thinking about fabricating my own gasifier boiler. few questions?

There are a few threads on this, and a few people who've done it. Some have been successful.

Gasifiers are a great example of hidden complexity - there's a great deal more to it than meets the eye. The dimensions and relationships between dimensions are critical in some cases (nozzle geometry, for instance). Primary/secondary air flows and the ratio between them is also critical. The materials are a challenge all their own. There are great resources out there, but it's a lot of work to build one and something less than 100% chance that it will work.

If you've gotten to the point where stoichiometric combustion ratio , high alumina, and superficial velocity are part of your everyday vocabulary, then go for it!


Here's a link to a paper on Superficial Velocity for your reading pleasure.....

nofossil said:

There are a few threads on this, and a few people who've done it. Some have been successful.

Gasifiers are a great example of hidden complexity - there's a great deal more to it than meets the eye. The dimensions and relationships between dimensions are critical in some cases (nozzle geometry, for instance). Primary/secondary air flows and the ratio between them is also critical. The materials are a challenge all their own. There are great resources out there, but it's a lot of work to build one and something less than 100% chance that it will work.

If you've gotten to the point where stoichiometric combustion ratio , high alumina, and superficial velocity are part of your everyday vocabulary, then go for it!


Here's a link to a paper on Superficial Velocity for your reading pleasure.....

Click to expand...

We need a (LIKE) button on here like there is on Facebook. I would hit it several times regarding your last sentence NoFossil.

As to Jerseycats question I would simply say that it should be remembered at all steps of the process what exactly you are and are not trying to build. What you are NOT building is a wood burner. The goal of a gasification boiler is not to burn the wood but rather the gases released by the wood as it turns to charcoal or changes state through the process known as pyrolysis . There is much more to it than meets the eye.

jerseykat1 said:

I am thinking about fabricating my own gasification boiler (most likely outdoor). But I have a few operational questions for those that are familier with them.

1. The firebox has a hole at the bottom for the gasses to escape and enter the blast chamber, but is there also another air entry point in the firebox say maybe at the top where the forced air enters?
2. How does the fire stay lite at idle is the an electronically controlled door that opens and feeds air to the firebox while at idle or does it use the same opening that's there for the forced air?
3. How does it operate without smoking when it is at idle? I would image an idle fire would produce a lot of smoke especially with wood just sitting on a bed of hot coals and very little air. Is there a cat as well?

That's pretty much the only part of the operation that I am not 100% certain of. Thanks for your help.

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To actually answer the questions that you asked (as opposed to the ones you didn't ask):

It's worthwhile to study (with calipers and a tape measure) an actual gasifier. The details will vary, but you'll find that there are two individually controlled air inlets - one for the primary chamber, and one for the nozzle. The primary air inlet can be in many different locations, but low and along the sides seems to be the preferred approach.

Air supply during idle varies. The EKO runs the blower for a few seconds every few minutes. Gasifiers do smoke a bit during idle, but there's typically an extremely limited air supply so most of the smoke just condenses internally.

The goal (and one of the reasons for storage) is to minimize or eliminate idling. An idling gasifier is just a wood boiler.

There are any number of people on here with the skills to fab. up a boiler, this is the easy part. You are trying to build a producer & carburetor to burn wood gas. Would you build a carb. for a gas engine? I found it better to buy an inexpensive gasser than waste a lot of time & money on a project that probably wouldn't have worked all that well anyways, Randy

My thoughts - some one will design one that is simpler, works well & is easy to build, wit every day parts. Just wait and see! Americans are such tinkers. This subject interest me and I all ready have my home built job [up gassier]. Using my hands and my brain is never a waste of time.

Great!
Depending on your goals on why to build it yourself this is my advise.
- first build a natural draft wood boiler with full water jacket and make it clean burning.
- 2nd, reverse the flue gas flow path (downdraft) of you first prototype but keep everything natural draft. Check this link http://www.wittus.com/wpwoodtwinfiremain.htm German design of course. If you need advise or literature call Niels Wittus, he can help you.
- 3rd, build a true forced draft gassifier with all the bells and whistles.
It's alearning curve and you need to build up your knowledge by experimenting.
A tool you could use would be SolidWorks CAD with "gas flow" extension module, but it's kind of pricy

bigburner said:

My thoughts - some one will design one that is simpler, works well & is easy to build, wit every day parts. Just wait and see! Americans are such tinkers. This subject interest me and I all ready have my home built job [up gassier]. Using my hands and my brain is never a waste of time.

