"Puffing" problem with my EKO

I had periods of that with my Econoburn. I determined that it was a combination of things. For me it was usually after starting a cold boiler and putting in too much wood. I have had on one puff this year and it was right after I loaded more wood and gasification restarted. These are the things I changed.

1. I initially split my wood to small. I had most of it playing card size. It created too much fuel for my set up. It is much better to have that size on the bottom and then bigger on top up to about 8".

2. I had been burning 50% red pine and spruce that I had cut down to build my building. Now there is nothing wrong with soft wood but it is much more volatile than the hard woods. Especially if it is split small. It creates too much fuel so it is choking out the flame.

I would try loading a armful of small stuff and then larger pieces above that.

I would not put in wetter wood. I think that could actually increase the problem. The moisture that is created to steam will extinguish the gasification flame.

gg

Here's how Ben Hoffman, who has an EKO 25, described it in the Fall issue of Wisconsin Woodlands, which I edit:

If the wood is too dry, or too small, it could burn too fast and cause small explosions in the firebox. If this occurs, throw in some wetter wood to raise the humidity. The explosions are not dangerous, and when they occur in a regular wood furnace or stove, the energy blows out the flue. In a gasifier, since the firebox is closed, explosions blow smoke out of the air intake and produce a smoky smell in the basement. My boiler allows me to adjust the primary (firebox) and secondary (gasification) air to optimum levels, depending upon the moisture content of the wood. Generally speaking, the larger the piece of wood, the higher the interior moisture. It’s difficult to accurately measure larger chunks because the prongs of the moisture meter aren’t long enough (nor are you strong enough) to penetrate very deep into the wood. Split a chunk for an accurate reading.

You are on the right track. I believe you fire is running too hot.

As you can see from my signature, I have a Lambda boiler, but I have experienced what you describe. Once, last season and once just a couple weeks ago. In both cases, the biggest cause was my laziness and letting too much of a coal bed accumulate in the boiler. I usually clean out the primary when ashes accumulate up to a certain level, but in these cases I let it go a bit too far.

Please understand I am not saying this is your problem - but just as an example as what was causing it for me. In my case, my theory is that with a deep enough layer of ashes, these ashes and coals fill all the nooks and crannies around the bottom of the wood, and thereby force the air through a very concentrated area in the wood and down into the secondary.

The two times this has happened I knew something was up. Initially, I can feel kind of a low frequency rumble in the house as the gassification gets going. If I check my boiler's control panel for residual oxygen content, I will start to see very, very low numbers - say 2-4 % whereas 6.5 to 7.5% is more normal for me. Then the puffing will start - I will hear the rumble build up, and then almost a suction sound as a large rush of air is pulled in, then a "woompf" sound as it puffs and then gassification starts again. During the puffing, residual oxygen content can drop under 1% for very brief moments.

Now, in my situation I am fortunate enough that the boiler can sense the condition and react accordingly. The boiler will drop the speed of the fan and close the primary - sometimes as low as 10-20%. Things will settle down, and after the wood has been burning for awhile the fan speeds up and inlets will adjust accordingly. Then I clean out the ashes as I should have in the first place and the problem doesn't happen again (until I slack off that is).

I am not an expert in this area, but my suggestion would be to make small adjustments to one parameter in your equation, whether it be your wood, fan speed or air ratios and record these settings and results until you find a less "aggressive" burn profile.

Good luck to you - I think this is a "better" problem to have as opposed to a lazy fire situation and creosote if that is any consolation.

I don't know if this has already been said above but I'd start by reducing your fan output. I normally run around 70% with shutters full open to start my boiler and then bring it down to the lowest output setting (50%) after I have good gassification. Shortly after that I'll begin closing the shutters as well. At peak burn I'm running 50% on the fan setting and 50% or less shutters open, depending on wood quality.

My two cents is you need less air...much less.

I agree with Hiker88, I think the ashes can restrict the nozzle opening (in a gasser) and cause an air pressure build up. I too have this happen on occasions, I don't like it because of the ash cloud it coughs back out my fans.

