I’m in Quinte West. Some day I hope to move up near your neck of the woods. I really like Bancroft, it has everything you need, but 10 minutes in any direction puts you in the sticks!
So it has been a productive day. I’ve located two hammermills, been in the barn for 35 years, my choice 50.00. I pretty much don’t care what condition they’re in at that price 
. Guy has a barn full of stuff from when his parents actually farmed, I’ll be bringing along some extra cash in case there are some other goodies I want but he doesn’t. Right now there is a pile of ice/snow preventing access to the barn so I’ll have to wait a bit to have a look at them. I also found a guy selling small bales of hay 2 minutes down the road, that task took about a minute:grinning_face_with_smiling_eyes:.
I am well along with the design, most of the parts needing cutting are figured out and drawn up, and I’ve sorted through and picked out some of the hardware items like hinges and knobs etc and drew them in. I found a good chunk of 6" Sch.40 pipe that will be the basis of it all.
If all goes well, all the design work will be done this week, and parts cut by Friday!
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I think my choice would be both expecially if they are the same brand. The second one for parts could be the best money you could spend.
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I know nothing other than one is a belt drive, has several screens, has a fan, and ducting that feeds two bags, with a gate that changes from one bag to the other. That must mean it fills the bags fast right?
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I think the hammers and stuff can wear out that is probably why they have two of them. One wore out. I don’t know if you can reface the hammers with hardening rod or not.
Since I work at a shop that has waterjet machines, I’d probably just pull one, draw it up and have a bunch cut from something like AR400 or 500. Each hammer has 4 edges to wear out, so it should be easily seen how much use is left on them. I’d think using hard facing would require machining where you built it up to provide a flat face with a sharp edge. Cutting new hammers here with say 1/4" AR400 would be so cheap that I wouldn’t even think about doing all that welding! Plus I’d be a little worried about balance if I started welding material on indiscriminately.
Good point - I’ll have to make sure I see them both - package deal! lol
Here it is thus far, I still can’t hang my hat on some of the details yet. The idea is to auger the milled straw up the tube past the air nozzles, suction is applied at the top through that 3 inch pipe welded on the cover. The air nozzles will be hex pipe plugs, and will be screwed into half couplings. I will be making 4 sets with 1/8", 3/16", 1/4", and 3/8" holes in them. There are 4 nozzles total in the unit. There is a cutout in the top right for the ash to fall out, the whole unit may be tilted towards that side a bit if I think it will help. There will be an ash hopper and some minimal cooling on the right side yet to come. I will be using a variable speed fan to help control airflow.
My hope is that after light off, a glowing bed of burning char will form above the nozzles and get to about 4-6" thick as the auger feeds fuel up the tube. For now, I’ll turn the auger by hand based on temperatures measured above the nozzles. The gas would be drawn through the bed, residence time will be short, but straw should be low tar. I’m thinking the air required to oxidize will be related to the weight of the fuel rather than volume, that is why the air jets are so small.
I’d love some feed back on this design, positive or negative. Best to hear the pitfalls before I commit - throwing steel in the scrap bin is expensive - changes on the screen are free!
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You might have issues with the auger and the round tube locking up especially after some wear. Things can get wedged between the auger and the side of the tube and lock the whole thing. You may also have issues with the hopper heating up from the heat of the reactor. I am unsure how well that is going to pick up material being vertical, but I guess the bowl shape of the auger will handle it, if it slides in. I have suspicion the material itself isn’t going to flow very well unless you pelletize it.
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I had a crappy pellet stove years ago that had a lifting auger, and it would jam up on wood pellets semi regularly. I fiddled with it and eventually realized that the reason it was jamming up, was because the auger was fixed on both ends. I cut it down so it was fixed on the driven end only, and never had a jam up again, not even one. There was a little slop in the fixed end, and a sloppy fit on the auger inside the tube, this allowed for some movement. Whenever a pellet got between the OD of a flight and the tube, the auger would deflect and keep pushing pellets eventually cutting up the stuck pellet or bypassing it. I would notice an occasional “blank” or near empty flight when feeding, but that was not a problem. It moved a lot, constantly actually, but worked great! This auger is an exact copy of what was in that old stove, a sloppy, wobbly, standing auger fixed driven end only. Hopefully it will work just as well.
