ChE 600 – Chemical Engineering Principles
Screening and Size Reduction
1. The opening of 200 mesh screen (Taylor series) is
a. 0.0074 cm b. 0.0074 mm c. 0.0047 cm d. 0.0047 mm
2. If the total percentage of particles larger than the screen opening in the feed, product, and
undersize 36%, 84%, and 3%, respectively, the effectiveness of the screen is _______%.
a. 93.4 b. 85.5 c. 95.0 d. 81.22
3. 1800 lbs of dolomite per hour is produced by crushing and then screening through a 14-
mesh screen. The screen analysis is as follows:
Tyler mesh (circulating load) Feed to screen Undersize (product) Oversize
4 on 14.3 --- 24
8 on 20.0 --- 28
14 on 20.0 --- 24
28 on 28.5 40 24
48 on 8.6 30 ---
100 on 5.7 20 ---
100 through 2.9 10 ---
The total load to the crusher is
a. 6300 lbs/hr b. 6510 lbs/hr c. 6400 lbs/hr d. 6320 lbs/hr
4. From the data in problem 3 calculate the effectiveness of the screen.
a. 62.5% b. 64% c. 66% d. 67.5%
5. Fine silica is fed at 1500 lbs/hr to a double-deck vibrating screen combination to obtain a
48/65 mesh (Tyler) product. The silica feed is introduced into the upper screen of the 48
mesh and the product is discharged off the surface of the lower screen of 65 mesh. During
the screening operation, the ratio of oversize to product to undersize is 2:1 – ½:1.
Laboratory analysis of the different fractions (in mass fraction):
Screen mesh Feed Oversize Product Undersize
10/35 0.2821 0.5855 0.3385 0.00453
35/48 0.2580 0.3370 0.3220 0.00360
48/65 0.2810 0.0660 0.5260 0.34400
65/100 0.0910 0.0050 0.0670 0.29900
100/200 0.0870 0.0060 0.0260 0.35300
Calculate the effectiveness of the screening equipment.
a. 58.7% b. 47.9% c. 68.6% d. 42.4%
Moh’s Scale Hardness
1. Talc 6. Orthoclase
2. Gypsum 7. Quartz
3. Calcite 8. Topaz
4. Flourite 9. Corundum
5. Apatite 10. Diamond
6. What is the specific surface in cm2 per g of quartz with a diameter of 2’’ and density 165
lb/ft3 and specific surface ratio of 10.
a. 4.5 b. 4.47 c. 5.10 d. 5.43
7. The critical speed of a ball mill in rpm whose diameter is 12 inches with grinding balls of
diameter ½ in is approximately _____ rpm.
a. 60 b. 50 c. 70 d. 80
8. The bond work index for a mesh-of-grind of 200 mesh for a rock consisting mainly of
quartz is 17.5 kWH/ton. How much power (in kW) is needed to reduce the material in a
wet-grinding ball mill from an 80 percent passing size of 1100 micrometer to an 80 percent
passing size of 80 micrometer at a capacity of 10 ton per hour?
a. 134 kW b. 143 kW c. 341 kW d. 413kW
9. Power of 3 kW is supplied to a machine crushing material at the rate of 0.3 kg/s from 12.5
mm cubes to a product having the following sizes: 80 % 3.175 mm, 10 % 2.5 mm and 10
% 2.25 mm. What power should be supplied to this machine to crush 0.3 kg/s of the same
material from 7.5 mm cube to 2.0 mm cube?
a. 3.6 kW b. 6.3 kW c. 4.3 kW d. 3.4 kW
10. 6000 lb of a material goes through a crusher and grinder per hour in succession (on the
same power drive). Screen analysis from the crusher shows a surface area of product of 500
ft2 per lb. Screen analysis of the grinder product indicates a surface area of 4,200 ft2 per lb.
The Rittinger’s number of the material processed is 163 in2 per ft-lb. The efficiency of the
crusher is estimated to be 25%, while that of the grinder is 30%. Estimate the total power
to be delivered to the equipment.
a. 38.4 Hp b. 30.6 Hp c. 26.4 Hp d. 18.5 Hp
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