EP0338099B1 - Process for drying and cooling humid crystalline sugar masses, and apparatus to carry out this process - Google Patents

Description

The invention relates to a method for drying and cooling moist crystal sugar masses, especially fine grain size, fructose, dextrose or the like. With the features of the preamble of claim 1 and a device for carrying out this method.

A device (prospectus from FMC Corp., Colmar, PA) is known which has an elongated, essentially horizontally oriented drum, at one end of which the moist sugar mass is fed in with the aid of a screw conveyor. The drum consists of an outer drum body, in which an inner drum body is arranged, the cross-sectional diameter of which widens continuously from the entry end to the discharge end of the drum, as a result of which the sugar mass receives a small migration component in the direction of the drum axis when the drum is rotated slowly. The inner drum is formed by a multiplicity of ventilation flaps which overlap in the direction of rotation and delimit a multiplicity of ventilation gaps, through which drying or cooling air enters the interior of the drum from the space between the two drums can. The ventilation flaps are fastened to the inner circumference of the outer drum body by means of radial webs, so that the space between the two drums is delimited by a plurality of circumferentially separate air guide channels parallel to the axis of the drum. The drum is operated in such a way that, depending on the added sugar mass, a sugar flow forms in the drum, which essentially remains in the lower third of the drum. The sugar flow is supported by the air flaps on the inner drum. When the drum rotates slowly Zucker the sugar particles move along a spiral path along the free surface of the sugar flow which is set in a circulating movement towards the discharge end of the drum. At the inlet end of the drum, in the area of the drum circumference covered by the sugar stream, frame-fixed supply devices for heated drying air and for cooling air are arranged such that the heated drying air initially only enters the first part of the drum, the drying zone, while the cooling air can only enter the last part of the drum, the cooling zone. In addition, the frame-fixed air inlets are arranged so that the air can only enter the longitudinal channels formed between adjacent ventilation flaps and their webs, which are each just below the sugar flow, so that the drying air and the cooling air each only through the interior of the drum the sugar stream can enter.

Due to the flowability of the sugar mass, it forms a flat interface in the drum on the top of the sugar mass flow, which is assigned to the drum cross section in the form of a secant. This means that the sugar mass in every cross-sectional area the drum has a non-uniform layer thickness, namely a layer with the cross-sectional shape of a circular section. The areas of greater thickness of the layer thus form an increased flow resistance for the air. Since the sugar mass moves in the form of a compact stream through the length of the drum, the drying and cooling performance is low. The sugar masses therefore require a relatively long residence time in the drum in order to be dried and cooled sufficiently.

It is known that with increasing separation of the particles of a bulk material flow, the heat and mass transfer and thus also the performance are increased. If it takes more effort or a longer time to separate the particles, the necessary dwell time of the particles in the drum also increases considerably. This applies especially to baked wet goods such as wet sugar with a fine grain size of e.g. 0.35 mm, as is usual with fructose, dextrose or the like. Freezing lumps of sugar mass offer the air only a small effective area of attack and take a correspondingly long time until they disintegrate and their individual parts are dried and cooled.

Significant cooling performance problems also arise when cooling the sugar stream. It should be noted that the speed of the cooling air flowing in countercurrent to the sugar mass in the drum is limited by the fact that as little abrasion as possible should occur on the sugar particles and as little sugar particles as possible be discharged with the air. The limitation of the cooling capacity is particularly noticeable in the case of drying coolers, in which the drum of the usual type is used to increase the sugar throughput Cross fittings are converted to so-called lifting vane fittings. Such lifting blades, which lift the material and cause it to trickle over the cross section of the drum, are generally known. The risk of sweeping sugar particles out of the trickling sugar masses by the cooling air is particularly great.

It is also known that flowable material can be dried particularly gently in so-called fluidized bed processes. Such fluidized bed processes are used to a large extent in the production of instant products in which granules are formed while the applied binder is simultaneously dried.

However, practice has shown that the known methods and devices for cooling and drying lead to a considerable limitation in performance both in the drying zone and in the cooling zone of the drum.

It is therefore an object of the invention to significantly increase the drying capacity and cooling capacity in the method mentioned at the outset, without increasing the dimensions of the drum, while at the same time the higher capacity is to be achieved with lower air flow speeds if possible.

This object is achieved by the features of the characterizing part of claim 1.

