US3687681A - Method and a device for preparing a quickly soluble powder - Google Patents

Abstract

FOR OBTAINING A QUICKLY SOLUBLE POWDER A CURTAIN OF FLOATING POWDER IS SUBJECTED TO AT LEAST ONE JET OF A MOISTENING GAS IMPINGING UPON THE CURTAIN UNDER AN ANGLE OF 30*-150*C. THE POWDER PARTICLES ARE THEREBY CAST AGAINST

A MOVING WALL MOVING THROUGH A DRYING ZONE, AFTER WHICH THE POWDER IS SCRAPED FROM THE WALL.

Description

1972 G. DE BOER 3,687,681

METHOD AND A DEVICE FOR PREPARING A QUICKLY SOLUBLE POWDER Filed Sept. 5. 1970 7 6 1 I m I9 2 5521 \-1' y g 4= 5 3 i 12 INVENTOR $554 7 A6 800? United States Patent Office 3,687,681 Patented Aug. 29, 1972 US. Cl. 99-56 7 Claims ABSTRACT OF THE DISCLOSURE For obtaining a quickly soluble powder a curtain of floating powder is subjected to at least one jet of a moistening gas impinging upon the curtain under an angle of 30-150. The powder particles are thereby cast against a moving wall moving through a drying zone, after which the powder is scraped from the wall.

BACKGROUND OF'DHE INVENTION The invention rel-ates to a method for preparing a quickly soluble powder, like e.g. milkpowder, starting from an already available powder which owing to its fine grain structure is rather hard to be moistened. The dissolution of such powders in water is often attended with the formation of clods and a more intense stirring is re quired to dissolve the powder eventually.

SURVEY OF THE PRIOR ART It is known that by moistening the powder slightly, whereby the particles agglomerate and by subsequent drying, a product is'obtained with a grain structure which can be easily dissolved in water since no formation of clods is produced and the particles, practically without stirring, dissolve. This is the so called instant powder.

Such a method is described in the U8. patent specification 2,934,434. The powder is introduced into a moist current of air and thereupon again separated from this current, after which drying air is supplied.

This method has the drawback that the separation of sufficiently moistened powder from the moist current of air can give rise to difliculties since the moist powder particles are tacky and easily cake together so as to form big lumps. These lumps can only be dried with difiiculty and should then be ground. On the other hand this stickiness gives rise to dirtying, possible obstruction of the pipe.

According to another proposal this trouble is overcome by supplying a warm drying gas to the stream of moistened gas and powder, so that prior to the separation of the current of gas the moisture content is considerably reduced. As a result the dirtying that is to say the adherence to the wall and the formation of clods can be more easily prevented, but the agglomeration has become more diflicult.

According to the aforementioned proposal it is tried to stimulate the agglomeration by making this moistened current of air strongly turbulent.

In practice, however, it has nevertheless appeared that in these two known methods, which are performed in a pipe, the dirtying on the one hand and the agglomeration on the other hand are not easily brought under control.

It should be noted that in the Netherlands Patent 107597 a system is described according to which the powder falls as a flat curtain from a conveyor belt. A fiat vapour jet is blown through this curtain. The powder moistened in this way falls on a slightly lower situated conveyor belt, is dried thereon and subsequently sieved and discharged. In this process the powder particles to be treated are heated by the vapour jet to a value which is considerably higher than according to the method in conformity with the invention. In this process the extent of agglomeration can only be controlled with difiiculty.

SUMMARY OF THE INVENTION It is an object of the invention to obviate these difiiculties. According to the invention the powder is subjected in a floating condition to the eltect of at least onev jet of moist gas, which is forced thereupon at an angle of at least 30, whereby the powder is cast against a moving wall and adheres thereto, whereupon the product is dried and removed from the wall. The powder is moistened by the jet of gas which has approximately the same width as the curtain of floating powder. The jet makes an angle ranging from 30 to 150 with the curtain and hits the powder curtain very fast. The powder particles are carried along by this jet and will thereby agglomerate and keepv their adhering condition due to the vigour of the impact. As a result of the spreading of the jet on the one hand and the displacement of the wall on the other hand alayer of moistened powder is formed on this wall the thickness of which can be regulated by adjusting the velocity of the wall and/or the quantity of powder falling down in a unit of time into the curtain. The density of the layer can be regulated by the velocity of thejet. The moisture content can be regulated by varying on the one hand the moisture content of the gas jet and on the other hand by directeing, if desired, additional jets of moist gas towards the layer of particles formed in this way and adhering to the moving wall.

