Page 552 - APPLIED PROCESS DESIGN FOR CHEMICAL AND PETROCHEMICAL PLANTS, Volume 1, 3rd Edition

518 Applied Process Design for Chemical and Petrochemical Plants

Maximum Pressure During Venting

�
l'I
� II.. t\. P,ed• bar ga
'I
� [\ 0.4 ---..
l'I ... t\. 0.6-1'\.
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I\. r\.
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[\ ' I 1.0 - );;;;; t- I, i.
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1.5 -
"\ 1'. " -, , v- � Dust class St-1 2.0- rs r r / I;' l,,i.i.
"'
I:'\ r-,
'/ � , .....
Dust class St-2
f'\. � "'" ..11/ Ir- >-Dust class St-3 '\ I'\ ['.. l'r V/ � � L, I,., �
'\ �II �I< ['..;) V'l v [/
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100 10 0.1 10 100 1000
Vent Area, m 2
----- Vessel Volume, m 3-----
Figure 7-65E. Venting nomograph for classes of dusts, Pstat = 0.2 bar ga. Reprinted with permission, NFPA 68-1988, Deflagration Venting,
(1988) National Fire Protection Association, Quincy, MA 02269. See note Figure 7-63A.
tures and energies required for a dust explosion are lower ignition energy, and moisture content. Therefore, the
than many common sources of ignition. Hence, caution data presented is useful for reference, but cannot be
must be used in handling dusting materials [34]. (Also counted as absolute. For serious design, actual tests
see Ref. [76]). should be performed on the dust by qualified laboratories
using standardized test equipment. See illustration in Ref.
Dust Explosion. Severity (34], pp. 4:94-95.
Explosion Suppression
Table 7-31 lists the explosibility index that is a relative
measure of the potential damage from a dust explosion. A Protection to guard against explosion has been classed
rating of 2 to 4 requires large vent areas. Above 4, for most as venting, suppression, and isolation. Ref. (54] discusses
cases, the explosion cannot be controlled by venting the subject rather thoroughly and Ref. 34 discusses some
design and therefore requires the use of protection such of the methods used to suppress explosions (see Figures
as inert gas or explosive suppression systems, some of 7-61, 7-62, 7-66 and 7-67). After an explosion has started
which are commercially available. special sensors are required, such as:
Unfortunately, rate of pressure rise and maximum
explosion pressure listed in Table 7-31 are subject to 1. thermoelectrical
uniqueness of the test conditions and are the function of 2. optical
particle size, dust concentration and uniformity, available 3. pressure