Process and apparatus for the centrifugal extraction of oil of first and second pressings

Abstract: A process and relevant centrifugal extraction equipment for the extraction of oils of different qualities from oily pulps, comprising the phase of separation of the different fluid and solid components making up the said pulp by centrifugal separation in a horizontal axis extractor, comprising the following phases: feeding of the product to the horizontal centrifugal extractor; centrifugation; retention in an axial direction of the lighter fluid component by radial means; drawing in an axial direction of the lighter fluid component retained axially and constituting a first quality of oil defined as first pressing; extraction in a radial direction of at least one further quantity of lighter fluid component consisting of oil defined as second pressing.

Description: The object of this invention is a process for the drawing of quantities of oil of different qualities by means of a centrifugal extractor and an appropriate centrifugal extractor capable of performing such differentiated extraction. There are known in engineering extraction processes and machines called centrifugal extractors, substantially comprising a scroll fitted inside a rotary drum and rotating in turn relative to the latter, which effect within the drum the separation and stratification of the various components of the product which is comprised of a solid part and two fluid parts of varying specific gravity. In the particular case of processing of olives, for example, the product to be separated comprises a substantially solid part, known as olive residue, which constitutes the waste; a first heavier fluid part, substantially consisting of water, which is also considered as waste; and a second, lighter fluid part substantially consisting of oil which forms the valuable part to be separated and recovered independently of the other two. In centrifugal separating machines of known type the product to be separated is normally fed to the machine in the form of crushed pulp with added water which, in the centrifugation phase becomes disposed radially to increase an intermediate separating layer between the solid and the oil, thereby bringing about improved separation of the oily component from the solid component. Once such separation is obtained, provision is made to recover the three components and cause them to flow out via different outlet ducts from the centrifuge respectively leading to the appropriate recovery channels. It is also known that, because of the structure of the olive and the distribution of the oil within the oil-bearing cell, the first oil obtained from pressing of the olives, however performed, is always of higher quality than the oil which is released in a second stage. In greater detail, the first oil to flow out is that extracted from the oil-bearing cell which, being already agglomerated, is readily extractable, while the last oil obtained from pressing is that located in the interstice between one cell and another, which is less mature and therefore of inferior quality. In the case of pressing effected with centrifuges, this means that the quality of the extracted oil is directly related to the time it spends in the said centrifuge or, in other words, to the time needed for the oil to emerge from the intermediate fluid layer and arrive at the outflow duct. Such extraction technique based on the use of centrifuges of conventional type has, however the disadvantage of allowing the extraction of the valuable component at a single drawing point from which, in substance, there is extracted a mixture of oils which have spent different times in the centrifuge and are therefore oils of different qualities which, on becoming mixed together, give rise to a mixture of oil of medium quality. In addition to this, the solid bottom residue, on flowing out of the centrifuge, carries with it part of such valuable fluid component with a consequent reduction of yield and/or the need for a subsequent additional recovery operation, as well as part of the heavy fluid component which makes it necessary to maintain the product at a low level within the drum to enable the solid residue to drain to the greatest possible extent from the valuable component prior to flowing out of the extractor. In order to recover such quantity of oil mixed with the solid residue, which would otherwise be wasted, it is therefore necessary to perform a second complete pressing cycle which is achieved by feeding the solid residue and water to a second centrifugal extractor in which is separated the so-called oil of second pressing, which is then further clarified by means of vertical axis disc separators, as was already done for clarification of the oil of first pressing. Such type of process is known from IT-1.176.649 in the name of the same applicant. There is therefore posed the technical problem of providing a process for the differentiated extraction of oils of different qualities, obtained by centrifugation within continuous centrifuges, so as to make possible the continuous drawing of oils differing from one another and being identifiable with certainty as of different pressings, and therefore of different quality in both relative and absolute terms, in order to be able to select and maintain oils of different quality separate from one another already on being drawn from the centrifuge and to increase the overall output of the extractor by recovering a greater overall quantity of oil. A further aim of this invention is the provision of a centrifugal extractor for products consisting of several components of varying specific gravity which make it possible to reduce to a minimum the quantity of valuable lighter fluid component flowing out of the separator together with the solid residue and to achieve at the same time the direct drawing of oils of different qualities including direct drawing of the oil of second or third choice which is normally lost with the residue, or recovered by subsequent separating operations applied to the said solid residue. Within