Actually you are smart to come on here and your questions are not stupid at all. Your first unit is very close to working that is an excelleant first build. Its a lot better than my first ones and I was reluctant to get involved in any forums for help. So I struggled through it on my own. It would have saved me a lot of money and time had I done so though. However, I am a manufacturer so I try and stay away from sites to keep my designs my own. This is the only site I belong too as far as gasifiers go.
Im glad you came here Im sure every one here will learn something form you on this build.
i agree with Matt, i think you have too much air at the nozzle area, and you may need to use some smaller fuel for that restriction sizeā¦ just my two cents, take them for what they are
Matt, Thanks for the kindness. After double checking for leaks, i found none except the top cover which i ran loosely for blow back protection. I did not dare to tighten the springs tight enough to seal the lid properly. Today i built a blow off valve similar to a supercharger burst panel to install on the top of the cover. Now i will be able to safely seal the top cover properly. I have decided to try a straight reduction tube. If i make it flush with the bottom of the hearth, i can get 4.00in maximum depth of char under the nozzles. I am planning to make the reduction tube 4.50 to 5.00in. ID, is this in the ballpark? What length would you recommend? How much space between the tube & grate?
Hi Pete, What I meant by wall to wall was simply to make a grate almost the same size as the tube itās in, which is a little different for my design. Your grate seems large enough but the distance from the nozzles to the grate is shy of the imbert spec(H+R) but it could work ok. Your char bed just wonāt be as deep as it could be and the residence time of the gas exposed to the char will be shorter and could affect gas production somewhat. Yes the deep bed of char rests on the grate and all the way over my nozzles approx 4" also. The fire between the nozzles is like a 3 dimensional oval with the bottom of it being drawn toward the restriction.
I did notice one potential site for an internal leak like I had in my fluidyne where the fire tube was only tack welded to the flange. This allowed gas to by pass the hot char bed and H20 (steam) also to by pass it and condense out further on. If your bolted on cone has no gasket, itās possible for gas to be drawn through the connection by passing the char bed and the H20(steam) gets passed through also and condenses out further down the line as waterā¦ Try a stove type rope gasket here and tighten well. Also cut the cone down to where the restriction approaches the 4 to 5 inch diam. As a general rule the distance from the nozzles to the restriction diameter should be approx the same-see the drawing of my GEK type to relate the numbers to the imbert chart lineC. You may end up rolling a new cone in order to meet this spec to the numbers,so try getting the 4" restriction first and see what happens.
I agree with Matt and Arvid, there are no stupid questions. Weāve all been there. Good luck with the mods.
Pepe
My drawing is a BMP file so Iāll scan and save as a jpeg and send it tomorrow.
To be honest I just run the little engines. So my units are small. Im actually in the process right now building an M-series II Gasifier. So as Im building this new one it is simalar in size to yours. Im specking this new one to the specs in the (Hand Book of down Draft Gasifer and Engine Systems)
The smallest restrictor openning is about 4" and the nozzle hight form the restrictor oppenning is about the same. My reduction zone is unique, but in any case it really depends on the fuel density how much depth you need after the restrictor openning. I would go with what has been suggested and fine tune later. If you get clogging you will want to resuduce the amount of reduction.
Matt, I was pondering whether or not to cut the bell top to 4.50in. dia. & try it. The problem is that the bottom of the bell is only 2.00in. deep. I think i will cut several flanges to experiment with.
Hi Pepe, Do you think it is worth playing with the bell vs. a straight tube? It is very easy for me to make a new flange & straight tube. How long should the tube or bell be from the bottom of the hearth or from the nozzles? What should the distance be from the bottom of the tube or bell to the grate? The flange has an 8 hole pattern on an 8.00in circle & both surfaces machined flat. The bell is fully welded to the flange. I see how your grate is adjustable, how do you shake the fines? Rotate?
Hi Peter, Iām stuck thinking in terms of the larger base I have for adjusting the height of the grate. Iām not sure you have the luxury of a lot of depth to play with. The tube may be easier but provides a smaller bed of char. Itās a hard call. Try the easiest cone fix first and see where it goes. No matter what, you will put another piece of the gasifier puzzle in your head.
