Chemical Engineering - Mechanical Operations

11. 

Pebble mills are tumbling mills widely used for grinding in the manufacture of paints & pigments and cosmetic industries, where iron contamination in the product is highly objectionable. Pebbles used in pebble mill are made of

A. bronze
B. stainless steel
C. flint or porcelain
D. concrete

Answer: Option C

Explanation:

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12. 

Filter aids like asbestos, kieselguhr, diatomaceous earth etc. are used to increase the porosity of the final filter cake & reducing the cake resistance during filtration. Filter aid is

A. added to the feed slurry.
B. precoated on the filter medium prior to filtration.
C. separated from the cake by dissolving solids or by burning it off.
D. all 'a', 'b'&'c'.

Answer: Option D

Explanation:

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13. 

Which of the following relationships between co-efficinet of friction (μ) between rock & roll and a (half of the angle of nip) of the particle to be crushed is correct ?

A. μ > tan α
B. μ ≥ tan α
C. μ > tan 2α
D. μ ≤ tan α

Answer: Option B

Explanation:

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14. 

Pick out the wrong statement pertaining to the roll crushers.

A. Maximum feed size determines the required roll diameter.
B. For hard material's crushing, the reduction ratio should not exceed 4.
C. Both the rolls run necessarily at the same speed.
D. Reduction ratio and differential roll speed affect production rate & energy consumed per unit of surface produced.

Answer: Option C

Explanation:

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15. 

Which of the following is not an ultrafine grinder (colloid mill)?

A. Micronizers
B. Agitated mills and fluid energy mills
C. Toothed roll crusher
D. Hammer mills with internal classification

Answer: Option C

Explanation:

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