Blackstaffe Woes

[RNoe]

Barry:
My boiler burns steam atomized diesel oil, because kerosene is obscenely expensive by comparison.
I only use propane gas during cold fire-up as mentioned above.

My engine/boiler power plant is "mathematically rated" at about 2 h.p., and moves my 17ft long hull at 5 knots.
Early calculations indicate the oil burn rate to be near 1 US gallon per hour at max cruise. With the 8 gallon fuel tank in the bow, I should get a day's cruising.

I am presently installing a new 1890's design steam launch prop and will post comparison performance data later, after testing again.
You can read more about my launch Cluaran, in the Members Websites and Boats section here:
viewtopic.php?f=4&t=2211

RussN

[Kelly Anderson]

I believe that a lot of your problem can be traced to the coils being too "open", i.e., there is too easy of a path from the source of the fire to past the coils, so a lot of the heat is passing them by without transferring. I had the same issue with my solid fueled Blackstaffe boiler. Initially, the bottom 2/3 of the coils didn't even have any soot on them.

I installed baffles from sheet steel across the top of the coils and hanging down between them, so the heat had to pass within close proximity to them on its way to the stack.

A temperature gauge on the stack is a worthwhile investment. Mine dropped by hundreds of degrees by adding the baffles, so all that heat was then going into the water.

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Also, I bend my economizer tube in a squared off coil around the top and outside of the coils to scavenge as much remaining heat as possible from the boiler, downstream of its coils.

[Old Steamer]

Hello Kelly,
The old casing had a bad case of tin worm and needed complete replacement. When I disassembled it I took my usual precaution of photographing each stage and your post sent me back to that record. I checked and there was no sign of a baffle across the top of the coils BUT then I saw a single photo I had missed and, sure enough, there WAS a baffle and I had not incorporated it into the new casing! That explains a lot and I am very grateful to you for pointing it out. It's an easy enough mod to make and it is now on the job list for the winter along with the downcomer insulation.
One query in respect of the perpendicular strips hanging from the horizontal baffle: its difficult to make out but is there a twist in those to promote a swirl?
Thanks again for pointing out my Senior Moment. The next steaming season should be far less frustrating.
Best Regards,
Barry

[Kelly Anderson]

One query in respect of the perpendicular strips hanging from the horizontal baffle: its difficult to make out but is there a twist in those to promote a swirl?

No twist, they are just straight when hanging down. At their top ends, they have a small tab pointing down that fits into holes in the top, horizontal strip. See the far end of that strip in my second photo for the hole. The hanging strip wasn't fitted there yet.

[fredrosse]

I run a one ton sidewheel steamer, propane fired with a simple VFT boiler. Typically running at 1 to 2 real horsepower, feeding propane at the standard USA pressure of about 11 inches water column gas pressure.

I use standard 20 pound USA propane cylinders (9 kg total propane fill), and they do get iced up in 1 to 2 hours of cruising. Usually I have spare full cylinders onboard, and changeout in a few minutes is easy.

Propane gas has a significant heat transfer disadvantage compared to oil firing. While an oil fire provides plenty of radiant heat, propane radiant heat is abysmal. The simple VFT has very low furnace heat transfer area, and this, combined with the low radiant properties of propane causes low output. The output on my VFT was increased almost 100% by placing stainless steel wound coils in each fire tube. Tube ID 1.06 inches, 18 inches long, stainless coils 1 inch OD, 1/8 inch wire diameter, one turn every inch of length. The stainless coils get red hot, and then transfer real radiant heat to the inside of the firetubes. The coils also restrict excess air flow, which in my boiler is very high without significant restriction added.

The VFT enjoys almost uniform draft across all fire-tubes, so about equal hot gas flow in every tube. The Blackstaffe does not have this advantage, and is prone to flue gas “short circuit”, bypassing the tube bundle where there is an easier flow path to the stack.

I believe your boiler type has performance problems with propane because the bulk of heat transfer needs to be by convection, where the hot gasses flow through and mix intimately in the tube coil area. With oil firing a large fraction of the heat transfer is via radiant process, you lose this with propane. This reasoning is in complete agreement with Kelly’s assessment, and baffles forcing the hot flue gas to flow into the lower vicinity of the steam generating tube coils, then upward while still within the tube coil areas will help significantly. If there is significant flue gas flow areas that can bypass the steam generating coils, they should be restricted with stainless steel sheet material.

As far as insulating the downcomers, a single layer of sheet stainless steel wrapped around each downcomer tube will be adequate. Use all stainless automotive hose clamps to secure them in place. Many hose clamps use low quality worm drive screws, be sure to get the “all stainless” type. Some thin high temperature insulation between the downcomer tube and its stainless jacket is not necessary.

[Old Steamer]

OK Gents, I am with you in respect of the baffles although I'm not sure how Kelly's perpendiculars function but then maybe I am just being dim. If I replace the missing baffles over the tubes exits to increase the flue gas dwell time in the casing and consider if I can fit some other form of baffling where possible, then I reckon that is about the limit. (Plus ensuring the downcomers operate as such.) A rough sketch of the result is attached.

Out of interest, I have also attached a shot of Woodbine's boiler taken some 20 years ago although I understand she is still operating in France. A smaller Blackstaffe than mine but a very similar layout.
Regards,
Barry

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[Old Steamer]

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Ignore the last line of that posting. I'm still struggling to post photos.
This is Woodbine's boiler.

[dampfspieler]

Hi Barry,

thank you for the picture. The flames are really close to the watertubes.

I have refitted some years ago a little gas burner for a KRICK steam engine with a "cover plate" to improve the Heat transfer to the boiler and to protect the flame from blowing out.
The cover plate was made from 3 mm copper sheet. Its temperature was about 750 °C.

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The video of the test - https://youtu.be/ee_S-Aj-BGo?si=hXyolv2cjjS_6-eU


The owner of the little ship was very happy. It might be a useful addition to your gas burners.

Best Dietrich

[RNoe]

Old Steamer said: "I'm not sure how Kelly's perpendiculars function"

I believe the vertical extensions from the top baffles act as additional barriers preventing the heat from quickly escaping the tube area.
They force the heat around and through the tube bundles, providing opportunity for additional heat transfer to the water tubes.
My interpretation.

And I agree with Dietrich that your 2 burners might be too far outwards and should be closer together in the middle.
Note: I don't have a technical analysis to back up my impression. I could be wrong...
RussN

[Old Steamer]

Gentlemen,
Don't read too much into my sketch which is not to scale; the scope for moving the burners further inboard is quite limited. The advice I had from the owner of Woodbine was to rotate the bar burners such that they were directed at the coils without flame impingement. I followed his advice and there is no flame impingement in my boiler.
I will try Kelly's perpendicular baffles but, where possible, give them a twist to create a swirl and slow down the flue gases.
I have toyed with the idea of some form of baffling on the fireside of the coils but Woodbine didn't need it (see photo) and neither did Volcania which had a similar size of Blackstaffe. I think it would be a lot of trouble for negligible gain.
However, all suggestions are welcome.
Regards,
Barry