GEK Wiki / Jay Martin: Spring Mills, Pennsylvania
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Jay Martin: Spring Mills, Pennsylvania

Page history last edited by Jay Martin 11 years, 6 months ago

 

Construction 

I received my GEK lvl III on Monday afternoon (March 9th). Started welding that day. Finished welding and assembly by Saturday (March 14th) working evenings. I found it pretty easy and straight forward to assemble. The most difficult was the cyclone. Welding the inlet to the swirl burner was time consuming due to some mismatch (had to close up a 3/8th in. gap). Once again, the construction was not very difficult for a novice welder. I used some cheap engine paint to protect the outer surfaces from rust. To bad the paint didn't withstand the heat very well.

 

 

I installed the new tar shield and stainless steel hearth. The resulting nozzle height is higher than indicated in prior designs. I insulated with perlite purchased from a local nursery. After getting some help from BK on the proper wiring of the fan motor, I was ready to go.

 

 

 

First Run Set-up 

My intended wood source is a local saw mill. They debark all of their lumber and chip their slabwood. I wanted to burn this slabwood. They are a softwood only mill, primarily hemlock and pine. I picked up 2 100 lb feedbags of nice, clean chips (mostly 1" square and about 3/16 " thick) with some fines mixed (sorry the picture is a little blurry). The only trouble with the chips is -- they are 36% moisture. Thanks for sending along a moisture meter with the GEK.

 

 

The next step was to load the hearth with charcoal and prepare it for lighting. Unfortunately, the bag of charcoal I purchased, though pure wood, was still not adequate for loading up the hearth; it had too much small, dusty charcoal pressed together, not the desired structure. I had some charcoal I had gathered from my woodstove, but I used all of that for the filter (still didn't have enough to fill it). I instead made a fire in the woodstove, allowed it to finish pyrolysis, and put the resulting hot coals directly into the hearth. This step greatly simplified the lighting process. I was generating gas right after I got the lid on and the fan running. It readily lit with a torch and was able to sustain the flame in the swirl burner without the continuous application of the torch.

 

First Run Results 

Everything started out great with my first attempt to generate wood gas. I did not have the thermocouple in place at the base of the reactor -- as measured from the access port in the front of the reactor between the stainless steel gas tubes -- so I do not know exactly what was going on inside. The sun was too bright to see the flame color in the swirl burner. This did not last very long. The extremely wet woodchips very quickly became a "wet blanket" on my successes. The flame in the burner stopped sustaining itself; I needed to keep a lit torch in the base of the swirl burner. I put the thermocouple in place and measured a temperature that started at 460 C and kept falling. This location corresponds to measurement point #7 in Test Report #3 on the AllPowerLabs site.

 

The fan motor speed was set to medium, and then I turned it to low to hopefully increase the temperature. It only kept the temperature from falling as fast. The reactor kept burning, but the temperature dropped to below 300 C until all of the woodchips were pyrolized, then the temperature started to increase again. I took the lid off and looked inside the reactor. There was a small amount of bridging. I just needed to shake the reactor to get it to break up. I added more woodchips to see if there was any way to get the temperature up to where it needs to be but to no avail. The temperature dropped to a point where the flame in the burner could barely be sustained even with the torch.

 

I decided to cut up some scrap wood I had lieing around outside into small blocks with the hopes that it would be drier and a higher temperatures could be achieved. I was met with limited success. The wood blocks were at 20% moisture. They were about 1.5"x 3/4"x3/4". The temperature increased as desired, but still not to the levels suggested by Jim. I could only get it up to about 480 C, not 600-650C. I did find that once I got the temperature upto 425C, the flame in the swirl burner would sustain itself. At this point, the sun was not as bright and I could see that the flame was dominated by the orange flame and not blue. From what I understand this is the result of the gas being primarily CO and not H2. I suspect higher temperatures are needed to generate H2.

