Peerless Flame Impingement on Refractory Target Wall

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Old 05-24-17, 11:18 AM
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Peerless Flame Impingement on Refractory Target Wall

On an older Peerless JOT series boiler, I' reading mixed suggestions about if the flame should be actually hitting the target wall or not. The combustion chamber is pretty small, and I'm already downfired considerably (.75) for a 3 section JOT. I cant imagine NOT hitting the target wall with a proper size nozzle.

So which is it? Is this flame impingement? Or is the flame supposed to directly heat the refractory? Just want to know a definitive answer, and the conflicting info online is killing.

Thanks
 
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Old 05-24-17, 01:16 PM
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flame

I've always understood that no part of the flame should touch the refractory. Supposedly cools the flame and causes soot. Steve
 
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Old 05-24-17, 01:36 PM
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As Steve said no part of the flame should be hitting the chamber. It is only there for containment. Any part of the flame that hits the chamber does not burn and results in carbon or as you know it as SOOt and will weaken the chamber and eventually destroy it.

If your flame it hitting the chamber there is something wrong with the setup of the burner or the wrong chamber could have been installed for the opening. There are different chambers for different boilers. You could possibly have the burner in too far also.

At any rate nothing should be hitting the chamber.
 
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Old 05-24-17, 01:39 PM
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Flame impingement is the flame continuously hitting the surface. Having the flame occasionally "brush" the surface is not impingement. If you have carbon building you have flame impingement. Discoloration or very slight soot deposits on the refractory is not uncommon.
 
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Old 05-24-17, 02:01 PM
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g,
One suggestion I have is to open the air band that you have closed and cut back on the other air if you have to. Opening up the band may pull the fire back. It sounds strange but it adjusts the air in a different way for lack of a better explanation. With your smaller, possibly mismatched nozzle you have to adapt. The settings they give you are perfect condition, lab tested recommendations. This is where the proper instruments come in to play. Field conditions vary and adjustments must be made at times.
 
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Old 05-24-17, 02:07 PM
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Thanks guys. Spott, you've been helping me in my other thread. I figured this was another(more rudimentary) issue, so I started a new thread, hope you dont mind.

This is an older Peerless cast iron wet base boiler with a new Lynn target wall and kaowool bottom blanket. The combustion chamber is only about 10 inches or so deep. The burner itself is set correctly, inset about 1/4" from refractory on the front panel.

As Spott knows from my other thread, this boiler has never run well, and has always had a mismatched gun (Beckett SR) on it.

I've been setting airflow by eye, looking for a feathery flame, that's not lazy, and just lean of smokey tips. Even with the .75 nozzle at 100 psi, its hard to contain the flame in such a small chamber without hitting the target wall. The boiler has always had a very light sooting at the end of the heating season. Just a dusting. Maybe 1/32 to 1/16 inch of loose black, fairly easily swept away. Every year I pull the stack and do a plates off cleaning, so it's not plugged.

Am I simply WAY off the mark in terms of airflow? If I really open up the shutter, the flame will both pull off the head, but will also pull back away from the target wall. The flames are no longer licking anything, its more like a blast from jet afterburner. I dont see too many sparkles or unburnt fuel hitting the wall, but it simply seems like too much airflow, and would send all the heat right up the chimney. Temps at the breach are already above 500* NET, which is the limit of my thermometer. My fear is adding more air will only raise the temps.

Anyway, the Beckett SR is not long for this world, as I will be replacing with a AFG shortly. I'm just worried Ill run into the same issue due to the small firebox.

And yes, it goes without saying that I should really have a pro come in and dial it in. I'm just not sure how soon that will happen.

Thanks guys.
 
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Old 05-25-17, 04:18 AM
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I opened the air shutter up to 7, from 4, and the flame did indeed pull back from the wall. The target only gets the very occasional lick of flame, and I hate to use the word "lick" because the flame is very forceful like a jet. This is now WAY more forceful a flame than how it was when we bought the house, or how it was when we had a technician in to clean and go over the system. I've since done a lot to it myself, but the airflow has always been around 4 on the shutter (0 band). But from what you guys are saying, I'm guessing the shorter, smaller, more forceful flame is correct, as opposed to a large sunflower against the target wall.

The draft over fire is nowhere near as strong as it was, but still seems to be pretty good in the stack. An old used draft gauge I picked up on ebay should be arriving soon, so Ill have hard numbers instead of a smoke test.

I also picked up an inexpensive thermocoupler thermometer to get a good stack temp reading. I know this is an old boiler, but my concern is that this will be in the 600+ range with this much airflow sending the heat up the chimney.

The new AFG burner should be arriving today. Before I install it, Ill brush and vacuum the boiler out. Even if there is a thin layer of soot, a cleaning can only help with both the draft and the temps.

