Mechanical Operations
SCREEN EFFICIENCY
AIM: -
To determine the efficiency of screen.
APPARATUS: -
Standard screen series, weighing machine, vibrator, sand sample etc.
THEORY: -
The effectiveness of screen is often called as an efficiency of screen. It is measure
of success in closely separating material A and B. If screen functioned perfectly
all the material A would be in overflow/oversize and material B would be in
underflow/undersize. Screen effectiveness can be calculated by applying simple
material balance over a screen which is useful in calculating the ratio of feed,
oversize and undersize from screen analysis of stream.
Let,
F = mass flow rate of feed
D = mass flow rate of overflow
B = mass flow rate of underflow
Let XF, XD and XB be the mass fraction of material A, in feed, overflow and
underflow respectively.
1-XF, 1- XD and 1- XB are the mass fraction of material B in feed, overflow and
underflow.
Department of Chemical Engg. DYPCET
Mechanical Operations
The screen efficiency is given by,
E = [(XF-XB) (XD-XF) XD (1-XB)] / [(XD-XB) 2 XF (1-XF)]
PROCEDURE: -
1) A set of standard screen are arranged in such a way that, the coarse screen is at
top and finest is at bottom.
2) Place the sample of 1 Kg sand at the top of screen and carry out sieve analysis.
Weight the material retained on each screen.
3) Mix the same material.
4) Take an intermediate screen which is used for separation of total feed into
oversize and undersize. Weight the oversize & undersize material.
5) Carry out separate sieve analysis for oversize and undersize.
GRAPH:-
Plot a Graph of Cumulative mass fraction Vs Dpi
RESULT: -
The efficiency of screen is
1) From calculation = …………. %
2) From graph = ………..%
Applications of Screening: -
Department of Chemical Engg. DYPCET
Mechanical Operations
DIAGRAM:
OBSERVATIONS: -
1) weight of sample (sand) = 1000 gm
2) weight of oversize material = gm
3) weight of undersize material = gm
Department of Chemical Engg. DYPCET
Mechanical Operations
OBSERVATION TABLE: -
A] For Feed:
Sr. Screen opening in Mass retained in Differential Comm. Mass
No. mm gm Mass fraction fraction
( Dpi ) ( Xi)
1
2
3
4
5
6
7
8
9
Total =
Department of Chemical Engg. DYPCET
Mechanical Operations
B] For Oversize:
Sr. Screen opening in Mass retained in Differential Comm. Mass
No. mm gm Mass fraction fraction
( Dpi ) (Xi)
1
2
3
4
5
6
7
8
9
Total :
C] For Undersize:
Sr. Screen opening in Mass retained in Differential Comm. Mass
No. mm gm Mass fraction fraction
( Dpi ) (Xi)
1
2
3
4
5
6
7
8
9
Total :
Department of Chemical Engg. DYPCET
Mechanical Operations
CALCULATIONS:
Screen efficiency = E = [(XF-XB) (XD-XF) XD (1-XB)] / [(XD-XB) 2 XF (1-XF)]
Where,
XF =
XB =
XD =
E= × 100
= % (By calculation)
By graph,
XF =
XB =
XD =
E= × 100
= % (By graph)
Department of Chemical Engg. DYPCET
