GB2046610A - Centrifuge - Google Patents

Abstract

A centrifuge capable of being continuously operated and being suitable for centrifuging sugar, of the kind comprising an upwardly divergent conical cage 1 rotatable about a vertical axis and located within a cylindrical housing 2 provided with a cover 17. A jacket 7 defines and separates two compartments 8, 9 in the housing, compartment 9 receiving, in use, the solid products of centrifuging and compartment 8 receiving the fluid products. A first baffle ring 5, a baffle wall 3 and a ring conduit 6 for directing liquid and/or steam or vapour against the first baffle 3 are utilised when the centrifuge is operated in a mashing mode. In a dissolution mode there is utilised a cylindrical second baffle 16 detachably mounted on the centrifuge cover 17, and a second ring conduit 18 for directing liquid and/or steam or vapour against the second baffle 16. <IMAGE>

Description

SPECIFICATION Centrifuge The present invention relates to a centrifuge which is capable of being operated continuously.

iCentrifuges of this general type are known. They are used in the sugar industry for the purpose of centrifuging sugar filler, expecially intermediatefil- less and final product filler. It is also known to subject the sugar crystals thus obtained, whilst still within the centrifuge, or immediately thereafter, to a mashing or re-dissolving operation.

For the mashing treatment, it is desirable to ensure that the crystals thrown out by the centrifuge cage are substantially decelerated before impacting the internal surface of the housing. Accordingly, centrifuges used for this purpose have a relatively large spacing between the rim of the centrifuge cage and the internal surface of the housing. The impact force is frequently additionally moderated by the use of a baffle having a suitable configuration.

On the other hand, in a re-dissolving operation, the crystals must be pulverized by impact against the baffle. To achieve this, centrifuges are used which have a relatively small spacing between the rim of the centrifuge cage and the baffle.

For both the mashing and for the re-dissolving operations, it is important that the ground mass or the solution is obtained free from lumps and preferably of uniform consistency. To fulfil these requirements, prior art centrifuges are generally suitable only for mashing or re-dissolving operations, but not both. Moreover, difficulties arise when a breakdown occurs.

The present invention seeks to provide a cen trifugewhich, merely by effecting minor modifications thereto may be used for centrifuging different materials and which is particularly suitable for both mashing and re-dissolving sugar.

According to the present invention, there is provided a centrifuge capable of being continuously operated and being suitable for centrifuging sugar, the centrifuge comprising an upwardly, outwardly conical cage, said cage being rotatable about a vertical axis, the cage being located within a cylindircal housing, provided with a cover, a base being formed within the housing, a vertically extending jacket surrounding the cage being provided within the housing so as to define and separate two compartments in the housing, one compartment receiving, in use, the solid products of centrifuging and the other compartment receiving the fluid products, the upper portion of the internal wall of the housing acting as a baffle wall and means for supplying liquid and/or steam orvapourto the interior of the housing wherein a first inwardly directed baffle ring defining the lower edge of the baffle wall is formed on the internal surface of the housing slightly below the level of the edge of the centrifuge cage, a ring conduit having apertures formed therein for directing liquid and/or steam or vapour against the first baffle being provided between the first baffle ring and the cover in the region of the cover, a cylindrical second baffle extending to below the level of the rim of the centrifuge cage being mounted on the internal surface of the cover but being detachable therefrom to provide a different mode of operation of the centrifuge, a second ring conduit being provided internally of the second baffle, said second ring conduit having apertures formed therein for directing liquid and/or steam of vapour against the second baffle.

Only a minor modification is necessary to adapt the centrifuge for use as in mashing sugar. A centrifuge according to the invention is suitable for redissolving sugar. If it is to be used for mashing sugar it is merely necessary for the second baffle and its associated ring conduit to be removed by, for example, slackening its retaining screws.

Improved mixing may be achieved if the first baffle ring extends substantially at right angles to the first baffle and has a width of between 10 and 100 mm, preferably between 15 and 35 mm.

Preferably, the base of the housing, at least in the outer of the two compartments defined by the jacket is inclined, two outlets located one above the other being formed in the region of the lowermost point of the outer compartment, a siphon plate extending between the two outlets and being open at both its upper and lower edges, the plate extending to at least the centre of the upper output such that an outflow passage is defined between the plate and the internal wall surface of the housing.

if the centrifuge is used for mashing, the upper outlet is closed and the product extracted through the lower outlet. In a dissolution operation, however, the lower outlet is closed and the solution is diverted along the outflow passage thus defined to be discharged through the upper outlet. Should the outflow passage become blocked, for example, due to the deposition of crystals, the solution can be banked up in the outer compartment until it reaches the upper edge of the siphon plate. Any overflow in the outer compartment can thus be prevented.

