Patent Description:
Separators for separating milk into different phases of varying density under the influence of a centrifugal force are called centrifugal separators. The milk is introduced in a rotating disc stack of the centrifugal separator. Under the influence of the centrifugal force, heavier components and lighter fat globules in the raw milk begin to settle radially outwards respectively inwards in the separation channels according to their density. The cream, i.e. the fat globules, has a lower density than the skimmilk and therefore moves inwards over the disks, towards the separator's axis of rotation. The cream continues to an axial outlet and the heavier phase, i.e. the skimmilk, moves outwards to the space outside the disc stack and from there to a skimmilk outlet. A problem with previous separators is that the efficiency is reduced in certain operating conditions. For example, the skimming performance may be reduced under low temperature conditions. Related prior art is described in patent documents <CIT> and <CIT>.

It is an object of the invention to at least partly overcome one or more limitations of the prior art. In particular, it is an object to provide an improved method of separating cold milk, in particular allowing for an improved skimming performance over a wider temperature range and which requires less maintenance.

This is achieved by a method using a centrifugal separator for separating milk into a cream phase and a skim milk phase. The separator comprises a centrifuge bowl and a disc stack of conical discs arranged inside the centrifuge bowl. The disc stack comprises a first set of discs, and a second set of discs. The discs in the disk stack comprises distribution openings such that the milk passes the first set of discs before passing the second set of discs. The discs in the first set of discs are separated from each other by a first distance, and the discs in the second set of discs are separated from each other by a second distance which is smaller than the first distance.

According to the invention the method of separating cold milk uses the separator. The method comprises providing a flow of the milk through a first set of discs in a disc stack arranged in the separator, and providing a flow of the milk through a second set of discs, stacked on top of the first set of discs.

Having first and second set of discs where the discs in the second set are separated from each other by a distance which is smaller than the distance between discs in the first set allows for an initial separation of larger flat globules from the milk in the first set of discs, with a lowered risk for build-up of fat between the discs, while the smaller separation in the second set of discs provides for maintaining a high skimming efficiency.

Embodiments of the invention will now be described, by way of example, with reference to the accompanying schematic drawings.

Embodiments of the invention will now be described more fully hereinafter with reference to the accompanying drawings, in which some, but not all, embodiments of the invention are shown. The invention may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein.

<FIG> is a schematic illustration of a separator <NUM> for separating milk (RM) into a cream phase (CR) and a skim milk phase (SM). The separator <NUM> comprises a centrifuge bowl <NUM> and a disc stack <NUM> of conical discs <NUM> arranged inside the centrifuge bowl <NUM>. The milk (RM), which typically is so called raw milk, enters the centrifuge bowl <NUM> via an inlet <NUM>, and is subsequently separated into the skim milk phase (SM) and the cream phase (CR) at the top of the centrifuge bowl <NUM>. milk (RM) flows from the inlet <NUM> into distribution openings <NUM> in the disc stack <NUM>, and the cream phase (CR) is centrifuged towards a center portion <NUM> or the disk stack <NUM> and flows from the center portion <NUM> to a cream phase outlet <NUM>, whereas the skimmed milk phase (SM) is centrifuged towards a periphery <NUM> of the disc stack <NUM> and flows from the periphery <NUM> to an outlet <NUM> for the skimmed milk phase (SM).

