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Title:
IMPROVED PRESS
Document Type and Number:
WIPO Patent Application WO/2020/104767
Kind Code:
A1
Abstract:
The invention describes a press for the mechanical extraction of oil or fat from solid oleaginous material comprising the following sub- assemblies mounted on a common steel frame: one or more feeder assembly or assemblies, a main shaft assembly, an oil drainage cage assembly (2.2) having a cylindrical internal shape of maximal diameter D, shaft thrust bearing assembly, motor, speed reducer or gear box assembly, wherein the main shaft assembly comprises individual shaft segments, at least distance elements, pressure elements and worm elements, characterized in that each worm elements contain at least two parallel flights.

Inventors:
MILES DAVID REX (GB)
Application Number:
PCT/GB2019/053087
Publication Date:
May 28, 2020
Filing Date:
October 31, 2019
Export Citation:
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Assignee:
DE SMET ROSEDOWNS LTD (GB)
International Classes:
B30B9/12
Domestic Patent References:
WO2017013282A12017-01-26
Foreign References:
CN101838096A2010-09-22
CN201009453Y2008-01-23
GB749215A1956-05-23
US4901635A1990-02-20
US5680812A1997-10-28
Attorney, Agent or Firm:
BARKER BRETTELL LLP (GB)
Download PDF:
Claims:
CLAIMS

1. A press for the mechanical extraction of oil or fat from solid oleaginous material comprising the following sub-assemblies mounted on a common steel frame:

a) one or more feeder assembly or assemblies,

b) a main shaft assembly,

c) an oil drainage cage assembly having a cylindrical internal shape of maximal diameter D,

d) shaft thrust bearing assembly,

e) motor, speed reducer or gear box assembly,

wherein the main shaft assembly comprises individual shaft segments, at least distance elements, pressure elements and worm elements, characterized in that each worm elements contain at least two parallel flights.

2. A press according to claim 1 wherein the feeder assembly comprise a vertical feeder assembly and/or a horizontal feeder assembly.

3. A press according to any of claims 1-2 wherein the gash angle of the worm elements is comprised between 90 and 270°

4. A press according to any of claims 1-3 wherein the pitch length of the worm elements of the feed end section of the main shaft assembly is superior to the diameter D.

5. A press according to any of claims 1-4 wherein said main shaft assembly shows reduced wear compared to prior art presses used in identical conditions.

6. A press according to any of claims 1-5 showing less vibrations than prior art presses used is identical conditions.

Description:
IMPROVED PRESS

FIELD OF THE INVENTION

This invention relates to a press for the continuous mechanical extraction of oil from oil bearing solid materials such as vegetable oleaginous material containing fat and/or oil. In particular, the invention provides a press that is more stable, reliable and economical. BACKGROUND OF THE INVENTION

The two most common processes to extract oil or fat from solid material such as oleaginous vegetable materials for example seeds, beans, and nuts are the mechanical extraction process where mechanical force is used to extract the oil by squeezing the solid material under high pressure, and the solvent extraction process where a solvent is mixed with the solid material to dissolve and extract its fatty content. Solvent extraction facilities are complex and expensive, but the experience shows that for large capacity and on the long run they are more economical compared to oil mill equipped solely with full presses. This is due mostly to two factors: firstly, solvent extraction extracts substantially more oil than full press (there is less residual oil in the residue), thus generating more valuable oil than a full press processing an equivalent quantity of oil bearing material; secondly, mechanical presses have high maintenance cost due to the huge mechanical constrains generated to continuously squeeze solid oleaginous material. The high force needed to squeeze solid oleaginous material demands also a substantial energy consumption, in particular electricity. Of course, solvent extraction is also energy intensive, but a substantial fraction of this energy is provided by steam that can be produced more cheaply and locally by burning waste materials such as hulls or by recovering steam generated elsewhere in the oil mill facility.

