Creosote condenser or gasifier furnace

[Laylow]

Maybe you all could help me arrive to some sort of conclusion here.

My advice to anyone that is trying to extract heat from their flue gasses in a woodstove is to not do it.  But what can I say, I'm a big hypocrite.  I want to extract all of the heat from the woodstove and use a blower to move the air and combustion gasses through the stove.  The problem with this of course is the condensation of creosote when the flue gasses encounter a surface with a temperature of less than 250°F.  I can easily build a woodstove where most of the heat is extracted from it but I'm not sure what to do with the creosote.

So the next thought I have is to send the combustion gasses to something like a condensor (or still) where the creosote could be collected in a safe manner and the rest of the gasses could pass on through.  I immediately began to think about gasifiers and wondered how close these two processes were to each other.

Now I've arrived to the conclusion that the best possible furnace would be a wood gasifier furnace.  It would take care of all of the drawbacks of a regular woodstove.  You could actually have controlled heat.  Maybe it would work to have an old propane furnace fed by a gasifier.  I don't know much about what kind of a fuel wood gas is or how dangerous it is.

I was only able to find one commercial product that does this and the site is located in Germany. http://www.zws.de/holzvergaser.php3?c=39&sprache=en  

Anyway, I would be interested in DIY wood gasifier furnace plans but I don't think it would be a project that I would be able to tackle right now.  I can buy or cut a cord of wood with pieces cut to 16" but coming up with 2" blocks of wood is another story.  Also, a gasifier is just a much bigger project than a woodstove.  So I'm back to looking at how to get the creosote out of the flue gasses.  It looks like all of the gasifiers just use filtration to remove contaminants from the wood gas.

I think that I still want to focus on building a wood burning stove and somehow removing the creosote from the flue gasses.

I'm open to any ideas about anything really.  Filtration of creosote, condensation of creosote, gasifier furnaces, anything.

[whatsnext]

If you're going with a combustion air fan anyway why not add some more air after the gasses leave your stove but before they have cooled down. Perhaps you could get a secondary combustion of the creasote. Make sure you have a catalyst too as you'd like your burnt gas stream to be as hot as possible before it leaves the stove and gets some more O2. I've seen gravity flue stoves that claim to use something similar to this and it should be much easier to control with a forced vent.

John...

[Gordy]

Laylow,

Check out http://newhorizoncorp.com  Their eko 25 is 95000 btu, 1,150 lb.s and $3,780.0o

 Gordy

[Laylow]

I don't really know much about catalytic converter design and I've heard that aftermarket converters aren't very good.  Using secondary combustion to burn creosote is an interesting proposal though.  I would also just be happy to get rid of it any way I can.

A catalytic converter might increase the efficiency of the furnace more than extracting the heat out of the flue gasses; I don't really know.  Maybe what I'm really interested in is just some way of getting rid of having to have an expensive chimney.  Also, in an outdoor wood furnace design that uses air to air heat exchanging there is a higher chance of overcooling the combustion gasses.

Maybe that's what I'm really asking for: A wood furnace design that doesn't require a chimney.

Thanks.

[Laylow]

Thanks, that's a very nice site.  I've also ran across this site http://www.alternateheatingsystems.com/woodboilers.htm  and I finally looked at the Tarm boilers.  http://www.woodboilers.com/wood-gasification.asp  I've skimmed over a lot of stuff that mentioned Tarm boilers before but I didn't know that they were something I would be interested in.

The pdf brochure on the eko almost shows enough detail to build one.  So far, everything has been a boiler.  I would rather stay away from heating water and just stick with a furnace design.  Also, everything has been about $4,000 and 1,000 lbs.  While I think it might be a good investment, I don't think I could do that right now.

I would like to try to build one of these some day but time is another thing that I'm short on.  I can see that there was probably a huge amount of trial and error involved in the designs of these gasifiers.  Fire is just plane hard to figure out.

