Gasifier Furnace Design

[Laylow]

Okay, here is a design inspired by a recent thread http://www.fieldlines.com/story/2005/12/13/193451/56 for a gasifier furnace.  I used the diagrams and concepts  from the pdf at http://newhorizoncorp.com/ as a reference.

The way I have this drawn, the unit is 17" wide and about 60" tall without legs.  This unit would be welded together out of 1/8" thick plate steel.  The front panel and doors are not shown but you can see where the air inlets are.  This is a furnace and not a boiler so the design is much simplified.  If the Primary air inlets are closed, this could be used as a charcoal maker.  The charcoal could maybe be used in the filter box.  For my purposes, insulation on the outside is not needed but it would be easy enough to add after it was built.  A fire could also be started in the ash pan if it was needed.

Notice the lack of refractory lining.  I'm sure that some areas would definately need some refractory but other places could do without.  The eko furnace uses a rafractory nozzle with a much smaller orifice.  My drawing just shows a slot down the length of the gasifier chamber for the gas nozzle.  What do you think happens with different shapes and sizes of gas nozzle?  Lazy flame, poor combustion, explosion, blow torch, even heat?

Filtering of the fumes may not be necessary but the cleaner the fumes the better I guess.  Wouldn't be good if the filter media caught fire though.  What would be in the fumes anyway?

I'm thinking about a lot of stuff here.  There are a lot of things that I intentionally haven't commented on beacause I would really like to hear what everyone's suggestions, comments, and criticisms are.  And most important, what are all of the safety factors involved?

Oh yeah, if anyone gets the notion to start building something like this, please go right on ahead.  I would be lucky if I could get started on something like this by next year and I don't have any interest in being the first person to ever build something.  In fact, if I could buy one that worked for a few hundred dollars I would jump on it.

You may have to download the picture from my files if the gif doesn't come out correctly.

[hobot]

Hey there LayLow,

I want to make one someday for tractor and small motorcycle use and

maybe to save chainsaws/gas/labor for home heat as well.

I've posted in past some sites on this, mostly cooking, heating in

India and Africa adaptations but also some goodies on WWII units durring

rationing. Search here and google on the various terms associated with

wood gasifier. Top, bottom, side drafter models out there with most

the complexity being filtering for burners or motors if end use.

If near a charcoal plant barrels of the raw stuff can be gone

rather cheaply or of course can breed your own.

Depending on state of burn and matterials, 'fumes' have ash to corrostive

acids and moisture to many combustables like methane to carbon monoxide

and tars or cerosote.

You are better man than I to decipher that commerial stove's poor pictures

and draw out a more elegant adaptation.

Hey its winter so try one and see what you learn I for one will be tuning

in to it.

hobot

Arkansas.

[farmerfrank]

You will need a second fan on the heat exchanger otherwise it will get so hot that the exhaust blower will probably malfunction. 1/8 inch steel might work if it sis corruagated....otherwise I am sure it will buckel. Even thicker metal will distort. Remember in the gasification process the temperature can reach 2000 degrees and steel turns red at 1200 and melts at 1600. That is why refractory is used along with the fact that refractory will relect the heat back and give a nice hot combustion temperature. I also what to attempt to build a wood boiler but tiem is always a problem. Have fun

[Laylow]

I hadn't really thought of using this design for gas production but I suppose it would work if you shut off the secondary air inlets.  The pdf file actually has a pretty good diagram of what they are doing.  I am surprised that they actually published that much.  There are a couple things that they are doing that I don't quite understand.  For instance, their design has a chimney flap that I can't figure out.

I know I haven't read everything on gasifiers but I have seen some good information on this site and others.  I'm just really surprised that everyone can tell you how to run a car off of wood gas but very few people seem to know how to heat their homes with it.

Well, I hope I get to build it.  I don't know if I'll be able to or not.  If you build one make sure and build two so that you can send one my way (MO).

