AU2811499A - Milling of sugar cane - Google Patents

Description

MILLING OF SUGAR CANE This invention relates to the milling or squeezing of sugar cane to remove sugar therefrom. More specifically this invention relates to apparatus for milling sugar cane and also to a process for the milling of sugar cane.

Known milling processes use a plurality of mills arranged in series and the whole assembly is called a mill train. Typically each mill includes three discrete rolls arranged in the form of a triangle when viewed in end view. The rolls are called respectively the top roll, the feed roll and the delivery roll. In addition further feed rolls are typically also required spaced upstream of the feed roll to facilitating feeding the cane into the three rolls. In its simplest form there is a single further roller called an underfeed roll. However more complex arrangements have more than one roller, eg three further rolls.

An example prior art milling train comprising four mills arranged in series is illustrated in FIG. 1.

Each mill in the train comprises broadly an inclined conveyor or carrier feeding the shredded ,cane intoa chute which feeds the cane into a first group of three rollers including an under feed roller. As described above the purpose of this first group of rolls is simply to feed the cane into the next group of rolls. As described above the next group of rolls which comprises the top roll, feed roll and delivery roll does most of the work in the milling process. Thus a lot of the apparatus in each of the mills merely facilitates the feeding process and is not actively engaged in milling or squeezing the shredded cane.

An important step being carried out in the mill train is the mixing of imbibition liquid into the cane material. Imbibition liquid is basically an aqueous solution which assists in washing the cane out of the sugar fibre.

Imbibition liquid is added to the second, third and fourth mills and is mixed in with the cane prior to it being squeezed or milled in the rolls. The imbibition liquid assists in removing the sugar from the cane. Typically the imbibition liquid is passed along the mill train countercurrent to the cane, eg from fourth mill to third mill to second mill, although other flow arrangements are possible.

All imbibition liquid is collected and sent off to the plant for sugar recovery.

Typically it is the imbibition liquid from the second mill together with the sugar solution squeezed out of the first mill which is sent off for recovery. The bagasse passing out of the fourth mill is used as a fuel to generate energy.

The apparatus described above in FIG. 1 is relatively large, capital intensive and unwieldy, and accordingly it is not surprising that efforts have been directed to simplifying the milling train, eg to reduce the number of rollers or rolls and to reduce the level of control required in the process.

One such example comprises a plurality of axially spaced pairs of milling rolls, each pair in addition to performing a milling function acting to feed cane into the following mill. The advantage of such an arrangement is that it drastically cuts down on the number of rollers required in the mill train. It also drastically reduces the size of the plant which is substantially more compact.

However a difficulty caused by having the compact mill train described above is that there is not sufficient distance between successive mills to mix the imbibition liquid fully into the cane to enable it to perform its function.

Satisfactory mixing is achieved in the prior art mills such as that shown in FIG. 1 because of the considerable distance between adjacent mills in the mill train.

Accordingly it would be advantageous if an apparatus could be devised for suitably mixing the imbibition liquid into the cane in a short distance. Such an innovation could be used on all mill trains and not merely the compact mill trains described above although it would have particular utility on compact mill trains.

3 According to an aspect of this invention there is provided a mill for milling sugar cane, the mill including: at least two opposed mill rolls defining a nip region therebetween for passing a mat of sugar cane therethrough; means for cutting into said mat of cane upstream of said at least two opposed mill rolls; and means for introducing liquid into said cut mat of cane upstream of said opposed mill rolls.

Thus the cutting means opens up the mat of cane and liquid is introduced through these openings into the cane. In this way imbibition liquid is able to penetrate deeply into the mat of cane.

In one embodiment the cutting means includes a pair of opposed cutting rolls having cane cutting formations on the outside thereof.

Optionally the cane cutting formations are teeth, eg spiked teeth.

Optionally the pair of cutting rolls are rotated faster than the local speed of the mat of cane so that the teeth tear and gouge at the cane, eg they cut bigger holes than would otherwise be the case.

In this embodiment the liquid introducing means includes a conduit having an open end as outlet and liquid is simply poured out of the outlet onto the back of the roll, eg the teeth, so that it is carried into the mat by the teeth.

