AU2012216273B2

AU2012216273B2 - Extraction of sugar cane juice

Info

Publication number: AU2012216273B2
Application number: AU2012216273A
Authority: AU
Inventors: Alan Lewis Fitzmaurice
Original assignee: Individual
Current assignee: Individual
Priority date: 2006-09-11
Filing date: 2012-08-17
Publication date: 2015-01-22
Anticipated expiration: 2027-09-11
Also published as: AU2012216273A1

Abstract

A process for extraction of sugar cane juice in a tandem mill assembly employs a first mill 10 and a preparation stage comprising a shredder 11 where a maceration carrier 12 is located between the shredder 11 and mill 10. The maceration carrier comprises a conveyor and drainage means 14 along the conveyor. The first mill 10 includes rollers 15 and 16 and collectors 17 and 18. Juice from collector 17 is applied to the shredder at 19 while juice from mill No. 2 (not shown) is applied to the fibre mat at 20 part way up the conveyor. Juice from mill No. 3 is applied downstream of mill No. 1 and so on down the tandem. Thus this process progressively delivers all the imbibition liquid from the trailing mills to the maceration conveyor for collection.

Description

1 EXTRACTION OF SUGAR CANE JUICE FIELD OF THE INVENTION [0001] THIS INVENTION relates to extraction of sugar cane juice in a sugar cane factory and in particular to extraction of sugar cane juice in a tandem mill sugar cane factory. BACKGROUND TO THE INVENTION [0002] Prior commercial processes for removing sucrose from sugar cane may be classified generally as tandem mill processes or diffusion processes. In tandem mill processes the fiberized cane is repeatedly subjected to high pressures in a series of mills formed as a milling train with usually four to six mills. The applied pressure is usually in the range of about 1,000 lbs./sq. inch, in order to press the sugar juice from the cane. In diffusion processes, solvent is allowed to percolate through a bed of fiberized cane by gravitational flow for dissolving and extracting the soluble sugar. Many modifications of the foregoing processes, of course, have been made; for example, imbibition liquid ordinarily is utilized in tandem mill processes to improve the extraction efficiencies. [0003] "Extraction" is that process whereby cut sugar cane is treated to separate the juice from the fibre. The cut sugar cane is usually shredded, crushed while hot water is added giving bagasse and juice which is further processed to dry sugar. [0004] "Imbibition" is referred to as the process in which water or juice is put on bagasse to mix with and dilute the juice present in the latter. The water so used is termed imbibition water. General terms in use are: single imbibition, double imbibition, compound imbibition, depending on the manner in which the water and/or juice is added.

2 [0005] "Maceration" is referred to as the process whereby liquid is applied to fibre to soak the fibre to thereby improve juice yield from a subsequent mill. [0006] "Brix" (Degrees) are unit divisions of the scale of a hydrometer, which, when placed in a pure aqueous sucrose solution at 200C, indicates the percentage by mass of dissolved solids in the solution. The reading obtained in an impure sucrose solution is usually accepted as an approximation of its percentage by mass of total soluble solids. The term brix is used in calculations as a measure of substance, e.g. tons brix. [0007] "Pol" is the apparent sucrose content of any substance expressed as a percentage by mass and determined by the single or direct polarisation method. The term is used as if it were a real substance. [0008] The extraction of sucrose in an existing milling train is typically within the range from 85% to 98% depending on: * the number of mills in the train or tandem; * the quantity of imbibition liquid added; " the PI result where PI is the "preparation index" or "the pol in open cells" (POC) which depends on the form of preparation prior to the first mill eg shredding. PI is also defined as the percentage ratio of brix in the ruptured cells to total brix in cane; and " the skill and knowledge of the operators. [0009] The extraction process is also very dependent on the mixing efficiency of the maceration system, that is the mixing of lower pol juice/water with the higher pol liquid remaining in the fibre mat leaving a mill. [0010] The mixing efficiency for an existing milling train is very low normally within the range from 30%-40% due chiefly to insufficient juice and maceration to create free flow of liquid within, and drainage from the fibre mat, and fully wet the bagasse. The maceration or 3 imbibition percent fibre for a milling train is normally in the range of 120% to 350% depending on the energy efficiency of a sugar factory. [0011] As a consequence, typically about 7% of the total sucrose content of the cane remains in the fibre mass leaving the final mill and is therefore lost. Since a sugar cane factory produces from 40,000 to 150,000 tonnes of sugar, the value of this loss is very high. OUTLINE OF THE INVENTION [0012] It is an object of the present invention to recover some of this lost content by improving the overall efficiency of the extraction process by creating an environment for higher mixing efficiency to promote free flow of liquid within and drainage from the fibre mat prior to entry of the fibre to the first mill in a mill tandem having at least three mills. [0013] It is a further object of the present invention to provide a compound maceration process involving application of imbibition liquid generated in the first or later mills to or just after the preparation stage, shredder and further imbibition liquid to the fibre mat after the preparation stage but prior to the first mill. [0014] In one aspect, the present invention broadly comprises a process for extraction of sugar cane juice in a tandem mill assembly having at least three mills, the process comprising maceration of sugar cane upstream of a first mill in the tandem using imbibition liquid generated downstream of the first mill, the maceration of the sugar cane being simultaneous with the cane being prepared for entry to the first mill in a preparation stage or just after preparation or a combination of the two. Typically, the preparation stage comprises a shedder producing a fibre mat delivered to a conveyor and thence to the first mill, the application of the imbibition liquid being directly into the shredder and/or to the fibre mat after leaving the shredder. Typically, the conveyor is part of an inclined maceration carrier and the imbibition liquid is applied part way along the carrier.