[Laylow]

Yes, I didn't really put any detail in to the heat exchanger.  I was thinking of running some pipe pieces through it with a blower pushing air through them.  I'm not sure what would be gained by filtering the exhaust but I would also have to worry about the filter media catching fire.  I think I like the idea of filtering near the heat exchanger in case anything does condense in there.

I was expecting to hear something about the 1/8" steel.  I'm thinking that to build something like this I would probably have to buy all of my steel new so I'm concerned about cost here.  1/4" steel would cost twice as much.  Do you have a recomendation on what gauge steel to go with?

I figure that refractory can be added just about anywhere pretty easily.  The only problem area, and probably the most important area, is where the secondary air mixes with the wood gas for combustion.  Still, I think it would be easy enough to do something similar to what eko did.  They made a nozzle out of refractory cement with holes in it for the secondary air.

Thanks for the input; this is exactly the kind of stuff that I was wanting to hear.

[farmerfrank]

Yes steel is becoming expensive, mainly due to energy. I only thing I do know is that it wont get cheaper.Distortion is always a problem with heat. I had seen a crude firebox made from pieces of angle iron welded together to make a Z pattern. This gives it a way to grow when heated without actually warping. Angle iro is easier to find in salavge yards as compared to sheet sheet. Im not sure about filtering. It the filter doesnt burn up it will most likely plug. I liked the Tarm idea. ...a small cyclone as a secondary solids collector. Damn if I dont get away from this thread soon, I'll be looking for my chequebook.

[alcul8r]

Laylow,

You can see mine at

http://www.fieldlines.com/story/2005/5/12/172658/242

Making the top (fuel door) air tight and warp-proof makes mine a lot more controllable.  

It burns just fine without power draft.  If you use the power draft check your flow.  A little bit of water column is more than enough to pull the air through, and more will pull ash and cinder instead of letting them burn all they can.

Mine does take a good heat to get it started, but for the efficiency I'd be willing to add a propane starter.

I'd suggest trying to preheat the secondary air as much as possible.

One of the questions we have not answered is what happens once the wood starts coking.  I've heard once it reaches 400 degrees it will continue exothermically even if the air is shut off.  Don't have the proper thermocouples to check, although they may be available at the lumber yard or hardware store.  My guess is no, because regular wood stoves should get that hot and they quit burning if the air is shut off.

Completely burn the secondary and there is no need for filter.  I'm not sure I like the air coming out the bottom because it may carry a lot of ash with it.  Perhaps you could swirl the air coming into the burn chamber and elevate the exhaust in the center with a peaked baffle above it.  Instant cyclone cleaner....

Good luck with your project.

Rex

[nothing to lose]

" In fact, if I could buy one that worked for a few hundred dollars I would jump on it."

Ok, I'll build you one, deliver it for 10-20 cents a mile to even

Actaully when we were in the other thread I did not see what you had planned here, yep I geuss this one is a gasifier all right

 Totally different than what I had in mind.

My first thought is if you don't have electric you won't have heat either since this will require the blower running for suction. Of course that may not be a problem depending on the source of the electric perhaps.

If you can adjust the primary and secondary inlets for proper air flow for a complete burn I think it will work good. You need enough suction on the fuel chamber above to draw air down through the hot coals where the oxygen is going to be burned up, more unburned gas will be created and the secondary inlets then need to be letting in air/oxygen to burn those gasses. This is where I invision the problem so far, not yet giving it alot of thought of course. How do you let in enough air for a complete burn at the secondary and yet maintain a proper draft on the primary? I think I would maybe heat the secondary air by running it through a pipe in the upper chamber or hot area in the lower chamber, would probably make a better burn with hot air and hot gas compared to cooling the gas with cooler air entering.

