I have a question for you wood gasification folks. I have been using an home-built out-door wood boiler but have been unhappy with it's demand for large volumes of wood. I understand the basic wood gasification concept and have looked at several boilers. My question has to do with the common practice of storing the heat in bulk water tanks. I have been thinking that if you could control the nozzle diameter then perhaps you could control how much heat that is put out over time by the wood gas flame and yet not shut it down. I'm thinking along the lines of having a large "cold" fire that feeds an adjustable nozzle or a group of nozzles so that the amount or volume of flame is changed by demand. Has anyone tried this?
Howdy from a new guy and a ?
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Nofossil
Moderator Emeritus
That's a really good question, and I suspect a viable answer would be worth a lot.
What you're getting at is increasing the ability to modulate the boiler output. That is, absolutely, the most significant shortcoming of log / chunk wood boilers - they cannot be modulated over a wide range of output and still maintain efficiency. My understanding is that in order for gasification to work, the primary/secondary air ratio must be close to ideal, and the gas velocity through the nozzle must be within a certain range. Some folks have blocked off one nozzle in a two-nozzle gasifier to reduce output. A variable nozzle could provide much more control, but I suspect that materials issues make it near impossible.
What you're getting at is increasing the ability to modulate the boiler output. That is, absolutely, the most significant shortcoming of log / chunk wood boilers - they cannot be modulated over a wide range of output and still maintain efficiency. My understanding is that in order for gasification to work, the primary/secondary air ratio must be close to ideal, and the gas velocity through the nozzle must be within a certain range. Some folks have blocked off one nozzle in a two-nozzle gasifier to reduce output. A variable nozzle could provide much more control, but I suspect that materials issues make it near impossible.
sdrobertson
Minister of Fire
nofossil said:
I always wondered what the temp would be at the top of the nozzles would be. I know that the bottom of the upper chamber is ceramic but I wonder if this is easier to install the nozzle material or if it is really needed for heat. Seems like the high temps would be out the bottom of the nozzles so maybe a steel plate would hold up on the top of the nozzles that could be varied in size over the nozzles.
Paul Downes said:
Welcome to the forum Paul,
There was a topic "Wood gas - for more than just a boiler" brought up by Ugly. Do a search for Ugly in the Forum Search box in the left hand corner area here in The Boiler Room. There was some discussion on variations on boiler/nozzle designs. You might PM him with some questions on design concepts.
What you are talking about, as Nofossil says, would be worth a lot but I think that with variable boiler flame output you would also have to control the amount of water actually being heated as well and diverted so that the water being heated by the smaller flame could address the heat loss created by the heat demand. (which almost seems like a frustration in design principle) OWB's generally use more wood because of the lower temperature of the flame and wide area displacement (caused by the water jacket) which effects the heat energy to water transfer. OWB"s larger wood capacity would be great for a gasifier though as you could load every other day in some cases and maybe more. Maybe what you are trying to do could be designed with a larger hopper/primary chamber and a smaller nozzle though I wouldn't give up too quickly on the variable nozzle design theory. As Nofossil stated some have tested two nozzle boilers by blocking off one nozzle with some degree of success though others have seen no gains or even a loss of efficiency. Those that had success indicate there is room for development in the way gasifiers are designed. Again referring to Nofossil's response getting the mixes at their best, via ratio, is something that was not directly addressed by those blocking off one nozzle but in a variable set up is something that would have to be built in to the boiler if you are going to have efficiency.
The EKO I use goes in to idle when the heat demand is satisfied and the boiler gets up to the preset temperature threshold because I do not have storage. It does not shut down unless it runs out of wood, but maintains a fire ready to go back in to gasification when the demand is received. In that consideration a larger "hopper" would be nice for extended run times.
Northwoodsman
New Member
I've pretty much got the primary and secondary settings on my EKO40 fine tuned and guess its now time to look at your question.
I agree that this is the biggest shortcoming of any brand of "chunk type" boiler.
My research also tells me that the ratios and velocities of the air going into the secondaries is extremely critical for proper/complete gasification to occur.