4 [0015] Preferably, the imbibition rate equals the drainage rate for free flow of liquid from the fibre bed. [0016] Preferably, this process aims to extract "freed" cane juice available after knifing or preferably shredding of the cane, but prior to the fibre mat entering the No. 1 mill. [0017] A similar process can also be used to improve the mixing efficiency of the inter mill maceration system and provide a sucrose extraction process between each mill in the milling train due to the free draining of the macerating liquid from each intermediate mill conveyor or hopper, and the compounding action of this maceration system. [0018] The process typically adds liquid from No. 1 mill (preferably juice from a pressure feeder or "fourth" roll) to: * The unprepared cane entering the shredder or knives, or. " The shredding process (knives or shredder), or " The spray of juice and fibre leaving the knives or shredder, or " The fibre mat leaving the preparation equipment on a conveying system leading to the No.1 mill. [0019] This (pressure feeder) liquid addition may then be followed by the addition of liquid drained from the second or top end drainage tray under the conveyor. About a third of the way up the conveyor, lower pol liquid from the No. 2 mill is added to the fibre mat on the conveyor. [0020] The greatly increased quantity of liquid now in the fibre (with reducing pol as the fibre mat moves toward the No.1 mill) creates a rapid flow of liquid through the fibre mat onto the two drainage trays below the conveyor. [0021] This flow of liquid includes much of the higher pol cane juice, which is then replaced by lower pol liquid from the No.2 mill.