 

I got quite a bit of tar, everywhere. Any good suggestions on how to clean it up? I also had a significant amount of condensation, it kept flowing into the swirl burner and half filled the quart jar at the bottom of the cyclone. I added another thermocouple at the inlet to the cyclone. The highest temperatures I measured there was about 115C.

 

Second Run 

The desire of my second run was to produce better gas (isn't that the intent of every experiment?). To prepare for this run, I spread out about 3 gallons of chips and dried them overnight to about 10-15% moisture. I agree with your assessment on the moisture meter readings Jim. I think it maxes out at about 36% moisture. I suspect my initial moisture content was greater than 35%. I lit the reactor in the same manner as in the first run; I stole some coals from my woodstove.

 

I dumped in all of my dry chips and within about 3 minutes, the reactor was generating gas of sufficient quality to sustain its own combustion. This cumbustion was dominated by an orange flame. I am assuming this is due to the lower temperatures at start-up in the reactor and from the need to pyrolize a significant amount of fuel. One interesting observations was the low temperatures coming out of the bottom of the reactor. I was only measuring temps on the order of 250-300C. I would attribute some of this to the reactor being cold, but as I would find out later, the temperature I measure at the bottom of the reactor has little to do with the quality of gas produced.

 

After running for about 10 minutes, the gas quality improved significantly. It had about equal amounts of blue and orange flame. I have noticed that the orange flame tends to not burn as quickly as the blue. It typically leaps out of the swirl burner, where the blue flame burns very quickly within the swirl burner. I was getting very little condensation burning these drier wood chips. Everything was operating great so far in my opinion.

 

The first problem then reared its head, bridging. I think bridging can be identified by an increase in the gas temperature at the bottom of the reactor and a decrease in the amount of orange flame in the swirl burner. Shaking the reactor didn't seem to be suffucient, I had to poke it down. To access the access the bridge required removing the lid from the bulk fuel barrel. I was a bit surprised at the amount of smoke filling the barrel. I pushed the rest of my dry chips around the top of the hearth and decided to add 2 buckets of my wet chips. My hope was that since things were running so well, the system may be robust enough at this point to handle the wet fuel. I was wrong.

 

The whole time, while burning the dry chips, the reactor exit temperature never got much over 400C even though it appeared to be generating lots of good gas. Once the reactor started to burn the wet chips, the reactor gas temperature did not decrease, but the quality of the gas did become quite poor. After about 15 minutes, it would no longer support it's own flame. I needed to put the torch back in to clean up the exhaust. I was also getting significant amounts of condensation.

 

I knew the water content in the chips was being a drag on the overall process. I thoguht that maybe if I could increase the temperature of the exhaust gas, I might be able to get through the wet chips. I started with trying a few differnt fans speeds. My 12v supply is a battery charger that permits me to set the voltage. The low setting tends to produce about 8v under load and the med setting about 11v under load. This provides me with a "6-speed" fan instead of just 3. It seems the best speed for me to operatre was the med fan setting and the low charger setting. I was finally able to eek out about 590C for a few minutes fairly early during the burning of the wet chips. This higher temperature still did not generate a gas capable of sustaining it's own cumbustion. The gas being combusted was well below 100C and as a result contained a great deal of water vapor. There was some CO in the gas, but the water vapor was too much of a thermal load on the combustion process for sustained burning. Looking into the swirl burner, I could see a nice orange flame once the blue propane flame impinged on the gas stream. I could barely turn the torch high enough to burn up all of the gas, yuck.

 

I had a difficult time keeping the temperature up; it kept dropping. Sometimes this was due to bridging. I repeatedly had to push the chips into the reactor. I noticed that once I did this, the temperature would increase. I found this a bit odd since I would have expected the temperature to decrease becuase of the increased moisture being drawn into the reaction from the wet chips as they were dried before pyrolysis. I determined later that it was due to my opening the top of the reactor. If I cracked the lid on the top of the draw a little, my temps would increase, but at the expense of gas quality. I think I was providing enough air in the reaction to get nearly complete combustion within the reactor leaving only CO2 and H2O (as well as lots of smoke/tar). I found I could not "burn" the exhaust clean when the lid was open.