If you can adjust for a clean burn of all the hot gasses I think Ash, Carbon Monoxide, and water will be your main concerns for byproducts. First two of course happen anytime you burn wood. Water though normally does not occure as the steam is vented out with the hot flue gasses. Wood has moisture, even dry wood, so you will have minor steam occuring, since you will be cooling the gasses as much as you can to extract the heat I expect you will get water in the heat exhanger or the pipe below it as shown in the drawing.

My geuss also is that you are going to cool the gasses as cold as you can for the least losses of heat. If this is the case I don't think you will need much for filtering before that blower. Any trash you do get such as creosote should condense in the heat exchanger, if getting a clean burn that should not happen either really. If you get a bit of ash flowing in the exhaust air I think it will also be lost in the exhanger, if not it should just be cold dust by the time it gets to the blower. So probably just a decent air filter  before the blower is all that's needed to keep the blower itself clean.

 I like this design but think I would do a few things different myself perhaps. For one thing a top loader might be easier to load in wood, but I would rather have the burn chamber on bottom. Use an updraft instead of down draft. With a down draft when you need to remove ashes you have to shut everything down, an up draft just open bottom door and add more wood as normal on grate or remove ashes from below grate.

 With inlets at center and top I wonder what happens if the blower stops? Will it suck in air from the secondary and let fumes exit the primary, reverse flow?  Not good if indoors, outdoors might not be a problem. Some day the blower motor may burn out un-expectedly. With the down draft you will need a good seal on the ash pit door to prevent sucking in air and loosing the draft, an up draft any door leaks at botttom would  just be part of the inlet air to the feul.

 If this were an up draft also you might be able to add a platinum catylist easy and cheap. I would worry about ash clogging it with a down draft though. My thought on this one is make a 3rd shelf/layer in the center. I can get those honey combs from car catylitic converters for $5lb or less. Placing these with holes vertical on a grate just below the secondary inlets (above inlets on a down draft) the hot gases are drawn through with the draft and I would then pipe the secondary inlet air through the burn chamber to heat it before entering above the catylist. How well this would work I don't know but it's something I would try myself if I built this. I don't think it could hurt anything as long as the holes did not clog up with creosote and with hot fires and gasses I don't think that would be a problem. If it was should be easy enough to remove them later if needed. With the burn chamber above and a down draft though I am pretty sure clogging with ashes could be a problem.

 This does look interesting and I like it, though I would do it a bit different if I build it myself, and I just might do that

How do you plan to use this? In the basement of the house, open air outdoors, in an out building and duct the heat to the house? Some of that might make a difference in building it also.

[nothing to lose]

" I'm just really surprised that everyone can tell you how to run a car off of wood gas but very few people seem to know how to heat their homes with it."

 Yes that is funny actually since in order to run the cars you want to cool the gas before it gets to the engine. Same thing with a generator running wood gas. So the LOGICAL idea would be pipe the heat to the house when you extract it from the gas.

I think many more people know how it's done though than actually do it. Probably not alot of people make charcoal like me too, though I haven't made much lately, been too busy to use it

 But then I am not actually using a gasifier to run an engine, it is a different proccess.

[nothing to lose]

Build it round like a barrel, not flat plates like a box, if you can. The steel will not warp as easily and thinner stuff can be used and still last longer do to less stress and distortion durring heating and cooling. As far as melting it with excessive heat, you need refractory if that's a problem but would probably need it with thicker stuff also.

Take my fireplace and barrel woodburner for example. The sheet metal liner in the fireplace is heavier than my barrel. It is flat, warped, and perhaps cracked a few places. I need to replace it really but is is fine for now, seldom used anyway and this part just reflects back heat so no fire danger.

 Cheap junk trailer house fireplace insert, looked decent before I built the first HOT fire, now looks like I drove over it with a truck and tried to straighten it back out

 On the other hand my barrel gets far hotter, much more often, and has no problem after many years of hot hot use! Other than surface rust from sitting outside in the summers it is still good as new. Don't know how old it is now, for certain over 6 years, maybe 8 years? Many hot fires and thinner metal but no distortion.

