The Jorgensen Wood Gasifier Prototype is up and burning.

[deerefanatic]

First off, I'd like to thank Nofossil for putting up with my frequent phone calls and brain-picking sessions. Without his help, this would never have come together......

First off: the albums of pictures:

Album #1: (broken link removed)

Album #2: (broken link removed)

And a series of Youtube videos of my second burn.... Video #1: http://www.youtube.com/watch?v=77mzA89ElHA

I have some tweaking and modifying left to do on the burner as well as getting the insulation put around it and the tin over the outside.

Tonight when I was burning; I achieved pre-heat exchanger exhasut temperatures of 1280F.. (Right before the boiler shut down from boiling the water!

I'm very pleased so far with the unit and am excited to see what happens when I get my storage hooked up and get the boiler insulated and sealed up. (I have a few air leaks in the secondary air circuits) I also have to do some tweaking of the fan air flows for primary and secondary air to see if I can improve combustion temperatures.. Right now when the boiler is running, there is 0 smoke, though there's alot of heat going up the stack. (With pre-heat exchanger temps of 1100, the stack temp is about 680) I'm planning on hanging some chains in the fire tubes to create more turbulence....

 

[jebatty]

Might be just a naive question. Gasification is supposed to generate temperatures of 1800-2000F (1000C). Should that then mean that pre-heat exchanger temp also should be about the same?

 

[Nofossil]

Might be just a naive question. Gasification is supposed to generate temperatures of 1800-2000F (1000C). Should that then mean that pre-heat exchanger temp also should be about the same?

In my EKO, the secondary combustion flame is above 2600 degrees. However, the temperature of the flue gas immediately after the actual flame (but before the water jacket) is more in the 1400 to 1600 degree range. I don't know the physics of what's happening, but there's a sharp temperature drop in the first 12" after the end of the visible flame.

 

[steam man]

I'm going venture a guess and say that the flame is either too rich or too lean. The gas temp before the heat exchanger is affected by the excess air being heated or lack of air keeping the flame cool. High stack temp can mean too much excess air. I see this all the time. Precisely where you are measuring will make a big difference. A stack O2 measurement should get you find out where you are. I don't know what gassifiers need for excess air but I would think no more than 15%. Keep tuning.

When these things going on the market?

Mike

 

[deerefanatic]

Yah, the combustion is over and hence, the gases start to cool. I know that I should have higher temps, I think my fans are blowing too much air and cooling things down... (I know I'm loosing alot of heat up the stack........)

Lots of tweaking to do..... But that's why it's a prototype......

Here's video Number 7: http://www.youtube.com/watch?v=UUiovnZNDHk It shows my primary and secondary combustion during a burn....

 

[deerefanatic]

I'm going venture a guess and say that the flame is either too rich or too lean. The gas temp before the heat exchanger is affected by the excess air being heated or lack of air keeping the flame cool. High stack temp can mean too much excess air. I see this all the time. Precisely where you are measuring will make a big difference. A stack O2 measurement should get you find out where you are. I don't know what gassifiers need for excess air but I would think no more than 15%. Keep tuning.

When these things going on the market?

Mike

Sorry steam man, you posted after I viewed my thread!

Yes, I tend to agree that my flame probably is over-fanned as I'm using fans that have a free-flow capacity of 415 cfm.......

Too much secondary air could definitely affect things as it won't get as hot from passing through the refractory.......


AS for when they go on the market.... I don't intend to try and sell these things until next summer. I want to make sure mine works correctly first.... If I do bring them to market, I think I can keep the local welding shop busy! Outdoor Gasifiers! Convenience and efficiency...........

 

[Nofossil]

I'll agree with Mike - seems like too much air, especially secondary air. That would account for your secondary temps being a bit low and your stack temps being high.

It's really tough to get a good estimate for how much air you really need. I think conventional wisdom is that you want about 60% more than the theoretical amount needed for complete combustion with no extra oxygen. Too low and you'll get some unburned fuel - stuff than never happened to bump into a free oxygen molecule. This type of gasifier has a fairly low 'dwell' time, so you need extra oxygen to increase the odds of complete combustion.

Sounds like you're at the other end of the spectrum with too much air.

I calculated the numbers for my EKO, and I think I ended up with about 23 CFM for primary and secondary air together to get 80,000 BTU/hour from wood at 20% MC.

 

[deerefanatic]

haha!! I'm defintely past that!

Funny part is, that the temps seem to climb when I turn the speed control on my fan up???? Must be one of those things that there are sweet spots throughout the scale, just not as sweet as the ideal one.... Or maybe just coincidence......