Therefore, there is a need for an improved press that would be more reliable and thus would require less costly maintenance. There is also a need for an improved press that requires less energy to process a given quantity of oleaginous material. Both improvements collaborate to a more economical mechanical extraction of oil from solid oil bearing material compared to presses of the prior art. The comparison of the respective performances of a solvent extraction facility and a mechanical extraction facility is feasible in the case of the full-press i.e. the mechanical extraction of most of the oil contained in an oleaginous material. However, presses are often used as pre-presses. A pre-press extracts only a fraction of the oil contained in the feed material. In a pre-press, the level of oil extraction is tuned to yield a cake containing the ideal amount of residual oil for a final solvent extractor. As a matter of fact, the discharge cake of the press (press-cake), as long some precautions are taken to maintain its integrity of shape and porosity, is ideal for downstream solvent extraction. Indeed, during mechanical pressing, the cellular structure of the feed material (which is often a vegetable oleaginous material) is severely distorted which tears open many of the cell walls, enabling the remaining oil to be extracted more readily during the downstream solvent extraction process.

Accordingly, this two steps extraction process combining mechanical and solvent extractions has proven to be advantageous over full mechanical or full solvent extraction for oleaginous material containing a large fraction of oil such as rapeseed for example.

However, maintenance cost of a pre-press is still high, and the energy consumption remains substantial, in particular electrical energy.

Therefore, improvements are equally needed for full-presses and pre-presses.

OBJECTS AND ADVANTAGES OF THE INVENTION

It is an object and advantage of the invention to improve the reliability of the mechanical press compared to presses of classical design. Improvement of the reliability reduces the maintenance needs and cost. It must be stressed that the improvement of the reliability of the improved press according to the present invention does not require a sturdier and substantially more expensive construction. The improved reliability is the results of improved an innovative design. The innovative design induces only a limited cost increase, but this one is rather negligible in regard to the overall price of the press and furthermore this limited cost increase will be totally compensated by the profits generated by the invention.

It is a further object and advantage of the invention to reduce the energy requirement to process a given quantity of oleaginous material. Further aspects and advantages of the present invention will become apparent from the description hereinafter.

BRIEF DESCRIPTION OF THE INVENTION

It has been surprisingly observed that the above listed objectives can be attained with a press for the mechanical extraction of oil or fat from solid oleaginous material comprising the following sub-assemblies mounted on a common steel frame: one or more feeder assembly or assemblies, a main shaft assembly, an oil drainage cage assembly having a cylindrical internal shape of maximal diameter D, shaft thrust bearing assembly, motor, speed reducer or gear box assembly, wherein the main shaft assembly comprises individual shaft segments, at least distance elements, pressure elements and worm elements, characterized in that each worm element contains at least two parallel flights.

It has been surprisingly observed that the above listed objectives can further be attained with a press as previously described wherein the feeder assembly comprise a vertical feeder assembly and/or a horizontal feeder assembly.

It has been surprisingly observed that the above listed objectives can further be attained with a press as previously described wherein the gash angle of the worm elements is comprised between 90 and 270°.

It has been surprisingly observed that the above listed objectives can further be attained with a press as previously described wherein the pitch length of the worm elements of the feed end section of the main shaft assembly is superior to the diameter D.

It has been surprisingly observed that the above listed objectives can further be attained with a press as previously described wherein said main shaft assembly shows reduced wear compared to prior art presses used in identical conditions.

It has been surprisingly observed that the above listed objectives can further be attained with a press as previously described showing less vibrations than prior art presses when used is identical conditions.

Thus, it has been found that the above objects are met with a mechanical press equipped with a screw having two or more flights extending over all the worm elements composing the screw. Surprisingly, the stability of the press was greatly improved compared to mechanical press equipped with a screw having worm elements with one flight or having only two flights in the feed end section of said screw. The improved stability materializes by less vibrations of the press and leads to less stresses and constrains inside the press and thus will improve the reliability which reduce the maintenance cost. In particular, the screw or the elements making of the screw show substantially less wear after a given period of service than any screw of the prior art. In particular, the drive elements of the press according to the present invention, such as the main electrical motor, the gear box and the bearings will on the long run show less wear than when screw of the prior art is mounted in the press. Without willing to be bound by any theory, it is believed that the observed reduction of specific electricity consumption is due to the improved stability of the press, in particular the stability of the screw, since less energy is dissipated and lost in vibrations. Surprisingly, a press equipped with a screw having two or more flights extending over all the worm elements of said screw has an improved output compared to mechanical press equipped with a screw having only one flight on the worm elements of said screw. It is also believed that the observed improved output is probably due to the improved stability of the press, in particular, the stability of the screw, since less energy is dissipated and lost in vibrations and that therefore all the energy input serves the purpose of pressing and pushing the oleaginous material forward in the most efficient way.

