Have any one know about "dual fired gasifier" that have low tar content< 50 mg / nm3?

Hello everyone !
I am new to gasifier. and new to this forum too.
My project is to made 20kW electric generator from wood chips. and I live off grid. So this sytem would require to stand by or run everyday.
I read a lot about gasifier I think the most problem in gasifier to IC engine is tar.
I am finding the way to minimize it as much as possible but their have multiple solution.
So I came across to this paper it claim to minimize tar to < 50 mg per nm3. with 1 dry filter.
sound cool !!
Have any one know or have drawing about this gasifier ?
“viking gasifier” is seem good too but it require a lot of control.
dual fired gasifier

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welcome to the forum c
To be short, there is only one way to deal with tar in a raw wood gasifier
Tar in no way can be actually filtered out, it will clog any filter we know of. If not condensed out and gas stream temps stay high, it will pass right through a filter and keep on going to a place we dont want it to be ie the engine.
That being said as far as users on this forum go we have 2 ways to deal with tar that will always work
1 The hot lobe inside the gasifier must remain at high enough temperatures throughout operation to never let tar pass by, but instead be thermally cracked into more gasses. This is very simple in theory, but in practice takes a skilled hand at operating the gasifier design you choose. Each gasifier is a female, they behave in the way they see fit regardless of how we may want them to, we are just along for the ride, and try to coax it in the direction we want to head.
Now keeping those temps up is a balancing act dependent on several variables, being size of wood feed stock such as
Too small of wood such as chips will cause a breathing restriction, not allowing air to penetrate into the hot zone and keep temps up, to stoke the fire per say
Too large of wood chunks will allow to much oxygen to penetrate the hot zone, which dilutes the gasses and potentially puts the gasifier into over pull mode and burns up the gasses

Also the load asked of the gasifier must be adequate to keep the right amount of oxygen flowing through the hot zone,
To little of a load and fire will not remain hot enough allowing tar to form and pass through the too cold of glowing charcoal
To MUCH load will instead put the gasifier into over heat mode which will either burn up all the produced gases and largely be useless, or conversly over heat the base steel materials it is made off and we can have a full blown melt down, destroying the gasifier

2 The other way we deal with tar, is to never give it a chance to enter the gasifier in the first place. Get rid of the tars FIRST by converting the feed stock to charcoal and baking out all the impurities that WOULD form tar in the gasifier. this method has been proven time and time again to perform VERY well, but then adds in the additional step of making charcoal before hand which can be a process unavailable for some who cannot release smoky emissions in their area due to laws or such. Then once baked must be either sifted or crushed and sorted to engine grade charcoal size. Many here have purpose built machines to do this for them it can be a dusty nasty business at first coating everything black with charcoal dust. but there are ways around that as well.
either raw wood or charcoal each comes with its own challenges, some designs will ease those growing pains, but non are really a walk away system.

building the gasifier is 25% ,
the other 75% is learning how to operate it

that being said there are industrial applications for biomass gasifiers that are much computer controlled and cost a whole pile of money
there are also small applications such as thrive offgrid, the owner of which is @Matt that makes small engine gasifiers and operate very well and are commercially sold to offgrid folks

Enjoy the forum, there is several lifetimes of woodgas and chargas knowledge here to be had, lots and lots of reading from every day users of both. Dont ever be afraid to ask a question, everyone here wants to see you succeed


Welcome CK,

Most of the folks here using wood or charcoal gasifiers for generators are aiming a little smaller than your target. 5k-8k watts is common. People that are gasifying vehicles are using far bigger engines so keep that in mind.

Charcoal gasification will leave you with far less tar in the fuel gas than wood, that’s just a fact. And the bigger the engine the bigger the worry about taring up an engine and ruining it. Charcoal also takes extra processing, which can be impractical depending on how much you are running the engine.

