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Renewable Energy (Other than Biodiesel) Description

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Old 11-02-2008, 03:39 AM
Todd T Todd T is offline
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Tim C Cook asked in another thread about my research into gasification. I'm currently involved with a few different R&D projects involving gasification. I haven't had this much fun in years!

We're working with wood in various forms: pellets, chips and blocks. One group I'm working with has also played with chicken litter, sanding dust and switchgrass. No charcoal. Eventually, I want to see us pelletize municipal waste after recycling the metals, plastic and glass.

We'll be using the woodgas to fuel gasoline or diesel engines as well as for heat. We area also working on BTL... Biomass To Liquid through Fischer Tropsch.

One of the gasifiers I've worked with came from China. Over there they use what they call a 'straw gasifier' in lieu of natural gas. This small gasifier came with a two burner stove included. I'm really tempted to buy one of Jim Mason's Gasifier Experimentation Kit units. It sounds like a researcher's dream.

Lots of exciting developments.
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Old 11-03-2008, 05:56 AM
Tim c cook Tim c cook is offline
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If you develop an efficient method of making wood blocks please post it, it is very time consuming doing it manually. Solid blocks will produce the most gas, from reading it looks like the best shape and size for a gasifier would be a golf ball sized sphere, it would feed nicely and allow enough air around the fuel to burn appropriatly even in a stationary gasifer, square blocks seem to feed acceptibly if the gasifer is bouncing around on a vehicle but can hang up in a stationary unit. My local group mounted a running lawn mower engine on the outside of our stationary gassifer to vibrate it a bit.

This links to a "GAS PRODUCERS" discussion in the "renewable energy" forum, I have some pics and info there of a couple types of gasifers that a few local folks are working with, mostly last winter, but it is about time to get back to this project. With our second gasifier design we have run a 10KW generator powered by a 1750CC 4 cylinder air cooled low compressioned flat head Wisconsin engine for a couple hours at a time but need to clean the gas better as the tar in the gas causes the valves to stick in there guides once the engine cools down.

We are concentrating on woodchips as out feed stock as we literally have tons of this available free at my village sewer plant yard. The village, as well as the power company and the local tree survice folks just pile it up, nobody wants it here and the village is happy to get some of it removed. Main problem with wood chips is that they hold moisture forever unless the pile is under a roof and stirred every couple of days. Another problem with wood chips is there size, the gasifier does not like sawdust well and any wood over about 3 inches long can cause the chips to "bridge" and hang up in the internal fuel feed area of the gasifier. It is looking like we need to first screen out the sawdust type stuff and then run the chips across a sloped classifer screen with big openings made from 2 layers of crossed rods so the usable stuff drops through and the big stuff slides off the top. In reading a lot of web info from other gasifier experimenters it looks like this is a common problem as many have built some sort of rotating screen apperatus to clean and size there wood chip feed stocks. The verious sources that make the wood chips all have big commercial chippers so there is a fair amount of 6-8 inch long skinny slivers to remove.
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Old 11-04-2008, 11:27 AM
Todd T Todd T is offline
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I agree with the challenges of a stationary gasifier operation. One tip I've heard was to make the slope at the bottom of the fire tube much steeper. Rather than 30 to 40 degrees, crank it up to 70 degrees or more.

Rather than shake it from the outside, I feel the best way to address fuel bridging would be to break it up on the inside. I've seen one system that would work great... but I saw it under a non-disclosure agreement. We're hoping to get an agreement in place with the owner of that technology in order to use it. Kind of frustrating to see something cool but not be able to use it. But, ethics are more important to me and my team than just making fuel.

I'd never thought of golf-ball fuel pellets. Unfortunately, most pellet machines make a cylindrical shape. It seems the larger ones would work better.

The ones I got last week were made at a plant in another state. The trick would be to develop a smaller system to do the pelletizing right there at the point of use.

Have you explored using the excess heat to dry your feedstock. I saw one system that had two hoppers. Chips go in one hopper and are dried from below while the fuel is used from the other hopper. It went back and forth between the two. I think a conveyor system would be better... almost like an assembly line where the fuel is dried as it gets closer to the point of use. It's almost in the mindset of the stratified downdraft gasifier but continued outside the unit.

