Page 546 - APPLIED PROCESS DESIGN FOR CHEMICAL AND PETROCHEMICAL PLANTS, Volume 1, 3rd Edition

512 Applied Process Design for Chemical and Petrochemical Plants

Vent Release Pressure Maximum Pressure During Venting

Pred = 0.2 bar ga ----...
''" t\. ir-P,lat=0.1 bar qa Pred =0.4 bar ga---..... � -, / .... �
11" �
"�
P,ed = 0.6 bar ga ----.._
,"'-.
\.
"
,�
�" / P,ed = 0.8 bar ga , � '\. ' i\ ./ � � ����
r- P>tat = 0.2 bar ga
I\. I'\
P,ed = 1.0 bar ga ---.
"'&. / / v-- P, 181 =0.5 barga P,ed = 1.5 bar ga ---"\ -, I'\ ' ' ./� � � /,
//
�
" �
r-
v
--�
!'\.�
@ �,
P red = 2.0 bar ga ----.._
/� /
' �" -i- '\. �- �
i'I
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.. � � r-
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� ./ ......... : v
"" � .......,:: v �� "
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v
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50 10 0.1 10 100 1000
------Vent Area, m 2 Vessel Volume, m 3 .,..
Figure 7-630. Venting nornograph for hydrogen. Reprinted with permission, NFPA 68-1988, Deflagration Venting, (1988) National Fire Protec-
tion Association, Quincy, MA 02269. See note Figure 7-63A.
A few selected values for zero turbulence are [54]: given constant relief venting area [54]. The nomographs
arc not applicable for detonations.
When systems involving solvent vapor are considered,
----·------ Kc, Bar meter/sec (average values) _
Methane 55 use the nomogram for propane/air mixtures because
Propane 75 most common solvent vapors have maximum explosion
Coke Gas 140 pressures of 7.1 to 7.6 bar, and the Kc falls between 40
Hydrogen 550 and 75 bar meter/sec (see Ref. [54)).
The effects of turbulence must be taken into account
when sizing a relief area. For example, the explosion vio-
lence of turbulent methane-air mixture is comparable to
The nomograms, Figure 7-63A through D, are based that of zero turbulence of hydrogen-air mixtures. From
on an operating pressure of 1 bar (absolute), bur may be the investigations [54], the nomograms from Figure 7-63
used without correction up to 1.2 bar absolute [54]. can be applied for turbulent gas mixtures under the fol-
There is insufficient pressure data available to recom- lowing conditions [54]:
mend using much above normal pressure. When the
operating pressure is raised above normal, the reduced • For large relief areas: Pred � 1 bar, valid but influence
explosion pressure will show a proportional increase for a of ignition energy must be considered.