Gasifier Design Pondering

This is just going to be a topic where I dump random questions running around in my noggin, feel free to chime in.

I’ve been studying the Missouri Gasifier again and I’ve wondered a few things.

Do sawdust/small chip gasifiers benefit from a straight walled hopper, AKA something the same diameter as the hearth? I’d be inclined to think so, less of a bottlenecking of the fuel to prevent hanging up in clumps.
It makes me wonder why the SMP designed that odd hopper setup in their chip fueled experiments. Was that to allow a larger hopper volume but to mitigate bridging?

Bear in mind the Missouri Gasifier can only reasonably use dried sawdust, and has the option for a fuel drying auger feed to keep the hopper topped off.

Why is the restriction so big for the blueprinted gasifier, 7 inches, if the fuel is so small?
(Edit: I completely missed the part where this gasifier was sized for a 450 cubic inch engine)
I understand the different nozzle lengths, since sawdust gets very dense you’d want a perimeter of nozzles and a few “Lances” of nozzles to ensure it’s still going in the center.


Yup if you go way back my hoppers where funnelled and then you see the transtion to straight hopper. Ideally you would want a cone shaped hopper (inverted “V” )

Solve the bridging; you solve the tar issue and inconsistancy of a small gasifier.


That also explains why Steve A’s “Constance” gasifier ran alright on pellets. Just a 2" pipe hopper.


Hi Cody, just as you say: straight walls better flow.
SMP/Volvo tried this with chips, and found out their gasifiers had way to good flow, after only 10 minutes they ran “constipated” pulling enormous vacuum, til engine would’nt rev anymore, their first solving of this was “agressive” grate shaker/cleaners, which increased fuel consumption 50-70% (!) And also increased the risk of making tar during load.
This was somewhat solved by don’t let all the fuel weight rest on the charbed, by “shelves” or funnels, or Volvo’s “upside-down bucket” with feeding holes along the sides.

Notice: chunks tends to flow “center first” the fuel put in last, reaches the hearth first.
Chips tend to flow like a “plug”.

I have some papers somewhere, which documents flows, “constipations” vacuum readings. See if i can find them :smiley:


Good feedback Goren.
One of the first modern-era common wisdoms I threw out from observed experiences was the one, “Now just make your extended run hopper as big as you like.” Every single designer builder struggles with this.

Many different small system I saw and some I did operate, did work O.K. on small 45 minute to one hour batches of wood-ish fuels.
But just as soon as you put a hopper on them for more than two hours of loaded operating then the multiple problems showed up. Flows clogging. Hopper taring/glueing.
As you say jigger past that all you want with mechanical forcing then introduces more complications and later points of failure from the added complications.
Thinking you finally have the problem beat on several runs to have it all flows clog to a stop on ONE gob of metal staples in a pallet board; a pitch pocket on one chunked up stick of wood; a long phone call stepping away; your system loading wife partner finishing up her combo of laundry, cooking electrical using; the battery bank did recharge fill and loadings cut back.

This is just the nature of using an energy resource in the raw state. Past each refinement step, usage results becoming more predictable and stable.
Slicing up the whale; working on the processing lines in any turning a killed carcus into sorted meat sections is a very messy process.
Live wood to actual useable portions is the same.
Processing has to be shut down; then moved along - in forest work; or detail cleaned out from all of the buildup wastes and debris - milling operations.

Easy is just operating for that 45 minutes to at the most two hours that woodgas drivers do.
Easy is just suppling for your self. Not for others.
Charcoaling would seem to be make it easy. Really? Even wood stove harvesting charcoal adds many dirty handling steps before the actual gasifier usage.

It is quite the thinking/expectations turning around to go to use as close in the raw from now hundreds of years of made-easy-for-you.
Usually taking a crushing war, or major natural disaster to do this forced thinking/expectations reset for you.

All my woodgasing just like my woodstoveing is to keep the possibilities awareness alive to be able to go back to more basic and direct use for making daily use energy.
Others do this with foods growing, harvesting and preserving.
Others do this with animals meats raiseing.

So Stephen Abadessa’s real contribution was in the total personal use scale of his DYI turn your wood into your electrical power. Winter sap down chipped to battery bank small batch recharging.
Same-Same with W.K.'s; J.O.'s; Tone’s and just a few others by turning their own woodmilling wastes into their driving fuels.

