Blackstaffe Woes

[Old Steamer]

<t>I have operated boilers the size of an apartment block without problem but this (expletive deleted) wee kettle is really trying my patience. Thus, my appeal for suggestions of what is happening and, equally important, how to fix it. <br/>
When I purchased this launch, it was semi-derelict. The boiler is a Blackstaffe type with nine coils per side and the casing was rotten with rust (see photo). It was paraffin (kerosene) fired by a single bar burner with some 5 or 6 nipples operating on a pressurised blow-lamp principle. The previous owner is now deceased and so I cannot ask him how it performed but one still alive who had witnessed the boiler in action, advised that these produced a modest but obviously sufficient heat. <br/>
To cut a long story short, liquid fuels are out for where I usually steam and a conversion to coal proved to be a disaster. Unless one was an articulated, treble-jointed, limbo dancer, it proved impossible to sight and maintain the coal bed, let alone get a rake/slice in there. The engine and boiler proximity made it a no-go. <br/>
The alternative was LPG and this was accomplished by fitting two bar burners firing over most of the length of the boiler. Air supply was via the trunk below the boiler formed by the redundant ashpit which was open both ends with 212 x 100mm apertures. So far, so good and following in the path of those who had created similar systems. Icing of the 6kg gas bottles was an initial problem solved by converting the gas locker to a water bath with its temperature boosted by heating coils if needed. <br/>
The problem is that it has proved impossible to reliably generate sufficient steam pressure despite the burners apparently generating more than sufficient heat. Recently, when the boiler had its Annual Survey, modest gas pressure raised the steam pressure to the point where the safety valve was popping at 150Psi, without problem. Launched this week, despite whatever tweaks were applied, the steam pressure would not exceed 60PSI. On all earlier outings, this has also proved to be the case; except frustratingly when, without any change in steam demand, feed or firing, the pressure suddenly climbed to working pressure and beyond, causing me to throttle back on the gas supply. Of course, on the return leg, the boiler just sulked. <br/>
Thinking that changing the boiler casing from a box-like configuration to a steeple, might be restricting heat flow around the coils, I modified the side doors to return the casing to a box shape. No change. On the advice of another with a similar Blackstaffe, I rotated the burners outwards such that they fired towards the coils. No change. I tried increasing the flue gas dwell time in the casing by fitting a restrictor in the funnel. No change. <br/>
At times the boiler appears to be ‘panting’, although air supply is more than adequate; other times under (apparently) similar conditions, no panting occurs. <br/>
I am drawing blank after blank and now starting to think about circulation – or clutching at straws? Are the bar burners firing too close to the downcomers and affecting water circulation? Is there anything more that can be done to improve flue gas passage through the coils? Do I have to placate the Boiler Pixies who live below the ashpit and, if so, how? <br/>
All suggestions of what is happening are welcome.</t>

4_bar Burners.jpeg

[Old Steamer]

<t>For some reason my first post will not load all the photos as intended. This shows bar burners prior to being turned outboard by about 15 degrees.</t>

[barts]

This sort of variable performance can be frustrating to track down.... some random thoughts:

I'd fit a bbq temp gauge to the stack, or use a thermocouple on a digital voltmeter - many inexpensive units have a temperature option.
Excess air is often the cause of low flue gas temperatures.
Variable output can be due to either varying fuel supply or varying air supply, of course. Are your regulators (if used) behaving? Do you monitor pressure to the burners?
If you can figure out a way to observe the fire under way, it can be very informative.
I've had issues with wind over the stack significantly increasing draft and disturbing the fire in the boiler.
Are you feeding both sides of the mud drum with water? Unequal temps can affect steam generation.

Icing of the 6kg gas bottles was an initial problem solved by converting the gas locker to a water bath with its temperature boosted by heating coils if needed.

Do be careful with the heating coils; the water bath temperature should not exceed about 100F or perhaps a bit more. We had a boat lost here due to overheated propane tanks venting (no injuries, but both people ended up going for a swim).

- Bart

[Old Steamer]

Bart,
Thanks for your quick reply and I will see what I can do with respect to uptake temperature. The gas pressure holds steady at whatever the regulator is set at.
I take your point about using the heating coils sparingly. In fact I have yet to use them (so far) as the water temperature has been sufficient to keep freezing at bay.
The air supply to the burners is not regulated although I can shut off one end of the supply trunk. However, surprisingly, this seems to starve the burners.
The engine-driven feed pump discharges into one mud drum, the feed injector into the other.
The burners are putting out a good, steady, length and height of flame but at times demand high gas pressure in order to force the boiler to keep up pressure. At times it doesn't matter how much heat is put in, heat transfer does not appear to be happening.

The frustrating thing is that this is a simple kettle where heat + water = steam - or it should. Nothing complex about it at all until it doesn't work. Oh for a bog standard coal fired VFT!

[dampfspieler]

Good morning,

the difficulty of a watertube boiler for a user is to understand how they work.

There must be constant water circulation, to achieve this the downcomers must be colder than the coiles. For this reason, the following should be checked and implemented:

• the downcomers must not be touched by the flames,
  the downcomers should be shielded from the heat of the fire, either with baffles or fireproof insulation,
  the two lower drums should be connected by a connector of sufficiently large cross-section outside the furnace to reliably allow interchange between them.

I think the burners are too long. They should only be long enough to be 75% of the length of the water coils.

