IE64376B1 - A process for recovering meal and oil from fish offal - Google Patents

Description

The present invention relates to a process for recovering meal and oil from fish offal. More particularly the invention relates to process in which fish offal is cooked and thereafter separated by centrifuging into oil, solids and stick water portions. The oil is usually purified, the solids are dried to give fish meal, and the stick water is usually evaporated and subsequently dried, also to give fish meal.

United States Patent Specification Nos. 4,344,976 and 10 4,335,146 (Alfa-Laval) described two such processes. It appears that both of these processes are largely dependent on heat input at an evaporator for separation of the various portions. Accordingly, there would be a relatively large heat input which would result in high energy costs and a lower nutritional value for the end products. Further, evaporators when used to handle a mixture with a relatively high solid content are difficult to clean and to maintain.

A process which appears to have been developed to overcome these problems, among others, is described in PCT Patent Specification No. 85/03415 (Alfa-Laval). In this process cooked offal is separated into a solid portion and a mixture of water, oil and sludge in a presser and in a sieve. The , mixture of water, oil and sludge is then separated into oil, stick water and solids in a tricanter. The stick water is evaporated to give solids which are subsequently dried together with the solids from the sieve, presser and from the tricanter.

While this process does not appear to have an excessive heat input requirement, it appears that separation in the tricanter is effective as re-processing of both the solids and stick water is required before evaporation of the stick water and drying of the solids. This clearly results in a lower throughput than would otherwise be possible, and in more expense for plant and energy.

The present invention is directed towards providing an improved process for recovering meal and oil from fish offal.

According to the invention there is provided a process for recovering meal and oil from fish offal, the process comprising the steps ofx► transferring fish offal from a buffer container to a . cooker; cooking the offal to obtain cooked offal; separating the cooked offal into a high solid contents mixture and a mixture of oil, water and sludge by straining; transferring the mixture of oil, water and sludge to a holding tank, and transferring the high solids content mixture to a presser; pressing the high solids content mixture to produce solids and a mixture of oil, water and sludge and transferring said mixture of oil, water and sludge to the holding tank; heating said mixture of oil, water and sludge to approximately 90°C to 95°C by injection of steam into the mixture and re-circulation of the mixture between a heating unit at which steam is injected and the holding tank, to obtain a coagulated mixture; separating by centrifuging the coagulated mixture into solids, stick water and oil; evaporating the stick water to obtain solids; drying the solids and milling the dried solids to obtain fish meal; and purifying the oil to obtain a purified oil.

Ideally, the mixture is re-circulated by an augur in the heating unit.

Preferably, the cooked offal is strained by agitation in a perforated drum. In this latter embodiment, the cooked offal is preferably agitated by rotation of the perforated drum.

Ideally, the cooked offal is also pressed by an augur within the rotating drum.

The invention will be more clearly understood from the following description of a preferred embodiment thereof given by way of example only with reference to the accompanying drawings in which:10 Fig. 1 is a flow diagram illustrating a process according to the invention; Fig. 2 is a diagrammatic, cross-sectional front view of a heating unit of the process; Fig. 3 is a diagrammatic partly cut-away side view of a 15 strainer for use in the process; Fig. 4 is a diagrammatic, cross-sectional front view in the direction of the arrows of IV-IV of Fig. 3; Fig. 5 is a diagrammatic, partly cut-away side view of a hopper and auger for use in the process of the invention; Fig. 6 is a cross-sectional, diagrammatic front view in the direction of the arrows VI-VI of Fig. 5.

Referring to the drawings, and initially to Fig. 1 there is illustrated a process for recovering meal and oil from fish offal. Raw fish offal is generally stored in large holding silos from which it is transferred to a hopper 1 which acts at a buffer to provide an even feed rate for the process. The offal is transferred by an auger assembly 2 to a cooker 3 . In this embodiment, the cooker 3 is of the continuous conveyor type with a steam heated jacket and shaft. The offal is heated to 95°C in the cooker 3. The cooked offal is then transferred to a strainer 4 which outputs a mixture of water, oil and sludge with a relatively high liquid content to a holding tank 5 and a mixture with a relatively high and uniform solid content to a presser 6. The presser 6 is of the conventional auger type and requires no further description. Solids from the presser 6 are transferred to a drier 7 which is of the rota-disc type. A mixture of water, oil and sludge with a relatively high liquid content is transferred from the presser 6 to the holding tank 5 together with a similar mixture from the strainer 4. The holding tank 5 provides an even supply of mixture to a tricanter 8. However, before the mixture is supplied to the tricanter 8 it is coagulated by re6 circulation through a heating unit 9 and the holding tank 5. The heating unit 9 is described in more detail below.

The holding tank mixture of water, oil and sludge is separated by centrifuging in the tricanter 8 into solids which are transferred to the drier 7, oil which is subsequently purified to form an end product and stick water which is transferred to an evaporator 11. This stick water contains approximately 7% to 8% solids. The evaporator 11 comprises evaporator tubes and energy from the drier 7 is utilized. Concentrated stick water output from the evaporator 11 is pumped to the drier 7. It will be seen, therefore, that the drier 7 receives solids from the evaporator 11, from the presser 6 and from the tricanter 8. Dried fish meal output from the drier 7 is then transferred to a mill (not shown) which provides the fish meal end product.