In terms of off-grid power generation, I would encourage you to consider a solar system along side any wood or charcoal fueled generator. Solar panels, together with batteries, can really reduce the burden on the generator. The solar has no moving parts and runs without any real operator attention, at least compared to a gasifier. You will have far fewer hours on your engine each year and can avoid sizing the generator to your peak starting loads. Instead a smaller generator can pick up the slack when solar output and battery charge is low. In the summer you may not have to touch the generator at all. That’s a nice feature.


Thank you for your explaination and your experience.
from my point of view create charcoal before gasification is waste some energy of biomass and release a lot of smoke.
I think if we put temp meter in middle of hot zone we can provide air volume more corectly is this a way to go ?


chacoal make is hard from my area.
Solar with battery is good idea to combo with gasification.
right now I aim to build gasification and buy solar cell.

Nope you dont lose anything. You just lose the energy in a different way than processing wood for gasification and the internal losses inside the reactor. A wood gasifier just loses the energy in a more discreet way.

Try running a wood chipper with a gasifier. Guess what? You are burning wood to produce the fuel to run the chipper. It will eat just as much if not more than a good charcoaling process.


As my understanding is
dried wood energy =about 17mJ/kg
if we made charcoal from biomass
charcoal energy about 25 mJ/kg
but we lose 70 % mass
That mean if we have 1 kg dried wood
we get 30 % charcoal yield = 0.33 kg of bio char
0.33 kg of bio char is about 8.25 mJ/ kg
if I understand correct if we feed chacoal instead of dried wood we only have about half of dried wood energy.

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Need to factor your energy to produce the raw plus the losses in a wood gasifier reactor typically 30% your not gaining anything.

Charcoal you add the water drip will add 10 to 20% back into the process.

A good charcoaling process can yield much better than 30%.

charcoal by weight is nearly twice as energy dense as typical dried wood.

I spent 8 years with this same thinking and gobbs of money developing raw wood gasifiers and built well over 300 machines. Then one day I finally tried charcoal and it took less than a month to switch. Producing dry fuel for daily off grid is not practical or viable. Charcoal processing is much faster plus they work without all the head aches.


A good charcoaling process can yield much better than 30%.

  • Do you have method name ? I will dig deep to the process
    Charcoal you add the water drip will add 10 to 20% back into the process.
  • Is this same as steam injection or something ?

This machine can produce a 50% yield by volume, if feed stock is dry and sized correctly. It can produce a days worth of fuel in an hours time and that fuel is ready to run. That wont happen with raw wood. Build a charcoal unit and try it first. They are stupid easy to make and the benefits far out way any advantage you may think your are getting with a raw wood gasifier.

You dont have to waste anything producing charcoal. That is a choice. Nothing stopping you from using that waste energy for something. Instead of putting energy and effort into building a tar free gasifier that will self sustain. We are way better off developing better charcoaling methods that use all the energy. You can use the heat energy, you can gasify the fuel and store that gas for other applications. Use engine heat to pre dry fuel prior to charcoaling. etc etc.


Yes the water injection cools the nozzle and converts to steam then converts to H2 and CO.


Listen to what @Matt says. I built a charcoal kiln by his design and it is a piece of cake to run and produces a lot of charcoal with VERY little smoke (except at startup). I am building a modified Wayne Kieth gasifier for my 97 Dakota pickup to run on charcoal. This way if I like it and it works well I can leave it that way, but I can change it by adding the WK hopper ect. to run on wood chunks if I want.

Garry C.


You are think the same as me Garry. I like the many nozzle firetube with preheating the incoming air to the nozzles. Building with barrels is the way to go for the diy ers. For DOW.


Hello, CK999!

You found a good description of a two-circuit wood gasifier. But maybe it’s worth putting together something simpler to begin with, with one contour, according to known dimensions? Or the same charcoal?

An electric generator that works reliably 365 days a year without stopping is a very non–trivial task. One lubrication of bearings is worth a lot! But something else needs to be thought up with the replacement of engine oil and filters, as well as with the disposal or cleaning of already used engine oil. But if you need 20 kW of electricity, it means that you have some definite plans for using it profitably in such volumes.

