For my filtering I use a series bank cyclonic final stage filter system. This has been very effective, as by the time the gas has reached this point, it is very wet / sticky. So when any left over debris hits these filters it like a fly landing on fly tape. They self wash, are non restrictive and are virtually zero maintenance.
On the Flex Power System there is an option for a marble bed filter with fluid wash system. It is very effective in cooling the gas and giving the moisture in suspension something to collect on to. Then after this the cyclone final filters aid in removing any left over moisture from this process.
When using just charcoal in your Gasifier you do not need to make real small like most charcoal gasifiers, because the wood size that the Ben Peterson gasifier uses normally cooks the wood into larger chunks of charcoal and then break down into smaller pieces as it moves down to the grate. If you put all grate size pieces in and above the nozzles it might consepate the fire tube and cause it to draw a higher vaccum to run. This happens on down draft gasifiers. I still think the filter media might be be the problem though, just to much restriction for the suction vaccum on the the genset to pull gas efficiently.
Bob
I tried to start my generator with a concrete mixer plugged in - thinking that it was powered off. Nope. The little engine could not get up to speed with the load on it, and would just sputter and die. Now I unplug everything before I start up.
Also, if I am understanding correctly, 20-30 minutes is a very long time to get a good strong self-sustaining flare on charcoal. My reactor is a lot smaller, so less ducting to purge at startup, but i usually have a good flare in 2 minutes or less. 4" wc is a lot of pressure drop on that filter, I would suggest you swap it out for something much less restrictive. I am using wool batting and a wool sock in an ammo can, and when I did some testing with and without the filter material, I only had about 1/8" wc of pressure loss. See: Nozzles for Charcoal gasifiers, part 2 - #195 by oregoncarl
Keep at it, and you will get it going. All this troubleshooting will make you a better operator, and teach you what to do (or not do) on your subsequent builds.
As mentioned keep the generator unplugged from loads till its got a chance to get up to speed for a little while , i had 1 engine that never ever liked starting up on straight charcoal gas from cold and it started and ran just like your engine . how i over come this was to start the engine up so it was running all be it slowly and spluttering and with small propane gas torch unlite turn the gas on low and aim it over the air intake that extra bit of gas may cause the engine to stop as it will be too rich , so move the gas torch away a little you will get a feel for it and once the engine has got up to speed you will find it will run happily on just the char gas .
Dave
Hi Matt,
I love your good work and enjoyed our conversations at Argos. I want to nitpick a bit in hopes that some clever person among us will help us solve the suspended tar issue.
I agree in general with your statement above, but WE CAN TRICK TAR INTO COMING OUT OF SUSPENSION by causing coalescence or agglomeration. There is a lot of science on this and many patents (some very old) for equipment to cause suspended tar vapor particles (microscopic or nano-tar?) to coalesce into larger globs that can be filtered or captured. Among the techniques used are condensation on a cool surface, water mist to create emulsions, alternating electrical fields, and rapidly reversing particle direction.
I noticed that some modern equipment uses metal scouring pad (toroidal metal mesh) to cause the suspended tar to coalesce into larger particles that can be captured. So, I incorporate SS scouring pads in my gas cleaning setup. I’m a charcoal guy, so tar is not a big problem, but I prefer to have any sticky tar to coalesce on my scouring pads instead of on my throttle plate.
Ive done a lot of experimentation as a whole. My conclusion is, when tar is produced there are multiple grades of it produced. When going through your filtering process this like an oil refining process. The Cyclone bank systems really show this. Ive seen clean clear water drop from the first, then the grape juice looking condensate out the next and then nasty gooey drop out the last. When any gasifier is up and running from cold start up to 2 hours into a run the gasifier has gone through warm up to many cycles through out the run. At times tar may have been produced and dropped through out filter system.
Maybe this is just me, but I do not consider any form of condensing as filtering. Filtering is just that you are using some sort of media or device to remove unwanted debris or particles. Condensing is bringing a gas to its dew point in any given environment. When the gas converts from gas to liquid it does not create a mist; it abruptly drops and forms very heavy droplets and is a very fast process/conversion. You can look at an automotive tail pipe on a hot and humid day to see this as the condensed water drops out the tail pipe. No need to filter it after dew point. However In our case the gases are in a vacuum. Some grades of tar will drop at a higher dew point while others will not and generally if you are making the first your are almost always making the later. The later the dew point is bellow 100*f at atmospheric pressure. If filtering prior you would need a micron filter to get it out and that is just not practical for wood gas as this would be very restrictive and clog in a heart beat. In a vacuum I suspect this grade of tar produced the dew point is well bellow ambient temperature.
I have heard of the SS pads, this I would consider a condensing process using a catylist. I would not consider the pads as an actual filter though. If the pads were acting as a catylist forcing the gas out of suspension then the tar would drop there regardless of the physical existence of the pads. On the FPS I use a wash system much like I had at Argos. This is like the mist system but on steroids. The pump flow is enough to fully flood the bed and gas is forced to mix with it and flow thru with it. The cyclones are very effective after this process and there is always mist in the gas after exiting the wash. As this moisture is whipped out in the cyclone anything in the gas also collects to the moisture along the walls. This is self replenishing and cleaning. The down side is the marble need changed and cleaned and is something I am trying to get away from. Handling any filter media is a no go, machines that go overseas there is big problems with this.