 

[Nofossil]

haha!! I'm defintely past that!

Funny part is, that the temps seem to climb when I turn the speed control on my fan up???? Must be one of those things that there are sweet spots throughout the scale, just not as sweet as the ideal one.... Or maybe just coincidence......

You might also have too much primary air for the size fire that you had. You've designed this baby for really high output, and with a small fire you built may not be reaching critical mass in terms of wood gas density. It looked like most of the burning was happening in the primary chamber. Given your nozzle cross section, you may need to build a bigger fire before you get happiness.

Did you have true secondary combustion? You should see blue/orange flames blasting into the secondary chamber, and you should hear a good solid rumble/roar from the secondary combustion.

 

[deerefanatic]

No, no blue flames..... More like reddish-orange.... Definitely too much air..... Somewhat of a roaring sound, but not much......

 

[deerefanatic]

Last night I got blue flames.... Unfortunately they originated in the upper firebox!!

I bought some different sealant to seal between the refractory and the side walls of the upper firebox... The stuff I've tried using cracks from the expansion/contraction of heat cycling.... The stuff I bought yesterday afternoon that I'm going to try is supposedly flexible. That will keep my secondary air from blowing up into the sides of the firebox.

Also, a design note: Using PVC pipe as forms for your secondary air paths in the refractory works great! Mine, after three fires, is gone without a trace. The refractory gets so hot it simply vaporizes the stuff.

 

[pybyr]

Matt- your home-built unit is TRULY impressive- both in terms of your willingness to take on, and ability to pull off, such a task

I would _reatly__ appreciate more details on the rack of PLC s that appear to be part of your control system; I have been thinking about maybe using PLCs in my system, but have no desire to re-invent any wheels if you've already grokked it out.

 

[winton]

How big is your secondary chamber ? Looks like 3x4x9" firebrick?

 

[deerefanatic]

Winton: The chamber is quite large... I'll get measurements tomorrow for you... I'm using splits, 1.25x4.5x9.........

Pybyr: The units are wired up for a sensor on the coldest part of my primary loop, then one for the water jacket of the stove, one for pre-heatexchanger exhaust and post-heatexchanger exhaust, then one for tank top and tank bottom..... Give me a call sometime and I'll explain it all out as it's to complicated to type and I'm lazy! 715-532-9938.... I'm self employed so I'm available by phone most days... I'll take calls until about 9pm Central time........ This goes for anyone else who has questions on my system..... Feel free to call.

 

[Wade]

Is it better to have a large secondary chamber? How much space and turbulence is needed to get a good secondary burn, or is it the maintained high temp of the secondary chamber that allows for a complete burn?
Matt how deep into the refractory did you put the pvc pipes, or how thick is you refractory?
Thanks

 

[deerefanatic]

The secondary chamber is a fairly important thing.. Too small and the gasses don't stay there long enough to get completely combusted... Too big and it will take a long time to reach temperature.

as for my refractory. It's 8" thick, and my secondary air jets start about 2" from the top at the edges and slope downward toward the slot exiting right about in the middle of the refractory. I sloped them to make the passages longer as well as let any soot, etc that gets in the jets be able to slide down out of them.

 

[Willman]

Matt,
Just wondering about the secondary chamber sizing process. Was your first size the one you went with or did it take a few tries ? Standard refractory cement or more exotic ?
Was it a WAG ? Or was there some actual engineering involved ? Not trying to be a wise A%% but am contemplating my own build in the future. Thanks.
Will

 

[deerefanatic]

Well.... I sized it by a reeaaaaaaalllllllll scientific method. A wild guess! No, not really. Nofossil and I had quite the conversation on that and it basically came down to needing to have enough cross section to keep exhaust velocity down to a reasonable level. I basically took measurements of his EKO and scaled them up.

I will say that apart from my air delivery issues, I can't see that my secondary chamber is sized too incorrectly. If anything, it's a tad large I think....

 

[Willman]

I figure that the secondary sizing is where it matters most. Could make a difference one way or the other.I am certain all the big names utilize plenty of combustion engineering to arrive at the sweet spot of gasification. Just trying to get a handle on it from an amateurs POV. Have you thought about getting some high temp glass for a peep hole into your chamber. I have seen them in a couple inch dia. Not sure where, proly Edmonds Scientific.

Will

 

[deerefanatic]

I have a piece of glass from a house-hold oven...... Not sure how long it would last though.......

