Structure for use in a sugar making process.

'STRUCTURE FOR USE IN A SUGAR MAKING PROCESS"

BACKGROUND TO THE INVENTION

THIS invention relates to a structure for use in a sugar making process.

Crystalline sugar is produced from concentrated syrup obtained from sugar cane or sugar beet juice. The process can be summarised as follows:

1. Syrup is concentrated by boiling it in a vacuum pan which operates under a partial vacuum that allows the syrup to boil at relatively low temperatures, thereby preventing the sugar from becoming caramelised;

2. Seed crystals produced in a batch pan are added to the vacuum pan and are allowed to grow by controlling the concentration of the syrup;

3. Once the seed crystals have reached a required size the pan is discharged or struck to a crystalliser wherein the sugar crystals are allowed to grow further by cooling the mass of crystal and syrup.

4. Centrifugals are then employed to separate the sugar crystals from the mother liquor. The process of evaporative crystallisation as summarised above is repeated until sufficient sugar has been produced.

Persons familiar with the operation of a sugar plant will be well aware of the fact that the pans are normally mounted several meters above the ground on dedicated steel structures. One reason for mounting a vacuum pan at a sufficient elevation above the ground is to allow the formed massecuite to overcome vacuum effects in the pan and flow under the influence of gravity to the associated crystalliser(s). By making use of gravity and not, for example, employing pumps, damage to the formed crystals is minimised. Another reason for elevating the vacuum pan above the ground is to provide space below the pan to allow the massecuite to be struck from the pan.

A drawback of the conventional arrangement as described above is the substantial cost of providing a dedicated steel structure of sufficient strength to support a vacuum pan, which itself could weigh several hundred tons. It is accordingly an object of the invention to provide an alternative arrangement for supporting the vacuum pan at the required elevation above the ground.

SUMMARY OF THE INVENTION

The abovementioned drawback is overcome, in accordance with the invention, by a structure which comprises a pan and a crystalliser structure including a crystalliser having an outer wall, characterised in that the pan is supported above the crystalliser by the crystalliser structure.

Conveniently the outer wall of the crystalliser extends vertically above the crystalliser and the pan is supported by the vertical extension of the outer wall. The arrangement may be such that a lower portion of the outer wall defines an outer wall of the crystalliser and an upper portion of the outer wall defines an outer wall of the pan with the outer wall supporting the weight of the pan above the crystalliser. The pan may be either a continuous vacuum pan or a batch pan for seed generation.

In the preferred embodiments, the outer wall includes an intermediate portion defining an internal space, between the pan and the crystalliser, which accommodates one or more crystalliser drive motors. Also, the space advantageously allows access by maintenance personnel.

In its simplest form the structure of the invention comprises a single pan and crystalliser structure configured in the manner summarised above. However the structure of the invention may also comprise first and second crystalliser structures, a continuous vacuum pan supported vertically above the crystalliser of the first crystalliser structure by a vertical extension of the outer wall of the first crystalliser structure and a batch pan for seed generation supported vertically above the crystalliser of the . second crystalliser structure by a vertical extension of the outer wall of the second crystalliser structure.

In such an arrangement, the structure may additionally include a seed receiver beneath the batch pan, a seed feed line extending from the seed receiver to the continuous vacuum pan and a pump operative to pump seed from the seed receiver to the continuous vacuum pan.

Also, the crystalliser of the first crystalliser structure is connected to the crystalliser of the second crystalliser structure by a riser pipe for feeding massecuite from the crystalliser of the first crystalliser structure to the crystalliser of the second crystalliser structure.

The structure of the invention may also comprise a plurality of continuous vacuum pans, a plurality of batch pans for seed generation and a crystalliser structure associated with each of the pans, each of the pans being supported vertically above the crystalliser of the associated crystalliser structure by a vertical extension of the outer wall of the associated crystalliser structure. -A-

According to another aspect of the invention there is provided a method of producing sugar, characterised by the steps of:

providing a first crystalliser structure which supports a continuous vacuum pan above it;

providing a second crystalliser structure which supports a batch pan for seed generation above it;

causing seed which has been formed inside the batch pan to be struck therefrom and fed to the continuous vacuum pan; and

causing massecuite which has been formed in the continuous vacuum pan to be struck therefrom and fed to a crystalliser of the first crystalliser structure.

The method may include the further steps of causing massecuite to be fed from the crystalliser of the first crystalliser structure to a crystalliser of the second crystalliser structure and of causing seed to be delivered from a seed receiver beneath the batch pan to the continuous vacuum pan.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described in more detail, by way of example only, with reference to the accompanying diagrammatic drawings in which:

Figure 1 illustrates structures according to the invention in a first sugar making arrangement; and

Figure 2 illustrates structures according to the invention in a second sugar making arrangement. DESCRIPT1ON OF THE ILLUSTRATED EMBODIMENTS

As pointed out above pans used in a sugar making process are normally elevated above the ground. This is conventionally achieved by providing a dedicated steel support structure on which the pan is supported several meters above ground level. However the cost of the dedicated steel structure is a drawback of such arrangements.

