Unit Operations - Size Reduction

size reduction

The term applied to all ways in which particles of solids are cut or broken into smaller pieces

a. size reduction

b. screening

c. comminution

d. crushing

sapphire

The hardness of a mineral is a criterion of its resistance to crushing. Which of the following is an example of a hard material?

a. talc

b. calcite

c. sapphire

d. feldspar

Rittinger's Law

States that the energy required for crushing is proportional to the new surface created.

a. Rittinger's Law

b. Kick's Law

c. Bond Law

d. Energy Law

Practical Energy Efficiency

It is defined as the efficiency of technical grinding compared with that of laboratory crushing experiments.

a. Grinding Efficiency

b. Bond Work Index

c. Practical Energy Efficiency

d. none of these

the initial and final sizes of the particles

In comminution, the energy requirement is determined theoretically by

a. the initial and final sizes of the particles

b. the type of equipment

c. the change in shape of the particle

d. none of these

it prepares raw materials of the desired sizes prior to processing

Size reduction is important in chemical engineering since

a. it prevents chemical engineers from becoming overweight

b. it makes products to become uniform in size

c. it prepares raw materials of the desired sizes prior to processing

d. none of these

41%

Based on Bond's Crushing Law, the power required to crush a certain material will change by _____ if the diameter of the product is made smaller by 50%

a. 50%

b. 41%

c. 25%

d. 75%

0.87

Sphericity for a cylinder whose length equals its diameter is

a. 1.5

b. 0.5

c. 0.87

d. 5

ratio of surface to volume as the actual volume

Equivalent diameter of a particle is the diameter of the sphere having the same

a. ratio of surface to volume as the actual volume

b. ratio of volume to surface as the particle

c. volume as the particle

d. none of these

compression

For coarse reduction of hard solids, use

a. impact

b. attrition

c. compression

d. cutting

attrition

Soft and non-abrasive materials can be made into fines by

a. attrition

b. compression

c. cutting

d. none of these

surface energy created by the crushing to the energy absorbed by the solid

Crushing efficiency is the ratio of

work required in crushing is proportional to the new surface created

Rittinger's Crushing Law states that

calls for relatively less energy for the smaller product particle than does the Rittinger Law

Bond Crushing Law

gross energy (kWh/ton of feed) needed to reduce very large feed to such a size that 80% of the product passes a 100 micron screen

Work index is defined as the

less than the critical speed

The operating speed of a ball mill should be

a. less than the critical speed

b. much more than the critical speed

c. at least equal to the critical speed

d. none of these

ultragrinding

A fluid energy mill is used for

a. cutting

b. grinding

c. ultragrinding

d. crushing

increases capacity compared to dry grinding

Wet grinding in a revolving mill

a. gives less wear on chamber walls than dry grinding

b. requires more energy than for dry grinding

c. increases capacity compared to dry grinding

d. complicates handling of the product compared to dry grinding

Tube Mill

Cement clinker is commonly reduced to fine size using a

a. Roll Crusher

b. Ball Mill

c. Tube Mill

d. Hammer Mill

Bond's Crushing Law

states that the work required to form particles of size Dp from very large feed is proportional to the square root of the surface to volume ratio of the product.

Kicks Law

states that energy required for crushing is proportional to the leg of the initial and final diameters.

Jaw Crusher

consists of a swinging jaw which moves back and forth, working against a stationary surface called the anvil jaw, with which it forms a V-shape chamber

Gyratory Crusher

employs a crushing head in the frame of truncated core, mounted on a shaft; employs a compressive force

Taggart's Rule

states that if the hourly tonnage to be crushed divided by the square of the gape in inches is less than 0.115, use a jaw crusher; otherwise, a gyratory crusher

Bradford breaker for coal

combines the two features of breaking and screening

Toothed roll crusher

breaking by pressure of the teeth against the larger lumps of the material

Hammer Mill

the hammer deliver heavy blows to the feed material while it is in suspension, driving against a breaker plate until it is fine enough to pass through the openings

Squirrel-cage disintegrator

for fibrous materials such as wood blocks and asbestos; two concentric cages rotate in opposite direction

Crushing Rolls

Two rolls, one in adjustable bearings, rotate in opposite directions. The clearance between them can be adjusted according to the size of feed and the required size of the product.

Cone Crushers

consists of a conical crushing head similar to that of the gyratory crusher

Edge runners

The only commonly used crusher of this general type is the one in which the pan rotates and the horizontal axis of the grinding wheels is stationary

Pebble Mill

Is a steel cylinder lying on its side and rotated about its long axis and containing an appropriate grinding medium. The material is introduced through a manhole in the center of the shell length after which the opening is closed hermetically by a cover plate.

Rod Mill

are similar to pebble mills and ball mills except that the grinding media are steel rods rather than balls. The rods are always longer than the diameter of the mills and therefore lie in the mill parallel to the axis.

Ball Mills

consists of a horizontal cylinder whose diameter is roughly equal to its length, lined with heavy liner plates. The feed end consists of a helical feed scoop which lifts feed into the spiral feed liner from which it enters the mill.