Day 2 - Par Tech Flashcards
1
Q
Increasing the capacity of screen
A
decreases the screen effectiveness
2
Q
Screen efficiency is
A
recovery x rejection
3
Q
As particle size is reduced
A
screening becomes progressively more difficult
4
Q
A screen is said to be blinded when
A
the screen is plugged with solid particles
5
Q
The material passing one screening surface and retained on a subsequent surface is called
A
intermediate material
6
Q
In screen analysis, notation + 5 mm/ -10 mm means passing through
A
10 mm screen and retained on 5 mm screen
7
Q
It is desired to separate a mixture of sugar crystals into two fractions, a coarse fraction retained on an 8-mesh screen, and a fine fraction passing through it. Screen analysis of the feed, coarse and fine fractions below
Mass fraction of +8 particles in feed =0.46
Mass fraction of +8 particles in coarse particles =0.88
Mass fraction of +8 particles in fine fractions =0.32
Calculate the overall effectiveness of the screen used for the separation purpose per 100 kg of feed.
A
45%
8
Q
Mesh number indicates the number of holes per
A
linear inch
9
Q
1800 lbs of dolomite per hour is produced by crushing and then screening through a 14-mesh screen. The screen analysis is as follows:
Calculate the total load to the crusher.
A
6300 lb/hr
10
Q
1800 lbs of dolomite per hour is produced by crushing and then screening through a 14-mesh screen. The screen analysis is as follows:
What is the screen effectiveness?
A
63%
11
Q
Limestone is crushed by six units operating in parallel and the products separated by six 35-mesh screens also in parallel, into two fractions. The effective dimensions of each screen is 6 ft by 20 ft. The common undersize from the screens come out at the rate of 50 tons/hour. Assume no losses.
What is the efficiency of each screen?
A
52.8%
12
Q
Limestone is crushed by six units operating in parallel and the products separated by six 35-mesh screens also in parallel, into two fractions. The effective dimensions of each screen is 6 ft by 20 ft. The common undersize from the screens come out at the rate of 50 tons/hour. Assume no losses.
Calculate the capacity of each screen in lb/24 hour per sqft.
A
5750
13
Q
Fine silica is fed at 1500 lbs/hour 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 2:1.5:1. Laboratory analysis of the different fractions:
Determine the effectiveness of the screening equipment.
A
49%
14
Q
Fine silica is fed at 1500 lbs/hour 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 2:1.5:1. Laboratory analysis of the different fractions:
If the screen measure 5 ft x 8 ft each, what is the capacity in MT/day-ft2 -mm of the 65 mesh screen on the basis of a perfectly functioning 48 mesh screen?
A
0.90
15
Q
Fine silica is fed at 1500 lbs/hour 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 2:1.5:1. Laboratory analysis of the different fractions:
Calculate the capacity in MT/day-ft2 -mm on the basis of the actual performance of the 48 mesh screen.
A
1.1
16
Q
A quartz mixture is screened on a 10-mesh screen. The cumulative screen analysis of feed, overflow and underflow are given in the table.
Calculate the following:
The mass ratio of overflow to feed
A
0.42
17
Q
A quartz mixture is screened on a 10-mesh screen. The cumulative screen analysis of feed, overflow and underflow are given in the table.
Calculate the following:
The mass ratio of underflow to feed
A
0.58
18
Q
A quartz mixture is screened on a 10-mesh screen. The cumulative screen analysis of feed, overflow and underflow are given in the table.
Calculate the following:
Over-all effectiveness of the screen
A
67%
19
Q
Sphericity for a cylinder whose length equals its diameter
A
0.87
20
Q
Size measurement of ultrafine particles can be best expressed in terms of
A
surface area/unit mass
21
Q
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
sapphire
22
Q
For the preliminary breaking of hard rock, we use
A
gyratory crusher
23
Q
Size reduction mechanism used in jaw crushers is
A
compression
24
Q
To get ultrafine particles, the equipment used is
A
fluid energy mill
25
To get fine talc powder from its granules, the equipment used is
ball mill
26
Maximum size reduction in a ball mill is done by
impact
27
The operating speed of a ball mill should be
less than the critical speed
28
The critical speed of 6 ft diameter ball mill where the balls are considered small compared to the diameter of the ball mill is
31.3
29
A ball mill 1.2 m in diameter is being run at 0.8 Hz. It is found that the mill is not working satisfactorily. Would you suggest any modification in the condition of operation?
