WO2009130711A1 - Improved diffuser for cane or bagasse - Google Patents

Abstract

The invention discloses an improved diffuser wherein the problems associated with diffusers with vertically disposed annular extraction stages when scaled to industrial level have been overcome by providing a simple but novel, economical and efficient solution. The improved diffuser has a smooth and continuous operation without requiring any additional or complex arrangements, controls or maintenance, as were required in the prior art.

Description

IMPROVED DIFFUSER FOR CANE OR BAGASSE

FIELD OF INVENTION

The invention relates to a mechanical device used for extraction of sucrose from sugarcane. More particularly, it relates to a diffusion apparatus.

BACKGROUND TO THE INVENTION:

The extraction of sucrose from sugar cane after cane preparation (slicing and shredding) may be carried out by crushing and/or diffusion. In diffusion, the prepared cane or bagasse is conveyed and by percolation and/or counter current flowing of a suitable water mixture, the residual sucrose is dissolved and extracted.

Various types of diffusers have been developed over a period of time to improve the efficiency of the extraction process. Broadly, the diffusers can be classified into two distinct categories, horizontal and vertical. Horizontal diffusers have enjoyed popularity in the industry and various designs of the same are in use. Attempts were made to develop commercial scale vertical diffusers but could not succeed due to challenges of scale up which confined the improvements to prototype stage only.

Horizontal Diffusers: These are of two types: fixed bed and moving bed. Experience with the different types of diffusers over many years has resulted in a situation where only moving bed diffusers are still used and have captured the cane extraction market to the exclusion of other types of diffusers. The moving bed diffusers are counter-current extraction devices, operating on a staged basis. They can have moving screens or fixed screens. These devices are about 50 — 65 m long, have long conveyors with cane or bagasse moving as a thick mat. A suitable water mixture (juice) is sprayed onto a moving bed of prepared cane or bagasse, about 50 - 65 m long, 4 - 12 m wide, with 10 - 18 stages. Their popularity is mainly owing to simplicity of operation and ability to achieve very high extraction efficiencies.

Disadvantages of horizontal moving bed diffuser: • Space requirement: They require a great amount of space in the treatment plant; and

• Cost: they are relatively expensive because of the necessary piping and conveyor elements which are required.

To overcome these disadvantages, attempts were made to design vertical diffusers.

Various designs of diffusion apparatuses with essentially doughnut configurations having vertically disposed annular extraction stages were proposed. The annular extraction stages are defined by annular concentric walls (shells). In fixed screen diffusers the annular extraction stage is usually divided into compartments by means of radially extending members or pushers. The said members move the cane or bagasse bed around the annular extraction stage. The annular wall (shell) to which the radially extending members are attached is supported on rollers or the like and is rotatably driven by any suitable means such as by sets of hydraulic rams which act against evenly spaced abutments or pins attached in the same horizontal plane to the rotatable annular wall.

Limitations of Vertical Diffusers:

Failure during scale up: Prototypes of number of such designs have been tried out in different places but suffered serious limitations of operation during scale-up. During scale up of the said apparatus to an industrial level, for example, for a sugar plant of approximately 2000TCD (tonnes crushed per day) capacity, the dimensions of the diffusion apparatus increase tremendously. It is noted that the diameter of the inner annular wall (shell) comes to about 8 metres and that of the outer about 13 metres. The height of the apparatus too is around 8 metres. For still higher crushing capacities, the diameter or the height of the apparatus increases further. Though various prototypes were described in the prior art, none was able to solve the problem of large scale operation as has been achieved in the present invention. Thus, present invention, discloses a novel diffusion apparatus which is fully operational at large scale commercial level owing to use of innovative approach in which smooth and continuous rotation of the shell has been achieved in a simple, economical and efficient manner which none of the prior art devices were able to achieve.

Technical barriers to scale up in prior art vertical diffusers: As proposed in the prior art, the annular wall (shell) supported on rollers was rotated with two sets of synchronous hydraulic rams mounted on a concrete bases. However, the system proved to be not only costly and complex but also troublesome and hence ineffective to rotate the annular wall (shell) in a smooth manner resulting in stalling of the diffusion apparatus when scaled up to the industrial level. None of such designs of diffuser are functional now.

