WO2001030182A1

WO2001030182A1 - Method and device for washing and peeling roots rich in starch

Info

Publication number: WO2001030182A1
Application number: PCT/SE2000/001959
Authority: WO
Inventors: Gösta Larsson; Jörgen LARSSON
Original assignee: Gösta Larssons Mekaniska Verkstad Ab
Priority date: 1999-10-28
Filing date: 2000-10-11
Publication date: 2001-05-03
Also published as: SE9903878L; AU1181701A; SE9903878D0

Abstract

In a method of washing and peeling roots rich in starch for the manufacture or starch, use is made of a drum (1), which has a perforated jacket and is provided with internal entraining means (26). The roots (27) are placed in the drum (1), which is rotated about its longitudinal axis. The roots (27) are made to rub against each other with the aid of the entraining means (26) while at the same time water is poured over them during rotation of the drum (1). The drum (1) has at least at one of its ends an end portion (3) which has a smaller diameter than the rest of the drum.

Description

METHOD AND DEVICE FOR WASHING AND PEELING ROOTS

RICH IN STARCH

The present invention relates to a method for washing roots rich in starch, such as tapioca, manioca and cassava roots, and removing an outer skin from the roots before using them as raw material for the manufacture of starch. The invention also relates to a device for carrying out the method.

Tapioca, manioca and cassava roots have an outer and an inner skin. The outer skin is thin and brownish and must therefore be removed for pure starch to be manufac- tured.

In a prior art method of washing and peeling roots of this kind, washing is carried out in a first step and peeling in a second step. In each of the steps, use is made of an elongate trough having a perforated bottom and, arranged in the trough, a shaft which is provided with paddles and extends along the trough. The roots are placed in the trough, and the shaft and, thus, the paddles are rotated to stir up the roots, the paddles rubbing against the roots to release earth from the roots in the first step and remove the outer skin from the roots in the second step. In the first step, in which earth is thus washed away from the roots, the trough is partly filled with water. In the second step, in which the outer skin is removed, the stirring operation by means of the paddles frequently takes place in an approximately dry state or semidry state. This contributes to the roots, especially in the second step, being exposed to a very rough treatment, which results in not only the outer skin but sometimes also the inner skin or parts thereof being removed from the roots and in many cases the roots being broken apart. This implies in turn that starch is washed away and small broken-away pieces of the roots are lost. As a result, the yield in the manufacture of starch from the washed and peeled roots is, of course, reduced.

An object of the present invention therefore is to provide a method and a device which make it possible to carry out the washing as well as the peeling of the roots in a manner that is considerably more lenient to the roots and, consequently, increase the starch yield.

According to the invention, this object is achieved by a method, which is of the type stated by way of intro- duction and which is characterised by the steps of placing the roots in a drum which has a perforated jacket and is provided with internal entraining means, rotating the drum, thereby making the roots rub against each other with the aid of the entraining means, and making the roots wet with water during rotation of the drum.

Use is preferably made of a drum which is open at both ends, the roots being supplied continuously into the drum at one end thereof and being discharged continuously from the drum at the other end thereof . During rotation of the drum, the roots are made wet with water, preferably by water being sprayed over the roots inside the drum and/or by the drum being made to rotate while being immersed a distance in water.

Before placing the roots in the drum, they are pref- erably wetted either by spraying water over them or by soaking them in water.

According to the invention, the above object is also achieved by a device, which comprises a drum which is open at both ends and rotatable about its longitudinal axis, the drum having a perforated jacket and being provided with internal entraining means, the drum having at least at one of its ends an end portion which has a smaller diameter than the rest of the drum.

The entraining means preferably consist of axially extending ribs, which are essentially uniformly distributed along the circumference of the drum jacket. The invention will now be described in more detail with reference to the accompanying drawings, in which

Fig. 1 is a side view of an embodiment of a device according to the invention, Fig. 2 is an end view in the direction of arrow II in Fig. 1 and shows the device in Fig. 1,

Fig. 3 is an axial longitudinal section of a drum included in the device according to Figs 1 and 2 , and

Fig. 4 is a cross-sectional view of the drum along line IV- IV in Fig. 3.

