Area of the invention

The present invention relates to an output arrangement for a screw tank.

Background to the invention

Screw tanks can be used in the treatment of food articles such as fish, chicken and vegetables. The food articles lie in a liquid and are transported by the screw blade of the screw tank from the one end of the tank to the other end. This can be for different types of treatments, such as cooling down, thawing, heating up, enzyme treatment, salting, etc. The screw blades of the tank divide the tank into different zones or chambers, such that one can have, for example, various treatments in the different zones/chambers. Today there are in principle two methods to feed food articles out from the tank. The one method is to let the screw feed them out with the help of carriers at the outlet end of the screw, or as a continuation of the screw. However, the carriers will only be able to lift the objects as high as the top of the core of the screw. The other method is to use a ladder transporter with a conveyor belt that collects the objects up from the water from a chamber at the end of the screw. With a ladder transporter, one can increase the level of water above the core of the screw.

However, this latter method has an obvious weakness when it is used for food articles that have approximately a neutral buoyancy in the fluid, such as, for example, fish. The weakness arises from the food article (the fish) not having sufficient time to sink down between the carriers of the transporter and then being whisked round in the last chamber for a while before it is transported out. Many food articles are sensitive, and in particular, fish species such as salmon and trout have a sensitive shell coat which is easily damaged in this process. This reduces the quality of the product.

Thus it is an aim of the present invention to provide a solution where the

disadvantages associated with the two methods for feeding out of a screw tank are reduced, i.e. to prevent that the food articles remain in the last chambers and are subjected to a long residence time and are damaged. Summary of the invention

Thus, the present invention relates to a screw tank for the treatment of food articles comprising a transport screw with a core and a number of screw blades,

characterised in that the transport screw at the outlet section of the tank is fitted with a number of carriers that are set up to lift the food articles up to a higher level than the upper part of the core diameter of the screw.

In a preferred embodiment the tank comprises a guiding arrangement that leads the food articles from the centre in the area where they shall be fed out so that they can be lifted considerably higher than the upper part of the core diameter of the screw.

In one embodiment the core has, in a section near the outlet end of the tank, a diameter (D2) which is greater than the rest of the core diameter (D1 ).

In one embodiment the core increases, in a section near the outlet end of the tank, gradually from one diameter (D1 ) to another diameter (D2).

In one embodiment the core in a section near the outlet end of the tank has a diameter (D2) which is larger than the rest of the core diameter (D1 ), and the tank comprises a guiding arrangement that leads the food articles from the centre, in the area where they shall be fed out, so that they can be lifted considerably higher than the upper part of the screw core diameter. In one embodiment, the transporter screw at the outlet section of the tank where the core has a diameter D2 is fitted with a larger number of carriers than if the core had had a diameter D1 .

In one embodiment the tank comprises a guiding arrangement that leads the food articles from the centre in the area where they shell be fed out so that they can be lifted considerably higher than the upper part of the screw core diameter.

In one embodiment the tank comprises means to prevent that the food articles float over the core of the screw in the areas it has a smaller diameter D1 . Said means can be chosen from; i) a supply of liquid over the screw core, ii) directional jets and iii) physical barriers. In a preferred embodiment said physical barriers comprise movable dividers (grids) set up to separate the liquid volumes on the upper side of the screw core.

Said movable dividers (grids) are preferably suspended above the tank and move with the rotation of the screw and that they return to the beginning of the screw after they have followed the screw a predetermined movement forward.

In a preferred embodiment the tank comprises means for the supply of liquid to the tank, and means for the outflow of liquid from the tank, and where the vertical position of the outlet can be regulated to regulate the through-flow of water in the tank.

The inventors of the present invention have found that one can increase the screw core diameter toward the outlet end of the screw tank and will thereby increase the water surface in the tank to a level given as V2 in figure 1 (from the normal level V1 ). With a such larger diameter of the core one will also be able to fit the carriers so that they lift the food articles higher above the centre where they shall be fed out of the tank. One can thereby have a larger liquid volume in the tank and the treatment process will thus have a greater capacity.