The speed of rotation should be halved
30
As the product becomes finer, the energy required for grinding
increases
31
An available crusher has been accepting hard rock with a volume surface mean diameter of 0.069 m and providing a product with a surface mean diameter of 5 x 10-3m. The power required for crushing 10000 kg/h of this specified rock is 6.35 kW. Assume that the mechanical efficiency of the unit will remain unchanged. The power consumption if the capacity were reduced to 9000 kg/h with the same feed characteristics but with a reduction in the volume surface mean diameter of the product is 4 x 10-3 m is
6.64 kW
32
In crushing a certain ore, the feed is such that 80% is less than 50.8 mm in size and the product size is such that 80% is less than 6.35 mm. The power required is 89.5 kW. Based on the Bond equation, calculate the power required using the same feed so that 80% is less
than 3.18 mm.
147 kW
33
It is desired to crush 100 ton/h of phosphate rock from a feed size where 80% is less than 4 in to a product where 80% is less than 1/8 in.
148 kW
34
Particles of an average size of 25 x10-4 m are crushed to an average product size of 5 x10-4 m at the rate of 15 tons/hr. At this rate the crusher consumes 32 kW of power of which 2 kW are required for running the mill empty. What would be the power consumptions of
10 tons/hr of this product to further crushed 1x10-4m size in the same mill? Assume Rittinger’s law is applicable
100 kW
35
A material is crushed in a Blake Jaw Crusher and the average size of particles reduced from 50 mm to 10 mm with the consumption of energy at the rate of 13 kW/(kg/s). The consumption of energy needed to crush the same material of an average size 75 mm to an
average size 25 mm assuming Kick’s Law applies is
8.88 kW/(kg/s)
36
The operation by which solids are separated from liquids due to difference in the respective densities is
sedimentation
37
Forces acting on a particle settling in fluid are
gravitational or centrifugal, buoyant and drag forces
38
Drag is defined as the force exerted by the
fluid on the solid in a direction opposite to flow
39
Stoke’s law is valid when the particle Reynolds number is
<1
40
The terminal velocity of a small sphere settling in a viscous fluid varies as the
inverse of the fluid viscosity
41
Buoyant force
depends on the weight of the floating body
42
Terminal velocity is
constant velocity with no acceleration
43
Determine the terminal settling velocity of dust particles having a diameter of 60 microns at 294.3 K and 101.32 kPa. The dust particles can be considered spherical with a density of 1280 kg/m3
0.14 m/s
44
The terminal settling velocity of a 6 mm diameter glass sphere (density: 2500 kg/m3) in a viscous Newtonian liquid (density: 1500kg/m3) is 100 μm/s. If the particle Reynolds number is small and the value of acceleration due to gravity is 9.81 m/s2, then the viscosity of the liquid (in Pa-s) is
196.2
45
Solid spherical particles of coffee extract from a dryer having a diameter of 400 microns are falling through air at a temperature of 422 K. The density of the particles is 1030 kg/m3. Calculate the distance of fall in 5 s. The pressure is 101.32 kPa.
7.3 m
46
A random handful of silica particles ranging in size from 28 mesh to 200 mesh is thrown to a very deep body of water (without tides or turbulence)
Data:
Viscosity of water = 0.01 poise
Density of silica = 2.65 g/cm3
28 mesh = 0.0589 cm
200 mesh = 0.0074 cm
The distance between the largest and smallest particles after 10 min is
4700 cm
47
In hindered settling, particles are
near each other
48
Solid spherical particles having a diameter of 0.09 mm and a solid density of 2002 kg/m3 are settling in a solution of water at 26.70C. The volume fraction of the solids in the solution is 0.45. The settling velocity is ___. For H2O: ρ=994.7 kg/m3 and μ=0.861x10-3 Pa-s.
