During the first half of the 20th century mercury vapor turbines were in use in commercial power stations. The mercury vapor was the working fluid for a high temperature Rankine cycle and the mercury condenser would raise steam for a lower temperature steam cycle. According to the article, increased efficiency of steam plants made the mercury turbine obsolete.

As far as I understand the main limitation on the efficiency of modern thermal power plants is the maximum steam temperature, which is limited by the creep temperature of steel alloys used in the boiler and turbine. But for that the choice of steam vs mercury+steam doesn't seem to matter. So now I am confused about how a mercury vapor cycle would make a thermal power plant more efficient, or if not, why it did so in the past.

So would a mercury vapor combined cycle be more efficient than a steam only cycle if both used modern techniques? If so, why? If not, why was it in the past?

  • $\begingroup$ have you calculated the temperature changes for a mercury vapor cycle? it isn't the max temp, it's the delta. $\endgroup$
    – Tiger Guy
    Commented Jan 16, 2023 at 16:23
  • $\begingroup$ Might be a wee bit of concern over toxicity. I suspect that the mercury vapor gives you a higher temperature working fluid at lower pressures than steam, or folks hadn't figured out turbine design well enough to extract all of the energy from super-high temperature steam down to slightly lower temperature steam. $\endgroup$
    – TimWescott
    Commented Jan 17, 2023 at 16:49
  • $\begingroup$ The temperature change over the combined mercury + steam cycle is the same as over a steam-only cycle. The high temperature limit is set by the creep temperature of the steel, the low temperature by the cooling water. $\endgroup$
    – JanKanis
    Commented Jan 17, 2023 at 20:14
  • $\begingroup$ Toxicity was probably also a factor in why we stopped using mercury turbines, which is why I didn't just ask why we are no longer using them. $\endgroup$
    – JanKanis
    Commented Jan 17, 2023 at 20:15


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