The main limitation encountered in the scale up of the said diffusion apparatus to the industrial level lay in the movement of the annular shell. There are two approaches employed for shell movement viz. hydraulic or gear.

Hydraulic Approach: The most common approach is the use of hydraulic rams to make the annular shell rotate. However, owing to large dimensions of the annular walls (shells) when scaled up to an industrial level, it is a challenge to keep the same in a perfectly circular shape, which is essential to rotate the shell. Obviously, rotation involves a circular path and whenever, this path gets changed e.g. due to ovality, motion of the shell gets affected, resulting in breakdown of the machinery, in case of existing design of the apparatus. Even minor inefficiencies in synchronizing the movement of sets of hydraulic rams results in imprecise position locking of the shell as a consequence of which it rolls back often and also at times resulting in breakdown of the drive.

Also as shown in Fig. 1, hydraulic system involves a multiplicity of components. This results in considerable wear and tear, noise and increased cost owing to complex arrangement as well as controls. Also, it is error prone and demands periodic maintenance and close monitoring.

Gear Approach: It is also noted that if gears rather than hydraulic rams are employed for rotating the said annular shell, there is a risk of a breakdown in the drive due to poor gear meshing due to ovalness in the shell. Additional arrangements entailing both cost and complexity are necessitated to accommodate relatively wide changes in position of the rotating shell so that the meshing arrangements are maintained at all times and there is no slippage i.e. gearing mechanisms also need high degree of preciseness. The manufacture, cost, timely availability and maintenance of gear mechanism to rotate a shell of the said dimensions is another bottleneck. The present invention overcomes the drawbacks of the prior art in a simple, economical and efficient manner owing to use of innovative approach in which smooth and continuous rotation of the shell has been achieved which none of the prior art devices were able to achieve.

OBJECTS OF THE INVENTION:

The principal object of the invention is to provide an improved diffuser for cane and bagasse which is simple, economical and efficient.

Additional objects & advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention will be realized and attained by means of the elements and combinations particularly pointed out in the appended claims.

STATEMENT OF THE INVENTION:

Accordingly, the invention provides an improved diffuser for cane and bagasse comprising, vertically disposed annular extraction stages defined by annular concentric shells; each annular extraction stage divided into compartments by means of radially extending members attached to an annular shell;, the said annular shell being rotatable and driven by any suitable rotating means, characterized by the fact that the means for rotating the rotatable annular shell comprise: at least one circular rack with a substantially serrated profile affixed to the rotatable annular shell of the apparatus; at least one planetary drive; a rotatable disc mounted on the shaft of the planetary drive and having at least one aperture into which a push-pin can be fitted; and the said push-pin adapted to engage with the serrated profile of the circular rack and moveable thereover. BRIEF DESCRIPTION OF THE DRAWINGS:

Fig. 1 shows the schematic plan view of the cane or bagasse diffuser constructed as proposed in the prior art.

Fig. 2 shows the schematic plan view of the cane or bagasse diffuser constructed in accordance with present invention.

Fig. 3 is the schematic elevation view of the cane or bagasse diffuser constructed in accordance with present invention

DETAILED DESCRIPTION OF THE INVENTION WITH REFERENCE TO THE DRAWINGS:

Corresponding and like parts are referred to in the following description, and indicated in all the views of the drawings, by the same reference characters.

Fig. 1 shows the schematic plan view of the cane or bagasse diffuser 1 constructed as proposed in the prior art. The diffusion apparatus 1 with essentially doughnut configurations has vertically disposed annular extraction stages 2. The annular extraction stages 2 are defined by annular concentric shells 3 & 4 and divided into compartments by means of radially extending members or pushers 5. The said members move the cane or bagasse bed around the annular extraction stage 2. The annular shell 3 to which the radially extending members 5 are attached is supported on rollers or the like and is rotatably driven by sets of hydraulic rams 6 mounted on a concrete base 7, which act against evenly spaced abutments or pins 8 attached in the same horizontal plane to the rotatable annular wall 3.

