My gasification furnace gives off either a blue flame or completely invisible flame.The surrounding refractory is bright orange but for the most part no flame is visible. Now all the advertisements and videos of other furnaces show an orange flame and a very visible flame at that. Which is better? All my research on the net tells me an orange flame is a cooler and sooty flame,and not a true gasification flame. Am i correct in saying that most gasification furnaces on the market today are not true gasification technology? Just wondering.
blue flame or orange?
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wantstoburnwood
Member
I have the same questions as you . What brand of gassifier do you have . I find that I have an invisible flame
free75degrees
New Member
I GET an invisible flame occasionally. I see it when I adjust my secondary opening to max secondary air. I can't do it every time though. It seems to happen more when the fire is not very intense. When I have a very intense fire the flame is yellow/orange at max secondary and blue/orange an min secondary. I have no idea how to know what the best flame is though, so I'd also like to hear some input from the experts...
Last year I had much more often the organge flames, poor quality and wet wood was the order of the day. This season so far it is very easy to get the blue flame. This is the cleanest burn you can achieve, look at natural gas burning equipment.
I found it to take me all season to learn the right settings to deal with different wood types and moistures. ;-P not the fastest learner here!
I also found when I tried to take some pic's of the flames that they often turned out orange while I saw blue in the furnace.
Henk.
I found it to take me all season to learn the right settings to deal with different wood types and moistures. ;-P not the fastest learner here!
I also found when I tried to take some pic's of the flames that they often turned out orange while I saw blue in the furnace.
Henk.
jebatty
Minister of Fire
I have a recollection that CO combusts at about 1200F and H at about 1400F. I suspect the output of each is CO2 and H20.
I don’t know, but doubt, that ordinary secondary combustion in a wood stove reaches these combustion temperatures in any sustained manner. I believe the gasification boilers not only reach but are designed to sustain these combustion temperatures.
Anecdotally, during the second half of the burn in my Tarm there is sustained “roaring” combustion through the nozzle and in the tunnel with little or no visible flame. I understand H has no visible flame when it combusts. I don’t know about CO.
My call is that orange to blue flame includes combustion of other components of wood gas, and also likely includes CO and H. As combustion continues towards the end, the ratio of CO and H to other wood gases increases; hence, more blue to invisible flame.
I don’t know, but doubt, that ordinary secondary combustion in a wood stove reaches these combustion temperatures in any sustained manner. I believe the gasification boilers not only reach but are designed to sustain these combustion temperatures.
Anecdotally, during the second half of the burn in my Tarm there is sustained “roaring” combustion through the nozzle and in the tunnel with little or no visible flame. I understand H has no visible flame when it combusts. I don’t know about CO.
My call is that orange to blue flame includes combustion of other components of wood gas, and also likely includes CO and H. As combustion continues towards the end, the ratio of CO and H to other wood gases increases; hence, more blue to invisible flame.
Nofossil
Moderator Emeritus
My thinking is that orange flame means lower temperature and/or higher volume of wood gas relative to secondary air. The flame zone in these things has some remarkably complex chemistry going on, and there is a sequence of chemical breakdowns happening throughout the flame zone. At first, larger hydrocarbon molecules are breaking down into smaller hydrocarbons on their way to carbon monoxide and hydrogen. I think some of these reactions give off the orange glow. As noted above, carbon monoxide and hydrogen burn clean and clear.
The cooler the temperature, the longer it takes for the sequence of breakdowns to complete. If the temps are cool enough, they may not complete at all and you'll have unburned hydrocarbons going up your flue. A portion of these are 'polyaromatic hydrocarbons' (PAH) that create the distinctive woodsmoke smell.
The hotter the fire, the faster the breakdown sequence. Also, once the bulk of the complex hydrocarbons are cooked off, the breakdown sequence is simpler and shorter. When you get down to charcoal, the breakdown sequence is
[primary] C + O -> CO
[secondary] CO + O -> C02
Hard to get much shorter.