2.369x10-4 m/s
49
Solid spherical particles having a diameter of 0.09 mm and a solid density of 2002 kg/m3 are settling in a solution of water at 26.70C. The volume fraction of the solids in the solution is 0.45. The settling velocity is . For H2O: ρ=994.7 kg/m3 and μ=0.861x10-3 Pa-s.
Calculate the Reynolds number
9.89x10-3
50
Particles of quartz having a diameter of 0.137 mm and a specific gravity of 2.65 are settling in water at 293.2 K. The volume fraction of the particles in the slurry mixture of quartz and water is 0.25. Calculate the Reynolds number.
0.30
51
If the radius of a basket centrifuge is halved and the rpm is doubled, then
centrifugal force is doubled
52
A centrifuge having a radius of bowl of 0.1016 m is rotating at N=1000 rev/min. Calculate the centrifugal force developed in terms of gravity forces.
Calculate the centrifugal force developed in terms of gravity forces.
114
53
A centrifuge having a radius of bowl of 0.1016 m is rotating at N=1000 rev/min.
Compare this force to that for a bowl with a radius of 0.2032 m rotating at the same rev/min.
227
54
A centrifuge having a radius of bowl of 0.1016 m is rotating at N=1000 rev/min.
A centrifuge bowl is spinning at a constant 1500 rev/min. What radius bowl is needed for a force of 500 g's.
0.2
55
If a centrifuge is 0.9 m diameter and rotates at 20 Hz, at what speed should a laboratory centrifuge of 150 mm diameter be run if it is to duplicate the performance of the large unit?
49 Hz
56
The capacity of a Sharples centrifuge is estimated to be
increase/decrease by % if its speed is doubled and the cut size of the product is reduced by 20%
156% increase
57
A centrifuge with a phosphor bronze basket, 380 mm in diameter, is to be run at 67 Hz with a 75 mm layer of liquid of density 1200 kg/m3 in the basket. What thickness of walls are required in the basket? The density of phosphor bronze is 8900 kg/m3 and the maximum safe stress for phosphor bronze is 87.6 MN/m2
15 mm
58
An aqueous suspension consisting of particles of density 2500 kg/m3 in the size range 1 to 10 microns is introduced into a centrifuge with a basket 450 mm rotating at 80 Hz. If the suspension forms a layer
75 mm thick in the basket, calculate the following
The angular velocity in rad/s
503
59
An aqueous suspension consisting of particles of density 2500 kg/m3 in the size range 1 to 10 microns is introduced into a centrifuge with a basket 450 mm rotating at 80 Hz. If the suspension forms a layer 75 mm thick in the basket, calculate the following.
The Reynolds Number
0.46
60
An aqueous suspension consisting of particles of density 2500 kg/m3 in the size range 1 to 10 microns is introduced into a centrifuge with a basket 450 mm rotating at 80 Hz. If the suspension forms a layer 75 mm thick in the basket, calculate the following.
The time will it take for the smallest particle to settle out
19.3
61
A filter press has a filtering area of 300 ft2. It operates at a constant pressure of 20 psig and give 10000 gal of filtrate in 3 hours. Assume θe=0.05 hour and Ve = 50 gal.
How much filtrate will be produced if the filter area is doubled, with other conditions maintained constant?
20050 gal
62
A filter press has a filtering area of 300 ft2. It operates at a constant pressure of 20 psig and give 10000 gal of filtrate in 3 hours. Assume θe=0.05 hour and Ve = 50 gal.
How much filtrate will be produced if the pressure is doubled, if doubling the pressure increases α by 25%?
12700 gal
63
A filter press has a filtering area of 300 ft2. It operates at a constant pressure of 20 psig and give 10000 gal of filtrate in 3 hours. Assume θe=0.05 hour and Ve = 50 gal.