DESCRIPTION OF THE FIGURES

Figure 1 is a representation of a standard screw equipped only with single flighted worm elements. The screw is lodged inside the cage (1.2) of diameter (D). The length of the pitch (LP) in the feeding end section (1.1) of the screw is inferior to the diameter (D).

Figure 2 is a representation of an embodiment of the equipment according to the invention said equipment having a screw made exclusively of double flighted worm elements. The screw is lodged inside the cage (2.2) of diameter (D). The length of the pitch (LP) in the feeding end section (2.1) of the screw is superior to the diameter (D).

In the figures, the dashed lines represent the continuation of the flights on the other side of the screw. DEFINITIONS

The terms defined below can be used in plural or singular number depending on the context and will maintain their meaning regardless of their number.

Press: in the context of this invention the term“press” refers to a screw-press and includes both the full-press and the pre-press.

Worm assembly: in the context of this invention the terms‘worm assembly” refer to the collection and arrangement of the worm elements but also of the pressure elements, spacers etc. mounted on the shaft that collectively when slid over the driving shaft form the screw of the press. Thus, the terms worm assembly is an approximation since elements other than worm are present. However, those terms are widely used in the field and by the skilled artisans. In the field (and at some occasions in this text, depending on the context) the expression“main shaft assembly” or‘screw” are used instead. Individual elements are arranged into multiple pressing stages. Each pressing stage typically consists of a mixing element (cylindrical element with lugs to mix the material), a worm element (cylindrical or conical element with screw-flight to convey the material forward), and pressure element (a conical element without screw-flights to exert pressure). Between those elements, distance element can be placed if needed. A stationary knife bar protrudes from the drainage cage into the space created by the conical shaft element to insure the material conveys forward by preventing the material from rotating with the shaft.

Feed material: it the context of this invention the terms“feed material” correspond to a solid material containing oil or fat. Usually the feed material is an oleaginous vegetable material having been treated by a variety of treatments such as dehulling and/or cooking and/or flaking. However, the feed material can also be animal tissues.

Press cake: it the context of this invention the terms“press cake” correspond to the at least partially defatted solid material exiting the press. In the case of pre-pressing, this press-cake still contains a substantial amount of oil (for example about 20 to 30%) and this oil is usually extracted in a solvent extractor. In the case of full-pressing, the press-cake does not contain a large amount of oil (usually not more than a few percent) and in that case this low-fat press-cake is directly used as feed ingredient. Vibrations: in the context of this invention the term ‘vibrations’ refers to any movements or displacements or shaking of the press including any movements or displacements or shaking of the subassemblies forming the press. Such vibrations are well known in the field of oilseed pressing and are due to the high forces needed for pressing and squeezing the feed material. It must be noted that those vibrations have no constant frequency or amplitude. Those vibrations are in fact mostly disordered which amplifies their deleterious nature for the reliability of the press. It is hazardous to quantify those vibrations, but a skilled artisan will undoubtfully notice and appreciate any improvement when occurring.

Prior art press: in the context of this invention, the terms‘prior art press’ refer to press equipped with screw containing single flighted worm elements. A large proportion of prior art presses are equipped with screw containing solely single flighted worm elements. Some of the prior art presses are nevertheless equipped with a screw containing a few double flighted worm elements localized in the feed-end of said screw.

Improved reliability: in the context of this invention, the terms‘improved reliability’ refers to a longer service period for parts such as drive, gear box, bearing, worms. The increase of service period may differ depending on the parts.

