OUTDOOR WOOD BURNERS

[bgcustomfab]

I have searched this site and have came up with some usefull info but have a few more questions I could not get answered thru the search.

I was looking to build my own stainless outside wood/coal furnce for heating my bussiness and home.  I have looked at some plans, and truefully they look like slapped together junk. I was going to try to make this as effecent as possible so I had a few ideas.

 1. Instead of having a (pot of water on top)  I was thinking of making a core(burn chamber), then a shell and have the core surrounded by water (would this even be worth doing?).  

 2. Having the exhaust gasses exit low and out the back of the core split into many small exhaust ducts instead of one big pipe. Giving these many smaller exhaust tubing running thru the water also than converging at the top and going out through the top of the burn box. (Thinking many small pipes would have more surface area then one big one as long as I make them so they can still be cleaned out) Would this be a problem if it actually chilled the flue gases to much?

 3. I would use a heat exchanger to steal off any heat that is left to be recycled thru the burn chamber(as someone on here suggested earlier in another thread)by forced induction (My specialty in another field)

 4. The out side of the water chamber would be surrounded by a heavy frame and filled with sand. My water piping would run from the top of the tank straight through the sand and to the house and shop. The returning hose would zig zag thru the sand then exit into the bottom of the tank. I was going to use a seprate pump and coils for the house and shop.

I have all the nessary machines to take on this project, even a cnc plasma cutter that we can cut up to 1 inch stainless with. What do you guys think? Is it worth my while? should I make it out of totall stainless? What thickness should I use? seems like everyone was using 1/4 mild steel in their burn chambers, don't this seem thin?

The house is 1500 square feet upstairs and the same in the basement (if I figured correctly) the shop is only 750 square feet. Is there any formulas that would help me figure out how much water I should use in my chamber. and totall system?  Is there a formula to figure out what size chamber would be the most effecent? Is this a major worry or am I just over thinking the project?  If I use a proper antifreeze mix would mild steel be good enough being in contact with sand?

Thank you guys for any replies,

Brian Horne

[John II]

I can't help you on the design... but if you have the equipment to build it.... I'd say by all means do it... you will enjoy a much lower fuel bill for years to come.

On another note... If you take most of the heat out of the flue gasses, then you are going to need a flue draft inducer on the smoke stack or a forced air blower on the intake draft.

Also I'm guessing you may generate enough hot water to run a steam locomotive ! haha Either that or smolder the fire so much that you'll have tons of carbon black and soot as well as possible creosote build up.

If the fire runs in smolder mode.. then a plan to take the wood gas that is boiling off of it and burn it in a secondary chamber might be worth looking into.

No help... but just some thoughts to look into : )

Keep us informed if you get one underway... and let us know how it goes ok ?

John II

[bgcustomfab]

"If the fire runs in smolder mode.. then a plan to take the wood gas that is boiling off of it and burn it in a secondary chamber might be worth looking into."

Can you explain this to me a little further? I never heard of such a thing (Im kinda new to this)

[nanotech]

One thing to remember at all times is SAFETY!!!

You're going to want to find (or make) a pressure relief valve.  As JohnII said, you have the potential of making steam there, which can cause all sorts of problems if it has nowhere to go when the sudden expansion happens when water turns to steam.

Something to look into is the possibility of using corn for fuel instead of wood.  I can't for the life of me find where I got it from, but I remember that the BTU output from corn was 2.5 times the output of wood!!  Plus it burns much cleaner as 97.5% of the original corn is turned into heat, versus the 55% of wood.  Hence the remaining ash is miniscule in comparison to wood.  Plus the ease of transporting corn to the burner in comparison to wood is beyond compare.  You could make a small metal conveyor belt (like is used on commercial toast machines) to bring in the corn.  Regulate the volume of corn introduced by speeding up or slowing down the motor with a thermally controlled resistor on/in the burner itself.

Plus the cost difference of purchasing a cord of wood versus purchasing several bushels of corn is phenominal.

One of my neighbors has both a wood pellet stove and a corn burner stove.  He did a comparison last winter and only used one at at time.  The wood pellet used $157.00 worth of wood for the month.  The corn stove used $23 in corn the next month and kept the house 15 degrees warmer in a colder month!!

[stevesteve]

Hi,

By "corn" do you mean 'sweetcorn' or 'maize'as we would call it in the UK?

Is this corn oil or the corn itself?

If it is corn itself presuably that is the loose grains rather than on the core?

Sorry about all the Q?s but I haven't heard of anyone using it for fuel.

[TomW]

Steve;

Its field corn, more specifically, shell or dent  corn which is corn removed from the cob so it is just the dried grains of corn. Cobs burn well too but have no weight.

Cheers.