Bottom line here is dont make tar to begin with, make it easy on your self.
A small bit of tar at start up or periodically during a run is not going to hurt an engine. This not desired and generally will not be the case on a machine dialed in and always running good fuel. So all the advanced filtering is really not needed. You just want to get the coarse ash out.
On the scouring pads, the explanation given in the research papers is mechanical, not chemical or catalytic. The twisting and tumbling of the gas cause the suspended substances to bump into each other and agglomerate (combine with other stuff) or coalesce (combine with the same stuff) and become heavy enough to drop out of the gas stream.
I like your bottom line and your noble goal of eliminating filter media.
I am also intrigued by hearing from wood gassers that soot is no problem, just burn it out occasionally. Is soot what we get when tars are cracked and burned?
I guess I would need to experiment with the pads. To me it looks like a mess to deal with and how would you clean them. Throwing them away would be a no go and very wasteful to me. This might work for the mist / fog stage but why not just fully condense the gases properly and get it all in one shot? Then all you do is drain it with out nasty media to deal with.
I can only see this working very marginal and collecting a small portion but then again I have not tried it. Do you have fog in your gas after leaving this process?
I will most likely be going to A/C systems if development is successful. Indeed the A/C will consume power, however restricted media also robs your power.
Here is an experiment for you. If you have an expendable A/C condenser or trans cooler, run some gas through it. It will blow you away how much junk falls out of your gas. Even gas you think is clean! Put some pressure behind it and this will amplify the outcome even more.
I don’t have this stuff figured out so i’m glad that you are thinking about it.
Your question about fog is a good one. I flare straight off of my reactor first to keep moisture out of my system, then I circulate the gas through my cyclone, cooler/coalescer and filter to reflare before starting my MGB.
Next time I startup I will compare the fog straight from the reactor with the fog after treatment.
Well thanks to all you guys’ help, this gasifier ran my 200cc generator for a long time yesterday, probably a total of over half an hour, though it also stopped several times and I had to restart. I threw together a video of one of the times when it ran. There were longer times, but I thought they would be too boring to watch.
Before this run, I checked the pressures in detail and found the pressure drop across the filter was quite small, but the pressure drop in the reactor was by far the bulk of it. The leftover charcoal from my last run was ‘constipating’ the reduction tube, like Bob suspected, so I vacuumed it all out and put in new charcoal. Also, the new charcoal was a lot bigger pieces, so it wouldn’t clog. But unfortunately in this batch, I forgot to follow Kristijan’s suggestion to add 15% by weight of water. So it started to get hotter than ever before and I was a little afraid, so I added a lot of water to the air intake. I couldn’t tell if it helped or not, but at the end of the day, there was too much water in the pipe going to the engine, so I will remember to just add it to the charcoal before I start the run.
I would like to know why it kept stopping, like it did at the end of the video. Also, it seems so weak compared to the propane. But it was a great feeling to finally get some electricity out of these trees, after starting this project in February, 2018.
Hi Greg , good to see it going at last, and i can imagine how happy you must be knowing your almost there , your question as to the why it keeps stopping is a mystery to me , but a guess would not be due to lack of water but maybe bridging or the size of charcoal, on updraft units we try and get the charcoal down to below 1 inch i think , i know that my charcoal is between 3/4 down to 1/4 in size .
Before you change anything i would try on the next run to load the generator up to max power before you notice it starting to struggle and then start dripping in a little water maybe one or two drips per second is all thats normally needed to increase the revs and power of your engine .
Dave
Hi Greg, I have forgotten, ? what is the restriction size before the Grate and how many nozzle are you using in this drown draft gasifier? You are plenty hot at the grate. That temperature looked good to me.
Yes, next time mix the water and charcoal together before you add the charcoal like Kristijan does. With it being a down draft system, be careful not to add to much water.
If your grate temperature is around 1500 *f that should be about right.
That was a good run, you are getting real close to having the genset go for the long haul in running.
Bob
Hi Greg,
Although we have different systems, I also had water going to my gasifier.
What I did was put a tee in the horizontal gas delivery tube and added a
removable drop out container to catch that unwanted excess water before
it entered the burner. The first part of the drop out tube had a shut off so I could
drain the container while it was running without disturbing the gas flow. Close shut off,
drain container. Close drain, reopen valve. No interruption of the gas flow. Drain on
the fly, so to speak.
Hi Bob, The restriction size before the grate is 2.4". There are 6 nozzles, each with 19/64" diameter.
I think it needs some vibration. At times, I could see some empty spaces between the bright glowing charcoal. And maybe I’ll make the lumps a little smaller.
It seems the down draft tends to compress the finer charcoal, making a restriction. With the updraft, I would guess the air flow would tend to disperse the charcoal, allowing better air flow.
Next time, I’ll have the water added first, the right size lumps, and I’ll measure how much load it will support. And maybe I can find a vibrator, or maybe bolt the engine to the gasifier for vibration.