[farmerfrank]

If you do a good job at the combustion end there will be very little creosote. By good combustion I mean burning is at a very hot temperature in a ceramic chamber with enough combustion air induced. Then by passing these gases through an adequate heat exchanger most of the heat will be removed....upwards of 80% as compared to the potbelly which is only about 35% efficient. I have done some searching on the net but can't find any homemade plans. Maybe someone out there has better luck and can pass the information along. As mentioned below Tarm does have a very nice system. A search on corn/pellet stoves will show several with efficiencies into the 90's. I would think that wood could approach this number also. Hopefully this interesting thread will grow.

[nothing to lose]

A thought I have had, but got design problems to figure out yet.

Placing wood into a sealed container with a pipe to vent out the gas will make charcoal when baked nice and hot. If you bend the pipe around under the container, cap the end, and put holes like a gas burner you can have a self feulling fire to bake the wood to charcoal. I have done this out doors to make charcoal

NOW, if you were to put the container near the top of the wood burner to bake it, use the charcoal from a previous batch to make the initial heat to start gas production you could vent the gas produced down under the charcoal. Adding in fresh air you should have near complete combustion.

 First any impurities are baked out of the wood while making the charcaol, these are burned up in the very hot coals and air when vented. This produces tons of heat. Creasote is also burned as baked out. All you have in the container is pure charcoal when done properly.

2 problems somewhat are how to controll the fire and baking temps so as to not produce to much gas too fast, outdoors this is not a problem with open fire, in the house it would be. Other problem is you have to let the charcoal cool after baking, if you open the container and let oxygen in while too hot the charcoal will burn up.

Now a thought I have not yet built yet, pipe the gas to a storage container and controlled flow into the wood burner both. Adjusting a gas valve would control the amount of fuel to the fire to continue baking the wood. Any extra gas at that time would flow into a storage container, maybe though a foot valve for one way flow.

Durring the cooling cycle for the charcoal after the fire is out, the stored gas could be used in a gas burner for heat. Sort of second furnace.

Once charcoal is cooled, load into bottom of wood burner, reload wood into charcoal maker for next batch and start over using the charcoal for heat to start the gasing again.

I think I make it sound more complicated than it would actually be to use the system.

The stored gas could be used for anything, heat, run a genny, cooking etc..

Using the system outdoors where safe could provide wood heating to the house through duct work. Gas could be flowed to gas furnace in house like propane while wood furnace cools to remove the charcoal produced. This is on my to do list, but too many projects already not getting finished.

 And I may be heading back to Canada agian too

[Laylow]

I was wondering when you were going to chime in.  I read your stuff on charcoal making; it's pretty interesting.  I'm working on a design that incorporates the charcoal processing idea.

I would really love to know how wood gas works in a propane furnace.  I have concerns about bringing a gasifier indoors though.  Mainly concerned with explosion and deadly fumes.  The charcoal fires are something else I would like more info on.  It sounds like they burn hotter but how hot?  What kind of stove can burn charcoal without cracking?

Anyway, I need to finish this drawing and then I'll post it in a new thread.

[nothing to lose]

"I would really love to know how wood gas works in a propane furnace."

I am sure it will depend on various things, type of furnace, pressure of gas, cleaness of gas, moisture content, etc.. but for outdoor uses I have used burners from old propane hot water tanks without problems. Also a junk vented type propane heater. But I have not tried a real furnace yet nor those ventless type wall units either.

 I think I might have adjusted the burner same as you would if changing from city natural gas to propane, that little air vent cover held on with one screw often on the burner itself. If your stored gas is cleaned and all correctly you should have just good clean methane I beleave. I have no way of checking that though.

"I have concerns about bringing a gasifier indoors though.  Mainly concerned with explosion and deadly fumes."

Me too somewhat, depending what I actually build. Actaully for various reasons I am not too concerned with those problems, but un-controled over heating is more what I worry about. Too hot a fire. First if the chamber holding the wood to be baked is sealed as it should be, no air gets into it, the reason the charcoal does not burn itself. No air/oxyegn means no explosion there either. Do not build up a pressure!