It is essential that the moist sugar mass to be fed is pulled apart into a thin layer on its way to the inlet end of the drum, with existing lumps or agglomerates already being largely dissolved. This Spread thin layer is then sprinkled in a large-area veil in a plane substantially transversely to the axis of the drum over almost the entire drum height, the veil being blown by the drying air essentially vertically and over its entire surface area. In this way, the particle surfaces are exposed mechanically for the attack of the drying air, so that it can absorb and dissipate a large part of the moisture with extremely high effectiveness even when the moist mass is introduced. All that is required is a relatively slow drying air speed. As a result, an extraordinarily high drying performance is achieved in the drying zone without increasing the dimensions of the drying zone and with a lower flow rate of the drying air. In the cooling zone, it is assumed that the cooling of the sugar masses is known to be particularly effective by trickling the lifting blades over a substantial part of the cross-sectional height of the drum, whereby it is ensured that the trickling sugar particles are caught by a fluidization bed which is spread over a large area in the cooling zone along one of the Horizontal axis lying drum axis is arranged. The arrangement of the fluidization bed on a plane oriented along a secant of the drum cross-section ensures that the layer height in the fluidization bed is uniform both in the longitudinal direction of the drum and transversely thereto, so that the cooling air can attack the sugar particles equally effectively in all areas of this fluidization bed . The sugar particles are not held together in a more or less compact stream that rolls in a spiral to the outlet end of the drum, as is the case with the known dryer and cooler discussed at the beginning the case is. Rather, the sugar particles remain in finely divided, fluidized form in the fluidization bed before they preferably migrate to one side towards the inner wall of the drum and are again picked up by the revolving lifting blades, lifted up and made to run off.

By collecting the trickling sugar particles, however, the mechanical stress on the sugar particles is also extremely reduced, so that the abrasion remains small.

By collecting the sugar particles in a fluidization bed, the cooling capacity is above all significantly increased. The result is that a high cooling capacity is achieved with small dimensions of the cooling zone and the cooling air speed can nevertheless be significantly reduced compared to conventional coolers to well below values of 2.5 m / sec. and preferably around 1.75 m / sec.

Further advantageous procedural measures result from claims 2 to 4.

The device-based solution of the invention takes place through the teaching of claims 5 and / or 6. The measures of claims 5 and 6 are preferably applied together to one device, since the performance of this device can be increased very considerably.

Further advantageous features of the device result from subclaims 7 to 14.

The invention is explained in more detail below with the aid of schematic drawings using an exemplary embodiment.

Fig. 1

in schematischer Seitenansicht, teilweise aufgeschnitten, eine Vorrichtung zum Trocknen und Kühlen gemäß der Erfindung,

Fig. 2

im größeren Maßstabe und im Schnitt das Aufgabeende der Vorrichtung nach Fig. 1,

Fig. 3

eine Draufsicht auf das Aufgabeende nach Fig. 2,

Fig. 4

im Längsschnitt den Kühlzonenbereich der Vorrichtung nach Fig. 1 und

Fig. 5

im Querschnitt und größerem Maßstabe die Kühlzone der Vorrichtung gemäß Fig. 4.

Show it:

Fig. 1

in a schematic side view, partially cut away, a device for drying and cooling according to the invention,

Fig. 2

on a larger scale and in section the feeding end of the device according to FIG. 1,

Fig. 3

2 shows a plan view of the end of the task according to FIG. 2,

Fig. 4

in longitudinal section the cooling zone area of the device according to FIGS. 1 and

Fig. 5

in cross section and on a larger scale, the cooling zone of the device according to FIG. 4.

The device designated overall by 1 according to FIG. 1 has an elongated drum 2. The axis 11 of the drum 2 is arranged slightly falling relative to the horizontal according to the angle 12, so that the discharge end 10 is slightly lower than the feed end 9 of the drum.

The moist sugar masses are fed to the drum 2 at the feed end 9 by a feed device 5. At this end the mostly tempered drying air is also fed axially according to arrow 6. In drying zone 3, the direction of migration of drying air and sugar mass is the same.

A cooling air box 15 is arranged in the cooling zone 4. The cooling air is supplied from the side of the discharge end 10 both to the cross section of the drum 2 and to the cooling air box 15 in accordance with the arrows 7. The dried and cooled sugar mass is discharged in the direction of arrow 8.

The drying air and the cooling air are taken up in the middle of the drum by a device 13 which spirally discharges the exhaust air in the direction of arrow 14.

The drum 2 is driven about its axis 11 at a slow speed.