Bottom line - I think orange is inevitable at startup, and more likely during the first burn phase when the more complex hydrocarbons are being cooked off. I'd expect that wood moisture would make it worse, and additional secondary air would make it better but only to a point. Beyond that point, additional secondary air would simply dilute the wood gas and increase the gas velocity without speeding combustion any further.
I've been burning REALLY dry wood this year. Mostly invisible flames, or really short orange flame zone. I also have an insulated labyrinth in my secondary chamber that provides a longer flame path at higher temperatures than the stock EKO.
The cooler the temperature, the longer it takes for the sequence of breakdowns to complete. If the temps are cool enough, they may not complete at all and you'll have unburned hydrocarbons going up your flue. A portion of these are 'polyaromatic hydrocarbons' (PAH) that create the distinctive woodsmoke smell.
The hotter the fire, the faster the breakdown sequence. Also, once the bulk of the complex hydrocarbons are cooked off, the breakdown sequence is simpler and shorter. When you get down to charcoal, the breakdown sequence is
[primary] C + O -> CO
[secondary] CO + O -> C02
Hard to get much shorter.
Bottom line - I think orange is inevitable at startup, and more likely during the first burn phase when the more complex hydrocarbons are being cooked off. I'd expect that wood moisture would make it worse, and additional secondary air would make it better but only to a point. Beyond that point, additional secondary air would simply dilute the wood gas and increase the gas velocity without speeding combustion any further.
I've been burning REALLY dry wood this year. Mostly invisible flames, or really short orange flame zone. I also have an insulated labyrinth in my secondary chamber that provides a longer flame path at higher temperatures than the stock EKO.
How do you see an invisable flame, just kidding ,I find when I first load I may see an orange blue flame, once the the wood is reduced to coals and charcoal I see no flame or invisable flame, also dryer wood really makes a difference and I know everyone knows that.
Steve
Steve
free75degrees
New Member
This is a good topic. As a new EKO owner, I was wondering how you can tell if you have gasification or just a flame coming through the bottom opening? Sounds like I need to moniter the flame color. Does it make a different sound during gasification?
Thanks
Thanks
nofossil said:
NoFo- not to hijack the thread, but I recall you mentioning your experimentation with the "target" in other places, and am curious where your experiments/ results stand.
one interesting thing on my Econoburnn (built in early August 2008) is that unlike the U-shaped target that they had on the earlier units (or in the photo below), mine has a flat, but sloped and heavily texttured, refractory target on the floor of the lower chamber. After talking with VP Mark Odell at Ecomoburn about a bunch of my other questions, and hearing of the various ongoing improvements that they're always considering/ looking at, I have to think that they did this to yield some improvement, not just simplification.
barnartist
Minister of Fire
So when I see (or don't) the invisible flame, I should or should not stoke the fire to get it to visibly return? The stack temp is much lower with no visible flame, and does not have the jet engine noise I love.
Nofossil
Moderator Emeritus
General replies....
Gasification has a distinctive rumble or roaring noise, at least in the EKO. This is louder during periods of high wood gas generation. If you don't see a flame, don't hear the rumble, and see or smell smoke, then you are not gasifying.
Later in the fire when you have mostly (or all) coals there will be little if any visible flame or rumble, but the exhaust will be clear and odor free.
My target / labyrinth is working, and I'm still experimenting with different materials.
I've been looking at the temperature drop between my secondary combustion and my flue. It's not as constant as you might think. Below is a graph from my last fire. I built it at about 5:30, and it went into roaring gasifcation immediately. I let it go about two hours on the initial load. At that point it was nearly down to coals, but still had a few distinct log sections. Clear flame, very little rumble. I added a few more pieces at 7:30. Back to rumble and a little bit of orange, but no flames going past the labyrinth.