5 [0022] Much of the pure cane juice is therefore washed out of the prepared fibre mat prior to entering the No.1 mill due to the high volume of circulating liquid and the compounding action of the maceration system. This process adds an additional extraction system to the front of the No. 1 mill where it is most beneficial. [0023] This process can also be used along the milling train on the conveyors between each mill, by circulating and draining pressure feeder (or fourth roll) liquid within the conveyor system preceding each mill. [0024] The conveyors must be set up to allow free drainage of liquid from the fibre mat traversing the conveyor system. [0025] Juice drained from the conveyor in front of the first mill is pumped away for process. [0026] The liquid drained from the intermediate conveyors is directed to the proceeding mill pressure feeder (or fourth roll) collection trough. [0027] Due to the high liquid flow created by this process more dirt may be washed out prior to the No. 1 mill or along the milling train reducing wear along the milling train and on boiler tubes. [0028] For ease of operation, a mixture of the total supply of liquid (No.1 mill liquid, liquid from the top drainage tray, and the extracted liquid from the No.2 mill) can be mixed and added to the shredder or knives or the leading end of the prepared cane conveyor. Similarly, the intermediate mill liquid, top drainage tray liquid and the trailing mill liquid can be mixed and added to the fibre mat leaving the mill at the leading end of the conveyor, especially if the conveyor angle is steep or if the conveyor length is short. [0029] In another aspect there is provided a tandem mill assembly having at least three mills 6 for extraction of sugar cane juice, the assembly having mills in series with imbibition liquid being delivered to the assembly in accordance with the process set out above. [0030] Preferably, the tandem mill assembly having at least three mills for extraction of sugar cane juice is one having a first mill, a second mill following the first mill and a preparation stage comprising a shredder upstream of the first mill, a maceration carrier located between the shredder and the first mill, the maceration carrier comprises a conveyor and drainage means along the conveyor, the first mill includes rollers and collectors, juice from one collector being applied to the shredder, while juice from the second is applied way up the conveyor. [0031] More preferably, the tandem mill assembly for extraction of sugar cane juice is one having a first mill, a second mill following the first mill, a third mill following the second mill and a preparation stage comprising a shredder upstream of the first mill, a maceration carrier located between the shredder and the first mill, the maceration carrier comprises a conveyor and drainage means along the conveyor, the first mill includes rollers and collectors, juice from one collector being applied to the shredder, while juice from the second is applied way up the conveyor, juice from the third mill being applied downstream of the first mill and so on down the tandem, thus this process progressively delivers all the imbibition liquid from the trailing mills to the maceration carrier for collection. [0032] Still more preferably, the tandem mill assembly for extraction of sugar cane juice is one having a first mill, a second mill following the first mill, a third mill following the second mill and a preparation stage comprising a shredder upstream of the first mill, a maceration carrier located between the shredder and the first mill, the maceration carrier comprises a conveyor and drainage means along the conveyor, the first mill includes rollers and collectors, juice from one collector being applied to the shredder, while juice from the second is applied way up the conveyor, juice from the third mill being applied downstream of the first mill and so on down the tandem, thus this process progressively delivers all the imbibition liquid from the trailing mills to the maceration carrier for collection, there being two final mills with hot water as the imbibition liquid applied at low brix liquid to an exit mat and 7 imbibition liquid being progressively applied to a maceration conveyor upstream of the preceding mill so that liquid works back through the mills to the maceration carrier before the first mill via the second mill. BRIEF DESCRIPTION OF THE DRAWINGS [0033] In order that the present invention may be more readily understood and be put into practical effect reference will now be made to the accompanying drawings and example which illustrate a preferred embodiment and wherein: Figure 1 is a schematic drawing of a typical preparation stage and first mill exemplary of the present invention; and Figure 2 is a schematic view of the penultimate mill and final mill in the tandem, it being appreciated that intermediate mills would be configured similar to this as far as the application of imbibition liquid to the penultimate mill. METHOD OF PERFORMANCE [0034] Referring to the drawings and initially to Figure 1 there is illustrated a first mill 10 and a preparation stage comprising a shredder 11. A maceration carrier 12 is located between the shredder 11 and mill 10. The maceration carrier comprises a conveyor and drainage means 14 along the conveyor. The first mill 10 includes rollers 15 and 16 and collectors 17 and 18. Juice from collector 17 is applied in this example to the shredder at 19 while juice from mill No. 2 (not shown) is applied to the fibre mat at 20 part way up the conveyor. Juice from mill No. 3 is applied downstream of mill No. 1 and so on down the tandem. Thus this process progressively delivers all the imbibition liquid from the trailing mills to the maceration conveyor for collection. [0035] Figure 2 shows the final two mills 21 and 22 with hot water as the imbibition liquid applied at 23 low brix liquid at 24 to the exit mat and imbibition liquid along line 25 to the 8 maceration conveyor of the preceding mill. This basic arrangement works back through the mills to the maceration carrier 12. [0036] An example of this extraction process follows: The milling train in this example shall include the following equipment: - A heavy duty shredder. - Four mills, each fitted with high drainage pressure feeders. - Cane rate- 500 tonnes of cane per hour. - Fibre percent cane- 13% - Juice percent cane- 87%. - Imbibition % fibre- 300% - Final mill bagasse moisture content - 50%. [0037] Partly chopped cane enters the shredder and is prepared to a preparation level of 90 P.O.C. (i.e. 90% of the juice will be separated from the juice cells in the cane fibre bundle and can be washed free of the fibre mat). [0038] Liquid expressed by the No. 1 mill pressure feeder is pumped into the shredder to promote mixing of this liquid with the cane juice "freed" by the shredder. [0039] Drained liquid from the top drainage tray is added to the fibre mat at the leading end of the conveyor. Liquid extracted by the No. 2 mill is pumped evenly onto the fibre mat traversing the conveyor, about a third of the way up from the leading end of the conveyor. [0040] The quantity of liquid in the prepared cane fibre mat is now of sufficient quantity to drain freely through slots in the conveyor floor onto the two drainage trays below. This process therefore extracts much of the cane juice prior to the No. 1 mill. [0041] In this example, the liquid recirculation rate is about 565 tonnes per hour, while the drainage rate through the conveyor floor is about 200 tonnes per hour. This drained liquid is 9 added to the liquid extracted by the No. 1 mill and is pumped away to process. [0042] By compound action the liquid from the No. 2 mill (abt.8 brix) displaces much of the No. 1 mill juice which in turn displaces high brix (18+ brix) cane juice. The sucrose content of the fibre mat leaving the No. 1 mill is therefore reduced by this process. The speed of the conveyor is controlled relative to the cane conveyor speed to provide complete coverage of the fibre mat over the conveyor floor. [0043] In the case of flooding, due to high dirt loading, a control system would increase the conveyor speed relative to the cane conveyor speed to provide increased drainage of liquid through the holes or slots in the floor of the conveyor. [0044] A similar process is used on each intermediate mill conveyor except the trailing mill pressure feeder liquid would be added to the fibre mat leaving the preceding mill. [0045] The circulation of pressure feeder liquid increases the volume of liquid in the conveyors until the drainage rate equals the imbibition rate. This free draining liquid provides additional extraction processes for the milling train. [0046] Whilst the above has been given by way of illustrative example of the present invention many variations and modifications thereto will be apparent to those skilled in the art without departing from the broad ambit and scope of the invention as set out in the claims. For example the use of the word "comprising" should not be taken as an intention to limit the invention to the features or process steps listed and it should be understood that the addition of features or process steps to those listed is still within the ambit of the invention.

