Technical Field

The present invention concerns a method of processing eggshell residues, which emanate from an egg breaking unit and comprise eggshell por- tions as well as membrane portions.

Prior Art

Eggshell residues emanating from an egg breaking unit form a valuable source of both minerals (mostly calcium) from the eggshell portions and proteins from the membrane portions. However, in order to make use of that source first the eggshell portions and the membrane portions have to be strictly separated, which has to be done in a careful way so that the protein content is not deteriorated.

From US 6 649 203 B1 an eggshell processing method is known, com- prising separation of outer eggshell portions and membrane portions. According to the known method fresh eggshell residues are first centrifuged to remove adhering liquid egg. Then the eggshell residues are washed in water to remove residual liquid egg. The next step of the known method comprises once again centrifuging and then, at a temperature of just slightly less than 90°C, drying to a low moisture content. Next comes vibratory screening aiming at removing loose membrane portions. The remainder is then milled coarsely and treated pneumatically to remove some additional freed membrane portions, and then milled finely before packaging.

The fact that the known method comprises a washing step, makes it require not only use of plenty of water but also of extra centrifuging and drying steps. Hence, the known method is neither particularly economical nor environmentally friendly, and above that the rather high drying temperature of just slightly less than 90°C tends to deteriorate quality of the proteins of the membrane portions. Object of the Invention

In the light of the above, it is an object of the present invention to mitigate the drawbacks of the prior art solution and to provide a method of processing eggshell residues which is economically and environmentally more feasible and further less harmful to the proteins involved.

Brief Summary of the Invention

According to the invention this is achieved by means of a method of processing eggshell residues, which emanate from an egg breaking unit and comprise eggshell portions as well as membrane portions, the method being characterised by the following steps:

feeding eggshell residues, having a particle size of 0,5 mm to 40 mm and a wet basis moisture content of 3% to 40%, from said egg breaking unit into a cyclone, which, at a speed exceeding 60 m/s, and preferably between 70 m/s and 340 m/s, is driven by a process gas, which has a temperature of less than 85°C, and preferably of less than 60°C,

in said cyclone, vortex processing of the eggshell residues to reduce particle size and to peel said membrane portions off of said eggshell portions, such that said eggshell portions become separated from said membrane por- tions,

through a top outlet of said cyclone, releasing mainly a mix of process gas, vapour and droplets,

through a bottom outlet of said cyclone, releasing mainly a mixture of separated eggshell portions and membrane portions, and,

in a sorting device, sorting of said released mixture into an eggshell portion part and a membrane portion part.

The method according to the invention does not comprise any washing step. This is environmentally beneficial and saves equipment and operation costs. Further, it does not comprise any centrifuging step to throw washing liquid off, which is advantageous for the same reasons as the lack of a washing step. And finally, the method according to the invention does not comprise an energy consuming drying step operating at a temperature just slightly below 90°C and therefore tending to deteriorate protein quality. Preferably the method according to the invention comprises the further step of controlling time between feeding eggshell residues into and releasing said mixture out of said cyclone by adjusting an eggshell residue feed rate in relation to a total process gas feed rate, wherein said time may be confined into an interval of 0,5 s to 20 s, and preferably of 1 s to 5 s. In other words, two factors that can be easily controlled, that is the eggshell residue feed rate and the process gas feed rate, are suitably used to arrive at an optimum result, while energy consumption is kept low and process time reduced to an extremely short time.

In order to take care of as much liquid egg as possible the method according to the invention preferably comprises the further step of centrifuging the eggshell residues prior to feeding them into said cyclone. This leads to the additional advantage that the following cyclone step can be performed under dryer and therefore better conditions.

According to a preferred embodiment the method according to the invention comprises the step of continuous feeding of eggshell residues into the cyclone. Continuous feeding leads to maximum use of the equipment at hand and helps achieving stable operating conditions for the cyclone used.

During the step of sorting blowing of process gas to pneumatically ex- pel said membrane portion part off of sorting screens and out of the sorting device has turned out to be most efficient. However, that does not exclude the possibility to use an all different sorting device, such as an aspirator.

Preferably, according to the invention both said eggshell portion part and said membrane portion part are dried after having been sorted. Further, said parts are optionally milled as well after having been sorted. In any case the goal of these measures is to arrive at end products which are of an even and high quality and suitable for packaging and transport.