 The gas comming out the pipe into the wood burner should be burning same as wood or anything else so no explosion there. This would be the exact same gas comming out of burning wood that make those pretty flames.

 Only fumes are what you would normally get from a wood fire in the wood burner anyway and of course if the wood burner is installed corectly those fume are vented outside, same as just burning wood itself.  So really my bigest worry is getting too hot a fire burning and making the gas too fast thus getting a hotter fire making gas even faster, thus un-controlled burning. This is my main reason for thinking about storing some of the gas, controll what gets into the fire chamber and pipe all other gas to storage when excess is being made. Done correctly there should never  or rarely really be any excess (unless you want it), but just incase.

"The charcoal fires are something else I would like more info on.  It sounds like they burn hotter but how hot?  What kind of stove can burn charcoal without cracking?"

Well basically any wood burner should be able to burn charcoal same as wood. After all when you burn wood all you are doing is driving out the impurities with heat and that gas makes flames, then you have glowing red hot charcoal left burning. So basically you are already burning the charcoal but losing alot of stuff up the flue pipe.

Now charcoal itself does burn faster and hotter than un-burnt wood and also far cleaner. To controll the heat just let in less air for a cooler fire slower burn, or to melt aluminum blow in more air

 For melting aluminum don't use the wood burner of course!

 Since the impurities have already been driven out and burnt when making the charcoal from wood there should be nothing like creosote left to worry about needing a hot fire for, just adjust air for the heat you want. This is also the best charcoal for cooking foods on the grill that you can get. Well figuring you are using good woods like oak or hickory, pine or cedar I might not want to cook with, but if pure charcoal really there should not be much difference by then anyway I geuss.

There actually is a big difference in baking wood into charcoal like this and a normal Gasifier. A gasifier many people would think of does not really make charcoal. You burn the wood completely up in a gasifier, the oxygen in the air is burnt up in the hot coals so nothing else can burn and the heat from the coals are baking gas out of wood which cannot burn because there is no oxygen left. However you do get carbon monoxides in that gas as well as unburnt creosote and other not so goodies. A gasifier therfore normally works on vacume, like connect it to a gas engine which will suck air through the fire and unburnt gas through a cooling and filtering system. Baking wood into charcoal a pressure (just enough to force out the gas) is created in the sealed container where nothing is burning and that pressure forces the gas out the pipe. Kinda like boiling water forces steam out a pipe.

Although perhaps making wood gas with either system could be considered a gasifier, most people think of the system to run engines on as a gasifier and thats the one with carbon monoxide also.

[Solardreamer]

Facinating discussion, brings me back to my chemistry lab days.  Creating charcoal is a basic reduction, and while you are "purifying" they fuel it requires energy to do so.  Basic thermodynamics says any change in form requires more energy than you actually gain so in the end you are actually loosing efficiency.  There are stoves on the market that have secondary combustion chambers which pass the offgas back across the heat source to combust this gas before you loose it up your chimney.  Of course you have to have a pretty hot fire to utilize this heat.

  I have been interested in the possibility of a passive radiant (from your woodstove) system.   Similar in concept to a wood boiler, but instead of heating water directly it would use a closed loop of copper tubing imbedded in the wall behind the woodstove.  Thermosyphoning would move the water until it all reached an even temperature, then when you let your fire burn down/out it would continue to release its heat to your room.  Seems alot safer than messing with gasification, but maybe I am just a whimp.  

[Laylow]

I think we have two different goals.  I am interested in keeping as much heat as possible from flowing out of the flue.  While accomplishing this would greatly improve efficiency, my ulterior motive is to have an induced draft system that would allow me to place the furnace in an outbuilding and pump the heat into the house without sending a bunch of smoke with it.  You, on the other hand, are wanting to improve efficiency by distibuting the heat in a more effective manner.