Drying is elfected thereupon by passing the wall with the product thereon through a drying space in which e.g. through warm dry air the product is dried and subsequently scraped from the wall and sieved. In this connection the layer of particles may at first be compressed by a roller. Prior to drying the wall iself may be heated. This wall consists preferably of a vertical conveyor belt.

According to this method the process is in all details well under control, while the risk of obstruction of a pipe is avoided since powder and gas are not conveyed together through a pipe. Especially for temperature susceptible powders with tacky properties (e.g. powders containing fat and sugars) the method according to the invention has considerable advantages.

Those and further objects and characteristics of the invention will be further clarified with reference to the accompanying drawing in which in outline a device for performing the method is represented.

DESCRIPTION OF A PREFERRED EMBODIMENT The device consists of a metering apparatus 1, conveying means, e.g. a vibrating trough conveyor 2, and a gas pipe 3 provided with a vapour inlet 4. On the metering device are provided a powder inlet 5 and a powder hopper 6. The device consists further of the conveyor belt 7 running over rollers 8 within the casing 9. At its lower end the casing is provided with a scraping means 10 and an outlet 11 for the product. The casing is further provided with an inlet 12 and a discharge 13 for drying air. The device is completed by sieving means 14 with a discharge opening 15.

The sieve is provided with an air inlet '16 and discharge 17 through which too fine particles are discharged back to the powder hopper 6. A ventilator 18 ensures the discharge of the moist gas flow by which the powder is transferred to the belt 7. The angle at which the gas jet strikes the belt is about Due to the vertical positioning of the belt its base is only small which in many cases will be a great advantage.

The velocity of the belt, the velocity of the gas, the gas moist content, the quantity of powder and drying temperature can all be regulated independently of each other.

If desired a plurality of moist gas jets or vapour jets may strike the layer of powder. One of those jets is denoted by the reference numeral 19 in the drawing. It is also possible to spout the powder between two jets on the belt. In this case a thicker powder curtain can be applied. The layer of particles can, before drying, be compressed on the belt 7 by means of a roller (not shown).

The sieve 14 with air inlet 16, 17 can be constructed as a fluid bed for finish-drying the product. The powder can also be carried in an air jet before being struck by the gas jet.

What I claim is: 1. A method for preparing quickly soluble powder, such as powdered milk, from a starting powder having poor solubility characteristics, which comprises the steps of:

feeding the starting powder as a curtain of freely falling particles;

moistening said freely falling particles and forcibly depositing them on a travelling belt by directing at least one substantially horizontal jet of moist gas against one face of the curtain while traveling said belt in a vertical direction in spaced relation on the other side of the curtain whereby the moistened particles impinge against said belt at about 90 so that the moistened particles are forcibly impacted within a closely confined and controlled zone upon the belt as a deposit thereon;

drying the material deposited on the belt; and

then scraping the dried material from the belt to provide said quickly soluble powder.

2. A method according to claim 1 including moistening the powder after it has been spouted on the wall belt and before being dried.

3. A method according to claim 1 including compressing the layer of powder before being dried on the belt.

4. Apparatus for making a quickly soluble powder from a starting powder having poor solubility characteristics, comprising:

a hopper for the starting powder;

feeding and metering means associated with said hopper for providing a controlled quantity of said starting powder as a descending curtain of freely falling particles; an endless belt disposed on one side of said curtain and presenting a pair of vertical flights extending generally parallel to said curtain; means for directing a horizontal stream of moist gas against said curtain to moisten and propel the particles thereof against one of said vertical flights at substantially right angles thereto; means for driving said belt to move said one vertical flight in upward direction whereby a layer of moistened particles agglomerates is deposited thereon;

means for drying said layer of agglomerated particles as same passes downwardly on the other of said vertical flights;

means for scraping said layer, after drying thereof, from said other vertical flight; and

means for receiving the scraped-01f material and discharging it to an outlet.

5. Apparatus according to claim 4 wherein the last means includes a sieving device.

6. A device according to claim 5, wherein the sieving device is pneumatically connected with the storage for the powder to be treated.

7. Apparatus according to claim 4 including a housing containing said endless belt, said means for drying including an inlet for heated air adjacent the lower end of said other vertical flight and an outlet for such air adjacent the upper end of said endless belt.

References Cited UNITED STATES PATENTS HOWARD R. CAINE, Primary Examiner US. Cl. X.R. 99-203, 246

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