WO2015022620A2

WO2015022620A2 - Diffuser

Info

Publication number: WO2015022620A2
Application number: PCT/IB2014/063846
Authority: WO
Inventors: Craig Jensen; Leon Smith
Original assignee: Tongaat Hulett Limited
Priority date: 2013-08-15
Filing date: 2014-08-11
Publication date: 2015-02-19
Also published as: WO2015022620A3; ZA201600462B

Abstract

This invention relates to a diffuser and more particularly to a chain diffuser for use in a sugar extraction process. The diffuser includes a diffuser floor, and a plurality of chain ladder assemblies being displaceable relative to the diffuser floor. Each of the chain ladder assemblies comprise two opposing chains being driven by drive sprockets, with the drive sprockets located on a drive shaft arrangement. The drive shaft arrangement includes at least two independent drive shafts located end to end, with each drive shaft driven by its own dedicated driving means. The diffuser is characterized in that the drive shaft arrangement includes synchronization means for ensuring that the two drive shafts rotate at the same speed.

Description

DIFFUSER

BACKGROUND TO THE INVENTION

THIS invention relates to a diffuser and more particularly to a chain diffuser for use in a sugar extraction process.

A diffuser is an apparatus commonly used in the sugar industry to extract sugar bearing juice from shredded cane or bagasse. The operation of a diffuser is based on systematic counter current washing of the cane or bagasse by means of imbibition water. This is achieved by forming a bed of cane or bagasse on a conveyor, while copious quantities of water and thin juice is allowed to percolate through the bed to wash out the sugar bearing juice. The water is added at the discharge end of the conveyor and is pumped forward stage by stage towards the feed end, with each stage defining a completed percolation cycle. The process is repeated until the juice reaches maximum concentration at the feed end of the diffuser.

A typical diffuser is 60m long and between 6 and 12m wide. The floor of the diffuser is made of perforated plate, over which a carrier rides. The carrier is in the form of conveyor grids or slats that are attached at their ends to drag chains, so as to form 'chain ladders' with a width of approximately one to two meters. The drag chains are supported and driven at the extreme ends of the diffuser by sprockets, and the drive sprockets are driven by a common head shaft. The chain ladders drag the cane along at a speed of about 1 meter per minute. Under the perforated floor, the diffuser is divided into 10 to 12 stages, each stage analogous to a single milling unit. Press water and imbibition are added ahead of Stage 12; thin juice from Stage 12 is recycled and added ahead of Stage 11; thin juice from Stage 11 is recycled and added ahead of Stage 10 - and so on until the juice is withdrawn from Stage 1. A portion of the Stage 1 juice is tapped off, heated, and poured onto the incoming cane to saturate and heat it. This fraction of juice is called scalding juice. The bulk of the juice is sent to the process stream for further processing.

The fluid discharge end of the diffuser is sealed by a rotating weighted drum which dewaters the cane to some extent. A spiked rotor called a kicker breaks off chunks of the hot fibre that then fall onto a carrier that feeds the dewatering mill.

Proper percolation through the fibre bed is critical in a diffuser. Batteries of lifting screws disturb the bed, preventing any packing that may occur during its hour long travel through the diffuser. A blinded bed results in juice travelling over the top of the fibre, and the diffuser is then said to be flooded, imbibition rates tend to be higher for a diffuser than for a mill, white similar extractions can be obtained. Where one (or two) conventional milts precede a diffuser, that diffuser is referred to as a bagasse diffuser. A cane diffuser handles prepared cane.

Current diffuser designs utilize a large head shaft and drive to drive the chain ⁽adders, which in turn drags the bed of cane through the diffuser. Although this works well from a process perspective, a number of disadvantages are associated with this configuration when viewed from a mechanical and structural perspective. These include: • The load on the head shaft is high and large amounts of steel are required for manufacturing the head shaft, resulting in high cost;

« The required foundation is substantial and expensive;

• A large and expensive single drive is required;

• The drive cannot be viably kept as a stock item, thus resulting in substantial downtime should there be a major failure; and

• The width of the diffuser is fixed at the time of manufacture due to the continuous head shaft, and expansion of capacity by widening the diffuser will entail replacement of the entire head shaft and drive, thus rendering expansion commercially not viable.

