ChE 134: Particle Technology > Size Reduction > Flashcards

Size Reduction Flashcards

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1
Q

it is the production of smaller particles from originally larger particles with the use of mechanical forces and without altering their states

A

size reduction

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2
Q

large particles undergo size reduction often called?

A

crushing and grinding

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3
Q

3 reasons why large particles undergo size reduction called crushing and grinding?

A
  1. to increase the number of particles
  2. to refine the shape
  3. to increase the surface area of the particles
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4
Q

this type of size reduction is often suitable for coarser/larger particles

A

crushing

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5
Q

this type of size reduction is often suitable for finer/smaller particles

A

grinding

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6
Q

4 importance of size reduction

A
  1. to meet product specifications
  2. easier handling and transport of sloid particles
  3. increases solid reactivity especially in catalysts
  4. allows separation of unwanted particles
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7
Q

what are the 4 methods of size reduction

A
  1. impact
  2. compression
  3. attrition
  4. cutting
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8
Q

in this method, material is subjected to a sudden blow of force

A

impact

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9
Q

an example of this method is the use of hammer

A

impact

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10
Q

in this method, material is subjected to use of external compressive forces causing it to rupture in many directions

A

compression

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11
Q

this method is used for reduction of hard solids to give relatively few fine particle

A

compression

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12
Q

an example of this method is the use of a nutcracker

A

compression

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13
Q

this method involves rubbing away or wearing down material by friction

A

attrition

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14
Q
A
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15
Q

an example of this method is the use of file

A

attrition

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16
Q

this method involves forcing a sharp thin knife through a material

A

cutting

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17
Q

an example of this method is the use of knife cutters

A

cutting

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18
Q

what are the 3 important factors affecting size reduction

A
  1. magnitude of the load
  2. rate of application of force
  3. hardness of the material
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19
Q

it is one of the most significant criterion of a material in size reduction because it creates large resistance to crushing and also has significant effect of wear and tear to size reduction equipment

A

hardness

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20
Q

what materials are under soft materials

A
  1. talc
  2. gypsum
  3. calcite
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21
Q

what 3 materials are under the intermediate hardness

A
  1. fluorite
    2 apatite
  2. feldspar
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22
Q

what 3 materials are under the hard materials

A
  1. quartz
  2. topaz
  3. corundum
  4. diamond
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23
Q

hardness is measure by what scale?

A

Mohs Scale

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24
Q

arrange the 10 materials from lowest mohs scale to largest mohs scale

A
  1. talc
  2. gypsum
  3. calcite
  4. fluorite
  5. apatite
  6. feldspar
  7. quartz
  8. topaz
  9. corundum
  10. diamond
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25
it is one of the most energy intensive yet least-energy efficient of all the unit operations
size reduction
26
laborator studies show that only less than __% of the energy input in crushing is delivered to the solids
1%
27
how much percentage of the energy input dissipated into the surroundings in the form of heat
99%
28
the remaining 99% of the energy input dissipated into the surroundings in the form of?
heat, friction, and sound waves
29
it is the main measure of efficiency for crushing operations
amount of energy required to create a new surface of particles
30
what are the 3 law governing the energy requirements in crushing operations
1. rittinger's law 2. kick's law 3. bond's crushing law
31
this law is suitable for finer particles
rittinger's law
32
thsi law states that teh work required in crushing is proportional to the new surface created
rittinger's law
33
in rittinger's law, what is the relationship of diameter to the surface area?
inversely proportional
34
in rittinger's law, what is the relationship between rittinger's constant and power requirement
inversely proportional
35
in rittinger's law, what is th relationship between rittinger's constant and hardness?
inversely proportional
36
in rttinger's law, what is the relationship between hardness and surface area?
inversely proportional
37
this law is suitable for larger or coarser particles
kick's law
38
this law states that energy required for crushing is proportional to the log of the initial and final diameters
kick's law
39
in kick's law, what is the relationship between the kick's constant and the hardness of the material
directly proportional
40
thsi 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
bond's law
41
this law is a more realisticway to approximate power requirement compared to Kick's law and Rittinger's Law
Bond's Law
42
it is defined as the gross energy requirement in kilowatt-hours per ton (2000 lb) of feed needed to reduce a very large size
work index
43
how much percentage of the product must pass a 100 micrometer screen for bond's law
80%
44
in this equation, the units must be specific
Bond's Law equation
45
size reduction equipment are divided into 4
1. crushers 2. grinders 3. ulrafine grinders 4. cutting machines
46
these are slow speed machines for coarse reduction of large quantities
crushers
47
3 examples of crushers
1. jaw crushers 2. gyratory crushers 3. smooth roll crushers
48
this type of crusher consist of one swinging jaw and another stationary jaw
jaw crushers
49
this type of crusher consist of a conical crushing head that yrates inside a funnel-shaped casing
gyratory crushers
50
this type of crusher consist of two rollers where feed is crusehd in between
smooth roll crushers
51
this type of equipment reduce crushed feed from crushers into powders
grinders
52
4 types of grinders
1. hammer mills 2. roller mills 3. attrition mils 4. tumbling mills
53
this type of grinder contain high-speed rotor turning inside a cylindrical casing
hammer mills
54
in this type of grinder, solids are caught and crushed between cylindrical rollers and a stationary
roller mills
55
in this type of grinder, particles of soft solids are rubbed between grooved flat surfaces of rotating circular disks
attrition mills
56
in this type of grinder, there's a cylindrical shell slowly turning about a horizontal axis and filled to about one-half of its volume
tumbling mills
57
this type of equipment acepts feed particles no larger than 6 mm
ultrafine grinders
58
2 types of ultrafine grinders
1. classifying hammer mills 2. fluid energy mills
59
this type of ultrafine grinder has hammer mill with internal classifying screens
classifying hammer mills
60
in this tyoe of ultrafine grinder, particles are suspended in high-velocity gas stream
fluid energy mills
61
this type of equipment give particles o definite size and shape from 2 to 10 mm
cutters
62
other term for cutters
granulators or pelletizers
63
most mills operate at speeds between _______ and _______ percent of critical speed
65; 79
64
this type of mill have been successfully run at speeds between 60 and 90 percent of critical speed
ball mills
65
this type of mill should have a speed limited to a mximum of 70% of critical speed and preferably should be in the 60 to 65 percent ciritcal speed range
rod mills
66
this type of mill are usually run at speed between _____ and _____ percent of critical speed
75; 85
67
it is a qualitative scale that ranks materials based on their ability to scratch or be scratched by other substances
Mohs Scale of hardness
68
in reduction ratio, this indicates more intensive size reduction, i.e., larger particles were broken into much smaller pieces
higher R
69
in reduction ratio, this indicates less size reduction, i.e., particles are only slightly smaller than the original.
lower R
70
it is a material-specific factor that accounts for hardness and brittleness
Rittinger's constant
71
this constant is dependent on the surface creation
rittinger's constant
72
this constant is dependent on the particle size reduction rate
kick's constant
73
it is a collective name for the generally known ball mills, rod mills, tube mills, pebble mills and autogeneous mills
tumbling mill
74
this have been successfully run at speeds between 60 and 90 percent of critical speed
Ball mills
75
the speed of this mill should be limited to a maximum of 70% of critical speed and preferably should be in the 60 to 68 percent critical speed range
rod mills
76
preferred critical speed of rod mills
77
this mills are usually run at speeds between 75 and 85 percent of critical speed
pebble mills
ChE 134: Particle Technology
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