At 9:30 I decided to add a few more pieces - a bit early, and there was a lot of unburned wood still in the firebox - maybe 1/4 or 1/3 full. After I added new wood, I got very loud rumble but almost no orange - none at all outside the top chamber of the labyrinth. I think there was a good thick coal bed so the wood gas was getting broken down a lot before it got to the nozzle.
You can see that secondary combustion temps (outside the labyrinth, about 18" flame path from the nozzle) get close to 1400 degrees, and the stack temp hovers around 500.
Gasification has a distinctive rumble or roaring noise, at least in the EKO. This is louder during periods of high wood gas generation. If you don't see a flame, don't hear the rumble, and see or smell smoke, then you are not gasifying.
Later in the fire when you have mostly (or all) coals there will be little if any visible flame or rumble, but the exhaust will be clear and odor free.
My target / labyrinth is working, and I'm still experimenting with different materials.
I've been looking at the temperature drop between my secondary combustion and my flue. It's not as constant as you might think. Below is a graph from my last fire. I built it at about 5:30, and it went into roaring gasifcation immediately. I let it go about two hours on the initial load. At that point it was nearly down to coals, but still had a few distinct log sections. Clear flame, very little rumble. I added a few more pieces at 7:30. Back to rumble and a little bit of orange, but no flames going past the labyrinth.
At 9:30 I decided to add a few more pieces - a bit early, and there was a lot of unburned wood still in the firebox - maybe 1/4 or 1/3 full. After I added new wood, I got very loud rumble but almost no orange - none at all outside the top chamber of the labyrinth. I think there was a good thick coal bed so the wood gas was getting broken down a lot before it got to the nozzle.
You can see that secondary combustion temps (outside the labyrinth, about 18" flame path from the nozzle) get close to 1400 degrees, and the stack temp hovers around 500.
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barnartist
Minister of Fire
I am reading your graph Nofo, but trying to still determine how this effects the water temp. Im sure it is spiking the water a bit too, so should we sprint here or run the marothon? Or spint and then let it level off?
Im pretty sure that if the upper chamber would allow the wood to fall into the nozzils, more like an hourglass effect, that the gasification would peak and valley on its own....? I think this has been discussed as well. Should that chamber be built to make this happen, or is it built the right way (Eko speaking).
Im pretty sure that if the upper chamber would allow the wood to fall into the nozzils, more like an hourglass effect, that the gasification would peak and valley on its own....? I think this has been discussed as well. Should that chamber be built to make this happen, or is it built the right way (Eko speaking).
Nofossil
Moderator Emeritus
barnartist said:
The whole water temp thing is complicated, since I'm opening and closing the recirculation zone valve as well as switching heat loads on and off and changing the wood circ speed to try and maintain the water temp in a target range. All of this has little to do with the combustion, so I left it off this graph.
Certainly some of the variation is logs moving around. The newer EKO has a sloped floor that tends to encourage logs and coals to move towards the nozzle - a distinct improvement over the old design, I expect. I may modify mine.
I spent some time last night observing the flame at different points of the burn cycle. With a large amount of wood in the boiler and towards the start of the cycle, the flame fairly long and was very bright yellow at the ends with blue flame at the base. Later in the cycle as the coals built up, the flame was shorter, more defined and almost completely blue. The low rumble sound was present during the entire cycle once the start up period was complete.
Wouldn't temperature be a better indicator of gasification than color of flame? I realize the flame color is indicative of temperature but if you have to open the door to view it the color changes according to people with windows on their secondary combustion chamber.
jebatty
Minister of Fire
Maybe, but what temperature, where measured, and how to do it? If in the stack, my stack will easily go over 1000F if I leave the damper open and draft fan on, and there is no gasification taking place.
I would think a thermo couple installed in the gasification tunnel at the end closest to the door would be a good place to look for peak temeperatures. A k type thermo couple capable of sustained 2500 degree temperatures cost approx $15, plus you need a meter to read it. I am just getting into install phase of my EKO 40 so it will be a while before I am able to experiment with a thermo couple but I will post results if I get around to installing one.
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