Is there an error in NFPA 58 calculation of equivalent SCFM of air regarding PSV relieving rate? 2

[SNORGY]

The equation that I see, based on an earlier version of the pamphlet, is:

SCFM (air) = (3.09)(W)[(ZT)/(M)]^0.5

where

SCFM (air) is equivalent air flow
W is relieving capacity of product vapor at relieving conditions in lb/hr
Z is compressibility factor of product vapor at relieving conditions
T is absolute temperature of product vapor at relieving conditions (degrees R)
M is product vapor molecular weight

I suspect - but have not confirmed - that "W" should be in lb/min. Otherwise, my answers are rather disturbing.

Any insight or update or errata note that people can share would be helpful.

 

[cdafd]

not an engineer and far from knowing anything about math

From the 2014 NFPA 58

same as in the 08 edition



SCFM (air) = equivalent airflow in standard ft3/min
W = relieving capacity of product vapor at relieving
conditions in lb/hr
Z = compressibility factor product vapor at relieving
conditions
T = absolute temperature of product vapor at
relieving conditions in °R
M = product vapor molecular weight

 

[chicopee]

The equivalency of SCFM for air is from which medium? Is it SCFM of air from steam in lbs/hr? or is it SCFM of air from air at ACFH? The only equivalency formula that I know is cfm of air from steam in lhs/min or hr.

 

[stookeyfpe]

Snorgy:

I recommend you talk to this gentleman. Bruce has been with NPGA for years and authors the NFPA 58 handbook:

Senior Technical Advisor: Bruce Swiecicki, P.E., bswiecicki@npga.org, 21200 S. LaGrange Rd., Suite 353, Frankfort, IL 60423, 815-806-9035

 

[SNORGY]

Thanks folks.
No need to pursue further, the equation of interest is (1) out of date and (2) wrong.