Screw press and its performance

Pragati SinghamM.Tech (FPEM)

CONTENTS

• Introduction• Types • Construction & working• Principle • Performance(design)• References

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”

TYPES OF SCREW PRESS

Horizontal screw press

Huber inclined screw press

CONSTRUCTION & WORKING

PRINCIPLE

• It works on the principle of ‘compression and shear’.

Compression ratio = volume displaced per revolution at the feed end volume displaced per revolution at discharge end

Compression curve

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

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

PERFORMANCE OF SCREW PRESS

• Design a screw press whose specifications are-Ds = 100 mm, ds = 50 mm, Ps = 50mm

Ns = 90.63 rpm, Φ = 0.8, Ρ = 740kg/m3

δ0 = 200 N/m2, T = 928.571 Nm, Dm = 75 mm

µ = 0.15 , θn = 150, θ = 30

h = 5mm, n = 9, Qv = 1.281m3 / hr ls = 500 mm , g = 9.81 m/s, F = 0.4

1. Diameter of shaft = 16 x 928.571 = 44.407mm 0.27 x 3.14 x 200

2. Load lifted by screw (We) = tan-1 (tan150 . Cos 30)

=14.980

= 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 = 10602.88 mm2

= 72.88 x 1000 = 6.87 N/mm2

10602.88

Capacity (Qe)

= 60 x 3.14/4 (100)2 - (50)2 x 50 x 90.63 x 0.8 x 740 = 948.249 kg/hr

Power requirement(Pe)

= 4.5 x 1.281 x 500 x 740 x 9.81 x 0.4 = 8.369KW

YIELD , EFFICIENCY, EXTRACTION LOSS

• Oil yield (OY) =

• Oil efficiency (OE) =

• Extraction loss (EL) =

• 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.

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) = 100 g

Amt. of oil present(x) = 0.40 Amt. of oil extracted(WOE) = 4.2 g

Oil efficiency (Oy) =

= 100 x 4.2 % 0.4 x 100 = 10.5 %

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 = 100kgExpected yield = 38 kgOil extracted = 3.7 – (3.7 of 5%) = 3.7- 0.185 = 3.515kgEffectiveness = calculated yield x 100 Expected yield = 3.515 x 100 38 = 9.25 %

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.htm

THANK YOU