Are you using a batch or continuous feed system?
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Old 11-08-2008, 04:59 AM
Tim c cook Tim c cook is offline
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Pellet size -- From reading it seems that about 1 inch size blocks are closet to ideal, several users indicate that grape sized fuel is too small and will produce more tar, our woodchip teating seems to create more tar also, still testing different settings of the char section of the gasifier, supposidly increasing the temps through the char should crack the tar better?

Making spheres would definitely be slower than pooping out a continuous flow. I am thinking something like converting a log splitter to compress the sawdust but the compressed sawdust also needs considerable heat applied, as well as pressure, to liquify the natural lignen binder in the wood, still thiking about this.

Drying fuel -- I ran across THIS 1040's something document about burning wet fuel, This discusses the use of a MONORATOR fuel storage hopper, it is much larger in diameter than the lower burner section and uses internal hot convection current gasses to remove moisture from the wood directly above the center burn heat and condense out the moisture as the wet gasses pass through the cool fuel located in the outer diameter portion of the hopper. In reading modern posts about gasifiers I find a lot of talk about there monerator hopper design but none of these gasifiers are actually using this large diameter hopper. it may work, he talks of dumping 8 pound snowballs in the hopper and the added water did not effect the gasifier operation. I hope to test this eventually.

The gasifier we have built is almost an exact copy of a test gasifier built by Fluidywn from New Zeland. Seems they have a fair history with commercial gasifers. This gasifier was designed to allow the verious sections to be reconfigured for verious different fuels and situations.

This gasifier is a batch loaded unit along the lines of the old WWII Imbert design.

This links to an 8 page PDF describing the Fluidyne unit and showing drawings.

This links to an archive list of Fluidyne info, the gasifier is the listing called "project design file PDF", I also found the "screw auger chippers" interesting, this is the only commercial wood chunker chipper that I have seen so far, sure would make fuel prep easy, lots of interesting info here.

Just cheaked the archive page, the top listing is new, another screw chipper document with a lot more info and pictures.

This links to
a good explination of how "superficial volocity" is the key to a good gasifier.
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Old 11-08-2008, 05:30 AM
john galt john galt is offline
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One inch diameter poplar and willow tree limbs cut easily\quickly with a lopping shear into the size 'blocks' you want.
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Old 11-08-2008, 06:50 AM
Tim c cook Tim c cook is offline
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This links to a website describing one fellows gasifier experiments. He has developed what he named a "spiralshear", He feeds limbes up to about 1 1/2 inch in diameter into the powered blade and 2 inch chunks come out the other side, looks interesting, not quite enough info to know exactly how to build the apiral blade but it would be a big time saver if you had the correct sized limbs. Don't know just how fast the power output shaft on this type of small garden tractor turns but the capition on one picture says the wood cutting blade turns slowy so it does the cutting using torgue rather than speed?
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Old 11-08-2008, 07:15 AM
john galt john galt is offline
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Ed's system is impressive. His rotating shear and horse manure gas filter is pure genius. I think you're right, it looks like the shear is geared down to a slow RPM to use the engine torque. A bit more automated than the lopping shears. I find they're still quite fast for limbs up to 1½", much easier than an axe or chain saw. I heat with wood and use the limbs for kindling. I especially like his 'pocket computer'. I still use mine, and find it better than the battery ones for many types of calculations. Thanks for that link, most interesting.
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Old 11-18-2008, 10:47 AM
broken_mold broken_mold is offline
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[quote]Originally posted by Tim c cook:

This links to an 8 page PDF describing the Fluidyne unit and showing drawings.

Hey Tim.
Have you worked with this Fluidyne unit or know anyone who has built a similar one using this info? I'm considering building one using their design but sized to run an air-cooled 1600cc VW Beetle engine that I have sitting around unused. Their idea of an adjustable throat tube/reduction zone and adjustable grate is interesting but I would like to hear from someone who has tried it or who understands it better than I before I spend time building it.
Also, they mention in the material accompanying the drawings "It is important to make a large outlet connection or you will throttle the hot gases exiting, and flange it to whatever you are going to connect onto the hearth." After reading scads of other studies I can't seem to find any hard figures that expalin how to size the outlet piping from the gasifier leading to the dust cyclone, coolers, and engine. Have I missed something or should common sense regarding flow, pressure, etc. dictate the sizing of that particular plumbing?

