Snuffing steam for sulfur storage tanks

[LaSalle1940]

This question involves ongoing practices with respect to supplying snuffing steam to sulfur storage tanks. According to NFPA 655 (2001), if used, snuffing steam should be provided at a rate of 8 lb/min per 100 ft³ of EMPTY tank volume. For a tank measuring 30 ft OD x 16 ft high, that amounts to something on the order of ~54,000 lb/hr, which in turn mandates a 12" line for 50 psig steam. That's pretty big.

What I would like to know is what others have encountered in terms of snuffing steam line size for a given tank size.

Thanks.

 

[JimCasey]

Don't know how you got a 12" line in your estimations. I ran some numbers through the FLowserve sizing program and show that a 6" high-performance butterfly would have enough capacity + change. THe flow downstream would be sonic, and it would make over 100 dB, but that's not bad because it would be only momentary. An audible alarm is a good thing to have when yur sulfur supply is on fire, anyway.

 

[sulphuric]

Found the report of the Committee on Handling and Conveying of Dusts, Vapors and Gases. The requirement of NFPA 655 4-4.1 (b) is based on the following:

"This recommendation brings the steam flooding requirements in line with NFPA 86. The recommendation is based on 1934 FMRC fire test of a gasoline fire where the steam was applied above the gasoline fire and combustion air was introduced below the steam injection point. It in essence requires supplying 200 ft3/min steam for every 100 ft3 of enclosure volume. For hot enclosures (above 220 deg F) where the steam is injected at the surface of the liquid sulfur, a supply capable of 4 ft3/min per 100 ft3 of enclosure volume would be satisfactory. This requirement ensures that the available steam supply is adequate to furnish enough steam at a rate sufficient to extinguish the fire."

There is a big difference between the stated 200 ft3/min and the 4 ft3/min that is deemed adequate for the liquid sulphur application.

 

[sulphuric]

Further to my previous reply. A sulphur storage tank designed for a small acid plant located in Canada was equipped with four (4) 2" dia. nozzle for snuffing steam. The nozzles are located on the tank roof. The tank is 30 ft dia. x 26 ft high. I don't know the basis for the number and size of nozzle.

 

[LaSalle1940]

Interesting note about that plant in Canada: the diameter of the tank in question is essentially the same as the one I'm dealing with. Would it be possible to find out the identity of that plant so that I can pick their brains a bit?

Note to Jim Casey: my comment about a 12" line was based on a quick glance at some of Sarco's steam line sizing tables which are, of course, intended for continuous process-related use (and therefore relatively low velocities) rather than intermittent/one-time emergency use. In the latter case, sonic flow is of course appropriate; therefore, my comment about a 12" line was tantamount to going off half-cocked. Your point is well-taken.

 

[sulphuric]

The plant is a small sulphur burning plant operated by Cameco in norther Saskatchewan, Canada. Sorry no contact information.