To reduce the cost of manufacture a "walking floor diffuser" has been suggested, and is currently used in industry, for example WO2007/015124. The walking floor diffuser utilises an established method for moving bagasse, and comprises a series of strips of perforated plates / panels that all move forward at the rate at which it is desired that the bagasse or cane mat will travel. The plates / panels are moved hydrauticaily, and this type of diffuser does not use a chain driven system. Plates or panels are rapidly returned to the feed end of the diffuser once the discharge end is reached. In this way the floor slowly moves the bagasse forward. The advantage is this is that there is no head shaft and drive, and the diffuser is therefore expandable in width by adding more rows of perforated plate / panels. However, there are a number of disadvantages with this particular arrangement. These include:

• The bagasse tends to block the perforated plate because the scraping action of the chain and slats are not present;

• The hydraulic drive arrangement is complex and expensive to maintain;

• Controls are complex and any sequencing problems result in fractures of the plates;

• The perforated plates carry the entire weight of the bagasse bed, thus resulting in excessive wear; * The bagasse tends to compact; and

• The rapidly returning strip of perforated p!ate results in juice bypassing the intended counter current flow path, and extraction efficiency is reduced.

A new diffuser has been proposed by the applicant to alleviate the above disadvantages, and comprises a chain diffuser characterized in that it is modulariy expandable by increasing the width, and thus the number of ladder assemblies, of the diffuser. This is invention is disclosed in the applicants co-pending application PCT/IB2012/053623 entitled "Diffuser". The diffuser disclosed in said application comprises a plurality of drive shafts instead of a single drive shaft, but it has subsequently been found that the proposed solution is not optimal in that the drive shafts are not properly synchronized, which is problematic.

It is accordingly an object of the invention to provide a diffuser that will, at least partially, alleviate the above disadvantages.

It is also an object of the invention to provide a diffuser which will be a useful alternative to existing diffusers.

SUMMARY OF THE INVENTION

According to the invention there is provided a chain driven diffuser for use in a sugar extraction process, the diffuser including:

a diffuser floor;

a plurality of chain ladder assemblies being displaceabie relative to the diffuser floor, with each chain ladder assembly comprising two opposing chains being driven by drive sprockets, with the drive sprockets located on a drive shaft arrangement; the drive shaft arrangement including at least two independent drive shafts located end to end, with each drive shaft driven by its own dedicated driving means;

characterized in that the drive shaft arrangement includes synchronization means for ensuring that the two drive shafts rotate at the same speed.

The driving means may be in the form of a motor and gearbox arrangement.

There is provided for the synchronization means to be in the form of an optical indexing arrangement.

There is still further provided for the dtffuser to include a secondary shaft located between the two independently driven shafts.

The secondary shaft may be driven by one of the adjacent shafts by way of a gear coupling that connects the independently driven shaft to the secondary shaft.

a diffuser floor;

a plurality of chain ladder assemblies being displaceable relative to the diffuser floor, with each chain ladder assembly comprising two opposing chains being driven by drive sprockets, with the drive sprockets located on a drive shaft arrangement;

the drive shaft arrangement including at least two independent drive shafts located end to end, with each drive shaft driven by its own dedicated driving means;

characterized in that a service tunnel is provided along the width of the diffuser adjacent the drive shaft arrangement in order to provide access to individual components making up the drive shaft arrangement.

BRIEF DESCRIPTION OF THE DRAWINGS

A number of embodiments of the invention are described by way of non- limiting examples, and with reference to the accompanying schematic representations in which:

Figure 1 is a simplified schematic representation of a diffuser in accordance with the invention;

Figure 2 shows one embodiment of a drive arrangement of the diffuser;

Figure 3 shows the drive arrangement of Figure 1 in more detail; and

Figure 4 shows a manner in which a diffuser, utilizing the drive arrangement of Figure 3, can be extended.

DETAILED DESCRIPTION OF INVENTION

Referring to the drawings, in which like numerals indicate like features, a non-limiting example of diffuser in accordance with the invention is generally indicated by reference numeral 10.

The diffuser 10 is in particular a chain driven diffuser, and includes a primary housing 11 having a perforated floor 15 for receiving shredded cane or bagasse. The cane or bagasse is fed into the diffuser 10 at a feed end 12, and is displaced towards a discharge end 13, while imibibtion water percolates through the bed of cane or bagasse in a countercurrent configuration. More particularly, the diffuser 10 is divided in a number of stages (14.1, 14,2 ... 14. n), each including a fluid collection hopper there below, and a fluid displacement means to pump the fluid to a subsequent stage. The effective movement of the imbibition water is in the direction of arrow B, i.e. from the discharge end 13 of the diffuser 10 towards the feed end 12, which is in the opposite direction to the movement of the cane or bagasse, indicated by arrow A.

The cane or bagasse is displaced along the floor 15 of the diffuser 10 by way of a mechanical displacement arrangement, and in particular by way of a plurality of parallel chain ladders 16. Each chain ladder 16 comprises two opposing drive chains 16.1 , with slats 16.2 extending therebetween so as to form articulated frames. The drive chains 16.1 are driven by drive sprockets 18 at one extremity, and mounted on idling sprockets 17 at an opposing end thereof.

