Boiler install questions

[farmerden]

I found this little tid-bit when doing some research into a hot-water boiler for my shop.A wet firebox creates a cold fire resulting in incomplete combustion and soot.It's sounds logical.The company involved lined there firebox with fire-brick creating a hotter burn and consequently more heat thru the tubes,cleaner air ,etc. BUT if 80% of the heat heat is extracted in the firebox and only 20% in the tubes? This obviously calls for more research!!! Please enlighten me more! Den

[artemis]

I found this little tid-bit when doing some research into a hot-water boiler for my shop.A wet firebox creates a cold fire resulting in incomplete combustion and soot.It's sounds logical.The company involved lined there firebox with fire-brick creating a hotter burn and consequently more heat thru the tubes,cleaner air ,etc. BUT if 80% of the heat heat is extracted in the firebox and only 20% in the tubes? This obviously calls for more research!!! Please enlighten me more! Den

What were they using for fuel? If it was propane or natural gas, then there is very little radiant flame ("blue" flame has very little radiant heat and that is the correct color for a gas flame) so no real loss. I seriously question the company's statement, although when simply making hot water (under 150deg. F) the whole equation is substantially skewed.

[DetroiTug]

Surface area is needed for heat transfer..

[farmerden]

This was a wood-fired outside-of-the-building boiler.These boiliers are terrible for smoke because they are damped down most of the time.I would assume they only make 150 degrees or so and the demand for a radiant floor probably amounts to 80-90 degrees.Whereas our steam boilers are running flatout and in constant burn mode so I would expect firebox heat to be at optimum burning temp Looking in my firebox after an hour or so of steaming and there is no incomplete combustion happening here!! But all is well we got another topic to gossip about Thanks Den

[dhic001]

Given this I'm slightly surprised that Daniel appears to favour a "dry" firebox for a vertical fire tube boiler rather than a "wet"/waterleg one,
(see paragraph 6. of his posting of 14th October concerning " Input on Boiler Design " in the "Technical-Engines and Boilers " section of this forum .) I think that all of the points he notes there are valid but given the greater exposure to radiant heat of the wet firebox I think he arrives at the wrong answer .

Regards Edward .

In a larger boiler I agree, a wet firebox makes perfect sense. In a small boiler, there are the diadvantages listed. In a small boiler, particularly a hard worked one, you are fighting a lack of grate size and a lack of combustion space and sometimes limited draft, while expecting the same proportions of performance from a larger plant. Some boilers will be better than other, but I have noted great fuel burn and a hotter fire in the middle part of the grate in a wetleg boiler than around the outside sections. In a larger firebox the large amount of burn going on in the middle of the fire helps the more sluggish outer parts.

In my view (and I don't expect everyone to take it as gospel), a small boiler is disadvantaged but a wetleg firebox for the reasons listed in the other thread. Certainly in Kapanui, the large diameter, low height boiler, with lots of small tubes and a large combustion space firebox has resulted in a very powerful free steaming and clean burning plant.

If tubes deliver so little performance advantage, why have them? Why not just a have a large wet leg with a few small tubes to act as flues to get rid of the smoke/allow fire draft. That would mean virtually all the boiler could be run off radiant heat, and it wouldn't be wasting tubeplate area with tubes. Maybe someone could build two identicle boiler shells, one with a few "flue" tubes, one with lots of tubes and see what the difference is in terms of performance. My vote is that the large number of small tubes will make a big difference.

Daniel

[daysaver1]

In regard to location of the blow down, the rational given to me for under water outlet is one can then see what's coming out of the pipe instead of the cloud of steam. Below water level allows one to actually know when you've about got all the crud out and shut off instead of blowing down more than you need to...or not all.

In regard to the electric pump, I use the little guy from Harbor Freight. I take along a 12 volt, 7.2 amp battery (lawn tractor type) that lives on a tiny 1.5 watt solar collector so it's always ready. Most lakes in our area require the boat be 100% dry before putting in the water for Quaga and Zebra Muscle inspection and they include boilers in that order. Sometimes it's tough to get the pick-up filter dry, but if it's not, you get sent home. I use washing machine hoses to transfer with the little pump and have fabricated a little filter made of a 3/4" aluminum tube drilled with 100 #50 holes which I drop over the side and in less than a minute the boiler is "full".

My Semple 40 foot boiler has the sight glass mounted such that at half glass, water level is still 9-10 inches below the top sheet. The boiler hasn't been opened up in almost 30 years so I guess covering the sheet isn't all that important in regard to tube damage.

[fredrosse]

I have some technical data that sheds light on these issues with boiler design, tube surface vs furnace surface, etc. This should really be in "Technical, Engines & Boilers", so I am starting a new topic there.

[stevey_frac]

Did you ever post that topic Fredrosse? I can't see any such topic, And it would be an interesting discussion.

Steve

[fredrosse]

This information is now being discussed in the "sizing safety valve" section of "Technical - Engines & Boilers"