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Steam Loco exhaust, ex-34081 - 92 Squadron

Discussion in 'Steam Traction' started by Spamcan81, Jul 6, 2017.

  1. thickmike

    thickmike New Member

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    Thanks Wayne - the smoke on Wednesday and Sunday wasn't too bad but it was fairly constant - what was good was the lack of evidence of water vapour - she was obviously superheating pretty well
     
  2. thickmike

    thickmike New Member

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    I think the Braunton guys might well be agreeing with you as we speak
     
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  3. 30854

    30854 Active Member

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    Having just seen photos of 34092 coating Sussex in a fine layer of soot (just below the one of 541 doing the same... and that of 21C123 - sadly, currently unable to play, due to knackered firebox), my enquiry re GPS stands.... and, yes, I do realise much of the smoke was for the benefit of photographers!
    https://m.facebook.com/bluebellrailway
    The front end mods Jos outlines may indeed solve the tendency of an overfierce blast ripping the fire bed apart, but would this represent the full extent of efficiency improvements? Correct me if I'm wrong, but isn't a feature unique to a GPS that exhaust steam supplied to the fire bed causes a chemical reaction creating further combustible gases?

    The other direct result of more complete combustion, of course, being that there will be far less scouring of internal surfaces. Considering the Bulleid boilers have rather more of these, in the form of thermic syphons (not cheap to replace!) the case for at least a closer look at the firebox surely wouldn't go amiss.

    Whether or not the costs of a conversion would be recovered in savings I can't begin to guess. Clearly, the potential for improving the economics of mainline operations is greater than for chugging up and down with light loads for a few miles at 25mph. Equally clearly, it's unlikely that a mainline operator would be willing to undetake such an exercise without any detailed analysis ahead of a significant outlay.
     
  4. class8mikado

    class8mikado Well-Known Member

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    aye
     
  5. 8126

    8126 Member

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    If I remember rightly, the combination of restricted primary air and steam supplied beneath the firebed in the GPCS causes the generation of CO and H2, both of which are then burned in the secondary air above the firebed.

    However, the effect of the steam is net negative on useful energy released, it just helps to keep the firebed temperature down and thus inhibit clinkering. If you had coal which absolutely would not clinker, even when fired as a massive thick bed, it's not strictly necessary for the other design intent of the system, which is to increase the useful steaming rate of the boiler by reducing the carry-over of unburnt fuel in the fierce primary airflow of a conventional firebox when working hard. In that sense, it would work just as well and release more energy if it was only producing CO.
     
  6. JJG Koopmans

    JJG Koopmans Member

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    Some 20 years ago a had a very interesting discussion with a South-African who had been involved in the process of making oil from coal during the apartheid days of the oil import ban in S.A. He told me that it was far more complicated to rip oxygen and hydrogen apart from their water composition than people thought. In his opinion this claim was just wishful thinking! Apart from his educated comment I would like to see proof! As, btw, of all other claims of GPS and Lempor!
    Kind regards
    Jos Koopmans
     
  7. Jamessquared

    Jamessquared Resident of Nat Pres

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    The net result of using a gas producer system is the same as just burning carbon in oxygen normally:

    H2O + C = CO + H2
    CO + H2 + O2 = CO2 + H20

    ==========
    (Net): H2O + C + O2 = CO2 + H2O - the water put in on the input side all emerges on the output side, except that it has been evaporated and heated up in the process..

    So in energy terms, the energy release in the firebox from burning stoichiometric ratio of carbon and oxygen is the same whether you do it directly, or in two stages using a gas producer system. The first reaction is endothermic, i.e. it absorbs energy, which is why it cools the firebed. The second reaction is then exothermic, and the sum of the two reactions releases the same amount of energy as just burning carbon normally - you don't get something for nothing)

    However ... the primary energy losses in a locomotive boiler is throwing hot gases away up the chimney. So using a gas producer system makes that worse, since effectively, for every mol of carbon that is burnt, you throw away a mol of hot steam.

    So overall, as you say, a gas producer system will require more coal to do the same amount of useful work. It is potentially beneficial with very clinkery coals, but there is no benefit if the coal isn't prone to clinkering, but it has a big cost. Not to mention the fact - who is going to redesign and recertify existing steam loco boilers with the necessary holes in them to admit the secondary air?

    Looking at a few films of current steam traction, smoke seems to be quite widespread: for example, the film of 35018 on its test run showed a lot of smoke even when working hard - when presumably it was being fired exactly as the fireman wished, with no consideration for what linesiders might wish to see. My guess is that we are simply at a point where there aren't too many different sources of locomotive coal available, and at the moment what is available is very smoky. On the positive side, what we have had recently on the Bluebell seems to be largely free from clinkering, which is a considerable benefit for things like firebar life - quite apart from meaning that there would be no benefit to having a gas producer system, even if someone could design and implement one before the source of coal changes to something else again!

    Tom
     
    Last edited: Jul 11, 2017
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  8. 30854

    30854 Active Member

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    Given that steam used is recovered from exhaust (the excessive draught caused by which is directly responsible for pertubation of the firebed), the "net negative" contribution of the process seems questionable within this application.