 

Third Run

I worked on drying my chips as best I could this week and got some more. Still only have it down to about 25%-30%. Much better than before, but, as I found out, still too wet for my GEK. I can get to to light easily and generate great gas with the dry charcoal, but things go downhill fast once the wet chips get going. I was measuring low temperatures through the measurement port at the bottom of the reactor. Early, when producing good, self sustaining cumbustion gas, things were quite cold, but I suspect that is only because the reactor is cold. Later, during the wet chip burning phase, the maximum temperature I could read was about 420C, still not nearly what it should be. I must use a torch all the time in the swirl burner to keep the smoke down when burnign the wet chips. My run was cut short when my gfi circuit cut out on my battery charger I use to run my blower motor.  The chips I have keep bridging, even with vigorous shaking of the reactor. I think they may be a little too long and flat to flow effectively.

 

Fourth Run

My chips are finally down to the 10-15% range. I haven't used the microwave test to confirm the accuracy of the moisture meter. I emptied out my previously unburnt chips, lit the torch in the reactor, started the blower, dumped some diesel fuel in the reactor and lit it. Started making gas in a minute or two. I dumped my dry chips (small cheer) in the fuel hopper. The swirl burner kept going without needing to use the torch to keep it lit.

 

I did not have nearly as much trouble with bridging when using dry chips. Things kept running quite nicely for over an hour until I allowed it to run out of fuel. During the run I opened up the top and added more chips 3 times to the hopper. I would shake the ash grate every 10 minutes or so. The temperature from the front port would get up to about 470C. It was a very satisfying run until -- the reactor "puffed", banging the lid quite loudly and scaring most people nearby. It is a good thing the lid is attached with springs to release the pressure or it may have gotten ugly. In hindsight, I now realize that I observed smaller versions of this puffing at times when replacing the solid end cap with one that has a small hole in it to permit the insertion of the temperature probe.

 

When I open the lid during a run, the fuel hopper is full of very dense smoke; smoke which I presume has a high concentration of CO. I suspect the cause of the "rapid combusion" was the fuel level dropped down to below the air inlets and enough oxygen was permitted to fill the fuel hopper and mix with the CO until a nice mixture existed to be ignited by the hot coals in the bottom of the reactor.

 

It is now time to clean out the ashes in the bottom of the reactor. I can hardly move the ash grate anymore.

 

Tear Down 

I decided to tear the system down tonight. I had noticed toward the end of the last run that my pressure drop to the measurement port at the bottom of the reactor had increased from the typical 1/4" to 1", a sizeable increase. I think I now know why. Internal tar buildup. Take a look at the following 2 pictures and decide for yourself.

 

 

 

It looks like I have made a royal mess of things. Most of this tar is the hard kind and is not loose. I will now need to clean up from my mistakes. I assume most of this tar is the result of burning wet, wet chips. One last picture I took was of the hearth. Notice that there is no tar build-up near the hearth, but the is some above it on the walls of the reactor.

 

 

Run #5

I got everything cleaned up and am ready to run again. I am no longer using the fuel storage hopper during my experimentation stage. I dumped some of my chips in and lit the reactor. I then dumped may recently created "blocky" fuel on top of the small amount of wood chips. I let it run, shaking and stirring away. I could not get the temperature up to desired operating temperaures. I drilled a small hole into the 1.5 in plug on the reactor lid to allow insertion of the 24" temperature probe and took some temp measurements through the reactor. I had a hard time sustaining any combustion with my new fuel. The moisture content is below 15%. The issue now is its size. It is too big.

 

My "blocky" fuel consists of branches from 3/4 to 1 1/2 in diam cut into 3/4 to 1" lengths. In a reactor the size of the GEK, this size of fuel will bridge even more than the wood chips I had previously used. The bridging is also more difficult too break down. I think it also has too large of a void fraction, and is too easy to draw too much air through it relative to the reacting curface area. After trying to make it work for 40 minutes, I stopped the run by turning off the fan and closing all of the ports. I now know another thing not to do. I will return to my original wood chips.