Thank you again Spott and everyone else for the input.
 
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Old 05-28-17, 08:29 PM
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Excessive draft can cause a longer flame. Is the SR rated low enough for a .75 nozzle? Try increasing the pump pressure which will shorten the flame and burn cleaner. You may have to drop the nozzle size a bit.
 
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Old 05-29-17, 03:54 AM
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Thanks, but I dont think it was excessive draft at least not draft over fire. At 7 on the air shutter, I had positive .01 draft over fire, and -.05 draft at the stack. I've since reduced airflow to 6 on the shutter, which puts me at about 0 draft over fire, and opened the damper up a bit to get the stack to about -.04. Any lower air and the flame doesnt pull back away from the target wall.

I plan on giving the boiler a good cleaning and brushing today, and replacing the burner with the AFG I have. I'll let you guys know how the new one does.
 
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Old 05-29-17, 10:32 AM
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I did a good cleaning on the boiler, and installed the new AFG burner. I set the pump to 100 PSI, with a .75 80 A nozzle.

It appears that I wire the black "L1" and red "Limit" wire both to the hot lead coming from the high limit of the aquastat, since I dont have a dedicated limit. Please let me know if this sounds incorrect or unnecessary, but the "limit" lead is listed as optional, and on the schematic, it shows them both coming from the L1 (hot) lead. Regardless it works as expected, and the hot limit correctly shuts the burner down. It just takes a few seconds longer before the burner spins up, which I guess is due to the controls "booting up".

Anyway, I wound up opening the air shutter all the way to 10 for the .75 nozzle, with the low air flow baffle installed. The flame is still doing a bit of a sunflower patter approaching but not really touching the target wall. The best draft readings I could get was -.01 to -,02 over fire, and about -.06 at the stack. I have the damper weight all the way in, so that's as low as I could get it.

Ill try to get some stack temp and smoke pump readings later today or tomorrow. Eventually Ill get some proper o2/co2/co readings as well. But for now, the burner seems to be running MUCH better than the old SR was.

EDIT: Smoke test shows ZERO smoke. I couldn't get my K-type working at the moment, so I used my pen that maxes out at 670F (gross, not net). It still maxed out, but climbed much slower since the cleaning and new burner.
 

Last edited by GuitsBoy; 05-29-17 at 01:25 PM.
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Old 05-29-17, 01:35 PM
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As rbeck said, try increasing pump pressure and dropping nozzle size. That's what I did and it worked great in my old Weil-Mclain. Good luck, Steve
 
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Old 05-29-17, 04:25 PM
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G,
This may give you more interesting info if you want to scan over it.

https://www.manualslib.com/manual/14...il-Burner.html

Just out of curiosity, what made you install the low air baffle, which by the way is why you had to increase your air.

Prepare burner
Low firing rate baffle
• The AFG Low Firing Rate Baffle (LFRB), item 7, page 11, reduces the air flow
(cfm). The LFRB is sometimes used for firing rates under 1.00 GPH as listed in
the table below. Refer to the appliance manufacturer's instructions or the
Beckett OEM Specification Guide part number 6711. Do not omit the LFRB
when specified. Omitting the baffle when specified or installing the baffle
when not specified could result in poor burner performance.

Page 5 of manual. Gives firing rate limits in manual under the heading above.

You're looking for -.01-.02 over fire and about -.03-.04 in smoke pipe between boiler and damper.

If you have too much draft (-.06) it will start to pull the heat from the boiler up the chimney and increase your stack temp. You want to keep as much heat in the boiler as long as you have a proper draft. You never want a positive draft on your boiler, especially over the fire.

As far as your wiring goes it depends what you have for a primary control. You may not have the red wire for the limit. If not it's fine. 8184G doesn't have as many wires.
 

Last edited by spott; 05-29-17 at 04:41 PM.
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Old 05-29-17, 04:47 PM
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Thanks Spott, and everyone else as well.

Spott, I have read over the manual that came with my brand new AFG. I kept the LFRB baffle in place since I am firing at 0.75 GPH, and while I cant check the beckett site right now as it seems to be down, I was pretty sure I had seen it specified to use the LFRB with a .75 F3 combination on the JOT. Still, the suggested airflow settings were band: 0 shutter: 8 or so, going by memory. So 10 seems a little high, since it was already expecting the LFRB.

As for teh draft, I'm right where I want to be over fire, with an air shutter of 10. If I back it down to 8, or under, the draft is a bit higher, -.02 to -.03. I know the stack draft is quite a bit high, and I may have to modify (counterweight) the damper in order to reduce the draft from -.06 to -.04

I have not had a positive draft since before cleaning and replacing the burner. I am aware of the dangers of a positive draft in a non-sealed boiler, which is why I didnt run the SR at a higher airflow than 7, which gave me just slightly negative draft over fire. Air shutter 8 or better pulled the flame back a bit more, but the draft went positive, so I didnt leave it. It's a moot point now since the AFG is now installed and the SR is sitting in the trash (fuel drained).

