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I am currently designing a prototype. I have asked to use low boiling point liquid to run a steam turbine. So i am thinking of using liquid ammonia.

What are the complications involved when using vapor ammonia in a steam turbine. Is it possible to run a small steam turbine using ammonia vapor?

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Of course it's possible, but the real question is, is there any advantage to justify using anything other than water?

Just run your steam plant off water, and if you want to use low boiling point liquid, just set the boiling point of water to about 40C.

To do this, you need a condenser, cooled to the point where the low pressure turbine stages exhaust into a pretty good vacuum (once air has been purged out of the system) and you'll find that allows you to use the energy in the steam down to about 40C.

Exact numbers relating temperature and pressure were traditionally published as "steam tables".

Using ammonia instead, you certainly wouldn't want to exhaust it to atmosphere, so either approach requires a condenser. Having added that, there is not much to be gained from moving away from water.

There may still be a thermodynamic advantage to ammonia (or diethyl ether) if it has much less latent heat of vaporisation than water; I can't comment on that.

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  • $\begingroup$ Thank you for your answer, Can you suggest me a better way to set the boiling point of water around 35C $\endgroup$ Nov 1 '16 at 15:44
  • $\begingroup$ This is technically correst but misses the point that at low temperatures, water has a low vapor pressure so you work with lower pressures and pressure differences overall. That's why ORC is state of the art in waste heat electrification. $\endgroup$
    – mart
    Jul 2 '18 at 6:20
  • $\begingroup$ @Mart ... where "state of the art" means "mostly in the prototype stage, and has been since the 1950s". Working with lower pressures has no large effect on efficiency, though it does require larger structures. Whether this is more expensive than the complications of a less friendly working fluid is a matter of engineering and economics. $\endgroup$ Jul 4 '18 at 11:47
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An established approach when you want a low boiling point in a steam engine is to use another fluid, just not ammonia - Organic Rankine cycle engines use flueorcarbons, hydrofluorcarbons (HFC) and hydrocarbons. Last time I talked to ORC producers, HFC seemed to be pretty much the norm since those are also used in refridgerators.

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    $\begingroup$ Ammonia is also used in refrigeration systems, partly because of the global-warming effects of HFCs but also because ammonia-based systems are cheaper both to build and to operate. Ammonia's main disadvantages are that it reacts with copper (so no copper pipes, etc!) and gas leaks are poisonous - but aside from catastrophic failures, leaks are easily detected because of the smell when the gas concentration is still much too low to injure humans. $\endgroup$
    – alephzero
    Nov 2 '16 at 17:35
  • $\begingroup$ From en.wikipedia.org/wiki/Hydrofluorocarbon#Hydrofluorocarbons "On 15 October 2016, due to these chemicals' contribution to climate change, negotiators from 197 nations meeting at the summit of the United Nations Environment Programme in Kigali, Rwanda reached a legally-binding accord to phase out hydrofluorocarbons (HFCs)" ... where does ORC go next? $\endgroup$ Jul 4 '18 at 12:19
  • $\begingroup$ Good catch. Last time I talked to ORC manufactueres was before 2016. My first guess is that ORC will use the same fluids as refridgerators will, it appears that R152a won't be phased out (low GWP compared to other HFC). German wikipedia has more and different info than the english one, here. $\endgroup$
    – mart
    Jul 4 '18 at 12:46
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The worst complication of the ammonia vapor is that its lethal dose is around 0.015 $\frac{mg}{kg}$. As comparison, cyan has 0.0015 $\frac{mg}{kg}$. (ref1, ref2)

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From the materials perspective you need to look seriously at NH3, not on Stack Exchange. Of course no copper,brass or bronze and monel should be checked. Steam turbines can be hot , like 1000 F , at this temperature you will nitride carbon steel with ammonia. GE condensing steam turbines had/have a problem with hydrogen stress cracking and/ or corrosion fatigue of hard 13 chrome blades ( GE has denied this). But one should be very careful with any hydrogen compounds around hard ( Rockwell C 23 ) steel . And , unrelated, anhydrous ammonia can stress corrosion crack moderate strength steels at ambient temperatures ( Re: Dr Phelps , USSteel, NACE Corrosion 1969-? ). This is prevented by addition of a few hundred ppm of water, so most engineers are unaware of it today. And ,furthermore, unrelated , is high temperature hydrogen attack ( Re: API 941 ,Nelson curves).This occurs above 500 F in high pressure hydrogen ; However ,corrosion can produce hydrogen with high fugacity ( relates chemical activity to pressure - No , I do not understand it). So hydrogen attack has occurred in steam boilers with essentially no hydrogen pressure.So, using ammonia as a working fluid does introduce potential materials problems. .PS , I love hydrogen it basically provided me a good career.

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