FR2626143A1 - METHOD AND DEVICE FOR STERILIZING MILK BY CENTRIFUGATION - Google Patents

Abstract

Milk containing bacterial germs reaches the centrifugal drum 1 through a supply duct 12 and passes into a stack of bowls 4. The separated germs collect in the concentrate chamber 5. Through the discharge channels 6 and the nozzles 7 , low-germ concentrate is continuously discharged from the middle region of the concentrate chamber 5. It enters the skimming chamber 8 from where it is recycled, using the skimmer member. 9, through the concentrate discharge pipe 10 and through the recycling pipe 11 in the feed pipe 12 of the drum. The rest of the concentrate, with a high germ content, is periodically discharged through openings 14 made in the casing of the drum.

Description

STERILIZATION METHOD AND DEVICE

MILK BY CENTRIFUGATION

  The invention relates to a method of sterilization of milk by centrifugation, in which the milk is directed towards the inlet of a centrifugal drum, in the concentration chamber from which the concentrate containing bacterial germs and having has been separated by centrifugation, a fraction of this concentrate being evacuated from the centrifugal drum by evacuation channels provided with nozzles, and the remaining concentrate being periodically evacuated by

  discharge holes provided in the drum casing.

  Processes of this kind scn. known and are preferably used to sterilize milk intended for cheese factories

  as well as fluid milk. A suitable centrifuge

  nant to the implementation of the process is known for example

according to DE-AS 29 13 406.

  It is withdrawn through the evacuation channels provided with

  nozzles, approximately 3% of the quantity of milk supplied to the

  entry of the centrifugal drum, in the form of a concentrate loaded with bacterial germs. Another 0.3% of the amount of incoming milk is periodically discharged through the discharge openings of the drum casing. The concentrate thus obtained contains in particular bacterial strains having harmful effects on the quality of the cheeses. This is why the two fractions are brought together again to undergo a heat treatment in a special sterilization installation, where all the strains are killed.

  bacterial. The sterilized concentrate can then be rein-

  body in milk intended for cooking. But when it comes to sterilizing drinking milk, it is not allowed to reincorporate in this milk the sterilized germ concentrate,

  so that during the production of fluid milk

  mation, the germ concentrate is lost. Currently, there are even steps tending to prohibit in principle the addition of sterilized germ concentrate in dairy products. This concentrate can then only be used as

  animal feed, sold at low prices.

  The aim of the present invention is to carry out a process for sterilizing milk by centrifugation, in which the quantity of germ concentrate produced can

be greatly diminished.

  This object is achieved by withdrawing the concentrate discharged through the nozzles from a central region of the volume.

  o collects the concentrate and recycles it into the

ment of the centrifugal drum.

  It has been found, surprisingly, that it is possible, with the method according to the invention, to completely recycle in the feed of the drum the quantity of concentrate discharged through the nozzles, without unfavorable effect

  on the quality of the sterilized milk leaving the centrifuge.

  This is due to the fact that the fraction evacuated through the nozzles was withdrawn from a central region of the

  concentration volume, where there are only a few pre-

  smells. In fact, the germs contained in the concentrate preferably gather at the periphery of the drum in the vicinity of the discharge orifices, while the other constituents of the concentrate, fats and proteins, travel through the discharge channels and the nozzles, so that there is no significant increase

  the number of germs in the incoming milk, as a result of the re-

  cycling. The expected increase in the number of germs in sterilized milk as a result of

this recycling therefore does not take place.

  It is necessary to choose the region from which the fraction intended to be evacuated by the nozzles is drawn, so that, on the one hand, skimmed skimmed milk with as few germs as possible, and on the other hand except that there

2626 1 43

  have no fatty particles entrained in this racking,

  because otherwise these particles would be damaged.

  In the case of the known centrifugal drum, the two fractions of the concentrate containing germs are drawn off at the periphery of the volume where the concentrate collects. This is why these two fractions contain a high concentration of germs. Recycling, in the centrifugal drum feed, of the fraction withdrawn through the discharge channels provided with nozzles would consequently give rise to an increase in the germ content at the outlet of the centrifuge, and therefore to an unfavorable effect.

  on the quality of sterilized milk.

  It has been found that it is possible, without inconvenience

  ents for the separating effect of the centrifuge, to start the channels leading to the nozzles from the middle region of the volume where the concentrate collects, and thus, to draw skimmed milk almost free of germs. In fact, the withdrawal of this fraction is only necessary to exert, in the volume where the concentrate collects, a suction effect on the germs, in order to entrain them

  towards the periphery of this volume. Without this suction effect

  tion, we would get a much worse separation effect. According to an advantageous form of implementation of the invention, the concentrate discharged through the nozzles is shared

  in two fractions, the first of which is recycled in the

  mentation of the centrifugal drum, the second being combined with the concentrate leaving the discharge ports, the flow rate of this second fraction being adjusted as a function of the flow rate of concentrate leaving the discharge ports, so as to

  obtain, after this meeting, a constant flow of concentrate.

