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Re: Sellers Immersion Fired Boilers

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Posted by GeneratorGrrl on March 25, 2005 at 13:41:12:

In Reply to: Sellers Immersion Fired Boilers posted by Bill on March 24, 2005 at 15:08:44:

: Does anyone have any comments on these boilers. We are looking into installing a high pressure steam Sellers boiler for our process. Would appreciate any comments. Good or bad.

Our plant operates a Liberty-Sellers immersion fired low-pressure steam boiler, MAWP 15 psi -- not what you're looking at, but might give you some performance insights nevertheless.

Our boiler is 25 years old (installed 1980) and operates 24/7/365 with variable steam loads. Feedwater is treated city water trucked to the site, blended with raw well water, both stored in a tank before passing through filters, softeners and steam-deaerating feedwater tank. Average hardness before softening is 200 - 250 ppm. The boiler is single-pass, operating between 10 - 13 psi.

The most recent combustion efficiency test was last year, showing the boiler to be operating at 83% fuel efficiency; design rating at the time (1980) was 85% efficiency, so not doing too bad for 25 years later. NOx, S03 and CO flue emissions were well within modern environmental guidelines (revised 2001, IIRC), which are considerably tighter than the 1980 standards that the boiler was designed for.

So much for combustion specs, now how does it perform? Our boiler is designed for fast start-up, even from cold, with tubes and crownsheets designed to flex and absorb the thermal expansion of cold start-up. This is an advantage to us, being on the Canadian prairies with frequent power-failures. Extended downtime leads to product loss for our plant, so getting up and running ASAP is important. After an ice-storm induced outage of 2 days, at -15C conditions, I had the boiler up and running in just over an hour, with no stresses to the welds or seams on subsequent inspection.
I don't know whether our burner type is common to all Sellers boilers; our burner is made by Liberty and mounted onto the Sellers boiler body. Our burner type allows the manual gas valve to be closed without interrupting the pilot (ours is natural gas with on/off control.) I don't know if this is unique; I do know that I could not do this on the other lp firetube boilers I've worked with. I like this feature as the pilot runners can act as 'low fire' and warm the firetubes, while I can control the length of full-burn exposure.

The Sellers firetubes are designed to expand and contract. When the boiler is cooled, any scale that may have accumulated will crack and flake off the firetubes when they contract. This has been our experience but the tubes will not clean themselves completely. If heavy scale-promoting conditions are occuring, scale will still adhere to the firetubes and build up, with shards collecting in the bottom of the shell.

The heat-transfer efficiency of our boiler has been good. The clean boiler gives a consistant 25C rise over the burn period (10 - 13 psi), giving us a reliable baseline by which to determine if scaling or sooting is occurring. In comparing the 1-pass Sellers lp boiler to the 3-pass lp firetube boilers I worked with in my previous position, I haven't found the Sellers to be less efficient. YMMV and I certainly acknowledge that the 35-y.o. 3-pass boilers weren't the most efficient to begin with ^_~ How the modern Sellers compare with other modern firetube boilers, that I cannot say.

So. Negatives? Not that many, off the top of my head. Our boiler's burner is the biggest complaint, mainly in its pain-in-the-buttness. In our boiler, each firetube has its own burner head, and running along each row of burners is the multi-tiered pilot piping, with well over 1000 teeny little holes that get plugged up with soot because, on our boiler, trying to adjust the combustion air for the pilot without wrecking the air for the main burners is more challenging than trying to balance a soap bubble on a frisky porcupine. So every summer, each and every one of these over-1000-because-I've-lost-count pilot holes has to be poked open with a paper clip or welding-tip cleaner wire. Our burner also uses three flame rods to sense the pilot flame, and these must be bent around and twisted into position - again, not really a complaint, just a pain in the butt. The last pain in the butt is that shrinking-firetube feature: If you *do* run into scale problems, the contracting firetubes will shell some of it off and your boiler shell will fill with shards .... which you then have to scrape out through the little 5" handholes. And this is necessary because, with it all piled up like that, acid cannot penetrate the mass fully, so the works turns to a corrosive sludge. Not pretty.

That's all I can think of to say about our Liberty-Sellers boiler. We also run a Liberty-Sellers lp immersion-fired hot water boiler, running a glycol mixture, and its even less trouble than the steam boiler.

Hope this helps
-- GeneratorGrrl

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