In another embodiment the cutting means comprises a cutting formation upstream of the pair of rolls, eg adjacent and upstream of the pair of rolls.

Optionally the cutting formation may be located closely adjacent to the pair of rolls of the preceding mill.

The cutting formation acts to cut the mat of cane into two mat portions.

Preferably the cutting formation is in the form of a stationary wedge, eg pointing upstream and extending substantially the full width of the rollers.

Preferably in this embodiment the liquid introducing means includes a conduit having an open end which directs liquid into the void between the two separated mat portions. Advantageously the nozzle is directed away from the wedge, eg directed in an opposed direction to the wedge, and sprays imbibition liquid into the void created between the mat portions created by the wedge.

In this embodiment imbibition liquid is preferentially distributed towards the centre of the mat, ie the line on which it is cut into two mat portions, by virtue of it being introduced in between the two portions.

In yet another embodiment the cutting means comprises a pair of shafts with cutting formations thereon for cutting the material into two mat portions upstream of said mill rolls.

Preferably the shafts have small toothed counter rotating gears thereon which act to aggressively cut the mat into said two mat portions.

In this embodiment the liquid introducing means comprises a conduit having an outlet directing liquid into the void between the two mat portions, eg downstream of the counter rotating shafts and upstream of the mill rolls.

This embodiment also preferentially distributes the imbibition liquid towards the centre of the mat.

In a yet further embodiment the cutting means comprises a feed chute into which the mat of cane is passed, eg by an upwardly inclined belt conveyor, the chute having a partition which acts to divide the mat up into two mat portions.

Thus as cane is tipped into the chute from the conveyor part of it falls into the first chute portion and the remainder falls into the more remote second chute portion.

Advantageously the mill rolls, eg three mill rolls arranged in triangular configuration, are arranged adjacent the downstream end of the chute.

Advantageously the leading edge of the chute partition is wedge-like and the trailing edge of the partition terminates short of the downstream end of the chute.

Advantageously the liquid introducing means injects liquid into the void between the two mat portions downstream of the trailing edge of the chute partition.

According to another aspect of this invention there is provided a mill train including a pair of mills as described above with respect to the first aspect of the invention arranged in series for milling a mat of sugar cane.

Each said mill may include any one or more of the preferred features described above with respect to the first aspect of the invention.

Typically there are at least three said mills arranged in series and each upstream mill feeds directly into the adjacent downstream mill.

Preferably there are four said mills arranged in series.

According to yet another aspect of this invention there is provided a process for the treatment of sugar cane to recover sugar therefrom, the process including: milling a mat of sugar cane in a sugar mill to express the sugar therefrom and separate it from the fiber bagasse; adding imbibition liquid to the mat of sugar cane to assist in expressing sugar, wherein the imbibition liquid is introduced into the interior of the mat of sugar cane.

Preferably the imbibition liquid is preferentially distributed towards a central region of the mat when viewed in side elevation, eg a central region sandwiched between top and bottom portions of the mat.

An apparatus and a process for milling sugar cane in accordance with this invention may manifest itself in a variety of forms. It will be convenient to hereinafter describe in detail several preferred embodiments of the invention with reference to the accompanying drawings. The purpose of providing this specific description is to instruct persons having an interest in the subject matter of the invention how to carry the invention into practical effect. It is to be clearly understood however that the specific nature of this description does not supersede the generality of the preceding statements. In the drawings: FIG. 1 is a schematic flow sheet of a mill train which is well known in the prior art; FIG. 2 is a schematic sectional side view of a mill in accordance with one embodiment of the invention; FIG. 3 is a schematic sectional side view of a mill in accordance with another embodiment of the invention; FIG. 4 is a schematic sectional side view of a mill in accordance with yet another embodiment of the invention; FIG. 5 is a sectional side view of a commercial mill in accordance with yet another embodiment of the invention; In FIG. 2 reference numeral 10 refers generally to a mill forming part of a mill train for milling sugar cane.