Nathan
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Old 11-19-2008, 02:53 AM
Tim c cook Tim c cook is offline
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Fluidyne -- Yes, the gasifer that several of us locally have built is an almost exact duplicate of the one in the 8 page Fluidyne PDF. I think we uses a slightly smaller diameter throat just because we used the materials we had on hand. This design is nice in that you don't have to rebuild the entire gasifier to juggle the sizing of the verious sections, it also does not require you to build any type of tapered cone above the hearth section, it cleverly uses the internally produced charcoal to form the cone, and the char around the outside of the pipe is somewhat isolated from air and gasses and acts as hot insulation to keep the throat from loosing heat.

This links to a similar gasifier discussion on this forum where I posted info and a few pictures of the unit we are testing. Our test engine is a 1750 CC V4 air cooled Wisconsin industrial engine turning a 10KW generator, we have run it for up to a couple hours continuously (one charge of the hopper) burning wood chips that have had the fine particals screened out but are still getting too much tar to the engine. The last picture does not show the latest gas cleaning equipment, a small cyclone has been added directly after the gasifier, the gas leaving this then passes through a filter, made up of a 30 gallon barrel full of wood chips, before then passing through a V8 engine sized radiator that has air blowing through it, then through a 8 ft length of 1 1/2 inch rubber hose to the engine, but we still get tar (need to add at least one last condensor tank directly at the engine as is shown on one of the Fluidyne history files).

From reading the verious Fluidyne historical info that I linked to in an above post (and a LOT of others) they indicate the wood chunk size and prep is the main thing that will cause the success or failure of a gasifier, our testing has found this also, you need uniform sized pieces sized for the particular gasifer, and the moisture content needs to be below 20%, preferably 12-15% max.

The drawing of the fluidyne unit says it is sized for about a 2000 CC engine, ours is 1750 CC and we are getting tar (the small wood chips cause higher tar apparently), from reading about "suspeficial volocity" the tar is likely due to the temp of the charcoal in the char throat not burning hot enough to crack all the tar into CO and Hydrogen, to raise the temp of the char we need to move the gas through it faster, this means the throat needs to be a smaller diameter, and to compensate for the faster flow of the gas being in the hot char for less time, due to the increased volocity, the char tube then needs to be lengthened by the same percentage to increase the "linger" time of the gas in the higher temps.

We also are producing one big clinker at the point that the upper outside burn (pyrolization) air is being injected through the 3 combustion air nozzles, reading indicates this "too much air" is causing too high a temp during the pyrolization, too much air raises the temp in this area and causes the ash to melt into the clinker, so - we need to make a couple changes and try again.

This has been a wintertime project so we will be getting back to it shortly, I intend to stop by the shop later this week and see what other changes have been made.

The 1500 CC air cooled VW engine is basically similar to our Wisconsin so the results will likely apply, except, depending on your fuel. If you burn seasoned blocks you will likely NOT have the same tar problem as we are experiancing, the small size of wood chips seems to restrict air/gasses through a gasifer much more than blocks, this differance is also known to produce more tars.

A gasifier is a big balance of temperature and velcoity of the gasses through the verious sections, compounded by moisture, and type of fuel, a big juggling act til you get all the veriables sorted out.

Output plumbing size -- I have not run across anything specific here other than general info based on the temp/velocity idea. You want the hot gas to pass out of the gasifier fast enough that it's hot temperature DOES NOT allow any moisture to condense in the gasifier, you then need to size the plumbing so the gas is cooled to the point that the water vapor WILL condense and the gas needs to then either be swirled fast through a cyclone to spin out the condensed water, or slows down enough that the condensed water has time enough to fall out of the slow moving cooled gas, or probably both, the size of the plumbing dictates the volocity of the gas so - smaller tubing produces faster flow, bigger produces slower flow, and it is all based on the size of the CC engine and the RPM's it wants to run at (gas volume), YEP - A big juggling act.

