FR2552777A1 - METHOD AND DEVICE FOR THE CONTINUOUS DEVELOPMENT OF PREFORMED MEDIUM AND HIGH PURITY CRYSTALS IN COOKED MASSES IN SUGAR TREES - Google Patents

Abstract

THE INVENTION RELATES TO A PROCESS AND TO A DEVICE FOR THE CONTINUOUS DEVELOPMENT OF MEDIUM AND HIGH PURITY PREFORMED CRYSTALS IN BAKED MASSES. THE DEVICE CONTAINS AT LEAST TWO SUPERIMPOSED CRYSTALLIZATION CELLS 20, 120, 220, EACH OF WHICH IS SUPPLIED BY THE PREVIOUS AND SUPPLIES THE FOLLOWING, CONNECTED TO A SOURCE OF DEPRESSION. TWO AGITATORS, PREFERREDLY MUS PER PROPELLER, ARE PROVIDED IN EACH CELL; THE UPPER AGITATOR 31, 131, 231 IS CAPABLE OF GENERATING THREE-DIMENSIONAL MOVEMENTS, WHILE THE LOWER AGITATOR 32, 132, 232 IS CAPABLE OF GENERATING SENSITIVE AGITATION MOVEMENTS IN A HORIZONTAL PLANE, TO FACILITATE THE NATURAL SEPARATION OF THE LARGER CRYSTALS AND PREVENT THEIR STAGNATION ON THE CONCAVE BOTTOM 21, 121, 221 OF EACH CELL.

Description

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  The subject of the present invention is a method and a device for the continuous development of medium crystals.

  and high purity preformed in mass-cooked.

  The treatment applied to the cooked masses in the sugar mills according to the known processes can be summarized as follows: The mass-cakes are discharged from their containers

boiling at about 75 C.

  Medium and low purity cooked masses are normally cooled by means of agitators, that is to say horizontal or vertical axis devices with means for stirring and feeding mass-cooked constituted by coils or by turning plates, crossed by cooling water. The temperature of the massecuite gradually decreases inside these stirrers until it becomes suitable

for centrifugation.

  During cooling in said stirrers, and because of the supersaturation of the sugar solution, a

  part of the dissolved sugar crystallizes, which develops the crystals already present in the massé-cooked.

  This known process which is, as mentioned, applicable to mass-cooked medium and low purity does not modify the

  the water content of the discharged massecuite and the crystallization of a portion of the sugar results only from the overall cooling.

  However, this known process is not applicable to high purity cooked masses; cooling with cold water would cause the formation of hard agglomerates

  mass-fired which would stick to the metal walls, singing the passages and eventually stop the agitators.

  In general, therefore, we send the hot masses-cooked,

  in the state, undergo centrifugation.

  In order to obtain the same high-purity advantages as medium-low-purity meats, some sugar manufacturers and installation engineers have used the vacuum cooling of high-purity meltblocks. this genre,

  briefly described below, are discontinuous.

  The mass-cooked medium or high purity is

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  of the boiling vessel in a closed mixer, provided with a shaft with stirring blades, which is connected to a vacuum generating apparatus, thereby cooling the mass-cooked

  In order to maintain the supersaturation between the desired limits, syrup is added, while the vapor evolved by self-evaporation is condensed by the condenser of the vacuum generating device.

  The disadvantage of a known method of this type, applied to medium and high purity melt-offs, is that

  the process is necessarily discontinuous and therefore requires the installation of one or two vacuum stirrers for each boiling vessel.

  For example, a candy maker with four boiling vessels will require four such vacuum agitators, at a minimum, or rather, for proper operation, at least eight of these agitators, with complications and expense.

resulting from it.

  In view of the disadvantages of discontinuous vacuum stirrers, attempts have been made to carry out continuous installations by means of subhorizontal vacuum stirrers. However, the expected results have not been obtained, since the evidence has been statistically massescuites can not pass through the sub-horizontal shaker in medium times with low standard deviation due to the inevitable presence of stagnation zones; therefore, there is a wide range of crystal particle size variation from said continuous subhorizontal vacuum agitators. On the other hand, it did not seem possible to go directly to a vacuum agitator vertical type, unless to introduce shutter deflectors, which however shows the same areas of stagnation as in the

  continuous sub-horizontal agitators.

  The problem of producing a continuous vertical vacuum stirrer suitable for medium and high purity cooked masses has been solved, according to the invention, by dividing the crystallization process into two stages in cascade; the desired consistency in the crystalline growth stage is preserved by mass additions

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  appropriate syrup; and we promote the separation of the most

  large crystals by making different the stirring conditions experienced by the mass-cooked during crystal growth, in each of the aforementioned stages.

