Over engineering filtration

Indulge me for a second while I ramble into my 3:00 a.m. sleep deprived insanity.

It’s been hitting me in the back of my skull for the better part of the last year of the importance of wood gas filtration. And I’ve reached the conclusion that I am going to design a complete Overkill and over engineered filtration system.

The general concept that I’ve been mulling about starts with combining medium filters such as straw or sawdust, multiple cyclone filters that are ran in a sequence, and a water filter of some sort. The ultimate goal of course is to have as clean of a gas as possible with the desired result being a nice clean blue flame. Once you obtained a clean blue flame devoid of contaminants, the applications that you can use that gas for expands greatly.

Of course this would make it necessary for this object to be module, and likely not be terrible mobile because the bulkiness would almost demand it to be a stationary unit. But I like the idea of trying to make a filtering system that is far more than what would be necessary to the point that I would almost not need to consider what types of wood or biomass it is that I’m cooking.

Has a slightly unintentional consequence of this design I’m trying to figure out in what order I can place the filters in order to try saving the tar for later use. I know that it may even seem unnecessary but I am almost ocd in my desire for efficiency, and I find it a shame to let what could be used as an industrial adhesive go to waste.

But, that’s just my thought for the morning. Happy to hear anyone else’s take on it


View from a newbie: I would be a little concerned about causing too much drag on the system with many things creating ’obsticles’ for the gas for the breathability on the system.
And as it is not proven (what I know) I believe obsticles causes CO to convert back to carbon as soot (seen in the intakes probably caused by the throttlebody).

Note that this is my view and based only from what I have learned here as I still have to build my own gasifier (changes on the Volvo 850 will come from what I have learned in the last month)

I am not saying don’t do it, just to be aware of it :blush:


Even thugh many have prooven soot is harmess to the motor, l still strongly advocate clean gas. The other things run better, valves, throtlebodys, and not to mention sensors on newer engines! And it can be done for sure.

About tar, a good gasifier will never make even a trace of it for you to collect from any kind of filter. You can only collect it from hopper gases.

You actualy dont need to complicate things that much. No need to cause aditional drag on the sistem and run in to space/weight problems. One good big sack filter is enaugh to do it all. And you actualy dont want the gas pre cleaned with cyclones and hay filters, as you want to have some corse particules to form a nice loose cake on filter sacks.

Only demand here is the gas in this filter MUST be dry. Any moisture will just wash the soot back out of the sack in the gas stream and form a hard to breath trugh cake.
Couple of ways to atack this, one is to filter the gas while its not quite cooled yet. This will require some ingenewity as the temp must be kept at above boiling point but not too hot to burn the sacks.
Other is to not make moisture in the first place. A good quality and size gasifier is a must, for good conversion of H2O to woodgas. Then the feedstock, dry as possible, and a good hopper steam condenser. That all shuld make dry enaugh gas and also a lot of tar you drsire.
Third is to run a mixture of wood and charcoal, aka rocket fuel. This will take care of the water for you, make wery rich gas but you will not get tar.


Yes, yes, I know that not many people believe this, but the Swedish state’s machine testing did these tests.
Might be of interest to someone anyway.


I belive those numbers 100% Jan.


What others said.
I trust the fabric filtration, hot, directly after gasifier, with enough filter area (no problem in a stationary setup) this works very well.
Look in my “woodrunner chevy” thread, it even surprises me how well it works, altought being a more “sensitive” filtering system (over temperatures, moisture, tar) this has worked perfectly well for me, and: i am lazy and careless, not following the rules of taking care of a hot fabric filter, and it works.
For a stationary setup i believe a hot-filter should have a pre-cooler, with possibility to by-pass the cooler/ only using it when temperatures get to high.
Some ideas of hot fabric filters:
Nomex cloth: temperature in filter 260°c 500°f, out of filter 100°c 212°f to keep temperature over dew point, to avoid moisture in filter.
Fibre glass fabric/welding blankets: 450°c 840°f out: over 100/212
Stainless steel mesh: 800°c 1400°f out: over 100/212.
This can be followed by cooler/ water separator and wet foam filter, or reheater and warm/dry filter, paper filter/ vacuum cleaner bag. But not necessary, a fine mesh acting as a safety filter is a good idea though.