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I agree with this statement, I know there is a lot more to it, however I do believe it is not rocket science with my boiler I have already made changes with good results. This has been keeping me up at night, to make one that works well, easy to build, with easy to get stuff for. and is cheap to buy or build. With the way things are going in this world now, and the sad position we the USA are in when it comes to oil, there is no question in my mind that the glassification wood boiler is going to be more main stream.
In the coming months, I believe the USA will be presented with a pile of new problems, and with new problems comes the opportunity for new business, you know find a problem solve it, and you now have a business, well sometimes. Well my point is a lot more people in the USA will be burning wood, so we here in the USA have to start tinkering, and as the saying goes "Get ur Done"

Steve

Singed Eyebrows said:

There are any number of people on here with the skills to fab. up a boiler, this is the easy part. You are trying to build a producer & carburetor to burn wood gas. Would you build a carb. for a gas engine? I found it better to buy an inexpensive gasser than waste a lot of time & money on a project that probably wouldn't have worked all that well anyways, Randy

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This may be part of the problems in the USA! where has the spirit of invention and exploration gone? This attitude does nothing to advance your skills or knowledge base. If you think you can do it, Go For It!! Biuld something better

jerseykat1 said:

I am thinking about fabricating my own gasification boiler (most likely outdoor). But I have a few operational questions for those that are familier with them.

1. The firebox has a hole at the bottom for the gasses to escape and enter the blast chamber, but is there also another air entry point in the firebox say maybe at the top where the forced air enters?
2. How does the fire stay lite at idle is the an electronically controlled door that opens and feeds air to the firebox while at idle or does it use the same opening that's there for the forced air?
3. How does it operate without smoking when it is at idle? I would image an idle fire would produce a lot of smoke especially with wood just sitting on a bed of hot coals and very little air. Is there a cat as well?

That's pretty much the only part of the operation that I am not 100% certain of. Thanks for your help.

Click to expand...

In answer to your questions I will relate the structuring of my EKO40
(1) Yes there is an air supply for the upper chamber that actually runs up the inside of the upper chamber on both side. This air supply provides positive pressure in the upper chamber (gasification chamber) during operation.

(2) The fire stays lit in my unit when idling in at least two manners. The air supply for the secondary air is in a direct line to the jets for the secodary air in the nozzle and this feeds the coals a minor amount of air and secondly boiler control module supplies a short burst of air via the blower to purge the gasses that build up in the upper chamber every few minutes. The purging blast helps to keep the coals active until there is a call for heat because the water temp has dropped below the set temperature.

(3)The EKO is a downdraft gasifier. That is.. the heated gasses have to go down through the nozzle down into the secondary combustion chamber to achieve the heat exchanger in the boiler and flow upward to escape from the boiler. A worthy note in this is if you have a very strong draft it can aid in the gasses escaping and prolonging the burn shutdown time after the boiler is up to temp. The downward direction at idle creates a pressure the gasses have to overcome before they can escape and there is usually only a little smoke visible while idling (there is no or next to no smoke once the wood has become charcoal. There is a bypass damper at the back of the upper chamber that if left open will pour out smoke and easily over heat the boiler if there is enough wood in the unit. The secondary burn process is easily equivalent to or better than a cat and as such there is no catalytic converter in the boiler.

It would be interesting to see your design as I have been contemplating and mulling design for building an outdoor gasser. Since I have a gasser already I can duplicate many of the physical attributes as I have a working model to base the design on. As was stated to me by a person of respect in this forum allow a large range of parameters for adjusting the primary, secondary and blower settings. Best to you... Cave2k

Along these same lines of restricted budget demands, and need for efficient wood heat, I have been considering a similar design thought. This involves the construction of a simple gasifier burner that will mate to an existing oil-fired boiler.

I believe the pressure / water side of the overall heater is the more difficult to fabricate and more likely to require complex welding and fab skills and tools. Therefore, finding a cheap (unwanted) boiler and removing the oil burner facilitates the heat-exchanger side of the project. I would then work on the design of a firebox, much the same as an EKO but scaled to suit the used boiler BTU rating. The burner/firebox would be ducted to the re-cycled boiler opening where the oil burner was mounted and close-coupled to reduce heat loss, but allow access to the boiler for cleaning.

