Jan, I never realised you didn’t have a grate. Your build looks pretty close to mine. The main difference I see is my outlet is positioned higher. I believe that’s what causes char and ash to lift and not pack. Still, too many shutdowns and idling around without giving the gasifier an opportunity to breathe properly, will eventually tighten the charbed.
I agree with @SteveUnruh, to be safe, grate and grate shaker is the proven way to success. Without them you’re left with adjusting your driving to manage the charbed and that can be very hard to do without vacuum guages. The vacuum ratio will let you know in an early stage what action to take. The balancing act is a lot harder to perform blindfolded.
I mentioned before I avoid spruce because it doesn’t create pieces of char, only thin flakes. Apart from containing a lot of tar and producing a lot of soot, pine shouldn’t be a problem. Birch is very solid but contains a lot of tar too.
Try alder if you have it. It’s extreemly bulky but contains almost no tar, produces very little soot and its ash is only fly-ash. Shouldn’t pack and settle too easily.
Thanks for all the tips, they are very welcome, I thought I would get this thing successful sometime, or if it is the machinist who needs to learn how to handle things.
This is how the coal looks both above and below the nozzles, do not know if the size should be different?
It is important to know that the reduction char fills above the restriction level. All this charcoal pluged your gasifier outlet! You probably made good gas but the engine was starving, hence the need to shut the air down entirely.
Fiting in a grate wuld be best for a beginer, grateless gasifiers are great but require some practice to master.
But, looking at your skiz, thats not realy possible. Not enough space, exept if you extend the tank under the restristion.
My advice is move the outlet as high as possible. See where this brings you. I had the same problem even with a high outlet, l then fixed in a mesh to hold down the char.
Hi, Jan!
18.5.2020
The height (distance) to the restriction should be no more than the restriction diameter!
For a strong swirrel not more than 0,3 diameters below the restriction.
Ash “settlement” below and around that plate.
Plate diameter 3 – 4 restriction diameters (or reaching to the ring of vertical anglebars).
Eventual? vertical angleiron ring (with vertical, welded to a ring, hanging anglebars) bolted to a cylindrical heart-bottom. Easy to screw down in one piece.
In that case, the “plate” can be hinged on an iron bar just under its diameter-line.
Screwed to the plate from below, a “flat bowl” insulation pan filled with mineral wool or ash.
That makes tilting and “raking” from the ashdoor very comfortable.
Max that sounds like the grate I have in my S10 except I also have angle iron bottom instead of flat plate. They are welded one side only so they can expand over the bar on the other end.
Hi, Don!
19.5.2020
Each second angle – bar welded on the opposite side; the same reciept as Tom tried out a few years ago…
Now I want to find out how a horizontal flat “violent” swirrel behaves on a “buckle – free” insulated plate… to preserve the process heat. Restriction (cold & empty) 2,5m/s at full WOT, top road speed at highest gear.
Additionally, plate “midship – tiltable” via the ashdoor… for easy cleaning.
Max
Hi, Jan!
19.5.2020
Your question does not start from the proposal presented, as your construction has a conically expanding reduction with a consequential reduction in flow velocity when reaching the grate.
The proposal presented starts with a cylindrical hearth and a flat bottom with the reduction opening in the flat bottom.
So, here the restriction sits in the flat metal bottom of the hearth cylinder.
A decreasing diameter from the nozzle–tips down to the restriction at the hearth bottom.
A ~60* oxidationcone.
The reduction happens directly under the horizontal flat bottom of the hearth cylinder.
On the described (downward insulated) tiltable flat plate.
The aim with this, 0,3 – 1 restriction diameter high FLAT chamber is to develop a tumultious, furious, mainly horizontal streaming toward the vertical hanging angle – bar grate at the perifery of the oxidation “barrel” bottom.
You mean the barrel rebar?
The rebar I used was the type in the pic below. I forced it into a round shape a few turns and tightened it with a couple plastic stripes, right where the barrel belly is the widest. That way the ring doesn’t fall down even with nothing but tension towards the inner wall holding it up.
Hi, Jan!
21.5.2020
To make easier dimensioning of the cut-cone oxidation zone in a cylindrical hearth, you can have some help by using this easy measure and volume calculator:
Conical Frustum Calculator
“allt mellan munstycksspetsar och restriktion”
In your case 6 – 8% process volume of the
“sekundenverbrauch”,
or consumption per second at WOT on highest gear. (full road speed)
l = liter deplacement
r = RPM : 1000
3 = all process factors together
l x r x 3
Remember to keep the slopes at 60 degrees!
This is giving the net gas consumtion per second.
And the active process volume is
6 – 8% of that. (for your size of motor)
Cold primary air consumption ~60% of the output cold gas…
Nozzle blast with cold air : 18 m/s, preheated x 2 – 3 K–steps.
Increases with the Kelvin factor 2 – 3 times !
Restriction (empty) velocity: 2 – 3 m/s,
with glowing, blasted char 4 – 5 Kelvin steps expansion and fuel–reduced area,
(area reduced by the fuel) the velocity reaches over 20m/s.
Usually the free area is ~40% of the total area (in a restriction)
I have trouble getting the lid tight and at the same time the pressure should go out easily.
What do you think of 2st stainless steel bowls with a rubber seal in between and springs for the pressure? https://www.clasohlson.com/se/Bunke-Coline/p/44-2148
Hi Jan!
23.5.2020
The sidways “rolling” stability is like a hat on a round skull!
There is no “bow” over the lid to give “roll-off” stability as traditional silo lids use to have.
Natural causes and natural results go hand in hand.
As you know normal lids do have “cylindrical” and plane contact surfaces.
Cylinder-head valves have ~45* mashined seats, but they are very strongly guided by the valve spindel… (stem)
You could ? weld a cylindrical ring under the lid, just passing the “bucket” opening on the inside. Make it hang down 50 mm or more inside the buckets edge.
This cylindrical ring welded ( or bolted ) to the lid gives sideways stability, but is still cumbersome to handle.
If this is a silo lid, having “puffs”, you better make the ring with big holes to release the gas without “piston” properties.
A broad band, perforated (with big holes) could probably work…
Still, a stronger than hen-net with big smooth squares would do… for concrete enforcement.
Automatic stability by turning the “lid” upside-down!
But it still needs some guidance, if the springs are not identical and symmetrically spread around the hole!
Jan, in my humble opinion a little short lived smoke at shutdown is no big deal. As long as the lid doesn’t leak in enough air under vacuum to cause hopper puffs you’re ok. Better to have a flimsy lid that seals under vacuum than be forced to use a crowbar to open it in the morning.
Yes, I have to make a new lid, what I have now is very tight but difficult to open in the morning as you say JO.
If I heat the outside it works, otherwise hopeless to open.
Think it is so on the grounds that the surfaces fit too well, will be too large abutment surface.
There was a German song from ww2 about woodgas maintinence, cant remember where l saw it but one part goes something like “grease all lids”. A good (prefferably graphite) grease on the lid seal will help seal better and help to get it loose once opening it cold. Thats what l did. I aplyed a thin layer of grease on the silicone seals and they never got stuck. After a while the grease melts and needs to be reaplyed but it will usualy hold for about 3 or 4 days of dayly use.
I have tried with copper paste, it keeps too high temperatures, but it has not worked so well, I will test with grease, the seal is very good in this way.
