Field of the Invention The present invention relates to a method for removing the shell from crustaceans as well as an apparatus for carrying said method.

Background of the Invention

In the art a number of methods and apparatuses have been suggested, and the present invention is an improvement of a device specifically suggested in US 4769870.

In the process plant suggested in US 4769870, the crustaceans and in particular shrimps are boiled before being introduced into a de-shelling system. After having passed through the de-shelling system, a suspension of crustacean meat, shells and wa- ter is pumped onto a wire conveyor belt in order to separate first the liquid from the suspension and thereafter the shells.

The de-shelling installation comprises an inlet funnel and a valve construction, which is operated by alternating between air pressure and air vacuum whereby the resilient valve member will open and close and thereby let crustaceans pass from the funnel and into the de-shelling chamber. In the de-shelling chamber, the crustaceans will, due to gravity and vacuum in the de-shelling chamber accelerate towards two oppositely inclined plate members such that the mechanical impact of the crustaceans on these inclined plate members in combination with the under pressure (vacuum) and the pre-heated crustaceans, cause the shells to separate from the meat part of the crustaceans. After having impacted the two inclined plate members, the shells and meat parts are collected in the bottom of the de-shelling system in a water pool. From the water pool, the water is pumped together with the shells and the meat to the above-mentioned wire conveyor belt. Object of the Invention

The present invention is specifically directed to an improvement in the de-shelling system in that the prior art device comprises a number of disadvantages that, although the apparatus when introduced into the marked provided substantial advantages to the mechanised de-shelling of crustaceans and a relatively high percentage of de-shelling was achieved with the prior art device, the inventors of the present invention has further improved this de-shelling system such that very high de-shelling rates are achieved. Tests with the apparatus according to the present invention indicates that when the crustaceans are shrimps, a de-shelling rate of above 95% completely de-shelled shrimps is achieved and furthermore the production rate is higher and the energy consumption is lower.

The invention therefore aims at alleviating the disadvantages of the prior art device and improving the de-shelling rate as well as the productivity of the prior art devices as e.g. suggested in US 4769870.

Description of the Invention

The present invention addresses this by providing a method for removing the shell from a crustacean. The method comprises the following method steps: a) the crustaceans are heated; b) the crustaceans are transferred to a funnel at the bottom of which, a valve is arranged, where said valve comprises a resilient cone shaped member, and a moveable valve plate, for opening and closing of the valve, such that as the valve is opened crustaceans are sucked through the cone shaped member, thereby arranging the crustaceans one by one during the passage through the cone shaped member; c) a separating chamber arranged downstream from the valve, and in communication with said valve, where a substantially lower air pressure is present in the separating chamber relative to the ambient air pressure, and where separating means are arranged in said separating chamber, such that as the crustaceans enters the separating chamber, the lower air pres- sure and the separating means will detach the shell from the crustacean, during the crustaceans fall through the separating chamber; d) where the crustaceans are collected in a water pool arranged in the bottom of the separating chamber, where the crustaceans on impact with the surface, if separation between shell and meat has not occurred by the separating means, will separate the shell from the meat; e) and that the water containing meat and shells is removed from the separating chamber for further separation of meat and shells.

In the prior art device mentioned above, the valve controlling the inlet of crustaceans from the funnel to the vacuum chamber/separating chamber was operated by a combined pressure and vacuum valve, such that by alternating opening and closing between two valves connecting one valve to a source of pressurized air and the other valve to a source of vacuum, a resilient pipe member arranged inside the connecting pipe between the funnel and the pressure chamber would open or close respectively thereby allowing crustaceans to enter the separating chamber. This led to a varying number of crustaceans entering the separating chamber by each opening and closing of the valve, and furthermore a relatively high vacuum was necessary inside the separating chamber in order to compensate for the opening and closing of the inlet valve. This in turn leads to a high energy consumption in order to provide both pressurised air and vacuum for the proper operation of the device.

