gasification tuning

[free75degrees]

I have been burning the new tarm for a couple weeks now and am still learning how to tune the fire. This past weekend I made some fires with some wood that had seasoned for 2+ years with a small roof over it, as opposed to about 1 year old wood that was in the open. The older wood burned WAY hotter. The gasification was so intense that it almost made me nervous. I almost though the Tarm was going to lift off.

Is it possible to have a flame that is too intense? I was able to remove heat by charging the tank but the temp on the tarm control panel was right at 90*C (194*), which is right about where the fan turns off.

Also, what is the best setting for the 2ndary inlet? If I open it all the way I get almost invisible flame, but very strong blowing, like a jet, with lots of burning embers blowing through. If I close it all the way I get a huge bilowing orangish bluish flame that extends out of the front of the tunnel and bends back a bit toward the rear of the boiler.

What is the description of the perfect flame?

 

[Nofossil]

This is good territory to explore. I've found that with drier wood, you don't want a lot of small pieces - too much surface area. I'm working on adding a lambda sensor to mine, but for now I'd say that the right amount of secondary air is just enough so that there's no odor at all in the exhaust. For me, that's when I have blue/orange flames that wrap around my combustion labyrinth about 8" to 12" from where they leave the nozzle.

 

[free75degrees]

This is good territory to explore. I've found that with drier wood, you don't want a lot of small pieces - too much surface area. I'm working on adding a lambda sensor to mine, but for now I'd say that the right amount of secondary air is just enough so that there's no odor at all in the exhaust. For me, that's when I have blue/orange flames that wrap around my combustion labyrinth about 8" to 12" from where they leave the nozzle.

Now I can see why you are looking into the lambda. I really notice a huge difference in where I need to set the 2ndary setting to get a consistent flame from fire to fire. Wood quality and type, how much wood is loaded, what stage in the fire, etc all seem to affect the flame. How are you doing the mechanical control of the 2ndary inlet?

 

[Eric Johnson]

When my boiler is gasifying well, I get the orange/red flames that nofossil mentioned, no visible smoke coming out of the stack and a slight odor of what I would describe as "toasted wood." Kind of a pleasant, nutty smell.

Earlier in the cycle, I tend to get a yellower flame, sometimes mixed with a little visible smoke in the secondary chamber. I have seen blue flames as well, but I can't remember under what conditions.

I've talked to people who operate wood-fired power plants, and they say the biggest challenge is maintaining a consistent burn across different fuel conditions. They're always changing, and keeping up with them is a big challenge--especially to operators used to dealing with fuel that has consistent predictable quality, like oil, gas or coal.

 

[jebatty]

Early on I spent quite a bit of time fiddling with the air lever adjustment. Finally, I did just what the manual said, put it in the middle and forget it. Maybe an adjustment one or the other would be in order based on a different wood type or level of dryness, but mine is pretty much all the same in both categories.

All of my wood is dry, now also split into 4-7" pieces, and mostly pine. It burns hot, and I have the draft fan dampered down a lot. I have the chain turbulators installed. Typical stack temp 400-600, with the 600 in the early part and most of the burn being 400-500.

 

[Nofossil]

I don't think there's any doubt that the fixed primary / secondary settings are a compromise that's less than ideal much of the time. I don't have a specific approach for computer control of secondary air at this point. I figure I'll start by at least getting a better understanding of the range of settings that you would want over the course of a typical burn.

There are people who know all of this, but that information seems to be proprietary or at least well buried.

 

[LarryD]

I'm curious as to how long it takes to get stack temps to 500-600. I have, what I think, is pretty dry wood. Cut and split for 2 years. I have to leave the by pass dampper open for 7-8 minutes to get to 400*. And once they are at 400* and I close the damper the temps drop pretty quick to 250*. I have been cleaning out the ashes off the refractory daily. I can get the flame to wrap around the refractory but once the temps drop that quits. I keep thinking I have a draft issue.

I know if I left the damper open on our wood stove it would have melted.

This forum has made this learning curve fun!

LarryD

 

[deerefanatic]

My stove burns much like Eric says on his EKO... Orangey-Blue flames, no smoke, and a hint of wood smell........ A very pleasant aroma indeed.

