Firing with Coal and Ash Pan question

[fredrosse]

With turbulators in a wood or coal fired boiler, some provision to remove (or rotate) them is advised, as a cleaning measure. My VFT is Propane fired, so no cleaning of the tubes is required, and when I added turbulators I cut my Propane consumption in half. There is a good discussion about turbulators in a previous thread on this forum, topic is "Stainless in the fire". You can find this by searching "stainless" in thread titles. If you just search "stainless" you will get way too many threads listed.

[Lopez Mike]

My hood comes off with four bolts so cleaning isn't a big issue. And any flow restriction might well be offset by a little judicious blower action.

I hope to have a stack thermometer installed before I add any turbulators or the blower so that I can collect a bit of data.

What diameter/wiregauge and heat treat are those ones in the picture made of? Just TIG wire?

I'm surprised that adding them helps that much even though I have seen them in several applications. I had always subscribed to the theory that the gas/water interfaces that could 'see' the flame did the majority of the work. Thus the good work done by the water legs in many or maybe most VFT boilers.

It will be difficult to quantify wood consumption as I spend most of my steaming time changing speed and direction. Gunkholing is the word I use. "Messing about in boats".

Mike

[barts]

I would guess that these function by inducing more turbulence in the tubes; this will disturb the boundary layer that forms against the tube wall, much as the pumping action in a Lamont boiler increases heat transfer on the water side. There's a interesting tension here between soot deposition and increased turbulence.

- Bart

[87gn@tahoe]

Using wire like that is pretty clever Fred. My father just used 16 or 18ga sheetmetal cut in to strips wide enough to fit closely with a 1/8" hole drilled at the top. Several can then be strung onto a steel rod in rows.

With oil firing soot becomes a hinderance, so a steam lance is used at least once during a long weekend of steaming. Then a final brush and vacuum at the end of the season. Messy job.

A friend of ours made his out of stainless for his VFT 40 and burned hardwoods like walnut and oak in 4" chunks. VERY little soot was produced, and only a light brushing at the end of the season was required. I think the small chunks allowed shorter flame lengths, more even distribution on the grate, and a cleaner burn.

[fredrosse]

The wound spring type turbulators are made from, 0.120 stainless wire, with a 1 inch OD (Outside Diameter) for the coils. The firetube ID (Inside Diameter) is 1.06 inches, so they have a very loose fit. At least 1/16 inch gap is good, it I were to make them again I would have the coil OD be 7/8 inch, to provide better break-up of the hot gasses.

For my VFT boiler I had no turbulator coils in the upper region, to avoid possibly overheating the tube upper regions which are not submerged in water.

I am told that “Brock” type turbulators are even better, although at the price of additional flue gas flow friction. These are probably expensive, but get a quote from these guys: http://www.fuelefficiencyllc.com

As far as heat absorption in a boiler goes, a VFT with a wet furnace absorbs a large fraction of the heat in the furnace walls, however my VFT is a Stanley type, with no water cooled furnace walls, so most of the heat must come thru the firetubes.

Another factor is fuel type, coal, wood, and oil fires release very high amounts of radiant heat, which is absorbed by surfaces that can “see” the fire. Gas firing (Propane or Natural Gas) however produces very little radiant heat transfer, so most of the boiler heat absorption is by way of hot gasses flowing close to the boiler tube surfaces, and this is where the turbulators are most effective. In addition, the lower parts of my turbulators get red hot at full fire, and then the stainless turbulator becomes a radiant heat emitter, providing extra heat transfer into the tubes.

[Lopez Mike]

Yeow! Those Brock turbulators are probably too complicated for me to experiment with. I think I'll try either the coiled ones like yours or a twisted blade as in my RV fridge.

I have heard speculations that in a VFT boiler, the part of the tubes above the water level might provide some drying effects. Also, when I hear about the heat problems in boilers I try to decide whether there is really a problem.

Yes, the upper parts of a VFT tube are under compressive stress when there is pressure in the boiler. I would avoid letting them get even to exhaust gas temperatures. But when I hear worries about blowing down such a boiler all the way when there is still some fire and/or worries about building a fire to dry out a boiler that is at atmospheric pressure, I am reminded that my boiler, at least, was welded at very high temperatures. If my whole boiler was raised to paint blistering temperatures it would probably only result in some relief of stresses. Of course my wood lagging would have long since charred!

Open to ideas as to why I might be 'all wet', so to speak. Wouldn't be the first time.

Mike

[Oilking]

In Steamboats and modern steam launches, April-May 1963 page 26, there is a short review of what Fred Semple called a tube retarder. This amounted to a strip of 1/8"x1"x24" steel strip twisted two full turns in that lenght. Semple stated that the redtatders would almost double the output of a FT-40 with no additional fuel consumption. The writer stated that preliminary tests showed at least a 30% increase in output. More tests were to be reported on after a summer of steaming, but alas, NOV/DEC 1963 was the last issue, and the furher results were not published.

The twisted "retarder" could be easily made in a lathe leaving a straight end above the water level if desired.

Does anyone have data on stack temp with or without the turbulators? I assume it would be lower if more energy is being transfered to the water for the same amount of fuel.

David

[Lopez Mike]

I had forgotten that article. And they look just like the one in my propane RV fridge.

I think I will install a stack temperature gauge and do a bit of steaming before I put in the turbulators. I suppose I could weigh the wood to measure consumption.

I have an array of efficiency affecting modifications planned for this Spring. Exhaust feedwater heater. Economizer. I'll have to see if I can phase them in to provide some data.

Mike

[JonRiley56]

Houston, we have a problem...............Check out the spacing ono the bars on my grate. It is worse than I thohght. They are about 3" part at the top of the bar, and ~2 at the closest point. I will get some stainless steel mesh to put in on top of them.

This could be part of my problem in keeping a consistent fire, my coals/embers were all dropping in to the ash pan.

jon

[barts]

Houston, we have a problem...............Check out the spacing ono the bars on my grate. It is worse than I thohght. They are about 3" part at the top of the bar, and ~2 at the closest point. I will get some stainless steel mesh to put in on top of them.

This could be part of my problem in keeping a consistent fire, my coals/embers were all dropping in to the ash pan.

jon

If you can change the grate to have angle iron that has the narrowest space at the top and make it 3/8" to 1/2" or so wide, you'll have a much easier time:

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- Bart