GB2121670A

GB2121670A - Method and apparatus for separating the kernels of palm nuts

Info

Publication number: GB2121670A
Application number: GB08316501A
Authority: GB
Inventors: Claude Ausset; Jean-Louis Bouju
Original assignee: Fives Cail Babcock SA
Current assignee: Fives Cail Babcock SA
Priority date: 1982-06-18
Filing date: 1983-06-17
Publication date: 1984-01-04
Also published as: OA07467A; GB8316501D0; FR2528670A1; FR2528670B1; GB2121670B

Abstract

In order to improve the quality of the products obtained and to increase efficiency, a mixture of shells and kernels is formed into a first fluidised bed (26) by means of a rising air current whose speed is such that almost all of the shells are entrained by the said air current, the products entrained by the air current are separated therefrom in a separator (24) and are formed into a second fluidised bed (26') by means of a rising air current whose speed is lower than that of the fluidization air of the first bed 26 such that the products entrained by the air of the second bed is constituted almost exclusively by shells, and the portion of the said products not entrained by the fluidization air of the second bed (26') is returned to the first fluid bed (26). <IMAGE>

Description

SPECIFICATION Method and apparatus for separating the kernels of palm nuts The present invention relates to the separation of the (palm) kernels contained in the mixture of shells and kernels obtained after crushing of palm nuts. This operation takes place after the extraction of the fibre from the latter.

Up to now there has not been a satisfactory solution to the problem of recovering the kernals. Use is generally made of separation by dense liquor or by hydrocyclone, although these two methods have the drawback that they moisten the products and consequently increase to a considerable extent the power consumption for subsequent drying of the kernals. In addition, the separation is incomplete as there are a number of impurities in the mixture whose densities lie between those of the kernels and the shells and which cannot be completely eliminated.

Use has also been made, in small plants, of dry separation devices utilising the difference in aerodynamic resistance between the concave shells and the globular kernels by exposing the mixture to a rising air current, either in a vertical duct or on a jigging sieve.

In plants of the first type, the shell and kernel mixture is introduced laterally into the duct at a zero or negative vertical speed.

Under these conditions, the air current only entrains the shells which, on penetration into the duct, have their concave side facing downwardly. The shells which are in different positions and in particular those shells which have their edges facing the air current are not entrained and drop down with the kernels.

This drawback may be remedied in part by increasing the speed of the air current, but this leads to a considerable quantity of irregularly shaped or broken kernels being entrained with the shells. Separation is therefore unsatisfactory in all cases.

In plants of the second type, this drawback is remedied by mechanical shaking of the mixture which enables the majority of the shells to be brought into a postionconcave side facing downwardly-facilitating their entrainment by the air current. The drawback of this type of plant is that it requires equipment which is subject to wear and needs considerable maintenance which may not always be carried out with the means available at the place of use.

The object of the present invention is to provide a method and a plant for pneumatic separation having an increased efficiency with respect to known methods and apparatus and enabling products of improved quality to be obtained.

A first aspect of the invention provides a method for the automatic separation of the kernels from a shell and kernel mixture obtained after crushing palm nuts, which method comprises subjecting the mixture to a rising air current whose speed is selected such that it entrains shells without entraining a substantial amount of the kernels, the said mixture being maintained in a fluidised state above a permeable support by the said air current which is blown below the said support and which extracts the shells from the fluid ised bed and entrains them in its upward movement, the mean dwell time of the kernels in the fluidised bed being between 10 and 30 seconds.

A second aspect of the invention provides apparatus for separating kernels from a mixture of kernels and shells comprising a fluidisation device having a permeable support at a lower portion, means for blowing air upwardly through the support and an air outlet at an upper portion, adjustment means for adjusting the rates of supply and extraction of the products and adjustment means for adjusting for the rate of flow of the air blown under the said support.

The method of the invention is characterised in that the shell and kernel mixture to be separated is kept in the fluidized state, above a permeable support, by air current which is blown under the said support and which extracts the shell from the fluidised bed by entraining them in its upward movement, the mean dwell time of the kernels in the fluidised bed being between 10 and 30 seconds.