A thick layer of soot is evidently deposited on the outside of the boiler, which prevents good heat transfer there. The soot should not be produced with a gas fire and its presence suggests that the flames are, firstly, too large and, secondly, that the supply of secondary air is insufficient.

Unfortunately, you cannot see what the inside of the boiler looks like, but I recommend boiling it with a 1% washing soda solution to remove deposits inside.

All my boilers i fire with gas and ceramic burners. There are no problems of soot and insufficient steam production.

If the gas bottle freezes, the gas withdrawal is too high or the surface of the gas tank is too small to provide the necessary heat of vaporization for the required amount of gas. For this reason, a larger gas cylinder should be used.

Best
Dietrich

[Old Steamer]

Hello Dietrich,
The soot you are seeing in the photo is that deposited on the coils when the boiler was oil-fired and is seen in the old casing. That casing is now scrap and the coils have remained clean under gas-firing.

I take your point about internal scaling but the boiler has been operated in soft water for most of its life. However, it's a point I'll bear in mind if all else fails.

I would like to increase the size of the gas bottles but within the confines of my launch, it is just not a starter for space and trim considerations. I suspect that some of the frosting is due in part to over-firing in an attempt to raise pressure. If the pressure problem can be solved, then lower gas pressure should result and some, at least, of the frosting problem may well disappear. I have spoken to several owners of gas-fired steamers and, where they have had problems a water drench/bath has been used effectively. (I will not dwell on the one who said he used a blowlamp to warm the bottles, although this appeared to concern onlookers! I hope he was joking....)

I think your point about circulation is very valid and confirms the direction of my thoughts. To paraphrase Sherlock Holmes comment, when all else is discounted whatever is left must be the solution.
The old oil-burner is long gone to the scrap bin and thus cannot be measured but I assume the jets were well clear of the downcomers which have always been uninsulated and without shielding. The distance between the fore and aft downcomers is 588mm, face to face. The gas flame length is 510mm and thus in excess of your ‘75%’ rule by 70mm approx.
Thus, the plan is: -
A. Reduce the burners flame lengths by 35mm at each end.
B. Shield and insulate the downcomers.
C. The bottom drums each have a blow-down cock at the for’d end. Remove the cocks and connect the drums with a header arranged with a single blow-down cock.

I would be interested to hear more about your ceramic burners and the boiler type they are applied to.
Thank you very much for your suggestions and taking the time to write. It is much appreciated.
Barry

[Old Steamer]

Has anybody anything to add to the above. I'm open to all (technical) suggestions.
BM

[dampfspieler]

Hi Bary,

thank you for the answer.

One more question about the burners, is there a type plate or do you have any information about it?
The background to my question is that I called the service for our gas heating system today because of problems with the burners and the fitter checked the gas pressure, which had to be at 30 mbar, among other things.

The same may apply to your burners and an increased gas pressure leads to undesirable flame patterns and poor efficiency.

Best Dietrich

[RNoe]

Old Steamer:
Looking at your Blackstaffe boiler design compared to my original boiler built in the 1960s by Cliff Blackstaffe, I see that your stack is mounted behind the steam dome.
That implies gases moving from the original end-mounted oil burner(?) lengthwise through the circulation tubes, and then up the stack.
The new gas burners installed don't appear to allow that lengthwise circulation.

My boiler actually has the smokestack surrounding the steam dome providing extra heating as the gases exit the main boiler. The original kerosene/diesel fuel burner is at one end, hitting a central metal target plate just above the grate location, and distributing the heat centrally and outward though the heating surfaces.

Below is a picture of the original 1960s Blackstaffe boiler, used to fabricate a new identical replacement unit.
You can see how a central flame target would distribute heat away from the down-comer tubes and around the side circulation coils, and then exhaust up along the steam dome, providing additional heating where the steam is drawn for the engine.

And here is a picture of the new boiler mounted in the original casing, open for inspection and cleaning.
Note the small propane cylinder, used for cold fire-up until the steam oil-atomizer can be used.

Not knowing the original fueling set up for your boiler, I can't offer additional understanding of the heating problems you are experiencing.
I'll keep watching your discussion.
RussN

[Old Steamer]

Hello Dietrich,
At first, I tried a single gas bar-burner intended to emulate the original single kerosene bar-burner. This proved to be a dead loss. I was lucky in that I had the attention of the Sales Manager at Stedmark Burners who was interested in the project and promised to provide a couple of bespoke burners capable of stable high volume throughput. In practice these have proved to give a stable flame across a wide pressure range from a flicker to greater pressure than I would expect to use if the boiler is operating properly. Thus, I can't quote figures but I am confident that they will do the job.

Hello Russ,
I like the idea of a steam dome within the funnel; very ingenious! In service, the funnel on my boiler is at the for'd end. The plans I have indicate this was the original fit and the steam dome was added at a later date when the boiler was modified.
The original installation of an oil burner was not end-mounted but a single bar-burner running lengthwise in the boiler, fitted with 6 jets and operating as a vaporiser supplied by a pressurised fuel tank. I never saw it in action but I'm told it provided satisfactory service with a modest output; a reason why I'm optimistic that with the boiler steaming satisfactorily, gas consumption should be reasonable.

A question for both of you gentlemen - what gas consumption are you incurring for a particular size of engine + boiler? When I asked this of other owners with gas boilers, I received some fairly vague answers. It was like asking the horse power of their engines: a question that often received some very optimistic answers...

Best Regards and thankyou for your information and help.
Barry