The mill 10 comprises a pair of opposed milling rolls, 11 and 12 defining a nip region therebetween through which a mat of cane 13 is passed, means for cutting the mat of cane 13 in the form of a pair of toothed rolls 15 and 16, and means for introducing liquid into the mat of cane 13 in the form of a conduit which is a pipe 20 having an open end acting as an outlet.

The mill rolls 11 and 12 are respectively known as the top roll and delivery roll.

The rolls 11 and 12 are arranged with a carefully engineered spacing relative to each other defining a nip region. Typically the rolls 11 and 12 have a plurality of circumferential ridges and grooves 24 over which the cane is passed. The ridges and grooves 24 serve to mill or squeeze the cane so as to remove sugar therefrom. Other known mill rollers for milling sugar cane include low pressure extraction perforated rollers, solid rolls, grooved rolls or any of the various drain passage rolls. The structure and function of the rolls 11, 12 would be well known to persons skilled in the art and accordingly will not be described in further detail.

The toothed rolls 15, 16 each have a plurality of radially extending spikes or teeth 30 projecting outwardly therefrom. The spikes 30 may each have the width of about 20 mm although obviously this specific width is not essential.

Typically the rolls have about 6 to 12 spikes spaced apart around the circumference of the rolls although naturally this number can vary. The spiked rolls are spaced apart from each other such that they penetrate deeply into a mat of cane which is passed between them without clashing or interfering with each other.

Imbibition liquid is deposited onto the back of the spikes 30 and the outside of the rolls 15 and 16 and the spikes 30 then convey the liquid into the mat of cane 13.

A pair of spaced plates 32 and 33 direct the mat of cane 13 from the spiked rolls 16 to the top roll and delivery roll 11 and 12.

The mill also includes further spaced plates 36, 37 for feeding the mat of cane 13 into the next succeeding miii.

Advantageously the toothed rolls 15, 16 are operated at a speed slightly higher than the speed of the mat of cane 13 as determined by the rolls 11 and 12.

This causes the teeth to tear at the mat and open up larger voids in the mat 13 than would otherwise be the case. These tears assist in the distribution of the imbibition liquid through the cane and particularly into the inner regions of the mat of cane.

Further the outer regions of the mat tend to be slightly more compressed than the central regions. This may be caused by the pressure of the teeth when the mat has passed through the centre of the nip region but where the teeth still engage the mat and apply pressure to the mat, ie just before the teeth release the mat. Without being bound by theory, applicant believes that this probably causes imbibition liquid to be preferentially distributed towards the central region of the mat.

In use a mat of canel3 is fed into the nip region of the toothed rollers 15 and 16. The teeth 30 puncture and penetrate into the mat and take with them imbibition liquid from the nozzle. The tearing of the cane is enhanced by the fact that the teeth travel faster than the mat 13. In this way liquid is carried into the inner or interior regions of the mat 13. This provides a workable distribution of imbibition liquid through the mat in the short space before it passes through the top and delivery rolls 11 and 12. The liquid distribution is however not homogeneous occurring in repeating pockets and being biased towards a centre region of the mat.

FIG. 3 illustrates a mill in accordance with another embodiment of the invention.

This embodiment shares some similarities with that illustrated in FIG. 2 and accordingly the same reference numerals will be used to refer to the same components unless otherwise illustrated.

The main difference between this and the FIG. 2 embodiment is the fact that the cutting means is provided by a wedge shaped formation 40 which is positioned upstream of the rolls 15, 16. The wedge formation 40 acts to split the mat of cane 13 into two separate portions 14 and 15. The pipe 20 is positioned behind the wedge formation 40 with the open end thereof directed downstream, ie in a direction opposed to the wedge formation 40. The nozzle 20 sprays liquid into the void defined between the two portions of the mat 13. This way imbibition liquid is introduced directly into a central region of the mat 13.

With this embodiment the imbibition liquid is also preferentially distributed towards a central region of the mat, rather than being evenly distributed throughout the body of the mat. This leads to some advantages in performance which will be described in more detail below.

FIG. 4 illustrates a mill in accordance with yet another embodiment of the invention. This embodiment is structurally and functionally very similar to the embodiment illustrated in FIG. 3 and accordingly the same reference numerals will be used to refer to the same components unless otherwise illustrated.