With the present invention, the cone shaped resilient member guides the crustaceans from the funnel towards the valve member separating the inlet from the separating chamber in such a manner that the crustaceans are arranged in "single file". By arranging the crustaceans such that they are introduced into the separating chamber one by one, a number of advantages are achieved:

Firstly, by introducing the crustaceans one by one into the separating chamber, it is assured that each crustacean will impact the separating means in the separating chamber. In prior art devices allowing more than one crustaceans into a separating chamber at a time, it was possible that one crustacean instead of impacting the inclined separating plate in the separating chamber impacted another crustacean. The crustacean being softer (resilient) would cushion the impact and thereby minimise the effect of the impact such that overall only very little de-shelling was effected in the separating chamber. Therefore, by separating the crustaceans such that they are introduced into the separating chamber one by one, it is assured that each single crustacean will impact the separating means arranged in the separating chamber.

Secondly, the wide opening of the prior art valve between the inlet funnel and the separating chamber required a substantial under-pressure/vacuum to be present in the separating chamber. The present construction, however, having an opening and closing valve with a movable valve plate, drastically reduces the pressure loss through the inlet funnel.

Thirdly, the resilient cone shaped member being separated from the valve assures that no crustaceans are caught in the valve closing mechanism, and furthermore the cone shaped member being dimensioned to that particular type of crustacean arranges the crustacean in a general uniform orientation and furthermore due to the design of the resilient cone shaped member it may be designed such that the passage of the crustaceans through the cone shaped member only has a limited influence on the constitution of the crustaceans. It is desirable to assure that all de-shelling occurs inside the separating chamber in that parts of shells stuck in the cone shaped member or the valve may deteriorate the process as such. Therefore, by designing the cone shaped member to correspond to the crustaceans being treated, further enhancement of the production process may be achieved. In the prior art device, the opening and closing valve would inherently squeeze crustaceans caught during passage of the valve member in its closing mode of operandi, and thereby partly ruin the crustaceans being caught there, but also under some circumstances not completely close off the valve between the funnel and the separating chamber such that a pressure loss could be present at all times.

In a further advantageous embodiment of the method according to the invention, prior to step a) of the method mentioned above, the crustaceans may be boiled and cooled, and that the heating in step a) is a very short heating, such that only the shell, and liquid and/or tissue immediately under the shell is heated, where a temperature of 50° to 150° more preferred 8O ⁰ C to 11O ⁰ C is achieved. By heating the shell and the liquid immediately under the shell prior to introducing the crustaceans into the separating chamber, an improved separating process is achieved. This is due to the fact that as the crusta- ceans are heated at ambient air pressure and thereafter introduced into an underpressure, the under-pressure will cause the liquid to expand rapidly almost having the characteristics of an explosion such that the shells will be jettisoned away from the meat portion of the crustaceans and thereby even prior to impacting the separating means in the separating chamber, the crustaceans will have been de-shelled to a large degree. This is due to the anatomy of the crustaceans which usually have a hard shell covering their sides and back but a relatively soft protective cover in their belly section. When they are exposed to the large pressure difference, which is enforced by the elevated temperature, the soft belly part will tend to rupture and allow the entire shell to be removed. The amount of heating shall also be seen in relation to the airpressure (see below) as the combination of temperature and air pressure will cause the desired effect.

The heating may be carried out by exposing the crustaceans to a gas flame, steam, hot air jets or the like immediately prior to entering either the funnel, the cone shaped resil- ient member or the space between the cone-shaped member and the valve plate.

In a further advantageous embodiment of the method, the distance between the cone shaped member and the surface of the water in the pool may be varied.

Tests have indicated that as the crustaceans leave the cone shaped member and are sucked into the separating chamber, they accelerate due to the combination of the influence of gravity and the influence of pressure difference between ambient pressure in the inlet funnel and the under-pressure in the separating chamber. By adjusting the distance between the inlet and the water surface, the crustacean has a distance available in order to accelerate in the separating chamber, where the impact with the water surface may be designed such that any remaining shell fraction still left after the crustacean has passed through the separating means in the separating chamber may be removed upon impact with the water surface. On the other hand, the water is provided in order to brake the fall of the crustacean, and as such the crustacean's speed should not exceed certain limits depending on the type of crustacean. For certain fragile types of crustaceans, it is desirable to be able to have a relatively low speed such that the impact with the water surface is as mild as possible and thereby the breaking effect as gentle as possible such that the crustaceans meat is not ruined by this impact. On the other hand, for certain type of more tough crustaceans the extra speed and the high impact with the water surface may result in even higher de-shelling percentages.