DETAILED DESCRIPTION OF THE INVENTION

A screw press is typically made up of a cylindrical stationary barrel, which has its surface composed of lining bars separated by shims. The gaps between the lining bars provide drainage slots for the oil released upon squeezing of the feed material processed by the press. Within this barrel a“worm assembly” is fitted. This is made up of a number of helical screw elements (worms) separated by mixing elements and distance element or pressure elements mounted on a central shaft.

The shaft and worm assembly rotate inside the stationary barrel. Over the distance elements and pressure elements, flat blades, known in the field as knife bars, are mounted to the stationary cage and protrude into the worm assembly. These knife bars together with the lining bars are designed to grip the feed material and prevent that it rotates with the shaft. Indeed, the feed material must not rotate with the shaft as it is the relative rotational movement of the worm assembly to the feed material that results in longitudinal forces that convey the feed material along the worm assembly. As a matter of fact this longitudinal forces conveying the feed material along the worm assembly is considerable because as the conveyed material is squeezed, it generates extensive back pressure.

Indeed, as the feed material is conveyed from the inlet to the outlet of the worm assembly, there is a progressive reduction in the swept volume of the worm elements. This volume reduction together with the back pressure from the pressure elements generate pressure on the feed material within the barrel. This pressure in turn releases the oil, from the feed material that is drained from the barrel through the drainage slots between the lining bars.

Typically, the worm elements are made up of a cylindrical, or conical, body around which a helical flight is wrapped. The flight will extend from the worm body to almost contact the inner surface of the barrel. The rotating action of the worm elements results in the flight pushing the feed material along the worm assembly. Due to the way in which the flight pushes the feed material into the reduced volume behind of it, an area of localized extreme high pressure is generated near to the discharge end of the flight.

In practice, a press is used in an oil mill in combination with other pieces of equipment notably feeders supplying the feed material (usually oleaginous vegetable material) that will be processed by the press and a cake handling and conveying system that treat the at least partially defatted material exiting the press. In case of a pre-press, the cake handling and conveying system preferably convey directly the cake to a solvent extractor. In that case no large cake storage equipment is foreseen. The horizontal feeder is a variable speed screw conveyor which sets the flow rate of the feed material into the press. Its rotational speed is set to maintain the press main drive motor at the required load, allowing maximum throughput without putting too much strain on the main drive motor of the press.

It is common that feed material that will be pressed, transitions from the horizontal feeder to the horizontal worm shaft of the press via a second vertical feeder, which is a constant speed vertical screw conveyor. The purpose of the vertical feeder is to put light downward pressure on the material being fed into the horizontal main shaft of the press to insure its flights are filled and that air is at least partially removed from the feed material at the beginning of the main shaft. Direct steam can optionally be injected in the vertical feeder to aid in heating up the machine upon initial start-up. The worm assembly (or screw) of the press rotates inside a slotted wall oil drainage cage to convey the vegetable material forward while applying pressure to exude the oil out through the slots of the drainage cage. The drainage cage consists of individually placed lining bars with slots between which are parallel with the main shaft. These slots are narrow enough to allow the low viscosity oil to pass through while retaining the solids inside. The slot width between lining bars decreases from feed end to discharge end as the pressure increases, to minimize the amount of solid material (typically known as“foots”) that passes through the slots with the oil. This oil is of course recovered and further processed according to the standard practices of the industry.

As the press cake discharges at the end of the main shaft and drainage cage, there is a significant pressure drop which causes moisture in the cake to flash evaporate. The escaping moisture helps insure the porosity of the cake which should be maintained for efficient solvent extraction. However, this newly formed press cake is easily damaged in mechanical handling system. But if some precautions are taken, notably the rapid cooling to the cake, its strength is improved so that it can withstand conveyance from the mechanical extraction building to the solvent extraction building. Therefore, such properly handled cake is an excellent starting material for a downstream solvent extractor. Of course, in case of full-pressing, such precaution concerning the handling of the press cake are superfluous since this one is not solvent extracted.