I could foresee a by-pass duct from the burner output to the exhaust flue to facilitate light-up and handling over-temp conditions, and an induced-draft fan in the exhaust flue to help flow through the boiler. It will likely be naturally-aspirated primary and secondary air, for simplicity. I will also consider using existing replacement refractory segments from various popular boilers in the burner assembly. The trick will be to make it simple, affordable, and do-able for the average handy-person.

Forum folks, your thoughts?

Cheers, Jim

thecontrolguy said:

Along these same lines of restricted budget demands, and need for efficient wood heat, I have been considering a similar design thought. This involves the construction of a simple gasifier burner that will mate to an existing oil-fired boiler.

I believe the pressure / water side of the overall heater is the more difficult to fabricate and more likely to require complex welding and fab skills and tools. Therefore, finding a cheap (unwanted) boiler and removing the oil burner facilitates the heat-exchanger side of the project. I would then work on the design of a firebox, much the same as an EKO but scaled to suit the used boiler BTU rating. The burner/firebox would be ducted to the re-cycled boiler opening where the oil burner was mounted and close-coupled to reduce heat loss, but allow access to the boiler for cleaning.

I could foresee a by-pass duct from the burner output to the exhaust flue to facilitate light-up and handling over-temp conditions, and an induced-draft fan in the exhaust flue to help flow through the boiler. It will likely be naturally-aspirated primary and secondary air, for simplicity. I will also consider using existing replacement refractory segments from various popular boilers in the burner assembly. The trick will be to make it simple, affordable, and do-able for the average handy-person.

Forum folks, your thoughts?

Cheers, Jim

Click to expand...

When your induced draft fan draws there is a lot of stuff that needs to happen in proper proportions. The wood gas needs to be produced in a proper quantity by carefull air control, it is drawn through a nozzle that has holes(the nozzle does not just have the large center hole, it has side holes for heated air) in it for the heated air mix & you need adjustment for these 2 air supplies. Thats the hard part, the burn chamber & exchanger are pretty straightworward although they need to be sized accurately, Randy

Heya Singed; I was thinking more of over-firing with excess air into the primary chamber, then through a ceramic nozzle (like an EKO) and then an enlarged secondary re-burn chamber for the magical combustion completion. I think the Garn more-or-less gets away with no secondary-air control, only I am talking down-draft into a box, rather than a tube. Is there a reasonably simple explanation that requires secondary air be injectedinto the nozzle / secondary chamber or why can't the excess primary air also be the secondary air? I realize this is NOT the exact definition of pyrolysis but I am trying to honor the KISS principles and home-make-able notions that are driving this idea. Also, without on-board Lambda control and variable fuel properties, I'd rather err on the excess-air, clean hot burn.

Sorry to maybe be hi-jacking this thread into something else ..

[/quote] When your induced draft fan draws there is a lot of stuff that needs to happen in proper proportions. The wood gas needs to be produced in a proper quantity by carefull air control, it is drawn through a nozzle that has holes(the nozzle does not just have the large center hole, it has side holes for heated air) in it for the heated air mix & you need adjustment for these 2 air supplies. Thats the hard part, the burn chamber & exchanger are pretty straightworward although they need to be sized accurately, Randy[/quote]

thecontrolguy said:

Heya Singed; I was thinking more of over-firing with excess air into the primary chamber, then through a ceramic nozzle (like an EKO) and then an enlarged secondary re-burn chamber for the magical combustion completion. I think the Garn more-or-less gets away with no secondary-air control, only I am talking down-draft into a box, rather than a tube. Is there a reasonably simple explanation that requires secondary air be injectedinto the nozzle / secondary chamber or why can't the excess primary air also be the secondary air? I realize this is NOT the exact definition of pyrolysis but I am trying to honor the KISS principles and home-make-able notions that are driving this idea. Also, without on-board Lambda control and variable fuel properties, I'd rather err on the excess-air, clean hot burn.

Sorry to maybe be hi-jacking this thread into something else ..

Click to expand...

