Soot in boiler

seized123

I just cleaned my 2 year old Weil-McLain WGO-3 (not 3R) oil boiler that has on it a much older Beckett AFG burner with an F3 head. To my dismay there was soot. Black and all over, though thin and easily removable. I was disappointed, especially since at the last cleaning a year ago (after a year of operation) there was none.

It's past time to clean the electrodes, change the nozzle, etc. (It's been going on two years since the thing was commissioned, I don't know why I didn't change the nozzle when I cleaned the HX and changed the filters and strainer about a year ago.)

So I figured that now before I changed anything out I'd do a smoke and CO2 test, if only to see if something stands out that might cause soot, and to have a baseline for comparison once I did change things out. (This is with my old Bacharach wet kit that I bought used, as I can't seem to justify to myself the expense and calibration hassles of an electronic combustion analyzer that I'd only use once or twice a year—decent ones seem to run over $1K.) The results were:

Temp: 360F at steady state (although when I took it again later it was over 400F, but I figure that was because the first time I really let the boiler cool own first, and the second time it had been running a short while before so maybe there was residual heat affecting the stack temp.)

Draft: -0.3 up top, -.02 over fire

Smoke: Zero

C02: Relatively high at 14.5

Pump pressure: 140 psi

Nozzle: Delevan .85 70B. This is the nozzle specified on the AFG burner itself as well as on Beckett's website for use with this boiler (although technically the decal on the burner says "Hago". And I found a statement on Inspectopedia that says: "Watch out: going from Hago nozzle to Delavan A, B, or W you may need to try the next wider spray angle. E.g. go from 60° to 65° or 70°")

The burner fan is clean, the air shutters look clear, it's warm so a window to the basement was open.

Glad there was zero smoke, not glad that it was 14.5 CO2; anyway I fired up the boiler again and opened the air shutters on the side of the burner all the way—they were already up to the number '9' on the side of the burner, so I went to 10 , as far as it will go, and got a reading of a little less than 14 CO2, not low enough.

So perhaps this post is premature because if I replace the nozzle and it all clears up, great. But I figure any problem with the nozzle (other than it possibly being the wrong nozzle despite the specs) like for example it being clogged, would only reduce the flow of oil, which should result in a greater air/fuel ration, and so a low CO2 reading, not a high one.

So my questions are:

1. If I clean the electrodes and replace the nozzle and still get high CO2, should I try opening the larger air bands, since the shutters are open all the way? My impression is nobody ever does that and if all is in spec you shouldn't have to.
2. What about that Inspectopedia idea of going to the next wider spray angle, since Hago was specified on the decal. (But Beckett's spec guide says ".85 x 70B (H)" and I assume the 'H' means Hago, and lists the exact nozzle (no 'H') as an alternate.)
3. Any other ideas why I might be getting soot, even though I have zero smoke now?

jesmed1

We have Beckett AFG's on our WGO-5's, running Delevan 1.0 80B nozzles at 140 psi with F3 heads, and they burn very clean. We just had both boilers serviced, and the tech remarked how clean they were. Maybe try the 80B?

seized123

@jesmed1 that’s just what Inspectopedia said, go up to the next wider spray angle. Can’t hurt to try.

EBEBRATT-Ed

Leave it alone your #s are good except your Co2 is causing smole regardless of what the smoke tester says. Open the air enough to get the C02 to 12 and you will be fine.

Don't forget when combustion air gets cooler in the winter #s change a little bit. You have to leave a margin.

Perfect Co2 is around 15 % you cant (and shouldn't ) get near 15%. Run it at 12 maybe 12.5 but thats it no need to change nozzles.

seized123

Ok @EBEBRATT-Ed, sounds good. But since the thin air shutters are already max open, to get to 12 or so I guess I’d have to open those wider air bands? (Which I’ve never had to touch before.) That would be okay? I guess they are there for a reason.

EBEBRATT-Ed

Yes the wide air band is the course adjustment and the other one is the fine adjustment. Just open it a very small amount then fine tune it with the other air band. Make sure to tighten the screws before taking readings. Even just tightening the screws can change the adjustment.

You draft and smoke seem pretty good. A little air to cut the Co2 and you shouldn't have any more soot.

seized123

@EBEBRATT-Ed I look forward to doing that tomorrow! I always used to worry that I someday might not have enough margin since the air shutters were so close to max, now I’ll get all the air I need to get to 12 or so.

I assume that when you say don’t change nozzles you mean don’t change the size and angle, but that I should still swap in a new identical one as a matter of routine yearly maintenance (even though I didn’t do it last year.)

HydronicMike

Your CO2 is way too high. Your soot came from lack of air. Without a combustion analyzer you aren’t getting the full picture. You don’t know your Excess Air or your CO, so you may get lucky with your adjustments, maybe not.
Also you’re making your adjustments when the weather is warm. Combustion and draft wlll change as the weather gets colder. Beckett & Carlin publish guides on adjusting CO2 based on temperature.
Also if your stack temp was 360 gross, you were probably 280-290 net…not good.

EBEBRATT-Ed

@seized123 yes change the nozzle keep it the same.

@HydronicMike

He is using a wet kit the same thing we did for 100 years before the electronics were invented. If he gets his Co2 down he should be fine. he had his stach temp at 36-400 so he is fine.