[Stoves] Use of preheated air for forging with wood.

[Carefreeland at aol.com]

In a message dated 8/5/2011 11:31:32 A.M. Eastern Daylight Time,  
crispinpigott at gmail.com writes:
 
DD: Dan Dimiduk comments

Dear DD 
> As  hot secondary combustion takes place, the stove pipe expands from 6" 
to 8"  diameter five feet up. This expansion causes additional suction. By 
allowing  additional room at this key point, the expanding gasses do not have 
to create  back pressure on the draft. 
That  seems really unlikely, unless there are flames burning in the chimney 
 at that point. If it slows the gas speed and allows additional heat to 
come  off the larger diameter tube into the greenhouse, it is actually reducing 
the  total draft.
DD Yes, when the after burner creates that much draft,  the final stages of 
burn are happening in leaps as the gasses pass through and  above the 
reversed reducer coupler. It is common to see large flames out the top  of the 16 
foot chimney if I am doing a chimney cleaning cycle. To do this I add  pine 
boards or polyethylene, both of which produce excess flammable gasses  
overwhelming the secondary air.  I don't do this for a long time because  the 
black sheet iron pipe upper chimney starts to glow. Kinda scarry in a wooden  
framed structure. I do it for a half hour or longer to warm up the stove on  
a cold night with the first charge of kindling.
     The front cooler part of  the stove is " up to temperature" when the 
stove thermometer exceeds  400F. I keep ruining the magnets putting the 
thermometers on the back of  my stove and scorching the painted numbers from 
heat. That is why I measure  the coldest part of the stove. Sometimes even the 
front get's to the hottest  range of the thermometer.
    During a prolonged high level  burn such as when I stay with it all 
night during -10F degree weather or colder.  I usually keep the flame height to 
about the top of the afterburner. No  additional heat makes it to the 
greenhouse by increasing at this point. I  have checked flame level with a mirror 
looking down the pipe from the roof. The  back part of the stove is a dull 
to cherry red on the outside. It takes a lot of  fuel to keep up with it at 
this level. If I don't have fuel cut, I often need  the chain saw to keep up 
because the hand saw gets too tiring. 
    I can burn an eighth cord easily  in 3- 6 hrs. but I have never kept a 
real accurate track of it.  Probably can burn 2 cu.ft. of loose broken 
branches stuffed in 15 min.  to 1/2 hr. That is about the capacity of the stove 
box. Of course there is  much charcoal left which should be deducted to get 
an accurate BTU count. If I  can get the greenhouse set up on my new lot 
someday, I intend to be able to  measure everything more accurately.
     I have had a large unique  burner designed and key parts accumulated 
for a number of years. I look forward  to being able to develop this 
prototype and work the kinks out of it. This  larger burner would need tested before 
being used regularly for heat as the EPA  regulates this size. My goal 
would be to produce 200,000 to - 400,000 BTU for  sustained periods such as 
overnight or longer with 1,000,000 BTU peaking for  greenhouse warm up. 
    Right now is a tense time  because I am forced to move the greenhouse 
and everything in my  business in less than 8 weeks. I still don't have a 
firm deal on a  location to move to. The seller and the city where I have an 
offer pending, on a  nice location close to home, are making my life miserable 
nit picking the deal  and delaying.  I have had to threaten to choose 
another location in a less  regulated rural county 20 miles away. There are 
plenty of mini- farms being sold  very cheap due to economic reason there. If 
they delay more it won't be a  threat. 

Do  you know, even at a guess, at the power level in kW?  
DD  Based on the comparison to kerosene convection  heaters. Then assuming 
that 30-40% of the heat ends up in the  greenhouse on high burn, I can say 
this: It takes a 10,000 BTU  heater to get the same heat on low burn, and 
about  a 30,000 BTU on a high burn. That makes it top in the 100,000+ BTU per  
hour range. Probably 20,000- 30,000 for 8 hrs. overnight low burn on a wood  
and charcoal bed. The rest of this heat is wasted up the chimney, or 
heating  the well ventilated head house where the stove is located. 
There is  so much cold air leaking into the head house I can only maintain 
a 15-20  degree lift over outside temperatures. On calm nights I get a much 
greater  heat retention. There are holes big enough to look through and on a 
windy  night- well. This has been a point of frustration not knowing when I 
will move  for the last several years. None of my temporary structures 
could be made  permanent, sealing the heat in. Not when they are being torn down 
soon. I have  plenty of wood to burn, it's just the time to cut and load it 
is an issue.   
Draft  is related to the average temperature in the chimney and to a lesser 
extent,  the diameter. I think if you have a large enough chimney (6” seems 
overly  large unless the fire is huge) you will ‘win’ by reducing the 
average diameter  to keep the hottest gases restrained in a taller, narrower 
space with a higher  average temperature. That gives more buoyancy which = more 
draft,  automatically.
DD I did not have nearly the draft with a 6 inch sheet metal pipe  going 
all the way up, as when I first installed the stove. The 8 inch made all  the 
difference.  The 6 inch tended to clog from burning wet wood with a  cold 
stove. The 8 inch could get the stove hot enough quick enough to burn the  
creosote back out of the system on a high burn. When I got busy plowing snow,  
I'd fall behind on bringing wood in to dry.  I'd run out of seasoned wood  
in the late winter some early years with the stove and mix in unseasoned. 
    I've added another section of 6" well casing to the  top of the first. 
I don't get as high of a high burn with nearly the same total  chimney 
height. I do however get a more even burn overnight with more thermal  mass in 
the chimney. 

Have  you tried different version of this? Be interesting to hear the  
results.
DD I played with a similar stove called " better-N- Ben's on the back  
sidewall of the greenhouse. It had several different chimney designs over the  
years. It was just thin sheet metal though and I couldn't get it nearly as 
hot.  I never tried to preheat the air in that stove for fear of melting it. 
It became  quite warped as it was from running it hot. I did set up a 
horizontal pipe from  the stove to condense creosote for various uses around the 
farm. Not really  intentionally, but took advantage of the feature. The 
condensation tube worked  wonders on cold nights with heavy snow or rain cooling 
the tube. I could clean  about 3 gallons of loose crispy tar from the system 
every month or two in the  winter. This stove is not nearly as tolerant of 
wet wood. Probably due to the  primary air preheating feature of the main 
front stove. The first stove  described can burn wet wood a log or two at a 
time with the drier wood, once  warmed all the way up. 
Dan  
Regards 
Crispin 




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