The main difference between this and the FIG. 3 embodiment reside in the device which is used to cut the mat of cane 13 into two separate mat portions 14 and 15. In FIG. 4 this is accomplished by means of a pair of driven counter rotating toothed gears 36, 37 having a diameter substantially less than that of the mat 13. The rotating tooth gears 36, 37 act to split the mat into two mat portions 14, 15, approximately along a center line of the mat when viewed in side view.

A nozzle 20 for introducing imbibition liquid is positioned between the tooth gears for introducing liquid into the void created by the toothed gears between the two mat portions 14 and 15. The rolls 11 and 12 of the previous mill essentiall perform a feeding function feeding the cane through the toothed gears into the nip region of the rolls 11, 12. This embodiment generates a distribution of imbibition liquid in the mat similar to that in FIG. 4.

FIG. 5 illustrates a mill 50 in accordance with yet another embodiment of the invention. This mill is quite different to that illustrated in FIGS. 2, 3 and 4 although it is designed to achieve the same effect, namely to split the mat into two mat portions so as to provide access of the imbibition liquid to a central region of the mat of cane.

Broadly the mill comprises a conveyor 51, a chute 52, and a triangular arrangement of rolls 52 similar to those described above with reference to FIG.

1. The conveyor 51 transports a mat of shredded cane from a previous mill up an incline and discharges it into the chute 52. The chute 52 extends diagonally downwardly from the top of the conveyor 51 into the nip region of the upstream pair of the triangular arrangement of rolls 53.

The chute 52 comprises two chute portions 55, 56 when viewed in cross section. The two discrete portions are formed by a chute partition 58 which extends down the chute 52 dividing it into two substantially equal chute portions 56. Part of the mat of cane issuing from the top of the conveyor 51 passes into the first chute portion and the remainder passes into the second chute portion. This way the mat of cane is separated into two mat portions.

The pipe 20 associated with the chute partition injects imbibition liquid into the void between the two mat portions. Typically the nozzle 20 is associated with a downstream end of the partition and directs liquid in a downstream direction substantially along the longitudinal axis of the chute. As one would expect, this embodiment preferentially distributes imbibition liquid towards the centre of the mat rather than towards the edges. In this respect it is similar to the FIG. 3 and 4 embodiments. The mat portions recombine downstream of the partition and pass into the triangular arrangement of rollers 53 which squeezes the mat of cane as has been described in detail above.

The partition terminates short of the downstream end of the chute to allow recombination of the two mat portions as it will be described in more detail below.

A possible disadvantage of this embodiment is that it requires conveyors between each of the mills and does not have the compact form of the FIG. 3 and FIG. 4 embodiments where the mat from one mill feeds directly into the rolls of the next succeeding mill.

A particular preferred compact mill train in accordance with one embodiment of the invention comprises four discrete mills as illustrated in FIG. 2 arranged in series with the mat of cane from one mill feeding directly into the next mill.

Broadly each mill comprises a pair of rolls defining a nip region therebetween through which the mat of cane is passed and upstream thereof a pair of spikey toothed rollers. The mat of cane issues from the rolls 11 and 12 and feeds directly into the spikey toothed feeders of the next succeeding mill. Imbibition liquid is poured onto the mat of cane as described with reference to FIG. 2.

An advantage of the mills described above with reference to the specific description, particularly FIGS. 3 and 4 is that imbibition liquid is introduced deeply into the mat of the cane. This causes the imbibition liquid to be preferentially distributed towards the centre of the cane, ie maldistributed towards a centre region of the mat of cane.

The improvements in displacement washing of sugar from the deep inner regions of the mat of cane generally acts to enhance sugar recovery.

An advantage of the mill train described above with reference to FIG. 6 is that it is simpler and more compact than prior art mills because the rolls of a preceding mill are used to feed the cane into the next mill. It thus avoids much of the apparatus and equipment of conventional prior art mills such as those illustrated in FIG. 1 while still delivering a satisfactory performance. Mill trains are fairly capital intensive and accordingly provision of a substantially more compact structure with the same performance will lead to considerable savings.

