Gasification of hammermilled straw

New guy here! See a lot of knowledge packed into these forums, more so than anywhere else on the net when it comes to gasification.

I’ve been thinking about getting a gasifier set up for heating purposes, and going the gasifier route to open the door for supplemental electricity generation down the road. My access to wood is good, but will be a big time commitment to collect it as I don’t have a woodlot so I’d have to run around with a trailer. Another thought is that if all goes well, I’d be using quite a bit of it to do anything more than just heating. On that note, I am surrounded by farms and can get those big round bales of straw delivered to my place (I have 4 acres - old 1800’s Farm) for peanuts, and there is more than I could ever use within 5 miles of my house. These are 800-1100 lbs each and are so cheap I’d probably blow more on gas collecting less wood compared to just buying the straw.

So surprise! I started scheming as to how I might gasify this stuff in a controlled fashion (ie not the whole bale at once in a giant boiler like you see on YouTube). I have a rough idea for attempt #1 that amounts to a current flow “upside down” imbert, bottom auger fed and top discharge of the ash with the gas travelling up through the coal bed, but who knows if this will work.

I have most of the parts I need to build this thing and start learning, but before I finalize the ideas in my head and start cutting, I’d like some input from the practical pro’s and theoretical experts I see on here. I’ve already shaped the “grand plan” around some of what I’ve learned reading these forums, but it seems foolhardy to not consult with you folks directly before I stop the wheel spinning in my head given the experience and knowledge displayed here.

So, anyone tried straw for fuel? How’d it pan out? Does (wheat) straw clinker up?



I had a couple customers try it and despite warnings, leafy material has always gone badly. Too much ash.


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In a regular gravity feed gasifier presumably?

Hi Will, welcome to the site.

The thing folks sometimes miss with gasification, is that burning the biomass is only half the process. You then have to use the resulting charcoal to thermochemically convert the pyrolysis gases into clean woodgas. So, a usable charbed is critical. Burnt wood leaves behind a very nice, dense charcoal and performs very well in this regard.

Straw could be made to work OK for just burning, like in a stove. But it makes poor charcoal.


Yes. In my Victorias.

Yes Chris, I was thinking that there would be no real coals at all, just a fast moving column of straw particles driven past the air feeds. I was envisioning a thick slice of red hot straw particles with the gasses coming from underneath where the raw fuel is heated up,and then sucked up through said slice of red hot straw where the (hopefully small quantity of) tar would be broken down. who knows if that’s how it would play out though. I did make flammable gas by putting straw in a sealed can and lighting a fire under it, burned orange. Was not milled either- just packed the stalks in there.

I figured a regular unit would have trouble, I figured the fuel would just be consumed too fast, and if it clinked or stuck together while burning I’d have no chance making a std gravity feed hopper fed gasifier ever work with fine lightweight fuel.

Hi Will. My few cents on straw burning…

As you read up on effective pyrolysis, you will see that there is a strong relation between the size of the combustible material and the flow rate of air pulled through the downdraft gasifier. Also the particle density is significant as mentioned by Chris, to produce a persistent reactive char bed to produce a quality syngas. To me it seems that straw particles will not be the right size or density to work in a conventional downdraft gasifier, unless it was very small scale.

There are viable commercial systems used for serious greenhouse heating using an updraft fluidized bed. Another commercial system I am aware of used a refractory lined swirl burn chamber, straw being metered into the chamber, another similar concept used to burn rice husks.

I think the turbulent combustion methods will be best for complete combustion, the fluidized bed approach could produce syngas, but it’s not likely to be as good in quality as from a downdraft wood system. Although I wouldn’t rule that possibility out with good design and control, as straw certainly lends itself to steady state operation.

I am attracted to the idea of chopped or hammer milled straw. As you say, it’s very cheap, and accessible, an over abundant waste material with tremendous heating potential, and with great potential for continuous automated systems. I don’t think it’s exaggeration to say that straw could transform the energy situation in North America.

Happy experimenting, and looking forward to more discussion,


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Hi Gary, good to see another that feels the same about straw. I have calculated roughly that I could heat my house for $225.00 worth of straw compared to 1500.00 worth of wood pellets I am using now. I live in Ontario Canada where we just got hammered with a new carbon tax, gas now costs $4.35/US Gallon (CAD), and electricity at $0.25/KWH (all taxes and misc. fees in), is one of the highest rates in the world. Government debt is piling up, and frankly the outlook economy and jobs wise is looking as bleak as it ever has for a long time to come yet. It’s time to start making changes in my energy use.

Straw is so cheap and plentiful, that I will consider pelletizing it if that makes it work where milled straw will not. I am aware of the condensation problem with pelletized fuel but am hoping it will not be a deal breaker in the design considered. At least I’d get a real coal bed then. Basically, I am open to any route that ultimately opens the door for straw as gasification fuel for heat, motor fuel, and electricity.

I work in a fabrication/machine shop and have access to, and can run well enough everything under the roof to take on a project like this. Even making the pelletizer myself is possible.

Hopefully next month I can get started on the unit which will be an experimental deal to see if there is any hope of success, or if I should be considering some other route.

I feel the same as you, the potential for straw is enormous IMHO. In Ontario, it is currently worth a lot of trouble to figure out how to do it.


Most commercial plants use a fluidized bed system for efficiency, but they are more difficult to work with, and don’t work well at all for non-constant flow applications. P&G just installed one of valmet’s for thermal and electric generation in Georgia. ( Albany Green Energy to develop 50 MW biomass plant in Georgia | )

Here is about the smallest one I have seen:

That being said… I would look at an anaerobic digester. I don’t know what the effect is of just using wheat straw for the production of methane, but usually the leftover residue is typically excellent for your soil which should result in higher yields of your peanuts with less fertilizer, water and pesticides inputs. I assume you are in the south and have eroded or depleted soils to begin with so the effect will be noticeable in a few years. The trick is to get yourself to a break even point or better with very little labor, and even if you give up on energy, you still have something to show for your efforts.