I have a link on file someplace to a good United Nations Forestry document about gasifier design (NOT the FEMA gasifier document), it compiles/condenses years of testing into detailed info about superficial volocity and sizing of the verious sections of a gasifier, and how fuel size effect everything, a wood chip burner needs to have a bit smaller throat section than a block burner, I will post the link once I find it again.
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Old 11-19-2008, 01:54 PM
Todd T Todd T is offline
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Tim, I can't tell who I learn more from... you or the career chemists (some with PhD's) I'm working with. I read and read and read but the lightbulb doesn't get turned on until I hear you describe what's happening inside a gasifier. Thanks for your description. Oh, as for those "professional" chemists, they are the kind who learn from guys like you and me as well. It's all about learning both in the classroom as well as in the 'real world'. It's a two-way street.

You are so right that it's a balancing act. Temperature, burn rate, air flow, air temperature, fuel type, fuel size, moisture content and so many other factors all come into play. And this is on top of the gasifier geometry. I'd love to get a gasifier Lego kit from Jim Mason. See his site here. That way you can start with some basic elements that work and then modify one variable at a time.

With regards to the hose size feeding the engine, I'm working with a trailer mounted gasifier designed to feed a 400 cubic inch big block and it uses a 3" suction hose to the engine. It also has a stilling chamber with a drain port to catch any remaining condensation.

I toured a research facility recently using a gasifier to convert wood chips to syngas in order to run a Vortec V-6 engine driving a 25kw generator. It was the first I know of in Louisiana connected to the grid. They use what ammounts to a glorified pillow case to filter out the particulates. They cool the gas first, then filter. Others filter the gas first and then cool. The best I recall, the line feeding the intake manifold on that engine was about 1 1/2", maybe 2".

Keep up the great work guys, I'm learning tons.
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Old 11-19-2008, 02:29 PM
Todd T Todd T is offline
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In some recent experiments which included GC analysis, we used some rather poor wood as fuel. This included a few chunks of 2x2, some partially burned wood from earlier firings and pine slabs from a sawmill. These had bark on one side.

Earlier GC analysis indicated the gasifier was producing a moderate amount of Hydrogen. This time, we had tons of Nitrogen indicating combustion was taking place. Hydrogen was low. Bear in mind, this was the same gasifier operating under the same conditions. The only variable was fuel.

To reduce the number of variables on my tests, I want to settle on a consistent feedstock. A buddy nearby has a pallet mill. I'd think he would have lots of end cuts from his pallet making process. What do y'all think?

I have a set of low profile platform scales I used to use in my chemical blending business that I'm having repaired. My plan is to use a large tub to weigh the fuel before each test burn. This will track the burn rate.

I'm also looking around for a four gas analyzer to test: H2, CO, CO2 and O2. Having access to a GC is great but I would like to be able to do more basic testing while we are running the gasifier. Any suggestions?
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Old 11-19-2008, 05:54 PM
broken_mold broken_mold is offline
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Thanks for the help. I'm gathering bits and pieces to assemble a unit before long. I've only been trying to get around to this for almost thirty years. I intend to build a cleaner and cooler section of some sort as well since I don't really want to screw up my "test engine" prematurely. I've built a cool adapter to mount on a VW transaxle which hooks it up to the PTO drive on my 25kW generator. Now that's a way to wear out an engine.

Quote:
From reading the verious Fluidyne historical info that I linked to in an above post (and a LOT of others) they indicate the wood chunk size and prep is the main thing that will cause the success or failure of a gasifier, our testing has found this also, you need uniform sized pieces sized for the particular gasifer, and the moisture content needs to be below 20%, preferably 12-15% max.
I have access to lots of hardwood slabs left from lumber sawing at local Amish sawmills and will start with those (cut into blocks) after they are air-dried a while. I guess I'll finally have to buy a moisture meter after woodworking years ago without one.