In Figure 2, the feed end 9 of the drum 2 is shown in longitudinal section. This end is closed by a guide device fixed to the frame in the form of a guide body 24 which can be connected to a source of drying air. The guide device 24 is connected to the rotating drum via a sliding seal. The guide body fixed to the frame is penetrated by conveyor troughs 28, 29, which in the example shown run in two horizontal planes one above the other. Outside the guide device 24, the conveyor troughs 28, 29 extend into a feed hopper of the feed device 5. The feed hopper is divided into two areas by a partition wall 27, via which a conveyor 28 or 29 is loaded in each case. By means of spreading edges which extend close to the respective conveyor 28 or 29 (see, for example, the lower end of the partition wall 27), it is achieved that the sugar mass is spread in a thin layer on each flat horizontal conveyor 28, 29, whereby lumps of sugar or the like. are already mechanically brought to partial disintegration. On the conveyors 28, 29, two of which are shown in FIG. 2 and of which three or more can also be provided, the respective sugar masses are spread out in thin layers on their way into the interior of the drum 2 in the transverse direction. The moist sugar mass reaches a trickle edge 30 and 31, respectively, over which the material trickles over a large area and in a veil-like manner over almost the entire cross-sectional width and the entire cross-sectional height of the drum 2. The trickle edges 30 and 31 are offset both in the direction of the cross-sectional height and in the direction of the axis 11 of the drum 2, so that separate veils in the mutual Distance and parallel to each other. In some cases it is also sufficient if only one conveyor with a single trickle edge is provided.

The drying air flow is expanded by the guide device 24 and possibly by further internals 22, such as baffles, when entering the feeding end 9 of the drum 2 such that the air flows in and flows through the veil approximately vertically over its entire surface area in a uniform flow.

The moist sugar mass, which is fed to the feed hopper in accordance with arrow 25 and trickles into the interior of drum 2, subsequently migrates in a conventional manner through drying zone 3, which can be equipped with appropriate internals 21, 23 in the form of webs. The drying air is then taken up and removed in the device 13 according to FIG. 1, while the dried sugar mass passes through the device 13 from the drying zone 3 into the cooling zone 4.

In the cooling zone 4, the drum 2 has on its inner wall a ring of lifting blades 45, the inward edges of which sweep over a common path, which is indicated by dash-dotted lines at 46 in FIG. 5.

The sugar masses located in the lower part of the drum 2 are grasped by the lifting blades 45 and raised up to the highest point of the drum 2. The sugar particles begin in a thin veil before the highest point of the lifting blades 45 is reached trickle down, falling freely over the cross-sectional height of the drum 2. The discharge end 10 of the drum 2 is supplied with cooling air distributed over the cross section in accordance with the arrow 7, which flows through the free-flowing curtain of sugar.

Below the drum axis 11 along a secant of the drum cross section, the flat and approximately horizontally arranged top 40 of a cooling air box 15 is provided. The top 40 of the cooling air box 15 is provided with openings and is charged with cooling air according to arrow 7 in FIG. 4 with such volumetric power that a fluidization bed 42 is formed depending on the grain size of the sugar particles on the top 40 of the cooling air box 15 Can form sugar particles. From Figure 5 it can be seen that due to the design and arrangement of the cooling air box 15, the fluidization bed 42 has constant thickness over its entire longitudinal and transverse extent, so that the same flow conditions and thus the same cooling effects are present throughout the bed.

In the preferred exemplary embodiment shown, the fluidization bed 42 is divided in the direction of the axis 11 of the drum 2 by transverse weirs 41 into a plurality of bed sections which are independent of one another. the arrangement is such that the particles from a bed section generally cannot pass over the upper edge 41a of the respective weir 41 into an adjacent bed section. Each fluidization bed section is only open upwards and towards the side of the drum circumference indicated by the arrow 51 in FIG. 5, on which the lifting blades 45 execute a descending movement.

Heat exchangers 50 can be arranged in individual or all sections of the fluidization bed 42, through which a coolant flows and with which the cooling air and the sugar particles can come into direct contact.

Because of the uniform layer thickness and the loose state of the sugar mass in the fluidization bed 42, an extraordinarily high cooling capacity is achieved in the area of the fluidization bed. At the same time, the sugar particles trickling down from the lifting blades 45 are reliably and gently collected by the fluidization bed 42. The residence time of the sugar masses in the fluidization bed sections and thus overall in the drum 2 can be varied and influenced to a high degree by the number and distribution of the weirs 41.

The cooling air is supplied to the cross section of the cooling zone 4 and the cooling air box 15 separately, so that the fluidization bed 42 can be controlled via the cooling air supply to the cooling air box 15 independently of the cooling air effect in the cooling zone 4. Due to the high cooling capacity in the fluidization bed 42, the total cooling air capacity can be adjusted so that there is only a comparatively low air flow rate in the cooling zone 4. For example, be achieved that the cooling air has a speed at the passage into the device 13 for discharging the exhaust air, which is well below 2.5 m / sec. lies. The arrangement is preferably such that the cooling air speed is only in the range of 1.75 m / sec. lies.