  This is advantageous for a sterilization stage arranged downstream, since this must be supplied at a constant flow rate. We can therefore dispense with the large intermediate storage tanks which were until now

  necessary to absorb flow fluctuations.

  Since the quantity of concentrate discharged through the centrifuge discharge ports represents only about 10% of the total quantity of concentrate, it is already enough to derive a small fraction of the flow rate of the recycling line for

  produce a constant volumetric flow.

  An exemplary embodiment of the invention is shown in the drawing and will be explained below in detail. In the drawing: Figure 1 is a schematic view of the centrifuge; Figure 2 shows the details along "X" in Figure 1; Figure 3 is a diagram of an installation in which a fraction of the concentrate is taken from the recycling line and is mixed with the germ concentrate discharged through the discharge orifices. In Figure 1, we see the centrifuge 1 whose feed chamber 2 is connected by channels 3 to the disc lining 4, which delimits

  radially inwards the concentrate chamber 5.

  From the concentrate chamber 5. From the concentrate chamber 5, discharge channels 6 provided with nozzles 7 terminate in a separation chamber 8 in which there is a separating member 9, this chamber 8 having a duct 10 evacuation of the concentrate, this conduit 10

  communicating with the supply duct 12 via the

  medium of a recycling conduit 11, the supply conduit

  tation 12 opening into the supply chamber 2 of the centrifuge drum 1. From the periphery of the drum discharge openings 14, the opening of which is regulated by a drawer 13, lead to a collector 15 for the germ concentrate. In the recycling duct 11 is

  provided with an adjusting member 16 for adjusting the concentration flow

  very many germs to recycle. The discharge channels 6 are

  formed between the cover 17 of the drum and an evacuation disc

  cuation 18 provided in the centrifugal drum at a distance "A" from this cover, this disc 18 being provided with grooves 19. The sterilized milk flows through the channels 20 into the separation chamber 21 and is then directed by the member

  separator 22 to the exhaust duct 23.

  The milk to be sterilized is brought to the centrifugal drum by the supply conduit 12 and reaches, through the supply chamber 2 and the channels 3 in the disc lining 4, in which the germs separate from the milk and

  then migrate to the concentrate chamber 5.

  Through the discharge channels 6 and the nozzles 7, a flow

  partial of low-germ concentrate is continuously withdrawn

  Lement from the concentrate chamber 5 of the centrifugal drum and is recycled to the supply conduit 12 of the centrifugal drum 1 via the separating member 9, the conduit 10 for discharging the concentrate, and the line 11. The germs that collect on the periphery of the drum are periodically removed from

  of the centrifugal drum 1 through the discharge openings 14.

  The discharge channels 6 provided with nozzles 7 start from a central region of the concentrate chamber 5, measured with respect to the radial extent of this chamber. Thanks to this arrangement, the concentrate withdrawn from the concentrate chamber 5 is particularly poor in germs, which avoids the danger of an increase in the number of germs in

  the supply duct 12 of the centrifugal drum 1.

  The distance "A" between the cover 17 of the drum and the evacuation disc 17 is chosen so that the resulting flow rate for the germ concentrate in the evacuation channels 6 still gives rise in these channels to a additional separation of germs. Due to the Coriolis forces exerted in the evacuation channels 6, a sufficient distance "A" is necessary, independently of the section of the evacuation channels 6. Good results have been obtained when the distance "A" was chosen as it resulted, for each of the discharge channels 6, a flow rate of about 15 liters / hour per ram of the distance "A". If for example the centrifugal drum

  is supplied with 20,000 liters / hour of milk

  ant germs, of which 5% is withdrawn in the form of concen-

  very loaded with germs through the discharge channels 6, which are constituted by eight grooves 19, we obtain for each discharge channel 6 a flow rate of: 000 lit / hx 0.05: 8 = 125 lit./h If this value is divided by the desired flow rate, ie 15 lit./h per mm of the distance "A", we then obtain,

  by this calculation, a value of the distance "A" equal to 8.33 mm.

  By means of the adjusting member 16 on the recycling line 11, the quantity of

  concentrate to be evacuated through the evacuation channels 6.

  In order to keep the amount of germ-laden concentrate small, the amount of concentrate discharged through the discharge openings 14 should reach a maximum of 0.4

at 0.6% of the feed rate.

  According to Figure 2, one can provide between the cover

  17 of the drum and the spout 18 of the additional bowls

  keep quiet 24 for even better post-separation

germs.

