ChE 600 – Chemical Engineering Principles
Filtration and Centrifugation
Constant Rate and Constant Pressure Filtration
1. What is the porosity of a solid if its bulk density is 1125 kg/m 3 and its true density is 1500
kg/m3?
a. 0.25 b. 0.75 c. 1.33 d. 0.33
2. Volume of the filtrate collected is 1 gal when the filtration rate is 1.5 gpm, and it is 5 gal
when the filtration rate is 0.6 gpm. Calculate the volume collected when the filtration rate
is 0.75 gpm. Assume constant pressure filtration.
a. 3.67 gal b. 4.22 gal c. 5.18 gal d. 7.43 gal
3. From # 2, what is the total volume collected in 10 min? Assume constant pressure
filtration
a. 3.67 gal b. 4.22 gal c. 5.18 gal d. 7.43 gal
4. In the filtration of Al(OH)3 the following data were obtained:
i. The pump is operated at maximum capacity (P = 50 psia)
ii. Filtration was completed at constant pressure
iii. Constant rate operation time is 15 min and 1/3 of the total
volume is obtained during this period.
Given the above, the total filtration time is
a. 20 min b. 25 min c. 50 min d. 75 min
5. If only ½ of the original filtrate volume of the above problem were to be collected with
the area remaining unchanged, the new filtration time is
a. 20.5 min b. 24.4 min c. 48.8 min d. 32.4 min
6. It is found that the filtration rate is doubled if the pressure difference is doubled. What
would be the effect of raising the temperature of filtration from 293 to 313 K? The
viscosity of the liquid is given by μ = μo (1 - 0.015(T - 273)) where μ is the viscosity at a
temperature T in K and μo is the viscosity at 273 K.
a. Filtration rate will increase by 75% c. filtration rate will increase by 50%
b. Filtration rate will increase by 57% c. filtration rate will decrease by 75%
Plate and Frame Filter Press and Leaf Filter
7. A laboratory leaf filter is run at constant rate. The initial pressure is 5 psig and the
pressure after 30 min is 65 psig during which 5 ft3 of the filtrate collected. The resistance
of the filter medium in terms of ft3 of filtrate is
a. 0.42 b. 0.84 c. 1.68 d. 0.21
8. A small leaf filter is run at constant rate. It is found that the time the initial pressure is 5
psig and the pressure after 20 min of operation during which 30 gal of filtrate is collected
is 50 psig. If this filter is used with the same slurry in a constant pressure filtration at 50
psig, the filtrate collected in 20 min is
a. 40 gal b. 42.4 gal c. 45 gal d. 47.2 gal
9. A plate and frame press delivers 50 L of filtrate in an hour at a constant pressure of 50
psig. The washing time using 50 L of wash water is
a. 1.6 hr b. 3.2 hr c. 4 hr d. 4.4 hr
10. A plate and frame filter press is used to filter a compressible sludge (s = 0.45) at 50 psia
for 2 hours. Washing is done at 30 psia with wash water equal to 10% of the filtrate
volume collected. The washing time is
a. 100 min b. 127 min c. 78 min d. 50 min
11. A standard leaf filter gives 20 ft3 of filtrate in two hours of filtration time per cycle. If
washing time is 30 min, draining time is 20 min, filling time is 25 min, and dumping,
cleaning, etc. is 35 min. The capacity of the leaf filter, in ft3/hr is
a. 5.2 b. 6.5 c. 2.5 d. 4.5
Clarifying Centrifuge
12. The capacity in cubic meters per hour of a clarifying centrifuge operating under these
conditions is?
Diameter of bowl = 600 mm Thickness of liquid layer = 75 mm
Depth of bowl = 400 mm Speed = 1200 rpm
Specific gravity of liquid = 1.2 Specific gravity of solid = 1.6
Viscosity of liquid = 2 cp Cut size of particles = 30 microns
a. 200 b. 220 c. 230 d. 210
13. A centrifuge with a 20 in diameter bowl 14 in deep operates at 1200 rpm giving a 2 in
thick liquid layer when used with a sludge whose liquid has a specific gravity 1.2 and a
viscosity of 2.5 cp. The solid component of the sludge has s specific gravity of 1.7. If the
cut size of the particles is 35 microns, what is the capacity of the centrifuge in gallons per
minute?
a. 843 b. 348 c. 483 d. 893
Basket Centrifugal Filter
14. Determine the filtration rate that can be expected from a basket centrifugal filter using the
data below:
Basket Height = 12 in Inside basket diameter = 26 in
Rotation rate = 2000 rpm Material to be filtered = gypsum slurry
Specific cake resistance = 2.52 E11 ft/lb Porosity = 0.5
Specific gravity of gypsum = 2.65
Assume that the cake is incompressible, filter medium resistance is negligible and the
liquid surface corresponds to the filter cake surface and the thickness of the cake is 1 in.
a. 0.598 gpm b. 0.698 gpm c. 0.985 gpm d. 0.895 gpm
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