The re-dissolution operation may be further improved if a heating device is provided in the outer compartment.

Advantageously, the heating device comprises a ring conduit for carrying a heating fluid, which conduit is located adjacent the base of the outer compartment and has apertures formed therein through which the heating fluid is emitted, such fluid being emittedsubstantially in the direction of the longitud final extension of the ring conduit. It is thus possible to produce a flow in the outer compartment which is in the same direction as the direction of rotation of the centrifuge cage. Heating and movement both contribute towards an increase in the effeciency of dissolution.

It has been found particularly desirable if the second baffle is defined at its lower end by an inwardly directed second baffle ring extending substantially at right angles thereto, the width of the second baffle ring being less than 150 mm, preferably less than 20 mm.

The invention will be further described, by way of example, with reference to the accompanying drawings, in which: Fig. 1 is a section through a centrifuge in accordance with the invention, for mashing sugar filler; and Fig. 2 is a section through a centrifuge in accordance with the invention suitable for re-dissolving sugar crystals.

The centrifuge shown in Fig. 1 comprises a conical, upwardly divergent centrifuge cage 1 rotatable about a vertical axis and which is motor driven. The cage 1, together with the other components of the centrifuge is located within a housing 2. The upper portion 3 of the housing 2 acts as a first baffle for sugar spun off the edge 4 of the centrifuge cage.

Slightly below the level of the edge 4, a dust shield 5 in the form of a continuous ring is secured to the housing 2. This shield 5 seals the lower end of the first baffle 3. A ring conduit 6 is located above the shield 5, the conduit 6 having apertures formed therein which directs the emitted liquid against the first baffle 3 and/or against the sugar which is flying about when the centrifuge is operating. The first dust shield 5 is located between 10 and 30 mm below the edge 4 and has a width extending at right angles to the baffle of 30 mm.

Within the housing 3 an intermediate jacket 7 is provided which defines and separates two compartments 8, 9, for the discharge of the sugar, from one another. The floor 10 of the outer compartment 9 is inclined. In the region of the lowermost point of the outer compartment 9 outlets 11, 12 are arranged one above the other. Between the two outlets 11, 12 a siphon plate 13 is provided. The siphon plate 13 is open at both its upper and lower ends and between the plate 13 and the internal surface of the housing 2 there is thus defined an upwardly, outwardly widening discharge passage. The outlet 12 is closed in this use of the centrifuge. Within the outer compartment 9, a heating device is installed.The heating device includes a ring conduit 14 having apertures formed therein through which a heating fluid, usually steam or vapour, may be emitted substantially in the direction of the longitudinal extension of the ring conduit 14, that is to say, substantially tangentially. The ring conduit 14 is not used in this use of the centrifuge.

The operation of such a centrifuge will now be described. Firstly, the sugar filler is supplied to the central region of the centrifuge. The filler arrives in the centrifuge cage I wherein it separates into sugar and a discharge. The discharge is extracted through the conduit 15. The sugar spun off by the rim 4 of the centrifuge flies freely within the housing 2 until it strikes against the first baffle 3 from whence it is washed by the mashing liquid. The mixture of mashing liquid, preferably a syrup of higher purity than the outlet/run-off, and sugar then runs over the ring or shield 5 along the internal wall surface of the housing 2, to be gathered and discharged through the outlet 11.

The quantity of mashing liquid for the centrifuge is controlled by a suitable regulator so that the ratio of the quantity of liquid to the quantity of spun-off sugar remains substantially constant. This measure ensures that the mixture of sugar and syrup discharged is of substantially uniform consistency and is hence readily further processable, i.e. is more centrifugable.

Figure 2 shows a sectional view of a second centrifuge in accordance with the present invention.

Such a centrifuge may be used for the re-dissolution of sugar crystals. The centrifuge shown in Fig. 2 is similar to that shown in Fig. 1. The major differiences lie in the selection of the inlet connections for the dissolution liquids and for the heating fluid, in the selection of the outlet 11 or 12 and in that an interchangeable second baffle 16 is installed on a cover 17 for the housing 2. In the region of the cover, inwardly of the second baffle 16, a ring conduit 18 for the dissolution liquid is provided. The baffle 16 and the ring conduit 18 are each secured to the cover 17, but are removable therefrom so as to be replaceable.