 

Run #6

I removed the wood blocks and went to just chips in the afternoon. It burns better on just chips than on chunk fuel. I still run into issues with bridging. I think the issue may be my chips are too big for the throat diameter. I kept measuring the temperature throughout the reactor to get a better understanding of where pyrolisis and reduction was occuring. Due to the bridging issue, my pyrolisis kept dropping inside of the hearth rather than 3 in above it in front of the nozzles. I then would remove the plug and smash the chips back down. The pyrolisis zone would then slowly move back up to the desired position and then drop back into the hearth as the chips above would bridge again.

 

At this point I am not sure if it would be better to put in a stirring mechanism or to increase the throat diameter.

 

Tar Fence Modification

Upon the recommendation of Jim, I modified the tar fence by cutting down from the top to the middle of each hole. I then cut across from each hole, leaving about 1.5 in of metal. I bent these "petals" out to match the inner diameter of the reactor wall. The final result, installed in the reactor is shown below.

 

 

I am still having some troubles with running the GEK. I think some of my issues may be with the fuel I am using. The chips I have, were wet. I dried them. They also contain a significant amount of fines. This was really brought to my attention when I cleaned out my unburnt chips and found the following in the reactor. I was surprised about the small size of the char. I took my existing chips and screend out the fines using about a 3/8 in mesh. This ended up removing nearly half of the weight of the chips. There was much more fine material in the chips than I thought there was.

 

I lit the GEK with the screened chips and had much more success. It still seems that I am having issues with bridging.

 

My fix to bridging is found here: Jay Martin: Bridging Fix

 

What's Next 

I am now considering making a new hearth. I want to make an hour glass shape, but I also want to make it out of cast refractory instead of stainless steel. I am also considering air passages in the crucible and setting it on the 1/2 in ells in the bottom of the reactor, doing away entirely with the tubes and nozzles. It should be possible to get a decent seal between the refractory and the 1/2 in ell. Rutland makes a decent portland based refractory that is good for over 2000F. Trying to decide if it should be cast as a solid block or as multiple pieces, possibly 5. Hopefully this wil help get the temps up higher. 

 

Comments (19)

bk said

at 5:25 pm on Mar 14, 2009

Re: the tar
I'd recommend wearing nitril/dishwashing gloves when handling tarry parts. Dewatered isopropyl alcohol has been effective. Rubbing alcohol may work too (still isopropyl, more water).

The condensate can be added back to the chips going into the gasifier, once it starts running properly.

jim mason said

at 7:49 pm on Mar 14, 2009


jay, great you got it welded together up and running. welcome to the cult of the black goo. fortunately we try to keep direct interactions with the sacrament mostly in the hands of new initiates. yes, the sacrament does remain ever with us in one form or another. but do know that progress up the cult hierarchy will eventually make its presence much less ominous, with a related transparency of your gas, and new revelations of clean gasifier equipment and happy engines.

36% moisture content is very high as you know. we started including the moisture meters with the default kit as so many get bit from the wet fuel problem. most of us are convinced we can tell the moisture content by looking at or touching the wood. i'm always surprised how poor my impressions are to the the real measurement.

there are many ways to dry. the most simply might be an old clothes dryer. another easy way is to stretch ground cloth over some frame and blow warm air up through the spread material. assuming your atmospheric moisture is reasonably low, your air flow over the material is more important than temp. both high temp and good circulation are of course the best.

do you have any pictures of how your build turned out? i'd love to see what you have on your end.

jim

Jay Martin said

at 3:08 am on Mar 15, 2009

I don't have any pictures because I don't have a camera. I have never been much of a shutterbug. I will look into getting one soon.

Any opinions on drilling a small hole in a 1/2" plug and JB welding a thermocouple into it? For the hard probe, I am considering drilling a hole in the 1/2" cap to just fit the probe to limit air infiltration and not require excessive use of the clay weather stripping.