Claims

1. In a sugar cane milling tandem comprising at least three mills, a process for extraction of sugar cane juice, the process comprising maceration of sugar cane upstream of a first mill in the tandem using imbibition liquid generated downstream of the entry to the first mill, the maceration of the sugar cane being substantially prior to the first milling of the cane and being applied to cane on a conveyor leading to the first mill.

2. A process for extraction of sugar cane juice in a tandem mill assembly according to claim 1 wherein a major proportion of the maceration referred to in claim 1 occurs in a preparation stage before entry to the first mill.

3. A process for extraction of sugar cane juice in a tandem mill assembly according to claim 1 wherein the maceration of the sugar cane occurs prior to and during entry of prepared cane into the first mill.

4. A process for extraction of sugar cane juice in a tandem mill assembly according to claim 1 wherein the preparation stage comprises a shredder producing a fibre mat delivered to the conveyor and thence to the first mill, the application of the imbibition liquid being directly into the shredder and/or to the fibre mat after leaving the shredder.

5. A process for extraction of sugar cane juice in a tandem mill assembly according to claim 1 wherein the preparation stage comprises a shredder producing a fibre mat delivered to the conveyor and thence to the first mill, the application of the imbibition liquid being directly into the shredder and/or to the fibre mat after leaving the shredder, the conveyor being part of an inclined maceration carrier and the imbibition liquid is applied part way along the carrier.

6. A process for extraction of sugar cane juice in a tandem mill assembly according to claim 1 wherein the imbibition liquid is applied at an imbibition rate and the imbibition rate equals the drainage rate for free flow of liquid from the fibre bed. 11

7. A process for extraction of sugar cane juice in a tandem mill assembly according to claim 1 wherein the process extracts "freed" cane juice available after preparation of the cane, but prior to the prepared cane entering the first mill.

8. A process for extraction of sugar cane juice in a tandem mill assembly according to claim 1 wherein the process extracts "freed" cane juice available after preparation of the cane, but prior to the prepared cane entering the No. 1 mill, the "freed" cane juice being available after preparation by knifing or shredding of the cane to form a fibre mat, but prior to the fibre mat entering the first mill.

9. A process for extraction of sugar cane juice in a tandem mill assembly according to claim 1 wherein mills are in series in a milling train, there being a mill conveyor or hopper between each mill and inter mill maceration is used between each mill in the milling train to promote free draining of macerating liquid from each intermediate mill conveyor or hopper to thereby compound maceration and extraction thereby across the milling assembly.

10. A process for extraction of sugar cane juice in a tandem mill assembly according to claim 1 having a shredder or knives upstream of the first mill and wherein liquid from the first mill is added to one or more of the following: " onto the unprepared cane entering the shredder or knives; " into the shredding process (knives or shredder); " onto the fibre leaving the knives or shredder; or " onto a fibre mat leading to the first mill.