The device shown in the drawings comprises a drum 1 which is arranged essentially horizontally and made of sheet metal, the jacket of the drum having perforations (not shown) in the form of apertures or slots. The drum 1 has at one end a supply portion 2 and at its other end a discharge portion 3. The portions 2 and 3 have, like the intermediate portion 4 of the drum 1, a circular- cylindrical form, the portions 2 and 3 having a smaller diameter than the intermediate portion 4. The supply portion 2 and the discharge portion 3 have the same diameter, which is at least about 100 mm smaller than the diameter of the intermediate portion 4, which in the shown example is about 1.5 m. The length of the drum 1 is in this case about 4 m. The drum is open at both ends. The drum 1 is suspended by means of two V-belts 5 and 6 extending round the supply portion 2, and two V- belts 7 and 8 extending round the discharge portion 3. The V-belts 5, 6, 7 and 8 each extend round a pulley 9, 10, 11 and 12, respectively, which is arranged above the drum 1. The pulleys 9, 10, 11 and 12 have the same diameter. The two pulleys 9 and 11 are non-rotatably connected to a rotary shaft 13, and the two pulleys 10 and 12, which in the direction of the discharge portion 3 are axially offset relative to the pulley 9 and 11, respec- tively, are non-rotatably connected to a rotary shaft 14. The shafts 13 and 14 extend in parallel with the drum 1. The shafts 13 and 14 are rotated by means of a motor 15, whose output shaft 16 supports two sprockets 17 and 18 of the same diameter, which are non-rotatably connected thereto. A chain 19 extends over the sprocket 17 and a sprocket 20 non-rotatably mounted on the shaft 13, and a chain 21 extends over the sprocket 18 and a sprocket 22 non-rotatably mounted on the shaft 14.

The centre distance between the shafts 13 and 14 is at least equal to the diameter of the supply or discharge portion 2, 3 minus the diameter of the pulley 9, 10, 11 or 12, which causes the drum 1 to be supported in a stable manner without oscillating. By the V-belts 5, 6, 7 and 8 extending round the portions 2 and 3 with a reduced diameter, the intermediate portion 4 of the drum 1 can be lowered a distance into a water bath 23 without the V- belts having to be lowered into the same (see Fig. 1) .

A water supply tube 24 extends essentially horizontally through the supply portion 2 of the drum 1 and along the drum in the upper portion thereof up to the discharge portion 3 of the drum. The tube 24 has a plu- rality of nozzles 25 which are uniformly distributed along the tube and adapted to spray water in the drum 1. The tube 4 is suspended outside the drum 1 and does not rotate therewith.

The drum 1 has internal entraining means 26 in the form of axially extending ribs, which are uniformly distributed along the circumference of the drum jacket and which in the shown embodiment are essentially triangular in cross-section.

The drum 1 is rotated by means of the motor 15 in the direction of arrow R in Fig. 4 at a maximum speed of about 25 rpm, and water is sprayed into the drum through the nozzles 25. Roots 27 rich in starch, such as tapioca, manioca and cassava roots, which are shown highly schematically in Figs 3 and 4, are supplied through the sup- ply portion 2 into the drum 1 preferably by means of a flow of water. The flow of water leaves the drum 1 through the perforations in the drum jacket. In the drum 1, the roots 27 are entrained with the aid of the entraining means 26 from the lower parts of the drum a distance upwards, as shown in Fig. 4, so as then to slide down towards the "bottom" of the drum 1. During this motion, the roots 27 are rubbed against each other, thereby removing impurities, such as dirt, from the roots and rubbing away the outer skin of the roots. The impurities and the outer skin are washed away by the water ejected from the nozzles 25 and the water from the water bath 23, which during rotation of the drum 1 trickles into and out of the drum through the perforations in the drum jacket, and are drawn off from the drum 1 through the perforations.