It has already been proposed to separate the products of a mixture penumatically by maintaining the mixture in the fluidized state by means of an air current which entrains a portion of the products from the bed. However, in all the known cases, this involved separating the products in accordance with their size or their density.

The invention is based on the fact that as the shells have acquired a certain speed in the direction of flow of the air current they continue to be entrained by this current even if their position changes during their displace ment. It is simply necessary therefore, during the period in which they are in the fluidised bed where they are agitated by the air cur rent, for the shells to assume a favourable positionconcave side facing downwardly at a given moment of time so that they may be extracted from the bed and entrained by the air current.

Passage into the fluidized state for several tens of seconds enables utilization, as a result of the mixing which it causes, of the differ ence between the apparent surface and the drag coefficient of the shells having a concave and irregular shape and the roughly spherical kernel. The shells are finally entrained by the air current despite their specific weight which is greater than that of the kernels.

In order to further improve separation, it is possible to form with the shell and kernel mixture to be sorted a first fluid bed by means of a rising air current whose speed is such that almost all of the shells are entrained from the bed by the said air current, to separate from this air current the products which it has entrained, to form a second fluid bed with these products by means of a rising air current whose speed is lower than that of the fluidization air of the first bed such that the portion of the said products entrained by the fluidization air of the second bed is constituted almost exclusively by shells and to return the portion of the said products not entrained by the air to the first fluid bed.

Separation is carried out continuously, the shell and kernel mixture to be sorted being introduced into the fluid bed from which the products not entrained by the air and constituted essentially by kernels are removed in a continuous manner either by overflow methods or by drawing off at the base of the bed. The speed of the air current and the dwell time of the products in the fluid bed are selected such that the kernels separated in this way contain few impurities. The dwell time may be modified by adjusting the height of the overflow threshold or by adjusting the drawing off and/or supply flow.

The invention will be further described by way of example with reference to the accompanying drawing which shows diagrammatically an apparatus according to the invention.

The plant shown in diagram form in the single Figure comprises two fluidization devices 10 and 10' each constituted by a cylindrical container which is closed and disposed in a vertical manner. A permeable support 12, 12', such as a grille, a perforated plate etc., is disposed with a small spacing at the base of the device and the space provided between this support and the base is connected to the delivery output of a fan or compressor 14, 14'.

Each device 10, 10' is provided with a supply apparatus 16, 16' constituted by a hopper and an endless screw enabling the products to be sorted to be supplied to the device whilst avoiding the air outlets. The device 1 6 enables the supply flow to be controlled.

Opposite the supply device there is provided a removal chute 18, 18' provided with a rotary screen 20, 20' enabling the flow of products extracted to be controlled.

A duct 22, 22' connected to the top of each device enables discharge of the air and the products entrained with it. A separator device 24, 24' such as a cyclone is located on this duct and enables the separation of the products entrained with the air current. The outlet of the separator 24 is connected to the supply device 16' of the device 10'.

This plant is designed to operate continuously. On starting of the plant, the shell and kernel mixture to be sorted is introduced at A into the apparatus 10 by means of the supply device 1 6 and the air is blown below the permeable support 1 2 by means of the fan 14 in order to keep the products in the fluidized state. The screen 20 remains closed until the bed 26 of fluidized products has reached a predetermined level. It is then caused to rotate in order to extract the products remaining in the bed from the device and the flow of products extracted is controlled such that the bed is maintained at this predetermined level.

The speed of the fluidization air and the dwell time of the products in the device, which depends on the depth of the fluidised bed, are selected such that the products extracted from the device 10 at B are almost exclusively constituted by kernels.

The shells and a few kernels and impurities are entrained by the air to the separator 24 where these products are separated from the air current. They are then introduced into the device 10' whose mode of operation is identical to that of the device 10. The speed of the fluidization air and the dwell time of the products in this device are selected such that the products entrained by the air current are almost exclusively constituted by shells. The speed of the air in this second device must therefore be lower than the speed in the first device. The products extracted from the device 10' via the chute 18', whose rate of flow is regulated by the screen 20' and which are constituted essentially by kernels and a few shells, are returned to the device 10 by means of suitable conveyor devices.The rate of flow of the products extracted via the chute 18' is adjusted so as to maintain the bed 26' at a predetermined level corresponding to the selected dwell time. The shells entrained by the air current are collected at the head -of the cylone 24'.