11. A process for extraction of sugar cane juice in a tandem mill assembly according to any one of the preceding claims wherein a pressure feeder is employed to supply the imbibition liquid. 12

12. A process for extraction of sugar cane juice in a tandem mill assembly according to any one of the preceding claims wherein a pressure feeder is employed to supply the imbibition liquid, and the liquid addition to the first mill is supplemented by lower pol liquid from another mill in the tandem.

13. A process for extraction of sugar cane juice in a tandem mill assembly according to any one of the preceding claims wherein a pressure feeder is employed to supply the imbibition liquid, and the liquid addition to the first mill is supplemented by lower pol liquid from another mill in the tandem, the addition of liquid being delivered about a third of the way up the conveyor leading to the first mill.

14. A process for extraction of sugar cane juice in a tandem mill assembly according to any one of the preceding claims wherein a pressure feeder is employed to supply the imbibition liquid, and the liquid addition to the first mill is supplemented by lower pol liquid from a mill directly following the first mill in the tandem.

15. A process for extraction of sugar cane juice in a tandem mill assembly according to any one of the preceding claims wherein a pressure feeder is employed to supply the imbibition liquid to fibre upstream of the first mill, and the liquid addition to the fibre upstream of the first mill is supplemented by lower pol liquid from another mill and/or other mills in the tandem, with the added liquid having reducing pol as the fibre mat moves toward the first mill creates a rapid flow of liquid through the fibre onto drainage trays below the conveyor carrying the fibre.

16. A process for extraction of sugar cane juice in a tandem mill assembly according to any one of the preceding claims wherein the imbibition liquid is a mixture of liquid from multiple mills in the assembly.

17. A process for extraction of sugar cane juice in a tandem mill assembly according to any one of the preceding claims wherein process juice is taken off from drainage from the first mill. 13

18. A tandem mill assembly for extraction of sugar cane juice, the assembly having at least three mills in series, a first one of said mills in the series having an entry, maceration means upstream of a first one of said mills in the tandem, imbibition liquid delivery means for delivering imbibition liquid generated downstream of the entry to the first mill, with imbibition liquid being delivered to the assembly in accordance with the process set out in accordance with any one of the preceding claims.

19. A tandem mill assembly for extraction of sugar cane juice according to claim 18 having a first mill, a second mill following the first mill and a preparation stage comprising a shredder upstream of the first mill, a maceration carrier located between the shredder and the first mill, the maceration carrier comprises a conveyor and drainage means along the conveyor, the first mill includes rollers and collectors, juice from one collector being applied to the shredder, while juice from the second mill is applied part way up the conveyor.

20. A tandem mill assembly for extraction of sugar cane juice according to claim 18 having a first mill, a second mill following the first mill, a third mill following the second mill and a preparation stage comprising a shredder upstream of the first mill, a maceration carrier located between the shredder and the first mill, the maceration carrier comprises a conveyor and drainage means along the conveyor, the first mill includes rollers and collectors, juice from one collector being applied to the shredder, while juice from the second is applied part way up the conveyor, juice from the third mill being applied downstream of the first mill and so on down the tandem, thus this process progressively delivers all the imbibition liquid from the trailing mills to the maceration carrier for collection.

21. A tandem mill assembly for extraction of sugar cane juice according to claim 18 having a first mill, a second mill following the first mill, a third mill following the second mill and a preparation stage comprising a shredder upstream of the first mill, a maceration carrier located between the shredder and the first mill, the maceration carrier comprises a conveyor and drainage means along the conveyor, the first mill includes rollers and collectors, juice from one collector being applied to the shredder, while juice from the 14 second is applied part way up the conveyor, juice from the third mill being applied downstream of the first mill and so on down the tandem, thus this process progressively delivers all the imbibition liquid from the trailing mills to the maceration carrier for collection, there being two final mills with hot water as the imbibition liquid applied at low brix liquid to an exit mat and imbibition liquid being progressively applied to a maceration conveyor upstream of the preceding mill so that liquid works back through the mills to the maceration carrier before the first mill via the second mill.

22. A pre mill extraction system when used for extracting juice from sugar cane upstream of a first mill in a sugar factory having at least three mills, the extraction system comprising a shredder followed by a conveyor, a drain below the conveyor and an imbibition liquid delivery means for delivering liquid onto cane on the conveyor to promote extraction of juice from the cane.

23. A process for extraction of sugar cane juice in a tandem mill assembly substantially as described.

24. A tandem mill assembly for extraction of sugar cane juice substantially as described with reference to the drawings.