Here is VesaM’s decades long evoked down maintenece points for a HOT membrane filtering system.

The WK’s as Wayne makes and operates them, is combination of first hot coarse separation; then still hot cooling to warm long pathways cooling separation; then cooled gas impingement filtering. He accepts soots building up in his intakes and has learned to in-place periodically burn them out.
He has his own video sets up showing his downstream mantneces. And doing his intake burn out restorations. He has also decades evolved to practical to do operational mainteneces.

TomasF. do not fall into the trap of delivering the Ideal fuel gas.
That elephant will rot and purify taking a perfect-each-step-at-a-time; then move onto to the next step.
Be Objective Goal orientated.
Can I make a mobile woodgas system get me where I need to go.
Can I make a stationary woodgas system Produce the power I need.
Make your actual needs to be the Driver. And how hard a system will work you to make it long term operate to satisfy those needs. VesaM’s, WayneK’s and just a few others commenting here shows this Objective Goals approch.

Lab-spec developments only work with lots of Graduate students slaving the glassware and lab equipments cleaning ups. Systems designed by chief Lab-Rats only work out in real world use with lots and lots of willing to work cheap, get hands dirty system points Maintainers.
Steve Unruh


The key component is cooling. If moisture, tar and soots are in gas suspension you cant filter it out. At least not at this level. If you want to boil water at a lower temp what do you? You apply a vacuum right? How do our gasifeirs work? Under vacuum!. So our technology by nature wants to keep everything in gas form until it exits the system. Thus is why you gennerally see tar drop at the throttle plate. It should also be understood a gasifier can produce many different grades of tar and gennerally most will be present if the machine is making tar. All have different due points and the worst have the lowest. Like petrolium fuel refining. keroseen, diesel, gasoline, benzene and other fuels all are refined and collected at different temperatures. Tar is the same way.

So first line of defense cool your gas!. Once the nasties are knocked out of gas suspension you dont really need a lot of filter media, it will drop out like rain but having some filter media will help collect the finer mist. I am developing a new machine that uses positive presure and that machines gas quality is astounding!


Jan, if I’m reading your notes correctly the best fuel is 99,99% filtered woodgas. On 2 outof 3 tractors the wear doubled running diesel only - and doubled again with unfiltered woodgas.
To me, the important question is - does it matter? How much wear is too much? I have no idea.
With most of the vehicles I’ve ever owned I’ve been the last owner, but the engine always outlasted the rest of the vehicle.
I’m not at all advocating to skip filters. I’m sure they help. But personally it would make me feel a little better if my vehicles at least started to get a little thirsty on oil the day frames and bodies are beyond repair :smile:


Not to get too much on a tangent but it’s important to keep in mind fuel and oil chemistry was not as good as it is today. Lots of paraffin based oils left nasty deposits that messed with oil flow, probably carried contaminants as well. Oil change intervals were much sooner than even the 3000 Mile interval popular from the 60s onwards.

I’d say metallurgy was about as good as ours though. Can’t make the cast iron bore and ring much better.

I think for gas filtration it’s important to find a balance between filtration and gas flow. Some guys I’ve seen videos they have just too much in series and either need a larger engine than anticipated or blower assist.

Cyclones do work, but might work against things like a bag filter like Kristijan mentioned. They also mess with your flow. Wayne has a good system because he understands the maintenance schedule. Great gas flow thanks to paralleling cooling rails and big filter with straw.

I’ve been studying Dutch Johns website again and I noticed his insistence on maintaining as much laminar flow as possible to keep the gas flowing quickly and keeping the pipes clean. “No such thing as too big a gas pipe” to paraphrase. Only a few places DJ said you needed turbulent flow mostly to drop particulate.