Becomes a whole different game doing wood-to-power for others. A whole diffnert game expecting others to keep supping you with fully processed fuels like pellets. Or keep supplying you their semi-refined Urban and processing wastes. Sawdust. Restaurants used oils. Central TIP, wastes collection centers separated out woody debris. Plastics. Broken, or mass accumulated wooden shipping pallets.
The DOW keep drifting topics and activities from DYI for DIY to these others-for-others.
People leave. Many reasons. Not sticking to basic use DIY, for DYI is one of the reasons.
Steve unruh


I agree Steve, I think we shouldn’t aim for mega-hoppers. Too much hopper space can give too much opportunity for catastrophy.

Even the Missouri Gasifier has a limited hopper, done on purpose. The auger feed is only meant to refill the hopper while drying the sawmill dust. Not a continuous feed de la drizzler. Leaves time for exhaust heats to dry out the dust, waiting for a refill.

Joni and his gasifier is another perfect example of a well balanced system. He has enough fuel at one time in his hopper for a 20km drive before refilling. That is roughly what his drive to work used to be as he has said previously.


I guess one point of this topic I made is a sort of “Why is it so?” Line of questioning. A lot of us here know about many designs, but sometimes I wonder what drove everyone to build it in the shapes they chose.

A way to help break it down for new people, to show them why it’s a bad idea to aim for stuff like a 12 hour hopper, and instead cut down to a 1 hour hopper. Or to keep away from the incredibly needs-specific fuels like wood pellets or plastic shavings.

Speaking of pellets I have a funny tangent that everyone who’s tried them in a gasifier will understand. My dad has a pellet smoker, it’s auger fed. He’s been running into problems with moisture in the pellets turning them to mush and gumming up the auger. He has switched over to Charcoal pellets with just a sprinkle of hardwood flavor pellets.


There is a lot of science to how bulk solids “flow” or don’t; how they pile or stack up. Mega hoppers cause the bottom bits of fuel to feel a great deal of pressure from the mass of fuel above them. That may prevent the bottom bits from flowing properly.

In order to flow downward fuel chunks need to be able to rotate a little to slip past each other. Pressure from above may keep those bits locked in place. I think that’s why mega hoppers are problematic - too much downward pressure for optimal flow and why agitation helps. Another solution is to configure the hopper to hold that pressure off. A sluice gate mechanism comes to mind. Alternatively a pusher bar/brush to dump fuel from a flat surface into a shorter / smaller hopper.

I have an automatic dog feeder (for my dogs of course) that has a compliant (slightly flexible) rotating tray to dispense the kibble. It gets jammed now and again but works ok. Conveying bulk solids is not an easy problem.

My understanding of bridging it is mostly an issue for wood fuel owing to tar than an issue for charcoal but experienced folks here will tell me otherwise. Again sluice gates could keep tar producing temperatures away from the hopper and held within the pyrolysis zone.

(edit: missed a word)


The auger systems worked the best. Well when they worked anyways. lol Note that the hopper charge was only half or less than actual hopper length. The hopper charge is part of the process, you can only release so much moisture from a small charge in the hopper. Add more fuel well you get a more moisture and then you have to manage that moisture.

If you can build an auger systems that wont break, jam and cost a million dollars its the way to go.


Cody, I think because sawdust is so dense. If I try sawdust instead of chips in my experiments the pressure gets real high. it tightens/klinks. Didnt see auger feeding on the Misouri, I think it is for drying. Just like the drizzler, the Missouri has no fuel hopper. You can see that in the YT videos. Like Tone shows in his design a straight pipe flows very well and his special nozzle keeps the clogging away. Combine that with a pyrotouch and augerfeed and you have got a nice running stationary solution. I think, or hope. :grinning:


They actually do have a hopper, but they have them carefully sized to mitigate issues.

The one in the PDF is sized for a 450 cubic inch engine, but the hopper space I think is over 40 gallons.

But based on what Doug has said about his small S-80 model which goes through 3-4 gallons of sawdust an hour, I’d bet money that this big boy goes through an easy 8-10 gallons of sawdust per hour.

He’s also stated that you want to agitate the contents of the hopper, with a rod or an S shaped rotating rod if you were to automate it.

Edit: I should also say this gasifier is really meant for wide open running a static engine in a sawmill or generator. It can idle during downtime but it’s advised to not idle it too long.