When your induced draft fan draws there is a lot of stuff that needs to happen in proper proportions. The wood gas needs to be produced in a proper quantity by carefull air control, it is drawn through a nozzle that has holes(the nozzle does not just have the large center hole, it has side holes for heated air) in it for the heated air mix & you need adjustment for these 2 air supplies. Thats the hard part, the burn chamber & exchanger are pretty straightworward although they need to be sized accurately, Randy[/quote][/quote] When my Atmos overfires it chatters & doesn't sound good. Others have huffing problems, I did also when using paper & cardboard when starting. I'd think you would be chasing your tail here as instead of leaning the mixture you would probably produce more gas. The primary air needs to be sized to the nozzle opening I believe. I believe the reason for the secondary(nozzle) air is that this is a rich poorly combustible mix as is & needs to be brought in line with a more (stochiometric I believe the word is) mixture. In Europe these need to meet very strict emissions standards. You can't do this by just pulling the smoke through a solid center hole nozzle as you are thinking. Thats my take on it anyways, Randy

ControlGuy, The mixture could conceivably be ignited in the secondary chamber with a glowing metal target & some air(oxygen). What I believe you would get though is a lazy rolling flame that wouldn't burn that clean. You want to introduce oxygen to the mix at its greatest temperature & thats as it just passes through the coal bed. That mixture at probably about 1400 degrees "wants" to light. The further it would drop down the colder the mixture would get. Sending unburned fuel up the chimney ruins the effeciency, even if emissions aren't a concern, Randy

Cowlick Jim

That pretty closely describes my boiler, except mine drafts out the side of the bottom of the primary chamber, has a combustion tunnel instead of nozzle, and uses a salvaged gas boiler core instead of oil, and mine is probably much more crude than most people would consider putting indoors. I have a draft inducer, but originally it worked OK with natural draft, probably plugged because of wet/dirty wood.

The biggest drawback is the cast iron sectional "pin" boiler's tendency to plug up with fly ash and gunk. It hoses out fairly easily and I may keep using this setup with some modifications and a floor drain, but now it's a PITA to clean.

As it currently functions the side outlet of the primary combustion chamber leaves a bed of coals that have to be pushed out the side to burn, or left to cool with the chimney drafting for hours, or risk CO if the damper is closed.

It will "huff" if loaded with too much small and/or volatile wood, especially when it is due for a cleaning. It is probably more "particular" to operate than more advanced units, and the efficiency is probably less as well. This unit does NOT idle.

The main advantage is the cost was a fraction of a new or used wood boiler, gassifier, or OWB. Total construction was simpler than the typical installation I see on here. For the most part, it burns clean, from sawdust to tires! no smoke, no smell and ash that routinely "fuses"

It's not hard to burn wood cleanly and efficiently without precise control and nozzles, just look at the garn, you just can't shut it off like you can with a gassifier, but then you're not supposed to so what's the point?

Ben;

That pretty closely describes my boiler, except mine drafts out the side of the bottom of the primary chamber, has a combustion tunnel instead of nozzle, and uses a salvaged gas boiler core instead of oil, and mine is probably much more crude than most people would consider putting indoors. I have a draft inducer, but originally it worked OK with natural draft, probably plugged because of wet/dirty wood. The biggest drawback is the cast iron sectional "pin" boiler's tendency to plug up with fly ash and gunk. It hoses out fairly easily and I may keep using this setup with some modifications and a floor drain, but now it's a PITA to clean.

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Cool!

Thought about the cast-iron sectional, and rejected it for that reason. (cleaning the dirt out) I am leaning towards a fire-tube or water-tube boiler but will likely have to accept what is available. I was also planning a combustion 'tunnel' as it seems the most structurally sound with regards to the thermal stresses and perhaps cleaning abuse. The 'rectangular' part mentioned was the transition from the nozzle to the tunnel that will likely be cast refractory slabs or stacked refractory bricks. I am hoping to wrap it all in high-temp batt insulation and then the outside skin that I'm hoping to grab from another reject boiler of close dimensions. I also considered a tube shape secondary burn area for the potential of introducing the gasses in such a way (offset) that it 'swirls' - promoting mixing and better combustion. If I go with secondary air, it will get introduced at the start of this tunnel and be drawn by the draft in that space.