Quote:
The drawing of the fluidyne unit says it is sized for about a 2000 CC engine, ours is 1750 CC and we are getting tar (the small wood chips cause higher tar apparently), from reading about "suspeficial volocity" the tar is likely due to the temp of the charcoal in the char throat not burning hot enough to crack all the tar into CO and Hydrogen, to raise the temp of the char we need to move the gas through it faster, this means the throat needs to be a smaller diameter, and to compensate for the faster flow of the gas being in the hot char for less time, due to the increased volocity, the char tube then needs to be lengthened by the same percentage to increase the "linger" time of the gas in the higher temps.
This should link to the pdf file on Superficial Velocity. http://www.woodgas.com/Superficial%20Velocity.pdf
Since the design calls for a (roughly) 4" throat to handle up to about a 2L engine, should the diameter be reduced 25% if the engine it will power is 25% smaller (1.5L)? Also, instead of lengthening the throat tube could you not just move the adjustable grate down and accomplish the same end?

Quote:
We also are producing one big clinker at the point that the upper outside burn (pyrolization) air is being injected through the 3 combustion air nozzles, reading indicates this "too much air" is causing too high a temp during the pyrolization, too much air raises the temp in this area and causes the ash to melt into the clinker, so - we need to make a couple changes and try again.
Shouldn't the tables and charts of nozzle to hearth diameters for Imbert gasifiers found in many of the studies apply here? Is the problem here too much air or that the current amount of incoming air is too hot/too cool? Most of the imbert designs pre-heat the incoming air. Is there a good reason why they do this?

Quote:
Output plumbing size
Some of the gasifiers I've ran across for similar sized engines to mine use 4" plumbing from the gasifier all the way through the system. Interesting. Most of the units use something along the lines of Todd's observation of 1 1/2" to 2". Here are a couple of links that I found since my last post relating to flow of gases through a system.
http://www.pipeflowcalculations.com/
http://www.engineeringtoolbox.com/pi...loss-t_18.html

Nathan
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Old 11-20-2008, 02:41 AM
Tim c cook Tim c cook is offline
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Todd t -- Pillowcase filter -- In reading through several Scandinavian gasifier articles they use a similar filter on several of the Imbert gasifiers on WWII farm tractors. Modern testing of this type filter used several paralell pillowcase type bags made with fiberglass cloth that have an internal wire form to hold them open. The article sayed these worked fine as long as the temp of the gas was hot enough that the water vapor did not condense and wet the bags, wet bags clogged fast from the soot in the smoke, dry bags allowed the soot to drop off the cloth and end up in the bottom of the filter box chamber. They then passed the gas through a cooler with large passageways that was placed in front of the normal tractor radiator, the gas was then fed to the engine. These gasifies were burning blocks and I assume this is the reason they can get away using this relitivly minimal amount of gas cleaning?

Research facility gasifier -- Were they actually producing "syngas" or were they making simple "wood gas". true syngas is combusted with pure oxygen rather than air, this eliminates the 60% innert nitrogen and produces MUCH more combustable gas with considerably higher BTU content. I have read about several outback type gasifiers that power internal combustion engines to make electricity or power remote sawmills, most were in South America. They used air to make woodgas from the sawmill waste, this was basicly green wood so they had considerably more types of cleaning for the gas, including water spray cleaning and cooling.

Pallet mill feedstock -- This should be fine, it will definitely be dry wood although the quality may be a bit lacking, also, the type of wood may very considerably unless he is getting his wood locally. I just sawed up some crates made from pallets that were terrible, they were made up from small slabwood about 2 inches wide, tons of cross bracing and nails just to keep them together. Other pallets are great, made from rough cut seasoned oak, you just never know with pallets. You will likely have to saw the material into more consistant size blocks, 1-2 inch blocks seem to be the most desirable unless you are feeding a really big gasifier. Unfortunatly, I have not yet found a automated way to size the blocks other than manually, I did see a youtube woodgas video (should be a link someplace in the other discussion I linked to in an above post) where they had made up a neat device to help make blocks, they used a chop saw to cut off short sections of tree limbs, about 2 inch long. They had a stop set up so they just moved the 2-4 inch diameter limb forward against the stop and cut the block off, the block then fell down about a 8 inch long vertical chute where a piston, driven by a lawnmower engine, pushed it forward though a 4-way splitting wedge. This made nice 2 X 2 inch (approx) blocks. if your pallet wood hase some size consistancy you may be able to use this idea?

