johnsmachines

machines which I have made, am making, or intend to make, and some other stuff. If you find this site interesting, please leave a comment. I read every comment and respond to most. n.b. There is a list of my first 800 posts in my post of 17 June 2021, titled "800 Posts"

Tag: model steam burner

At Last, a burner which does the job!

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.

 

Experiment Failure

Sometimes information derived from a failed experiment is just as useful as a successful experiment.  Several readers predicted that burning coal would not not work in my dredger engine boiler, but I had to be convinced.

So, I removed the gas burner.

I have 3 types of coal.  One is Welsh steaming coal in 25-30mm lumps.  It has an attractive shiny appearance.  The other is coal lumps which were picked up next to a local railway line and are probably from Newcastle NSW.  I also have some brown coal, but it is in the form of briquettes, and I did not attempt to use them.

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Welsh steaming coal top, railway line droppings bottom.  All too big. 

Both black coal types were too big for the ~60x40mm diameter firebox in the dredger engine.  How to make them smaller?

Smash them up with a hammer and pass them through a sieve?  That would leave a lot of unusable tiny fragments as well as bigger bits.  And be very messy.  And require making a sieve.   If my experiment was successful that is what I would do in future.  Did not happen.

Meanwhile, I tried a hammer with a splitter edge.  The Welsh coal had definite layers, and split fairly predictably, with not too much dust or tiny fragments.   The Australian coal crumbled unpredictably into many fragments with a much lower usability fraction.

I started the fire with newspaper, then pine and hardwood kindling.  I should have paid more attention to the wood sizing, because it was problematic getting the wood alight.  Also, I had not set up a blower for the chimney.  I was relying on a really long chimney extension to provide enough draught.

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Chimney extension.  worked well.  Now what is that black circular patch on the ceiling?

Got the fire going with the assistance of a gas torch.  When the fire got going the draught seemed adequate.

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The wood fire at its best

Tried to add coal lumps, but they would not fit the firebox while the wood lengths were in place.  Firebox is just too small.  So I persisted with wood.  Soaked some in mineral turps.

I was not impressed with the appearance of the fire, but surprisingly, eventually, steam was produced, but never enough pressure to run the engine.  And the fire did require constant attention.  The front of the boiler was quite dirty after all of this.  I am glad that I have not yet painted it.

I will give the wood + coal fire another attempt, but size the pieces better (smaller).  The Sievert type burner is looking more likely.

Later in the day…..

…after a further discussion with Stuart I have decided to try the Sievert burner.   Made some steel rings which are a press fit on the burner, and an easy sliding fit inside the firebox.

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This is the new burner inside the firebox.  Not exactly @Trevithick, but I bet that he would have used it if it had been an option.

I still need to make a fitting to hook up a valve and the propane hose.  And try it out maybe tomorrow.  Another experiment.  I hope to not see flames shooting out of the chimney.