Oh, you can scratch the southern comments. I think I misread something. Since your primary goal is heat, not electric. You might be better served with a fluidized system.

You might also look at compost heat. Most of those systems I have seen use green wood chips or bark. But you could probably use anaerobic digester sludge as well. I haven’t seen a system that used straw, but It seems like it should work.


That’s a cool vid - thanks. I know squat about fluidized bed gasifiers, would look cool going down the road though :).

I thought it was a cool vid. I just saw it yesterday, and was trying to figure out where to drop it into a discussion. :slight_smile:

It would but it is almost totally worthless for driving. :slight_smile: You essentially need to have a constant flow rate for a fluidized bed reactor, and vehicle stopping and starting isn’t exactly conducive to constant rpms unless you are using a small motor to supplement say an EV. You also have a pressurized flame system, that might break, and if it does maybe due to bouncing through potholes, you have one heckuva fire. The imberts are -far- superior for that purpose. The controls are harder and you have to grind everything prior to use.

Now, if say you were trying to heat a powder coating kiln, you might wish to use the fluidized system.

Otherwise for just building heat, insulation and the pile of compost will probably serve you well, and will be far cheaper and easier, with far less maintenance/labor especially if you have a front end loader. I think I have seen them where they poked holes in the round bales. I just haven’t looked at it that closely. You also need a place to dump the compost at the end of the season, but a big garden or farm field is good for that. The hardest part will be the circulating pump and the heat exchanger/radiator and fan to keep a more or less constant temp.

It also doesn’t have the coolness factor of a gasifier nor does it generate electric if that is an issue.

What I do know is @Calvin_rader heats/heated his house with straw. Hopefully he will see this post and shed some light for you

Strawman. Thanks for your input. I can see why you are leaning towards straw pelletization, if you are already invested in a pellet system it makes good sense. And far more practical to handle indoors.

From an energy recovery standpoint though it is relatively costly. The pelletization will be a technical challenge, probably require a binding agent. Look up this recent article from Farm Show:

2016 - Volume #40 issue#6 page #08 How They Started Their On Farm Pelleting Business

Didn’t sound like fun or very cost effective.

For a completely new build I would tend towards using the straw in a minimally processed form. A tub grinder for round bales, or some simpler form of straw chopper would be the minimal processing.

The first use of straw for space heating I became aware of was a greenhouse operation in Manitoba roughly 20 years ago. They had a conveyor chain to bring in a continuous row of straw bales, once inside they were processed in a tub grinder, then metered through a reciprocating piston into a refractory burn chamber, then fully combusted with secondary air in another chamber, flue gases passed through a heat exchanger.

Here’s a video of a similar system using wood chips.

Coupled with a chain feed bed system there are examples which can be optimized for producing biochar, various possibilities.


This is reminding me of Garry Gilmore ’ s video where he adds different fuels to his charcoal gasificer from a secondary fuel bin. I wonder if that would be a good starting point for testing straw.

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Hopefully pelletization can be avoided, it’ll be near the bottom of the list of things to try. I have read that making a good hard fuel grade straw pellet is indeed difficult, more so than the softer bedding pellets. I think you really have to mill it fine to get the density up, but at least this has been done before even if the energy input and headache factors are high! Pellets would be great if I ever got to driving on straw though, I could see 300-400 miles per fuel up being possible with a pure, dry, high density fuel like this!

I’m going to go ahead and start drawing something up and trying to visualize any improvements that can be made while it’s still on the screen, and when the well runs dry I’ll start building. First attempt will be roughly a 6" tube to suit the auger I have, and try to generate a 6" thick bed of red hot particles on top of a moving column of milled straw with slow air movement, probably blow it in for starters.

If this works, I’ll try sucking thru the holes in the tube wall and also through the hollow auger stem to see if I can get that bed of straw particles nice and thick again. Sucking thru will get any gasses produced moving up thru the bed at this point also. I think maintaining a thick bed of red hot fuel may be tough as those little particles will disappear quick, I have a method of compressing the fuel stack while in operation to increase density in anticipation of this. But I will probably run straight into airflow complications as I squeeze it tighter and tighter.

I’m really not going to get anywhere with these ideas until I build something and start playing with it trial and error style. The theoretical side of gasifying milled straw is pretty barren.:anguished:


As a testbed could you try a 50 gallon barrel tlud like we do for charcoal generation? It would be a batch system but easily implemented and a cheap build… by the way we have high costs for electricity in ontario but they are similar to the maritimes, in line with new York state, cheaper then California, and downright cheap compared to most of Europe. Still a good time to reduce your dependence.
Best regards, David Baillie


Oh! I didn’t realize canadian electric rates went up. You guys had the lowest in the world because of all the hydro. There is all sorts of research on biomass and fluidized bed systems, since it is efficient and is used for coal. Most of the commercial biomass operations use it.

David: Are you talking about something like the sawdust stove?

I was thinking the SimpleFire would be more conducive to a bubbling fluidized design since you are already recirculating the exhaust gas.

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Actually I was thinking more along gary’s 2 stacked barrel charcoal maker; even simpler. Not sure how compacted you could get the straw and still get the airflow through the barrel though. Electric Rates in canada vary a lot depending on province. Quebec has low rates due to efforts to develop their hydro resources in the 1970’s. They have higher debt levels then ontario and correspondingly higher taxation rates though. I’ve lived in both and prefer ontario.