Fire space for solid fuel firing

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SL Ethel
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Fire space for solid fuel firing

Post by SL Ethel » Mon Oct 30, 2017 3:29 pm

Does anyone have any data or experience to share with regard to fire space in a small wood fired boiler?

My larger boiler (18" diameter grate, 5hp) had 16" from grate to tubes, and this seemed to work well, but it would be problematic for the little boiler I'm putting together for a canoe plant.

Current plan is for a 12" diameter grate, with an Offeldt pressure vessel above. Fuel would normally be 1.5" square cedar sticks (4x4 cedar fence post off-cuts). I am thinking about making up a fire box that extends 10" above the grate, with another section of casing above that which would support the pressure vessel. That would make it fairly simple to raise or lower the pressure vessel over the fire to experiment with the fire-space.

Is anyone else firing with wood in tiny boilers? I would love to hear your experiences.

Thanks,
Scott
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Re: Fire space for solid fuel firing

Post by cyberbadger » Mon Oct 30, 2017 8:26 pm

When I came to Jeff Lund at LundMachineWorks to get an ASME code boiler for what would become Nyitra he started by telling me the some details of 3 boilers he had built for my consideration.

The one was a simple horizontal with one main 3-4" diameter tube for a launch (Don't know which one). This was a little small because the owner found that nothing much larger then twigs or kindling would suffice. I kind of shied away from that design because of that. :) Eventually I would like to try Scotch Marine someday though.

When you say 'Fire Space' and what you are describing doing is similar to extending/playing around with your furnace. This is has been done in various ways and is one valid approach to maximizing BTUs for such a boiler. There is a guy that was mentioned to me locally who will make larger furnaces for vertical boilers as well as getting more desirable designs to facilitate ash removal.

My first 16"OD boiler(Not LundMachinWorks) of ill repute had very difficult ash removal which lead to fires that made the grates and ash pan door distort such that welds on bar supporting the ashpain gave from thermal expansion.

I had enough of that and vowed never to be stuck with that condition on any new boilers I bought, so one feature of Nyitra's boiler is, which luckily at this point I don't need, is the ability to separate the base to be completely removed. 4 bolts hold the base to the main pressure vessel part of the boiler.

This is one area we you can have a lot of flexibility because the welds are not holding steam pressure - so anyone decent using any welding technique can do it.

There are also a lot of options and things you can do with soft or hard firebricks and ceramic insulation in this department.

Some inspiration...
Image
http://www.hamadaboiler.com/en/biomass/wood.html

-CB
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Re: Fire space for solid fuel firing

Post by barts » Mon Oct 30, 2017 8:38 pm

SL Ethel wrote:Does anyone have any data or experience to share with regard to fire space in a small wood fired boiler?

My larger boiler (18" diameter grate, 5hp) had 16" from grate to tubes, and this seemed to work well, but it would be problematic for the little boiler I'm putting together for a canoe plant.

Current plan is for a 12" diameter grate, with an Offeldt pressure vessel above. Fuel would normally be 1.5" square cedar sticks (4x4 cedar fence post off-cuts). I am thinking about making up a fire box that extends 10" above the grate, with another section of casing above that which would support the pressure vessel. That would make it fairly simple to raise or lower the pressure vessel over the fire to experiment with the fire-space.

Is anyone else firing with wood in tiny boilers? I would love to hear your experiences.

Thanks,
Scott
For a canoe, you might wish to consider a more horizontal boiler; something along the lines of the Blackstaff design would work pretty well. Given that you want to use wood, I'd see if a all-steel Ofeldt is practical, since boilers w/ copper coils are quite sensitive to water level. Winding the coils from 1/4" pipe should work; certainly the experiment there seems worthwhile and inexpensive enough if tried in the home shop.

- Bart
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Re: Fire space for solid fuel firing

Post by DetroiTug » Mon Oct 30, 2017 8:55 pm

Scott,

12" diameter grate is pretty small, if possible, I would go at least 2" diameter larger grate area than the Ofeldt assembly. Bigger fire is always better. Of course, with the refractory it's going to get quite large for a canoe. On second thought, I'd stay with the 12" and make it detachable, worst case, just have to make another if needed.

