Can someone explain HOW a wood gasification boiler works.

[bulldogbones]

Like the title says can someone explain HOW a wood gasification boiler works. I built my own little gassifyer but I dont understand how a real wood boiler gassifier works.

Here is my vid of what I did.

http://www.youtube.com/watch?v=YXUSwxP70sk

also what is a youtube string

 

[Singed Eyebrows]

Well, I'm far from an expert, that hasn't stopped me before so I'll have a shot at it. In a downdraft gasser you typically have 2 chambers. In the top chamber wood is burned slowly with a controlled amount of oxygen & the gas is either pulled or forced through a nozzle or nozzles at the bottom of this chamber. This gas burns very hot as it goes through a bed of coals (2000 f area) This 2000 degree gas then goes to whatever heat exchage system you have, typically firetubes. What is important to understand is that a gasser is a very "balanced" boiler. You want just the right smoke production & ability to burn it. Thats where all the R&D comes in. Good Vid, I'm not sure that was a gasser though, Randy

 

[Gooserider]

Pretty good basic description - Essentially in the video, we had a good basic demonstration of the concept of gasification - where heating wood causes it to break down and give off flammable gas... A gasser just does the same thing on a larger scale, and harnesses the output a bit better...

The upper chamber gets loaded with wood, and a controlled fire is built in it, with limited airflow. This fire's function is mostly to "cook" the wood and make it produce gas. The gas feeds down through the coals, which superheats it and the ceramic pieces that make up the bottom of the chamber. In the center of these ceramics is a jet orifice that the gas exits through into the bottom chamber, additional air is fed into the gas as it goes through the jets, and again the air is highly superheated by the ceramics that it passes through. As the gas comes out of the jet it burns with a flame very much like a giant blowtorch, at temperatures in the 2,000°F range. This is enough to consume nearly all the combustible gasses and other material in the jet, so there is virtually nothing in the exhaust but CO2 and water vapor.... The lower chamber will also have a lot of ceramics in it to act as stops for the flames, which would otherwise be hot enough to burn through the steel boiler shell. The ceramics and the slightly cooled flames transfer their heat into the boiler water jacket, (and some of the heat goes back to the upper chamber to continue the cooking process) and the exhaust exits the boiler at around 4-600°F, which is basically the lowest temp you can run and reliably not have water vapor condensing in the chimney...

If you look on You-tube, you can find many videos from boiler manufacturers and several of our users that show very nice demos of how it works.

Gooserider

 

[Badfish740]

The upper chamber gets loaded with wood, and a controlled fire is built in it, with limited airflow. This fire's function is mostly to "cook" the wood and make it produce gas. The gas feeds down through the coals, which superheats it and the ceramic pieces that make up the bottom of the chamber. In the center of these ceramics is a jet orifice that the gas exits through into the bottom chamber, additional air is fed into the gas as it goes through the jets, and again the air is highly superheated by the ceramics that it passes through. As the gas comes out of the jet it burns with a flame very much like a giant blowtorch, at temperatures in the 2,000°F range. This is enough to consume nearly all the combustible gasses and other material in the jet, so there is virtually nothing in the exhaust but CO2 and water vapor.... The lower chamber will also have a lot of ceramics in it to act as stops for the flames, which would otherwise be hot enough to burn through the steel boiler shell. The ceramics and the slightly cooled flames transfer their heat into the boiler water jacket, (and some of the heat goes back to the upper chamber to continue the cooking process) and the exhaust exits the boiler at around 4-600°F, which is basically the lowest temp you can run and reliably not have water vapor condensing in the chimney...

I think I've been posting on hearth.com for five years now and that's the best explanation of how a gasification boiler works I've ever read!