Jay M

jim mason said

at 5:54 pm on Mar 15, 2009


jay, thank you for the pictures. those are very helpful.

the burnt paint at grate level indicates either poor paint and/or overpulling the reactor. if you only had the fan on medium, it is likely the former. we use duplicolor 500F high temp paint and it stays intact as long as the reduction finishes in the bell properly. melting paint indicates the incorrect state of affairs here. but that is just our particular paint. your "paint thermometer" could be calibrated on a different scale.

from the pictures it appears you have raw wood around the outside of the tar fence. this should ideally be charcoal or more insulation. that area is all static insulation, not fuel feed area. it is essenailly another jacketed insulation area, this time to also prevent tar circulation behind the nozzles. J tube type reactors give you a good architecture to the heat transfer issues, as well as easily adjust nozzle height, but at hte cost of the nozzles coming out a ways away from the walls. the tar fence is the solution for this. or one can go to the full imbert hourglass insert, as seen here: http://gekgasifier.pbwiki.com/Jay-Martin%3A-Spring-Mills%2C-Pennsylvania

are you getting any reading on the manometer? the bung at the base of the reactor should show below 1" it seems. i often find our runs in the .25-.5 range when things are running well, though this seems on the low side. over 2" is likley going to be in the overpull regime.

jim mason said

at 6:05 pm on Mar 15, 2009


as for thermocouple probe points, we similarily drill a hole in the cap or plug at the bung points, for probe insertion. we then plug the small hole with the provided clay. you can do htis more fancy with purpose made probe ports, or 1/8" brass compression fittings from the hardware store, but a hole and clay works just fine. you might also want to put one in the fuel feed port lid, so you can push the probe down into the reactor, in front of hte nozzles.

this combustion area temp is the most important one to monitor. later you will likely want to hard install a TC probe to somewhere in this area for more consistent reading. the coming GCU will enable one to read 16 points of TC reading and 4 vac/pressure points simulataneously, with data logging, and control decisions in relation to these temps and pressures. see here: for the details: http://gekgasifier.pbwiki.com/Gasifier-Control-Unit-(GCU)

be cautious on your confidence in the moisture meter readings. these resistive meters need to be corrected for wood species and ambient air temp. we need to get these charts up on the wiki, as well as run purpose heated wood moisture tests to compare absolute results against the meter readings. these meters are not the most expensive on the market. on the contrary, they are about the cheapest, thus why i can include them free with the kit. but a raw resistive reading between two spikes is not a complicated instrument, and likely they are an ok tool for an approximation. certainly better than nothing. and with some modest shared configuration and compensation, they will rise to an acceptable accuracy for our purposes. no resistive moisture meter has scientific accuracy. they are instruments for a quick approximation, which i find critical to understand your fuel.

j

Jay Martin said

at 3:26 am on Mar 16, 2009

Jim,

I did fill the area around the tar fence with perlite to just below the nozzles. I finished the bulk tank and put it on the reactor. This may make measuring the hearth temperature a bit more difficult. I may need to go in through the iginition port. I am drawing at the most a 1/4" of vacuum through the reactor and about 1/2" after the filter.

(account deleted) said

at 12:48 pm on Mar 16, 2009

Hello Jay M.
We also found it very beneficial for gas quality output on Marcus B.s GEK to rotate and shake the ash grate every three to four minutes of operating time. I Think this breaks up the char and shakes off the ash to expose fresh char surface for the reduction process.
Kerosene/lamp oil is the traditional cleaner for pitch and coal/wood tars. Safer than gasoline. Less smelly than diesel. Cheaper than alcohols. Use cotton rags to wipe and then burn up.
I predict 1200F (630C) black stove paint will become the most popular GEK color (hides the tar stains).