    Regarding non-clinkering coal, does such a thing exist? I've some small experience with vitrification in a different industrial context, hence the effects of clinker when needing to maintain a decent fire is a subject I can understand reasonably well. Obviously, as with any non-refined fuel (or any other substance, for that matter), the quality of coals varies greatly, so application of laboratory standards of measurement is always going to be less useful than might at first be thought.

    I seem to remember methane mentioned as another product of GP tech, but noting the comment from Jos regarding theory vs hard experience, I'd also like to see far more hard evidence. With the bulk of steam loco technology dating back to the EMMM school of investigations, the same applies to much of the field. Well, as there IS now a GP fitted loco, in the form of the L&B's new LYN, scope for useful measurements now exists. Methinks interesting times lie ahead.

    One area of fuel supply interesting me is the development of torrified biomass pellets. Although in comparatively early days, as far as railway applications go, the notion of bespoke and consistent carbon nuetral fuel looks attractive. Quite how the comparative costings will pan out if and when commercial production begins, it's too early to say. Experiments being undertaken across the pond suggest this may be a useful way forward if even heritage steam operation is to survive in a post-fossil fuel world. I include a URL to the Coalition for Sustainable Rail for any who've not come across this fascinating website.
    http://csrail.org/
     
  9. The Saggin' Dragon

    The Saggin' Dragon Nat Pres stalwart Staff Member Moderator Friend

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    Fires caused by such an occurrence in ships exhaust gas boilers were quite commonplace at one time, very difficult to extinguish apparently (I never experienced one myself).
     
  10. 45045

    45045 New Member

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    The water shift reaction ( the first one) is not very efficient. When using this in a Primary steam reformer to produce hydrogen or ammonia commercially you need a catalyst (nickel I think but it has been almost 25 years since I was involved in this) to get a reasonable conversion. Controlling the pressure and temperature was also important to shift the equilibrium of the desired reactions to the desired products. So in a steam loco firebox, the amount of hydrogen produced will be limited.
     
  11. class8mikado

    class8mikado Well-Known Member

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    From my understanding of the GPCS, the steam isn't there to be part of the combustion process, its there to moderate it. The point of it is to reduce the amount of unburnt fuel loss in conjunction with a strong draft by a more complete combustion ie fuel has already given up its juice and broken down before it gets whisked off.
    Could never quite understand how its sustainable if you are chucking fresh coal on top but I think one variation did use an underfeed stoker.
    The bigger picture with increasingly inconsistent 'heritage ' fuel and new manufactured 'designer' fuels becoming available - will fireboxes have to change to use these, or can the fuels be designed/ manufactured to suit our fireboxes ? If they can be manufactured to a high degree of consistency is the steam traction movement as a whole prepared to agree on a standard to make bulk production viable - could solve a few problems. We will still have to chuck in a bit of the black stuff either at production stage or on the footplate - otherwise it just wont smell right.
     
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  12. 30854

    30854 Active Member

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    To paraphrase Homer Simpson "In the heritage steam sector, we obey the laws of thermodynamics"! The issue of complete combustion (with associated lack of clagging and/or firethrowing) being the desired result. If front end mods alone can acheive this, there would obviously need to be a compelling case for further expenditure, or complication. Perhaps the performance of LYN may go some way to clarifying the value (or otherwise) of GP systems.

    On the "designer" fuels front, experiments (detailed on csrail.org website) stateside have been on a Romney sized 15" gauge beastie, operating on a fairly short line. It seems that an optimal size and shape for the pellets has yet to be established. Even once this happens, how valid results will prove when upscaling to standard gauge boilers looks like anybody's guess!

    I wonder if the RH&DR (long run, near identical locos) might be a suitable location for initial testing in this country? Some good publicity to be had there, I suspect. That'd have to work out cheaper than jumping straight into comparative tests with biofuel vs coal on Black 5s, Halls or WC/BoBs. As Class8Mikado mentions, just which, if any, of existing firebox geometries best suits biofuel pellets will be interesting to find out.

    The olfactory issue occured to me too, not knowing what burning biofuel pellets smell like in the first place .... perhaps "essence of coal" somewhere in the manufacturing process, à la domestic scented oil evaporator?
     
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  13. Allegheny

    Allegheny New Member

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    One of the problems is that the reaction between steam and hot coal is endothermic (absorbs heat) so if you add too much steam, you can overcool the fire and eventually put it out, or a least reduce the temperature to a point that is detrimental to combustion. It would be good to have a system that automatically regulates the flow of steam, but I don't know how you would do it.
     
  14. Jimc

    Jimc Well-Known Member

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    I imagine it will depend on the feed stock, and possibly vary quite a bit.
     
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  15. 30854

    30854 Active Member

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    OK... you got me.... should've been "biomass". Not editing, as last time I tried when there was a quote, it totally cocked up the whole post!

    On biofuel.... beaver pellets (need more beaver ... obviously) probably beat cowflop, and just about anything would be preferable to fox droppings!!
     