the context of such problem, a further aim of the invention is to provide centrifuging systems capable of performing differentiated extraction of oils of different qualities. Such technical problems are resolved according to this invention by a process for the extraction of oils of different qualities from oily pulps comprising the first phase of separation of the different fluid and solid components making up the pulp, by means of centrifugal separation in an extractor which provides for the following phases: feeding of the product to the horizontal centrifugal extractor; centrifugation; retention in an axial direction of the lighter fluid component by radial means; drawing in an axial direction of the lighter fluid component retained axially, constituting a first quality of oil defined as first pressing; extraction in a radial direction of at least one further quantity of lighter fluid component consisting of oil defined as second pressing. According to this process, provision is also made for at least one further radial extraction for the recovery of the low quality oil which is normally lost with the solid residue. Provision is furthermore made for such process to be implemented by means of a centrifugal extractor equipped with at least one device for the separation in an axial direction of such oils of first and second pressings, located coaxially to the axis of rotation of the separator, and at least one tubular piece capable of being inserted therein in a substantially radial direction across the lateral surface of the drum, up to different levels corresponding to the level of stratification of the lighter fluid component, the tubular piece being inserted at a suitable axial distance from the rear wall of the extractor and downstream of the said device for the separation of the oil of first and second pressings in the direction of outflow of the solid residue. Further details may be obtained from the following description, given with reference to the attached drawings, which show: In figure 1 : a view according to A in fig. 2; In figure 2 : a section according to plotting plane II-II in fig. 1; In figure 3 : a section according to plotting plane III-III in fig. 1; In figure 4 : a view according to B of the extractor in fig. 5; In figure 5 : a section according to plotting plane V-V in fig. 4; In figure 6 : a section analogous to that in fig. 5 illustrating a further form of implementation of the extractor according to the invention, and In figure 7 : the section according to an axial plane of a single-stage decanter according to the invention, with multiple radial outlets. As shown in the figures, a centrifugal extractor is essentially comprised of a fixed, substantially cylindrical casing 1, provided at its opposite ends with annular sections separated from one another and opening downward, forming radial collectors 1a, 1b, 1c for the recovery of the different components of the product to be separated which, in the particular case of processing of olives, are formed respectively by solid residue, known as olive residue, heavy fluid residue, consisting of water, and oil. Within fixed casing 1 and coaxially thereto is located a rotary hollow drum 2, of substantially cylindrical-truncated cone shape, which is mounted on bearings 2a to enable it to rotate relative to casing 1, the drive for the said drum being of conventional type and therefore not shown in detail. Within drum 2 and coaxially thereto is also fitted a scroll 4 supported at the ends by bearings 4d integral with drum 2 in relation to which the scroll is able to rotate. Such scroll 4 is substantially comprised of a hollow cylindrical-truncated cone body on which are formed outflow apertures for product 5 fed into it, in the direction of arrow P, by means of a pump, not shown, and a coaxial duct 5a. To the outer surface of the scroll is furthermore made integral a helix 4b which, on rotating in the direction opposite that of the drum, forces the solid residue to flow toward appropriate outlet 1a. As shown in figure 2, concentrically to tube 5a is located a further tube 105 for the supply of water to the extractor. Such water flows under pressure from holes or nozzles 105a and brings about fluid stratification which tends to promote a cleaner separation between the oil and the olive residue in the water outflow zone. Front wall 2b of drum 2 has three pairs of holes, the first two pairs 6 and 7 of which are respectively located according to diameters perpendicular to one another, with different circumferences concentric to one another, and the third pair 8 is located according to a diameter forming an angle of 45° relative to the other two and a circumference with a radius smaller than that of the two pairs of holes 6 and 7. In other words, the two pairs of holes 6 and 7 are located at a greater distance from the axis of rotation of scroll 4 and drum 2 than that of the third pair of holes 8, which are therefore closer to such axis of rotation. As shown in fig. 2 relating to an extractor with separate outlets for the three components, holes 6 are associated with an outflow duct 6a ending in radial collector 1b where the lighter fluid component is collected, while holes 7 are associated with an inverted overfall duct 7a ending in radial collector 1c where the heavier component of product 5 is collected. Holes 6 are furthermore closed in the axial direction by plugs 6b shaped with extensions 6c in order to bring about the opening or closure of duct 6a following the rotation of plug 6b in one direction or the other, thereby bringing about, in one case, the outflow of water on its own via hole 6 or, in the other case, the outflow of water together with the solid residue via opposite collector 1a. In the latter case the extractor operates with only two outlets (figs. 5 and 6): one 8 for the oil and one 1a for the olive residue and water. On such front wall 2b of drum 2 is furthermore fitted a disc 9 provided with a concentric circular aperture having diametrically opposed, substantially rectangular slots 9a, capable of bringing about the opening