Thanks again for all your help
 
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Old 05-29-17, 05:09 PM
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G, I couldn't get on the sight either but if you're interested just click on the link I sent and it will get you there.

Have a good night.
 
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Old 05-30-17, 10:42 AM
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Hi Spott -

Yes, I saw the link to the manual that you sent yesterday. It is pretty much the same information as the hardcopy manual that came with my AFG.

I am running the LFRB because both page 5 of your manual states I should run it below .85 GPH, as well as the Becket Residential Oil Spec Guide suggests running it on the JO/JOT-TW-075. That was the only peerless JOT series boiler I could find originally spec'ed for an AFG and F3 head. The JOT3H/L is spec'ed with an AF burner and F6 head. Either way, I am firing at 0.75 so I chose to leave the plate in there.

I may try running a .65 nozzle at 140 to see if the flame pulls back any due to better atomization.

Also, I was able to add a couple nuts and bolts to the damper to add weight and allow it to open a bit more. I am now getting good draft readings both over fire (-.01) and at the stack (-.04) with an air shutter setting of 9. Still 0 smoke.

As for the primary, its an R7184P, with 15 minute startup delay and 15 second cooldown. I may simply run a new always-hot wire to the controls, and separate the hot and limit wires. This may shave ten seconds or so on startup after a call for heat. Not really a big deal though.

Thanks again for all the help.
 
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Old 05-30-17, 05:33 PM
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I cant edit my previous post anymore, so for the sake of being thorough, Ill update again.

I did wind up rewiring the primary to drag a new constant hot, in addition to the switched limit wire. The reason this may be important is because of the cooldown fan delay. With only the high limit feed, if the aquastat cuts off due to high temp, all power to the burner is killed, and there is no shutdown (blower only) phase. With the separate hot and limit wires, when the aquastat kills the limit circuit, the burner will shut the fuel, but keep the blower going for cool down. If the boiler bounces off the high limit all winter long, then you're effectively removing the cooldown phase.

Anyway, after realizing this would happen, I spent the last couple hours rewiring it. It was a pain in the butt since all my AC cable will only fit 3 wires, and not 4, so I had to scavenge some older AC sheathing from a circulator pump which would fit the four wires and use that instead, then replace the circulator feed with the smaller AC cable. Time consuming, but its done, and everything works properly now.
 
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Old 05-31-17, 10:28 AM
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G,
Congrats on a job well done. A lot of work but now you have a properly running burner and peace of mind.

Enjoy your summer if it ever gets here.

SKIP
 
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Old 05-31-17, 03:49 PM
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Please post photos of the flame.
 
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Old 06-12-17, 10:08 AM
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Sorry this took so long to get, I've been very busy the last week or two. Anyway, here is a link to a video of the flame through the observation door. This is at 0 band / 9.5 shutter air settings. This is with a .65 nozzle at 140 psi. The video doesnt really show up the same way that the eye sees the flame. While the cone of the flame ends well before the target wall, the flame "feathers" sunflower out in all directions. Also, the combustion chamber appears to be only 9 inches deep, from the front plate insulation, to the target wall. Not much room in the firebox.

https://www.amazon.com/photos/share/...fVj8bqm0Qi6Wsb

https://www.amazon.com/photos/share/...mgudRx3KADlv1u

I picked up a cheap TPI combustion analyzer kit from amazon, but it's in for sensor repair/re-calibration right now (under warranty). I hope to get some o2/co2 readings soon. But the smoke pump shows 0 smoke now, and its just past trace.
 
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Old 06-20-17, 05:13 PM
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I got my combustion analyzer back from calibration today. I'm still learning how to use it, but set to light oil, I'm seeing 10.2% to 10.5% CO2, Stack temps of 500 net, and between 0 and 2 ppm CO. My guess is this is way to lean with an air shutter of 9.5.

I backed the air shutter to 6, but the CO2 only came up to 11 to 11.5%, still at the same 500*. Through the observation door, the flame looks more like what I would think it should look like. Fuller and brighter, and filling a lot more of the combustion chamber. The flame is certainly licking the target wall though. But with the combustion chamber less than 10 inches deep, I just dont see how it can be avoided. I have to believe the JOT was intended to be this way.

Anyway, the high temp limit kicked in before I could play with it any more. I set the air band at 8 to split the difference, at least until I can dial it in a bit more and then take some smoke readings.

So assuming I can get it to run at 12% CO2 with zero smoke, am I all good regardless of the flame hitting the target wall? I have to believe sensor readings trump visual inspection all day long, no?
 
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