In a still further advantageous embodiment of the invention, the removal of water in method step e) is carried out in a batch- wise fashion, such that the surface of the water is clear from debris such as meat and shells, and that extra water is added corresponding to the removed water quantity.

By removing the water batch- wise e.g. by arranging a system of two valves arranged in a pipe at a distance and then sequentially opening and closing one or the other valve and at the same time adding water to the pool inside the separating chamber, a substantially clear water surface is provided. When debris such as shells and other foreign matter are floating on the water surface, the impact between the crustaceans being transported to the separating chamber and the surface debris on the water may be so violent that the meat portion of the crustacean is damaged. Furthermore, an important feature of the invention is to design the speed with which the crustaceans hit the water surface such that complete de-shelling is achieved without damaging the product, and the floating debris in the surface may render this design useless in that other parameters need to be taken into consideration if there is a risk of the crustacean travelling through the separating chamber hitting debris instead of a clear water surface.

By furthermore removing the water batch-wise and at the same time adding an equal amount of fresh water to the pool, the water level will remain more or less constant relating to the level inside the separating chamber such that also the under-pressure in the separating chamber will be uninfluenced by the batch-wise removal of water and crustaceans.

In a further advantageous embodiment of the invention, the under-pressure in the separating chamber is 10 % to 90% lower more preferred 30 % to 70 % lower than ambient air pressure, whereby the combination of the lower pressure and the temperature of the shell and the tissue and/or liquid in the immediate vicinity of the shell causes the water to turn to steam thereby loosen or separating the shell from the meat. In the prior art devices, it is necessary to have a substantially lower air pressure inside the separating chamber in order to achieve the separating process which in turn requires a larger vacuum generator and thereby increased energy consumption. By being able to operate with under-pressure in the range 30 % to 70 %, less energy is spent maintaining the under-pressure. The level of under-pressure where 30 % relates to 30 % less than ambient pressure and 70 % corresponds to 70 % lower air pressure than ambient air pressure, the under-pressure inside the separating chamber may be selected according to the type of crustacean being de-shelled in the installation. The air pressure will be adjusted according to the type of crustacean, the age of the crustacean, the temperature, the duration of treatment and other factors such that the entire production process is optimized with respect to both productivity and energy cost.

The invention is also directed to an apparatus having the inventive features as set out in the independent apparatus claim with dependant claims defining further advantageous embodiments of the invention.

Description of the Drawing

Fig. 1 illustrates a simplified cross section through a de-shelling apparatus; Fig. 2 illustrates a more detailed view of the inlet arrangement.

Detailed Description of the Invention

Fig. 1 illustrates a simplified cross section through a de-shelling apparatus according to the invention. The apparatus comprises an inlet funnel 1 arranged at an upper end of the apparatus. At the bottom of the inlet funnel, a resilient cone shaped member 2 is arranged. The cone shaped member is easily replaceable such that cone shaped mem- bers having different openings both inlet openings 3 and outlet openings 4 may be utilised depending on the type of crustaceans which is to be de-shelled in the apparatus.

Immediately adjacent, the outlet 4 of the cone shaped resilient member 2 is provided a valve construction 5. The valve in this embodiment comprises a valve stem 6 and a valve plate 8 connected to a valve motor 8 such that the valve plate may be manipu- lated from a position as illustrated in full lines in figure linto a closed position illustrated by dash lines reciprocally as indicated by the arrow 9.

The valve 5 is arranged in valve chamber 10 which has an opening 11 into the main separating chamber 12.

Inside the main separating chamber 12, separating means are provided in the shape of a maze 13 such that crustaceans being introduced into the inlet funnel 1 will pass the cone shaped member 2 when the valve 5 is in its open position such that the crusta- ceans will enter the maze 13.