The prior art system involves a multiplicity of components such as main cylinder 9, small cylinder 10, motor 11, pump 12, distributor 13, oil-cooler and various other parts associated therewith. It has complex arrangement as well as controls e.g. sensors, actuators, timers, control panel 14, VFD (variable frequency drive) 25, etc. During scale-up of the apparatus to the industrial level, the prior art systems proved to be not only costly and complex but also troublesome primarily owing to ovalness in the shell. This, coupled with even minor inefficiencies in synchronizing the movement of sets of hydraulic rams resulted in breakdown of the machinery. The system has thus been ineffective to rotate the annular shell in a smooth & continuous manner resulting in stalling of the diffusion apparatus when scaled to an industrial level.

According to the invention there is provided a diffusion apparatus comprising, vertically disposed annular extraction stages defined by annular concentric shells; each annular extraction stage divided into compartments by means of radially extending members attached to an annular shell;, the said annular shell being rotatable and driven by any suitable rotating means, characterized by the fact that the means for rotating the rotatable annular shell comprise: at least one circular rack with a substantially serrated profile affixed to the rotatable annular shell of the apparatus; at least one planetary drive and gearbox; a rotatable disc mounted on the shaft of the planetary gear box and having at least one aperture into which a push-pin can be fitted; and the said push-pin adapted to engage with the serrated profile of the circular rack and moveable thereover.

The invention will now be described by way of example with reference to the accompanying diagrammatic drawings.

Referring to figures 2 & 3, the cane or bagasse diffuser 1 provided according to the invention comprises vertically disposed annular extraction stages 2 defined by annular concentric shells 3 & 4; each annular extraction stage 2 divided into compartments by means of radially extending members 5 attached to an annular shell 3;. the said annular shell 3 being rotatable and driven by any suitable rotating means, characterized by the fact that the means for rotating the rotatable annular shell 3 comprise: at least one circular rack 15 with a substantially serrated profile affixed to the rotatable annular shell 3 of the diffuser 1; at least one planetary drive 16; a rotatable disc 17 mounted on the shaft 18 of the planetary drive 16 and having at least one aperture 19 into which a push-pin 20 can be fitted; and the said push-pin 20 adapted to engage with the serrated profile of the circular rack 15 and moveable thereover.

In the exemplary embodiment the annular shell 3 to which the radially extending members 5 are attached is supported on rollers 21 or the like and the means for rotating the rotatable annular shell 3 comprises of two racks 15 with identical serrated profiles affixed to the rotatable shell 3 of the cane or bagasse diffuser 1 with a predetermined distance between the two racks 15.. The serrations of the two racks 15 coincide. A set of four planetary drives 16, mounted on separate support structures 22, are arranged advantageously at diametrically opposite ends of the circular racks 15 at right angles to each other. The number and arrangement of drives 16 can be varied according to the dimensions of the diffusion apparatus 1.

A rotatable disc 17 is mounted on the shaft 18 of the planetary drive 16. The said disc 17 has at least one aperture 19 into which a push-pin 20 can be fitted. The exemplary embodiment has six such spaced apart apertures 19 in the rotatable disc 17 into which the push-pins 20 are fitted. The push-pin 20 is fitted in the aperture 19 in a manner such that approximately equal lengths of the push-pin 20 extend out from either ends of the disc aperture 19. The portions of push-pin 20 extending out from the either ends of the disc aperture 19 are covered with a sleeve (not shown), moveable thereover, to reduce wear and tear of the push-pin 20 and provide rolling friction instead of sliding friction. The push-pins 20 are arranged and adapted to be engaged with the serrations of the racks 15. The planetary drive 16 with the rotatable disc 17 mounted on the shaft 18 is installed to position the said disc 17 in the intervening space between the two racks 15 affixed to the rotatable shell 3 at a predetermined distance. The rack 15 serration profile and pitch, and the spaced apart disc apertures 19 are designed and arranged in a manner to ensure continuous engagement of the push-pins 20 with the racks 15 so that there is no breakdown in the drive and the shell rotates continuously. The shaft 18 is supported at its free end by a bearing mounted within a bearing housing 23 affixed to a support member 24 extending from the support structure 22. The support at either ends of the shaft 18 ensures longer bearing life. To synchronize the planetary drives 16 all prime movers of the said drives 16 are controlled by a variable frequency drive 25.