For me, it's just as easy to open the door!

yah, I know there's engineering going on at eko and tarm and such to determine the secondary chamber size...... I'm just going for "close enough" on this unit to see what happens.......

 

[jebatty]

FWIW some amateur input. I think size of firebox, gasification chamber sizing, tunnel, air flow to each side, etc., all are very important. The gasification chamber has to be sized to accept the wood gas emitted by the firebox. Bigger firebox means more wood gas generation from combustion.

The firebox has to be designed to quickly generate and maintain a good bed of coals on the firebox floor around the refractory nozzle, as the downdraft drives the volatile wood gases down through the hot coals to ignite them. Once the refractory is really hot, this may become less necessary as the refractory floor itself may provide this heat, but to start and for early stage gasification it would seem to be essential.

The gasification chamber also has to get adequate mixing of wood gas and O2 so that nearly complete final combustion occurs before the velocity of hot unburned gas moves up the flue. And I would guess you want most if not all of that gas combustion to take place in the refractory tunnel both to maintain high heat in the tunnel and to protect the steel components down line.

And as those of us with gasification boilers know well, wood is not wood is not wood. Sometimes it seems that every load of wood burns differently. Moisture content varies, size of splits - surface area, and a myriad of other factors. So the gasifier needs to be able to operate reasonably well over quite a broad range of quality of wood fuel being burned. Not at all like burning oil or NG.

That "sweet spot" sometimes is elusive. I puzzle as to why some wood loads hit the sweet spot the entire burn, and a few seem to be nothing but problems - and problems usually mean smoke out the stack.

BTW, the Tarm has a glass viewing port into the gasification tunnel. It is really helpful and easy way to get a quick view to determine if gasification burn is going as intended. The fault with the viewing port is that often in early stages of the fire the port becomes clouded and sometimes even blocked by creosote condensation. The glass needs to be cleaned (lacquer thinner works well) frequently. Extra care to get a quick, hot fire going with kindling and small splits so that gasification starts very fast minimizes this fault.

 

[deerefanatic]

Very good explanation. I know my design isn't too far off.. So I should be able to get it going well once I get it set up right.

As a little side-topic, I had gasification going, but it was happening in the primary chamber due to some massive air leaks... open the loading door and see these nice blue flames! I now have those leaks sealed off, so when I get fans back on the stove, we'll see what happens.

-Matt

 

[jebatty]

I submitted a post earlier today in the following relating to secondary burn and gasification, which I copied below. I don't think you are getting gasification in the upper chamber, although you may be getting a little of the low end gasification.

https://www.hearth.com/talk/threads/24164/

The following is copied from the above post.

Secondary burn as understood by most I think is the visible, sometimes rolling, hanging, or flickering flame at the top of the firebox and around or below the top firebox air inlets. This can occur over quite a broad temperature range, and is related to the amount of combustible gases given off, oxygen available, and a source pilot flame (surface combustion flame on the wood piece). Typically it will occur with a source flame at around 500-600F and as low as about 350F, and continue up to about 1100F. The “secondary” flame occurs away from the wood surface because there in insufficient mixing of the combustible wood gas with oxygen near the wood surface to sustain combustion, and this additional mixing to permit combustion is occurring around the top air inlets in the stove.

Obviously, without the additional oxygen the otherwise combustible gases would simply go up the chimney and efficiency would decline considerably.

Starting at around 1100F and up entirely different processes start taking place. I don’t believe it would be normal in a wood stove for these processes to exist to any great extent due to the very high heat, except possibly at the very low end. Gasification boilers operate in the 1100F and up range, with the combustion taking place in specially designed ceramic chambers that can withstand heat up to 2000F and more.

The combustion “flame” at this high end is not visible, and therefore cannot be said to be secondary combustion as usually understood. Carbon monoxide is igniting invisibly at about 1350F, hydrogen at about 1200F, about the same for acetic acid, methane at about 1100-1600F.

In a gasification boiler, the invisible combustion of these products is evidenced simply by a roaring sound - totally invisible. It also may be mixed with some visible, orange to blue, flame, with the flame being representative of other, lower temperature gases also being combusted.

 

[deerefanatic]

That's a very interesting read......

I do believe I was acheiving secondary combustion down by the wood due to the fact that my secondary air inlets were unsealed and blowing air up the firebox walls right at the wood pile, vs into the nozzle area......

I now have that sealed up... Now to just get some fans and get back to work.

As a side note, I'm making some angle iron girdles for the heat exchanger to strengthen it in preparation for a pressurized system....

 

[Willman]

Very clear explanation Jim. Thanks
Will