Why grass and trash gasification has more potential than wood gasification

Wood gasification has seen limited applications across the world.

There are a few inherent disadvantages:
(1) Wood gasifiers are bulky. It looks like the only successful wood gasifier vehicles are pickup trucks, neither vehicles smaller (like a car or SUV) nor larger (a bus or semi) have practical wood gasifiers.
And you lose a bit of cargo space,which is fine for a home use pickup truck, but means lost revenue for commercial trucks.

(2) Cannot use whole wood, must chunk or pellet: the underlying reason is the low energy density of wood, plus the low volumetric efficiency of piling chunks of wood, plus wood conduct heat slowly, so a large surface area is needed in the gasifier to heat wood to the gasify temperature, which mandates chunking the wood.

(3) It costs money to grow and process wood. Wood is hard, which requires heavy duty shredder/pelletizer, which costs tens of thousands of $ to feed a fleet of commercial vehicles.

Compared to wood, trash and grass have advantages:

(1) They are softer and easier to shred down to very small particles, allowing using smaller gasifier of a fluidized bed design, more compact than our fixed-bed wood gasifiers.

(2) Trash contains plastic, which is a semi-fluid under gasifying temperature, the flow and heat conduction properties of melted trash are better than wood.

(3) Biofuel grass, such as pennisetum and switchgrass, cost less to grow, use less water, and grow faster compared to trees. Trash is negative cost, you receive $49 in average to reduce a ton of trash from landfill.

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Cow Dog,
If you will study the history of gasification for non-industrial applications, I think you’ll find that wood or charcoal win hand down. Wood pellets are also an efficient option as Matt has pointed out. I think you will also find that the historical and practical evidence will disagree with some of your conclusions. I expect that density of the fuel is the a primary reason. The other doers on DOW can provide additional support, I expect.


I suppose this is what you are talking about:

But even there, they seem to be headed for sugar cane. And I didn’t see any reference to using it as a motor fuel.

It will be interesting to see how your hypothesis “pans out”.
Maybe it is time for you to start experimenting yourself. It is clear that you don’t give much credibility to what we have to say.


Haha, This looks like a topic that might bring out the torches and pitchforks! This forum is pretty much exclusively backyard tinkerers, small-scale DOers, and people who border on being religious about their wood.

The points you make are mostly all valid, but only if you are talking about building something on a gargantuan scale. (The only point I would argue is that large vehicles are possible, and believe have been done on woodgas). I dont think anyone on DOW has any illusions about woodgas being able to replace ordinary fuel consumption at a national level. The numbers, as you point out, simply do not add up. However, none of us are engineers working on solving the nations fuel problems, and once you scale down to a hobby level, wood starts to look better and better.

But if your wife doesnt mind you spending lots of time in the back yard grinding up the garbage and feeding it into the family car, by all means do that :grinning: And take pictures! Everyone on here likes pictures of contraptions, even if they do not include any nice neat stacks of wood in the background!


Out west here we have a big problem with wild fires. It has been this way for thousands of years. So maybe it wouldn’t a problem if we lived in tipis. We could just move. But we live in European style houses. So, I think if people learned to use the scrub wood as a resource life here would be a little better. Not that I want to cut down all the forests or anything like that, just use up all the garbage wood.


Guilty! Today’s morning service lasted all day :smile:


I think using those materials is a fine idea for energy replacement. Just not so much for transportation. I like them for stationary gas supply systems. We used to have “town gas” systems that made use of city garbage, etc. Which were essentially gasifiers mixing coal and trash and organic debris to make on demand “natural gas”.

or for stationary industry heat generation needs…

No pitch forks though, I’m all for someone figuring out that the status quo is wrong about something like that. I have been adding in plastic bottle material and styrofoam cups and plastic bags and plasticware to my hopper for a long time now. I have a feeling that it helps a little on mileage…


There was a fellow on here posting a year or two ago who works in a large industrial concern using fluidized beds, might have been trash incineration even. At that scale it’s probably by far the best use of trash. As mentioned, plastic waste can be used to advantage as a supplement in a mobile gasifier. Too much and it will gum up the hopper and not form the essential charcoal bed.

Switch grass and other crop residue has issues due to the low ash melting point requiring very careful management of parameters to avoid a gummy meltdown / lava bed.

Mr Charlton, site member has probably the most experience by far of small scale fluidized bed reactors.