If you check scrap yards you should be able to get all kinds of good round steel from various uses. I have found about anythng you could ever want in round scrap from thick heavy pipe, maybe 1/2" thick any diameter. Even some type of drum with flat ends, 1/2" thick and 1/4" tapped holes all over it, about 48" diameter, 6' long. No idea what it was or what to use it for with all those holes drilled in it so I passed it up at only 8 cents per pound, now I wish I had gotton it since I found a use for such a thing now. It was like brand new, probably part of some machine, but who needed a gaint heavy drum full of drilled holes??

[hobot]

Here's some more fuel on this

http://www.repp.org/discussiongroups/resources/stoves/Anderson/GasifierLAMNET.pdf

http://www.gengas.nu/byggbes/11.shtml

[Laylow]

Thanks for all of the info so far.  There is a lot of information to process and respond to here so I am going to print it out and try to answer everything.

One question that has been plaguing me though is how would I light this thing?  I thought I would start a fire in the lower chamber to heat the upper chamber but I just don't really see that working.  Any idea how they do it in the eko?

I really hope that we can come up with a working design here.  If anyone has a different approach to building a gasifier furnace, I would love to see more pictures or drawings.

By the way, I tried some small scale charcoal making and I think I have a simpler design.  Instead of putting the hole on top of the can, put it on the bottom.  No need to duct the pipe from the top to the bottom.  The test I did was just two soup cans; one larger than the other.  Fill the small can with wood and place the larger can over it.  You can place it in the fire any way that you want to.

[Laylow]

Okay, I am just going to try to address some issues as I read through this list.  Sorry for not quoting stuff.

Building stuff round has it's own problems that I won't get into but the biggest problem is just finding suitable round material.  Water heater tanks are still a little thinner than I would like. As for scrap metal yards, for some reason our's does not allow anything to be sold out of the yard.  I have no idea why but I hope it is not a trend for everyone else.  Also, my experience with the water heater tank shows that it is a lot harder to get an air tight seal on a curved surface and I really want this to be an airtight unit.

With the air coming out the bottom I am really just copying the Eko design again.  I think for the most part the ash should be able to settle into the ashpan while the rest of the air moves around.  It will depend greatly on the velocity of the airflow which I will look into later.  I am not against swirling or doing something like the Tarm but I just haven't given it much thought yet.

AS for the previous thread, I was just thinking about a regular wood furnace with a totally cooled and filtered exhaust.  I said that I didn't want to get into gasifiers but who am I kidding?  I already had plans to build an outdoor kitchen that featured a woodgas cooking range.  The problem is that it's already December and I still need a cleaner form of heat in my house.  I can't keep our woodstove from dumping a bunch of smoke into the house several times a day.  I think we just have one of those bad microclimates around our chimney.

We're on the grid and subject to it's wanes and wants but in reality it's really never off more than a few hours.  We're lucky if the woodstove is still hot at 3am.

According to the Paul Anderson and Tom Reed paper on small gasifiers a 1:5 ratio of primary to secondary air is required.  The restriction of the fuel in the pyrolisis chamber also has to be factored in.  That's easy to say but harder to do.  We may be looking at designing some low tech flow meters to place on the air inlets.  I have two designs in mind already.  One is to make something roughly like one of these http://www.dwyer-inst.com/htdocs/flow/SeriesRMPrice.cfm  It's and egg shaped steel ball inside a slighty larger diameter cylinder.  When air flows past it the egg rises in proportion to the flow.  The simpler and more practical solution is to just use a couple of monometers to measure the static pressure of the airflow.  We just need to see the 1:5 ratio so it doesn't need to be any more complicated than that.

It would also be nice to be able to see the flame but that is an optional detail that can be worked out by the builder.

What concerns me about the temperature of the secondary air is not the combustion temperature but the cooling of the surface that it runs through.  If I understood how the unit should be lit, I might not be concerned.

