Field of Invention The invention relates to a screw press apparatus for extraction of oil from material such as seeds.

Background A conventional oil seed press comprises press worms (collars on which flights are mounted), separated by collars (without flights) along the shaft axis, hence it is known as an 'interrupted screw press'.

This type of screw press requires guide bars at the collar positions to resist the rotation of pressing material within the press cage, so that the pressing material can flow or move forward along the shaft axis from one press worm to the next.

The flights are screw threads which normally extend circumferentially up to around 340° around the shaft.

The conventional design allows the build up of the press pressure at each individual worm stage in order to drain out the oil gradually. However, the interrupted rotational movement of material at the collars causes vibrations and fluctuation in the torsion load of the bearings and gearboxes resulting in their premature failures. This also increases the power consumption. In addition the use of collars with non- continuous pressure reduces the extraction rate of seed oil. Furthermore, the arrangement of press bearings for the press shaft, which are in contact with the dirt from the pressing material, results in frequent failure of the bearings, and using individual worms and collars slotted onto the press shaft will inevitably allow material to squeeze through the gaps therebetween, causing wear and tear to the press shaft. An aim of the invention is to provide a screw press which overcomes one or more of the above issues.

Summary of Invention

In an aspect of the invention, there is provided a screw press apparatus comprising: a feed chamber for receiving material;

a press chamber including a press shaft with a substantially helical and/or spiral flight for pressing the material;

the radius of the press shaft increasing as it extends through the press chamber;

characterised in that the feed chamber includes cutter bars for breaking up material, the press shaft extends through the feed chamber, and the flight is continuous through both chambers.

Advantageously, the cutter bars break up the material to reduce the amount of voids therein, so that the material is more easily compacted.

Typically the material is any or any combination of palm kernel seeds, sunflower seeds, rapeseed, cottonseed, copra, soya bean, and/or the like. Advantageously the continuous flight allows the pressure to be increased smoothly to facilitate higher extraction rate of oil, with the majority of the oil being extracted at the start of the press chamber. In addition the compression ratio can be easily calculated, and the thickness of the resultant press cake can be controlled. Furthermore as the pressure increases gradually there is lower stress on machine parts, which reduces wear and tear.

In one embodiment the radius and/or pitch of the flight is greater in the feed chamber than in the press chamber. Typically the pitch of the flight is constant within the feed chamber. Typically the pitch of the flight reduces as it extends through the press chamber. In one embodiment the press shaft is connected to an output shaft of a power source via an intermediate shaft. Typically one or more support bearings are located at the intermediate shaft. Advantageously, as the intermediate shaft does not contact the material, the material does not wear the bearings and the oil lubricating the bearings does not contaminate the material.

In one embodiment the power source rotates the output shaft with a substantially constant torque. This is due to the continuous flight, which advantageously results in reduced power consumption compared to conventional apparatus.

Typically the one end of the press shaft is connected to the intermediate shaft in or adjacent the feed chamber. Typically the other end of the press shaft is provided with adjustment means for adjusting the press pressure. Typically the adjustment means comprises an axially adjustable portion comprising a frustoconical section mounted on the press shaft. Typically the press shaft includes a screw thread and a hollow threaded bolt mounted thereon for axially adjusting the portion.

Typically the other end of the press shaft is provided with a supporting bush to prevent flexing of the shaft.

In one embodiment the apparatus can be operated at lower temperatures than conventional apparatus. For example, where the material is palm kernel seeds the apparatus is operated at around 60°C. This 'cold press process' is possible due to the continuous flight, which generates less heat through friction than the conventional screw presses which typically operate at temperatures of around 80-90°C using the same material. Advantageously the oil extracted is of better quality than that extracted under higher temperatures, and the press cake produced is less carbonised so is of better quality for subsequent use e.g. in animal feeds. In one embodiment the feed chamber and/or the press chamber comprises two parts. Advantageously the chamber has just a top part and a bottom part to facilitate ease of removal for maintenance. In one embodiment the press shaft can be substituted to suit pressing of hard or soft seeds, with different moisture and/or oil content. Typically the substituted press shaft can have a different shaft radius, flight radius and/or flight pitch. For example, for seeds having low oil content, it is more desirable to provide a press shaft wherein the compression is increased slowly.

In one embodiment the flight is formed from a plurality of worms mounted on the press shaft, and aligned such that the flight is continuous. In a further embodiment the press shaft comprises a plurality of sections, each section including a flight mounted thereon, such that when the sections are connected together, the flights are aligned to be continuous.

In a further aspect of the invention there is provided oil extracted from material using the apparatus as herein described.

In a yet further aspect of the invention there is provided a method of pressing material comprising the steps of:

receiving material in a feed chamber;

pressing the material in a press chamber with a press shaft including a substantially helical and/or spiral flight;

the radius of the press shaft increasing as it extends through the press chamber;

characterised in that the material is broken up with cutter bars in the feed chamber, the press shaft extends through the feed chamber, and the flight is continuous through both chambers.

Brief Description of Drawings It will be convenient to further describe the present invention with respect to the accompanying drawings that illustrate possible arrangements of the invention. Other arrangements of the invention are possible, and consequently the particularity of the accompanying drawings is not to be understood as superseding the generality of the preceding description of the invention.