Pepe
Pete. I agree with Arvid with your having too much air although this does not come from my experience just a āmatching upā of your numbers to the imbert charts. If you decide to increase your hearth diam, try temporarily plugging every other nozzle. Having fewer nozzles will increase the velocity of air in the remaining open nozzles and allow deeper penetration into the combustion zone. Pepe
Hi Pepe, You were right, I had leakage between the flange & the bottom of the hearth. I machined the bottom of the hearth, but did not machine the flange after welding ------ must be getting old & forgetful !! Did not look at the flange until today. Is that area too hot for silicone? I was thinking of cutting the upper part of the bell off flush with the flange. This will leave a 5.750in hole. Then i was going to make another 8 bolt flange with my desired reduction hole cut in it & bolt the two up together. What do you think?
No, better not. Coal has a lot of nasties in it that have to be burned out before it is useful. Youāre thinking of coke, the coal equivalent of charcoal - pre-cooked coal that has all the impurities removed, and is mostly pure carbon. Good luck finding that. You should probably just pick up some natural lump charcoal at Walmart and break it into small pieces. Or make your own, thatās always fun. In fact you can do it right in the gasifier, just run it backwards. Blow air in the gas outlet and leave the lid open. Light it at the top and wait. It will smoke a lot, but youāll end up with decent charcoal. Sometimes you can flare off the smoke if youāre clever about it.
Chris, Well, looks like i did not miss anything, I did everything wrong!! I think i should junk the operator & keep the gasser. Of course, i used anthracite coal on my first try. (readily available out here) Looking like my next try will go much better.
Peter, My current trailer has 8 nozzles in around a 9 inch circle that are drilled 5/16" in the pipe caps. The restriction is around 4 inches below the nozzle plane and is 3.5" in diameter. My grate is fixed and around 4 inches below the restriction. It is bars at 3/8" spacing. It looks like if you trim around an inch off that cone, it will put you at around a 4 inch restriction and maybe 4 inches down from the nozzle plane. This may leave you with 6" of reduction height before your grate ā¦ Looks good to me ā¦ I havenāt had any problems with this current unit but I only have around 600 miles on it so far ā¦ Mike L
Hi Pete,
Glad to hear of your findings and progress. That first flare is well on the way !
Buy a few bags of natural lump charcoal and after you have hacked the larger opening for the restriction bel, start filling from the grate all the way up through reduction cone all the way up to the nozzles with that natural charcoal. You can use even more if you like, but when you light it up it WILL be making some heat for sure. Probably like more than 2000 F degrees of heat once you put some air to it - think of how the blacksmiths used to work with a bellows, and wood fire to make red hot metal kind of heat from charcoal and some air being blown in. Some of the odd shapes and protrusions inside the gasifier will cause spent (fully gasified) charcoal to remain in layers , and that leftover charcoal will act as natural insulation to support the combustion and reduction that makes the really extreme temperatures. So if you cut the cone, you may benefit by leaving it sticking up 1/2" to 3/4" above the hearth floorā¦ that will give you a 1/2" to 3/4" layer of charcoal insulation on the metal āfloorā and along the sides up to where the nozzles stick outā¦ all that outer region will fill with dead charcoal that acts as insulation.
I would guess that within 10-15 minutes of lighting off the charcoal you will be making some billowy white or grey smoke that will start to support a flare, as long as you have control of the air to make the fire hot enoughā¦ did you make an ejector ? I measured the one I posted a photo of to move 5-10 CFM of air through a packed bed of pellet charcoal (pretty dense stuff to draw air through) on about 10-20 PSI. Pressure is just part of what you need to make the air flow you need the CFM too, or the volume of air moving through the system.
The inner parts of the gasifier, (inside the nozzles towards the center of the burn chamber and down to the opening on the restriction bell and down to the grate) will all be hot, hot, hot buring fuel or hot charcoal with depleated oxygen for reduction - the chemical and heat reaction process for the breakdown of combustion byproducts into quality woodgas or āproducer gasā.
People use the word"coal" as short for charcoal sometimes, not meaning to use coal from a old locomotiveā¦ I have a couple of chunks of antrhicite and was wondering if I should grind it up and try it, but now thinking its not a good idea. Thanks for the lesson.