My stack temps are kinda hi, usually around 700F with a 1450F combustion temps. I have small chain inside six of the firetubes... I'm going to try making twisted metal turbulators and see what I can accomplish with that.

 

[Nofossil]

I'm curious as to how long it takes to get stack temps to 500-600. I have, what I think, is pretty dry wood. Cut and split for 2 years. I have to leave the by pass dampper open for 7-8 minutes to get to 400*. And once they are at 400* and I close the damper the temps drop pretty quick to 250*. I have been cleaning out the ashes off the refractory daily. I can get the flame to wrap around the refractory but once the temps drop that quits. I keep thinking I have a draft issue.

I know if I left the damper open on our wood stove it would have melted.

This forum has made this learning curve fun!

LarryD

There's two answers to that question. With the bypass damper open, it doesn't take long. Once you've switched to gasification mode, it takes a bit longer to get everything up to temp. Note that flue temperature measured by an external flue thermometer is often much lower than what you measure with a probe that's in the flue gas path. My external reads 250 while my internal reads 450.

Here's a graph from a recent fire. The red and purple traces are secondary combustion and flue temperatures, both divided by 10 so they'll fit on the graph. Secondary combustion is measured well out of the flame zone, near the water jacket and after the gases have passed through a labyrinth.

At about 7:55, I put a torch to the newspaper. Flue temp starts climbing immediately, as the bypass is open.

At about 8:00, I shut the bypass damper and the doors, and turn on the controller. At this point, the flue temperature drops and secondary combustion starts to climb. Secondary combustion is working, and by 8:04 the secondary combustion temperature breaks 1000 degrees. At this point, flue temp is a bit under 400 degrees.

As time goes on and the boiler heats up, secondary combustion reaches about 1300 degrees and flue temp reaches a bit over 500.

For the real control freaks out there: Note that the tank circulator is running before the fire starts. At 7:57, my controller detects that I've started a fire. It keeps the tank circulator running, opens the wood recirculation zone valve (input temp protection) and starts the wood boiler circ on low speed. This results in a boiler inlet temperature that's higher than the boiler outlet temperature. Just using storage to help get the boiler up to operating temp more quickly.

At about 8:16 the controller shuts off the tank circulator, and at 8:22 the recirculation valve closes.

At 8:30, the controller starts switching in low priority heat loads - the hot tub and DHW superheating.

 

[stee6043]

Geeze...my head hurts with all of that controls talk! Very impressive.

 

[Nofossil]

Back to LarryD's question....

In my experience, once secondary combustion starts it should never stop until the wood load is burned down to coals. Are you having situations where you lose secondary combustion with a healthy wood load? If so, are you seeing smoke in your secondary cahamber or out your chimney?

Secondary combustion can be tough to get started especially with less than ideal materials, but it seems pretty robust after that.

 

[LarryD]

At the moment we have one zone and our storage tank as a load for the boiler. Within a week we will have 3 more zones added. With that said I learned that if I loaded the boiler 3/4 the way with wood it ideled and created Mucho creasote. Perhaps my wood isn't as good as I thought!!

So back to your question, yes it does seem that I am losing secondary burn. The odd thing is that the wood isn't hissing. At all. There is smoke unless I leave the bi pass damper open for 15 minutes and/or have the lower ash clean out door open. Smoke in the fire box as well as coming out the chimney.

I think I had better at some point describe my chimney situation. I have to go back to work. I will post that later on today (this evening)

Nofossil-Thanks for your reply

LarryD

 

[Nofossil]

At the moment we have one zone and our storage tank as a load for the boiler. Within a week we will have 3 more zones added. With that said I learned that if I loaded the boiler 3/4 the way with wood it ideled and created Mucho creasote. Perhaps my wood isn't as good as I thought!!

So back to your question, yes it does seem that I am losing secondary burn. The odd thing is that the wood isn't hissing. At all. There is smoke unless I leave the bi pass damper open for 15 minutes and/or have the lower ash clean out door open. Smoke in the fire box as well as coming out the chimney.

I think I had better at some point describe my chimney situation. I have to go back to work. I will post that later on today (this evening)

Nofossil-Thanks for your reply

LarryD

Maybe someone who knows something about the Tarm Excel 2200 could chime in, but I'm thinking there may be a real problem here. Just to be safe, let me review the steps in starting an EKO so that we can compare to your situation:

1) Build a fire in the upper (primary) chamber.