Is the “charcoal bed” still necessary, if the device is rotating or vibrating, instead of static?


You might be thinking of Kyle DiMario, apparently the only other DOWer in North Carolina and who has visited my place a couple of times. Some time back he posted this on DOW:


Yes, as far as I understand the process, the charcoal bed is essential for the reduction reactions in a downdraft gasifier. Envision near incandescent glowing char…

(Well, at least if you want to avoid creating tar).


Cow Dog,
Here is one historical publication–short on technical information, but good to show the extent of small scale gasification from WWII to more recent times with lots of pictures:

In addition to the DOW library, there are a lot of valuable publications about gasification found here:


Hello Cow Dog,

Right in my alley i would say…
I believe your writing is an expression of your opinion, based on what you have been reading…
Not based on your own experiences with building gasifiers…
Did you ever gasify gras, plastic, waste into fuel ?
I do… and i do it in huge numbers…

A small test would most certainly bring you to the dark side… :grin:
Try to collect, process into fuel, and gasify any of your proposed fuels… have an engine running on it with reasonable energy efficiency… produce your electric and your heat with it…

Then try to do the same with wood, woodscraps, and or charcoal…

Try to build an environmental acceptable system…
have an idea on what the overall effort is, supply chain , maintenance , etc…

DO surprise us with something you actually did build, proofed, put to a test and what you can showcase us…
Doing is not about reading out loud words written by someone else…

Welcome to the club, opinions are welcome, but deeds where we can learn from are more appreciated…


I forgot to mention about plastics, keep away from the chlorinated plastics, toxic chemical risks, plus production of hydrochloric acid that will damage gasifier and engine.


Yes. You-Say-It; You-Do-Actions speak much louder that re-quoted reference materials.

So far as pitchforks and tar&feathers coming out that comes in the form of Eco-Ultra-Greens who will trash-talk and voting kill off ANY large scale energy project that is not their darling PV solar. Even wind and tidal and new hydro efferts gets trashed by them here in the evergreen Blues-voting PNW.
ALL municipal and private power MSW, Bio-material Gasifier efforts are now shut down for inability to meet their never ending finite goaled emissions. No matter how many scrubbers and washers are stacked on . . . . ppb and ppt will “fail” them.
The Green-Wins are systems blocked from starting up. And in-use systems forced shut down.
Wanna buy a 35kW private wind system for cheap now? Courts idled by the bird lovers as a bird killer.

Wood-for-power here where the trees grow as weeds gets folded in as an individual archaic pursuit done by 19th-20th century throwbacks they wait to age out and Covid-19 die off. “Those planet killing, greedy, ignorant, toothless, woodburners!”


???!!! I don’t like the thought of ‘town gas’ in people’s homes. People used to get poisoned that way. Yes, I know if its done right it can be safe… But too often there are unforseen circumstances. Three Mile Island, Chernobyl, and Fukushima happened, despite humanity’s BEST efforts to be careful.
But mobile systems, seem inherently safer to me, just because mass quantities of flowing air are there to dilute any leaked fuel gas.


Some time ago, one guy posted a clip on this forum and also his website, all credit to the successful work. I also believe that high-quality waste incineration is the most ecological process for maintaining a clean and healthy environment (look, huge amounts of plastic in the seas, huge landfills from which groundwater is poisoned)


You know, I never thought of it that way. Maybe you are right. Alternative Producer gas made and used by the same person is inherently safer than gas made by one person and used by the uneducated.
I rarely consider things that way, because I always imagine myself doing it. I was not really thinking about town gas systems the way they would be for market. I was thinking of personal systems used locally. But you are right, on a large scale that would be a problem probably.


I am yet to start testing my idea of makeng a charcoal gasifier/pirolitic oil distilator idea but it is avoiding me for years… some day… if someone doesent do it first.

Pirolitic oil can only be made out of certain plastics. But, l think on a large scale all plastics could be gasifyed. Halogenated plastics (PVC, PTFE,…) can be gasifyed in a good gasifier together with a bit of biomass (for maintaining a charbed, reaction surface) and then the clorine, bromine, flourine and their acidic compounds can be scrubbed with lime milk. Or even lye. Runing the scrubbed gas trugh a burner or engine, then potentialy scrubb again l am sure is the cleanest way to dispose trash.


Are you not simply going to end up with halogenated sludge that needs to be disposed of? Seems to me that the best way to deal with our plastic waste problem is to not produce it in the first place.