Air adjustments

[rreihart]

Reading about secondary air adjustments from the EKO user has me wondering what I should be looking for with the Biomax. The attached photos show the primary blower and the air passage ways behind it. The upper passages come into the sides of the firebox. I think the passage at the bottom center leads into the holes in the nozzle.

Any thoughts on what I should try to optimize burning?

Thanks,

Rob

 

[Eric Johnson]

If you're getting smoke, then open up the secondary air ports.

If you're not getting smoke but you are getting high stack temps, then I'd try limiting the flow of air and see how far down you can take it. Be aware that outdoor temps affect the air requirements, but I'm not exactly sure how.

As to the blower air intake, that's a big mystery to me. But I've been told that you need to open it as the outdoor temps decrease. The EKO 60 has two blowers. How many nozzles does the BioMax have, Rob?

 

[Bartman]

Eric,
I have a question about the "outside air temps" affecting secondary air adjustments. Is it that you need more secondary air for colder outside air temps, and less secondary air when it's warmer? Or vice versa? This should affect not only gasification boilers, but conventional ones as well. Is it that lower outside air temps lower stack temps too. (assuming pre-heated flue)? Does the colder outside air increase or decrease draft? The reason why I'm asking this is that with all the talk of running "full bore", then idling, I'm thinking I can improve what I have to get better burn efficiency and burn time with my old geizer. On eBay ther are loads of actuators, and with PLC control, I may be able to modulate combustion air with an electric damper on my blower. With the use of digital temperature controllers feeding back to the PLC I might be able to maintain optimum burn when at full bore.

 

[rreihart]

When you say the EKO 60 has 2 nozzles, do you mean there are 2 holes per side in the refractory? The opening in the Biomax refractory is about 1 1/4" wide x 11" long x 5" deep. There are 7 holes in each side. The attached photo shows what I'm referring to.

I opened the bottom center passage and the burn looked and sounded hotter. Makes me wonder if I was doing much gasifying previously. I'm kind of anxious to see the exhaust tomorrow.

 

[Eric Johnson]

Bartman: My understanding is that colder air requires more combustion air, both secondary and primary. And colder air outside definitely increases draft. Somebody else is probably better qualified to comment on efficiencies at different burn rates, but my understanding has always been, the hotter the better with wood, assuming that you have heat transfer capability to handle the load.

Rob: The slot in that piece of refractory is the nozzle. I have two of those. When it's gasifying, you have yellow, orange and blue flame blowing out the bottom of that slot and into the gasification chamber. From there, it exhausts through the hx tubes at the back of the boiler and out the stack. Under a full load the refractory glows cherry-red or orange.

I'm not sure what you mean about the seven holes, but I'm guessing those are the holes that deliver the super-heated air to the nozzle to ignite the wood gas. I can't see them in the photo. In the EKO, they're encased in the refractory mass, which you don't seem to have, surrounding the nozzle. The bottom of my firebox, in other words, is all refractory, instead of welded steel plate like yours. You must have water down there behind that plate.

 

[rreihart]

So you actually have 2 separate slots? I have just the one. The holes are about half way down through the slot. I do believe they deliver air to the flame as it travels down through the nozzle.

After opening up the secondary air, I checked the flue pipe with an IR thermometer. I was about 20-30 degrees higher, but still only about 270 degrees. I think I might be better off being hotter to help keep things cleaned out. Sound right?

 

[termite]

Rob,
I have my primary and secondary adjustment flaps closed down a little more than yours. I've been playing with the flap on the fan as I fire and it seems that about a 3/8" to 1/2" opening is about right. Close it down more and the gasification fire turns yellow and has low velocity. Open it up to about 1/2" and the gasification fire has higher velocity and has the right color and sound. Open it up too much and it may gasify nicely for a while but as the wood load shifts and repositions during the burn the gasification flame can be overwhelmed by the amount of secondary air. I get the same temps you are getting on the outside of the stove pipe. I need to get a meat thermometer to check the exhaust gas temp though. I adjusted the fan speed via the controller to 80% with the flap and primary and secondary adjustments and I can get nice 12hr burn times at 175 degrees (with significant idle time). These above observations are for getting extended burn times. Since my tank isn't fully insulated yet I don't know what's optimal for hot tank charging fires but I'm assuming more air will be in order.
By the way, did you resolve your "FUEL" mode problems?

