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A Home-Built Biomass Gasifier for Producing Wood Gas

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Step 9: The Fuel

Picture of The Fuel
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I failed to do a lot of basic research about gasification before just diving in and trying to build a gasifier. So I wound up repeating a lot of the same mistakes other people made before me. So this gasifier went through many versions, re-designs and re-builds before getting to this state. You can see the complete evolution of this project, including the spectacular failures, on my web site at http://www.mdpub.com/gasifier/.

One early mistake I made was poor initial choice of fuel. It turns out gasifiers are finicky about what you feed them. They like fuels that are uniform in both particle size, shape and composition. Non-uniform fuels produce lots of gunky tars. My first choice of fuel was about as bad as it gets. I tried to run the first version of the gasifier on wood mulch.

1st Photo:
My dream fuel for the gasifier in the early days was free wood chips and mulch available from lots of places nearby. I know of at least three places I pass on a regular basis that have signs offering free wood chip mulch to anyone who would come and haul it away. There are probably dozens of other sources I could find with a little research. So I got myself a bag of wood chip mulch. The chips were very wet. So here I am drying them with a fan. After 2 weeks under the fan, they were bone dry and ready to burn in the gasifier. I realized that if this worked, I'd have to find a less energy intensive way of drying the wood chips in the future. But it didn't work. The gasifier didn't really work at all on wood chips. The non-uniform size and shape of the chips, combined with their mystery composition led to terrible problems. The chips didn't feed right, didn't burn right, didn't pyrolize right, and often wouldn't even burn at all. When the gasifier was running on these chips I got far more tar than gas out if it. Out of frustration I hit the books to try and figure out what the problem was. That's when I learned about gasifier fuel needing to be uniform to work well. So I started groping around for a better fuel option.

2nd Photo:
I thought wood pellets would be a good fuel. Unfortunately I live in Florida, and nobody burns wood pellets here. They are essentially impossible to obtain here. So I settled on hay pellets. I could get them from feed stores. They are more expensive than I would have liked, but they didn't break the bank for testing purposes. with their uniform shape, size and composition, they seemed like a reasonable substitute for wood pellets. The gasifier worked much better on hay pellets. There was more gas and less tar. The pellets fed nicely through the reaction tube and exited as little beads of char. I could start seeing the potential of this machine.

3rd Photo:
I finally found some wood pellets. On one of my trips to my Arizona property, I bought back two 40 pound bags of wood pellets. They were dirt cheap too. Less than $6 per bag. I couldn't find them to save my life in Florida. Every hardware and homecenter store in Arizona seems to carry them though. Later I also found them on a trip to the North Georgia mountains, and brought back some more. Now I have plenty of high quality fuel for test running the gasifier. Fortunately I drive out to Arizona twice a year. So bringing a few 40lb bags of wood pellets back home on each trip in my big truck was not a problem.

4th Photo:
A close-up of some wood pellets. The gasifier runs even better on the wood pellets than on the hay pellets. The wood pellets are designed to be a fuel after all. The more or less uniform size, shape and composition of the pellets is just what is needed for good gasification. Wood pellets are also dirt cheap if you can find them.
 
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