Some amount of water is necessary for pyrolisis.  Just thought I would throw that in; don't really know much about it.

Maybe I should design a cleanable heat exchanger capable of collecting creosote in a safe place.  Self scrubbing?  I would really like to know more about scrubbing methods.

I'm thinking downdraft because I want to be able to add wood continuously for as long as I can.  I can shut her down and clean the ashes out once a week.  Maybe make a batch of charcoal once a week too.

With inlets at center and top and fan failure, disaster is sure to ensue.  Or maybe not.  I have some numbers to crunch on airflow before I can be sure but maybe the inlet holes are too small to allow enough airflow without the blower's assistance.  Just to be safe though, I could probably add some flaps to the primary air inlets so that air can only flow in and not out.  This might be enough to starve any potential runaway fire.

The way that I would intend to use this furnace is to place it in an out building and circulate the heated air under the house.  I think I have also been designing in my mind a unit that could work inside the house as well.  Just like a really efficient wood stove or furnace.

The Eko uses plate steel that is 6mm and 4mm thick or .236" and .157" respectively.  I think the most important part about using plate steel is the use of refractory cement, fire brick, and insulation.  I think these drawings will need to be changed to reflect the use of refractory and fire brick.  I don't think I will worry about insulating the outside.

The Paul and Tom paper refrenced above also states that for each kg of fuel burned, approximately 6 cubic meters of air needs to be delivered.  This is equal to 2.2 lbs and 211.9 ft³ or 1 lb to 96.3 ft³.  I think we can just say that we need 100 ft³ of air for every pound of wood.

The small Eko can use wood with a 7" diameter and 20" long which is equal to .445 ft³.  A good average for split wood around here might be a 5" diameter by 16" piece of wood which would be equal to .182 ft³.

Oak has a density of 45 lbs/ft³ and pine has a density of 25 lbs/ft³.

The Paul and Tom paper was talking about small bits of wood though so I don't know if there will be a direct correlation.  Perhaps available surface area will make a difference in the amount of airflow needed.

The Eko claims it can burn sawdust.  Any ideas on how this might be done?

Some designs call for having enough air space within the fuel in order to operate properly.  Do you think this is necessary in all designs?  If you were making charcoal in a 55 gallon drum, couldn't you throw a big ole tree trunk in there and turn it into a big ole hunk of coal?

Sorry for the painfully long post.

[nothing to lose]

You did the can stuff too eh

I been burning sawdust various ways like that.

 Dump sawdust into can, turn upside down on hot coals. Sawdust bakes and gas comes out the bottom and burns in coals.

Also sit can of sawdust in hot coals open end up, sit large can over it. Gas comes out top inside outer can and forced down to coals to get out, again it burns well.

Tossed a pipe full of saw dust into coals also. One end caped, other end had holes in a plug, got nice little flame jets comming out once heated and gassing well.

Have fun, many ways to do it, I've done alot of them but probably not all of them yet.

Try packing some sawdust into toilet paper tubes. I just press tight with my finger or use a small stick to pack them lightly. Once lit they burn pretty well and hold together decent too if you don't poke them or move them much. I think after the tube burned pretty well I was getting gassing out of what was left, kinda charcoal wrapper with burning jets out the side.

 I think I may have pics of some in the fire place before and durring burning.

Who needs TV when you have a wood burner for entertainment

Yes a hole in bottom of a barrel over hot coals probably will work for making charcoal, but then you have no way to pipe gas elsewhere. Metal around the hole may have a tendancy to burn out also, might want to re-enforce it with a thicker metal ring.

 Not really a problem when we are doing cans, but if building a 55gal barrel one I would think about it.

 The main thing I would worry about with that big one would be once the fire is out under the barrel air could get into the hot coals inside easier, if oxygen gets to the baked wood (still very hot charcoal, not burning) inside the barrel the charcoal can light up and burn. As long as it can get air it will burn untill all the charcoal is gone. That's another reason I put a pipe at top, harder for air to feul the charcoal inside the barrel. A bottom hole could have a simple slide cover to slip around and block air pretty well, don't forget to open it before starting next batch

Then again too, with a bottom hole smaller pieces may fall out of the barrel.