Brief Description of the Drawings

On the drawings figure 1 shows a flow chart which illustrates steps of a method according to a preferred embodiment of the invention. Detailed Description of a Preferred Embodiment

Hundreds of thousands of tons of eggshell residues are produced at egg breaking facilities worldwide. While eggshells contain substances with high potential economic value, eggshell residues are often disposed as waste. Meanwhile, the demand for pure and clean, natural mineral and protein ingredients is growing in a number of industries, including cosmetics, cosmeceuticals, nutraceuticals, pharmaceuticals, functional food, animal feed, etc. Against that background an object of the present invention is to provide a method of processing eggshell residues in order to produce eggshell derived ingredients.

Eggshell residues comprise protein rich membrane particles and mineral rich shell particles which are entangled and must be separated into two separate material flows to allow further processing and commercial application. Besides problems caused by particle entanglement, another problem met in this context is that proteins are sensitive to temperature and must be kept at temperatures below 55°C to avoid product degradation.

This has made the inventors look for a method more lenient than known solutions and made them finally arrive at a method comprising use of a low temperature, high speed cyclone. By this is meant a cyclone driven by a process gas holding a temperature of less than 85°C and a speed exceeding 60 m/s.

It turns out that such a cyclone is able to peel membrane particles off eggshell particles within a few seconds or even fractions of a second, thus guaranteed keeping temperature of the particles involved sufficiently low to avoid degradation. Within the cyclone the separation process makes use of the difference in brittleness and elasticity between the eggshell particles (predominantly containing minerals) and the membrane particles (predominantly containing proteins) to separate entangled (composite) particles into pure mineral and protein particles.

In the following the above is illustrated by means of a detailed description of a preferred embodiment of the method according to the invention with reference being had at the enclosed drawings. In the drawings box 1 illustrates an egg breaking step in an egg breaking unit. This unit outputs egg white and yolk (c.f. box 2) and eggshell residues. These comprise eggshell and membrane portions as well as some liquid egg and are fed into a centrifuge (c.f. box 3).

In the centrifuge most of the liquid egg is thrown off the eggshell and membrane portions and led to an output (c.f. box 4), while the remaining eggshell residue particles, having a size of 0,5 mm to 30 mm and a wet basis moisture content of 3% to 40%, are fed into a high speed cyclone (c.f. box 5).

The cyclone is driven by a process gas, which holds a temperature of preferably less than 60°C and a speed preferably within an interval of 70 m/s to 340 m/s. Within the cyclone the process gas causes a vortex flow, that entangles the eggshell residues and makes them collide with each other and cyclone walls. This makes the brittle eggshell portions break into smaller pieces while the elastic membrane portions are peeled off, all within a stay time inside the cyclone of preferably between 1 s and 5 s.

Through a top outlet of the cyclone a mix of mainly gas, vapour and droplets is released (c.f. box 6), and through a bottom outlet of the cyclone a mixture mainly containing separated eggshell portions and membrane portions are released (c.f. box 7).

Said mixture of eggshell portions and membrane portions is then fed into a sorting device (c.f. box 8), in which sorting into an eggshell portion part and a membrane portion part is performed, for instance by means of vibrating screens and/or an aspirator, i.e. means well known to a person skilled in the art.

From the sorting device the eggshell portion part is optionally fed into a dryer (c.f. box 9), in which the moisture content is lowered to an adequate level, e.g. for packaging and storing. The same goes for the membrane portion part, which is fed into a dryer (c.f. box 10), also in order to arrive at an appropriate moisture content level for packaging, transport and storing with- out degradation.

From the dryer the eggshell portion part is then led into an optional mill (c.f. box 1 1 ), in which particle size is reduced to a desired even level, before the particles reach a final packaging stage (c.f. box 13). The membrane portion part is optionally led from the dryer into a mill (c.f. box 12), in which it is ground before packaging (c.f. box 14).

It is obvious to a person skilled in the art that there are several ways of altering the method described above within the frame set up by the appen- dent claims. However, no matter how the method is altered, it is important that the protein content of the membrane portions always is treated carefully and not exposed to temperatures causing degradation.