of ducts 8 for the outflow of the light fluid component, in the case of an extractor having only two outlets. The scroll of the centrifuge according to the invention is completed by a disc 11 or like solid piece fitted concentrically to said scroll 4. The outside diameter of such disc is greater than the diameter of the circumference on which are located holes 8, so that the disc constitutes a barrier for separation in an axial direction of the oil of first pressing, which is forced into the drawing zone in an axial direction via such holes 8. As will be seen from the figures, the centrifugal extractor according to the invention also provides further means for drawing the lighter fluid component in a radial direction, consisting of tubular pieces 12 inserted radially into drum 2 via holes 2d thereof, in such a way as to emerge at a point axially posterior to disc 11 in the direction of flow of the solid towards its own outlet 1a. Such tubular pieces 12 have an inner end 12a located in relation to the level of stratification of the fluid component which it is required to collect, while opposite end 12b, located outside drum 2, flows into a collector 101 within fixed casing 1. Such collector makes it possible to convey the drawn fluid toward duct 101a for the outflow and collection of the said fluid. According to the invention, provision is also made for such tubular pieces to be located on the circumference of the drum in positions such as to maintain the dynamic balance of the separator during rotation. Furthermore, although the inclination of the tubular pieces with respect to the surface of drum 2 may be at any angle, it is obvious that the arrangement of radial tubes makes it possible to utilize the full centrifugal force determined by the rotary movement for the extraction of the oil in a radial direction. The operation of the device is as follows: whether it is desired to process the product according to a so-called two-phase cycle (that is, with a single axial outflow of the valuable fluid and a single outlet for the intermixed solid residues and fluid), (fig. 5), or whether it is desired to process the product according to a so-called three-phase cycle (that is, with separate outflows of oil, water and solid), (fig. 2), there is brought about via disc 9 the opening or closure of the various extraction ducts from wall 2b, so that, as shown in fig. 5, that is, in the two-phase system, the valuable fluid, which is effectively separated from the solid residue by the heavier fluid component, is retained lengthwise in the vicinity of wall 2b of the drum by circular baffle 11 which allows instead the passage of the heavy fluid which, on becoming mixed with the solid residue, is made to flow out together with the latter from radial collector 1a of fixed casing 1. Simultaneously with drawing in the axial direction via holes 8 of wall 2b, the setting of inner end 12a of radial tube 12 in relation to the level of stratification of the oil makes it possible to draw, in the radial direction, a further quantity which, on being mixed with the water and with the solid, crosses disc 11 and stratifies beyond the latter in the direction of outflow of the said solid. Such radial drawing therefore reduces the quantity of oil which flows out with the residue, thereby increasing the overall output of the centrifugal extractor. Such radially recovered oil constitutes the so-called oil of second pressing, i.e. that which requires longer centrifugation time in order to become separated from the oily pulp and which therefore, by not emerging rapidly, cannot be extracted axially to avoid reducing the quality of the oil of first pressing. It is also shown that the application of the centrifugal extractor according to the invention may be extended to processing with a liquid ring of thick section (fig. 5) and to the production of olive residue with a high moisture content. The outlets in this case would be three in number, because of the presence of the new radial outlet. Many variants may be introduced in the implementation of the extractor according to the invention. In particular, as shown in fig. 6 it is possible to locate coaxially to scroll 4 a further disc 11, placed in axial direction from the part opposite tubular piece 12 which is located radially in relation to the other disc, which constitutes a further barrier to the flow thereof toward the outlet of the solid. There is thus defined an annular zone of containment of the valuable fluid of second pressing which, in addition to being maintained more steady with respect to the direct current flow toward the outlet of the solid, may be better purged of the occurrence of any residues of water and solids still suspended in the oil. It is also possible to supply or not to supply hot or cold water together with the pulp or separately from the latter in order to increase the separation of the oil both in the case of the two-phase extractor and in the case of the three-phase extractor. As shown in fig. 7, by prearranging a multiplicity of tubular pieces 12 suitably distanced from one another in an axial direction and each associated with a corresponding retaining disc 11, it is possible to draw radially the oil emerging at the different axial positions, thus ensuring qualitative selection of the said oil effected on the basis of the position in an axial direction of the radial drawing and therefore on the basis of the time spent by the said oil in the centrifugal separator. Each radial drawing corresponds to a well-defined quality of oil which, if drawn via corresponding collectors 101 independent of one another, may be maintained separate. Such process and the relevant centrifugal extractor therefore make it possible to avoid the use of equipment for the second pressing, resulting in a significant saving of energy since it is not necessary to accelerate a second time the product to be pressed, previously discharged from the centrifugal separation units. It is a known fact that such acceleration accounts for more than 60% of the overall energy absorbed by the entire process.