  Figure 3 shows a device in which a concentrate line 24 runs from the recycling line 11 to a device 25 for collecting the concentrate discharged through the concentrate line 24 and the concentrate discharged through the discharge openings 14. To the device 25 is associated a regulation system 26 which is connected, by connections 27, 28 and a control device 29, with the adjustment member 16 and with an adjustment member 30 disposed on the recycling pipe 24. The device is connected an adjustable pump 31 which draws at constant flow the germ concentrate from the device 25, and directs it to a sterilization installation, not shown. Via the concentrate line 24, a fraction of the germ concentrate withdrawn by the nozzles 7 reaches the device 25, in which the

  concentrate discharged through the discharge openings 14.

  Depending on the liquid level in the device 25, the adjustment members 16, 30 are adjusted by means of the adjustment system 26 and the control device 29 so that the liquid level in the device 25 does not undergo significant modifications. By means of the manually actuated adjustment members 32, 33, it is possible to adjust the basic values of the flow rates. The basic adjustment of the flow rate of the concentrate line 24 can be exceeded by means of a by-pass line 35 provided with an adjustment member 34 when the liquid level in the device 25 drops lower than the threshold authorized, although the regulating member 30 is completely open. When using the adjusting members 32, 33 and 34, the adjusting members 16, 30 and 34 actuated by the control device 29 can be made in the form of simple remotely controlled stop members, which provides a possibility

  particularly economical adjustment.

2'626143

Claims (9)

CLAIMS R E V E N D I C A T I O N S   1. A method of sterilization of milk by centrifugation, in which the milk is brought to the feed duct of a   centrifuge drum, in the concentrate chamber of the   which collects the germ-rich concentrate separated by centrifugation, a fraction of the concentrate being evacuated by evacuation channels provided with nozzles, the remainder of the concentrate being evacuated periodically by evacuation openings provided in the drum casing, characteristic erected in that the concentrate discharged through the nozzles is withdrawn from a central region of the concentrate chamber and is recycled into the conduit   of the centrifugal drum.   2. Method according to claim 1, characterized in that the concentrate discharged through the nozzles is divided into two fractions, a first fraction being recycled into   the centrifugal drum supply line and a second   th fraction being combined with the concentrate leaving the discharge openings, the flow rate of the second fraction being adjusted   depending on the amount of concentrate leaving the openings   evacuation tures in such a way that after the union of said second fraction with said concentrate leaving the evacuation openings, a stream of concentrate is obtained under a constant flow.   3. Method according to claim 1 or 2, characterized in that the flow of concentrate discharged through the nozzles represents at most 1 to 10%, preferably 4 to 6%, of the milk flow   brought to the centrifugal drum supply line.   4. Method according to one of claims 1 to 3, character-   in that the quantity of concentrate discharged through the discharge openings of the centrifugal drum represents 0.1 to 1.0%, preferably 0.4 to 0.6%, of the quantity of milk   supplied to the centrifugal drum supply duct.   5. Device for implementing the method according to claim 1 with a centrifugal drum (1) provided with a   supply line (12) and a stack of bowls (4), the   which delimits radially inwards a concentrate chamber (5) from which flow evacuation channels (6) provided with nozzles (7), as well as evacuation openings (14) for evacuation periodic concentrate, the nozzles (7) opening into a skimming chamber (8) in which is provided a skimming member (9) for directing the low germ content concentrate withdrawn through the nozzles to a conduit evacuation of the concentrate (10), characterized in that the evacuation channels (6) start from the central region of the concentrate chamber (5) relative to the radial extent of this chamber, and in that the concentrate discharge pipe (10) is connected by a recycling pipe (11) with the supply pipe (12) of the centrifugal drum (1).   6. Device according to claim 5, c a r a c t é -   ris in that from the recycling line (11) detaches a concentrate line (24) provided with an adjusting member (30) and in that there is provided a device (25) for collecting together the concentrate discharged through the concentrate pipe (24) and the concentrate discharged through the discharge openings (14), an adjustment system (26) being associated with the device (25) for adjusting a constant volumetric flow rate of the flows concentrate combined, this adjustment system (26) being connected via the connections (27, 28) and a control device (29) with the adjusting member (30) on the concentrate pipe (24 ) and with a   adjusting member (16) on the recycling line (11).   7. Device according to one of claims 5 or 6,   c a r a c t é r i s in that the discharge channels (6) consist of grooves (19) disposed between the cover (17) of the drum and an evacuation bowl (18) provided   in the centrifugal drum at a distance "A" from the cover.   8. Device according to claim 7, characterized in that the distance "A" is chosen so that it results, for each of the discharge channels (6) formed by the grooves (19), a flow rate of 5 at 25 liters / hour, preferably 12 to 18 liters / hour per millimeter of the distance "A".   9. Device according to one of claims 7 or 8,   characterized in that bowls (24) are provided between the cover (17) of the drum and the evacuating bowl (18) additional.