Regards
SteveU.

jim mason said

at 1:54 pm on Mar 21, 2009

jay,

great report. thank you for it.

you are relearning the two great challenges of a fixed bed, closed top, downdraft gasifier: moisture and fuel shape.

moisture content can quickly send your thermal releationships into a tailspin. the heat sink of vaporizing water is so high that it will quickly overwhelm desired combustion characteristics. see the energy balance work here for a summary of how significant miosture is: http://gekgasifier.pbwiki.com/Modelling-Gasifier-Energy-Balance

this is one of the core problems with a standard closed top imbert gasifier. they are extremely sensitive to moisture in the fuel. with a closed top, all the moisture in the fuel is going to get vaporized and all of it is going to be forced through the combustion zone.

the GEK air preheating system will give you a little improved moisture tolerance as it removes the air thermal load on the combustion. the greater improvement will be the fuel drying and preheating systems that are just around the corner for the GEK. this is the point of double jacketed auger feed systems recently announced on the wiki. both the horizontal and vertical forms of these automated feed systems include fuel drying/heating systems. see the gek improvements page for details: http://gekgasifier.pbwiki.com/GEK+Improvements%2C+Add-ons%2C+and+Customizations







jim mason said

at 2:08 pm on Mar 21, 2009


the second eternal problem you rediscovered is the fuel shape issue, and how easily this can lead to bridging. for a constriction type gasifier, it is CRITICAL that the fuel is chunky. either round or squarish is good. flat strips and stringy fuel is very bad. it will always bridge. even good fuel will still have bridging problems. this is the major challenge as one downsized a gasifier for small scale engine running. larger gasifiers have larger constrictions, thus much less of a problem here. at a 3" constriction, this is about as far as i think possible to downsize unless you are running pellets. i used to run a 2.5" restriction with walnut shells and got reasonable flow. but i would have had a mess with wood chips.

there are two main types of wood chippers: disk and drum. the disk chippers will produce a much more chunky chip than a drum chipper. drum chippers are what produce the long cupped slices chips. make sure you use a disk chipper, and best to still sieve it afterwards.

the best solution is some other type of chunking machine. this has been a topic recently on the woodgas list. search here: http://tech.groups.yahoo.com/group/WoodGas/

you might want to just cut up some small blocks on a table saw or with a skil saw. many people do this. steve u has some thoughts on this.

j

jim mason said

at 2:17 pm on Mar 21, 2009


and yes, a stirrer rod is very important for more difficult fuels. the bridging is actually mostly at the intersection of the pyrolysis and drying zone. it is not primarily a problem that follows from internal reduction bell char flow, as misclaimed in other parts recently.

the intersection of the drying and pyrolysis zone is where the black goo is cold enough to form a glue and make a cap. the hole starts here, then the lack of weight on the bed prevents the char in combustion zone from refilling the reduction bed. soon you have a channel through the reduction bell, reduction doesn't complete, gas quality plummets, and the temp of gas coming out the bottom of the bell goes up quickly. char tends to not bridge inside the reduction bell, as it is size reducing while chemically reducing, so even a straight pipe reduction bell will tend to flow ok.

detecting bridging is one reason why it is so important to have a thermocouple immediatley at the bottom of the bell. not at the side by the gas cowling. but right at the edge of the bottom of the bell, sticking into the char/gas stream about 1/2 inch. this TC will tell you a ton of things. it is the most important point to start a TC install.

it will tell you when you bridge by a sudden temp rise. it will tell you when you overpull by a slow temp rise above 650C. it will tell you when you have too moist of fuel you never get up to the proper 625-650C you should see at the end of the bell, indicating reduction has run to its usable completion.

of course you can't know the high temp from which this reduction started until you TC the combustion zone. this TC also tells you if you are getting up to the 1000C needed to fully crack tars. so maybe the combustion zone and end of the reduction bell are tied for first in importance for TC location points.

never start a gasification project without TCs. this is why they come standard with the GEK kit. you are driving blind without them.

jim

Jay Martin said

at 3:35 am on Mar 22, 2009

Jim,

Thanks for the great comments. The one thing that would be a great help then is to include an indication of thermocouple locations on your drawings. This should make it very clear where these measurements are being taken and can be used by others to provide a consistent standard by which to compare results.