The cover 17 may be hingedly mounted on the housing 2. The ring conduit 18 has apertures formed therein through which the dissolution liquid, usually water or an unsaturated sugar solution, is directed against the second baffle 16 and/or against the sugar which is flying free whilst the centrifuge is in operation. The second baffle 16 extends below the level of the edge 4 of the centrifuge cage 1 by substantially 40 mm. Between the baffle 16 and the jacket 7, a second baffle ring 19 extending at right angles to the baffle 16 is provided. This ring 19 is narrow and may have a width of 5 mm.

The operation of such a centrifuge will now be described. A mixture consisting of, for example, sugar and liquid arriving from a mashing-in centrifuge is supplied to the central region of the dissolution centrifuge and is separated into discharge and sugar. This discharge is extracted through the conduit 15. The sugar spun off by the edge 4 flies freely, but for only a short distance, until it strikes against the second baffle 16. Due to its high impact velocity, a high percentage of grain destruction occurs. The sugar is then rinsed off the baffle 16 by means of a dissolution liquid discharged from the ring conduit 18. The mixture of water and sugar runs over the second baffle ring 19, drips downwardly and is collected in the outer compartment 9. Steam is emitted in a tangential direction from the ring conduit 14 for heating fluid and assists in causing the mixture to flow annularly. Because of the heating and the annular flow, the sugar becomes substantially completely dissolved. The solution is extracted at the lowermost point of the outer compartment through the otlet 12 due to the action of the siphon plate 13. The outlet 11 is closed in this use of the centrifuge.

The quantity of dissolution liquid is automatically controlled in the same manner as the quantity of mashing liquid in the mashing centrifuge.

It has been proved desirable, particularly for reasons of optimum space utilisation, to arrange a mashing centrifuge immediately above a dissolution centrifuge, the centrifuges being mounted on a turret-like frame. Thus, the magma or mixture arriving from the mashing centrifuge is discharged directly into the dissolution centrifuge.

Claims (9)

1. A centrifuge capable of being continuously operated and being suitable for centrifuging sugar, the centrifuge comprising an upwardly, outwardly conical cage, said cage being rotatable about a verti cal axis, the cage being located within a cylindrical housing provided with a cover, a base being formed within the housing, a vertically extending jacket sur rounding the cage being provided within the hous ing so as to define and separate two compartments ip the housing, one compartment receiving, in use, the solid products of centrifuging and the other compartment receiving the fluid products, the upper portion of the internal wall of the housing acting as a baffle wall and means for supplying liquid and/or steam orvapourto the interior of the housing wherein a first inwardly directed baffle ring defining the lower edge of the baffle wall is formed on the internal surface of the housing slightly below the level of the edge of the centrifuge cage, a ring con duit having apertures formed therein for directing liquid and/or steam or vapour against the first baffle being provided between the first baffle ring and the cover in the region of the cover, a cylindrical second baffle extending below the level of the rim of the centrifuge cage being mounted on the internal sur face of the cover but being detachable therefrom to provide a different mode of operation of the cen trifuge, a second ring conduit being provided inter nally of the second baffle, said second ring conduit having apertures formed therein for directing liquid and/or steam or vapour against the second baffle.

2. A centrifuge as claimed in claim 1 wherein the first baffle ring extends substantially at right angles to the first baffle and has a width of between 10 and 100mm.

3. A centrifuge as claimed in claim 2 wherein the width of the first baffle ring is between 15 and 35 mm.

4. A centrifuge as claimed in any one of claims 1 to 3 wherein the base of the housing, at least in the outer of the two compartments defined by the jacket is inclined, two outlets located one above the other being formed in the region of the lowermost point of the outer compartment, a siphon plate extending between the two outlets and being open at both its upper and lower edges, the plate extending to at least the centre of the upper outlet such that an out flow passage is defined between the plate and the internal wall surface of the housing.

5. A centrifuge as claimed in any preceding claim wherein a heating device is provided within the outer compartment.

6. A centrifuge as claimed in claim 5 wherein the heating device comprises a ring conduit for carrying a heating fluid, which conduit is located adjacent the base of the outer compartment and has apertures formed therein through which the heating fluid is emitted, such fluid being emitted substantially in the direction of the longitudinal extension of the ring conduit.

7. A centrifuge as claimed in any preceding claim wherein the second baffle is defined at its lower end by an inwardly directed, second baffle ring extend ing substantially at right angles thereto, the width of the second baffle ring being less than 150 mm.

8. A centrifuge as claimed in claim 7 wherein the width of the second baffle ring is less than 20 mm.

9. A centrifuge constructed and arranged to operate substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.