I think an electriclly operated pilot valve could be adapted to the front end of the secondary air tubes and thus the amount of air being fed into the secondary chamber could be instataneously/variably controlled based on the temperature/demand of the boiler.
In the second stage gasification your distilled fuel is CO CH4 N H. Combustion of these compounds isn’t very thorough in other wood burning appliances or even very common in nature. Primarily because this second stage combustion requires the presence or high temps 2,200F and a specific ratio of O2 to gas. The equations for these reactions can be looked up, but it becomes clear that these gases create an exothermic reaction that results in the 30%+ increase in energy output. The ultimate exhaust should consist primarily of CO2 and H20.
Thus, I think it would be difficult (but not impossible) to make this mixture adjustable using O2 sensors similar to that on a vehicle.
While we are thinking out of the box here, why not add an auger to the upper primary chamber and variably feed wood chips vs. "chunk wood" into the chamber (lets copy the pellet stove technology)
!
NWM
I agree that this is the biggest shortcoming of any brand of "chunk type" boiler.
My research also tells me that the ratios and velocities of the air going into the secondaries is extremely critical for proper/complete gasification to occur.
I think an electriclly operated pilot valve could be adapted to the front end of the secondary air tubes and thus the amount of air being fed into the secondary chamber could be instataneously/variably controlled based on the temperature/demand of the boiler.
In the second stage gasification your distilled fuel is CO CH4 N H. Combustion of these compounds isn’t very thorough in other wood burning appliances or even very common in nature. Primarily because this second stage combustion requires the presence or high temps 2,200F and a specific ratio of O2 to gas. The equations for these reactions can be looked up, but it becomes clear that these gases create an exothermic reaction that results in the 30%+ increase in energy output. The ultimate exhaust should consist primarily of CO2 and H20.
Thus, I think it would be difficult (but not impossible) to make this mixture adjustable using O2 sensors similar to that on a vehicle.
While we are thinking out of the box here, why not add an auger to the upper primary chamber and variably feed wood chips vs. "chunk wood" into the chamber (lets copy the pellet stove technology)
!NWM
Northwoodsman
New Member
Guys,
You gotta download the follwoing document that Jim just posted on my other topic:
This is better than pretty good.
“THEORIES OF THE COMBUSTION OF WOOD AND ITS CONTROL”
http://www.fpl.fs.fed.us/documnts/fplr/fplr2136.pdf
This goes into an extemely detailed (69 page) discussion with all the details/chemical formuls etc.
NWM
You gotta download the follwoing document that Jim just posted on my other topic:
This is better than pretty good.
“THEORIES OF THE COMBUSTION OF WOOD AND ITS CONTROL”
http://www.fpl.fs.fed.us/documnts/fplr/fplr2136.pdf
This goes into an extemely detailed (69 page) discussion with all the details/chemical formuls etc.
NWM
The idea of a variable sized nozzle(s) is very interesting. I am not aware of anyone doing this and it does strike me that the materials might be a challenge. The Froling Turbo 3000 addresses the modulating issue not by varying the nozzle size, but by varying fan speed and primary and secondary air settings. The boiler monitors flue gas makeup and adjusts the air settings to achieve the ideal fuel/air ratio for the burn rate, fuel type and moisture content.
It would seem that the variable nozzle concept paired with the Froling technology could provide a pretty wide range of modulation. Maybe the next big step in boiler development? Although at 92% I think we are starting to plateau on the efficiency side. Maybe a wider modulation range would allow for smaller heat storage volumes?
cool idea.
It would seem that the variable nozzle concept paired with the Froling technology could provide a pretty wide range of modulation. Maybe the next big step in boiler development? Although at 92% I think we are starting to plateau on the efficiency side. Maybe a wider modulation range would allow for smaller heat storage volumes?
cool idea.