Claims (14)

1. A process for drying and cooling humid crystalline sugar masses, in particular those of fine grain size, of fructose, dextrose or the like, using a slowly rotating, elongate drum, which is arranged so as to slope downwards slightly in the throughfeed direction and which has a drying zone and a cooling zone, drying air and cooling air being supplied separately to each respective zone in the longitudinal direction of the drum, the sugar masses being charged at one end of the drum and drawn off at the other and being lifted continuously by means of lifting scoops, at least in the cooling zone, and allowed to trickle down through the cross-section of the drum, characterised in that the humid sugar masses are charged at the charging end of the drum in a thin veil which extends in a sheet substantially over the height and the entire width of the drum cross-section, and the drying air flows through the or each veil of sugar mass in a substantially perpendicular direction over its entire surface area, and in that the sugar masses trickling down from the lifting scoops in the cooling zone are collected in a fluidisation bed after falling through more than half the height of the cross-section.
2. A method according to Claim 1, characterised in that the humid sugar masses are spread into sheets at the charging end to form several parallel thin veils, the drying air flowing through these veils one after the other.
3. A process according to Claim 1 or 2, characterised in that the sugar masses trickling down in the cooling zone and the cooling air are brought into direct contact with cooling surfaces in the fluidisation bed.
4. A process according to any one of Claims 1 to 3, characterised in that the trickling sugar masses and the cooling air are received in defined, independent regions of the fluidisation bed, and in that the sugar masses are allowed to move out of each portion of the fluidisation bed only in the direction of the drum periphery where the scoops are moving downwards.
5. A device for drying and cooling humid sugar masses according to the process of Claim 1, having an elongate rotatably driven drum, an axis of rotation inclined downwards slightly relative to the horizontal, a charging device for the humid sugar masses at one end and a discharging device for the dried and cooled sugar masses at the other end, lifting scoops arranged on the inner periphery, at least in the portion of the drum used for cooling, separate supply devices for the drying air and the cooling air, and a device for carrying away the exhaust air, characterised in that a conveying channel (28,29) is provided at the charging end (9) of the drum (2), which conveying channel (28,29) extends axially above the centre (11) of the drum cross-section into the end of the drum, spreads the humid sugar mass into a sheet and supplies it in a thin layer to a horizontal trickling edge (30,31) which extends over the greater part of the cross-sectional width of the drum (2) at the level of the conveying channels (28,29), and in that a guiding device (24) is provided, which supplies the stream of drying air (26) in the direction of the drum axis (11) and diffuses it over the area between the trickling edge (30,31) and the regions of the drum periphery lying therebelow.
6. A device for drying and cooling humid sugar masses according to the process of Claim 1, in particular with the features of Claim 5, characterised in that there is provided in the cooling zone (4) a cooling air box (15), whose substantially horizontal upper side (40) extends beneath the drum axis (11) across the entire free inner space of the drum (2) and, in dependence on the stream of cooling air which can be supplied to the cooling air box (15), forms a fluidisation bed (42) for collecting the sugar masses lifted by and trickling down from the scoops (45), this fluidisation bed (42) overlying the upper side (40).
7. A device according to Claim 5 or 6, characterised in that the conveying channel (28,29) has two or more conveying planes lying one on top of the other, each of which ends in a trickling edge (30,31), the trickling edges being arranged offset to one another both in the vertical direction of the cross-section and in the direction of the axis (11) of the drum (2).
8. A device according to any one of Claims 5 to 7, characterised in that the or each trickling edge (30,31) is wedge-shaped in order to lengthen the veil of sugar mass and to centre the stream of drying air over the surface area of the veil.
9. A device according to any one of Claims 6 to 8, characterised in that several weirs (41), oriented crosswise to the longitudinal direction of the drum, are provided on the upper side (40) of the cooling air box (15) in order to divide the fluidisation bed (42) into several independent bed portions.
10. A device according to any one of Claims 6 to 9, characterised in that the fluidisation bed (42) or each portion thereof is open at the top and only towards that side of the peripheral wall of the drum where the lifting scoops (45) are descending.
11. A device according to any one of Claims 6 to 10, characterised in that heat exchange elements (50) are arranged in the fluidisation bed (42), which heat exchange elements (50) can be connected to a cooling agent circuit.
12. A device according to any one of Claims 6 to 11, characterised in that a device (13) is arranged between the ends (9,10) of the drum (2) for carrying away the exhaust air from the drying zone (3) and the cooling zone (4) in a spiral manner, and the cooling air box (15) and the fluidisation bed (42) extend from the sugar-discharging end (10) of the drum (2) into the device (13) for carrying away the exhaust air.
13. A device according to any one of Claims 6 to 12, characterised in that the cooling air can be supplied separately both to the cross-section of the drum (2) at the outlet end (10) thereof and to the cooling air box (15).
14. A device according to Claim 13, characterised in that the volume of cool air supplied to the sugar-outlet end (10) of the drum (2) can be adjusted to the cross-section of the drum, so that the cooling-air speed is distinctly below 2.5 m/sec., preferably about 1.75 m/sec or lower, in the cross-section of the drum at which the cooling air passes into the device for carrying away the exhaust air.

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