Page 544 - APPLIED PROCESS DESIGN FOR CHEMICAL AND PETROCHEMICAL PLANTS, Volume 1, 3rd Edition

510 Applied Process Design for Chemical and Petrochemical Plants

Vent Release Pressure Maximum Pressure During Venting
11 1
P,.d = 0.2 bar ga --...
P,ed ;;; 0.4 bar ga -,. ,"
P,ed=0.6 bar ga -
Pied= 0.8 bar ga --... � rs..."
�' c-Pstat�0.1 bar qa P,00 = 1.0 bar ga --... I',:-,.. ' .......
�-
'\" . � / P,ed = 1.5 bar ga ---.,. '"" I'\" I'\ '\ ,/' :; v
I'-
r.
ir-- P,tat = 0 .2 bar ga
P,od = zo bar ga
I\. 'i; \. // ...--P,, •• �o.5 bar ga !"-..' ' � ,"'-. / II' .....
-, !'\.'
/
'� rt- / -, !'\.' )A. / '/ � P'
,, /
'
\.� /V 1, " ' � � Po' ..... ��
' � � ; ...., ..... � i/ )"
..... �-
"'�\. ....,/ .,. ... � �"'
�_,
I\ ' � ,_ /" '/ h
' -- - -- -- - -- - - -- p(,; 0 ; � /
�
IY/ � ..... � ..
... �
� �
! '� ......... � / � /
.....
I '/ v ... Vj / �
I ""' �� v '/ �� �
I / / ,;
I ;
/'.'.
I "'"� v/ � ... � I
I \� /h v: ..... � ........ :
: '\� ':/ � t> I
I \ � ........::: /' I
I \."\ v :
; � I
t :
50 10 0.1 10 100 1000
...,._ Vent Area, rn 2 Vessel Volume, m'-----
Figure 7-638. Venting nomograph for propane. Reprinted with pennission, NFPA 68-1988, Deflagration Venting, (1988) National Fire Protec-
tion Association, Quincy, MA 02269. See note Figure 7-63A.
For systems without test data or literature data of similar configuration and same type ofignitor and igni-
tion energy [27]
(I) vVhen test data for a particular gas-air system is not
available, the nornograph for hydrogen air system, *Must not exceed mechanical strength of vessel; use
Figure 7-630, can be conservatively used. Ref. [27] design or MA,.\<'P.
reports the additional vent area determined in this **Must be lower than x or not more than 10% above
manner will usually be small. lYV\WP.
(2) Interpolation of existing nornographs to determine
deflagration vent area of different gas-air mixtures: Refer to the propane and hydrogen nomographs (Fig-
Ang= area required for new gas or mixture. ures 7-63B and 7-630). The required vent area to protect
the vessel specified from each of the charts will be a and
Assume vessel volume = V' b, square meters, respectively.
Establish", maximum allowable value for P red = x The maximum rates of pressure rise for propane and
Establish**, Psiat = y hydrogen are r and r', respectively, bar/sec in the same
Maximum rate of pressure rise, Kc, for gas in question vessel. For linear interpolation:
in a specific vessel = z bar/sec.
Required vent area for new gas =
Note: Kc values are not constant and vary with test condi-
tions. Kc provides means of comparing maximum rates of [ ]
pressure rise for various gases, but should only be used for [a + (t. - r) ( b - a)]= vent area, sq meters (7- 7])
,
deflagration vent sizing if test data comes from test vessels (r - r)