TomW

[DanG]

Some more info:

Animal feed corn can vary in moisture. Corn kernels that have started to dent have about 50 percent moisture. The best harvest moisture level is between 22-26%. Any reduction below harvest moisture levels is done by forced drying and that costs real money w/ todays energy prices. Below 8% no insects can thrive, and below 14% no fermentation and rot occurs.

So 10-12% moisture is the usual design point of corn stove heating - above 14% will void some warranties. Corn will readily take on moisture when relative humidity is above 60% so proper storage is required. Even after drying and bagging costs since its done in such high volume corn heat usually is economical.

[mikey ny]

"if the fire runs in smolder mode"

    They say around 50 percent of the energy produced by a wood fire is in the smoke that goes up the chimny. Some of the newfangled boilers (gasification boilers) actually have a way to collect or produce the wood gas (smoke) and burn it in a separate chamber by injecting preheated air. These chambers are generaly made of some type of ceramic stuff because the temp can easily reach aver 1000 degrees f. This is the part of the boiler where you want to do most of the heat exchanging. If you google seton boilers or  hs tarm boilers you will some some info on this. I have an older tarm boiler that adds combustion air at the bottom of the combustion chamber to help burn the wood gas that is exciting through the bottom of the combustion chamber. It is called an underburn. The smoke must travel through the fire in order to exit and is concequently burned as it exits if the temp in the burn chamber is high enough. Hope this helps.

[mikey ny]

one thing I forgot to mention about these gasification boilers. They are designed to run at full throttle to achieve the most efficiency. They almost always work in conjuntion with a large volume of water in a separate storage tank in order to soak up the excess heat when you don't need it and save it for later. Typically you would fire the boiler once or twice a day.

[whatsnext]

I've burned corn in a pellet stove and it's really a hassle. The sugars in corn do not burn and form very hard 'clinkers'. These have to be ground up, somehow, and ejected or they will eventually snuff the fire. Long before I burn corn again I will perfect my wood pelletizer. The raw material is scrap, unlike corn, and people who have it want to get rid of it not eat it. Wood can be burned very well if done right. The first thing I would do is find the cheapest fuel that is also close by. For me that's WVO but wood dust from furniture building is also available.

John.........

[whatsnext]

 "but I remember that the BTU output from corn was 2.5 times the output of wood!!  Plus it burns much cleaner as 97.5% of the original corn is turned into heat, versus the 55% of wood.  Hence the remaining ash is miniscule in comparison to wood."

This is false. Both corn and wood pellets deliver about 8000 btu/pound. Corn may be more dense but not by much. Corn also leaves more ash in the firebox because it it much denser than wood ash which blows out the stack. If you look at volume purchases you'll see that corn and wood pellet prices are about the same. If not there is some odd market forces going on in your area. The good thing about corn prices is that it's cheapest when you need it.

John........

[Chagrin]

The Tarm furnaces are quite fascinating in their design. Before you go through with any design, take a look at their furnaces at http://www.woodboilers.com/

In order to have a proper fire you need a HOT fire, lined with ceramic brick. It doesn't make sense to me to encase a fire in a tube of water because you're just guaranteeing that you'll never have a HOT fire and you'll just be blowing all the wood's energy out as smoke.

[DanOpto]

Calculate the present size of your heating system.

Most furnaces are about 75,000 to 125,000 btu per hour output.

Look at the calculators here.

There is information on wood, corn, installation and sizing

http://hearth.com/what/specific.html

 

[DanOpto]

Do not cool the fire until all the fuel is burnt.

For best fuel efficiency.

Create a firepot that burns very hot, with good air supply.

Line the firepot with fire brick so the heat is reflected back into the firepot to improve the burn.

When all the heat has been released by burning the fuel in the firepot, then route the exhaust gasses over your heat exchanger to collect the heat from the spent exhaust gasses.

Do not put your heat exchanger in contact with the flame.

The metal cools the burn and creates incomplete combustion and soot deposits.

[farmerfrank]

Instead of encasing the waterjacket with sand, place the waterjacket,or tubes in the sand. The sand will stand the high heat necessary for complete combustion.Also make sure that any exchanger can be mechanically cleaned be it by scraper,high pressure water etc.

[nothing to lose]

" It doesn't make sense to me to encase a fire in a tube of water because you're just guaranteeing that you'll never have a HOT fire and you'll just be blowing all the wood's energy out as smoke."

Actaully it does not work like that really. I have seen some of the comercail units working, they get as hot a fire as anything else would built in the same way other than the water tube. As a matter of fact a friend that had one heated steel for blacksmithing in his a few times. May just be all in how you run one?

In a way I think it's all the same thing really. You build a fire to produce heat, heat the steel, cool it to remove the heat and use elsewhere. If your not cooling the steel with air or something then your not getting heat either, you have to remove the heat from the furnace in order to heat the house. Just with these water type furnaces you use water to cool the steel instead of air.