Four gas analyzer -- Sounds usefull, unfortunatly, I don't have a clue about these, our testing is much more trial-n-error.

broken_mold -- Modified VW transaxle -- I may be interested in how you did that. Just some info, VW made a power takeoff unit for there engines in industrial use, these look something like a transaxle as they mount to the engine but they had a simple dry disc clutch and an output shaft that came straight out of the front of the unit rather than coming out like the normal transaxle axles. I have seen these available but they are rare.

Throat diameter -- The gas volocity is based on "volume" of the opening, reducing the diameter by 25% would reduce the volume of the throat by not quite half, 4 inch diameter = about 12.5 sq inch volume, 3 inch diameter = about 7 sq in volume. This is a pretty big reduction but may work ok, it should increase the gas volocity something like twice (same gas volume in same amount of time has to move twice as fast).

Moving grate up/down -- I think this adjustment is there to get the top of the throat closer or farther away from the pyrolization zone, this changes the starting heat into the throat as well as the amount of pyrolization that has taken place before the fuel enteres the throat, more pyrolization produces smaller bits of charcoal and more pyrolization gas (water vapor, CO2, tar). To increase the time the gas is in contact with the hot char I think you need to increase the length of the throat pipe, then probably adjust the longer pipe up/down to find the correct pyrolization height. this is supposition on my part as I have not done any detailed testing on this yet.

Nozzle air -- From reading - The clinker problem is caused because the pyrolization temps are too hot, the high heat melts the mineral content in the wood ash and causes it to become glued together. The high heat is caused by too much air.

Imbert charts -- The Imbert charts should be a starting place but probably not directly applicable except as a percentage amount of change based on what is going on in the zone. There are several variables here, overall diameter of pyrolisis zone, diameter of char throat, height between the two zones, number of nozzles, diameter of nozzles, how far the nozzles protrude into the pyrolisis zone, ETC, probaly some I forgot, LOTS of stuff to tweak.

Preheating of pyrolisis air -- I know the Imbert usually preheats this air, I don't know why exactly. I don't think the preheat is needed except to possibly increase efficiency of the unit a bit, it may also improve combustion a bit, but then again, cold air is denser and carries a bit more oxygen, seems to me to be sort of a tradeoff, you need less cold air to produce the same burn as with warm air but warm air reduces the amount of BTU's needed to keep the fuel up to it's combustuion temp. Using cold air through simple nozzles through the side of the gasifier is much easier to fab, and you don't need to add the flap-type "chuff" valves since the nozzles open directly to the outside rather than into a manifold (although it does get your attention when fire shoots out of all the nozzles during a "chuff", we added pipe 90's pointing down). Once the gasifer is running reliably it would be fairly easy to add an external manifold to conduct hot air from around the hot gas output tube over to the nozzle inputs.

Plumbing -- Everybody seems to use what ever they have on hand, I have seen web posts using anything from 3/4 inch for lawnmower engines up to 6 inch for V8 engines. I think this will be one tweak area that will wait til the gasifier is up and running. Making the outlet port from the gasifier larger would seem to be the easiest, it is much easier to make an adapter to smaller tubing than it will be to re-fab the opening larger. From looking over many web articles showing gasifiers that others have up and running I don't see any reason for anything larger than 4 inches for anything up to even a V8 engine, there are several pickup trucks running on wood gas on the net, they pass the gas through 1 1/2 to 2 inch tubing assembled as rails along the pickup bed for cooling, they work just fine with this size tubing. Some of the small tubing is run in paralell but the tubing they join into as end manifolds looks to be the same size so there are several points in the gas flow that are restricted by there diameter, the volocity will just go up through these restrictions, if done well the volocity could be used to toss soot out of the gas stream.
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Old 11-20-2008, 08:38 AM
Tim c cook Tim c cook is offline
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I found the link to the United Nations forestry department document about gasifiers

This is the table of contents that you can use to download seperate sections. Chapter 3 has the tech info about gasifier dimensions, fiberglass filter bag tests etc.

This link will start a PDF download of the entire 139 page document.
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Old 11-20-2008, 09:40 AM
Tim c cook Tim c cook is offline
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I recently became aware that there is a different type wood chipper available, these are refered to as "screw chippers". They have been around since the 1970's apparently but I never heard of them til recently, they make block-type chunks rather than the normal small chips. They come in different screw lead sizes that produce different sized chunks.

