Sizing steam header

Jim Pompetti

We need to pipe in 2 -262500 btu steam boilers(existing) . What size should the header be . Is it a good idea to stage the boilers , and what would be the best controls to use .

Brad White

Input or Output?

Hi Jim!

Assuming the higher output, two boilers at 262.5 MBH output  (about 275 pph call it) and a total of 550 pph steam,  I would size the header at 4" IPS minimum. I presume that this is low pressure heating? Or process at higher pressure?



But as a double-check, if the final near-boiler piping cumulative cross sectional area is "x", I would make the header equal at least to that number. No point in speeding up what you took pains to slow down, all that. This could bump the header up a size.  If the out-going branches are also large, that too may factor in to the equation but less so than what is feeding in to the header.



If you send me a simple diagram with particulars, I can size that for you and state my assumed criteria (velocity, pressure drop rate, etc.). Also the boiler make and model so I can get their recommended near-boiler piping requirements.



As for staging them, if low pressure,  I would not recommend automatic valve isolation but to leave them open to one-another. One important feature is an overflow F&T trap just above the waterline on each, to equalize and keep them from flooding each other when only one is calling. The Burnham handbook (the small one) has some good diagrams. I am sure there are specifics and particulars unique to your project so want to keep this general.



As for staging controls,  Heat Timer Platinum MPCQ comes to mind.  A recent but larger plant I designed, we used a Hayes-Cleveland panel and I do not think it would be cost effective on a smaller plant. The key principle and challenge would be firing to pressure and bringing on the second boiler enough ahead of time so you do not "lose it" and down-fire the lag boiler early enough without overshooting. If you have low-high-low burners, great. If modulating, one can hope, even better, but the sizes seem too small for that. If single stage burners your control interstage delay will be critical, so proportional and integral controls or full PID may be necessary.



I am not sure if Tekmar makes something like that along the lines of their 269 control. Your application may also be handled by regular analog controls and simple is often the best.

I will stand down on that one and let others who know a lot more than I do have their say.



Brad

nicholas bonham-carter

2 boiler piping

i notice that burnham piping arrangement shows no hartford loop, and i wonder if that is a sort of typo.

maybe a gifford loop would control the waterline in the inactive boiler, as it decouples it from the pressure-rising in the return.--nbc

Rod

Staged Boilers

Jim- You might want to contact Dave Bunnell, "Boiler Pro". He's done quite a few staged boilers. I was expecting him to come on here though maybe the way Chicago is snowed up he's probably  been pretty  busy.

- Rod

Charlie from wmass

Jim what is the manufacturer?

265 kbtu times 2 I would say 4" is good 6" is better. Drop headers are a definate here.