2) Open the bypass damper and the lower (secondary) door. Light the fire and close the primary door.

3) Wait until fire is well established, somewhere between 5 ad 15 minutes.

4) Close the bypass damper and secondary door. Start the controller.

At this point, secondary combustion should start - the rumble / roar sound, clean exhaust, orange / blue flames in the secondary chamber. No further attention should be necessary until reloading time.

As the water jacket temperature approaches the maximum setpoint, the fan slows down. If the setpoint is reached, the controller goes into 'idle'. On the EKO, than means running the fan for a few seconds every few minutes. Once the jacket temp drops enough, normal operation resumes.

Can you describe anything in your operation that differs from this?

When it goes to idle, is your storage up to temp? When it idles, how long before it goes back to normal operation?

Mine will not idle until the storage temp is pretty hot, and it typically won't idle if there's demand from the zones.

 

[LarryD]

Nofossil-

That describes the way I operate the boiler pretty accurately. If the boiler is up to temp the fan will shut off while the circulator pumps pull heat out of the boiler. Once the boiler reaches its low limit the fan re starts. It does this until it needs to be reloaded. I assumed this was the wway it was supposed to work!!

My Chimney-18' of class A pipe to a 30* to a 1' piece to another 30* up through roof to another 5 feet of class A pipe. This is all through a chase way in the center of the house. I would assume that I would have a pretty strong draft. It is not as strong as I would have thought.

What could be casuing the smoke? I have a friend that has a moisture meter, I will borrow and double check my wood. I have a hard time believing it is the wood. Anything is possible

LarryD

 

[Nofossil]

What's your chimney diameter?

 

[Hansson]

Here is a guy that have build his own lambda control to his tarm
http://www.byggahus.se/forum/biobraensle/58915-lambda-styrd-vedpanna.html
Look at the pictures
I also want lambda control

 

[LarryD]

Nofossil-

6" Metal Fab HT. I did post several weeks ago, and that seemed like it would be "ok". What are your thoughts?

LarryD

 

[Nofossil]

Nofossil-

6" Metal Fab HT. I did post several weeks ago, and that seemed like it would be "ok". What are your thoughts?

LarryD

I don't know. My chimney is about 30' straight up with 8" square tile. The connection between my boiler and the chimney is 7" round with a 90 degree and a 45 degree bend. What does Tarm recommend?

 

[free75degrees]

Here is a guy that have build his own lambda control to his tarm
http://www.byggahus.se/forum/biobraensle/58915-lambda-styrd-vedpanna.html
Look at the pictures
I also want lambda control

Cool, I can't understand the words, but I can see how he attached a controller to the secondary knob. I'm still not even done with all of my controls and now I want to add some lambda control!

nofo - how is yours coming?

 

[LarryD]

I don't know. My chimney is about 30' straight up with 8" square tile. The connection between my boiler and the chimney is 7" round with a 90 degree and a 45 degree bend. What does Tarm recommend?[/quote]

Tarm said 6" round is a minimum 8" is recomended. The collar on the boiler is 6". It is one of those situations that I had the 6" pipe and it is only 3 years old. FYI-We installed a barometric damper in the smoke pipe. The flap seems to "flap" a lot. I adjusted the weight further in last night on a wim and that seems to have lessened that. One thought I had, because it seems that it is a draft issue, is to add another 3'-4' of pipe at the rain cap. I would rather drill down the exact issue prior to that. One last thought that I had was that perhaps this draft issue is magnified by truly warm weather for burning wood. It has been in the 50's and mid 40's at night. It is on the low 40's now. I just put a full load of wood in the fire box and got the stack temps to 400*. After 10 minutes it dropped to 350*. It didn't really rumble this time. The flame in the secondary chamber was orange but short. By the way I have left the secondary air all the way open, thinking I am fighting a draft issue.

Any further thoughts??

LarryD

 

[jebatty]

I have the Tarm Solo 40, went with the 6" stainless Class A, about 22' total with a cap. I had a lot of early on draft issues, solved one by one. Also added a barometric damper in this process because I was burning too hot, but now have disabled it (screwed it shut).