I have always been interested in thermosyphoning but was always doubtful about whether the rate of flow would be adequate for my application.  I assume that someone has some simple formulae for calculating that but I've never run across them or tried to figure it out.  I would think that the same formula could be used to calculate how much draw there is in a chimney.  Thermosyphoning with a wood stove for heat sounds a little more promising than using passive solar panels.  I'm sure that all the info I want for that is just a quick site search away.

Making charcoal for charcoal's sake is pretty inefficient but if all of the heat produced is used for heating then there is little or no loss of energy.  A regular wood fire goes through all of the same changes of form that a gasifier fire goes through but more of the woodgas that was produced travels up the flue without ever being combusted.  Secondary combustion chambers and catalytic converters are both good ways of burning more of the off gasses.

Another motive that I have is to have a completely clean exhaust.  It's not really fair for me to complain about factories and power plants dumping dirty exhaust into the air if I am not trying to clean up my own.  For all the years that we've been heating with wood, and all of the technological advancements that we've made in the past 100 years, it's amazing that the preferred method of heating with wood is to just throw some logs in a metal box and set it on fire.

As for safety, I don't think that there really is much danger.  I do believe that we have a personal responsibility when it comes to the exchange of free ideas and in a DIY community it is very important that all possible dangers be discussed and disclosed for the safety of it's own members.  Manufacturer's cover their butts in every way possible to the point of absurdity but we shouldn't assume that we would not be held any less responsible.

[Solardreamer]

Facinating discussion, sounds like you are attempting to create a forced air biomass system.  While I can see the wisdom in what you are attempting to accomplish, I just question if your methods will in the end achieve those desired results.  For starters, you are attempting to use air to heat your house.  If you are producing the heat in an outbuilding you have to consider the energy lost in the transmission of the air from one location to another, plus the loss of energy heating the air and ceiling that does not heat you.  Next, even though you are producing charcoal using its own heat( brilliant idea by the way) you still use energy in this transformation.  Even though the charcoal once burned is cleaner than the wood that produced it you cannot regain the energy lost in the transformation.  So while charcoal is an effective heat source it is not efficient, as it takes more energy to produce it than it gives when it is burned.

  So in my mind even if you were able to create a scrubber to purify the air from your flue (haven't heard of these used in a residential application) and got your particulates down to 1%, I still think you would be less efficient than a decent woodstove in your house.  You have to account for the loss of energy in a remote air application and weigh it against the same energy released directly into your home via radiation which is inhearantly more effective at heating than forced air.  Personally I think a super efficient pellet stove would in the end be a better option . I have not heard of any woodstoves that can get their particulates under 1%, have you?

[Laylow]

In my particular application the outbuilding is very close to my house.  It is nearly attached.  Duct can be insulated to a suitable degree.  Hydronic systems are still susceptable to the same losses although they should be easier to insulate.  In either case, choosing a heat source usually comes after deciding on the heat delivery system.  If you have PEX tubing in your floors you will obviously want to go with a hydronic system.  If you have a duct system, you would probably be most interested in just utilizing what you have.  It is also possible to run a boiler to a water-to-air heat exchanger in order to use a ducted system but there would be very little reason to do so unless you had to move the heat a great distance.

What system do I have?  Neither.  I have what is referred to as a conditioned crawl.  That is, I have a crawl space where the walls are insulated and the floor is covered in 6 mil plastic.  When I circulate warm air under the house, the effect is the same as a radiant floor system.  I would love to have a hydronic radiant floor system but when your house is on a crawl space and you compare the two methods, the conditioned crawl is just way easier and way cheaper.  In fact, I would argue that in any one-story house on a crawl space there is absolutely no advantage to using a hydronic system.  For a hydronic system you are probably looking at about $3,000 just to get started.  That is figuring for the PEX tubing, valves, pumps, fittings, headers, staples, minimal insulation, and glycol.  Then there would be the hours of work involved laying on your back and trying to force tubing between floor joists that have exactly the wrong spacing for whatever diameter PEX you are using.  For a conditioned crawl you need about $100 for the plastic and insulation which can be installed in just a few hours and then you'll need a little more cash for one run of supply duct and a blower.  Also, if your house is on a crawl space you probably have a humidity problem that you may or may not be aware of.  The conditioned crawl space fixes that problem.  Sorry, this whole part belongs in the Rants & Raves.  I was so close to installing a hydronic system but had never heard of a conditioned crawl before.  Now I know that anybody living on a crawl space should have a conditioned crawl.

