Bolsover boiler?

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DetroiTug
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Bolsover boiler?

Post by DetroiTug » Fri Sep 29, 2017 6:59 pm

The plan is to reboiler the tug and was leaning toward a large Ofeldt.

Been looking and learning about the Bolsover design just to try something different. A friend of mine has built several of them over the years and said it's about the best boiler he's had.

The way they are configured, there are four manifold branches equidistant about the radius on the lower part of the center drum and four manifolds at the top of the drum. The tubes come out of the manifold every other one an opposite direction - angled up, then the tubes coil around the circumference of the center drum up to the top, by alternating the directions of the coils, they are naturally spaced apart to allow flue gases to flow through.

This sounds like a good configuration for the tube bundle. The other thing that interests me is omitting the need to wind coils on a mandrel. And there would be no large gaps vertically between the coils as with the Ofledt, which the jury is still out on if that is a big issue or not.

Any of you have any experience with a boiler of this type? sorry I don't have any pics.

-Ron
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Re: Bolsover boiler?

Post by fredrosse » Sat Sep 30, 2017 3:58 am

I have considered making a variation of the traditional Bolsover Boiler, which basically has a cylindrical outer casing. Same configuration as what you described, although using 90 degree bends to wrap around the center drum rather than a standard type coil. This would result in a boiler with a square outer casing.

The advantages here would be that a 90 degree bender only would be needed, possibly using the cheap hydraulic bending machines sold for around $100. Any reasonable pipe/tube bender could be used to do the job. This strikes me as far easier than winding a large pipe/tube coils.

The square outer casing would also be simplified, using the semi-rigid refractory board for the furnace/casing liner, then less expensive outer insulation (fiberglass board), then finally wood outer lagging.

The sketch shown is conceptual only, and would be modified according to the available bend radius of the bending machine. Note that the bends are close to 90 degree bends, but are actually less than a full 90 degree bend. The math to figure out the bends and the length of the straight segments is a little complicated for this old brain.
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BolsoverElev.jpg
Conceptual Modified Bolsover Elevation
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Bolsover.jpg
Conceptual Modified Bolsover Plan
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Last edited by fredrosse on Sat Sep 30, 2017 1:11 pm, edited 1 time in total.
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Re: Bolsover boiler?

Post by cyberbadger » Sat Sep 30, 2017 5:25 am

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Re: Bolsover boiler?

Post by Mike Rometer » Sat Sep 30, 2017 8:17 am

fredrosse wrote:I have considered making a variation of the traditional Bolsover Boiler, which basically has a cylindrical outer casing. Same configuration as what you described, although using 90 degree bends to wrap around the center drum rather than a standard type coil. This would result in a boiler with a square outer casing.

The advantages here would be that a 90 degree bender only would be needed, possibly using the cheap hydraulic bending machines sold for around $100. Any reasonable pipe/tube bender could be used to do the job. This strikes me as far easier than winding a large pipe/tube coils.

The square outer casing would also be simplified, using the semi-rigid refractory board for the furnace/casing liner, then less expensive outer insulation (fiberglass board), then finally wood outer lagging.

The sketch shown is conceptual only, and would be modified according to the available bend radius of the bending machine. Note that the bends are close to 90 degree bends, but are actually less than a full 90 degree bend. The math to figure out the bends and the length of the straight segments is a little complicated for this old brain.
Certainly could be easier (in some cases) to make, but the large unfilled spaces in the 'corners' of the central stack could waste a lot of heat. Could they not by filled with some Lifu tubes?
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Re: Bolsover boiler?

Post by fredrosse » Sat Sep 30, 2017 1:04 pm

".....but the large unfilled spaces in the 'corners' of the central stack could waste a lot of heat. Could they not by filled with some Lifu tubes?"

Yes, that could be an option, although I had considered only some simple baffles within the boiler casing to stop the flow in the "short circuit" paths near the central drum and corners of the casing. The sketches I posted are conceptual only, and one could get around the disadvantage you mention by using a somewhat larger bend radius on the tubes, such that the unfilled spaces are minimized. Another sketch.

In developing a detailed design there are many more considerations, for example: Inner coils vs outer coils, maintaining sufficient slope, perhaps twice around on the inner coils vs the outer coils. Sizing the various components for adequate circulation, staggered left hand and right hand coils vs. all coils right hand (or left hand), adding slope to the four radial headers, arranging the burners to avoid heating the place where mud would accumulate, etc, etc... A virtual field day of design details to consider if one is to make an optimized design.
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Larger radius bends on Square Casing Bolsover
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Re: Bolsover boiler?

Post by Mike Rometer » Sat Sep 30, 2017 7:01 pm

fredrosse wrote:".....but the large unfilled spaces in the 'corners' of the central stack could waste a lot of heat. Could they not by filled with some Lifu tubes?"