As for lighting your gasifier furnace. You could put a pipe in the side of it at the level your kindling will be. Uncap the pipe lite fire, cap the pipe again. I think I had used a 2" or 3" pipe nipple and cap for lighting a bottom fire before, not realy sure the size, scrap I had laying around. Probably any size you could run a burning stick or long match through with out it going out would work. I used what was handy.

 Make sure there is not unburnt gas in there of course since you  will have let in air loading it.

You could also load it partly full, light fire with blower running for suction then finish loading it. Some down draft models are not even capped at top just open  top for loading fuel as needed, cover to keep rain out, but those are not furnace units and they don't have the after burners (second air inlets).

Not sure about this idea, I think it would work. Maybe get some fireplace door glass and install a small piece in the side at top burn level. I would make it just a window not a door (no air leaks or seals to worry about). Then you could see the fire burning. It might make lighting easier too if using a pipe nipple and cap as I mentioned. You could have the blower running for suction and adjust the primary and secondary air inlets as needed to get the best draft for getting the fire started.

 I think the glass should be fine as far as temps go, might want it a bit away from the fuel and maybe a screen of some type to prevent anything from falling into it.

[Laylow]

I'm going to add a few more figures and recap the old ones.

Primary to Secondary air ratio is 1:5

100 ft³ of air for every pound of wood burned.  (I think this means primary air).

5" x 14" log is equal to .159 ft³ of wood.

Oak is 45 lbs/ft³

Pine is 25 lbs/ft³

Dry wood can give 8660 BTUs/lb

Wood with 20% moisture content can give 6930 BTUs/lb

I changed the log dimension because I am thinking that the the unit should be about 30" deep and 14" logs could make two face stacks.

I am assuming that my figures for wood density are for wood with 15-20% moisture content.

The heat loss of my house is somewhere between 21,000 to 42,240 BTUs.  I think it would be good to design for a 50,000 or 75,000 BTU unit.

The Eko claims to only use 35 watts of power.  This would mean that it uses a very tiny fan.  Their literature is likely to have some translation problems though.  I'm pretty sure that this is a European design.  When I get some time I'll see if those numbers are possible.

It would be nice if we could control the rate of burn just by delivering a predetermined flow of primary air but that seems unlikely.  I don't think I can handle the other factors involved though so it's still a good place to start.

Okay, Merry Christmas.  When you are done building it, I will just swing by and pick it up.

[Laylow]

For 50,000 BTUs/hour I need to burn 7.215 lbs of wood an hour.  I need 721.5 ft³ of primary air per hour or about 12 CFM.  I would need 60 CFM of secondary air.

We are assuming everything is perfect of course.  Still, so far it looks like all the numbers are making sense.  35 watts still seems a little low for 72 cfm plus their other controls but it's still pretty close.

If I knew what a good velocity was for the combusting gasses I would know exactly how to size the burner orifice (nozzle).

[wdyasq]

Laylow,

http://sharron_reive.tripod.com/index.html

An interessting design that is said to be adaptable to sawdust.  As I read it there is a 'basket' one uses for small material to keep it off the sides and allow it to get heat and outgas. It also requires no fan.

Ron

[nothing to lose]

One thing I have found to make an air tight seal on a round tank better is to use a flat door

Well, actually make a square box to stick out from the tank, cut a curve into the top and bottom to match the tank, weld it all in and cut opening in tank to match inside of box. Use a flat door on box.

If finding a usable round tank is a problem though??

"We're on the grid and subject to it's wanes and wants but in reality it's really never off more than a few hours.  We're lucky if the woodstove is still hot at 3am."

