Making POWER from wood

[gadget]

It's been on my mind for years. Now that I am off grid, I'm MORE interested. I have 8,000 watts of solar but sometimes there is near zero output like in the winter when wood heat is needed.

I've been thinking about the easiest most reliable way to get some power, maybe just a few thousand watt hours a day.  Efficiency does not need to be high, maybe 10% since the wood will also be used for heating.

I see 2 main options, steam generator or gas turbine. Steam needs lots of watching, the turbine may be less tending if there was a way to keep it from running away and over spooling.

I have seen lots of videos of people running auto turbos of wood for fun but no one has yet captured power so I have no idea what power is available to pull from the turbine. They do over speed very easily. There is a 48v brushless DC motor integrated turbo in to a Mercedes motor but $$$. I have been looking at mounting an RC motor on to the end of compressor shaft.

This may be a winter project........

[Forsythe]

I'm pretty sure a downdraft wood/biomass gasifier —making producer gas, which is then cycloned and filtered through straw or wood shavings, then fed into a carbureted generator— would be a lot more reliable, safer, easier to cobble together, and give a steadier electrical output. 

Steel components in a turbine running at red heat like that won't maintain tolerances or structural integrity for any extended duration. That's why you only see videos of people "experimenting" with such things... rather than people actively using them for regular electrical power production.

FEMA plans for DIY woodgas conversion kits are available online, and the technology has seen periods of widespread (although intermittent) adoption since the second world war...with incremental improvements to design prodded along by the energy crises of the 1970's/early 80's

if you coupled that with a stirling engine running off of the waste heat generated by the internal combustion generator, you might be able to net a pretty decent energy conversion efficiency... with machines that don't eat themselves along with their fuel.

[Forsythe]

...a stirling engine being all-the-more efficient in the wintertime, because it runs off of the temperature difference between the two sides of the "external combustion" piston's housing... Waste heat on one side and cold winter air on the other would make a stirling engine zip right along at an admirable clip.

[Vortex]

Or Thermoelectric generator en.wikipedia.org/wiki/Thermoelectric_generator There were a few designed for use with woodstoves available a few years back, I don't know what the situation is with them now.

[gadget]

Thanks everyone for the feed back, from what I have read over the years everything has one problem or another and this is what I know of.....

Thermo electric would be nice but I figure I would need between 50-100 modules. Decent modules would be about $30-$60 each plus all the heat sinks etc. I figure it would be between $3,000-$5,000 to build a large one. Also, they need to be matched to a loads resistance to work right. If they get too hot, they can be damaged. I have researched them many times over the years. The modules are getting better but the good ones are still to pricey for the number of modules needed.

As far as going mechanical, I really like the turbo idea because there is potentially only 1 moving part depending on how the oil system is handled. Turbo's can be had new for under $100 and they are pretty easy to rebuild. I've rebuilt a few. They are designed to get way hotter then I would need and go for 200,000 miles on a car with constant heat cycling. Most spool up to over 100,000 RPM and glow a dim red under heavy usage. They are designed to be abused. I would need to run at around 10-15k RPM. The high voltage DC, I would run through an MPPT solar charge controller. Figure it would operate at about 10-30% designed load. I don't know how much power would be available.


Bio gas seems like an easy route but consistent operation is difficult from what I have seen in videos. Also, like you said the gases can be very corrosive and take lots of refining to get any decent life out of your motor. There is issues with keeping the A/F ratio consistent???


I have not ever seen a good and simple DIY sterling motor but would be very interested if someone figured this out.

I've gone through all the options and I really like the simple turbo idea but there is no way to figure the power output without just building it. 

[Forsythe]

Oct 5, 2022 17:53:18 GMT -8 gadget said:

Bio gas seems like an easy route but consistent operation is difficult from what I have seen in videos. Also, like you said the gases can be very corrosive and take lots of refining to get any decent life out of your motor. There is issues with keeping the A/F ratio consistent???

There was a time period (lasting a few years) when virtually every private vehicle in continental Europe was converted to run on wood producer gas because of the fuel shortage under the Nazi regime. Those cars ran well (albeit at a lower horsepower — which is why they all switched back to petroleum following the liberation of Europe) and did not experience corrosion issues due to the filtering of the gas. It's the liquid condensate which is corrosive, and that is what you filter out via the cyclone (which spins out the heavier liquids via centrifugal force) and then pass it through a bed of wood shavings or straw to catch the last of the moisture — before feeding into the engine's fuel rail (if a car) or the carburetor (if a combustion generator.)