<FIG> and <FIG> show an example of the disc stack <NUM> in an exploded perspective view. The disc stack <NUM> comprises a first set of discs <NUM> and a second set of discs <NUM>. The discs <NUM> in the disk stack <NUM> comprises the aforementioned distribution openings <NUM> such that the milk (RM) passes the first set of discs <NUM> before passing the second set of discs <NUM>. The discs <NUM> in the first set of discs <NUM> are separated from each other by a first distance <NUM>, and the discs <NUM> in the second set of discs <NUM> are separated from each other by a second distance <NUM>. <FIG> is a further detailed perspective view of the first and second sets of discs <NUM>, <NUM>, having respective separation distances <NUM> and <NUM>. The second distance <NUM> is smaller than the first distance <NUM>. the spacing between the discs <NUM> in the second set of discs <NUM> is smaller than the spacing between the discs <NUM> in the first set of discs <NUM>. The distance or spacing between the discs <NUM> in the first and second sets <NUM>, <NUM>, is sometimes also referred to as the caulk height. The caulk height in the second set of discs <NUM> is thus smaller than the caulk height in the first set of discs <NUM>. Having discs <NUM> in the first set <NUM> which are separated from each other by a distance which is larger than the distance between the discs <NUM> in the second set <NUM> allows for an initial separation of larger flat globules from the milk in the first set of discs <NUM>, with a lowered risk for build-up of fat between the discs <NUM> due to the larger separation thereof, while the smaller separation in the second set of discs <NUM> provides for maintaining a high skimming efficiency for a given size of the separator <NUM>. When the milk flows into the second set of discs <NUM>, the fat globules has decreased in amount and/or size. The risk of occlusion or plugging of fat in the disc stack <NUM> is thus reduced while a high efficiency can be provided. This is particularly advantageous in low temperature conditions where the milk is not heated, as the tendency for accumulation of the fat is increased in these cases. As the risk of fat occlusion is reduced, there is also a reduced need for cleaning the disc stack <NUM>. less resources has to be spend on the maintenance of the separator <NUM>, and the throughput in the production line can also be increased due to less interruptions from maintenance operations.

The number of discs <NUM> in the second set of discs <NUM> may be higher than the number of discs <NUM> in the first set of discs <NUM>, as schematically illustrated in <FIG>. This provides for achieving a high skimming efficiency, as the number of discs <NUM> in the second set <NUM> can be increased more by having a smaller separation distance <NUM>, compared to the discs <NUM> in the first set <NUM>, for a given size of the separator <NUM>. At the same time, the discs <NUM> of the first set <NUM> provides for the initial separation of larger fat globules as described above, although being fewer in number than the discs <NUM> of the second set <NUM>. A compact separator <NUM> with increased low temperature efficiency may thus be provided.

A ratio between the number of discs <NUM> in the second set of discs <NUM> to the number of discs <NUM> in the first set of discs <NUM> may be in the range of <NUM> - <NUM>. This allows for a reduced risk of fat occlusion in the disc stack <NUM> while the skimming efficiency is increased. The ratio between the number of discs <NUM> in the second set of discs <NUM> to the number of discs <NUM> in the first set of discs <NUM> may be in the range of or <NUM> - <NUM>, which provides for a separator <NUM> which is particular advantageous in terms of skimming efficiency.

The number of discs <NUM> in the first set of discs <NUM>, having the increased separation distance <NUM>, may be in the range of <NUM> - <NUM> discs. Having a number of discs <NUM> of the first set <NUM> in this range provides for facilitating the initial separation of fat globules with a lowered risk of blockage by fat between the discs <NUM>. At the same time this allows for having a plurality of discs <NUM> in the second set <NUM> that increases the skimming performance for a given size of the separator <NUM>. In one example the number of discs <NUM> in the first set of discs <NUM> is in the range <NUM> - <NUM>, and the number of discs <NUM> in the second set of discs <NUM> is in the range <NUM> - <NUM>.

A ratio between the first distance <NUM> to the second distance <NUM> may be in the range of <NUM>,<NUM> - <NUM>,<NUM>. the first set of discs <NUM> are separated from each other by a first distance <NUM> which is larger than the separation distance <NUM> between the discs <NUM> of the second set <NUM> by a factor which is in the range <NUM>,<NUM> - <NUM>,<NUM>. This provides for an increased skimming performance at low temperature conditions. A ratio between the first distance <NUM> to the second distance <NUM> in the range of <NUM>,<NUM> - <NUM>,<NUM> provides for a particularly advantageous separator <NUM> with an increased skimming performance at low temperatures for a given volume of the separator <NUM>.

In one example the ratio between the first distance <NUM> to the second distance <NUM> may be <NUM>,<NUM> for an optimized skimming efficiency of the separator <NUM> in some low temperature operating conditions.

The discs <NUM> in the first set of discs <NUM> are separated by <NUM>,<NUM> - <NUM>,<NUM>. Having a separation of the discs <NUM> in the first set <NUM> in this range provides for a particular advantageous separation of larger fat globules in the milk with a further reduced risk of occluding the space between the discs <NUM> with fat.