Preferably, both the supply and the discharge of roots 27 into and out of the drum 1 take place continuously. However, the roots 27 will have a sojourn time in the drum 1 which is sufficient for washing and peeling thanks to the fact that they are retained by the wall that exists in the transition between the intermediate portion 4 and the discharge portion 3 having a reduced diameter. A corresponding, braking diameter reduction can, of course, also be accomplished in some other way, for instance, by means of an internal transverse wall. In large plants, use can be made of a plurality of successively arranged devices according to the invention, in which case the roots 27 that are discharged from one device are supplied to and treated in a subsequent device etc .

As will be evident, the washing and peeling of the roots 27 in the inventive device take place in a very lenient manner without the inner skin of the roots being removed or the roots being broken apart . The treatment of the roots can be made still more lenient and be improved further by wetting the roots 27 before supplying them into the drum 1. By such wetting, which can occur by the roots being sprayed with water or soaked in water, the outer skin of the roots is made soft and the adherence to the inner shell decreases, which facilitates the peeling operation.

The device and the method described above can be modified in various ways within the scope of the appended claims. For instance, either the water bath 23 or the water supply tube 24 with the spray nozzles 25 can thus be omitted. The drum 1 can be made of a material other than sheet metal, such as wood laths, which define between them longitudinal slots which replace the above- mentioned perforations. The entraining means 26 may consist of other means than the ribs described above. In some cases, they may consist of the inside of the actual drum jacket when this causes sufficient friction to entrain the roots 27 a distance during the rotation of the drum 1, for instance when the drum 1 is made of wood laths .

Claims

1. A method of washing roots (27) rich in starch, such as tapioca, manioca and cassava roots, and removing an outer skin from the roots before using them as raw material for the manufacture of starch, c h a r a c t e r i s e d by the steps of placing the roots (27) in a drum (1) which has a perforated jacket and is provided with internal entraining means (26) , rotating the drum (1) , thereby making the roots (27) rub against each other with the aid of the entraining means (26) , and making the roots (27) wet with water during rotation of the drum (1) .

2. A method as claimed in claim 1, c h a r a c t e r i s e d by using a drum (1) which is open at both ends, and supplying the roots (27) continuously into the drum at one end (2) thereof and discharging the roots continuously from the drum at the other end (3) thereof.

3. A method as claimed in claim 1 or 2 , c h a r a c t e r i s e d by making, during rotation of the drum

(1) , the roots (27) wet with water, the water being sprayed over the roots inside the drum.

4. A method as claimed in any one of claims 1-3, c h a r a c t e r i s e d by making the roots (27) wet with water during rotation of the drum (1) by making the drum rotate while being immersed a distance in water (23)

5. A method as claimed in any one of claims 1-4, c h a r a c t e r i s e d by wetting the roots (27) before placing them in the drum (1) .

6. A method as claimed in claim 5, c h a r a c t e r i s e d by wetting the roots (27) by spraying water over them.

7. A method as claimed in claim 5, c h a r a c t e r i s e d by wetting the roots (27) by soaking them in water.

8. A device for carrying out the method according to any one of claims 1-7 for washing roots (27) rich in starch, such as tapioca, manioca and cassava roots, and removing an outer skin from the roots before using them as raw material for the manufacture of starch, c h a r a c t e r i s e d in that it comprises a drum (1) which is open at both ends and rotatable about its longitudinal axis, the drum having a perforated jacket and being provided with internal entraining means (26) , the drum (1) having at least at one of its ends an end portion (3) which has a smaller diameter than the rest of the drum.

9. A device as claimed in claim 8, c h a r a c t e r i s e d in that the entraining means (26) are axi- ally extending ribs which are essentially uniformly distributed along the circumference of the drum jacket.