Flitration Solutions

Hello My name is Eric Cartier I hail from northern Arizona and have been interested in wood gas for some time now. I have been reading everything I can find on wood gas for about a year now, and purchased Vesa Mikkonens book on woodgas for mobile applications. Highly recommended especially for your first introduction to woodgas. It taught me more in 2 months than I learned searching the internet for 10 months. I have been following this website pretty much since it first came on line and am very exceited about the practical content that circulates here. Look forward to becoming an ongoing participant here.

On to the heart of the matter. I am currently in the design phase. I have pretty much settled on the dimensions of the furnace, however there are still some issues relating to inexperience when it comes to filtration solutions. For those of you who have read Mr. Mikkonens book he strongly advocates dry PTFE (Nomex, Gore-tex) based fabric filtering. The complexity and expense of such a filter does not correspond with my budget. Right now I have figured a finned cyclone separator immediately after the furnace outlet to cool the gas as soon as possible, followed by a sort of bubbler/condenser/radiator (with a small bypass to prevent the pressure drop from killing the engine on idle). Lastly followed by some sort of organic media filter. I suppose I am curious to hear about peoples experience with organic media filters. I know Mr. Kieth ran a hay filter in his F250. I believe Mr. LaRosa runs a combination organic media filter in some of his rigs.

Just looking for practical advice and experience. I appreciate it very much.

Hello Eric and welcome aboard,

In the early days ( about 8 years ago ) I tried a lot of different filter material and I ended up using hay.

Mike LaRosa also uses hay.

after I get it in the filter housing I wash it down good with water to remove any dust that might be on it.

I think Woody and Sean also uses hay?

Hi Eric, I am more into charcoal gasifiers but it still needs some type of filtration to remove dust and any tars that may sneak through. Initally, I used wood shavings. The dust would stick to it, much like it would to damp hay. Recently, I have been trying charcoal as the filter medium. Two advantages. 1. the charcoal actually adsorbs any tars into the matrix inherent in the porus charcoal. Ie, it doesn’t just “stick” to the charcoal, it is “held” by it. 2. the charcoal can be used as fuel in the charcoal gasifier instead of dumped out. Here is a video of my set up. Made for a smaller engine but no reason it cannot be scaled up. http://www.youtube.com/watch?v=VAyItWMNl2A
Gary in PA

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The Charcoal media seems like a great candidate. As long as it does not get too dry and create more dust. But I suppose that’s doubtful in the humid environment from the condensate? I really appreciate the video. Whats this VW project I hear speak of? The engine I have access to for this project is 1974case bored to 1835cc. Good power to weight ratio on gasoline for my type 1. I Figure on wood gas the performance will downgrade to around the stock region. Not thrilled with the long intake manifold in relationship to possible gas explosions ( the shorter the distance the produce gas/ air mixture has to travel coalesced the better I understand). But it’s what Ive got to work with.

I like to use animal bedding for rabbits or whatever. It may be simmilar to what Gary is using, but what I have is pretty fine.
It’s perfect for the lawnmower but on the Ranger there is a lot more cfm/sq" so I’m getting more blow by. I either have to increase the filter size or find finer mat’l.
Charcoal might work in a charcoal gasifier, but there might be too much moisture for a “woody”. I wonder if some of the charcoal would end up as sludge on the bottom of the filter.

Yep we use hay. We tried packed bed and thought about the fabric, but then Dutch John posted he was getting away from the cloth fabric because of space and cost and the problem with ruining the fabric if a little tar shows up. I get soot in my intake but it does not affect the engine after 3 trucks and several gasifiers. Wayne uses his truck everyday for years with hay filters and never had any issues after six years with his Ford F250 with a 460 V8. The packed bed works about the same as hay but is more time consuming. With hay you never have to open the filter, just wash it down and drain off the carbon and water. Very clean and easy. If you do get tar in the system, and I’ll bet you do, just take the hay out and burn it in the gasifier a little with each load of wood. Very clean and easy.

There are things covered in Waynes book that no one else touches on for design and maintenance. The Europeans are big on Stainless steel , but I have been at this for two years and never seen the need for the extra cost if these units are operated right, used frequently, and kept air tight. There is no rust that can form in an oxygen free environment.

Thank you for the suggestions. My concern with using a hay filter is pretty well settled. I like the charcoal filtering bed in theroy but im not sure how efficiently it will work if not enough water condensation is removed. Plus hay is cheap, simple, and tested.

Woody: Im curious how you keep gasifier constructions (out of mild steel I assume) from corroding. I was always under the impression that heat alone even in an oxygen deprived environment would increase corrosion. I had planned to use a bi-metal generator, with the inner furnace shell of stainless (nozzles, grate, restriction ring) and the rest out of mild, But if I could build the whole thing out of mild steel it’d save me a lot.

Wet filtering will never beat dry filtering. Not even a tiny black stain is to be found on the Volvo’s gasifier guts after the filter. Maintenance is easy and not frequently needed. The setup is not necessarily more complex compared to wet filtering. You need a huge filtering surface to overcome the pressure drop, but a wet filter that is as efficient as a dry filter is much more bulky. But the risk of gumming up the fabric on that rare occasion you mess up remains. Experimenting with different sizing or wood is not something you do with dry filtering.

I do not have much experience with wet filtering yet. What I did find out is that a final filter after all cooling is done takes out an astounding amount of soot. On the Dinyfier this filter is an oil bath filter. Drained settled soot comes out with some oil like jelly pudding. On Tiny I use a compressed air dryer/filter. You know, these are used in front of air tools. A combination of cyclone and filtermaterial, where the ceramic filter is replaced by household fiber.

Dry carbon dust does not want to stick to water very easy; it takes a long time. This does explain why the above mentioned end-of-line filtering works so well. Dry carbon dust is also easier catched by oil than by water. Unfortunately the oil mixes up with condensate very fast, so an oil bath filter needs a large oil tank, in which the water can settle on the bottom and thus be drained separately. On the “microgasifier” part of my website woodgas.nl you find a pic with a fill/drain combination. Note that at the time of building I did not implement that large oil tank…

About corrosion. I am a fan of stainless. But there is no need for full stainless gasifier systems that are used on a daily basis. Most important is to use non oxidating material for the tubing between final filter and engine. Condensate in ready gas contains ammonia. Condensate in the hopper contains acetic acid. Still I found the later to be no problem, because fuel hoppers become covered with Stockholm tar. Grates, nozzles and restrictions live longer when stainless, because they do not flake off. Thick walled mild steel will do too, but beware of heat sinks in the hearth.

Back to the workshop, locking myself up…


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Just to add onto DJ’s comment about the post-filter plumbing. Here’s a solution which is cheap, seals well, never corrodes - PVC pipe. Long as you keep the heat off of it, you can plumb most of your vehicle using this. The fittings are watertight and strong, there are flex fittings for tight spots. Lightweight, no corrosion, easy to fit together with no welding - did I mention it’s cheap too?