I do not see hand cutting small chunks of fuel as being a viable option for anyone to generate any volume of fuel. I also see it as being potentially dangerous cutting small chunks with power saws by hand.

Jay M

Charlie Sellers said

at 7:42 am on Mar 22, 2009

Jay,

The cutting small blocks (or spheres, I am just afraid to try) can be only a one time affair - for when you want to try the flow characteristics of a fuel through a hearth. For a given restriction there will be some maximum size of fuel which flows easily and reliably, and we can imagine that it is some number X which is a divisor of the maximum restriction (diameter). In my experiences X is on the order of 6-8, so for example if the maximum is 3" and X is 8 then cubes of 3/8" will tumble easily and you may never see "bridging" (fuel blockage of the hearth). In reality the real diameter of blocks is the diagonal, you mention tar sometimes adding some stickiness that aids bridging, and other fuel characteristics come into play that determine the "angle of repose", which determines how fuel flows towards the hearth. In real fuel these include shape (Jim mentioned fibrous ones, which always flow poorly), density, and moisture content. So if you happen to want to carefully cut cubes (instead of using this as a thought experiment, and you can also use real fuel with your hearth on a bench) then practice safe sawing by using bundled sticks, a chops saw, and a jig. This all will cause you to consider you candidate fuels more (What is X? Note that too small is a problem since then fuel can flow right through with no residence time in the hearth.) and may lead you to choose different chipping methods, partial drying, or quick sieving to get optimal fuel for your GEK experiments into gasification " practicals". It also makes us think about how aspects of a gasifier design might be optimized for the specific fuel that you have lying around in great quantities. This all leads me to using woodstove pellets for some model runs and better repeatability - they can have a good size and reliable flow characteristics for the GEK

Charlie (Berkeley, CA)

Charlie Sellers said

at 7:44 am on Mar 22, 2009

Pertaining to fuel moisture measurements, I also use a microwave (or toaster oven) and a postal scale for rapid and very accurate measurements, Tom Miles has recently posted on the standard method the Gasification site (http://gasifiers.bioenergylists.org/milesmccontent), and I agree heartily with limiting yourself to 30 second pulses when the fuel is approaching dryness (and the weight stays the same) to eliminate the chance of smelly kitchen pyrolysis. I'll post soon about my own measurements as a function of microwave/oven "on" time, and on moisture reabsortion from the air as it seeks to go back to its equilibrium value (http://www.csgnetwork.com/emctablecalc.html). I feel for those living in the tropics (hard to get below +20%).

Charlie

Jay Martin said

at 8:53 am on Mar 22, 2009

I have been thinking more about the fuel bridging question. I think a nice test may be the "slump" test, something similar to what is done for testing the stiffness of concrete. Pour you fuel into a smooth-walled can, tap it a few times to settle the fuel and lift the can off the fuel. Measure the height of the pile after removing the can. This should provide some insight into the ability of the fuel to either flow nicely or tend to bridge. My opinion of the fuel briding issues I am having are from two sources: the relative flatness of the chip and the moisture content of the chip. My chips have been laying out on my garage floor with a fan blowing over them for a few days now. The moisture content is down to the 10-12% range for most of them. They seem to be much more "free-flowing" when dry. We shall see how things go once I get my GEK back into runnign order (clean it out after the last, aborted run).