As it currently functions the side outlet of the primary combustion chamber leaves a bed of coals that have to be pushed out the side to burn, or left to cool with the chimney drafting for hours, or risk CO if the damper is closed.

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My assumption was that the rectangular nozzle of the existing commercial gasifier boilers was shaped so that not only the gases could be metered through, but to also expedite pass-through of the burned ash. The tunnel then would be accessible for cleaning.

It will "huff" if loaded with too much small and/or volatile wood, especially when it is due for a cleaning. It is probably more "particular" to operate than more advanced units, and the efficiency is probably less as well. This unit does NOT idle.

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I have considered this from many other posts and feel that at the point of 'huffing' you are exceeding the draft capabilities of the I.D. fan (or natural draft) and producing more gas than it can handle. My immediate answer was a 3-speed furnace fan motor driving the ID fan and a simple liquid manometer tube to see if the combustion chamber and secondary burn chamber were being held in negative draft by the ID fan. If not, next faster speed, etc. Also, an unusually high temporary draft would be good to ease or negate smoke getting out when loading.

The main advantage is the cost was a fraction of a new or used wood boiler, gassifier, or OWB. Total construction was simpler than the typical installation I see on here. For the most part, it burns clean, from sawdust to tires! no smoke, no smell and ash that routinely "fuses"

Click to expand...

Woohoo! Fractions of too much $$$ sounds good to me and is what is primarily driving this fact-finding mission. I want something that I can build, that burns cleanly, more or less, and produces the heat that we need. AND, if I can boast that it was cluged together with used boiler bits, and parts from other (much more expensive) boilers, all the better. Do you have pictures that you'd be willing to share? I am particularily interested in construction pics, but anything wuold be appreciated.

It's not hard to burn wood cleanly and efficiently without precise control and nozzles, just look at the garn, you just can't shut it off like you can with a gassifier, but then you're not supposed to so what's the point?

Click to expand...

AMEN

This guy sells blueprints to make the home made boiler in this video: http://www.youtube.com/user/horobey

FYI - I don't know this person, buyer beware... I did not buy anything but the fellow did answer an email I sent him. You need an English converter in your email program because the person does not speak or write in English.

website for prints: www.myhouse.name/a.html

Jim

Huffing is absolutely the result of too much gas and not enough draft. I burned lots of old scrap lumber without problems, but when the core got plugged up it would puff a little with too many small splits and puff really bad with what would have worked fine at the start of the winter with a clean boiler. I bought a "Dwyer Magnehelic" guage off ebay (under $20) that reads up to .25" water, with a foot of tubing and some strategically placed 1/8" holes, I can check the pressure anywhere in the system in a few seconds. I had to clean the boiler once late last winter, then cleaned it again in the spring, started this winter clean, and had to clean it again a few weeks ago, but definitely should have cleaned it midseason, I just forgot what it had done last winter.

I believe that better control of primary vs secondary air could be part of the huffing solution, in case of huffing reduce primary and increase secondary air? but my system does not have that kind of control.

My issue with not being able to burn completely out is caused by using a propane tank as the "fuel hopper", the bottom is dished. I figured that it would just fill up with ash and the coals would mostly fall out the side and down the tunnel, but when I drop in a large piece of wood, it buries itself in the coals and ashes and I get fresh hot coals remaining at the end of each burn. As there's a lot of masonry that's heated up I'd like to be able to close off the heat loss up the chimney immediately after the fire goes from roaring to completely out.

Mine is not insulated at all, aside from some masonry over the firebrick. The only part that gets too hot to touch is the former propane tank primary combustion chamber and the cast iron access door to the secondary combustion chamber. The propane could be jacketed with water but mine is a open system shared with open drainback solar, hence the cast iron. If I use this boiler again next winter it will probably be modified to run only on sawdust, eliminating the burn hazard.

Google

Design, Construction and Performance of Stick-Wood Fired Furnace

and you'll find the research paper that documents the design genesis of pretty much all of the modern efficient wood boilers--

pybyr said:

Google

Design, Construction and Performance of Stick-Wood Fired Furnace

and you'll find the research paper that documents the design genesis of pretty much all of the modern efficient wood boilers--

Click to expand...

It's right here:

http://hotandcold.tv/wood furnace.html

Be sure to use the whole line of the link!

Thanks all, for the info, and discussion.

Jim