I’m afraid to imagine a solar system with such power. The dimensions, the number of components, the amount of very toxic garbage that had to be produced when it was created in factories, the size of the grave pit that will have to be dug on its own land for its burial after its inevitable failure. I try not to think about its possible cost at all…

With respect. Marat Lysenko.


Will try that for sure.
the video is very infromative


Does chacoal gasifier for your pickup need any filter ?
and is it practical to use it daily ?

Hello @Marat_Lysenko
I dont have any drawing yet. Maybe need to create one but I am considering 2 system

  1. is making chacoal first and gasification it. this method provide lower tar and less complicate system.
  2. making low tar gasifier from dried wood.

it is like dual fire gasifier that I have mention above. top one is pyrolysis. bottom is chacoal gasifier.
It is actually chacoal gasifier with chacoal maker on top of it. just to make it has more efficient.
I agree with maintainance cost of engine. but it quite lower from solar cell panel and years of payback time. Also that we need to buy everything.
solar cell take a lot of space we cant rely on 1 system. if it rainny solar cell cant provide electricity enought for 2-3 days even have battery.

You are not the first to think or even attempt this. Im not going to say it cant be done but not without a ton of complexity and it will take a lot of time to develop.

All you have to do is remove the grate of an Imbert gasifier and add a nozzle into the bottom to oxidize the charcoal. This does work and I have done it. However the challenge is balancing both processes that is easier said than done. Me personally Id like to see you build this. I simply did not have time or the money to further develop and just never got back to it. As I have shifted my development to something I think will be better and more viable without the complexity of this combined system.

This system is made up of both a wood gasifier and a charcoal gasifier. However they are two stand alone system. The wood gasifier makes fuel for the charcoal gasifier. The gas produced from the raw wood is not used for engine fuel. It is instead used to supply gas direct to the home to run all gas appliances. This is more efficient as you do not have the engine losses converting the gas to electric energy. Gas appliances are a direct energy conversion and these gas appliances then reduce your electric power consumption especially since these are typical high energy consumption devices. This is your water heater, stove/oven, clothes dryer, evaporative refrigeration and home heating. In the end the result is the same your using a different fuel for these appliances instead of electric power and without tar issues in your engine. The gas produced from the wood gasifier is temporarily stored in a gasometer (very important>>>>> under POSITIVE presure. Under positive presure this raises the due point while in the cooling stage to drop the tar / soots and moisture out. Then the gas can be supplied with simple inline filtering. All while its doing this, the gasifier is optimized to produce a daily amount of charcoal for engine fuel. You are typically not going to need to run the power generator everyday. The idea is to accumulate this engine fuel over time for reserve. You will more charcoal than you will know what to do with and it basically comes free of any labor.

You can read more about this here. We are currently developing this system now. https://www.thriveoffgrid.net/forum/charcoal-production/versifire-this-will-change-the-game?origin=notification


Another big point is the wood gasifier in my system is not small it is the size of a truck gasifier. So chunked fuels can be used. Plus gas quality is not a concern as it is scrubbed in the gasometer. So less energy and labor intensive fuel to produce and higher moisture levels are less of an issue.


You have made no mention of what kinds of wood you have available CK. There is no way to discuss design without knowing the type of fuel source, hard, soft, ect. Keeping an engine large enough to run a 20kw system on a daily basis fueled with any type of feed stock is quite a job and very few designs are load up the hopper and walk away for the rest of the day. I haven’t looked that closely at Matt’s Versifire system, so perhaps that would lighten the fuel processing time. Rather than one large generator I think you would be better off to research how MattR runs his shop, using multiple gen sets as demand requires. On a regular basis running a large generator just wastes a lot of excess power unless you have a large battery bank to store it in. I have no experience with a Gasometer and though it is intriguing it seems it would require a lot of retrofitted infrastructure.