Jay M

jim mason said

at 3:27 pm on Mar 22, 2009


now jay, those "explosions" are properly referred to as "puffs" in proper company. yes, it is an issue to run a reactor down to the exposed coals. there will always be some mixture of fuel gas and air in the area above, and it will ignite. if the volume is significant, like in an empty hopper, you can get quite a boom. this is why it is held on by springs. make sure the rubber weather stripping is installed on the lid edge so you get a good seal.

we do not use a puff lid on the reactor itself. i originally set it up to have one, but it proved unnecessary given the small internal volume. with a hopper, it is required.

small point of vocabulary. to keep things straight, we usually refer to the thing you put the fuel in to make the show go, as the "reactor". not the burner as you are using above. the "burner" is the thing where the gasses swirl and the syngas burns. the "reactor" inserts into the "gas cowling". the "cyclone" attaches to the gas cowling. then the "packed bed filter" and "vac/blower" attach to it.

your flame temps still seem very low. the 470C you report is the flame in the swirl burner, right? are you moving the probe around to find the hotter point? this is usually about half way down against the wall opposite the entrance. you are keeping the nozzle into the swirl burner about even with the orifice entry so a venturi is created to pull in air?

you should be seeing temps between 800 and 1000C in the swirl burner. if you are only getting 500C, i'm surprised you can even keep it lit. it seems you must be measuring this temp in some different manner. can you clarify exactly what it is you are measuring jay?

j









jim mason said

at 3:35 pm on Mar 22, 2009

also, your hearth ideas sound VERY interesting jay. i had not thought about getting rid of the risers and nozzles themselves by casting these pathways into refractory. i like that idea very much and see great potential in it. please do build this.

i think you'll still need to have the short 1/2" npt nipple stubs in there, then holes in the refractory hearth block that slip down over them. you'll still need to fixture this refractory block to the base, or air will leak back down the slip joint and out the bottom of the hearth seal. or maybe with a very accurate base plate in the casting, you could use the edges of the 90 elbows as the flange surface, with some goop to help get a seal. i can make such a plate for you if this would help. though i think the more flexible solution will be the slip joints.

luc up in bc is similarly interested in casted hearths. you might also want to talk to him about his ideas.

jim

Jay Martin said

at 3:30 am on Mar 23, 2009

Jim,
Appropriate edits have been made to be more clear.

Jay M

Jay Martin said

at 4:46 am on Mar 23, 2009

I do have a few small concerns going forward. One being quite minor, but a potentially dangerous situation. How do you suggest sealing the flexible hose in the PVC connections. I have tried using an all-purpose PVC cement but have not been very successful getting an airtight seal. I have repeatedly added more of the cement but without much success.

On a "properly" running GEK, do you get any condensate in the quart jar at the bottom of the cyclone filter or only fly ash? I presume one would want only dry ash there since all of the water vapor should be getting reduced in the char bed.

On reviewing the Test Report section on the All Power Labs website, I now see the locations used to measure temperature in test #3. I have been reporting temps from test point "8". I am not quite sure how to put a TC into position "7" as Jim has indicated is the most critical position to measure temps and know what is going on with the reaction. I suspect a TC with a much longer lead will need to be installed permenantly into the reactor. See http://www.allpowerlabs.org/gasification/gek/gekreports/report3/tempprofilev0.9-800.jpg for TC locations

Jay M

(account deleted) said

at 6:05 pm on Mar 23, 2009

Hello
Been unable to participate untill now.
To seal your hoses I would recommend using a Permatex #101BR 700F (371C) Ultra Copper Silicone then hose clamp. Would work good on the flange joints also. You Must razor cut to break the seal for removal.
Yes I have recommended powersawing pallet wood for testing purposes. You don't have to do this yourself if are uncomfortable. With the 600,000 construction guys and gals out of work I am sure you can find someone willing. You don't think I wipe and debug my own PC do you? Naw, too scary for me. Allmost all of the pictures and vidios (except the Finns) show chunked wood in the current Imbert styles. Dutch John says he buys his wood preprocessed. Jay your chips look good enough, I just think while learning gasification operation we would all benefit from using the easiest fuel first. Then with known good operating characteristics you could adjust, adapt for the fuel of choice. All of the GEKs commented have wet condensate in the cyclone. Jim has even talked of using this to wash flush the cyclone walls.

I would like to send you two Australian articles about your deleted proposal. PM in the owners site? And tell this powersaw brave PC chicken old man how to delete this comment line.

Regards tree farmer SteveU.

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