Page 560 - APPLIED PROCESS DESIGN FOR CHEMICAL AND PETROCHEMICAL PLANTS, Volume 1, 3rd Edition

526 Applied Process Design for Chemical and Petrochemical Plants
--
5.0 _ i__.- _ ..

2.5 - - _ ...
2.0 ......
�
..:- � ....... .. ---·
ca
e 1.0 ...... --
..s
u ............. ------
::,
"O 0.5 ... .... -
.s=
.'!::: Gases
a::
� - Duct Length > 3 m
D. ----- Duct Length � 3 m
I I I I Figure 7-66. Increase in the reduced deflagration pressure for gases
0.1 due to the effect of a vent duct. By permission, American Institute of
0.1 0.2 0.4 0.6 0.8 1.0 1.5 2.0 Chemical Engineers, Meeting Mar. 6, 1988 by I. Swift (deceased)
P without duct, (bar) [56], with data from Ref. [54].
red

5.0 -- _.. --- �
....
....
2.5 - .. ....
2.0 .... -
..:- :...--- ----
,e. � __
1.0 .... -
ti ...........
::, ........
'O 0.5 .... -
:5 .....
'!!: Dusts
"
D. � - Duct Length > 3 m
----- Duct Length s 3 m
0.1 I I I I Figure 7-67. Increase in the reduced deflagration pressure for dusts
0.1 0.2 0.4 0.6 0.8 1.0 1.5 2.0 due to the effect of a vent duct. By permission, American Institute of
Chemical Engineers, Meeting Mar. 6, 1988, by I. Swift (deceased)
P red without duct, (bar) [56], with data from Ref. [54].

120 (trx! continued from page 523)
L= Distance between deflagration vents not be reduced due to backpressure on the valves' dis-
100
charge side (outlet). The total backpressure of the system
or must be limited to 10% of the set pressure of each pres-
80
sure relief valve that may be relieving concurrently [33].
i Length of pipe or duct having one e[!d open When balanced relief valves are used, the manifold back-
s 60 pressure can be higher, less than 30% of the valve's set
:::i
.._..
40 pressure, psia [33].
Dusts with K., :!: 200
20 The key detail of a seal drum is the liquid seal:
Propane, dusts with K., > 200
00 1 2 3 h, = 144P"/p, see Figure 7-70 (7-77)

Diameter, meters where h. = seal, submerged, ft
P" = maximum header exit pressure into seal, psig
Figure 7-68. Maximum allowable length of a vessel vented at one p = density of seal liquid, lb/ cu ft
end, or maximum distance between vents as a function of the vent Calculate the cross section of the drum volume for
diameter for the safe venting of deflagrations of dusts and gases. By
permission, American Institute of Chemical Engineers, Meeting Mar. vapor above the liquid level, establishing the level refer-
6, 1988 by I. Swift (deceased) [56], with data from Ref. [54]. enced to h., plus clearance to drum bottom, h., normally