Referring now to Fig. 2, the heating unit 9 is illustrated in more detail. The heating unit 9 includes a tube 13 housing an auger 14 driven by a geared motor 15. The tube 13 has an inlet 16 and an outlet 17 for reception and delivery of the mixture of water, oil and sludge. A steam inlet 18 is also mounted on the tube 9 for reception of steam for heating of the mixture as it passes through the heating unit 9. The action of injecting steam into the mixture as it passes through the heating unit tends to coagulate the solid components in the holding tank 5 before the mixture is delivered to the tricanter 8. It has been found that heating the mixture to a temperature in the range 90°C to 95°C is suitable.

It has been found that because the mixture of water, oil, and 5 sludge is coagulated in the holding tank 5 before being pumped to the tricanter 8, the centrifuging operation is particularly effective and no re-processing is required as the stick water output from the tricanter 8 does not need to be either centrifuged again or re-circulated back through the strainer 4. Further, the solids separated in the tricanter 8 do not need to be re-circulated back to the strainer 4. It will be appreciated that this arrangement leads to considerable savings in energy costs and to improved throughput for a given plant capacity.

Referring now to Figs. 3 and 4, the strainer 4 is illustrated in more detail. Parts similar to those described with reference to the previous drawings are identified by the same reference numerals. The strainer 4 comprises a rotating perforated drum 20 mounted in a casing 21. Mounted within the drum 20 there is a rotating auger 22 which is a neat fit within the drum 20. A sump 23 is provided for holding a mixture of water, oil and sludge which escapes through the perforated drum 20 under the centrifugal action of the drum and the pressing action of the auger 22. A pump 24 pumps the mixture to the holding tank 5.

The strainer 4 outputs a mixture with a relatively uniform and high solid content to the presser 6 which is designed to effectively separate solids from liquids at this solid content. It has been found that this arrangement of strainer 4 is particularly suitable for separation of the abovementioned mixtures, this allowing effective operation of the presser 6. Accordingly, the use of the strainer 4 helps to eliminate the need for re-processing of the offal.

Referring now to Figs. 5 and 6, the hopper 1 and auger 10 assembly 2 are illustrated in more detail. The auger assembly comprises an auger 30 mounted within an inner tube 31 for portion of the length thereof. The inner tube 31 has an opening 32 below the hopper 1 for reception of offal. The auger 30 is surrounded for it's full length by an outer tube 33 connected at the lower end to the hopper 1. The auger 30 is a neat fit within the inner tube 31.

In use, the offal contained in the hopper 1 is maintained at or above a minimum level, which is indicated by level detectors, not shown. The offal drops by gravity through the opening 32 into the inner tube 31. Although the offal may have a relatively high liquid content, the auger is effective at pumping it upwards because the auger 30 is a neat fit within the inner tube 31. Any over spill at the upper end is directed downwards back into the hopper 1 and through the opening 32. It will be appreciated that this arrangement provides for a steady, even flow rate of offal to the cooker 3 irrespective of the liquid content. This is a very important feature of the invention as is allows for the optimisation of through-put.

Needless to say, the invention is not limited to the embodiment hereinbefore described. It is envisaged, for example, that the mixture of water oil and sludge may be coagulated in a different manner to that illustrated. The mixture may, for example, be heated and circulated within a holding tank only by convection. The important point is that the mixture is heated to a temperate suitable for coagulation of the mixture.

Claims (8)

CLAIMS:

1. A process for recovering meal and oil from fish offal, the process comprising the steps of:transferring fish offal from a buffer container to a cooker; cooking the offal to obtain cooked offal; separating the cooked offal into a high solid contents mixture and a mixture of oil, water and sludge by straining; transferring the mixture of oil, water and sludge to a holding tank, and transferring the high solids content mixture to a presser; pressing the high solids content mixture to produce solids and a mixture of oil, water and sludge and transferring said mixture of oil, water and sludge to the holding tank; heating said mixture of oil, water and sludge to approximately 90°C to 95°C by injection of steam into the mixture and re-circulation of the mixture between a heating unit at which steam is injected and the holding tank, to obtain a coagulated mixture; separating by centrifuging the coagulated mixture into solids, stick water and oil; evaporating the stick water to obtain solids; drying the solids and milling the dried solids to obtain fish meal; and purifying the oil to obtain a purified oil.

2. A process as claimed in claim 1, wherein the 5 mixture is re-circulated by an auger in the heating unit.

3. A process as claimed in any preceding claim, wherein cooked offal is strained by agitation in a perforated drum. 10

4. A process as claimed in claim 3, wherein the cooked offal is agitated by rotation of the perforated drum.

5. A process as claimed in claim 4, wherein the cooked offal is also pressed by an auger within 15 the rotating drum.

6. Fish oil whenever produced by the process of any preceding claim.

7. Fish meal whenever produced by the process of any preceding claim. 20

8. A process substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.