Vigas 80LC front nozzle won't gas (as well )

[700renegade]

Are there any other Vigas 60 or 80 guys having problems getting their front nozzle to gasify properly? My 80 has been running for a month or so now and I notice every time I peek in the lower door the rear nozzle will be gasing like crazy and the front has a lazy flame, bursts of flame, or no flame at all.

My wood is averaging 18% moisture, and the problem doesn't seem to change if I change species or quality of firewood. My flue temps tend to run in the 170 - 210 range at most and I have a very sooty lower chamber - both I attribute to the flood of 'unburnt' air out of that front nozzle.

Reaching in there with a cold boiler, as near as I can tell ( I can barely reach the rear) the front nozzle is delivering as much or more air as the rear. I have no idea where the lambda control is sending the air when I stick my hand in there, so I don't know if it's all primary or secondary air. I was suspicious the holes thru the nozzle perhaps don't line up with those in the outer portion of the floor, but don't know how else to check ( perhaps a borescope ? )

Since I don't have my 2000 gal storage hooked up yet, I'm idling a lot and my boiler is way oversized for my loads ( but man do I love that huge firebox ). Even when I'm playing catch-up on water temp and it's burning hard for a while it works the same.

Any thoughts are welcome.

 

[henfruit]

700, You need to be sure you have a good bed of coals and fire over both nozzles.

 

[700renegade]

Henfruit, both are present and it still won't gas in front like the rear. If I have a high demand I can open the upper door mid-burn and the whole firebox is glowing solid red, front to back, but poor front flame.
The only good thing about this operating this way is under modest demand it usually leaves a 18" tall pile of charred wood in front - I shove it back to level out and I have a fantastic bed to start out from.

 

[BoilerMan]

To be honest I'd cover up the front nozzle with firebrick for now and run it that way. Or try covering the rear nozzle and see how the front reacts. If the boiler is way oversized due to no storage yet, then the reduced output would be better anyway.

TS

 

[JP11]

Are you raking the coals around? If you cover the nozzle with ashy stuff.. it will clog and not gas.

I've learned to not move the coals around much at one time. Let the ashy stuff blow thru. Don't think you're going to pile it up and get it to burn right.

I've had better luck moving the coals outboard, away from nozzle. Especially on relights.

JP

 

[700renegade]

I normally don't rake around much before reloading. If I do muck around in there it's because it's pretty well empty and I'd leave the same conditions at both nozzles.

I'll alternate closing off the front and rear nozzles with firebrick as suggested and see what the results are. The secondary air will still be fed thru the nozzle, so I'm not sure how the O2 sensor will react with the Lambda control. I wish I had a logic table of how the EGT / O2 sensor / air shutter / all interact. I see the lambda % vary from 0% to 100% but don't know what ratio of air is being fed where, and why.

Someone privately mentioned the issue of draft - I'm running about 17' of 8" stainless insulated flue with a rain cap. It was suggested I may be low on draft and that is the culprit. I don have another 30" stick of pipe I can install on top.

 

[JP11]

Wow.. that's a short stack for an 80. Got anyone near by with a manometer? I bought a cheap one off Ebay.

I've got near 40' of chimney, got the dampener set to .05 inch WC. I think that's what the value is.

JP

 

[TCaldwell]

what parameters can be monitored or manipulated through the controller with regards to combustion? A value, you say lambda, that goes from 0-100% , does it cycle full range when not gassing, startup, reload or random. Sounds like this value might be the controller output with respect to damper movement. If the controller op is quickly oscillating, rapidly modulating the secondary damper rapidly, that can cause instability providing either too much or too little air to support secondary combustion.

 

[700renegade]

TCaldwell, the air diverter shutter is controlled by a Belimo actuator. It takes many minutes to go from one extreme to the other. I know 100% is full air to both primary and secondary, 45% is secondary closed but primary still open, 0% is everything closed.
The controller apparently tries to maintain a set lambda 'value' of 1.35 ( I have no idea what that number represents - perhaps the voltage returned from the 02 sensor ??). The value of 1.35 is user adjustable, but I'm not changing it from the factory default till I know what it represents and what higher/lower would mean. Even if a change made it better I'd want to know why.

Too little draft could certainly be an possibility - the manual calls for minimum height of 40' measured from the chimney connection (44' from floor). I can't imagine many installs run this height but mine could be at the low end.

