GB2115302A - Method and apparatus for the manufacture of milk powder - Google Patents

Abstract

In the manufacture of milk powder an evaporator is normally used to concentrate the milk before being dried in a spray dryer. The evaporator is more efficient in its use of steam for the removal of water from the milk so it is desired to feed the milk to the dryer in as high a state of concentration as possible. The increasing viscosity of the higher concentrate adversely affects the atomising which is necessary for spray drying. It has been found that the milk exhibits a delay of a few seconds in thickening to its full viscosity. Therefore a final finishing stage 3 is mounted so as to discharge into the spray dryer 4 through as little pipe line 5 as possible to maintain a relatively short residence time in the final stage. It is preferred for a plate evaporator 3, forming the final finishing stage, to be mounted directly on top of the spray dryer chamber 4. Refer to Figure 1. <IMAGE>

Description

SPECIFICATION Method and apparatus for the manufacture of milk powder This invention relates to the manufacture of milk powder, either from whole milk or from milk which is partially or substantially skimmed.

Skim and whole milk powders are conventionally prepared by first preconcentrating the milk in an evaporator and then passing the concentrate into a spray dryer. The evaporator is used to preconcentrate the milk because the energy consumption per unit of water removed in it is very much less than the energy consumption per unit of water removed in a spray drier.

It is, therefore, desirable to limit the water which has to be removed in the drying part of the process by concentrating the milk in the evaporator to as high a percentage total solids as possible. This is illustrated by the fact that in order to produce 100 Ibs of milk powder at 4% moisture, 92 Ibs of water have to be evaporated in the dryer, if it is fed with concentrate at 50%; 60 Ibs of water have to be removed in the drier, if it is fed with concentrate at 60%; and only 47 Ibs of water have to be removed in the drier if it is fed with concentrate at 65%. The problem, however, in increasing the total solids fed to the dryer arises from the increasing viscosity of the concentrate as the solids are increased which makes it difficult to achieve good atomisation in the dryer and, therefore, prevents its satisfactory operation.

The object of the present improvement is to enable the extension of the evaporation process to produce higher concentrations at the dryer inlet while still permitting its satisfactory operation, and thereby achieving reduced energy consumption in the overal process.

The invention is based upon the surprising discovery that concentrated milk products do not exhibit their maximum viscosity immediately upon concentration, but that this develops within a short time after concentration.

The time taken following concentration for the development of maximum viscosity in the concentrate is variable and depends on the actual properties of the milk handed and the time of the year, and other factors. However, the time taken would certainly be less than 10 seconds, and would probably lie in the region of 5 to 7 seconds. It is difficult, however, to be totally specific about this as, of course, the milk is not concentrated instantly in any evaporator. What has been discovered is that over a period of a few seconds after leaving the evaporator, the milk concentrate does exhibit an age thickening process.

In conventional practice milk evaporators are situated sufficiently far from the inlet to the driers they serve, for the time taken to convey the concentrate from evaporator to dryer inlet to be considerably in excess of that required for the concentrate to develop its maximum viscosity.

The invention is therefore based upon locating an evaporator which carries out the final evaporation as close as possible to the spray drier inlet to enable the concentrate to be fed to the drier in time to be atomised before the full viscosity is developed.

In accordance with a first aspect of the invention, there is provided a method of manufacturing milk powder by concentrating the milk in one or more evaporation stages and passing the concentrate into a spray drier for atomization and drying, in which a sole or final evaporation stage of concentration is.

sufficiently close to the spray drier and operates with such a short residence time that the concentrate is fed into the spray drier and atmoised before developing its maximum viscosity, which would be sufficient to impair atomization.

In accordance with a second aspect of the invention, there is provided apparatus for the manufacture of milk powder comprising an evaporator and a spray drier, in which the evaporator has a final stage designed for short residence time and located with its outlet located immediately adjacent the inlet of the spray drier.

This in practice normally involves the mounting of the final evaporation stage on the top of the spray dryer chamber, and in view of the restricted headroom likely to be available in such a position, a low height of evaporator construction, such as that utilising plate and frame type construction is especially suitable.

This evaporator is then used as the final concentration stage, and its close proximity to the dryer atomiser enables the more highly concentrated milk to be admitted to the dryer and atomised before developing its maximum viscosity and, therefore, permits a higher concentration to be utilised.

The evaporator concerned can be a separately heated finishing stage following the main evaporator in the process or, alternatively it can be integrated into the heating system of the main evaporator as a stage of one of the effects of the latter or, alternatively, a stage within the recompression circuit, if the evaporator is of the mechanical vapour recompression type.

Integration in this way with the main evaporator requires considerable lengths of vapour ducting to and from the finishing stage, but provided this is adequately designed this feature has no adverse affect on the overall performance and does not limit the ability to achieve higher concentrations in the finishing evaporator. Integration of the finishing stage in this way enables the efficient operation of the main evaporator in terms of the utilisation of energy to be applied in equal measure to the finishing stage and, therefore, maximises the benefit resulting from this improvement.

The reduction in water removal in the dryer for a given quantity of powder produced, enables an existing dryer of established water removal capacity to produce more powder and the method described can be usefully employed, therefore, to extend the capacity of existing dryers.

The invention will be further described with reference to the accompanying diagrammatic drawings, in which: Figure 1 is a layout diagram showing the salient items in a apparatus for manufacturing milk powder in accordance with one form of the invention; and Figure 2 shows a modification of part of the apparatus of figure 1.

Turning first to figure 1, there is shown a five effect evaporator to concentrate milk feed coming in through a line 1. The concentrated milk is drawn through a line 2 to a finishing stage formed by a plate evaporator 3 which is mounted on the top of a spray drier chamber 4 so that the final concentrated milk in a lins 5 is fed directly to the spray drier chamber for atomisation. The residence time of the concentrated milk in the plate evaporator 3 is of the order to one second, so that the concentrate has not reached its full viscosity before it enters the chamber 4.