There are variable nozzles out there, but I've never heard of one used in wood gasification. The Renzor waste oil burner comes to mind. I know a guy who has burnt everything from heavy weight oil to gasoline in a renzor. The Nozzle senses the flame somehow and adjusts for output regardless of fuel. One thought is to use a supercharger blower with speed controls. Another thought was to use a bank of smaller nozzle tubes with a rotary plate valve to block/open multiple tubes per demand. I am new to the science of all this so these are just thoughts. I wonder if the tubes should be made from 400 series stainless because of it's red hardness. O2 sensors might work to control oxygen levels. I would think that electronic controls for air flow and gas flow would be workable.My thought is to have in the neighborhood of 4-500 gallons of water in the loop.
I'm in the just wondering stage of all this. My current boiler is rather old and I'm hoping to have a workable design within a year or so. I'm thinking about building a 1/2 or 1/4 scale prototype to test out ideas. I could always use it to heat a workshop. Maybe one could tap into some of that "green" money the new gang of mobsters in Washington are talking about.
I'm in the just wondering stage of all this. My current boiler is rather old and I'm hoping to have a workable design within a year or so. I'm thinking about building a 1/2 or 1/4 scale prototype to test out ideas. I could always use it to heat a workshop. Maybe one could tap into some of that "green" money the new gang of mobsters in Washington are talking about.
steam man
Minister of Fire
I've thought about the variable nozzle concept at times. After all-who would have though about variable valve timing/ignition on cars 40 years ago? I would think a bank of nozzles with the capability to turn one off at a time, perhaps with a ceramic plug would be easiest. Next you could keep track of the differential pressure between the first and secondary chamber. Depending on the number of nozzles open, the air pressure could be regulated to maintain the airflow velocity through the nozzles to be higher than the wood gas flame speed and maintain the right fuel-air ratio. Nozzles could go in and out based on boiler temp. I am not sure what kind of turndown ratio you could get but certainly there should be an ideal number of nozzles.
Just a thought.
Mike
Just a thought.
Mike
Steam man,
EKO is supposedly manufacturing a new nozzle that uses multiple 10mm holes per side for the secondary air instead of the two larger holes per side supposedly to create a better mix blend of gasses. The primary portion of the nozzle is relatively the same but the secondary outlets exit the nozzle from a recessed/stepped in face. A sliding refractory piece that mated the new bottom dimensions of the nozzle would be a great place to start. I believe air pressure could all be maintained in a mechanical sense with proper gearing though finding the right ratio would be a must. For example: push the handle down the nozzle "plug" slides in and shuts down all secondary outlets in its path as the primary air is also closed down to the new size via primary air adjusters linked to the same handle. A unique possible perspective on the supposed newer EKO design is that the moving part of the adjustable nozzle would be sort of self cleaning since it could track below the primary portion of the nozzle but would act as a shelf for ash and embers that would fall off as the plug or slide is retracted. Using secondary air flow to purge the gear area then supply the the O2 for the fire is probably the best way to control unwanted flammable gas flow. Sound do-able?
EKO is supposedly manufacturing a new nozzle that uses multiple 10mm holes per side for the secondary air instead of the two larger holes per side supposedly to create a better mix blend of gasses. The primary portion of the nozzle is relatively the same but the secondary outlets exit the nozzle from a recessed/stepped in face. A sliding refractory piece that mated the new bottom dimensions of the nozzle would be a great place to start. I believe air pressure could all be maintained in a mechanical sense with proper gearing though finding the right ratio would be a must. For example: push the handle down the nozzle "plug" slides in and shuts down all secondary outlets in its path as the primary air is also closed down to the new size via primary air adjusters linked to the same handle. A unique possible perspective on the supposed newer EKO design is that the moving part of the adjustable nozzle would be sort of self cleaning since it could track below the primary portion of the nozzle but would act as a shelf for ash and embers that would fall off as the plug or slide is retracted. Using secondary air flow to purge the gear area then supply the the O2 for the fire is probably the best way to control unwanted flammable gas flow. Sound do-able?
steam man
Minister of Fire
Cave2k,
There's nothing time and money can't solve. (My boss is not sure if he likes that line). Sounds like the EKO is going to be pretty sophisticated. Hopefully it will be a bullet proof design so you won't need an engineer operating and maintaining your unit. A simple fuel-air ratio control mechanism could be used. I have seem some 50-75 year old designs that could be brought back to life. Typically some kind of cam is used to "characterize" the air or fuel flow. I've thougth about doing my own project at times but I just don't have the "time" part of the equation right now. Sounds like you have it pretty well thought out.