[nothing to lose]

Corn is good and cleaner by far, but cheapness varies, especailly if you live close to a sawmill producing tons of nearly free scrap

Myself I pay $5 for a huge bundle of slabs from a mill when I buy it. Maybe 2 or 3 bundles equals a cord. Unfortunately I do get ALOT of ash since this is mostly the round bark part of the trees that is cut off to make squares and flat boards. The wood burns great, bark leaves lots of ash.

 I was looking for a corn pellet burner awhile back and one company that was making them had the wood pellet stoves but stopped making the corn pellet stoves. Sales agent said it was because the moisture content of the corn was too had to control. Does not make sense to me though since it seems wood would have about the same problem also, but that's what he said.

So your friend uses either in his burner? I thought you should be able to do that, but the same sales guy told me you could only burn wood pellets in the stoves he sold and corn would not work for some reason, he lost a sale also when he said that.

Don't know how much corn pellets cost now, but I was paying about $6 for 50lb bags of whole corn and a little more for the cracked stuff for feed when I had pigs and goats. Been a few years since then. Pellets might be less I geuss, they could be made from scrap corn not good for feed I geuss.

[nothing to lose]

"The sugars in corn do not burn and form very hard 'clinkers'. These have to be ground up, somehow"

Hey you may be on to something then. Burn the corn for winter heat, save the sugar clinkers. Use the sugar to make Alcohol feuls

[pwr]

You don't want stainless steel.  It's a poor conductor of heat, and changes dimensionally with repeat hot/cold cycling, so it's likely to crack after a few such cycles.  Plain old carbon steel from a U.S supplier would probably be your best bet, and its a whole lot easier to work with.

[steak2k1]

Brian:

Totally agreed with comments regarding use of SS material.  There is, besides the problem of low heat conductivity (and it is poor indeed), is that it may loose it's "stainless steel" chemistry, particularly if held around 900F for long periods. Putting SS within contact of MS steel as well may set up a corosion cell that can be greatly accelerated with the addition of heat.  In other words SSteel can and will rust.!  

MS PLate is your best bet. Besides it's a lot cheaper/easier to work with.

IMHOP

rgds,

Stk - CWI, WET

ESAB Welding/Automation applications Eng.

[whatsnext]

steak2k1, Do you know who ESAB's reginal sales guy is in the Kansas City area? Miller is the big brand here and everyone I've found who carries your product does not seem too interested in actually selling them.

John.........

[steak2k1]

John:

E-mail on the way.

stk

[whatsnext]

Just in case my email didn't reach you I'm at johnsbmw[at]planetkc[dot]com.

Thanks, John.......

[bgcustomfab]

Welp I have alot to chew on so far.

Also what are you guys using for antifreeze?

I havent really found anything affordable to treat 1000+ gal of water. ANy quick ideas?

Thanks,

Brian

[mikey ny]

hello,

 last year I aquired an HS Tarm combo- wood-oil boiler. I installed it in my detached garage so we would'nt have the mess inside. I threw it together quickly on a weekend in Dec. When I tried to buy anti-freeze (non-toxic) it was 9 bucks a gallon. The cheaper stuff (rv antifreeze) is not suitable for high temps, I am not sure why but i do know it won't work. I needed at least 75 gallons to get a 50-50 mix. I could'nt afford it. I ran straight water all season in upstate NY. I have pipe above ground insulated with fiberglass and foam. It was a pretty cold winter. It never came close to freezing, because I kept it running all the time. I was told by many people that i would not make it through the winter no mater what. I took the gamble and made it. I am not normaly much of a gambler but this time it paid off, although I did keep a speed boat with a hole in it in the water for 2 seasons, never sunk, bilge pump worked good. So anything (almost) can be done with a little detrmination.

[BoneHead]

Here in GA, a lot of corn is used for feeds and there are major packaging companies here who dry their corn similar to the way the peanut guys dry their peanuts. This is to prevent the feeds from molding in the bag. They just use a hot air blower hooked into the bottom of a large wagon. The wagon has a layer of wire that forms like a hot air chamber in the bottom and the peanuts can't fall all the way to the bottom. The hot air rises and takes moisture with it as it goes.

Some 1/8" hardware cloth bent to form a seat about 4 or 5" up in a steel drum would work well if someone had an old woodburner in the yard or something. Someone could dry a good deal of corn in half a drum even with running a small pipe out of the house chimney. In 5-6 hours this method can remove up to 15% moisture. (I even heard some people were using this method to dry out straw bales to make them suitable for building purposes.)

Of course, you would really have to develope a commitment to burning corn to justify all that work, but it would work and it would last a long time if you could keep the pipe hot all the way to the drum.