1.
Screw press and its performance
Pragati Singham
M.Tech (FPEM)
2.
CONTENTS
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•
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Introduction
Types
Construction & working
Principle
Performance(design)
References
3.
INTRODUCTION
• It is the simplest machine for separation of solids and liquids.
• It is a cage style press.
• It is used for separation of –
– Oils from various oilseeds
– Fruit juices
• Screw pressing is a continuous operation, hence these are
also known as “expellers”
6.
PRINCIPLE
• It works on the principle of ‘compression and shear’.
Compression curve
Compression ratio = volume displaced per revolution at the feed end
volume displaced per revolution at discharge end
7.
DESIGN OF SCREW PRESS
•
Diameter of shaft (ds)
where,
T = torque transmitted by shaft
δ0 = yield stress
•
Load lifted by screw (We)
where, Dm = mean thread diameter
T = torque transmitted by shaft
µ = coefficient of friction
α = tapering angle
θn = thread (lift) angle
•
Pressure developed by screw thread (Pr)
where, Ap = pressing area
h = screw depth at max. pressure
area (discharge end)
n = no. of threads
Hall et al., 1961
8.
Capacity (Qe)
where, Ds = diameter of the screw thread
ds = base diameter of the screw shaft
Ps = screw pitch,
Ns = rotational speed of the screw shaft
φ = filling factor,
ρ = bulk density
Power requirement(Pe)
where, Qv = volumetric capacity of the screw shaft
ls = length of screw shaft
g = acceleration due to gravity
F = material factor
Hall et al., 1961
9.
PERFORMANCE OF SCREW PRESS
• Design a screw press whose specifications areDs = 100 mm,
Ns = 90.63 rpm,
δ0 = 200 N/m2,
µ = 0.15 ,
h = 5mm,
ls = 500 mm ,
1.
ds = 50 mm,
Φ = 0.8,
T = 928.571 Nm,
θn = 150,
n = 9,
g = 9.81 m/s,
Diameter of shaft
2. Load lifted by screw (We)
Ps = 50mm
Ρ = 740kg/m3
Dm = 75 mm
θ = 30
Qv = 1.281m3 / hr
F = 0.4
= 16 x 928.571 = 44.407mm
0.27 x 3.14 x 200
= tan-1 (tan150 . Cos 30)
=14.980
10.
= 928.571 x 75/2 tan30 + 0.15
(1-0.15 tan 30 cos 14.980)
=72.88KW
Pressure developed by screw thread (Pr)
= 3.14 x 75 x 9 x 5
= 72.88 x 1000
10602.88
Capacity (Qe)
740
= 10602.88 mm2
= 6.87 N/mm2
= 60 x 3.14/4 (100)2 - (50)2 x 50 x 90.63 x 0.8 x
= 948.249 kg/hr
Power requirement(Pe)
= 4.5 x 1.281 x 500 x 740 x 9.81 x 0.4
= 8.369KW
11.
YIELD , EFFICIENCY, EXTRACTION LOSS
• Oil yield (OY) =
• Oil efficiency (OE) =
• Extraction loss (EL) =
•
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•
where,
OE = % extraction efficiency
OY = % oil yield
EL = % extraction loss
WOE = weights of oil extracted(g)
WRC = residual cake (g)
WFS = feed sample (g)
x
= oil content of seed in decimal.
12.
1. NUMERICAL
• Soybean seeds contain 40% oil on weight basis and 4.2 g of oil is
extracted by screw press from 100 g of soybean seeds. Calculate
the oil efficiency of the soybean seeds.
weight of soybean(WFS)
Amt. of oil present(x)
Amt. of oil extracted(WOE)
Oil efficiency (Oy)
= 100 g
= 0.40
= 4.2 g
=
= 100 x 4.2 %
0.4 x 100
= 10.5 %
13.
2. NUMERICAL
•
Calculate the effectiveness of an screw press, which yields 3.7 kg oil containing 5%
impurities from 100 kg mustard seeds. The oil content of the mustard seeds is
38%.
Weight of mustard seeds
Expected yield
Oil extracted
Effectiveness
= 100kg
= 38 kg
= 3.7 – (3.7 of 5%)
= 3.7- 0.185
= 3.515kg
= calculated yield x 100
Expected yield
= 3.515 x 100
38
= 9.25 %
14.
REFERENCES
• Deli, S., Farah Masturah, M., Tajul Aris, Y. and Wan Nadiah, W. A.
The Effects of physical parameters of the screw press oil expeller on
oil yield from Nigella sativa L seeds. International Food Research
Journal 18(4): 1367-1373 (2011)
• Hall, A. S., Holowenko, A. E., & Laughlin, H. G. (2002). Schaum’s
outline series theory and problems of machine design. (1st ed.).
New York: McGraw-Hill Companies, Inc., (Chapter 12).
• Handbook of Food Processing Equipment by Geōrgios D.
Sarabakos, Athanasios E. Kosaropoulos
• http://www.reinartz.de/index.php?id=27&L=1
• http://www.fao.org/docrep/t0532e/t0532e04.ht
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