What took me the longest to discover was that there was more adjustment to the draft fan damper than I thought. Take a look closely at this, it may be possible to open it more by moving the fixed vs the adjustable adjustment. I had the opposite problem. The draft damper was open more than I needed and I was burning too hot. I had to adjust the fixed adjustment to close the damper and then fine tune with the adjustable adjustment.

Try burning loads about 2/3-3/4. Use fairly small splits, 4-6". Is your wood dry? Mine is dry. What wood are you burning? Are you sure it's dry. Try moving away from hard "hard" wood and move to softer hard wood or pine. Try some dry pine in the mix if you have or can get any. If your wood is not dry, you very likely will have problems.

Secondary air adjustment. If you move it all the way secondary, then you might not be giving enough air to primary combustion. I would put the adjustment in the middle and leave it there. Work with that setting to solve problems. You should work fine with it in the middle. Changing multiple variables really makes it difficult to solve problems.

My probe stack temps run 400-600 if the fire tubes are clean, with 400-500 being the bulk of the burn, 600 or a bit higher on the front side when the fire is burning the hottest.

Flapping of the barometric damper: caused by starting and stopping of gasification. Is the nozzle being plugged by a large piece of wood falling over the nozzle? Are you loading to cover/plug the nozzle? Are bridges being created? I load a bit carefully with the intent of not allowing a large split to fall right over the nozzle. Put lighter, smaller pieces on the bottom, heavier, larger pieces on top.

I have a great sense that your problems are solvable, work with one variable at at time. Regardless, make sure you are burning dry wood, small splits, not overly full until you solve problems.

Addition: barometric damper is used if too much draft, not if there is too little.

 

[rickh1001]

With all this discussion of finding optimal burn conditions, what about an oxygen sensor? In principle, it seems that an O2 sensor in the stack could be used, in principle to adjust the secondary air. The ultimate system might be something like a modern automotive closed loop feedback type arrangement.

 

[LarryD]

Jebatty-

How do you adjust the "fixed" primary air. I'm Not seeing what you are saying.

I have a barometric damper because of the oil side to this boiler. I was under the impression that this was required.

Our wood, I thought, was pretty good. It has been cut and split for 2 years! All Scarlet Oak (in the red oak family). I have been loading the boiler 1/3-1/2 full based on outside temps. Tonight I freighted it! I am aware of the concept of bridging but haven't perfected my loading technique. I am aware of not "blocking" the nozzle. If I am or not that is another story!

The boiler is ideling right now, with the adjustment to the barometric damper it is not allowing air into chimney.

Any further thoughts?

LarryD

 

[free75degrees]

With all this discussion of finding optimal burn conditions, what about an oxygen sensor? In principle, it seems that an O2 sensor in the stack could be used, in principle to adjust the secondary air. The ultimate system might be something like a modern automotive closed loop feedback type arrangement.

This is what hansson and nofossil are talking about when they refer to a lambda sensor. Some of the more expensive boilers come with one while some people are making their own.

 

[jebatty]

Our boiler are different, as mine is wood only, so yours may have a different primary/secondary air control. Mine has one lever for primary/secondary air control. Move it all the way to the right, most air is primary, and as the lever is moved to the left, air is diverted from primary to secondary; all the way to the left results in maximum air to secondary, minimal to primary. Try a middle setting to start with.

Barometric damper - my comments related to a wood-only boiler. I have no knowledge of what is needed for an oil boiler.

Some oaks, depending on conditions, take a surprisingly long time to really dry. So I still would suggest trying different wood that is dry.

For burning oak, especially during the first 1/2 of the burn, unless it is really dry, I would try providing more primary air. You may not be getting enough combustion to provide a steady source of sufficient wood gas, resulting in intermittent gasification. Once it is mostly charcoal or coals, the setting could shift more to secondary air, but again, I suggest not overly fiddling with air control, except to the extent of trying to find a reasonable middle setting.

My intuition tells me that the Tarm was not designed to burn 100% oak-type woods; that it's design was geared towards northern European woods, which I'm going to assume are "softer" hardwoods or perhaps softwoods. Nothing wrong with oak, but just give different woods a try and see if it makes a difference, and I would include some softwood in the mix, maybe some lumber2x4 or 2x6 lumber pieces if you don't have access to dry pine.

I even would try a 100% softwood load to see how that works. Might as well try the extreme opposite of oak.