By way of example, it is possible to use fluidisation air speeds (air flow divided by the cross-section of the device) of 8 to 1 2 m/s for the device 10, and 7 to 9 m/s for the device 10'. The dwell times of the products in the fluidised beds will generally be between- 10 and 30 s.

Clearly, modifications may be made to the plant described by the use of equivalent technical means. In particular, it would be possible to replace the rotary screen removal device by an overflow having an adjustable threshold.

Although the plant described comprises two separation stages, it is understood that the invention extends to methods and plants comprising a single separation stage in a fluid bed apparatus, such as the device 10, the speed of the air current and the dwell time of the kernels in the fluid bed being selected as a function of the required results.

Claims

1. A method for the automatic separation of the kernels from a shell and kernel mixture obtained after crushing palm nuts, which method comprises subjecting the mixture to a rising air current whose speed is selected such that it entrains shells without entraining a substantial amount of the kernels, the said mixture being maintained in a fluidised state above a permeable support by the said air current which is blown below the said support and which extracts the shells from the fluid ised bed and entrains them in its upward movement, the mean dwell time of the kernels in the fluidised bed being between 10 and 30 seconds.

2. A method as claimed in claim 1, wherein a first fluidised bed is formed with the said mixture by means of a first rising air current whose speed is such that almost all the shells are entrained by the said air current, the products entrained with the air current being separated therefrom, and formed into a second fluidised bed by means of a second rising air current whose speed is lower than that of the first air current such that the portion of the said products entrained by the fluidization air of the second bed is almost exclusively constituted by shells, and the portion of the products not entrained by the fluidization air of the second fluidised bed is returned to the first fluid bed

3.A method as claimed in claim 1 or 2, wherein the shell and kernel mixture is introduced continuously into the fluidised bed or beds, the products not entrained by the air are extracted substantially continuously from the bed or beds and the supply and/or the extraction flow is adjusted so as to maintain the fluidised bed or beds at a predetermined level.

4. A method as claimed in claim 1, 2 or 3, wherein the speed of the fluidization air is between 7 and 1 2 metres per second.

5. A method as claimed in claim 4 when dependent upon claim 2, wherein the speed of the fluidization air of the first bed is between 8 and 1 2 metres per second and the speed of the fluidization air of the second bed is between 7 and 9 metres per second.

6. A method of separating kernels from shells in a mixture formed by crushed palm nuts, substantially as hereinbefore described with reference to the accompanying drawing.

7. Apparatus for carrying out a method as defined in any one of claims 1 to 6, comprising a fluidisation device having a permeable support at a lower portion, means for blowing air upwardly through the support and an air outlet at an upper portion, adjustment means for adjusting the rates of supply and extraction of the products and adjustment means for adjusting the rate of flow of the air blown under the said support.

8. Apparatus as claimed in claim 7, com prising two of said fluidization devices con nected in series, the products blown from a first one being supplied to the bed of the second.

9. Apparatus for separating kernels from shells in a mixture thereof, substantially as herein before described with reference to the accompanying drawings.

10. A method of separating kernels from a mixture of kernels and shells, comprising forming said mixture into a fluidised bed and controlling the air flow through said bed such that substantially all of the shells are entrained in the air flow and carried thereby out of the bed.

11. A method as claimed in claim 10, wherein the dwell time of products in the bed is sufficient to enable shells to adopt a configuration for entrainment by the air flow.

12. A method as claimed in claim 10 or 11, wherein products entrained by the air flow are fed to a second fludised bed having an air flow which is controlled so that substantially only shells are entrained thereby and carried out of the bed.

1 3. Kernels separated by a method as defined in any one of claims 1 to 6 and 10 to 12.

1 4. Products derived from kernels as claimed in claim

1 3.

1 5. The features hereinbefore disclosed or their equivalents in any novel combination.