correct 'margin of safety' once establishing CO escalation in gas combustion

archibald tuttle

so careful study of a number of somewhat aged manuals on combustion testing gives careful reference to the graphs that balance excess air and CO and demonstrate a steep climb in CO either way with too little or too much air compared to ideal combustion.

so i'm trying to dial in a carlin conversion on an old steamer. the firing rate theoretically approx matched in BTUs although i should have run a test on the old oil install just for a baseline -- not so much for efficiency but stack temp. etc.

started at the recommened air setting from carline and back down another 15% and still under 10 ppm CO but stack temp is 525. i can bring that down 10 degrees and bump the efficiency 2.5 or 3% by throttling the air a little more and CO starts to rise into the 30s. so i think i've established that i hit the bottom and i'm headed back up but the old manuals all say once the CO starts to rise then add a little air back for a margin of safety.

Well if 100 is considered the action level, maybe i'm there but they don't really suggest what the margin should be, only that there should be one. they don't speak in terms of halfway between 100 and 10 (meaning a setting halfway, not a reading but i suppose that wouldn't be that far afield).

i don't set up a lot of conversions on steam. I haven't faced stack temps this high and always tend towards the teens for a CO setting but I would really like to lower the stack temp. on this a little. But maybe with steam i'm just going to be on the high end. but i bumped it back to 10 PPM for the time being and headed for heating help.

I wonder if maybe the boiler was well cleaned before conversion so i'm going to take some brushes back too.

brian

Steamhead

What make and model is the boiler? Is the burner the EZ-Gas?

don_9

Sound like you have hit your sweetspot on the fireside.After reading your thread you got me thinking about the arco leader hydronic boiler we pulled out on monday. I was shock to see just how much grud that came out of that boiler.Even tho the fire side of that hx was clean n ppm co and o2 were in line with a boiler that age the stack temps were very high.So to me i would assumed there was a problem on the water side of the hx.I wonder if in many cases we are not doing wrong by our customer by keeping an old beast going after seeing all that thick stuff ooze out of the boiler.Sorry to get off topic tuttle.

icesailor

@Archibald Tuttle:

You know far more than I do about it.

I only worked on oil until the end with my Bacharach Wet Kit. I didn't have the luxury of a DA until the end. I always noticed on old oil boilers that they had high stack temperatures, no matter how well I cleaned them. I always felt that those old boilers leaked air like a leaky row boat leaks water. And funky draft had a place in it. No way to measure excess air. Putting a smaller nozzle in usually helped lower the stack temperature. Too low and the CO went up and smoked. Old boilers weren't manufactured with the tight standards of today. Dry base boilers like New Yorker AP's loose their seal around the base and suck huge amounts of air. Positive pressure and they burn through the jacket. Dry base boilers like Smith 2000 series suck around the floor and the base/section connection. From the factory design. Weil-McLain 66 and 68 boilers don't have rope seals between the sections like WGO's do. You can jab a soot saw right out the side of a 68 boiler and never know it.

IMO, some that don't want to change a old boiler like a Arcoliner, are just wasting their hard earned money on a gas conversion burner. Especially if there is combustion staining above the front cover and it isn't removed to install a new rope seal.

One thing about oil that I found is that with a RC Barometric damper, allowed to swing normally, when you stick a MZF Bacharach draft gauge in the test hole at the breeching, and took a measurement, if you hold the gate closed and the draft doesn't go up appreciably, the boiler leaks like a sieve. If the draft is low to start with, and doesn't much change, you probably have a poor drafting chimney.

In my experience (with oil)

archibald tuttle

thanks all for quick thoughts. Steamhead this is a Burnham V8 series. 4 section i think, might be three. so it isn't a snowman.

it is a carlin EZ -Gas burner.

as i recall - not standing there - it was labeled 7/32 orifice which actually would be a little undersize compared to the old oil tags which are for 1.05 nozzle. it's got unions so i can check it.

don't think it is old enough to have the water side sludged (although i take don's point. recently have had chiller problems for that reason) but, i concede, i wasn't thinking soot cleaning on a gas burner when i went over. i should have had brushes, it was just an after work visit to a friend - what with oil prices down and gas prices up folks are thinkin' about this stuff. esp. with the high stack temps I want to check. it's my own fault, i made my own callback. and at least there is always a beer waiting at this stop. just trying to load up on a little knowledge before the visit.