The maze is dimensioned such that it has a number of inclined surfaces 14 on which the crustaceans will impact, whereby the shells will be loosened from the meat section of the crustacean. The distance between two adjacent peaks 15,15' in the maze is dimen- sioned such that they do not overlap. This is due to the fact that by having a small gap between the two peaks 15,15', it is assured that crustaceans, shells and other debris may pass at a relatively high speed through the separating maze 13, thereby increasing the productivity. Tests have furthermore shown that if a shrimp should pass completely unhindered through the separating maze, the combination of high temperature in the outer section of the crustaceans and the under-pressure inside the separating chamber will cause the shell to more or less explode free of the meat portion such that a relatively high de-shelling percentage is achieved anyway.

In the bottom of the separating chamber a water pool 16 is arranged having a water surface 17. Furthermore, means for supplying fresh water (not illustrated) may be controlled such that the water surface 17 is maintained at a fixed or constant distance in relation to the valve 5. In this connection, it should also be noted that the separating chamber is provided with inlets and outlets for generating an under-pressure inside the separating chamber in the range of 30 % to 70 % of the ambient pressure but for clarity purposes the installation relating to the under-pressure generation has not been indicated. At the bottom of the separating chamber 12, an outlet 18 is furthermore provided such that the water from the pool 16 may be extracted together with the shells and the meat from the crustaceans. In order to provide a batch- wise extraction of water, crustaceans and shells, two valves 19,20 are provided in the outlet pipe 21. In this manner when opening valve 19, the water 16 will flow into the outlet pipe 21, afterwards the valve 19 is closed and the valve 20 is opened whereby the water containing water, meat and shells may be pumped on to further processing and separation. At the same time, the water pool is replenished by means not illustrated such that the water level 17 is maintained at a substantially constant level in relation to the valve installation 5. In this manner, the under-pressure inside the separating chamber 12 is not seriously influenced by the draining of liquid, meat and shells from the separating chamber, and neither is there any influence from the valve 5 due to the quick action of the valve seat in combination with the cone shaped member 2, such that only negligible pressure loss is experienced.

The valve 5 will be further explained with reference to fig. 2. Like features are provided with like reference numerals.

As the crustacean enters the inlet funnel 1, the cone shaped resilient member 2 is shaped such that the outlet of the cone shaped member 4 has a diameter slightly larger than the largest diameter of the crustacean to be de-shelled. The crustacean has a substantially longitudinal body shape and by passing through the cone shaped member 2, the longitudinal axis of the crustacean will be guided into a substantially vertical orientation. By furthermore designing the opening 4 such that the opening may be 1-3 mm larger that the diameter of the periphery of the crustaceans cross section perpendicular to the longitudinal direction of the crustacean, it is assured that only one crustacean is forced through the cone shaped member at a time. By having an opening time that is to say when the valve plate 7 is in the position as indicated in bold lines in fig. 2, the crustaceans will be able to pass through the valve and thereby enter the separating chamber 12. The valve is opened depending on the size of the crustaceans but between 0,2 to 0,6 seconds allowing one to four crustaceans to pass at any one opening cycle. For other types of crustaceans and at other temperatures and air pressures it will be necessary to vary the cyclus-time between 0,1 to 30 seconds, more preferred 0,2 to 8 sec- onds and most preferred 0,6 to 5 seconds. Preferably, only one crustacean will pass through the valve construction, and due to the very rapid cyclus time of opening and closing the valve 5, approximately one to five shrimps may pass into the separating chamber per cone shaped member per second. By arranging an array of cone shaped members and valve mechanisms a relatively high production may be achieved.

In the embodiment illustrated in fig. 2, the valve plate is mounted on a valve stem 6 being operated by the valve motor 8. Alternatively, a rotating valve member may be arranged in the vicinity of the outlet 4 of the cone shaped member such that by rotating the valve member, it will very rapidly open and close and thereby achieve the same functionality as a valve illustrated with reference to fig. 1 and 2. The valve may also be in the shape of a circular valve plate being rotated in the same plate as the valve plate 7s closed position illustrated by dash lines such that as the valve plate is rotated, apertures provided in the valve plate may be superposed the outlet 4 of the cone shaped member 2 such that crustaceans may pass through the apertures until the solid part of the valve plate is rotated into a position where it blocks the outlet 4 of the cone shaped member 2.

Although the invention has been explained with reference to specific embodiments, these shall only be construed as illustrations only and variations may be contemplated without departing from the scope of the appended claims.