Figure 1 is a view of the screw press apparatus according to an embodiment of the invention (a) from the end; (b) from above; (c) from the side.

Figure 2 is a sectional view of the screw press apparatus.

Figure 3 illustrates the parts of the feed chamber (a) isometric view; (b) end view. Figure 4 is an isometric view of parts of the press chamber. Figure 5 is a side view of the press shaft.

Figure 6 is sectional partial view of the area around the discharge gap (a) where the gap is minimised; (b) where the gap is maximised.

Detailed Description

With reference to Figures la-c and 2, the invention provides a screw press apparatus 2 comprising a feed chamber 4,a press chamber 6, and a single press shaft 8 extending through both chambers.

The press shaft 8 has a constant radius in the feed chamber 4, but increases in radius as it extends through the press chamber 6 towards the discharge gap 10.

The press shaft 8 has a continuous substantially helical flight 12 as illustrated in Figure 5. The radius and pitch of the flight is greater in the feed chamber than in the press chamber. The pitch of the flight is constant within the feed chamber, but reduces as it extends through the press chamber

The design of the flight allows the pressure to be increased smoothly to facilitate higher extraction rate of oil and the compression ratio to be easily calculated. The press shaft 8 is connected to an intermediate shaft 18, which in turn is connected to an output shaft 14 of a power source in the form of electric motor 16 via a coupling 40. The press shaft is thus driven via the intermediate shaft, which is supported by support bearings 20. The power source 16 rotates the output shaft 14 and hence the intermediate shaft 18 and press shaft 8 connected thereto with a substantially constant torque.

The constant torque is due to the continuous flight, which advantageously results in reduced power consumption compared to conventional apparatus. For example, for processing palm kernel seeds a conventional apparatus may require lOOkWh/t. However, using the same material with the invention may only require 60kWh/t.

The provision of an intermediate shaft means that the maintenance is easier and lower cost, because the press shaft will need changing more regularly, and therefore other parts of the apparatus do not need to be dismantled. In addition there is less risk of contaminating the extracted seed oil with machine oil, as the bearings supporting the intermediate shaft are located away from the press shaft and oil extraction sections. The discharge end of the press shaft 8 is supported by a bush 30 and provided with an adjustment portion 46 with a frustoconical section 22 mounted on the press shaft. A hollow bolt 24 is threadedly mounted onto the press shaft for axially moving the section 22 using handle 32 and adjusting the discharge gap 10 and thus the press pressure to suit the material and composition thereof.

With further reference to Figures 3a-b the feed chamber 4 is illustrated, which is separated into two halves for ease of maintenance, the upper half being provided with an opening 38 on which a hopper is mounted. The feed chamber has a plurality of cutter bars 28 for breaking up large pieces of material and slits 36 for draining oil therefrom.

Similarly with regard to Figure 4, the press chamber 6 is also separable into two halves as illustrated, for ease of maintenance. The press chamber includes a plurality of slits 32 and holes 34 (where appropriate for the material) for draining oil therefrom. The holes typically get smaller towards the end of the press chamber where the press shaft increases in radius, to limit the amount of fibrous material being collected with the oil.

With reference to Figures 6a-b, the area around the discharge gap can be seen in greater detail. A handle 32 is locked onto the press shaft 8 with a locking nut 44, and can be rotated to adjust the axial position of the adjustment portion 46 with the frustoconical section 22 such that the gap 10 is minimised (as illustrated in Figure 6a), or maximised (as illustrated in Figure 6b). This allows the pressure of the system to be easily adjusted to suit the material being pressed.

In use, material such as palm kernel seeds are poured into hopper 26 as indicated by arrow 48 where they are fed into the feed chamber 4. The press shaft 8 is rotated to break up larger pieces of material against the cutter bars 28 in the feed chamber before being transported by the flight 12 out of the feed chamber as indicated by arrow 50 and into the press chamber 6 as indicated by arrow 52.

In the press chamber the pressure is substantially increased to compress the material due to the flared inlet 56 and the initial increase in radius of the press shaft 8 as defined by section 58. Most of the oil is released at this section whereafter it flows back to the feed chamber and drains into oil chamber 42.

The material is pressed further in the press chamber to extract as much as possible of the remaining oil (which drains through the slits and/or holes into oil chamber 60) as the flight decreases in pitch and the press shaft radius increases, until the press cake exits at the discharge gap 10 as indicated by arrow 54. Around 80% of the oil obtained is released into the feed chamber, so is less contaminated with fibrous material than conventional methods, with the remaining 20% being extracted in the press chamber.

In a conventional method of extracting palm kernel seed oil, about 80% of the oil is extracted in a first press, with a further 12-13% being extracted in a second press. This means that the press cake after two presses has a residual oil content of about 7- 8%. Advantageously, the press cake resulting from the invention has a residual oil content of around 6%, and therefore the invention provides a better result with a single press than the conventional method which requires two presses. A further press may be used to recover any residual oil from the material collected in oil chamber 60.

A conventional method requires three supplementary presses to further recover oil from all collected material (including first press cake) for three extraction presses, whereas in the invention, only one supplementary press is required to recover residual oil from material collected in oil chamber 60 for every three extraction presses.

It will be appreciated by persons skilled in the art that the present invention may also include further additional modifications made to the device which does not affect the overall functioning of the device.