As explained before, presses are either used as full-presses, with the aim of extracting as completely as possible the oil from the feed material, or either they are used as pre-press with the aim of extracting only a fraction of the oil contained in the feed material, the remaining part of it being extracted by classical solvent extraction process. In this later case, the pre-press has thus the supplementary function of preparing the material for the subsequent solvent extraction i.e. breaking and tearing apart the cells containing the oil to ease as much as possible the diffusion of the solvent in every part of the material. This condition is primordial to ensure a fast and as complete as possible extraction of the oil from this pre-pressed material. In particular, a stringent request for all seeds crushers is to leave the minimum residual oil in the solvent extracted material. With this stringent request in mind, it has been theorized that a press equipped with double flighted worms would work and prepare more intensely the pre-pressed material and hence should improve the extractability of said pre-pressed material in the downstream solvent extraction. Indeed, as previously mentioned, a zone of localized extremely high pressure is generated in the area around the discharge end of the flight, this being even amplified if the flight end is mounted just before a pressure element. Therefore, the presence of double flighted worm’s elements on the screw should give rise to a doubling of such extreme conditions and thus further breaking and tearing the cells of the pre-pressed material. Thus, a decrease of the residual oil in the material left after the solvent extraction of the cake produced in pre-press having the design described by the present invention should be observed. However, screw for which all the worm elements are twin flighted is not available. In some presses, twin flighted worm elements can be found at the feed inlet of the worm assembly. Indeed, it is sometimes found advantageous to use a screw element that has two flights of the same pitch arranged on its outer diameter. This twin flighted arrangement is known to help improve the feeding characteristics in particular when the volume of the material to be pushed by the flight is large, which is particularly the case at the feed end of the press. Having the two flights starting on opposite sides of the worm reduces by 50% the amount of the material being pushed by each individual flight. But to our knowledge twin flighted worms are not used other than at the very feed end of the press.

Therefore, a worm assembly containing only twin flighted worm elements has been designed to replace the standard worm assembly of a well-known commercial press (800 Series Press from Rosedowns, UK). Therefore, comparison of the results obtained with the two worm assemblies will be possible on a fair basis.

Thus, the worm assembly has been designed for an 800 Series Press (in its pre-press version), that was identical to the standard one, but the worm elements throughout the screw assembly were all replaced with twin flighted version. Except for the worm elements that were all replaced by twin flighted versions, the other elements (pressure elements, mixing elements, etc.) were not modified. So, all the single flight wrapped around the length of the worm body were replaced by two flights, starting 180° apart on the worm body for each worm elements. Each flight had a gash angle of 180°degrees and consequently a pitch approximately twice that of the original worm element. A gash angle is measured as the angle around the circumference where there is a break in the flight when viewed from an end. The linear length of the replaced worm elements was of course kept identical to the original elements.

The pitch for the worm was calculated such that the worm element had a similar calculated swept volume as a conventional single-flighted worm element. It must be noted that this concept of using multiple start flights with large gash angles is not normal practice. Our thinking behind this unusual combination was a potential problem with using two standard length pitch flights. Whereby feed in the middle of the part would be surrounded on both sides by one of the two full 360° wrap round of flights. This feed would not be exposed to the anti-rotation effects provided by the knife bars. Using the 180° gash angle meant that any element of feed material would still be moved from the feed end of the worm element to its discharge end in a single rotation of the shaft and then contacted by a knife bar exposed to it. If more than two flights were to be used, for example a triple start worm, than the gash angle would need to be further increased to ensure that the pressed material all along the part is still open to the anti-rotation effects of a knife bar. The flighted portion of a worm would be approximately 360 / number of flights.