Yes, but from 3pm to 3am ain't that a bunch of nice cozy heat and pretty cheap too

"The Paul and Tom paper was talking about small bits of wood though so I don't know if there will be a direct correlation.  Perhaps available surface area will make a difference in the amount of airflow needed.

The Eko claims it can burn sawdust.  Any ideas on how this might be done?

Some designs call for having enough air space within the fuel in order to operate properly.  Do you think this is necessary in all designs?  If you were making charcoal in a 55 gallon drum, couldn't you throw a big ole tree trunk in there and turn it into a big ole hunk of coal?"

Too tired to psot much now, but a bit.

 There is a bit of diffence in how you can burn things or bake them at times. Bits or chunks of wood probably will not settle in (pack) airtight, sawdust can very easily. So there is a big difference in say burning random 1/2" chunks with lots of airgaps or a semi solid sawdust pile with no airgaps. I burn alot of sawdust different ways, as we said before, toss a bunch in a can and toss over hot coals and let the gasses bake out and burn. I am sure there are ways to do it in gasifiers too, too tired to think of any I may have ran acroass or tried so far to post them.

If I were making charcoal in a 55 gallon drum, I could throw a big ole tree trunk in there and turn it into a big ole hunk of coal, yes. But it would be better to use many smaller pieces of wood than one big one, and the heat in the barrel will bake the gasses out of many pieces of wood better than one large piece. It would be far better. Can't think exactly why at the moment, but I think it has to do with smaller surface area and less thickness per peice, more peices then would be more area exposed to heat, thinner peices less density for the heat to penetrate. So where one large chunk of solid wood has less surface than 100 smaller chunks, it is much thicker also. If expose to sufficeint heat long enough it will bake into charcoal same as smaller chunks, but over a much longer time.

I guess like baking a roast or turkey. The larger/thicker it is the longer to cook it.

 A large oven at 350F could bake several smaller 5lb roasts in less time than 1 20lb roast at the same tempature.

[Laylow]

Earlier I said that I wasn't really concerned about preheating the secondary air.  I can see now that I should be.  I'm not sure what the best way would be to preheat it or just how hot it neeeds to get.

Also, I can see that the unit will need a refractory nozzle instead of a slot so as to concentrate as much heat as possible in the combustion zone.

Closing the primary air inlets and building a fire in the lower chamber to produce charcoal in the upper chamber won't work.  If someone really wanted to do charcoal batches they could add more air inlets at the bottom and have a second flue that ran out through the top.  Personally, I would just build a seperate charcoal producer if I wanted charcoal.

I found an excel spreadsheet that shows how to make a cyclonic dust collecter over in the yahoo woodgas group.  I'm considering using one now but I'm still not sure.  Anyway, it looks like it can be added anywhere on the exhaust duct.

More later. Gotta go.

[Solardreamer]

Posted a new comment on your furnace idea in your other post.  A heat storage idea.  Let me know what you think.  Later.

[Laylow]

That's been a problem that I haven't quite figured out yet.  So far I keep getting images of trying to suspend some form of thermal mass under the floor.  Nothing pretty.  I think the tank of rocks might work.  The best solution would probably be to install heavy tile floors.  Or maybe a rock floor in the center of the house to act as a heat sink.  I doubt that will happen anytime soon.

Happy New Year!

[whatsnext]

Here's a thought that may get rid of the heat storage issue. Two stoves. If you made two two chambered stoves with each one having a charcoal making and a charcoal burning chamber. Then stagger the two stove's start times so that only one needs to be shut down to let the charcoal cool. Of course this idea would only work if there is enough heat in the remaining charcoal and the emitted wood gas to make the next batch of charcoal.

Just a thought, John..

[zukecanoe]

Gasifier furnace's are great... have been using a commercial one for 5 yrs and I figure it paid for itself in less than a year in savings.  I have no assoc. with them other than a happy customer...

http://woodboilers.com/wood-gasification.asp

zukecanoe