What will the time of washing if the press is washed under the original conditions with 2000 gal of wash water after 3 hours of filtering?
4.85 hrs
64
A plate and frame filter press containing 24 frames, each 1-inch thick and has inside dimensions of 2 ft by 2 ft. Filtering time is 2 hours. Wash water volume is 10% of the filtrate volume per cycle. Filtering and washing are done at the same pressure. The final cake is 0.05
ft3 per ft3 of filtrate. If the time for cleaning and reassembling is 30 min/cycle, the capacity of the press is
936 ft3/d
65
The equation: Vf2 = 22.5x103 (θf + 0.11) gives the relation between the filtrate volume and the operating time under pressure of a certain P and F filter press where Vf = ft3 of filtrate delivered in time θfhour.
If θc = 6 hours per cycle (dismantling. dumping and reassembling), and Vw = (1/16) Vf the total cycle time for maximum filtrate output during each 24 hr is
12 hours
66
A plate and frame filter press with 10 frames is used to filter a slurry at a constant pressure. Total filtration area is 75 ft2 and the filter delivers 400 lbs of filtrate in half an hour. If 10 more frames are added to the filter press, while other conditions remain the same, the time produce 400 lb of filtrate, assuming Rm = 0, is
7.5 min
67
A slurry of CaCO3 is filtered in a plate and frame filter press with a total area of 86.1 ft2, and operated at constant pressure drop of 2 atm. The mass of dry cake collected is 742 lbs and the volume collected is 68.1 ft3. The following data have been determined for the said slurry.
Viscosity = 0.982 cP
Specific cake resistance = 1.27 x1011ft/lb
Resistance due to the filter medium = 1.55x1010/ft
Calculate the filtration time in minutes.
36
68
Filter aid is used
to increase the porosity of the cake
69
The porosity of a compressible cake is
minimum at the filter medium
70
Which of the following may prove unsuitable for filtering volatile liquids?
vacuum filter
71
The constant pressure (38.7 psia) filtration equation for a filtration system is
t / V = 9.05 x10-5 V + 0.01, sec/L
If the slurry is filtered at constant rate of 10 L/s, how long will it take to reach 50 psi filtration pressure.
132 s
72
The PV relationship for slurry filtering at constant rate of 0.2 ft3 of filtrate per s is P = 16300 V + 220
where P is filtration pressure in psf and V = filtrate in ft3 If the slurry is filtered at constant pressure filtration of 20 psi, how long will it take to filter 10 ft3 of filtrate. Assume the cake is incompressible.
24 min
73
In the filtration of a sludge, the initial period is effected at a constant rate with the feed pump at full capacity until the pressure differential reaches 400 kPa. The pressure is then maintained at this value for a remainder of filtration. The constant rate operation requires 900 seconds and 1/3 of the total filtrate is obtained during this period. No washing of the cycle is done. If the time for removing the cake and reassembling the press is 1200 seconds determine the total time per cycle.
5700 s
74
A rotary drum filter with 35% of its filtering area submerged in the slurry, turns at 0.5 rpm. The filtrate production is 0.61 cubic meter per min per square meter of filtering area submerged when filtering lime
slurry. Average production is 20.4 cubic meters of filtrate per hour. The estimated area of the filter cloth in square meter is
1.6
75
Solid particles having a size of 0.12 mm, a shape factor of 0.88, and a density of 1000 kg/m3 are to be fluidized using air at 2 atm and 250C. The voidage at minimum fluidizing conditions is 0.42.
If the cross section of the empty bed is 0.30 m2 and the bed contains 300 kg of solid, calculate the minimum height of the fluidized bed.
1.72 m
76
Solid particles having a size of 0.12 mm, a shape factor of 0.88, and a density of 1000 kg/m3 are to be fluidized using air at 2 atm and 250C. The voidage at minimum fluidizing conditions is 0.42.
Calculate the pressure drop at the minimum fluidizing conditions.
0.098 x105 Pa
77
Solid particles having a size of 0.12 mm, a shape factor of 0.88, and a density of 1000 kg/m3 are to be fluidized using air at 2 atm and 250C. The voidage at minimum fluidizing conditions is 0.42.