Feeding from the hopper may be an issue, I may revise the geometry of the hopper and tilt the whole unit to ease entry and exit. Vibration and stirring could be incorporated if needed. I’m going wait and see if it makes gas before I go too hog wild.
What do you think the chances of this design actually making decent gas? I’m a little worried that the char bed won’t build up, or last as long as I hope it will. What happens is the char bed is minimal?
If the char bed becomes the issue, I don’t see it ever working unless I Pelletize as you mentioned. I’ll probably make a big set of nozzles and try it out on pellets for it’s maiden voyage, that will slow things down a lot, and if it makes good gas, then at least I know the design works.
I think the gasfier I was thinking of was this one, but that doesn’t look exactly like it, so it might be v2 or a totally different one. It is a different video then I remember at the very least.
Have no experience with chopped straw, but once ran an auger nearly vertical to carry away fines and sawdust from a large wood chipper. Only clogged if something oversized got into it. Finely chopped straw should feed well as long as nothing stringy gets in. Good luck, be fun to watch, have lots of sawdust to try.
I agree, any auger issues I think can be overcome, hopefully there will be none. Hopper flow might be a different story! The only real hard to solve issue I think I’m guaranteed to run into is making good gas!
I have decided to rework the design to have the tube running horizontally. I think Sean is right after staring at the drawing for a while, there will be issues feeding the auger from the hopper. I am going to proceed with the idea that the straw contained in a hopper will “lock” together somewhat, and resist changing shape enough that gravity alone will not convince the mass of straw to flow in a tapered hopper, or make a right angle turn at the bottom of the hopper. Would be nice to have a mill right now so I could experiment with some straw particles to see how they behave.
So, the tube opening feeding the auger will be doubled in size, and the hopper will have straight walls and be the same width and length as the auger opening making it more of a feed “tube” than a traditional hopper. I’ll also increase the height of the “hopper” to gain back some capacity. This hopper will allow the straw a straight shot down into the auger without asking it to change shape at any point. There will have to be some kind of restriction along the auger tube such to require some pressure to move the fuel/ash to ensure the fuel fills the tube top to bottom while running horizontally. I will add an ash dump hopper and might have it feed finally into a 55 gal drum to act as a drop box and for cooling to save my squirrel cage fan.
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I have reworked the design to be horizontal. Things got big quick. I found I was making a lot of assumptions regarding flow characteristics, and weight per cubic foot - just nothing out there on milled straw gasification. I feel the unit density is a critical design detail. Wood is a lot heavier, and known restriction and nozzle sizes for wood chunks are likely relative to the density of the wood. I’m thinking milled straw with the same wood use nozzle and restriction diameters will need a much larger hearth size to throughput a large amount of the lightweight fuel.
The design is done, and the BOM is made, but I am going to wait until I can get that hammer mill and find a way to drive it so I can run some tests to verify a few things before I start spending all kinds of money on a bunch of guesswork.
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This wasn’t the article I was looking for, but it is still fairly interesting. They show both a design and their math for a fluidized reactor, and it is a far simpler design then the commercial design. It is worth looking it. It might give you an idea.
http://www.scielo.org.ar/scielo.php?script=sci_arttext&pid=S0327-07932007000400011
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These guys are saying 80% sand and 20% dolomite will give a 40-50% reduction in tars (with their design). I didn’t read the full article.
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Thanks for the info Sean, I’ll check it out.
I’ll be having a look at those hammer mills tomorrow aft, all this rain has really knocked the snow down, and guy says we can get in there now.
Do check it out. It is the first design I have seen for something of that scale that includes the mathematics behind the design. It still may have to be fudged for what you are using, but it is a great known starting point and looks fairly simple. I really think it will work better then a char bed for your material without making pellets, which is what you initially asked for.
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I recently found quite a few successful rice hull gasifiers on YouTube that are doing essentially the same thing I’m trying to do. The husks might as well be milled straw, small lightweight pcs of biomass. It’s all being gasified loose so that is encouraging. I’m going to look at these units some more, pretty clean looking gas, some could be made continuous feed easily.
I also stumbled across a great method of turning rice hulls into charcoal, that is also possible to work with milled straw. I’ll be keeping that in the back of my head for possible future use!
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This PDF has useful information about various straw and ag waste combustion.