The above description describes state of the art diffuser equipment, and is therefore not the primary focus of the present invention. The gist of the present invention resides in the modular nature of a new diffuser, and in particular also the new and inventive drive and synchronization configurations that enables the diffuser to be modular. In the context of the specification, modular should be understood to mean the addition of more ladder assemblies (and of course the corresponding expansion of the floor and primary vessel) in order to increase the width of the diffuser. It would typically also entail the extension of the head shaft.

A number of options are proposed to achieve this functionality, and are described in the applicant's co-pending application, PCT/IB2012/053623. However, the common denominator is that none of the proposed new drive arrangements uses a single headshaft to drive the driving sprockets. Until now the single headshaft, which is consistently used in chain driven diffusers, has been the primary impediment to the modular expansion of chain diffusers. However, this problem is addressed by utilizing, inter alia, the drive arrangement of Figure 2.

Figure 2 shows a drive arrangement in which the headshaft has been split into two separate drive shafts 22, each of which is driven at one end by a driving means 20. The driving means 20 is typically in the form of a motor and gearbox combination. An additional bearing point 21 is provided between the two drive shafts. This is typically in the form of two bearings, one for receiving an end of each drive shaft. it will be appreciated that it is imperative for the two independently driven drive shafts 22 to remain synchronized during rotation. As shown in Figure 3, this may be achieved by utilizing synchronization means 30, which may for example be in the form of an optical synchronization arrangement, which is known in the art. The synchronization arrangement will give feedback from the master drive to the slave drive to ensure that the two shafts rotate at the same speed.

The arrangement shown in Figures 2 and 3 also lends itself to modular expansion, as is shown in Figure 4. More particularly, in Figure 4 a secondary shaft 40 is installed between the two independent drive shafts 22. It is foreseen that the secondary shaft will be driven by at least one of the other drive shafts 22, and this will typically be achieved using a gear coupling 35. in addition to driving the secondary shaft 40, the gear coupling 35 will also ensure that the secondary shaft 40 remains synchronized with the independently driven shaft 22 to which it is linked. The opposing end of the secondary shaft 40 is synchronized with the other drive shaft 22 using an optical synchronization arrangement 30 as described above.

The use of the synchronization arrangement 30 is an important feature, because this allows the drive shaft to be divided into structurally separate units, while remaining functionally integrated. The use of a gear coupling 35 in turns allow for the modular expansion of the diffuser, without the need for additional drives to drive additional drive shafts.

A maintenance tunnel (not shown) is provided in the structure of the diffuser 10 immediately below the drive shaft(s). This is a very important feature that is linked to the present invention in that the maintenance tunnel will provide access to the bearings, synchronization means, gear couplings and potentially even drives, which are now located towards a central zone of the diffuser. In the prior art, the bearings were located at the sides of the diffuser, and access to a central zone of the drive end of the diffuser was not critical. However, by moving some components of the drive arrangement into the proximal zone of the diffuser, the need to access such components without having to dismantle large parts of the diffuser becomes critical, and the maintenance tunnel provides the necessary access.

It will be appreciated that the above are only some embodiments of the invention and that there may be many variations without departing from the spirit and/or the scope of the invention.

Claims

CLAIMS:

1. A chain driven diffuser for use in a sugar extraction process, the diffuser including:

a diffuser floor;

the drive shaft arrangement including at least two independent drive shafts located end to end, with each drive shaft driven by its own dedicated driving means; characterized in that the drive shaft arrangement includes synchronization means for ensuring that the two drive shafts rotate at the same speed.

2. The chain driven diffuser of claim 1 in which the driving means is in the form of a motor and gearbox arrangement.

3. The chain driven diffuser of claim 1 or claim 2 in which the synchronization means is in the form of an optical indexing arrangement.

4. The chain driven diffuser of any one of the preceding claims in which the diffuser includes a secondary shaft located between the two independently driven shafts.

5. The chain driven diffuser of claim 4 in which the secondary shaft is driven by one of the adjacent independently driven shafts by way of a gear coupling that connects the independently driven shaft to the secondary shaft.

6. A chain driven diffuser for use in a sugar extraction process, the diffuser including:

a diffuser floor;

a plurality of chain ladder assemblies being disp!aceable relative to the diffuser floor, with each chain ladder assembly comprising two opposing chains being driven by drive sprockets, with the drive sprockets located on a drive shaft arrangement;

the drive shaft arrangement including at least two independent drive shafts located end to end, with each drive shaft driven by its own dedicated driving means; characterized in that a service tunnel is provided along the width of the diffuser adjacent the drive shaft arrangement in order to provide access to individual components making up the drive shaft arrangement.