Mike
There's nothing time and money can't solve. (My boss is not sure if he likes that line). Sounds like the EKO is going to be pretty sophisticated. Hopefully it will be a bullet proof design so you won't need an engineer operating and maintaining your unit. A simple fuel-air ratio control mechanism could be used. I have seem some 50-75 year old designs that could be brought back to life. Typically some kind of cam is used to "characterize" the air or fuel flow. I've thougth about doing my own project at times but I just don't have the "time" part of the equation right now. Sounds like you have it pretty well thought out.
Mike
Steam man,
Thought about maybe. Well though out??? The new EKO nozzle was just a reference for a possible variable nozzle configuration. From what I hear and the video I saw the newer nozzle addresses uncontrolled turbulence in the secondary chamber and forces a better blend of gas mixes. The older nozzle has two larger holes on each side of the nozzle and when secondary air is up too high you can see gaps in the flame (in my boiler anyhow). The nozzles are supposedly replaceable and for the engineering entrepreneur could lend themselves to a variable set up.
I know what you mean about the time factor. Just when you think you are going to have a little more time so you can do a "little" project you find the iron in the fire is bigger than what it seemed. For me (LOL) it's always a part of the equation so maybe you could help me and tell me how you get it to be a selectable commodity?
Thought about maybe. Well though out??? The new EKO nozzle was just a reference for a possible variable nozzle configuration. From what I hear and the video I saw the newer nozzle addresses uncontrolled turbulence in the secondary chamber and forces a better blend of gas mixes. The older nozzle has two larger holes on each side of the nozzle and when secondary air is up too high you can see gaps in the flame (in my boiler anyhow). The nozzles are supposedly replaceable and for the engineering entrepreneur could lend themselves to a variable set up.
I know what you mean about the time factor. Just when you think you are going to have a little more time so you can do a "little" project you find the iron in the fire is bigger than what it seemed. For me (LOL) it's always a part of the equation so maybe you could help me and tell me how you get it to be a selectable commodity?
Cave2k
Is the new eko nozzle installed in the new model (dark grey, different fan cover, top & bypass)?
Is the new eko nozzle installed in the new model (dark grey, different fan cover, top & bypass)?
Hydronics said:
That information I don't have. The information I received was in mid Dec 08. Nothing was said about the new color models just the nozzles. If you have one you can look at use a collapsible inspection mirror and let me know will you? It is possible it will be in the gray models but it also may depend on current stock stores which units actually get the the new nozzle. Bear in mind I was only told and not guaranteed that EKO was pursuing the new design for future production. Since then it has been wait and see but the design concept sounds good and if the video I saw was indeed the new nozzle it looked good in operation too.
One question I have had is; How much does the wood gas ratio/mixtures vary depending on wood species and condition. In other words, does say dry elm generally produce 5% methane when gasified and rotted elm 10% methane?
The reason I ask this is because it seems logical to control the wood gas burn by temperature (which is simple) and not worry about oxygen % per say. If you knew that the general wood gas mixture stays the same then you would have a target temperature of something like 2300 F and the blower velocity or mass air would increase/decrease to hit that target temp. I also wonder if air for the secondary burn chamber should be at a constant velocity. I'm thinking about how a welders torch works. It seems like you would want to have constant velocity but variable #'s of tubes. On the other hand if the wood gas chemical composition changes a lot then it might be hard to have a target temperature. (I haven't read the paper Theories of the combustion of wood..yet, but I will.)
