Centrifuge for oil extraction from oily slurries working without addition of drinkable water

Abstract: Horizontal centrifuge comprising a drum (1), a helicoid screw (2, 2a) coaxial to the drum (1) and arranged inside the latter, two closure heads (14, 15) located at the ends of the drum (1) and provided with nozzles (4, 6) for discharging to the outside oil and water/solid remainders respectively and an inlet tube (3) for the oily slurry ending inside the hollow body (2a) forming the helicoid screw (2, 2a). The horizontal centrifuge is provided with a plurality of diaphragms (11, 12, 13) which allow an almost perfect separation of the columns formed by the oil and water/solid remainders. The nozzles (4) providing the way out for the oil are adjustable and allow to maintain constant the height of the oil column inside the drum (1). The independent rotary motion of the drum (1) and the helicoid screw (2, 2a) is performed by means of an epicyclic motor reducer (7).

Description: The present invention relates to a horizontal centrifuge or "Decanter", for oil extraction from an oily slurry obtained from the drupes of the olive-tree or possibly from other oily products, and in particular it relates to such a type of centrifugal separator in which it is not necessary to add drinkable water to the slurry. Several years have passed since horizontal centrifuges of the above cited type have first become known and made available to the oil industry. Those types of centrifuges also known as "Decanters", essentially comprise the following elements: a drum with two or more sectors and with a cylindrical or conical end; a rotating helicoid screw located within the drum for conveying solids towards the outlet, the latter being provided on the end portion of the cylindrical or comical end; an inlet head with nozzles providing a way out to liquids, i.e. oil and water; a closure head with nozzles providing a way out to wet solids, located at the end portion of the cylindrical or comical end; an inlet tube for the oily slurry from which oil is to be extracted; mechanical devices for starting and controlling the independent rotary motion both of the drum and the helicoid screw. In a first application stage, the outer body of the "decanter", formed by the drum having a conical (or cylindrical) end, included only two nozzle systems, one of which served for providing the way out for the oil-water mixture and the other one for providing the way out for wet solids. A second generation of centrifugal separators, included three nozzle systems in order to obtain a higher efficiency, one of which provided the way out for oil, the second one served to remove the water contained in the slurry and the last one was used for providing the way out for wet solids. However, both generations of horizontal centrifuges required the addition of a considerable amount of drinkable water, in order to operate at an excellent level. This considerable amount of water added to the oily slurry increases the volume of waste water to such an extent as to cause problems, since the waste water of those types of centrifugal separators is classified as industrial waste and is subject to the relative laws, and as a consequence the costs are increased. Furthermore, waste water gives rise to huge difficulties both under the technical and the economical point of view because of the absolute absence of adequate water conditioners. The applicantion EP-A-0 488 086 discloses a decanter which is used for dewatering a slurry. This decanter comprises diaphragms which increase in diameter size towards the discharge port of the decanter. This allows a consolidation of the slurry which is dewatered step by step All diaphragms include overflow holes to enable the passage of water to the preceding centrifugation stage. JP-A-59 169 551 discloses a decanter centrifuge provided with a weir plate fixed to the drum and located near the solid discharge nozzles. The object of the present invention is to find a remedy for the above mentioned disadvantages, by providing a horizontal centrifugal separator capable of working with a greater efficiency as compared to the conventional centrifugal separators, and which doesn't need drinkable water addition. Furthermore, the separation of oil from the solid remainders is best obtained by using only the water contained in the drupes or oily fruits, and this water is conveyed to the outside together with the solid remainders, without producing considerable amounts of polluting substances. The present invention will now be illustrated in detail with reference to the annexed drawings, which show a particular embodiment of the invention, and in which: Fig. 1 is a longitudinal partially sectional view of a conventional horizontal centrifugal separator; Fig. 2 is a transverse cross section of the closure head of the conventional centrifugal separator of Fig. 1, where the nozzles A-B-C and A'-B'-C' providing the way out for the oil and water respectively are shown; Fig. 3 is a longitudinal partially sectional view of the horizontal separator of the present invention; Fig. 4 is a transverse cross section of the closure head of the centrifugal separator of Fig. 3, taken in the region with the greatest diameter; Fig. 5 is a perspective view of the helicoid screw effecting the separation of the different "phases" oil-water contained in the drupes-solid remainders. In the figures, corresponding elements are indicated by the same reference numbers. With reference to Fig. 1, reference number 1 indicates the external body or drum of the conventional centrifuge, comprising a cylindrical part 1a and a conical end 1b. A helicoid screw is mounted in the inside of the external body 1, which is formed by helicoidal coils 2 and a hollow body 2a, which is provided with a plurality of substantially rectangular apertures. These rectangular apertures are located at regular intervals on the surface of the hollow body 2a, and they form different sets 8a, 8b, 8c and 8d of apertures, the sets being spaced apart by an angle of 90°. The row or set 8d of apertures is not shown in Fig. 1, since it is arranged on the opposite side of the helicoid screw with respect to the set of apertures 8a. The centrifugal separator of Fig. 1 is further provided with two closure heads 14, 15, the first one 14 being located on the left end (in Fig. 1) of external body 1, and the second one 15, on the right end of the same. The centrifugal separator is filled with the oily slurry obtained by the processing of olive tree drupes or other oily products, through the feeding duct 9 which ends into the inlet tube 3. The inlet tube 3 extends inside the hollow body 2a by more than one half of its length and the oily slurry reaches the region bounded by the surface of the hollow body 2a and by the inner part of the drum 1, by passing through the apertures 8a, 8b, 8c, 8d. This type of conventional centrifuge is provided with oil exit nozzles 4a, 4b, 4c (Figs. 1 and 2) and with water exit nozzles 5a, 5b, 5c, the direction of the oil and water flow being shown by the arrows a, b, c and a' , b' , c' respectively. The nozzles 4a,b,c and 5a,b,c are provided on the closure head 14, whereas the closure head 15 has nozzles 6 for the removal of solid remainders. The centrifugal separator also comprises a motor reducer 7 for effecting an independent rotation of the external body 1 and the helicoid screw 2, 2a. Fig. 3 shows the horizontal centrifuge of the present invention. It is provided with an inlet tube 3, having a very short length, since it terminates at the left end of the hollow body 2a (with reference to the figure). This feature is also disclosed in EP-A-0140672. Furthermore, the water exit nozzles 5 are not provided, but only those nozzles 4 are present, which serve for the discharge of the oil to the outside, as can be seen also from Fig. 4. With reference to Figs. 3, 4 and 5, which show the device of the present invention, the helicoid screw comprises two or more diaphragms. These diaphragms, indicated in the figures by reference numbers 11 and 12, have different dimensions, wherein, in particular, diaphragm 12 has a smaller diameter than diaphram 11. The diaphragm 11 is provided with central passages 16. Another diaphragm 13 is integral with the drum 1 and is located near the nozzles providing the way out for the olive husk and the water contained in the drupes. The horizontal centrifugal separator also comprises an epicyclic motor reducer 7 which performs the speed differentiation between the drum and the helicoid screw. The means provided by the present invention, that is the diaphragms 11, 12 in which 12 has a diameter smaller than 11, in combination with diaphragm 13 and a shorter inlet tube 3 allow to carry out an excellent separation of the oil (which is discharged through the nozzles 4) from the solid remainders and from the water originally contained in the drupes (which are both discharged through the nozzles 6), without any addition of drinkable water; the centrifuge is also more efficient because, no drinkable water being added, the overall volume of material introduced in its inside is much less. The reasons why the present invention is so effective are the following: the short length of the inlet tube 3 increases the centrifugation area used for the separation of the oil from the wet solids; the diaphragm 11 allows the formation of an oil column which develops in the cylindrical part of the drum 1 and, at the same time, it allows the oil formed on the conical end of the drum 1, to reach the oil column, passing through the central passages, the oil of the oil column being discharged through the nozzles 4; the diaphragm 13 stabilizes the water level inside the drum 1, conveying the water to its outside by letting it pass through the nozzles 6 together with the solid remainders; the nozzles 4, which are adjustable, i.e. which may be screwed or unscrewed, allow to obtain an almost perfect separation of the oil column from the water column, by adjustment of the dimension of the oil column. In the embodiment shown in the drawings, there are three adjustable nozzles 4 for discharging oil to the outside, and they are separated from each other by an angle of 120° (Fig. 4), but obviously their number could also be different, or they could be arranged in a different fashion.