...They don't work on the newer fuel-injected engines, however. The on-board computers lose their minds and light up the dashboard like a christmas tree with warning indicators 🤣







A documentary, A Hundred Years of Firewood-Powered Vehicles:




PDF primer on wood gasification:
www.netl.doe.gov/sites/default/files/netl-file/Session-6-Jenkins-Biomass-Gasification-101.pdf

The FEMA Gasifier:
www.osti.gov/biblio/6054362

A website dedicated to woodgas production specifically for operating motor vehicles, tractors, etc.:
www.driveonwood.com

Fairly comprehensive "Handbook of Biomass Downdraft Gasifier Engine Systems" from the US Dept.of Energy:
www.nrel.gov/docs/legosti/old/3022.pdf


...and this guy built the FEMA generator (he's firing it with wood pellets, probably because he live in the desert where there are no trees... but it's the same principle with wood chips or other decently-dry biomass.)

[Forsythe]

...there's a PDF somewhere of a professor that developed a rocketstove-like home gasification electricity generator that could be installed in a basement... as part of a DOE report on energy independence in natural disasters or extended periods of international conflict.... but I'm having a hard time locating it at the moment. IIRC it was published in the mid-to-late 1980s....

[Forsythe]

Also worth noting that those corrosive pyrolysis compounds of pyroligneous acid are mostly formed only as a byproduct of incomplete pyrolysis — when the fire is kept too cool and the organic long-chain hydrocarbons don't undergo sufficient cracking... which a downdraft gasifier mostly solves-for (and the filtration method scrubs the rest.)

[martyn]

How about this ….

[Vortex]

That's a great find Martin, I know someone who will love that.

Oct 5, 2022 17:53:18 GMT -8 gadget said:

Thanks everyone for the feed back, from what I have read over the years everything has one problem or another and this is what I know of.....

Thermo electric would be nice but I figure I would need between 50-100 modules. Decent modules would be about $30-$60 each plus all the heat sinks etc. I figure it would be between $3,000-$5,000 to build a large one. Also, they need to be matched to a loads resistance to work right. If they get too hot, they can be damaged. I have researched them many times over the years. The modules are getting better but the good ones are still to pricey for the number of modules needed.

I looked into it for myself about 20 years ago and came to the same conclusion, ended up building a hydro-electric generator with some solar PV backup. I reviewed it all again a few years ago for a friend and he built something from these guys that gives him enough for lights and laptop:

tecteg.com/

[gadget]

The main problem with motors is they wear out so fast when you run them for hours a day. I really like the idea of a single mechanical part power generator. Of course, the turbo will have about the same life expectancy hours wise as a motor but its super simple to rebuild.

4-8 hours a day = 1-2 years life expectancy for a very well built motor.

My current generator has 800hrs on it from just this summer. It's starting to show signs of dying. Of course next year I won't need it as much since my solar is now good enough to run AC next year.

Running some numbers I found last night, it looks like the Garret 48v turbo Mercedes is using can generate about 5-6kw in regenerative mode. I'm thinking 500 watts running it at lower power looks possible


.....The results showed that the implementation of a motor-generator could contribute to reducing the response time of the engine by up to 90% while improving its thermal efficiency and generating up to 6.6 kWh of energy.....


www.researchgate.net/publication/315780561_Electric_Turbocharging_for_Energy_Regeneration_and_Increased_Efficiency_at_Real_Driving_Conditions

[Forsythe]

Supposedly the NASA-designed free-piston stirling engine is more efficient than the flywheel type. As I understand it, the piston only moves a magnet up & down in a copper coil, generating electricity by the shifting magnetic field within the wire.

Robert Murray Smith built a small scale demo prototype of one here:

[gadget]

Here is a 2.6kw turbine generator. The design by IHI uses the impellers from an automotive turbos compressor and turbine.

www.gasturbineworld.co.uk/dynajetmicroturbine.html



Here is a small 400w test unit, also form IHI

[Forsythe]

so maybe if you put the wood through a gasifier first, and then fed it into the turbine?

I feel like the raw wood heat would destroy the components rather quickly otherwise...

[Forsythe]

The other thing to consider is what will happen when the components *do* wear out. At high speeds and red heat, I'm thinking you'd have to house this kind of thing in a blast bunker to contain the shrapnel and fire when they each give up the ghost and fling themselves into molten oblivion.