The discs <NUM> in the second set of discs <NUM> are separated by <NUM>,<NUM> - <NUM>,<NUM>. Having a separation of the discs <NUM> in the second set <NUM> in this range, e.g. in combination with a separation in the range <NUM>,<NUM> - <NUM>,<NUM> of the first set <NUM>, allows at the same time for increasing the overall skimming performance for a given volume of the separator <NUM> while avoiding blockage problems when separating milk of low temperature. In one example the discs <NUM> in the first and second sets <NUM>, <NUM>, may be separated by <NUM>,<NUM> and <NUM>,<NUM>, respectively, for an optimized performance in some operating conditions, e.g. with a temperature of the milk in the range of <NUM> - <NUM>.

The discs <NUM> in the first set of discs <NUM> may have an open center portion <NUM> for receiving a centering element <NUM> arranged in the centrifuge bowl <NUM>. The open center portion <NUM> in the first set of discs <NUM> is illustrated in the example of <FIG>, and the centering element <NUM> is shown in <FIG>. The discs <NUM> in the first set <NUM> may thus be accurately aligned with the axis of rotation of the centrifuge bowl <NUM>.

The discs <NUM> in the second set of discs <NUM> may have a reduced diameter center portion <NUM> coaxially aligned with the open center portion <NUM> of the discs <NUM> in the first set of discs <NUM>. The reduced diameter center portion <NUM> of the discs <NUM> in the second set <NUM> is shown in the example of <FIG>. In this example the opening in the center of the discs <NUM> of the second set <NUM> is partly closed in comparison to the discs <NUM> in the first set <NUM>.

<FIG> illustrates a flow chart of a method <NUM> of separating cold milk using a separator <NUM> as described above in relation to <FIG>. The method <NUM> comprises providing <NUM> a flow of the milk through a first set of discs <NUM> in a disc stack <NUM> arranged in the separator <NUM>, and providing <NUM> a flow of the milk through a second set of discs <NUM>, stacked on top of the first set of discs <NUM>. The discs <NUM> in the first set of discs <NUM> are separated from each other by a first distance <NUM>, and the discs <NUM> in the second set of discs <NUM> are separated from each other by a second distance <NUM> which is smaller than the first distance <NUM>. The method <NUM> thus allows for an efficient separation of cold milk with a reduced risk of blockage in the disc stack <NUM> by the fat in the milk, as described above in relation to the separator <NUM> and <FIG>.

The cold milk may be milk which is not heated. The temperature of the cold milk is below <NUM> or below <NUM> in some examples. The temperature of the cold milk may also be below <NUM> or below <NUM> in some examples. The temperature of the cold milk may also be below <NUM> or below <NUM> in some examples. The tendency of the fat to form larger aggregates of fat particles may increase with the lowering of the temperature. Thus, the separator <NUM> provides for a particularly advantageous increase in skimming efficiency and reduced risk of such fat blockage of fat blockage as the temperature of the milk is reduced further across the ranges as exemplified above.

Claim 1:
A method (<NUM>) of separating cold milk, the method
using a centrifugal separator (<NUM>) for separating milk (RM) into a cream phase (CR) and a skim milk phase (SM), the separator (<NUM>) comprising a centrifuge bowl (<NUM>), a disc stack (<NUM>) of conical discs (<NUM>) arranged inside the centrifuge bowl (<NUM>), the disc stack (<NUM>) comprising a first set of discs (<NUM>) and a second set of discs (<NUM>), the discs (<NUM>) in the disk stack (<NUM>) comprising distribution openings (<NUM>) such that the milk (RM) passes the first set of discs (<NUM>) before passing the second set of discs (<NUM>), the discs (<NUM>) in the first set of discs (<NUM>) being separated from each other by a first distance (<NUM>), and the discs (<NUM>) in the second set of discs (<NUM>) being separated from each other by a second distance (<NUM>) which is smaller than the first distance (<NUM>),
the method comprising
providing (<NUM>) a flow of the milk through the first set of discs (<NUM>) in the disc stack (<NUM>) arranged in the separator (<NUM>), and thereafter
providing (<NUM>) the flow of the milk through the second set of discs (<NUM>), which is stacked on top of the first set of discs (<NUM>), characterized in that
the discs (<NUM>) in the first set of discs (<NUM>) are separated by <NUM>,<NUM> to <NUM>,<NUM> and the discs (<NUM>) in the second set of discs (<NUM>) are separated by <NUM>,<NUM> to <NUM>,<NUM>, and
the temperature of the cold milk is below <NUM>.