Thanks Joep for your support in sharing ideas, well I’ll just list some facts for shaping a chip or sawdust gasifier:

  • the same diameter of the reservoir and the hot zone, but it is good to do it separately due to temperature expansion below in the hot zone
  • good preheating of fresh air and a highly heated tank, so the fuel does not stick and remains “liquid”
  • the densely installed top nozzles, which are small in diameter, serve for pyrolysis and gasify the fuel against the wall, so the contents collapse nicely
  • the charred pieces of wood thus fill the lower part, where the central nozzle for the air intake is installed, this enables the gasification of these small particles, and the gases that are created at the same time literally lift and shake the ash and the remaining fuel and carry it to the side through the vertical grate
  • it is good to have a rotating disc at the bottom, which is used to remove clinker and ash when stopping

Read: pyrothouch. Mine is to heavy. Redo the thing.
And if you take a look at Dougs vids you see there is almost no fuel above the fire, no filled hopper.


Thanks Tone. Lets see how to integrate this in my experiments. Heat is the key.


Here it is time to stop, pause and reflect, “Who serves, who.”

If you have woodmills turning tree trunks into boards you are going to be making sawdust.
It accumulates. Needs moving out of the way. Becomes an expense to get rid of to get it out of the way.
In the meantime your mill operations does need many inputs of various energies to power its self.
So make good sense to turn a by-product into a power input as an offsetting asset then.
My oldest brother-in-law, his father were buy-in shareholders into a PNW Co-Op plywwoodmill. I even worked time there for a short time as hired labor. Sweeping cleaning, roller bins collecting all sawdust, slivers, core-blows and shreds. And dumping them into a grinding up hog-mill. That all course ground up fed into a forced air steam boiler. The steam used for a 20hp/steam-electric generator. That steam used on the log peeler knifes. That steam heat even used to cure plywood lay-ups. AS simple and direst as possible. Straight forward existing proven engineering. No mad scientist needed. No separate gasification process needed.
Waste woods were not enough. They still did need to buy out Grid electricity. Still n need to buy out some equipments diesel, and even gasoline.

A Stud-mill the same.
An OSB mill the same.
A furniture factory the same.

The advantage is to always as simply as possible take blood wastes and make sausages.

Any centralized consentrating processing will have these make-something usable from by-products.

Fine. Fine.
Once the process is developed it is a whole different situation to have to intentional make the once by-product as the primary input to serve the process.

The prefect example being woodpellets for power. When the wood pellets are made from existing milling wastes these work economically. When there is no waste due to low building activity not driving the mills . . . the 2007/8 housing meltdown; COVID lockdowns . . .
Then to serve the now dependent wood pellets needing heats users . . . then the economics to manufacture wood pellets go upside down. Having to whole log grind all up for feedstocks.

This same who serves who applies to ALL things. All endeavors. All pursuits.
Clothing. Shoes. Cars. Airplanes and ships.

With your own timber land and trees then the gasifier fuel will be chunked and coarse chipped woods.
Because energy/time/equipments-wise that will be all you can afford to support.
Steve unruh


Maybe I should state I was only studying it for the sake of studying, not because I am particularly interested in building one. But yes I agree with you again Steve Unruh. You have to look at all the moving pieces that you have, and look to see if something is worth the effort.
This gasifier was built for a specific need, which I doubt will ever align with mine.

I’d just as soon use sawmill dust as a filter media or oil spill cleanup, or spread it on the ground during icy days for roughage. If I had a sawmill.

Chunked wood and burned limb charcoal is I think ideal in my Derelict Tree Farm scenario, least amount of work needed to process both.

I’m at best a copycat with some hat tricks which isn’t necessarily bad, but I am driving myself to study designs a bit harder to see the Why’s of a design when I look at it.


This looks interesting, any thoughts?


Makes sense to only suck air for a gasifier when it’s actually in use. Positive blowing to the intake isn’t bad for starting up I’m sure.

Though these are being used for boilers. I like Lagunov’s design for boilers, no over-complicated heat recovery mantles where water would accelerate rusting.


I am more interested in the gasifying plastics


I wanted to try something like this for a long time, but never got to it. Makes a lot of sence to me.
However, plastic is a wery broad term. There are plastics chemicaly identical to petrol (polimerised hydrocarbons) but also nasty nasty stuff like halogenated plastics (PVC). That “C” stands for cloride and pumping the stuff in the air isnt a good idea… also probably horible for the engine.