FR2493679A1 - Powdered whey prodn. - by lactose-crystallisation and spray drying - Google Patents

Abstract

Prodn. of powdered prods. from whey or other lactose solns. is carried out by (a) crystallising part of the lactose in a continuous evaporative crystalliser; (b) passing the resulting crystal slurry through a continuous basket-type centrifuge to separate lactose crystals from mother liquor; and (c) recycling part of the mother liquor to the crystalliser and spray drying the rest. Recycling the mother liquor provides seed crystals for the crystalliser and reduces the load on the spray drying tower.

Description

 It is known that whey contains nutritive constituents and in particular lactose. The process generally used to recover these products consists in concentrating the whey and then drying it in an atomization tower; the powder obtained is then packaged, in particular mixed with proteins, so as to obtain various products for human or animal consumption.

Before concentration, the whey can be treated to remove proteins and / or the mineral salts it contains.

 The known methods have the disadvantage of requiring expensive equipment and consuming a lot of energy.

 The aim of the present invention is, on the one hand, to produce installations whose cost and energy consumption is lower than that of known installations and, on the other hand, to modify existing conventional installations to reduce their consumption by adding quickly depreciable equipment thanks to the energy savings it allows.

 The process which is the subject of the invention is characterized by the fact that a part of the lactose is crystallized in a continuous evaporation crystallization apparatus, the mixture of lactose crystals and mother liquor leaving this apparatus is subjected to a spin in a centrifugal sieve wringer, with continuous operation, to separate the lactose crystals from the mother liquor, part of the alumina is returned to the crystallization apparatus and the other part is dried mother liquor by atomization.

 As a result of the use of a screen wringer, the mother liquor separated by wringing contains small crystals whose dimensions are smaller than those of the screen openings. The small crystals contained in the mother liquor fraction recycled to the crystallization apparatus serve as crystallization seeds. These crystals must be small enough to allow atomization of the other fraction of the mother liquor by means of the devices usually used.

 In the case where one starts with whole whey or skim milk, the rate of recycling of the mother liquor in the crystallization apparatus will be of the order of 5 to 20%, the 80 to 95% of water- remaining mother being spray dried.

 In the case where the product obtained is treated by subjecting the whey to ultra filtration, in order to remove the proteins (deproteinized whey), it is possible to recycle 50 to 60 Vo of mother liquor in the crystallization apparatus. The mineral salts absorbed by the crystals can be removed at least in part by washing the crystals with water or with water added with hydrochloric acid at the end of the spin cycle.

 If the treated product has been obtained by subjecting the whey to ultrafiltration and demineralization by electrodialysis or by means of ion exchange resins (deproteinized and demineralized whey), it is possible to recycle in the crystallization apparatus 70 to 80% of the mother liquor from the spin. The absorption by the lactose crystals of the mineral salts and residual flocculated proteins will, in this case, make it possible to eliminate, by crystallization and spinning, almost all of the dry materials contained in the initial product and we will be able to dispense to dry the remaining 20 to 30% of mother liquor which could possibly be recovered by other known methods.

 The crystallization apparatus is advantageously constituted by a horizontal tank divided by transverse partitions into several compartments which are successively crossed by the mixture of mother liquor and crystals moving from one end to the other of the apparatus, each compartment comprising heating means and an inlet for the solution to be treated. The heating means consist of hollow elements, plates or tubes, heated by steam, a fraction of which is constituted by steam produced in the crystallization apparatus and recompressed by means of a thermocompressor or a motor compressor.

 Depending on the importance given to recompression, this device requires 0.25 to i kg of steam to evaporate a kilo of water while in an atomization tower it takes 2.5 to 3 kg of steam to evaporate a kilo of 'water.

The invention therefore makes it possible to achieve a significant saving in vapor which will be all the greater the higher the fraction of mother liquor recycled into the crystallization apparatus.

 The centrifugal wringer of the conical sieve type will advantageously be provided with a system making it possible to spray a washing liquid on the layer of crystals formed on the sieve.

The following description refers to the accompanying drawing and on which
Figure i is a diagram illustrating the method of the invention; and
FIG. 2 schematically shows part of the installation for implementing the invention.

 The method of the invention makes it possible to treat whole or deproteinized and / or demineralized whey, skimmed milk, or other lactose solutions.

 The product to be treated is first concentrated at 14 in an evaporator or a series of evaporators to a dry matter content of about 50 - 55%. The concentrated product is treated in 16 in a continuous evaporative crystallization apparatus where part of the lactose crystallizes. The mixture of mother liquor and crystals extracted from the crystallization apparatus is subjected to a wringing in 18 in a centrifugal wringer with continuous sieve where the crystals whose dimensions are larger than those of the sieve openings are separated of mother liquor and discharged at 19. In the wringer, the crystals can be washed with water, optionally with hydrochloric acid. The mother liquor containing the small crystals, the dimensions of which are smaller than those of the sieve openings, is divided into two fractions. One fraction is dried in 20 in an atomization tower where it is reduced to powder. The other fraction is returned to the inlet of the crystallization apparatus.

 Concentration and drying in an atomization tower are conventional operations in the treatment with whey and derived products and the apparatuses used for these operations are well known and will not be described here.

 The apparatuses used for carrying out the crystallization operations -16 and of wringing 18 will be described with reference to FIG. 2.

 The crystallization apparatus consists of a cylindrical tank 21, closed, arranged horizontally and divided into several compartments 1 to 5, for example, by transverse partitions 22. These partitions are lower than the tank so that the different compartments communicate between them at their top. Openings are drilled in the partitions 22 to allow the passage of the treated product from one compartment to the other.