Calculate minimum velocity for fluidization.
0.005 m/s
78
To clean a sand bed filter, it is fluidized at minimum conditions using water at 240C. The round sand particles have a density of 2550 kg/m3 and an average size of 0.40 mm. sphericity = 0.86 and ε=0.42.
If the bed diameter is 0.4 m and the desired height of the bed at these minimum fluidizing conditions is 1.75 m. Calculate the amount of solids needed.
325.25 kg
79
To clean a sand bed filter, it is fluidized at minimum conditions using water at 240C. The round sand particles have a density of 2550 kg/m3 and an average size of 0.40 mm. sphericity = 0.86 and ε=0.42.
What is the pressure drop (kpa) at this condition?
15.4
80
To clean a sand bed filter, it is fluidized at minimum conditions using water at 240C. The round sand particles have a density of 2550 kg/m3 and an average size of 0.40 mm. sphericity = 0.86 and ε=0.42.
What is the minimum velocity for fluidization?
0.0016
81
Given xF=0.36, xP=0.89 and xR=0.03, find the effectiveness of the screen
88.6%
82
Two centrifuges rotate at the same peripheral velocity of 53.34 m/s. The first bowl has a radius of r1=76.2 mm and the second r2=305 mm. Calculate the rev/min and the centrifugal forces developed in each bowl.
N1=6684 rpm, N2=1670, F1=3806g, F2=951g
83
Sphericity for octahedron is
0.85
84
A material consisting originally of 1.1640 mm particles is crushed to an average size of 0.2588 mm and requires 22.08 kJ/kg of energy for this size reduction. What will be the consumption of energy needed to crush the same material of an average size 1.872 mm to an average size of 0.7282 mm using Rittinger's law.
6.17 kJ/kg
85
A material consisting originally of 1.1640 mm particles is crushed to an average size of 0.2588 mm and requires 22.08 kJ/kg of energy for this size reduction. What will be the consumption of energy needed to crush the same material of an average size 1.872 mm to an average size of 0.7282 mm using Bond's law.
9.37 kJ/kg
86
A material consisting originally of 1.1640 mm particles is crushed to an average size of 0.2588 mm and requires 22.08 kJ/kg of energy for this size reduction. What will be the consumption of energy needed to crush the same material of an average size 1.872 mm to an average size of 0.7282 mm using Kick's law.
13.89 kJ/kg
87
A glass sphere having a diameter of 1.554x10-4 m in water at 293.2 K and the slurry contains 60 wt% solids. The density of the glass spheres is 2467 kg/m3. The settling velocity of the glass sphere is m/s is
1.5x10-3
88
It is desired to crush 10 ton/h of iron ore hematite. The size of the feed is such that 80% passes a 3-in screen and 80% of the product is pass a 1/8 in screen. Calculate the gross power required.
18 kW
89
Aluminum sulfate rock is fed to a crusher reducing the average size from 369 mm to 2.48 mm at a rate of 76.4 tons/hr. The product
is then reduced further in a second crusher to 1.23 mm. If the work index is equal to 3.1, calculate the total power needed to crush
the rock from its initial size using Bond Law.
63 kW
90
A centrifuge bowl is spinning at a constant 2000 rpm. What radius bowl is needed a force of 455 g's?
0.1018 m
91
During constant rate filtration, 30 gallons of filtrate is collected in 20 minutes. If this is continued for 15 minutes, after which constant
pressure filtration follows for 30 minutes, determine the total volume of filtrate collected. Assume that the fictitious filtrate volume
due to filter medium is equal to 2.5 gallons.
87 gal
92
A volcano has erupted, spewing stones, steam, and ash several thousand feet into the atmosphere. After some time, the particles
begin to settle to the ground. Consider a nearly spherical ash particle of diameter 60 μm, falling in air whose temperature is –50 °C and whose pressure is 65 kPa. The density of the particle is 1,300 kg/m3. Estimate the terminal velocity (in m/s) of this particle at this altitude.