Claims: A horizontal centrifuge, used for the extraction of oil from an oily slurry, including a drum (1) with a conical portion and a cylindrical portion and two closure heads (14,15), an inlet tube (3) of the oily slurry crossing the first (14) of said closure heads and ending close to said first closure head (14) into a hollow body (2a) forming the centrifugation helicoid screw together with helicoid coils (2), a set of apertures (8a,8b,8c,8d) arranged along the length on the hollow body (2a), nozzles (6) providing the way out for water and solids, and mechanical means allowing an independent rotation of the drum (1) and the helicoid screw (2,2a), characterized in that it comprises adjustable nozzles (4) providing the way out for the oil, a diaphragm (13) integral with the drum (1) and located near the nozzles (6) for the discharge of water and solids, which nozzles are themselves located on the second (15) closure head, two further diaphragms (11,12) integral with the hollow body (2a) the first (11) of which has central passages (16) and has a greater dimension as compared to the second (12), wherein said first diaphragm (11) is located in the transition region where the form of the drum (1) changes from that of a cylider to that of a frustum of a cone, whereas the second diaphragm (12) is located between said first diaphragm (11) and said diaphragm (13) integral with the drum (1).

Inventors: RAPANELLI EZIO, RAPANELLI, EZIO
Applicants: RAPANELLI FIORAVANTE SPA, RAPANELLI FIORAVANTE S.P.A.
Application year: 1993
Main classification: B04B1
IPC codes: B04B1