This links to info about a currently available 7 inch chipper.

This links to tech info about these Laimet screw chippers.
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  #16  
Old 11-25-2008, 08:10 PM
broken_mold broken_mold is offline
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Quote:
Originally posted by Tim c cook:
Fluidyne -- Yes, the gasifer that several of us locally have built is an almost exact duplicate of the one in the 8 page Fluidyne PDF.
Tim,
I'm curious about some of the specifics on the Fluidyne units that you and the others have built. I'm strongly considering building an almost identical unit to the Fluidyne unit but some of the measurements don't follow most of the Imbert tables that I find. I've figured and calculated and scratched my head 'til I'm developing a bald spot and still don't understand. For instance;

1. The distance between the nozzles is greater on the Fluidyne unit. Is that a design optimized for wood chips? Since I will be using small hardwood blocks do I need to stick with that same measurement or should that be increased or decreased?

2. The inner diameter (dr = 380mm [14.96"]) of the reactor is larger than the tables specify. Again, does that measurement vary with the type of fuel or is there some "wiggle room" in that
measurement so that I can use scrap tanks which may not be exactly that size?

3. Char tube vs. conical throat. Does the grate inside the char tube serve the same purpose as other designs which have a grate below a conical throat? If so, why is the distance between the char tube opening and the top of the grate so much less than would be the distance between a conical throat opening and the grate below it on other designs?

4. Is the distance between the bottom of the char tube and the "floor" of the reactor important? Is it just ash that makes it through the grate? Can I lengthen that measurement to cause the gas to travel farther up and maybe lose more particulate matter in so doing?

5. The small Fluidyne unit only has 3 nozzles ( ~1/2" ID/ea) whereas most of the charts say that a unit with this dr/dh should have from 5-7 nozzles with an ID ranging in size from about
5-12mm/ea. Is this some slick trick by Fluidyne for a specific purpose or should I just increase the number of nozzles and their individual IDs according to the charts? I understand how the lobes of air should be pulled toward the char tube but I fail to see how only 3 nozzles can do this in a reactor with this large of a dr. Does this, too, have something to do with fuel size- chips vs. chunks?

6. Should the hopper top be sealed tightly or just covered? Why?

7. Is the insulation in the optimum place or does more of the reactor need insulation?

8. Is that enough stupid questions?

My first test engine will probably be a VW engine between 1.5-1.7L operating mostly between 2000-2300rpm, stationary until I can get it bolted back onto something with wheels again.

Here's a link to the Fluidyne unit under discussion for late readers of this thread who may not have caught it earlier.
http://www.fluidynenz.250x.com/_framed/250x/fluidynenz/...pecial%20Project.pdf

Nathan
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Old 11-26-2008, 06:41 AM
Tim c cook Tim c cook is offline
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My error, stated it poorly, there are several of us contributing to the building/testing of the same ONE Fluidyne gasifier, not several differant units.

Imbert tables -- The tables are all somewhat different depending on who developed them, they are mostly guidelines rather than specific info. Every gasifier is somewhat different than any other and the tables were developed experimentally on a specific gasifier.

Fluidyne unit -- From reading the Fluidyne historic info it looks like there designs have been developed from trial-n-error testing, so they likely won't conform to the imbert info. The Fluidyne gasifer linked to here is stated to be a lab development design, that is why all the verious sections are designed to easily be changed, Unfortunatly, you get to build something and then tinker with it til it works using your specific gasifier and fuel chericteristics.

I don't think the Fluidyne unit was designed for wood chips directly, there other documents show a lot of effort testing chunks rather than our common small wood chips, they are currently testing several type feed stocks chunked up using one of the screw chippers. My referance to the differance in hearth dimensions optimized for woodchips can be found in the U.N. forestry doccument.

Wiggle room -- everything wiggles, I have not found any absolutes with gasifiers, you build it out of what you have available and make changes and see what happens.

Grate -- The grate simply keeps the char from dropping out the bottom of the throat.