Also, I would put a heat deflector on the bottom of the center drum to keep it cooler and up the internal circulation, the center drum is the downcomer. The Ofeldt type burner we use in our cars produces a ring of fire - there is no fire under the center drum.

-Ron
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Re: Fire space for solid fuel firing

Post by SL Ethel » Mon Oct 30, 2017 9:08 pm

Bart,

Thanks for the response. The horizontal Ofeldt certainly appeals from a height perspective - I'd like the boiler not to tower above the gunnel. And in the canoe, there would be no objection to making it very wide (relatively speaking). However, I've always been suspicious about the flow path for the combustion gas in such a boiler. From the pictures, it looks like most of the gas would pass up through the top of the coil stack without actually passing through most of the turns of coil. Is there usually an internal baffle? Or does it turn out not to matter that much? I've read Cliff Blackstraffe's article on these in SMSL (which looks a lot like the picture you posted).

Do you know if anyone is running something like this in a small size with wood fuel?

Cheers,
Scott
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Re: Fire space for solid fuel firing

Post by barts » Mon Oct 30, 2017 9:29 pm

Hi Scott -

The advanced search here is useful: http://steamboatassociation.org.uk/page-1117882
I can find one boat w/ a Blackstaffe boiler that is coal fired. I think a stainless baffle over
some economizer tubing would handle any errant gas flow issues - certainly easy enough to do,

Keeping the weight low is really nice in a narrow boat - they can be exciting enough w/o tall
boilers.

- Bart
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Re: Fire space for solid fuel firing

Post by Lopez Mike » Mon Oct 30, 2017 10:28 pm

This coming from a VFT devotee . . .

I wouldn't put a VFT in a canoe. Too high a C.G. and too heavy.

For what it's worth, my VFT-30 has a 12" diameter firebox with a water leg and I can drive my 3 x 4 single fairly hard. I fire it with 2" x 4" lumber cut offs around 4 to 6 inches long. Anything that I can get in there and still close the door seems to work fine.

I would consider a horizontal fire tube design both for the lower C.G. and the slower response to changes in load and firing. Hard to beat those Blackstaffe WT designs though.

He used to visit us about once a year and my dad and he would stay up half the night jabbering.
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Re: Fire space for solid fuel firing

Post by RGSP » Wed Nov 01, 2017 4:18 pm

Roger Calvert has been running "Senta" for many years on wood, on Lake Windermere, UK: she's a converted Flying Dutchman sailing dinghy, and very light. I'm sure he'd tell all.
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Re: Fire space for solid fuel firing

Post by barts » Wed Nov 01, 2017 4:47 pm

RGSP wrote:Roger Calvert has been running "Senta" for many years on wood, on Lake Windermere, UK: she's a converted Flying Dutchman sailing dinghy, and very light. I'm sure he'd tell all.
A Flying Dutchman is 20' x 5' 11" - not really a canoe; they're plenty stable. Cut that beam down to 3' or 4', and you'll want to lower the CG.

See the steamboat register for canoe type hulls: http://www.steamboatassociation.org.uk/page-1117882

- Bart
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Re: Fire space for solid fuel firing

Post by marinesteam » Wed Nov 01, 2017 5:49 pm

I had the pleasure of spending a day on Senta with Roger and Marguerite. What bart said is correct, Senta is a surprisingly stable platform and her boiler is fairly squat in form. In my observations it does seem like the UK side tends toward short & wide vertical boilers whereas the Americans tend to go tall & skinny.

Salome has a VFT with 18" long tubes (200 of them) and a 5' beam so not out of the question but as previously mentioned narrow beam also means low CG. At some point you just run out of room for both a firebox and tubes of any significant length. I think all of the canoes in the SBA fleet (Sandpiper, Nyra, Laughing Water) have horizontal boilers apart from one with a monotube. An Ofeldt certainly should help in keeping the CG lower than a VFT but I'd agree that going with a Blackstaff would be a wise move.

Idris will have a 5' 2" beam and I'm still waffling on the type of boiler to use. Because I'm trying to keep weight to an absolute minimum a watertube is preferred but also would like to keep the mass of water higher for stability and grate larger for wood firing. Would also like to side fire as I think it would be a bit more convenient for running solo. I'm leaning toward a two drum WT. It's all about compromises so make the best one that you can.

http://www.steamboatassociation.org.uk/page-1117882

Cheers

Ken
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