At Last, a burner which does the job!

by John

You are probably fed up with my burner trials.  I certainly was.

Fundamentally, I was trying to get enough heat into the Trevithick model dredger engine boiler, and just not managing it.  My boiler is a scaled down version of the original, in copper.  It takes a lot more heat than the 6″ vertical boiler which I made last year and I think that the reasons are…

  1.  The Trevithick design, although revolutionary for 1800 was and is a very simple, primitive, relatively inefficient design by later standards.   No water tubes and only one fire tube (the flue).
  2. The linear dimension is scaled down 1:8.  The surface areas (heat exchange surfaces) are scaled down 1:64.  The volumes, representing power output, are scaled down 1:512.  So the scale is a major factor.
  3. The firebox is 60mm diameter.  I had no success burning coal or wood, although I gave up on that one quickly after one attempt.
  4. Absence of lagging.  Reproductions of Trevithick’s engines have wooden lagging, but there was no indication of lagging on the LSM engine, or in the 1819 drawing.  I do intend to install wooden lagging, in fact I have cut and prepared the strips ready to install.

So my colleague Stuart suggested that I try his Sievert burner…

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This is a Sievert 2954.  Stuart tells me that at full blast it puts out over 40kW!   The ring is steel, machined to fit the firebox, and a close fit to prevent cold air being sucked around the edges.

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Fitted into the firebox.  It coped reasonably well with the back pressure at about 1/2 strength. 

This unit raised steam from 2500cc of cold water in 10 minutes, and got to 20psi in 14 minutes.  The target of 40psi was reached in 18 minutes.

At 40psi the safety valve operated, and despite continuing to pour in the heat, the pressure did not rise above 40psi.  So I am expecting that the boiler inspector will be happy with the safety valve.

I then ran the engine for 45 minutes, turning the boiler feed pump on and off to keep the boiler water level up.  All went well.  I have made a video of the event, but the upload failed last night, so I will try again later.

Next, to contact the boiler inspector for the final (I hope) inspection.