0.17 m/s
93
Drops of oil 15 microns in diameter are to be settled from their mixture with air. The specific gravity of the oil is 0.90, and the air is at 700F and 1 atm and a settling time of 1 min is available. How high should the chamber be to allow settling time of 1 min is available. How high should the chamber be to allow settling of these particles.
1.2 ft
94
A shaking screen has a capacity of 4 metric tons per sq. m-h-mm mesh size. If the feed to the 8-mesh size screen (aperture is 2.38 mm) is 100 metric tons per hour, the area of the screen in m2 is
10.5
95
A ball mill grinds plastics to make a very fine powder. At the present time, 10000 kg of powder are produced per day. You observe that the process (shown by the solid lines) is inefficient because 30% of the feed is not recovered as powder – it goes to waste. You make a proposal (designated by the dashed lines) to recycle the uncollected material back to the feed so that it can be re-milled. You plan to recycle 70% of the uncollected material back to the feed stream. If the feed costs $1.20/kg, how much money would
you save per day while producing 10000 kg of fine powder.
3600
96
A particle ‘A’ of diameter 10 microns settles in an oil of specific gravity 0.9 and viscosity 10 poise under Stokes law. A particle ‘B’ with diameter 20 microns settling in the same oil will have a settling velocity,
Four times as that of ‘A
97
The capacity of a Sharples centrifuge is estimated to be increase/decrease by _____ % if its speed is doubled and the cut size of the product is reduced by 30%
96%
98
A vacuum leaf filter gives a total value of 10 m3 of filtrate of 30 minutes. If the resistance of filter cloth is negligible, the time taken for the collection of 40 m3 of filtrate is minutes
480
99
Granular feldspar is produced by beneficiation of high alumina river sand. After screening, drying and magnetic separation, the recovery is only 21%. The screen analysis of this product on a dry basis as shown:
In a specific application, this product must be reprocessed to remove all the grains finer than 100 mesh where 2 MT reprocessed product is required. The MT of river sand with 10% moisture that would have to be beneficiated is
12.2 MT
100
The power drawn for grinding mill can be calculated from the empirical formula:
Hp = 1.341 Wb {D0.4 CS (0.0616-0.000575Vp) – 0.1(2)[ (Cs-60)/10 ] – 1}
where:
Hp = required horsepower
Wb = weight of the ball charge in tons
D = inside mill diameter in ft
Cs = percentage of critical speed at which the mill is operated
Vp = percentage of mill occupied by balls
A ball mill with an inside diameter of 12 ft is charged with 129 tons of balls that have a maximum diameter of 3 in and occupy 46.3%
of the mill volume. The mill is operated wet at 62.4% of critical speed. The horsepower needed to drive the mill at this percentage
of critical speed is
1010 hP
101
A screen is used to separate the product from the oversize. The feed rate is 10 kg/hr with 30% of the desired product. 80% of the desired product is recovered in the 6 kg/hr product stream. Determine the effectiveness of the screen.
39%
102
The mesh number of this 40 mm x 40 mm (approx.) wire cloth is ____
9
103
A screening operation involved a feed containing 10% 1-mm spheres and 90% 2-mm spheres, If 6/7 of the 1-mm spheres ended up in the underflow while ¾ of the 2 mm spheres ended up in the overflow, then the screen effectiveness is
64%
104
Which is the driving force behind free falling body?
gravitational force
105
Which of the following types of filter are made to operate continuously?
rotary drum
106
It is the separation of fluid-solid mixture involving the passage of most of the fluid through a porous barrier which retains most of the solid particles contained in the mixture
filtration
107
The filtration of certain sludge is carried out in a plate and frame filter press with 40 frames and dimensions of 3 ft x 3 ft x 1 inch thick. The volume of cake collected is 8% of the filtrate volume. Filtering time is 4 hrs and washing time is 8 hrs. If both filtration and washing are done at the same pressure, what is the volume of the wash water used in cubic feet?
94 cu ft
