushion "turndown ratio" required of a typical automobile engine. Smart!!)
Relax Paul, I'm just trying to make a joke here.
Honestly, no-one would be more happy than me to see steam come back, in whatever form. Maybe it's possible, maybe it's not. Probably not.
Keep in mind a whole industry that no longer exists would have to be re-created from scratch. It's all gone! Baldwin, ALCO, Lima, all of them. The manufacturing equipment was scrapped a long time ago, the men that built the locomotives are dust, or the very few that are left soon will be, and all the appliance makers are gone too. All that remains are the blueprints.
There's a much better chance of wholesale mainline electrification where feasable than there is a return to steam. Or another power source may be waiting in the wings for some genius to find it or for God to reveal it in His own good time.
But steam? Man I LOVE steam, and I think the world changed for the worse when steam died, but it ain't gonna happen. More's the pity.
Hence my statement that this thread is all fun speculation.
Paul,
A couple of quick comments on the Rankine cycle.
One larger contributor to efficiency is that liquid water is nearly incompressible, so pumps can be made to be very efficient. Gas based cycles have to contend with the gas heating when compressed, which provides all sorts of ways for the entropy to increase.
One limit on maximum steam temperature is that the fraction of water that breaks into H+ and OH- increases with temperature. 1200F appears to be the practical limit for steam temperature in order to keep corrosion under control.
- Erik
Any locomotive that would be designed today using steam, would look nothing like the steam engines that the diesels phased out. The maintenance cycle would have to be such that other than putting in fuel and steamable fluids (if not a closed loop system) there would be no need for maintenance other than replacing brake shoes and adding sand for the 92 day inspection cycle. Anything more maintenance intensive is a not-starter.
Never too old to have a happy childhood!
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