  This latter effect is preferably obtained by a stirring operation which causes horizontal and vertical movements in the upper parts of the massecuite and a horizontal movement in the lower parts o, in spite of the effect of double stirring. big crystals come together. The device according to the invention makes it possible to implement each step of the method in a cell with concave bottom, in order to eliminate the stagnation zones; two superimposed helices are preferably provided inside each cell, the upper helix being shaped to cause stirring movements of the mass-cooked

  both horizontally and vertically, while the second, lower, helix generates substantially horizontal movements.

  Consequently, the second, lower, helix does not interfere with the separation of the large crystals towards the bottom of each chamber and serves to prevent the stagnation of the lower part of the massecuite with a higher degree of crystallization. upstream of the discharge outlets at the base of each cell, said discharge outlets being provided with means for adjusting their degree of opening sensitive to

  operating parameters of each cell, for example at the filling level reached in each cell.

  The desired degree of consistency within each cell is achieved by the addition of syrup; the temperature control within each cell is achieved, as indicated above, by connecting the inner portion of each cell to a source of depression and providing, if necessary, a water jacket on the concave bottom

of each cell.

  The objects, advantages and features of the invention will become more apparent from the description given above.

  certain embodiments, chosen purely by way of example, with reference to the appended drawing, in which: the single figure shows in section a vertical type of agitator, divided into three cells mounted in cascade,

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  according to a preferred embodiment.

  In the figure, a cylindrical vertical envelope can be seen, closed at the top by a cover 11 and subdivided into three cells 20, 120, 220 by three concave hoppers 21,

121, 221.

  Preferably, as shown in the figure, said concave hoppers are composed of an upper section of generally frustoconical shape and a lower section shaped

spherical cap.

  On the bottom of each chamber is provided a discharge duct 22, 122, 222, provided with a corresponding controlled valve 23, 123, 223, the first two ducts discharging the contents of the associated cell on the bottom of the hopper.

  of the underlying chamber, while the third is externally connected by means of a pump 24.

  The upper chamber, or upper cell 20, is provided with a conduit 25 for supplying mass-cooked from a

  or several boiling vessels.

  For each cell 20, 120, 220 are provided syrup conduits 26, 126, 226 which feed the upper central portion of each hopper 21, 121, 221.

  More particularly, the outlet of the conduits 26, 126, 226 is at the midpoint of the frustoconical section of each of the

  hoppers above, for reasons which will be explained hereinafter.

  The frustoconical section of each hopper is further provided with a jacket 27, 127, 227 defining a gap in which flows water arriving via conduits 28,

  128, 228 and discharged through conduits 29, 129, 299, respectively.

  However, to evaporate the water contained in the massecuite present in each cell 20, 120, 220, relies mainly on a source of depression to which each cell is connected by means of conduits 30, 130, 230. therefore, the conditioning water circulating in the aforementioned interstices only plays an auxiliary role of adjustment

  the temperature of the massecuite.

  Two superimposed propellers are provided in each cell, the upper propellers 31, 131, 231 having a greater pitch than the lower propellers 32, 132, 232; these may actually be not true propellers, but horizontal rotating bars, capable of causing only a substantially horizontal circulatory movement of the crystalline material during the separation step at the bottom of the hopper; thus, the lower propellers do not hinder the natural separation of the larger ones

  crystals present in the mass-cooked.

  In fact, it is even possible to dispense with the lower propeller, provided that the upper propeller is capable of

  shake the crystals present on the bottom of each hopper.

  The lower propellers 32, 132, 232, capable of causing a substantially horizontal movement of agitation, are

placed at the bottom of each hopper.

  On the other hand, the upper helices, 31, 131, 231 are placed in the upper part of the mass-cooked, where the mass-cooked is more fluid and they generate three-dimensional stirring movements, both vertical

  and horizontal, as indicated by dashed lines 33, 133, 233.

  The upper helices 31, 131, 231 are placed relatively high with respect to the thickness of the bunker contained in each cell, so that their movements have no effect at least three-dimensional on the lower part of the massecuite containing the larger crystals Therefore, not only the concave shape of the bottom

  Each cell is passive to the stagnation of the material, but the type and location of the helices actively promotes the separation of the large crystals, and consequently their passage to the next stage.

  This dynamic separation of the large crystals of each cell is furthermore favored by the presence of a nozzle

  cylindrical 34, 134, 234 surrounding each of the upper propellers 31, 131, 231.