 

[700renegade]

As an update - I cranked up the telehandler and got up above my roof yesterday. I removed the top rain cap and installed another 3' stick of metalbestos chimney. Total height is now about 24'.
Unfortunately it doesn't seem to have made any difference in getting the front nozzle to gasify.

I threw a firebrick over the rear nozzle and covered about 75% of it - it still was the only one burning well. Front one was still a dead fish even when I run my in floor system to suck up every BTU it could make. Next step is to get a bore camera and peek inside those air holes in the front nozzle.

Rechecked oak wood supply and it's still measuring 18% average on fresh split face.

 

[foamit up]

How are the heat exchanger tubes? Are they full of creosote? If so clean them. It sounds to me you are using green of wood. As a true 18% split will burn at over 200 degrees. If it is not the wood moisture it is creosote some place. Put a wire in the nozzles holes and see if the align and are open. Foamit up

 

[JP11]

I think at this point… I'd pull the fans, and stuff a shop vac and blow some air thru. You must have some sort of blockage. Maybe even pop those nozzles out to get a look. Or.. even better. Call MARK at AHONA. His advice would be best.

JP

 

[mr.fixit]

Is it possible that the front nozzle is receiving to much air,and blowing out the secondary flame?
Did you try blocking a portion of the front nozzle?

 

[700renegade]

Boiler tubes were just cleaned with wire brush last week - shouldn't be a creosote problem ( though they were pretty dirty as it burns cold in the lower chamber ). I pulled the front fan cover and ensured the 1.25" dia secondary air tubes are clear of debris all the way to the back. Reset the lambda rotary valve on the Belimo actuator to make sure it zeros out OK.

I'm hesitant to knock the nozzles out of it for fear I'd crack something. I'll try to get after it with a borescope first.

I now see that when the actuator is set at 45% it's valved so all the air is directed at the primary circuit and the secondary is cut off. Since the rear will gasify in this valve position and front will not, it tells me the secondary air is not the culprit, so I don't expect to find anything wrong when I scope the nozzle holes.

If nothing else, I now understand what the controller is doing with respect to O2 levels and the valve setting. Valving of 0%, 45% and 100% are now relatable in my mind to the % of oxygen in the exhaust.

 

[TCaldwell]

lambda relates to the ammt of air in the combustion process related to the ammt of air needed. A lambda of 1 would mean that exactally the theoretical quantity of air needed for complete combustion is present. There is a balancing act between lambda and carbon monoxide, too much air will lead to stack losses, too little air increases co production and incomplete combustion. the goal is complete combustion with minimum excess air. Lambda=20.95-measured o2%, / by 20.95. A lambda of 1.31=5% residual o2 in the fluestream, at about 30% excess air. If your fluegas temp is in the 200s that is a well designed combustor and hx. If what you say is true about the relation of damper pos to o2 then the controller is not interperting a low enough lambda to request a higher output to introduce secondary air. I would try stacking the deck with a small to medium load of known very dry wood and watch the lambda vs controller output.

 

[TCaldwell]

have you cleaned the o2 sensor with compressed air, if impacted with flyash it will read high and be relatively unresponsive to what the fire is actually doing causing the response you are seeing, try that before a dry load.

 

[700renegade]

Thanks TCaldwell !
Your Lambda info is great - I could tell the higher readings related to higher sensed O2, but didn't know what the number represented till now. At first I was thinking voltage off the sensor, but those should never reach higher than 0.9v.

I'll clean my sensor and scrounge up a different source of even drier wood for a test. A few old pallets in the shed should work nicely. I'll be startled if it's wood related, as I still couldn't explain why the rear nozzle works so well

Your formula doesn't quite work right to produce results greater than 1.0 - should it really be of the form L= 1+( measured O2/20.95) ? If so, a reading of L=1.31 (the Vigas default is 1.35) represents an excess of O2 of 31%, not excess air. We're getting off into the tall grass here, but I haven't seen this info elsewhere, so am glad to take this segue.

 

[TCaldwell]

20.95-5% measured 02=14.95, 20.95/15.95=1.31 so if you are displaying a lambda of 1.31 it represents 5% residual o2 in the flue stream. the max o2 reading in ambient air is 20.9%, the balance is primarily nitrogen, not possible to extract 31% o2 from 20.9% 02. let me know how the dry wood burn goes after cleaning the sensor with compressed air.