The invention proposes to do away with the need for the dedicated steel structure traditionally used for supporting the pan. In accordance with one embodiment of the invention this is achieved by vertically extending an outer wall of an associated crystalliser and using the vertical wall extension to support the pan.

Figure 1 shows a first sugar making arrangement 10 that includes two structures in accordance with the the broadest aspects of the present invention, generally indicated respectively with the reference numerals 12.1 and 12.2.

The first structure 12.1 includes a continuous vacuum pan 14 of the type described in the specification of published international patent application WO 01/91875. The content of this publication is incorporated herein in its entirety by way of reference. The continuous vacuum pan 14 is separated from a large bore vertical crystalliser 16 which is housed at the base of the structure 12.1 by a distancing strake 18 which defines a space accommodating crystalliser drive motors 20. The internal space provided by the distance strake 18 also facilitates access for workers when maintenance is to be carried out on, for instance, the bottom of the pan 14 or the crystalliser drive motors 20.

A riser pipe 22 is connected, and provides fluid communication, between the vertical crystalliser 16 and a second large bore vertical crystalliser 24 at the base of the second structure 12.2. The second structure 12.2 includes a batch pan 28 towards its top. The purpose of the batch pan 28 is to generate crystal seed which can be used in the continuous vacuum pan 14. A seed receiver 30 is located below the batch pan 28 for receiving seed crystals which are struck from the batch pan 28. The seed receiver 30 is separated from the vertical crystalliser 26 by a distancing strake 32 defining an internal space accommodating crystalliser drive motors 34 and a seed pump 36 which is located in a seed feed line 38 extending from the seed receiver to the continuous vacuum pan 14. The internal space provided by the distancing strake 32 facilitates access for workers in the event that maintenance is to be undertaken on the crystalliser drive motors 34, the seed pump 36 or the bottom of the seed receiver 30.

A riser pipe 40 extends from the crystalliser 24 for feeding formed crystals to a centrifugal, not shown.

As discussed in the specification of WO 01/91875, the continuous vacuum pan 14 comprises an upper massecuite pan and a lower massecuite pan, here respectively indicated by the reference numerals 44 and 46. The first structure 12.1 is provided with a conduit network which is configured as shown and generally indicated with the reference numeral 48. In the conduit network 48 a discharge point 50 for the upper massecuite pan 44 is provided with a valve 52 which allows the upper massecuite pan 44 to strike to the lower massecuite pan 46. The conduit network 48 further includes a massecuite line 54 with a valve 56 allowing the upper massecuite pan 44 to strike to the vertical crystalliser 16. The conduit network 48 also includes a massecuite line 58 with a valve 60 enabling the lower massecuite pan 46 to strike to the vertical crystalliser 16.

The conduit network 48 also includes massecuite lines 62 and 64 fitted with valves 66 and 68 that allow the upper massecuite pan 44 and the lower massecuite pan 46 to be struck to other crystallisers, not shown in Figure 1. The vertical crystallisers 16 and 24 each include a rotor shaft 70 with mixing arms 72. Although not shown it is envisaged that the rotor shaft 70 could include cooling fins.

The operation of the structures 12.1 and 12.2 can be summarised with reference to the following example: crystal seed is boiled inside the batch pan 28 after which the formed seed is struck to the seed receiver 30. The formed seed can now be pumped by the seed pump 36, through the seed feed line 38, to the continuous vacuum pan 14. Crystals are allowed to grow inside the continuous vacuum pan 14 whereafter the massecuite is discharged from the lower massecuite pan 46 and fed to the vertical crystalliser 16 via the massecuite line 58, with the valve 60 open and the valve 68 closed. The massecuite is allowed to cool inside the vertical crystalliser 16 whereafter it is fed via the riser pipe 22 to the vertical crystalliser 24 to undergo a further cooling cycle. Thereafter the massecuite may be fed to centrifugals, not shown, where the crystals in the massecuite can be separated in a conventional manner, via the riser pipe 40.

Although not described above, it is envisaged that a suitable conduit network can be provided for draining the seed receiver 30 to either one of the vertical crystallisers 16 and 24.

An important feature of the invention is the fact that the continuous vacuum pan 14 and the batch pan 28 are supported vertically above the associated crystallisers 16, 24. In effect, the crystallisers 16, 24 each form part of a crystalliser structure 15, 23 which supports the respective pan. In each case the crystalliser structure also includes an outer wall 27, 29, in this case of round cylindrical shape, around the crystalliser. These outer walls are extended vertically above the crystallisers 16 and 24 in order to provide support for the pans 14, 28. In the illustrated arrangement, a lower portion of the wall in each case forms an outer wall of the crystalliser while an upper portion of the wall forms an outer wall of the associated pan. lntermediate portions of the walls, provided by the distancing strakes 18 and 32, provide the internal spaces mentioned above.

