Colby build your self a woodgas camp stove. just look one up on youtube and you could have one built in a half hour. This is a great experiment to learn from. If you try and boil water or cook something the tars it makes will reveal itself on the pan. Run different fuels in this stove and take note how much char is left after each burn. The amount of char in your process is critical for the most opportunity for reactions to take place. I encourage you to do your experiments we all still have much to learn. I agree with the above you can not filter tar, if tar is present in a filter and not any where else its not because the filter is actually filtering it, it is because this is where the tar is hitting its due point. The only way to filter tar is by condensing and it does not readily drop like moisture will. So building a gasifier to run in the correct parameters that will not create tars is your best defense. This is where sizing the reactor to what you are running is important, just because your flare running off your blower looks a certain way an engine will pull much harder getting the gasifier to much higher operating parameters. Good luch with your experiments, I look forward to seeing what you come up with.
Colby,
I am a Controls Engineer with a BSEE, and share your ‘holy grail’ desire for a fully automated gasification system. I built my first gasifier a little over 5 years ago, and have yet to reach my goal. I started with free mulch for fuel and learned a valuable lesson regarding bridging. Mulch, with all of its sharp edges, has a high angle of repose. This is exaggerated in the steamy atmosphere found in a gasifier, especially in the hopper/monorator. Here’s the result: https://lh4.googleusercontent.com/-2M4VL_VKoH4/SoYX58fq27I/AAAAAAAAAGY/LGX9Yh8ocAM/s800/%5BUNSET%5D.jpg
Many have tried to solve bridging with agitation, vibration, plungers, etc. with varying degrees of success. This was the first of many hurdles I encountered. My point? Building a gasifier is easy. Getting it to perform to your expectations is not. A popular statement here on DOW that carries much truth is that building a working gasification system is only 25% of the process. Learning to operate your system reliably and consistently is the other 75%. Prepare yourself for the long, frustrating, satisfying, disappointing, promising road ahead! I look forward to following your progress!
Searching through old folders for the pic in the post above has brought back some memories, good and bad! Another lesson I learned when using mulch: clinkering. The ratio of surface area to volume of mulch is much higher than chunked fuel, theoretically resulting in higher ash generation. This ash, when superheated, melts into a glasslike material causing it to stick together. As these globs of melted ash work their way down towards the restriction, they cool as a result of the endothermic nature of pyrolysis. The result is clinkers.
As the other posters mentioned above, the occurrence of tar should be prevented to avoid the greatest challenge.
But as you stated to find fun in experimenting, its maybe also a good experience to actually taking the challenge , learning by doing… not learning by talking about it…
One experiment i once performed was drying woodchips in a micro wave… try to clean that out afterwards… 
The articles you did read are 1: sewage sludge - tar removal… 2: low temperature tar removal…
I think both off them are to far away from your plan to use mulch as fuel.
As you will notice, by doing the tests, any different fuel has its specific contents - reactions towards gasifying temperatures.
I for myself, to avoid the tar and moister challenge, i first convert the green waste into charcoal, by applying external heat.
( same as your idea to produce gas )
This process teaches me a lot of the behavior of the feedstock and the relating issue’s.
The above posters are all experienced “raw wood users” and learning by doing.
Its their combined knowledge that basically paves the road for you and me, to be able to create solutions…
If mulch is your goal to use it as fuel ?, go for it … try , experiment, share your results … we all will love your successes.
Nobody is going to laugh with any failure or set back.
Main point is; not give up, focus , ask advice, take advice, testing and enjoy…
Welcome in the world of real life challenges
I will definitely start with a wood stove. But I still think there are ways to filter the tars out of the gas. The paper I linked to shows a method of bubbling the gasses up through an oil that collects the tar in it. I will also try wood chips, maybe some electrostatic filtering… I don’t know I will research cleanable filters.
My thinking is that by controlling the flow of wood gas out of the gasifier with a constant flow rate valve, you can keep the operating conditions fairly constant, so that engine draw does not affect the amount of wood you use. Basically I want to add a constant flow rate of wood gas to my engine, and pick up the difference with gasoline. I think this is one thing that will make it easier to tune.
Also, you said you can condense tars right? Does that mean you could possibly just cool the gas way down to turn it liquid or does it not work like that? I have heard that the non-condensable tars are acceptable to run in an engine. Is this true?
The stuff about bridging is interesting. What exactly is it and why is it a problem? Also, would this be eliminated when you use a heated chamber full of mulch vs a pile of mulch being burned from the middle? Are the “clinkers” also a problem or can they be removed easily?
This is the link to the referred book i mentioned in an earlier posting
http://driveonwood.com/sites/default/files/pdf/A_Treatise_on_Producer_gas_and_Gas_Produ.pdf
what also might be interesting for you to read about is anything you can find on 2 stage gasification.
Hi Colby
I have tried the oil bath filter and a water bubbler as well as a shower scrubber and a venture scrubber, none of them will be affective against TAR. If you make tar you are going to shorten your engine life considerably!