Yes, that could be an option, although I had considered only some simple baffles within the boiler casing to stop the flow in the "short circuit" paths near the central drum and corners of the casing. The sketches I posted are conceptual only, and one could get around the disadvantage you mention by using a somewhat larger bend radius on the tubes, such that the unfilled spaces are minimized. Another sketch.

In developing a detailed design there are many more considerations, for example: Inner coils vs outer coils, maintaining sufficient slope, perhaps twice around on the inner coils vs the outer coils. Sizing the various components for adequate circulation, staggered left hand and right hand coils vs. all coils right hand (or left hand), adding slope to the four radial headers, arranging the burners to avoid heating the place where mud would accumulate, etc, etc... A virtual field day of design details to consider if one is to make an optimized design.

If the radii increased the further out from the central drum then the spaces would be further reduced, but in the end you come back to the original coil which you were trying to avoid.

Definitely an interesting concept.
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Re: Bolsover boiler?

Post by DetroiTug » Sat Sep 30, 2017 7:23 pm

If I go this route, I'm going to use 1/4" A53 pipe for the tubes, all else will be schedule 80 A180, should be no trouble to form up large radii with a ring roller. I have the heavy duty horrible freight pipe roller unit, duck soup for that thing. The way the multi-tube circuits criss-cross one another circling to the top (imagine looking at it from the side, it will be a bunch of X's, sort of like a woven wicker basket) all flue gas must come in close proximity to a heated surface to pass-thru, snaking back and forth, no straight shots for it. The more I think about it, the more I like it.

The only draw back I see is wood-firing it, it will be difficult to clean the bundle of tubes. Might incorporate an easily removed insulated jacket in the area of the tubes. With hardfiring/ exhuasting up the stack, it may not require much cleaning. The VFT on the tug now, the flues stay very clean.

My only manufacturing concern is welding it up - welding the tubes to the manifolds, might be sort of tricky, then again it may not be that bad. My buddy said he brazes his together. I like using the stick welder if I can.

Anywho, this will probably be a next winter project.

-Ron
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Re: Bolsover boiler?

Post by DetroiTug » Sat Sep 30, 2017 11:41 pm

Talked to my buddy about this some more this afternoon, he said he uses 1/2" OD steel hydraulic tubing which is good to around 5000 psi and easily brazed. He also said that each tube makes about 3 wraps around on it's way to the top. He said he has 6 tubes per manifold.

Another issue I have, I don't like wasting material, the Ofeldt coils, one 21' stick of pipe makes two coils exactly with very little waste. With this tube nest, I see a lot of tubes of varying length and will wind up with a lot of odd sized pieces left over. I will draw it up in a 3D cad program and plan it out to minimize waste beforehand.

I also asked him how does all this tubing not wind up looking like an old fishing reel with a backlash. He said lay in the inner most 4 tubes first, then the next 4 go the opposite direction over those and so on all the way to the outside.

-Ron
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Re: Bolsover boiler?

Post by DetroiTug » Sun Oct 01, 2017 1:22 am

Drew up a concept in a modeler for a better illustration. I'm not so sure about this three wraps... Looks like the water would have hard time finding it's way to the top :D

It's drawn sorta loose, the coils could have been closer to one another. They are on 1" centers, could be dropped down to like .6"

That is a 8" Schedule 80 center drum, 1-1/4 water manifold and 1-1/2 steam manifold, 24" tall over all, 23" diameter overall, 20" spacing between manifolds on center, 1/4" schedule 40 tubing.

Looks like it would make lots of steam.

That top would be good to lay an economizer. The manifolds could be used for mounting too.

-Ron
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Re: Bolsover boiler?

Post by fredrosse » Sun Oct 01, 2017 5:03 am

Watertube boilers need to have good circulation for long life,and there are some thumb-rules with regard to this condition. For boilers operating at 100 - 150 PSIG, a reasonable criteria is as follows:

Tube slope, 15 degrees upward slope, 100:1 maximum tube length/inside diameter (L/d). This criteria allows adequate circulation, and avoids the possibility of reverse flow in the tubes.

This criteria is conservative, I am sure that a lower tube slope (less than 15 degrees), and longer tube length (greater than 100:1) would still generate steam, but the potential for overheating tubes, especially when the heat flux is high, will increase as these criteria are violated. When too much steam is generated in a tube section, and the flow friction is too high to allow positive circulation, reverse flow in a tube circuit can occur. This tends to create a large steam void (very little water) within a tube section for some period of time, an invitation to overheating the metal. Water will eventually re-enter the tube, due to the positive head pressure with the water level in the drum forcing flow into the tube.

What is the slope of tubes, and L/d ratio in the Oldfeldt type boiler you have made? It is my understanding that you have had satisfactory operation with your Oldfeldt, so it may serve well as reasonable criteria in the design of your Bolsover boiler. Note that lower operating pressure will result in larger steam volumes (per BTU input), so if your steamboat boiler operates at lower pressure than your automobile Oldfeldt, it would have a higher tendency for reverse flow in the tubes.
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