Distance is less - Hmm, I think the Fluidyne char tube is longer than the char section in most Imberts, I would have to look back over things to be sure. The length of the char that the gas has to pass through, along with the gas volocity, deturmines how well the CO2 and water vapor and tar get cracked into CO and hydrogen. This throat restriction also creates a pressure differentiol between the top and bottom of the char tube, this pressure differance can easily be measured using water filled tubing, There is a suggested pressure differance in the Fluidyne paper, you have to balance the char time against the pressure differance across the throat, there apparently is a sweet spot compromize for these, you tweek the unit til it works, this will give you the info to moniter the unit in the future.

Grate to floor distance - don't think this is critical other than for space for ash and adaquate space for gas flow.

3 nozzles -- Someplace I saw that a gasifer was built with 6 nozzles originally but after testing they plugged 3 of them, don't remember now if it was a Fluidyne unit or not now. Again, trial-n-error. One of the changes we will make shortly is to reduce the diameter of the nozzles, we are getting too much air to the pyrolisys section and are burning too hot and making clinkers, reducing the nozzel I.D. will reduce the total air, increase the volocity through the nozzles, and hopefully shoot air deeper into the chips, won't know til we try it.

Adding more nozzles will require each of them to have a smaller diameter to allow the same amount of air as 3 nozzles. More nozzles will likely produce a more uniform burn around the diameter of the pyrolization section but from looking at a lot of gasifiers on the web that use similar nozzles they mostly use just 3 nozzles?

Hopper top -- This needs to be sealed so all the air comes through the nozzles, air getting in from the top will cause the wood to burn at the top rather than the heat from the pyrolization zone burn heating it to drive off the volitals to make charcoal out of it. They top needs to be air tight but done by using a spring loaded latch so it can pop open against the spring when the smoke in the hopper ignites and explodes (this WILL happen, rather regularly), you want the wood in the hopper to dry out and char rather than actually burn.

Insulation -- haven't got that far yet, we don't have any insulation installed. I think the insulation is mostly needed in very cold weather and is there mainly to hold heat inside the char zone, and to keep the gas hot enough to be above the dew point so the water vapor won't condense out into the ash.

My intent is to use a small gasifer to power air cooled 1800 RPM 800CC 2-cylinder Onan flat head engined generators. I have an old 5 KW 110/220 volt AC one from a motor home, and another one that is a 180 amp DC welder that also works well as a battery charger for my 12 and 24 volt forklift battery banks.

I intend to use a section of a 100 pound propane bottle for the pyrolization and lower char section, and a 55 gallon barrel as the upper much larger diameter Monarator style moisture condensing fuel chamber.
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Old 11-26-2008, 12:27 PM
broken_mold broken_mold is offline
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Tim,

Thanks for the help. I'm presently trying to decide whether to go with the Fluidyne design or something along the lines of a more "conventional" Imbert. My present needs are pretty much the same as yours (stationary gen. duty) but I would also like to have a unit that can be used in mobile application on a similar size engine. I plan first to power the air-cooled VW engine that I currently have a couple of to drive a 25kW PTO drive Winco generator (via transaxle for 540rpm). The gen. will power my shop when I throw the transfer switch and "extra" power will run a couple of 45A chargers to bulk charge my battery bank so the PVs don't have to work so hard while the gen is off.

I plan to debug the gasifier while in stationary duty but want to be able to then either build another identical unit or use the same unit for mobile duty on an identical engine. I've heard that the Fluidyne unit doesn't lend itself to mobile applications very well for some reason. I'm still investigating that and will try to keep you posted here.

Nathan
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Old 11-26-2008, 09:32 PM
Todd T Todd T is offline
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What are y'all planning with regards to agitation? Vehicle mounted gasifiers shake enough going down the road. I know the FEMA plan has a shaker rod.

Yesterday I toured a facility with a gasifier running on pine chips driving a 25kw generator. I'm still absorbing all I saw but it answered a TON of questions. For instance, that gasifier had a vibrator attachment set up on a timer to periodically shake it to stop bridging.

This gasifier is open to the top and does not have any issues with liquid being generated. The operator said the temps are high enough to crack the tars. I saw temps of 800 to 956 degrees C on the computer display monitor.
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