It will of course be realised that the above has been given only by way of illustrative example of the invention and that all such modifications and variations thereto as would be apparent to persons skilled in the art are deemed to fall within the broad scope and ambit of the invention as is herein set forth.

Claims (24)

1. A mill for milling sugar cane, the mill including: at least two opposed mill rolls defining a nip region therebetween for passing a mat of sugar cane therethrough; means for cutting into said mat of cane upstream of said at least two opposed mill rolls; and means for introducing liquid into said cut mat of cane upstream of said opposed mill rolls.

2. A mill according to claim 1, wherein the cutting means includes a pair of opposed cutting rolls having cane cutting formations on the outside thereof.

3. A mill according to claim 2, wherein the cane cutting formations are spiked teeth.

4. A mill according to claim 3, wherein the the pair of cutting rolls are rotated faster than the local speed of the mat of cane passing through the mill so that the teeth tear and gouge at the cane.

A mill according to any one of claims 1 to 4, wherein the liquid introducing means comprises a conduit having an open end which directs liquid onto a said cutting roll or the mat of cane upstream of said cutting roll.

6. A mill according to claim 1, wherein the cutting means comprises a cutting formation upstream of the pair of rolls.

7. A mill according to claim 6, wherein the cutting formation is in the form of a stationery wedge pointing upstream which acts to cut the mat of cane into two mat portions.

8. A mill according to claim 6 or claim 7, wherein the liquid introducing means includes a conduit having an open end which directs liquid into the void between the separate mat portions created by the wedge.

9. A mill according to claim 8, wherein the open end of the conduit is directed in the opposite direction to the wedge.

A mill according to claim 1, wherein the cutting means comprises a pair of shafts with cutting formations thereon for cutting the material into two mat portions upstream of said mill rolls.

11. A mill according to claim 10, wherein the shafts have small tooth counter rotating gears thereon which act to aggressively cut the mat into said two mat portions.

12. A mill according to claim 10 or claim 11, wherein the liquid introducing means comprises a conduit having an outlet directing liquid into the void between the two mat portions downstream of the counter rotating gears and upstream of the mill rolls.

13. A mill according to claim 12, wherein the liquid introducing means distributes imbibition liquid towards the centre of the mat.

14. A mill according to claim 1, wherein the cutting means comprises a feed chute into which the mat of cane is passed, the chute having a partition which acts to divide the mat up into two mat portions.

A mill according to claim 14, wherein there are three said mill rolls arranged in triangular configuration adjacent the downstream end of the chute.

16. A mill according to claim 15, wherein the leading edge of the chute partition is wedge-like and the trailing edge of the partition terminates short of the downstream end of the chute, and the liquid introducing means is a conduit having an open end directing liquid into the void between the two mat portions downstream of the trailing edge of the chute partition.

17. A mill train including a pair of mills as defined in claim 1 arranged in series for milling a mat of sugar cane.

18. A mill train according to claim 17, wherein each of the mills is as defined in any one of claims 2 to 16.

19. A mill train according to claim 17 or claim 18, having at least three said mills arranged in series and wherein each upstream mill feeds directly into the adjacent downstream mill without intermediate feeding apparatus.

A mill train according to claim 19, including four said mills arranged in series.

21. A process for the treatment of sugar cane to recover sugar therefrom, the process including: milling a mat of sugar cane in a sugar mill to express sugar therefrom and separate it from the fiber bagasse; adding imbibition liquid to the mat of sugar cane to assist in expressing sugar, wherein the imbibition liquid is introduced into the interior of the mat of sugar cane.

22. A process according to claim 21, wherein said step of adding imbibition liquid to the mat of sugar cane includes preferentially distributing the imbibition liquid towards a central region of the mat.

23. A mill substantially as herein described with reference to the drawings.

24. A mill train substantially as herein described with reference to the drawings. A process for the treatment of sugar cane to recover sugar therefrom substantially as herein described with reference to the drawings. DATED THIS Twelfth DAY OF May 1999. STG HOLDINGS PTY LTD BY PIZZEYS PATENT AND TRADE MARK ATTORNEYS