  In the embodiment shown in the figure, the helices of the two upper cells are driven by a common shaft 35 driven by a motor 36 mounted on top of the

cover 11 of the envelope 10.

  The helices of the last cell, or lower cell,

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  220, are driven by a second shaft 135, itself

  driven by a second motor 136 mounted under the casing 10.

  We can conceive that we can adopt any other mechanical solution. The operation is as follows: each of the cells 120, 220 is connected to a source of depression (preferably 93 K Pa), by means of conduits 30, 130, 230 provided with

  a vacuum control device.

  The baking liquid from one or more boiling vessels is fed into the first cell,

  higher, through a conduit 25.

  When it is fed to the upper cell 20, the starting batch-cake has, for example, the following characteristics: percentage of crystals of the mass-batch of starting 50.5% percentage of water of the starting massecuite 11.0% of the starting mass 100.0% of the temperature 75 o C. After the start-up period of the device, a distribution of the massecuite is established inside the cell 20 such that the large crystals tend to sink to the bottom while being horizontally humbled by the lower propeller 32, while a higher laminated paste

  is agitated along the three-dimensional paths indicated by the broken lines 33.

  Syrup is added through the conduit 26 so as to maintain the desired consistency. The degree of opening of the controlled valve 23 may be

  adjusted according to the level reached on the massecuite in the upper cell 20.

  At the outlet of the first cell 20, the crystalline growth appeared with respect to the starting massecuite

is about 20%.

  The process is repeated in the second cell 120 and 35 in the third cell 220.

  At the exit of the second cell, the crystalline growth appeared compared to the starting massecuite is

about 36%.

  At the exit of the third and last cell, the crystalline growth appeared compared to the starting mass-cuite is about 50%, which corresponds to a crystalline growth of about 70% compared to the mass-cooked

departure.

  The strong crystalline growth achieved through the claimed process and device does not imply any significant increases in fuel consumption: indeed, any

  Sugar refinery has a steam production facility.

  From the point of view of maintenance, by providing one cell more than is strictly necessary, it is possible to isolate the cells one by one for the purposes of cleaning and washing.

  The description given above as an example and the

  The drawing which illustrates it is devoid of any limiting character and it will be possible to adopt various modifications and variants without departing from the scope of the invention.

Claims (8)

  A process for the crystalline growth of medium and high purity meltblocks, characterized in that it is carried out under vacuum, in at least two stages in which the filler is subjected, vertically, to at least two stages agitation: at the first stage, on the upper level, the massecuite is subjected to a three-dimensional stirring movement, whereas on the lower stage, said massecuite is subjected to a substantially horizontal stirring movement, this being on the one hand, to favor the natural separation of larger crystals and, simultaneously, to   avoid unwanted stagnation.   Process according to the preceding claim, characterized in that the consistency of the massecuite is adjusted at each stage by the addition of suitable syrup.   Process according to the preceding claims, characterized in that the temperature, and thus the crystallization, of the massecuite is constantly adjusted under the effect of both   depression and cooling.   4 Device for implementing the method according to   the preceding claims, characterized in that it comprises at least two superposed cells (20, 120, 220) of which   each has a concave bottom (21, 121, 221) and is provided at the top with a conduit (25) for supplying the massecuite whose crystalline size must be increased and, at the bottom, with a conduit ( 222) for discharging the massecuite thus treated; an additional conduit (30, 130, 230) being provided for connecting each cell to a vacuum source; each of said cells being provided with stirring means (31, 131, 231, 322, 132, 232) capable of generating three-dimensional stirring movements in the upper portions of the massecuite and substantially horizontal stirring movements   in the lower parts of it.   Device according to the preceding claims, characterized in that the concave bottom (21, 121, 221) of each   cells has an upper section, of substantially frustoconical shape, and a lower section, substantially shaped spherical cap.   Device according to claims 4 and 5, characterized   characterized in that it has syrup supply ducts   (26, 126, 226) opening into the central part of the mass-cooked fraction present in each cell.   7 Device according to claims 4 to 6, characterized in that said stirring means are provided with two   superimposed propellers (31, 131, 231; 32, 132, 232), the upper propeller (31, 131, 231) being surrounded by a deflector cylindrical (34, 134, 234).   8 Device according to claims 4 to 7, characterized in that the lower discharge duct (22, 122, 22 Z   of each cell is set by a controlled valve (23, 123, 223), preferably depending on the level reached by the   mass-cooked in the corresponding cell.   9 Device according to claims 4 to 8, characterized in that the upper part of the bottom of each cell   is provided with a packing gap defined by a   outer jacket (27, 127, 227).