Advantages of the present invention:

• Smooth operation: It is noted that in operation, such a simple but novel system ensures smooth and continuous drive to the rotatable annular shell of the diffusion apparatus. Not only it is easy to operate on variable speed as per process requirement but also it is possible to run at lower capacity on lesser number of drives in case of maintenance of one or two drives.

• Simpler construction: As the present invention is able to accommodate wide changes in position of the rotatable shell owing to ovalness, need for additional arrangements/components or controls as required in the prior art is completely eliminated. Apart from maintaining rpm (rotations per minute) of the drive or drives, there are no other controls required for the efficient functioning of the diffusion apparatus.

• Reduction in manufacturing cost and time: Not only the number and complexity of components in the system has been reduced, but also the cost and time required for manufacturing the components of the inventive rotating means is considerably less as compared to other arrangements.

• Reduction in maintenance: The wear and tear is highly contained and the inventive rotating system requires very less maintenance and supervision. Only the sleeve covering the push-pins may require replacement without dismantling in any manner the other component parts of the rotating means. This is in sharp contrast to the means used in the prior art.

• Less Inventory: Due to lesser number and complexity of the components in the system and also much reduced maintenance requirements, the inventory of spares required for the inventive system is considerably less

In the preceding detailed description, the invention is described with reference to specific exemplary embodiments thereof. Various modifications and changes may be made thereto without departing from the broader spirit and scope of the invention as set forth in the claims. The specification and drawings are, accordingly, to be regarded in an illustrative rather than a restrictive sense. Thus, without further analysis, the foregoing will so fully reveal the gist of the present invention that others can, by applying current knowledge, readily adapt it for various applications without omitting features that, from the standpoint of prior art, fairly constitute essential characteristics of the generic or specific aspects of this invention.

List of Reference Numbers:

1. Cane or Bagasse Diffuser 14. Control Panel

2. Annular extraction stage 15. Circular Rack

3. Inner shell 16. Planetary drive

4. Outer shell 17. Rotatable disc

5. Radial members / pushers 18. Shaft

6. Hydraulic rams 19. Disc aperture

7. Concrete base 20. Push-pin

8. Abutments or Pins 21. Rollers

9. Main cylinder 22. Support structure

10. Small cylinder 23. Bearing housing

11. Motor 24. Support member

12. Pump 25. VFD (Variable frequency drive)

13. Distributor

Claims

CLAIMS:We claim:

1. A diffusion apparatus comprising vertically disposed annular extraction stages defined by annular concentric shells; each annular extraction stage divided into compartments by means of radially extending members attached to an annular shell; the said annular shell being rotatable and driven by any suitable rotating means, characterized by the fact that the means for rotating the rotatable annular shell comprise: at least one circular rack with a substantially serrated profile affixed to the rotatable annular shell of the apparatus; - at least one planetary drive; a rotatable disc mounted on the shaft of the planetary drive and having at least one aperture into which a push-pin can be fitted; and the said push-pin adapted to engage with the serrated profile of the circular rack and moveable thereover.

2. The diffusion apparatus of claim 1 wherein two circular racks with identical serrated profile are affixed to the rotatable annular shell of the apparatus with a predetermined distance between the said two racks.

3. The diffusion apparatus as claimed in claim 2 wherein the serrations of the two racks correspond to each other.

4. The diffusion apparatus as claimed in claim 1 wherein four planetary drives are arranged at diametrically opposite ends of the circular rack at right angles to each other.

5. The diffusion apparatus as claimed in claim 1 or 2 wherein the disc mounted on the shaft of the planetary drive is positioned in the intervening space between the two racks affixed to the rotatable shell.

6. The diffusion apparatus as claimed in claim 1 wherein the disc mounted on the shaft of the planetary drive has spaced apart apertures, preferably six.

7. The diffusion apparatus as claimed in claim 1 or 2 wherein the push-pin is fitted in the aperture in the disc in a manner such that approximately equal lengths of the pushpin extend out from either ends of the disc aperture.

8. The diffusion apparatus as claimed in claim 6 wherein the portions of push-pin extending out from the either ends of the disc aperture and adapted to engage with the serrations of the circular rack are covered with a sleeve.

9. The diffusion apparatus substantially as herein described in the specification with reference to the accompanying drawings.