EXAMPLE

We designed a worm assembly, for an 800 Series Press, that was similar to our standard pre-press one, but where the worms throughout the assembly were all replaced with twin flighted versions made with the same steel grade and the same surface finishing that the ones used for the standard worm assembly. Basically, instead of a single flight wrapped around the length of the body we replaced this with two flights, starting 180° apart on the body. Each flight had a pitch twice that of the original part but also had a gash angle of 180°degress. A gash angle is measured as the angle around the circumference where there is a break in the fight when viewed from and end. Of course, the linear length and diameter of the twin-flighted worm elements was exactly matching the ones of each corresponding standard single-flighted worm elements. Despite the long pitch and large gash angle, design choices have been taken that resulted in a worm with the same calculated swept volume than a conventional corresponding standard element. This idea of using a much longer pitch together with a large gash angle, is not normal practice but nevertheless this design is expected to provide a satisfactory conveyance of the feed material throughout the screw, however no superior conveyance compared to a standard design having thus short pitch single-flighted worm elements should be expected. In other words, the throughput of a press equipped with a screw having the innovative design as described in the present invention should be similar to a standard press but not superior, all other conditions being similar. Indeed, the swept volume of each worm element are the same and the exposition of the feed material to the knife-bars is exactly identical. It is probably because this new design is not expected to bring tangible advantage to the mechanical pressing step per se that it was never experimented before.

The testing of industrial scale piece of equipment is only possible in real production facilities due notably to the prohibitive cost of processing large quantity of raw material. Therefore, no lab experimentation has been performed but the concept of the full twin- flighted worm assembly has been evaluated at one of the production facility of a world major oil seed crusher under a secrecy agreement. The crusher accepted to evaluate on long terms (during 18 months) the twin-flighted worm assembly in one of its 800 Series Press. The experiment started after a scheduled maintenance stop during which the above described twin-flighted worm assembly was mounted. During the period of production before the maintenance stop, a standard worm assembly was used, and therefore constitute an adequate base line. The experiment has been pursued over 18 months in real production environment and using standard conditions identical to the ones used when the standard worm assembly was equipping the press. The feed material and the feeding assembly were the same. Therefore, the obtained results are significant. It must be mentioned that the produced cake was directly solvent (hexane) extracted, the solvent extractor being located at the same production facility but confined in a specific explosion proof building at safe distance of the mechanical extraction hall.

The initial start-up with the innovative worm assembly was more difficult. It is believed that the extra flight surface together with the longer pitch made it more difficult to prevent the feed material partially rotating with the shaft before the worm assembly elements had polished in. However, the performance was back to normal after the initial few days, thus after the polishing in of the worm assembly.

As a matter of fact, in term of extraction, no performance differences were observed as compared to the standard worm assembly. Indeed, unfortunately, it can be safely concluded that not significant difference was observed in the extractability of the press- cake produced. In other word, the use of the twin-flighted worm assembly does not result in less residual oil in the final defatted material obtained after the solvent extraction step. As a matter of fact, the final residual oil, after the solvent extraction is similar, but the intermediate residual oil of the press-cake was even slightly higher. However, this slight difference has no detrimental consequence of any sort since this oil is not lost because it is extracted in the solvent extractor anyway. Therefore, the initial goal of reducing the amount of residual oil in the final solvent defatted material is not achieved. However, unanticipated side benefits have been clearly observed: the throughput was slightly higher, the specific electrical power consumption per tonne was slightly less and the stability of the main shaft assembly was better (less displacements and vibrations of the main shaft assembly and of the frame of the press). Furthermore, during the scheduled and normal maintained stop realised 18 months after the start of the experiment it has been observed that the wear of the elements of the main shaft assembly was substantially reduced in comparison to standard worm assembly. Therefore, the elements of the worm assembly of the new design as described in the present invention will have a longer life span which constitute a significant advantage.

No definitive explanation can justify those observations, but it is possible that the increased symmetry of the worm assembly of the innovative design improves its balance hence its stability. The press, and the worm assembly being more stable, it could be conjectured that less energy is dissipated in vibrations and that a more efficient pressing process result in term of energy consumption. However, it is believed that the major benefit of the press according to the present invention is the reduction of the wear of the worm assembly and the anticipated improvement of the reliability due to reduced vibrations/movement of the shaft. On the long run this stability will be beneficial to any critical parts such as for example the main electrical motor, gears/reducer, bearings and of course the worm assembly and therefore it can be safely concluded that reliability of a press equipped with a worm assembly having the design as described in the present invention will be improved which constitute another significant advantage. The experiment has been carried with a twin-flighted worm assembly. It is believed that similar results will be observed for triple-flighted worm assembly provided proper gash angle and pitch are calculated to sufficiently exposed the feed material to the knife-bars.