  16. Allegheny

    Allegheny New Member

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  17. JJG Koopmans

    JJG Koopmans Member

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    Mm, this one is split off because it treated firing non-steamcoal. Bulleids could be combined.
    However, the Jubilee is a totally different issue, please do not combine.
    Kind regards
    Jos Koopmans
     
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  18. 242A1

    242A1 Active Member

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    You can design a locomotive so that the exhaust system fitted is unable to drive combustion beyond the point where carryover makes the machine unacceptably uneconomical. On the other hand the exhaust system can be designed so that the point can be reached where the level of carryover is at such a level that more fuel is being expelled in an uncombusted state than is being satisfactorarily used. So you have an exhaust limit and a grate limit.
    Primary air, being drawn through the grate, takes fuel off the firebed. Secondary air being supplied above the grate and firebed does not do this. For many years changes in free area through the grate were used to address combustion issues. What was not appreciated were the problems that primarily air could cause particularly with the thin fires found on wide grates.
    The GPCS uses a pinhole grate, or a Hulson so that the airflow through the fire is less likely to drive carryover. The grate is also designed to ensure an even flow of air though the bed, avoiding channeling, ensuring even combustion. The steam supplied to the bed, though it can be source of noise for the crew, should keep the the temperature of the bed below that of the melting point of the ash being formed and so avoid clinker.
    The fires are deep, not shallow, so grates can need dropping on engines being modified to accept this system and this can create problems.
    When working in a satisfactory manner the gases liberated in the firebox burn in the secondary air which what has been described as a bright, white flame. The flow of secondary air is designed to retain small particles in the firebox and so give them a a greater chance of combustion. This desire to try to minimise uncombusted losses gave rise to the work carried out on cyclonic combustion.
    The vacuum losses through these systems need exhaust systems designed to cater for them.
    So, round we go, you can work on exhausts but these only drive a combustion system which may not be fed with the fuel best suited to it. It is a fact that the fuel used today is more inconsistent than it perhaps ever was and is of lower overall quality. And the operating environments are frequently less than ideal.
    Jos is right in that many locomotives are fitted with a less than optimised exhaust system. Some engines are fitted with modified combustion systems but these are mainly narrow/miniature gauge types. We need to be brave enough and have resources sufficient to allow some serious experiments and testing to be carried out.
     
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  19. 8126

    8126 Member

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    I always enjoy a good theoretical discussion. Thanks for clarifying the chemistry side of it, I was going on half-remembered stuff during my lunch break. My understanding is that the 'ideal' amount of steam for a GPCS is sufficient to get the firebed temperature below the ash fusion temperature for that coal and no more, so balancing the carbon/steam reaction with carbon/primary air to minimise that wastage of hot steam.

    I think it's fair to say that unless a loco is being worked at a very high combustion rate, for which a thick heavy fire with lots of secondary air is necessary to minimise carry over of unburnt coal and corresponding loss of efficiency, the claimed advantages of the GPCS become a lot more marginal. Wardale writes that the reducing region in a thick heavy fire produces different iron oxides, FeO rather than Fe2O3, thus sometimes creating clinkering problems where they would not exist with a thin fire. This may be part of the reason why there have been more experiments in this country on narrow gauge; not only are the modifications cheaper due to scale, but a lot of the narrow gauge railways work their engines very hard compared to standard gauge lines.
     
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  20. 30854

    30854 Active Member

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    The chemical equations are fascinating. When regarded in terms of loco firing, it becomes glaringly obvious that the vast majority of design and operating issues revolve around that content of coals not directly involved in the desired reactions. Those problems noted as arising specifically from iron rich coals are a prime example, but checking data from various sources (mainly US and China these days) highlights other products of combustion now regarded as undesireable pollutants. Sulpher and heavy metals seem to head up the list.

    Modern coal supplies have been noted as extremely variable. Due to changes in procurement since steam was in daily commercial use, the reasonably consisent supplies of yesteryear simply cannot be assured (actually, nothing new as anyone with any knowledge of the coal supply situation in the Irish Republic during and immediately after WWII will tell you). Given this, it's hard to see how any amount of research could produce any one optimal solution.

    As an aside, it's often crossed my mind over the past decade whether the combined consumption heritage sector (plus maybe model engineering hobbyists) is high enough to warrant reopening a mothballed pit known to have produced steam coal of reasonable and consistent quality.

    Sticking with coal, the alternatives would seem to be:
    1) Struggle on as at present, hoping pollutants (or lineside fires) don't rattle the cage of legislators. Realistically, for how long is this state of affairs likely to remain acceptable to operators and government?
    2) Pay substantially more sourcing coal of least dreadful quality, meeting minimum standards agreed across the heritage sector (calorific value, graded size, %age of non-combustibles), with the attendant risk that legislation will tighten up incrementally to the point where use of fossil fuels becomes impossible in financial terms.

    Over the longer term, the best option looks to be to apply research efforts to develop steam locos to make best use of biomass fuels (including the option to make them smell like coal.... if we must!). I'd suggest that not only would this produce those desired results next to impossible with inconsistent coal supplies, but would greatly improve the chances of generations yet unborn seeing steam locos in action.
     
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