Just for a test take a pile of mulch and dig away at the bottom, this will give you a good indication of the slip angle of the mulch, where as a dry wood fuel ranging in size from 3/4 in 20 mm to 4in 100mm will have a slip angle of about 45deg.
Fuel smaller than that will constipated your gasifier!
Thanks Patrick
I hope this image shows up. It is TAR. Tar does NOT drain out. When it condenses, it STICKS! This picture shows one of my many mistakes. Getting the non-condensed tar in that’s in the fuel stream to the place where you want to filter it is a huge job in itself.
Think Chimney fire.
Pete Stanaitis
Hello Colby,
Welcome to the site. I’ve been working on gasifiers for 2 1/2 years and have a unit that produces a very good gas. This after quite a few modifications. It is an imbert design. I’ve spent days reading stuff, maybe weeks. One of the best all around teaching tutorials is on the All Power Labs site by Jim Mason. I’ve posted a link for part 4, but when you get to the site start with the part 1 of 10 series. It’s long but very good and long on relevant info. He gives good info on the entire process including tars. Check out my posts in the Small Engine User’s Corner here under Forum.for my fails and wins. I’m presently building a version of the monorator hopper you mention. Mr. Teslonian’s adventures leave a lot to be desired. Your best source of info is right here on this site, and well worth the membership as it will save you both time and money.
Also check out my FEMA vid, fast forward to 7 min mark for tars sizzling in the flare tube. That stuff cannot be filtered out and will ruin an engine, seizes valves up. I never ran an engine on it because I caught up on my reading by the time I got this built and realized I didn’t want to sacrifice an engine. I moved on to the fluidyne and then my present build.
Pepe
Avoid making tar. It is not easy to filter out.
http://driveonwood.com/sites/default/files/100_1052.JPG
In response to Koen’s post again, I noticed you said that you turn the green waste into charcoal? Would that work with mulch? If so I could convert the mulch to charcoal, then use that in the gasifier and produce clean gas. Can you give me some more details about the process of making charcoal?
Thanks
Just found an awesome video on making charcoal here:
Would this charcoal produce tars at all?
I have some movies on youtube. http://www.youtube.com/channel/UCjxz4pZv01dW7Bxe28-xArw
The mulch is worth to try it.
The briquettes shown in the movie you linked to are an higher content of moist and volatiles.
The links on my website www.renewableenergythailand.com brings you to MITdlab and their charcoal project, they would like to copy our idea’s.
The hotter you cook charcoal, the better quality you’l get
Some very useful research would be to watch the videos starting with this one Gasification 101 - Part 1 - YouTube
The title is Gasification 101 and it will give you a very good insight into how and why gasification works, it will also help you understand what does not work.
A big problem you will have with mulch is a lot of fine pieces that will cause the gasifierers charcoal bed to pack tight and not allow gas to flow. At best it will not leave enough space in the charcoal for the gas to spend sufficient time to crack the tar.
If you can at all avoid making charcoal you will save a lot of energy. All that gets burned off can be put to good use in your engine and will give you more power than a charcoal only system. Charcoal is great for simplicity, however a wood gasifier will save a lot of work making charcoal and you will travel much further with more power running on wood.
Sorry, but…
I agree with using mulch as is, that it would cause “difficulty’s”
But i sincerely disagree with your statement that charcoal only, is a less power full system.
“au contraire” as they used to say in France.
With the same amount of weight, you travel almost double the distance, with less difficulty’s on the road. Thats my experience, mile after mile…
Little edit:
I prefer someone making charcoal from green wastes ( as mulch) and using it in a charcoal gasifier… better then not using the mulch.
Next step can be : using the vapors from the charcoaling process to be lead trough the charcoal gasifier… ( two steps , but starting with one )
Selective using the vapors increases the power efficiency from the end product
"Next step can be : using the vapors from the charcoaling process to be lead trough the charcoal gasifier… " I think you are describing what a wood gasifier does.
Awesome! This is exactly what I am looking for, a way to use mulch as fuel. Again, I am not really concerned with efficiency, so this seems perfect for me. All I have to do is cook up a batch of charcoal, and I have fuel for a long time. Could you point me to some plans for a preferably inexpensive charcoal gasifier? What plans did you use if any?
Oh and also, is there a way to use the gas coming off of the charcoal being made to fuel the heating of the charcoal itself? In your video I see you light a fire underneath the barrels full of green waste. Basically couldn’t you redirect the tube coming from the barrel into the fire underneath the barrel? That way you could use less wood to heat the barrels. I want to use the least dry wood I can.
Edit: Ahh I think that’s what you meant by the next step. I am definitely going to try this.
Yes, Those are next steps … and yes Gary, same as a wood gasifier does but hopefully easier to control 
The issue i have with wood-gas from “raw” fuel is, the non constant quality during 1 batch run.
The moister plays a far to important role and is not so easy to control the way as it goes now…
( this goes for the automotive gasifier, not for stationary )
I based my design on Gary Gilmore’s simple fire…
You’ll find most of my work , self explained , in this section…
and about numbers with gas contents;
and about the charcoal making;
Make sure you read the topic of Gary Gilmore;