Now that I'm 5 or 6 years ahead on my wood and the average moisture content is down to 5% or so, I'm finding that I need larger splits in order to reduce the surface area of the fuel. Real dry wood split small produces too many coals too rapidly trapping excess gas before it can exit into the burn chamber and explodes uncontrollably when the air/gas mix is just right. Now that I know that I will be burning real dry wood I'm splitting much larger now and enjoying the results. I run my combustion fan at 50% and have the shutters set at 50% and never change them. Found the sweet spot years ago but I never found it to have any effect on reducing puffing.

I've found that my boiler works better when there are some ashes accumulated in the secondary burn chamber. No idea why that would be, but that's the way it works. Kind of like a bicycle: works better with a little gunk on the chain that it does with a clean, freshly lubed chain. Go figure.

Lowering the fan speed will lower overall btu output, but most importantly reduce primary airflow and increase secondary until it settles out, could be 20 minutes. By then the batch should be reduced to restore settings. As stated larger splits will and smaller loads will greatly help, settings might have to be evaluated based on overall wood consistency

You'll never see puffing when there's bridging and you'll never see it when there's a thin layer of burning charcoal over the nozzle. Only when there's a thick bed of charcoal.

Perhaps I can share what my father has run into with the new EKO 25 install and puffing issues at my sister's place - and revive this thread?

First got him a digital manometer to check the draft because it was my #1 suspect. Had too much (above 0.12 in H2O). He removed a 4 ft section in the chimney and changed the cap. Now we only see spikes of 0.08 in H20 in high winds.

Fan opening was 100% and fan speed 80%. He closed the fan opening to 20% and may have dropped the speed of the fan also. Forgot what was the mm opening for primary air - I think it's at 9mm. Don't know for the secondary air (measured in rotations... ?) - he told me 2-3 turns.

Puffing was occurring after 45 min of a hot start. He noticed that all the wood in the primary chamber was glowing red and gassing - which probably meant primary air supply was way too much. Bridging ensued in the following hours. This doesn't occur in his Biomass60.

Stack temp was also very high, above 400F. With adjustments to the fan and air openings above, its around 325-350F and lambda sensor always around 1.3-1.4 until you get in the charcoal burn phase.

The O2 lambda sensor was also erratic after the hot start. It was high (around 1.8) because of the bridging that occured in the next hour. After poking the wood in the primary chamber, it then puffed. The lambda went from 1.8 down below 1.0 and never stabilized in between puffs.

I have also been lucky to see how the FHG 50kW reacts to puffing at our demonstration setup in Kingston, ON. The O2 went below 6% and the primary air almost closed completely (about 20% which is set in the Lambdatronic) after the puff. Took a while until the primary air went back to what is was before. I think what happened was that the biomass briquettes where bridging and then crumbled down - we heard a thump about a minute before the puff. The load was about 70 lbs of briquettes to match the ASTM/CSA or EPA charge (ie 10 lbs/ft^3 of firebox volume).

So bottom line what you need:
Manometer;
O2 sensor (Innovate Motorsport MTX-L works with us fine);
Type K thermocouple and digital reader; and
other tools to change the air openings

I may also add that the O2 sensor helps when switching between fuel supply (unseasoned to somewhat green wood), thus helps you out with your air adjustments in the first place. We have to double check our TESTO350 data, but from what I remember when running the lambda sensor in the stack at the same time of the TESTO350, a labmda of 1.3 was about 6-7 %O2. I was surprised because I believed that the sweet spot was a lambda of 1.5. When we ran at a higher secondary air, it was more at around 10-11 %O2 for a lambda of 1.5. We are using the MTX-L which uses a Bosch LSU 4.2 (not the LSU 4.9 on the Froeling). So now we are running the Polar G2, the Biomass60 and the EKO 25 at a lambda of 1.2 - 1.3. No smoke either, but we still get a lambda above 2.0 when we get in the charcoal phase.

Good luck everyone!
Trex83