Page 258 - APPLIED PROCESS DESIGN FOR CHEMICAL AND PETROCHEMICAL PLANTS, Volume 1, 3rd Edition

228 Applied Process Design for Chemical and Petrochemical Plants

AIN .MIST � DSMOKE
GROUND LIMESTONE ROSIN SMOKE

=

c __ DIAMETERS OF
-------
GAS MOLECULES
ALKALI FUM
DUST
METALLURGICAL FUME
TYLER
VIRUS S PROTEIN
ACT ER IA
Figure 4-2. Particle-size ranges for aerosols, h � S H_3 5 ��� ...L...L;,!!,_ILL....l'---L � ,J;-.L....,__-L.... � '----.-);-.L...l.---'- � -L----;; � -'--c � - :- : � -=c, , � 1 ,.---- �� __j_
Ei
dusts, and fumes. Courtesy, H. P. Munger, Bat- 1000 � �
telle Memorial Institute. PARTICLE SIZE - MCRONS
93% efficient. Selection of a good wet collector will show The fundamentals of separation for a particle moving
an efficiency of 98%. The effluent leaving this collector with respect to a fluid are given by the drag coefficient of
will have a concentration of 2.25 (1.00 - 0.98) = .045 Figure 4-6.
grains/ cu ft. Using the line initially drawn, at the point The motion of particle and fluid are considered rela-
where it intersects the line of 0.045 grains/ cu ft will indi- tive, and the handling of the relations are affected only by
cate a mean particle size in the effluent of 1.6 microns. conditions of turbulence, eddy currents, etc.

Guide to Dust Separator Applications Terminal Velocity

Table 4-5 [10] summarizes dry dust particle separators When a particle falls under the influence of gravity it
as to general application in industry, and Table 4-6 and will accelerate until the frictional drag in the fluid bal-
Figures 44 and 4-5 [ 42] compare basic collector charac- ances the gravitational forces. At this point it will contin-
teristics. Figure 4-5 presents a typical summary of dust col- ue to fall at constant velocity. This is the terminal velocity
lection equipment efficiencies which have not changed or free-settling velocity. The general formulae for any
significantly for many years except for specialized equip- shape particle are [13]:
ment to specialized applications.

Guide to Liquid-Solid Particle Separators
(4-1)
Table 4-7 summarizes liquid particle separators as to
the general process-type application.
For spheres:
Gravity Settlers

(4- 2)
The use of these settlers is not usually practical for
most situations. The diameters or cross-section areas
become too large for the handling of anything but the
very smallest of flowing vapor streams. In general, gravity (a) Spherical particles between 1500 and 100,000
settlers of open box or tank design are not economical for microns; Newton's Law:
particles smaller than 325 mesh or 43µ [23].
They are much more practical for solids or dusts,
although even for these situations the flow quantities
must be small if the sizes are not to become excessive. (4- 3)
With unusually heavy and/or large particles the gravity
separator can be used to advantage. C = 0.445 average drag coefficient