Assuming that some lucky (and very wealthy) alchemist was on the right track, what is the earliest time that the hydrothermal carbonization process can be both discovered and implemented on a large scale.


  • For the sake of the question, lets assume our alchemist lives near some particularly spicy hot springs that they can use for their experiments. Especially if there is diluted sulphuric acid in it.

  • While a small scale set up is within question, I would preferably like a answer where it could be scaled up for brown coal production via human waste. That is not the only use but one that I think anyone from the past would agree to be pretty useful.

  • Assume any metal in sufficient quantity is available.

  • 1
    $\begingroup$ Just for clarification, it takes place at approx. 1 Megapascal, 180 Celsius. $\endgroup$ Mar 24 at 8:13
  • 2
    $\begingroup$ @Escapeddentalpatient.: Alchemists and 10 atmosphere pressure vessels should not mix. $\endgroup$
    – AlexP
    Mar 24 at 8:56
  • $\begingroup$ How is @Escapeddentalpatient.clarifying Seraphim's question? $\endgroup$
    – jdunlop
    Mar 24 at 11:01

1 Answer 1


Without pressure vessel you need the pressure at 100m depth. You need natural hot spring where such depth can be accessed by lowering the pipes and reactor. That kind of spring with deep shaft is scarce resource.

Then, the technology itself, perhaps it could be done with cast iron pipes but I suspect not, the environment is too corrosive.

Even if such problems could be overcome, doubt it will be scalable and cheap.


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