I’m not competent to comment on the “engineering” filtering of wood gas, I can only say that I like simple solutions that do not cause harmful waste, so I only use hay, sawdust and sheep’s wool in the filter container, I cover everything with cotton on top a cloth moistened with engine oil. I changed the oil in the engine of my Fergie for the first time after 100 hours of operation, and now it has been about 150 hours since the change and it is still “clean”, I would almost say that it is suitable for salad.


Matt, my observations show that not to be the case. Yes, tar and soot collect at extremely turbolent places, like throthe plates and sharp corners, but l dont think its the pressure drop to blame. I think its the pure velocity, the whipping effect. Like a milk separator, or even a butter churner. Just get those micro particles to colide and form biger and biger globs that cant split any more.
On my charcoal kiln, l sometimes let a bit of gas in a condensing barrel to catch some tar. Even thugh there is quite s few square feet of cold surface area, most of the smoke (tar aerosol) will leave the barrel as such. But on every crack or pinhole that blows out gas when the kiln is at peak performance, there is tar spitting out. The velocity/turbolence whips the tiny drops togerher.

Edit: about the soot l do agree. It enters as soot dirthy fog and the pressure drop evaporates the water and throws out the soot. The text above is ment just for tar


Yeah thats part of it. But physics is physics man presure determine due point.

Re reading you post you get it, but if tars and soots are in gas suspension there are no micro particals to colide. Thats my point you have to get them out of gas suspention first.

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Gas suspension literaly means to have solid or liquid particles in suspension in a gas. So tiny droplets or solid particles. Those can colide, just like fat particles can in agetated cream to form butter.
What you probably have in mind is a mixture of gas and gaseous tars. But since the boiling point of tar is so high, l dubt much of them are in gaseous form to begin with. And for sure, no soot is in a gaseous form. It just cant. Its carbon and as such it has the higher boiling point of all elements.


Matt, you and l both have a lot of experiances with this. As smokers :smile: cigatete smoke is nothing but a tar suspension. Tiny droplets of tar that form suspension, smoke. Lungs have a rather laminar flow so much of the tar gets out where it came in. But if you pull real hard on a cigarete, you can feel a gross feeling where the smoke colides with the back of the mouth or tounguue, the tars…
Even more is this effect seen by smoking a cigarete trugh one of those de-taring mouthpeaces. They were popular when l was a kid. They had 3 tiny holes trough wich you pulled the smoke and the high velocity separated the tar out of the smoke. Werry effective! Hard to smoke but it got nearly all the tar out. Problem was, with it also all the taste and the joy whent with it so they fell out of fasion soon.


I just want to add a few things if I can gentlemen. First, I am skipping the salad if I ever eat with Tone. Next when designing any type of heat exchanger turbulence is your best friend. If you have laminar flow in the region next to the tubing walls, your exchange rate will be poor. Turbulence is the cause of better heat exchange. Trials/test. Wash a room with carpet and direct a fan parallel to the floor and on the other side of the room, point a fan directly down at the wet floor. The one pointing down at the floor will be dry multiple times faster due to the turbulence.
Speaking of turbulence, why things drop out where there is turbulence is velocity. Say if you want to keep something suspended in the airstream, you need a high velocity for a heavier particle and a lower velocity for a lighter particle. Turbulence causes the velocity to drop and therefore things drop out in these areas. To filter small particles, you need a large or fat cyclone to lower the velocity near the outside rim. I had a job where I had to design for this. fine dust is difficult.
Lastly pressure does have to do with condensation of moisture or any liquid that can be held by air. When you look at a psychometric chart it is usually at sea level, but if you are several thousand feet above that the chart is wrong and you need a specific chart for that pressure. More importantly is temperature. when you lower temperature air can not hold as much moisture. Should you want to dehumidify on a grand scale in one pass, you would want to pass the air through an air conditioner coil that is cold as possible without freezing the moisture and is as slow a velocity as possible. To review, super hot air like gas in from a gasifier, special charts or software, high pressure/altitude changes, special charts or software.
Hope the principles help someone, designing these systems in my career was stressful and I just want to pass on the insanity.