I absolutely agree with you that making a batch of charcoal outside just to use the charcoal for heat would be highly inefficient.  I don't think that anyone was saying that that would be a viable method of heating one's home.  Nothing to lose's description was more of a charcoal producing gasifier adapted to a heating application.  This is helpful because the process of making charcoal and the woodgas byproduct is probably the easiest way to describe gasification or pyrolosis.  In the next thread: http://www.fieldlines.com/story/2005/12/16/17744/404  I proposed a rough design for a gasifier furnace.  The goal of a gasifier is not to produce charcoal but to produce woodgas for heat.  In this design the charcoal is consumed in the process and provides the heat necessary for further pyrolosis.

Now just to be clear, if you are indoors and take a pound of wood, and use part of that pound of wood to turn the rest into charcoal, and burn the woodgas, and then burn that charcoal you would not be losing any more energy to conversion than you would if you just set the pound of wood on fire.  There's two issues here; first, the heat used to convert the wood to charcoal is indoors.  Any excess heat escaping the process is simply delivered to the place that it was intended.  Second, a regular fire goes through all of the same conversions that a gasifier fire goes through; the difference is that it happens all at once in the same place.

wood and air > charcoal and wood gas > ash and exhaust gas.  Both fires have to go through the same process.  In an uncontrolled fire, the problem is that some of the woodgas is produced in an area that is too cold to burn it which can result in lost fuel.  So far I can count four ways of tackling this problem: use a secondary combustion chamber, use a cataylitic converter, forced hot air at the point of combustion, and the gasifier approach.  I think any one of those approaches can compete for the most efficient design.

No, I've never heard of a residential scrubber either.  I don't even know how the industrial scrubbers work.

I have a decent indoor wood stove; the problem has more to do with the loaction of the chimney and the air pressure on that side of the house.  I get inversions there regularly and have a hard time keeping smoke out of the house.  I also think that a gasifier furnace could function as a good woodstove.

Not being able to use the radiant heat off of the stove or furnace is unfortunate.  Radiant heat alone doesn't work very well for transmitting heat to more than one room.  Another problem with my current woodstove situation is that it is located in a small room in the corner of the house.

Pellet stoves also use forced combustion air.  The exhaust from a pellet stove should be similar to the exhaust of a wood gasifier furnace.  I don't know what the exhaust temperature is of pellet or corn stoves.  That would be good to know.  Neither pellets nor corn are as a cheap as wood for heating.  Corn would be a good option if you can buy it direct from a farmer or grow it yourself.

Small gasifier cookstoves burn clean enough that they can be used inside without venting.  While the exhaust from a gasifier wood furnace could be just as clean, I doubt it would be safe to dump into the house.

I don't know how clean the exhaust can be or even what would be considered clean.  Tell me what you get when you burn CO 22%, H2 18%, CH4 3%, CO2 6%, N2 51%, and enough air and then we can figure out what needs to be taken out.  There might not be a good enough reason to scrub the exhaust in a high efficiency burner but I don't know yet.  There could be toxic or corrosive condensate or there could be another usuable byproduct that is worth keeping.

Learning how to scrub a smoky exhaust might lead to a viable way of preventing flue fires.

So I admit, I have to eat my words.  There may not be very many gasifier furnaces out there but there are other designs that may burn just as clean and maybe even cleaner.

As for how much energy is lost through the flue by heat, I guess I will need to calculate that and compare it against the cost of running a small blower.