I notice that some designs have the secondary burn directed into a chamber that is less contained meaning that the high temps generated are kept away from the chamber walls. Kind of like having the fire in the middle of the tepee. This must help eliminate chamber wall erosion. So I guess I need to think about how to marry the wood gases and secondary air without melting everything. (In an aside remark, a friend of mine had a wood gasifier boiler that nearly burnt down his furniture factory because the secondary burn chamber was poorly designed and burnt the insulation away and burnt through the stove roof. Good thing he had a sprinkler system installed.) He is installing a EKO boiler now.
My thoughts of a variable nozzle would be something that looks like a Gating gun from the business end. A cluster of tubes with a plate that slides out of the way to control the amount of air entering into them. The other idea was to make an iris valve similar to a camera f stop mechanism but that seems a juvenile thought given the hostile environment. I know the controls aspect of all this is more complicated. For instance, if a temperature control is calling for more air flow but the wood gases aren't yet available because you just fired the stove..Now yer talking timers..or more sensors....a lot of messing around is called for here. it's getting closer to the time to quit talking and get working.
The reason I ask this is because it seems logical to control the wood gas burn by temperature (which is simple) and not worry about oxygen % per say. If you knew that the general wood gas mixture stays the same then you would have a target temperature of something like 2300 F and the blower velocity or mass air would increase/decrease to hit that target temp. I also wonder if air for the secondary burn chamber should be at a constant velocity. I'm thinking about how a welders torch works. It seems like you would want to have constant velocity but variable #'s of tubes. On the other hand if the wood gas chemical composition changes a lot then it might be hard to have a target temperature. (I haven't read the paper Theories of the combustion of wood..yet, but I will.)
I notice that some designs have the secondary burn directed into a chamber that is less contained meaning that the high temps generated are kept away from the chamber walls. Kind of like having the fire in the middle of the tepee. This must help eliminate chamber wall erosion. So I guess I need to think about how to marry the wood gases and secondary air without melting everything. (In an aside remark, a friend of mine had a wood gasifier boiler that nearly burnt down his furniture factory because the secondary burn chamber was poorly designed and burnt the insulation away and burnt through the stove roof. Good thing he had a sprinkler system installed.) He is installing a EKO boiler now.
My thoughts of a variable nozzle would be something that looks like a Gating gun from the business end. A cluster of tubes with a plate that slides out of the way to control the amount of air entering into them. The other idea was to make an iris valve similar to a camera f stop mechanism but that seems a juvenile thought given the hostile environment. I know the controls aspect of all this is more complicated. For instance, if a temperature control is calling for more air flow but the wood gases aren't yet available because you just fired the stove..Now yer talking timers..or more sensors....a lot of messing around is called for here. it's getting closer to the time to quit talking and get working.
Nofossil
Moderator Emeritus
I don't think the composition of wood gas varies a lot from species to species, but is most definitely varies over the course of a fire. As the percentage of charcoal in the primary chamber increases, I suspect that you get a lot less of the more complex hydrocarbons and a lot more CO. Certainly, the length of flame drops considerably, and I suspect that means that the chemical reaction chain is much shorter towards the end of the burn.
So a variable nozzle would help regulate this issue. I wonder how much the flame temperature varies over the course of a load burn? It seems logical that primary air should be varied over the course of the burn.
How about just a smaller nozzle so that burn times increase at less btu's/hr? Is that the difference b/t the different sizes of boilers within one line (EKO 25, 40, 60)? You could sort of tailor the nozzle to average heatloss per hour plus some factor for those really cold days (say heatloss + 50% extra). Isn't this the reason why you do not want to oversize the boiler?
That's the basic idea. As you well know, BTU's per hour (demand) varies quite a lot. I think that multiple nozzles makes more sense. They would be fired as demand increases. The exception is that I want to oversize the primary fire chamber so that I load the stove less often. I also want to avoid having to store bulk excess heat generated. It's not a problem to have 3-500 gallons in the system so there's enough buffer. I currently heat my wood shop and house and domestic hot water. My OWB is sadly undersized and the heat exchanger is also undersized per demand. The idea is to build a new system in the next few years.
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