 One or more heating bundles 24 formed of horizontal tubes arranged parallel to the axis of the tank are placed in the lower part thereof. These tubes are supplied with steam by a thermo-compressor 26 and provide heating for the various compartments; they are permanently embedded in the treated product filling the lower part of the tank. The thermo-compressor 26 is used to recompress, by means of live steam, part of the steam produced in the crystallization apparatus and taken from the upper part of the tank. Alternatively, a motor compressor could be used.

 Inlets 28 for the product to be treated are provided in each compartment and in the last compartment an outlet is connected to a pump 30. An inlet is also provided in the first compartment for the mother liquor from the spin.

 The centrifugal wringer is of the type described in French patent 79 06829. It comprises a frustoconical basket 32, flared upwards and rotatably mounted inside a tank 34. The basket is mounted on a vertical pivot and is rotated about its axis; its inner surface is covered with a sieve.

 A supply pipe, connected to the pump 30, pours the product to be wrung on the bottom of the basket.

The mother liquor and the crystals, the dimensions of which are smaller than those of the sieve openings, are collected in a chamber 36 constituted by a ferrule, the upper end of which is located near the upper edge of the basket and by a fixed bottom. to the ferrule. The lactose crystals whose dimensions are larger than those of the sieve openings are moved upward on the sieve by centrifugal force and are finally ejected, at the upper end of the basket, into the tank 34 from where they fall into a hopper 38 connected to the bottom of the tank.

 Watering ramps 40 placed inside the basket make it possible to wash the lactose crystals before they are expelled from the basket.

 When the treated product is whole whey or skim milk, the fraction of mother liquor sent to the crystallization apparatus represents between 5 and 20 Vo of the total flow of mother liquor obtained by spinning. Indeed, the low lactose purity of these products and their high content of proteins and mineral salts prohibit greater recycling which would lower the purity.

 The remaining 80 to 95% mother liquor is dried in an atomization tower.

 Instead of directly treating the whey according to the process of the invention, it can be subjected beforehand to an ultrafiltration to remove most of the proteins. It is then possible to recycle in the crystallization apparatus from 50 to 60% of the air resulting from the spinning.

 The ultrafiltration permeate can also be demineralized by electrodialysis or passage over exchange resins. In this case, 70 to 80% of the mother liquor from the spin can be recycled into the crystallization device.

 It is not possible to return all of the mother liquor to the crystallization apparatus as this would lead to a non-negligible increase in the concentration of the lactose crystals in mineral salts, which are not completely eliminated by the operation. demineralization, and low molecular weight proteins, amino acids, etc ... which have crossed the ultrafiltration membrane.

 The absorption by the lactose crystals of the mineral salts and flocculated residual proteins will make it possible, in this case, to separate by draining almost all of the dry materials present in the treated product and it will be possible to dispense with spray-drying the 20 to 30 Vo of remaining air which can be exploited by other processes.

 At the end of spinning, the lactose crystals can be washed with water or with water acidulated with hydrochloric acid at pH 2.5 to 3.5 by means of watering ramps 40. This operation allows to eliminate, at least partially, the mineral salts absorbed by the crystals.

 The openings of the sieve of the wringer will have dimensions between 40 and 90 microns and preferably equal to 60 microns.

 The lactose crystals separated by spinning are ground and mixed, in suitable proportions, with the spray-dried powder, with other products in order to obtain powdered foods having the desired composition.

 It is understood that all the modifications made to the installation described by the use of equivalent technical means fall within the scope of the invention.

Claims (9)

 by atomization (20).  mother liquor, the other part of the mother liquor being dried  returns part of the crystallization apparatus  separate the lactose crystals from the mother liquor, and  continuous sieve centrifugal reuse (18) for  mother coming out of this device to a spin in an esso  the mixture of lactose crystals and water is subjected  continuous crystallization by evaporation (16),  crystallize part of the lactose in a  spray dry, characterized in that  both to concentrate the solution by evaporation and then to  whey and other lactose solutions, consis  ~ | , 1. Process for manufacturing powdered products from 2. Method according to claim 1, characterized in that,  in case the treated lactose solution is  whole whey or skim milk, water fraction  mother returned to the crystallization apparatus (16)  represents from 5% to 20% of the total mother-water flow  from the spin (18). 3. Method according to claim i, characterized in that,  in case the treated lactose solution is  deproteinized whey, the fraction of mother liquor returned  in the crystallization apparatus (16) represents  50 to 60 Vo of the total mother-water flow coming from the esso-  rage (18). 4. Method according to claim 1, characterized in that,  in case the treated lactose solution is  deproteinized and demineralized whey, the water fraction  mother returned to the crystallization apparatus (16)  represents from 70 to 80% of the total flow of professional mother liquor  from the spin (18). 5. Method according to any one of the preceding claims  teeth, characterized in that the lactose crystals  separated from the mother liquor by wringing (18) are washed with  water or water containing hydrochloric acid. 6. Installation for implementing the method according to  any of the preceding claims, charac  terrified in that it includes a crystallization apparatus  continuous running station consisting of a horizon tank  plate (21) divided by transverse partitions (22)  in several compartments (1 to 5) which are crossed  successively by mixing the concentrated solution-and  of crystals moving from one end to the other of  the apparatus, each compartment comprising means  heater (24) and an inlet (28) for the solution  treat. 7. Installation according to claim 6, characterized in  what the heating means (24) consist of  hollow elements heated by steam supplied  by a compressor (26) supplied by pre-steam  lifted in the upper part of the tank of the appliance. 8. Installation according to claim 6 or 7, characterized  in that the centrifugal wringer is equipped with a basket  frusto-conical (32) provided with a sieve whose openings  have dimensions between 40 and 90 microns and  preferably equal to 60 microns. 9. Installation according to claim 8, characterized in  what the centrifugal wringer has a spray bar  sage (40) placed inside the basket (32) for washing  crystals before they come out of the wringer.