Also, if you haven't figured it out yet, I may be completely insane.  Okay, I'm not insane but I have so many different reasons for pursuing this approach that I couldn't possible sit down and describe them all.  Thanks for the input; it did help me think about some things.  Also, it's always good to hear the voice of reason nearby.

[Solardreamer]

I guess everyone on this forum must be insane to some degree or another.  After all we are trying to save a planet bent on destroying itself.  After reading your post I did some research on gasifier furnaces and found out some interesting stuff.  Instead of re-iterating and possibly messing up I will give you the links so you can do your own research.  

http://www.woodheat.org

Good information about outdoor furnaces/boilers in general as well as some discussion on central heating with wood.

http://www.woodboilers.com/

http://www.newhorizoncorp.com/index.php

In my mind these companies will be revolutionizing wood heat, by importing state of the art biomass systems from Europe, where it has been perfected over the last 50+ years.  New Horizons is selling 80+% efficient wood boilers for $3,000, much more affordable than the Cadilac Tarn boilers.

I understand that the conditioned crawl was your most affordable option, but you cannot compair it's effectiveness/comfort to a staple-up hydronic system.  I agree it is more expensive to install, but in the long run it pays for itself with the lower thermostat setpoint(usually at least 5 degrees lower achieves same comfort).  I fully am aware though of the cost/benefit questions you are facing as I am in the same boat.  I am partial to hydronic sources as I have suffered from allergies all my life, and finally am in a position to seperate myself from forced air heating.  For me now the question is whether I can afford the solar radiant system I dream of or will I end up with a Biomass hydronic baseboard setup.  I moved to the mountains and a solar home to decrease my impact, so I cannot in good concious use an electric source to heat my home.

I think the main issue with a forced air biomass system is the extreme inefficiency with cycling on/off.  You cannot modulate the heat like you can with a condensing gas furnace.  A woodfired boiler, especially one with a heat sink or large storage tank, lets you burn at max efficiency, with the excess heat stored for later release.  In this case a water to air exchanger would be one option, but I think you would gain alot more comfort with hydronic baseboard if you did not want to deal with the radiant floor  install.  Anyways best of luck on your endevors, hope you know I am not trying to disuade you from any course you choose, actually have really appreciated the dialog as I learned alot!

Kevin

[Solardreamer]

Hey LaidLow,

  Wanted to start by saying that I think I finally understand what you are trying to do with your gasifier furnace.  I guess I was confused thinking you were attempting to create charcoal and woodgas to be stored for later use, not I see that may not be the case.  Anyways I had this idea for you on your furnace, that is a heat storage tank/area in your insulated crawl.  So here is my idea, make your furnace and set up your delivery to your crawl, but in yor crawl space use a solar technique which is to pass your air through a bed of rocks (maybe a tank inline with your vents).  Then you can blast your furnace and heat your home, and at the same time heat the rocks so when you burn down your furnace you have a small fan circulating the air through the storage tank and warming up your home.

  Would not be as efficient as a boiler, but could be pretty damm cheap to make and might just work.  Would keep your furnace from having to cycle to keep your home warm and would be much less polluting than if you had it smoldering at a low heat to keep the house warm.  Anyways just one of those ideas I get sometimes.....Happy New Year!

[Laylow]

I was going to say about the same thing.  A definate advantage to the hydronic system is the ability to store heat.  I was thinking along the same lines about adding some thermal mass to store heat.  Not sure how I would do it though.  I think the storage medium would need to be insulated from the ground though.  So far your idea to put rocks inline with the duct is better than anything I've come up with.

I just wanted to clarify here what a conditioned crawl was.  A conditioned crawl is not to be confused with a crawl plenum.  No air moves from the crawl space to the living space in a conditioned crawl.  All heat radiats up through the floor thereby giving you the same kind of heat that allows you to turn your thermostat down.  A crawl plenum uses the crawl space as a large plenum.  Air is pumped into the crawlspace and enters the  living area through registers cut into the floor.