Claims: A process for the extraction of oils of different qualities from oily pulps comprising the phase of separation of the different fluid and solid components making up the pulp, by means of centrifugal separation in a horizontal axis extractor, characterized in that it provides for the following phases: feeding of the product to the horizontal centrifugal extractor; centrifugation; retention in an axial direction of the lighter fluid component by radial means; drawing in an axial direction of the lighter fluid component retained axially, constituting a first quality of oil defined as first pressing; extraction in a radial direction of at least one further quantity of lighter fluid component consisting of oil defined as second pressing. A process according to claim 1 characterized in that it comprises a multiplicity of extractions in radial direction of the lighter fluid component effected at preset axial distances, each radial extraction bringing about the selection of an oil of well-defined quality in relation to the oil drawn in other positions. A process according to claim 1 characterized in that such substantially radial extraction of the lighter fluid component is effected downstream of the axial flow of the solid from such radial means of retention of the said lighter component. A process according to claim 1 characterized in that such radially drawn lighter component flows out together with a preset quantity of heavier fluid component. A centrifugal extractor for the processing of oily pulps, comprising a fixed casing (1), a drum (2) frontally closed by a wall (2b) provided with outflow ducts (6, 7, 8) flowing substantially in the axial direction of the fluid component(s) forming the product to be separated, and a scroll (4), both of which rotate, characterized in that it comprises at least one device (11) for the retention in an axial direction of the lighter component of the product and at least one piece (12) for the drawing in a substantially radial direction of at least one of such fluid components of the product to be separated, associated with means (101) for the collection and outflow of such drawn fluid component. A centrifugal extractor according to claim 5 characterized in that such means (12) of radial drawing are located downstream of the means (11) of axial retention orientated in the direction of advance of the solid. A centrifugal extractor according to claim 5 characterized in that such means of radial drawing are preferably comprised of tubular pieces (12) inserted in a substantially radial direction in corresponding sealing seats (2d) of rotary drum (2) up to the preselected level of drawing. A centrifugal extractor according to claim 5 characterized in that such means of collection of the component drawn in a radial direction are comprised of a collector consisting of a circumferential double bulkhead (101) integral with fixed casing (1) provided with an aperture (101a) for the outflow therefrom. A centrifugal extractor according to claim 5 characterized in that such tubular pieces are preferably located according to radial directions capable of maintaining the dynamic balance of the separator during rotation. A centrifugal extractor according to claim 1 characterized in that such tubular pieces are arranged in pairs, each item of the pair being located diametrically opposite the other with respect to the axis of rotation. A centrifugal extractor according to claim 5 characterized in that such device for the retention in a longitudinal direction of the lighter fluid component of the product to be separated is preferably comprised of at least one disc (11) or like device made integral with scroll (4) between two turns of the latter and with its profile coaxial to and intersecting the said turns. A centrifugal extractor according to claim 5 characterized in that such disc (11) has an outside diameter of greater length than the distance of holes (8; 6) outflowing in the axial direction of the light fluent component with respect to the axis of rotation of the centrifugal extractor. A centrifugal extractor according to claim 5 characterized in that such devices (11) for the retention of the light fluid are two in number, located on opposite sides of radial drawing means (12) in an axial direction to define an annular section of drawing. A centrifugal extractor according to claim 5 characterized in that it comprises means (105, 105a) of supply of water to the drum located concentrically to the means of feeding in an axial direction of the oily pulp to be separated. A centrifugal extractor according to claim 5 and 14 characterized in that such means of supply of water are comprised of radial nozzles or holes of a tube (105) coaxial to the pulp feeding tube.

Inventors: PIERALISI GENNARO, PIERALISI, GENNARO
Applicants: NUOVA MAIP MACCHINE AGRIC, NUOVA M.A.I.P., MACCHINE AGRICOLE INDUSTRIALI PIERALISI S.P.A.
Application year: 1995
Main classification: B04B1
IPC codes: B04B1