It is an advantage that the food articles come out of the tank as smoothly and evenly as possible over time. The stirring of the food articles and the liquid will give the mixture a density which is as constant as possible. This will also lead to a good contact (coating of) between the treatment liquid and the food articles, as described in NO308282 and WO2010125589.

Detailed description of the invention

The present invention will be described in more detail below with reference to the figures, in which;

Figure 1 shows a longitudinal outline of a screw tank with a transport screw, where the outer diameter of the shaft of the transport screw is greater at the outlet end of the tank than in the rest of the tank. The screw blades are not indicated in this figure.

Figure 2 shows in perspective the same screw tank as in figure 1 but where the screw blades are also included. Figure 3 shows a section immediately on the inside of the end section of the tank for the feeding out of food articles, where the carriers are shown. Figure 4 shows a section immediately on the inside of the end section of the tank for the feeding out of food articles where the carriers and guiding arrangement are shown.

Figure 5 shows a section that indicates how the carriers are arranged.

Figure 1 shows in a longitudinal outline a screw tank 10 fitted with a transport screw 12. The diameter of the transport screw is given in the figure as D1 . According to prior art, the transport screws have the same core diameter along the whole of the longitudinal direction of the transport screw 12. Food articles 14 that shall be subjected to a treatment such as thawing, freezing, enzyme treatment, etc., are transported through the tank in a controlled way by screw blades 16 that rotate with the core of the transport screw 12. Carriers 18 arranged at the outlet end of the tank to lift the food articles 14 out of the tank 10 can only lift the food articles to the same height as the top of the core of the screw, which is the level V1 , for normal water levels.

However, in one aspect of the present invention it deviates from known solutions in that the diameter D2 of the core is greater near the outlet end of the tank, so that one can increase the water level to V2 and so that carriers 18 can be constructed, which lifts the food articles up to a higher level. With a greater circumference one can also increase the number of carriers 18 and the feeding out of food articles 14 will therefore be smoother over time. Because of the increased water level one also achieves a larger total liquid volume. It is an advantage that food articles come out of the tank as smoothly as possible over time. It is a disadvantage if the float over the screw core in the area where it has a smaller diameter, because one will then to some extent lose the control of the residence time for the objects in a chamber. Many treatments have a fixed

prescribed residence time.

One can use different solution to prevent that the food articles 14 float over the core. It is likely that there will be an advantage to use several such solutions simultaneously. One can, for example, pump the same amount of water from the one and as from the other, which corresponds to the transport amount of the screw. One can also add liquid over the screw core according to the principle relevant for hot air curtains that are use at exit doors from building to separate inside air from outside air. One can also use directional jets along the outer diameter of the tank volume to supply a moment in the same direction as the rotation of the screw.

In a preferred embodiment of the present invention, longitudinally running, movable dividers (not shown) can be fitted above the tank that separate the volumes on the upper side of the screw core. These can preferably be suspended above the tank so that they move forward with the rotation of the screw and that they are moved back to the starting position when they have followed the screw sufficiently far forward. These physical barriers comprise a wall or a grid that hangs completely flexibly or partially flexibly in between the threads (16) and in towards the core diameter D1 with a gap, and which follows the forward movement in the space between the threads when the screw rotates, until they are pulled out where the transition to D2 is, and enters a return path back to the opposite end of the screw, from where they enter the gap between the threads again to repeat the cycle. The inventors of the present invention have found in a parallel patent application that it is possible to use an active flow of water to transport food articles efficiently out from a screw tank. This is described as water carried outflow and is a principle that works independent of the increase in diameter of the core which the present invention relates to. However, these two solutions can be combined.

The active flow of water is set up by the difference in the water level (given as AV) between the water surface in the tank (gives as V2) and the flow in the outlet end (given as VO9. Thus, the level D2 can be determined by the dimention of the core and/or the supply of liquid to the tank, and the level VO is determined by the vertical position of the outlet.

In an alternative embodiment of the invention the tank is fitted at the end where the outlet is with a guiding arrangement (19) as shown in figure 4 which lifts the food articles 14 up to a higher level. A such guiding arrangement will function independent of the diameter of the core, but in a preferred embodiment the guiding arrangement (19) is combined with an increased diameter.