The multiple effect evaporator is shown as the five effect evaporator and is fairly conventional in layout.

It will be understood that although a five effect evaporator is illustrated, this is in no way limitative, nor is the fact that the milk outlet line 3 comes from the third effect.

The milk feed in the line 1 is fed to a first evaporator effect 11 where it is heated by steam entering through a thermocompressor 12 which entrains part of the vapour from the second effect via a line 13. Discharge lines from the various effects for the condensate are omitted from the drawing. The concentrate and vapour from the effect 11 passes to a conventional separator 14 from where the concentrate passes via a line 16 to the second effect 17 and the vapour is passed as heating medium to the same effect. The concentrate and vapour from the second effect passes to a separate 18 and the concentrate is passed to the fourth effect 19 while the vapour is partially re-entrained through the line 13 to the thermocompressor 12 and partially passed to the third effect via a line 21.In the fourth effect, the concentrate is further concentrated by vapour from the third effect and passed to a separator 22 where the concentrate passes into the fifth effect 23 for heating by vapourfrom the fourth effect and from the finishing stage 3, which vapour comes in via a line 24. The concentrate and vapour from the fifth effect 23 passes to the separator 25 and the concentrate passes via a line 26 back to the third effect 27 where it is heated by the remaining vapour from the second effect. The concentrate and vapour from the third effect 27 passes to a separate 28 and the concentrate passes via the line 2 to the final finishing stage 3 while the vapour goes partly to the fourth effect 19 via a line 29 and partly as vapour to the finishing stage via a line 31. The vapour from the fifth effect separator 25 is passed to the condenser 32.

The concentrate and vapour from the plate evaporatorfinishing stage 3 passes into a separator 33 and the vapour is taken back via the line 24 to the fifth effect 23 while the concentrate is taken by an extraction pump 24 and discharged directly into the spray drier atomiser via the line 5 without any significant length of piping. The control system is arranged to ensure that the separator 33 is kept drained by the extraction pump 34.

The final stage of concentration in the plate evaporator 3 is operated on a once through basis so that the residence time is very short (of the order of one second) in order to take advantage of the period of age thickening.

It will be seen that the finishing stage or plate evaporator 3 is operated, from the point of view of vapour, in parallel with the fourth effect 19, but it will be understood that the invention is not so limited.

Turning now to figure 2, there is shown an arrangement of a vapour recompression evaporator for basic concentration, and it will be understood that this is in replacement of the fifth effect evaporator and it feeds a similar arrangement of finishing stage 3 on the spray dry chamber 4. For ease of recognition, the concentrate output line from the vapour recompression evaporator is shown as 2 while the heating vapour to the finishing stage is shown as entering a line 31 and the vapour returning from the finishing stage is shown by a line 24. In the vapour recompression evaporator, which is shown as being in three effects, the vapour from the third effect separator 41, together with the vapour from the finishing stage in the line 24, is mechanically compressed by a compressor 42 and used to heat the feed coming in via the line 1 to the first effect 43.

The vapour line from the compressor is indicated at 44, and it will be seen that the vapour line 31 to the finishing stage is connected to the line 34.

The concentrate and vapour from the first effect 43 is passed to a separator 45 from where the concentrate and vapour are feed separately to the second effect 46 for further concentration. From this effect, the concentrate and vapour are fed through a separator 47 and again the concentrate and vapour are fed separately to the third effect 48. The separator 41, and the concentrate is then taken via the line to the finishing stage while, as indicated above, the vapour is passed to the compressor 42.

Again, the condensate lines from the effect 43,46 and 48 are not shown.

Various modifications may be made within the scope of the invention.

Claims (14)

1. A method of manufacturing milk powder by concentrating the milk in one or more evaporation stages and passing the concentrate into a spray drier for atomization and drying, in which a sole or final evaporation stage of concentration is sufficiently close to the spray drier and operates with such a short residence time that the concentrate is fed into the spray drier and atomised before developing its maximum viscosity, which would be sufficient to impair atomization.

2. A method as claimed in claim 1, in which the said final evaporation stage is the final concentration stage of a multi-effect evaporator.

3. A method as claimed in claim 1, in which the said final evaporation stage is a separate steam heated evaporator.

4. A method as claimed in claim 1, in which the said final evaporation stage is operated by mechanical vapour recompression.

5. A method as claimed in claim 4, in which the said final evaporation stage is one stage of an evaporator operated by mechanical vapour recompression.

6. A method of manufacturing milk powder substantially as hereinbefore described with reference to the accompanying drawings.

7. Apparatus for the manufacture of milk powder comprising an evaporator and a spray drier, in which the evaporator has a final stage designed for short residence time and located with its outlet located immediately adjacent the inlet of the spray drier.

8. Apparatus as claimed in claim 7, in which the said final stage is mounted on the top of the spray drier.

9. Apparatus as claimed in claim 7 or 8, in which the said final stage is formed by a pack of separable plates in a frame.

10. Apparatus as claimed in claim 7,8 or 9, in which the said final evaporation stage is the final concentration stage of a multi-effect evaporator.

11. Apparatus as claimed in claim 7,8 or 9, in which the said final evaporation stage is a separate steam heated evaporator.

12. Apparatus as claimed in claim 7,8 or 9, in which the said final evaporation stage is operated by mechanical vapour recompression.

13. Apparatus as claimed in claim 7,8 or 9, in which the said final evaporation stage is one stage of an evaporator operated by mechanical vapour recompression.

14. Apparatus for the manufacture of milk powder substantially as hereinbefore described with reference to the accompanying drawings.