Yes to what Kristijan is saying, I agree. Keep , It, Silly, Simple. K.I.S.S. on your design. The Rocket Fuel will work wonders for what moisture is in the system.


You are so right, it is not my opinion that everyone should clean the gas 100%, just think that it should come across that it will be a wear and tear.
This test is also done on a mixture of gas and diesel, no one knows if it will be better or worse with only natural gas.
But if what I did at Illern works, there is probably no easier way to make a filter, which looks like both the clean gas and very low resistance.


to clarify, i have a few fairly important reasons for striving for clean blue gas. there are so many applications if its achieved, such as blacksmithing and powering dozens, if not hundreds of appliances that were made for as usage. im aware that with motors its not as important, but i KNOW clean gas is achievable. there are examples ive found online, but most of them are old videos on channels that have since stopped activity, or reclaimed videos that are difficult to see the method of filtration.

im sure that many would see it as a waste of effort, but i feel pretty strongly about striving for clean gas. im not sure what methods ill need to go through in order to get there, but what methods ive seen work the best include water filtration of some sort. im actually not th biggest fan of media filters because theyll naturally decrease in efficiency and produce more and more resistance over time unless you replace the media regularly., but i dont want to ignore a filtration method if it can possibly work

im thinking about weather or not some sort of water cooled cyclone filter would have a good result. that way there is the benefit of the cyclone filter as well as cooling the air down faster than what would be achievable with an open air system. that way it would not reduce the flow, but help the efficiency of filtration.


ThomasF. will all respect on this your topic . . .
you have trapped yourself into the blue-flare thinking trap.
I have personally used four stage filtered/cleaned woodgas in loaded IC engines.
It made less power. Less engine shaft power than if I tapped the made gasses mix earlier in the filtering stages.
For internal combustion engines most of what you are laboriously, expensively removing are just more carbons chained fuels.
And every additional cleaning filtering step you add will INCREASE the types and volume/weights of contaminate wastes you must dispose of.

Do you know how they power remote oil and gas well pumps?? With purpose designed and manufactured internal combustion engines fueling on acidic, wet well head gases. The special engine designs are for easier cylinder bore sleeves, pistons and valves replacing.
Do you know how they dispose of highly mixed industrial wastes oils and greases? In the big ocean cargo ships internal combustion piston engines. That industrial mixed wastes on-board steam heated thinned to be able to pump it thru injectors with some kind of useable spray pattern. I’ve been charter fishing offshore of the Washington coast and seen the 12 miles out change over on the Asian ports returning freighters as they changed from fueling burning industrial wastes oils to cleaner burning spec fuel. US air pollution laws.
In the US and other countries now with strict air pollution laws on venting of sanitary landfill gases; instead of open flaring them off Mitsubishi Industrial; Kubota and others are suppling adapted over IC piston engines to eat-fuel on this variable mixed self-cooking urban wastes stink methane gas. Making at least enough electrical power to supply the whole landfill operation and then some.

The reasons the Blue-Flare advocates sites are down unsupported is they are a an unsustainable fail.
Predictable. The estimated 4,000-6,000 old city gas-plants sites to supply the cities and urban areas with their clean blue flame towngas are now toxic wastes contaminated areas.

You yourself how long would you remain healthy if all you ate was expensive overly refined wedding and sheet cakes, eh?
The poor humans and animals living on the wheat portions milled away in husks, midlayer and germ, to make the perfect cake making flour would eat healthier.

Striving for blue-flare gas is not being practical use Objective Goals thinking.
It is wanting to cater to the world of the pampered Cake-Eaters.