Compared to conventional arrangements in which the continuous vacuum pan and batch pan are supported by dedicated steel structures it will be understood that the illustrated arrangement is advantageous in that the crystalliser structures 15, 23 are able, through extensions of their walls 27, 29, to support the weight of the respective pans 14, 28 located vertically above them. It will of course be also be understood that the foundations of the crystalliser structures and the walls themselves will be designed appropriately to take the applied loads.

Massecuites are generally classified in order of descending purity as A, B or C massecuite. This convention is well known to persons skilled in the art and will be used to describe the structures employed in a second sugar making arrangement in accordance with the invention. In this convention, by way of example, the term "A vacuum pan" refers to the first vacuum pan in which the highest purity syrup is used as feed to produce the highest quality crystals, while the term "C continuous vacuum pan" refers to the vacuum pan in which sucrose is crystallised from the molasses resulting from the second boiling and has the lowest purity.

Figure 2 shows a second sugar making arrangement 100 and six structures in accordance with the present invention, generally indicated respectively with the reference numerals 102.1 to 102.6. The structure 102.1 comprises an A continuous vacuum pan 104, similar to that described in WO 01/91875, having an upper massecuite pan 106 and a lower massecuite pan 108. The A continuous vacuum pan 104 is supported by a vertical extension of the wall of a first A vertical crystalliser structure 110. In the structure 102.2 an A batch pan 112 and an A seed receiver 114 are supported by a vertical extension of the wall of a second A vertical crystalliser structure 116. The A seed receiver 1 14 is in fluid communication with the A continuous vacuum pan 104 via the seed feed line 118. It will be readily appreciated that the structures 102.1 and 102.2 function in the same manner as the structures 12.1 and 12.2 described above.

The structure 102.3 comprises a B continuous vacuum pan 120, similar to that described in WO 01/91875, having an upper massecuite pan 122 and a lower massecuite pan 124. The B continuous vacuum pan 120 is supported by a vertical extension of the wall of a first C vertical crystalliser structure 126. The structure 102.4 includes a B batch pan 128 and a B seed receiver 130 which are supported by a vertical extension of a second C vertical crystalliser structure 132. The B seed receiver 130 is in fluid communication with the B continuous vacuum pan 120 via a seed feed line 134. The reference numerals 137 and 139 indicate discharge feeds from the B continuous vacuum pan 120.

The structure 102.5 houses a C continuous vacuum pan 136, again similar to that described in WO 01/91875, having an upper massecuite pan 138 and a lower massecuite pan 140. The C continuous vacuum pan 136 is supported on a vertical extension of the wall of a third C vertical crystalliser structure 142. The structure 102.6 includes a C batch pan 144 and a C seed receiver 146 which are supported by a vertical extension of the wall of a fourth C vertical crystalliser structure 148. The C seed receiver 146 is in fluid communication with the C continuous vacuum pan 136 via a seed feed line 150. As shown, the C massecuite discharged from the C continuous vacuum pan 136 can either undergo repetitive crystallising steps in the crystallisers of the first, second, third and fourth C vertical crystalliser structures 126, 132, 142 and 148 or could be discharged, as indicated by the reference numeral 152 to another crystalliser (not shown in the drawings).

It is also pointed out that the A massecuite need not necessarily be discharged to the crystalliser of the first A crystalliser structure 110 but could be fed, as indicated by the reference numeral 154, to another crystalliser (not shown in the drawings). Figure 2 shows a normal installation for a three stage boiling system without any B crystallisers. It will, however, be appreciated that different massecuites could be boiled in the upper and lower pans of the various described continuous vacuum pans and could, as a result, be discharged to different points in the crystallisation process.

It is also pointed out that although only six structures are shown in Figure 2 for the second sugar making arrangement 100, the arrangement will typically comprises eight structures. In this case the two structures which are not shown will typically comprises a duplication of the A structures indicated with the reference numerals 102.1 and 102.2.

It will be understood that in its simplest form, the structure of the invention comprises a pan, being a continuous vacuum pan or a batch pan, and the associated crystalliser structure which supports it vertically above the crystalliser. However, as indicated above, the structure of the invention extends to arrangements with a plurality of pans, both continuous vacuum pans and batch pans for seed generation, with each pan supported vertically over a associated crystalliser by the associated crystalliser structure.

The above described arrangements allow the respective pans to be mounted above and supported by the associated crystalliser structures, conveniently with appropriate walkways between them for operating personnel. This is advantageous in that it obviates the need for further, dedicated steel support structures to support an operating floor.

A further advantage is the fact that the footprint of the overall structure used in the sugar making process is related to the footprint of the individual crystalliser structures, for example eight. In other words, a structure according to the invention may be expected to occupy less area than a conventional arrangement in which there are also dedicated support structures for the continuous vacuum pans and batch pans. Yet another advantage of the illustrated structures is that fact that there is no need to pump massecuite from the pans to the crystallisers as flow will take place under gravity, with the associated benefits resulting therefrom.