 

[rreihart]

I forgot that I can adjust the fan speed through the control. Increasing the draft blower might all but eliminate the basement smoke when loading. You may already know this Termite, but I started out using the stop button on the control during loading as the manual said. However that shuts down the draft blower. So now I open the door slightly until the limit switch shuts off the primary blower but the draft blower remains on. Much better.

I never did determine why I got the no fuel signals when I first started. Unless I had the timers set too quick. I don't recall what they were at that time.

One other problem I came across was I blew the 2A fuse in the back of the control which shut everything down except of course the fire. I had a slight overheat, but fortunately we found it quickly. The draft blower is rated at 1.4 amps and I couldn't find the primary rating but a 2 amp fuse seemed too small. I asked Zenon and he told me 2A was good for the 230V electric in Europe. Over here it should be a 4A fuse. So if yours is 2A still you may want to change it.

Thanks for the info,

Rob

 

[Eric Johnson]

Rob,

Yes, I have two slots like that. And I forgot about the airways halfway down, but mine has those as well. That is, as you point out, how the secondary air is injected into the gas stream. But the whole slot assembly is technically the nozzle. I believe a Tarm 60 has just one nozzle as well. So the secondary air goes into the steel tubes, through the channels in the red hot refractory mass and into the nozzle, where it hits the wood gas being blown down and ignites. The heat from the gasification chamber below helps keep the refractory mass hot, in large part because the flame is directed back up when it hits the brick below the nozzles. In the EKO and EconoBurn, it's a series of u-shaped bricks.

Here's a pic of my lower chamber and one of the Biomax from the Biomax manual.

One more thing I don't understand about the Biomax firebox. Your nozzle seems to be surrounded by welded ss or boiler plate. The EKO is all refractory. I'm assuming you have a layer of refractory under the steel. Does it glow red when the thing is cranking?

 

[termite]

I'll change that fuse today, thanks.

I got rid of the "FUEL" messages by disabling that function in the controller. The manual says you can adjust the time it takes to get up to temp from 1 to 99 minutes. There are also settings up to 4 hours and "--" which I think disables it altogether. You can also adjust the time it allows the boiler to remain below setpoint after it reaches it for the first time. Those settings are the same.

 

[barnartist]

Eric, I forgot about the fan adjust on the back of the control, I do remember though that when I used to play with that, it did not change the fan speed.
My 60 is 3 years old, is it just a control thing? How will this adjustment effect the burn? High speed with fan opening small, or low speed with opening bigger?
Or what combo? Now I am thinking do I need to adjust for outside temps?
Also, when I adjust secondary air, I really can't SEE the flame change much, but havent monitored stack and such temps.
Lastly, I am going to try and cover my rear nossle with a piece of steel. Sound good?

 

[Eric Johnson]

Steel should work OK. You can pick up a piece of refractory brick at most hardware stores or concrete/cement supply places for about $5.

I've never fooled around with the settings on my controller, so I really don't know. Mostly--on my controller, which may be different from yours--I just went with the factory settings. You can adjust things like the time between idle refreshes (the blowers kick on to keep the coals alive) and if you have a pump or t-stat hooked up to the controller, you can adjust those settings as well.

Like you, I don't see immediate results from adjusting the secondary air control screws. But it does make a difference over the course of a burn cycle. Generally speaking, I'd say that if you're getting smoke beyond the startup period, give the nozzles more air and the smoke should dissipate.