EP3423179B1 - Device, system, and method for mixing at least one first material and a second material so as to form a base material for forming a mixture - Google Patents

Description

The invention relates to a device for admixing at least one first substance and one second substance to a base substance for the continuous formation of a mixture. The invention also relates to a system with a device according to the invention. Finally, the invention relates to a method for admixing a first substance and a second substance to a base substance to form a mixture. The device according to the invention, the system according to the invention and the method according to the invention are particularly suitable for admixing a first substance and a second substance to a urea melt, a dispersion then being formed from the first substance, the second substance and the urea melt. This dispersion can then be processed into pastilles in the plant according to the invention. The invention is therefore particularly suitable for producing a fertilizer that is easy to handle, in particular urea fertilizer.

From the German Offenlegungsschrift DE 10 2010 028 774 A1 a device for admixing at least a first substance and a second substance to a base substance for the continuous formation of a mixture is known. The device has a first mixing container and a second mixing container. The first and second mixing containers each have an inlet opening, an introduction opening for admixing the first or second substance, and an outlet opening. The first and the second mixing tank are each provided with an agitator. The outlet opening of the first mixing container and the inlet opening of the second mixing container are connected to one another by means of a connecting line, the connecting line being open during mixing operation of the device. The mixing containers of the device should be operated with the exclusion of air. Since the system works with the exclusion of air and the components to be emulsified are continuously introduced into the mixing device, the components located in the mixing device are continuously transported away in the direction of the discharge line.

From the German Offenlegungsschrift DE 103 61 307 A1 a device for admixing at least a first substance and a second substance to a flowable base substance is known. The device has two mixing containers connected in series, each with an agitator. A return line is provided to return fluid from the second tank to the first tank.

From British Patent Specification GB1 310 725 a device for admixing at least a first substance and a second substance to a flowable base substance is known. The device has a first mixing tank and a second mixing tank, each of the mixing tanks being provided with an agitator. A mixture is mixed in either the first mixing tank and the second mixing tank and then transported via a discharge line to a downstream processor. While one of the containers is being emptied, another container is being loaded or is on hold. The transport of fluid from the first mixing container into the second mixing container is not provided.

From the German Offenlegungsschrift DE 30 32 384 A1 a plant for the emulsification of heavy oils with two tanks is planned. The containers each have a pressure equalization opening.

The aim of the invention is to improve the production of mixtures from a first substance, a second substance and a base substance.

According to the invention, a device for admixing a first substance and a second substance to a base substance to form a mixture, in particular for admixing a first substance and a second substance to a urea melt to form a dispersion according to claim 1, is provided for this purpose, the device for admixing the following features

The admixing device has a first mixing container and a second mixing container. The first and second mixing containers each have an inlet opening for admitting a base material or an intermediate mixture, an outlet opening for letting out the intermediate mixture or the mixture, an inlet opening for admixing the first or second substance and a pressure equalization opening. The pressure equalization openings of the first and second mixing containers are connected to one another by means of a pressure equalization line, with the pressure equalization openings being above the fluid levels present in the mixing containers when the device is in operation when the device is in operation, so that the interior of the first mixing container and the interior of the second mixing container the same pressure is present, and the outlet opening of the first mixing tank and the inlet opening of the second mixing tank are connected to one another by means of a connecting line, which enables flow during operation of the device, with the outlet opening of the first mixing tank, the connecting line and the inlet opening of the second mixing tank being connected during operation of the device Mixing tanks are below the fluid level in the mixing tanks, so that fluid can pass from the first mixing tank into the second mixing tank.

Since a first and a second mixing container are provided in the device according to the invention and fluid can flow from the first mixing container into the second mixing container through the connecting line, which is open during operation, an intermediate mixing stage is thus produced in the first mixing container and this intermediate mixing stage is then fed to the second mixing container , where a second substance is then added. This achieves particularly good and rapid mixing of the first substance with the base substance and then subsequently of the second substance with the intermediate mixing stage. The multi-stage admixing prevents the admixed substances from influencing one another and/or the admixing of the at least one further substance is facilitated. Since the mixing intermediate stage gets from the first mixing container into the second mixing container only by gravity, it can be ensured that a mixing time in the first mixing container is long enough to achieve a particularly uniform mixture between the first substance and the base substance. A sufficiently long mixing time to produce a particularly uniform mixture can also be achieved in the second mixing container. Due to the connecting line, which is open during operation of the device and lies below the fluid level, the fluid levels in the two mixing containers are always essentially at the same level. If, for example, the fluid level in the second mixing tank is higher than in the first mixing tank, then fluid can also reach the first mixing tank through the connecting line from the second mixing tank. As a rule, however, the intermediate mixture stage produced in the first mixing container flows through the connecting line into the second mixing container as a result of gravity. Continuous mixing operation is possible with the device according to the invention. The mixing containers and/or agitators can be designed differently.

In a development of the invention, the first mixing container and the second mixing container each have an essentially the same basic shape with essentially the same volume, and the first mixing container and the second mixing container are arranged essentially at the same height.

In this way it can be ensured that the mixing time in the first mixing container and the mixing time in the second mixing container are essentially the same, so that a very uniform mixture of the base substance and the two supplied substances can be achieved.

In a further development of the invention, the inlet openings and/or outlet openings of the first and the second mixing container merge within the mixing container into an angled piece of pipe, preferably into a piece of pipe bent at an angle of 90°, and the center planes of the angled pieces of pipe are each aligned essentially perpendicularly to a center longitudinal axis of the first or second mixing container.

Fluid thus emerges from the inlet openings perpendicularly to the central longitudinal axis of the containers and also enters the outlet openings again perpendicularly to the central longitudinal axis of the containers. This is particularly advantageous when a flow movement about the central longitudinal axis is generated in the mixing containers, for example by means of an agitator. The inlet openings can, for example, also be aligned in such a way that they support a flow movement within the mixing container around the central longitudinal axis. To generate turbulence, however, it can also be useful to direct the inlet openings against the flow generated by the agitator and also to align the outlet openings against the flow generated in the container by the agitator. The inlet into the second mixing container is preferably in the direction of flow. The angled pipe sections can also be left out at the outlet openings.

In a further development of the invention, the openings of the angled pipe sections, which form the inlet opening or the outlet opening within the mixing container, point in the same tangential direction when viewed parallel to the central longitudinal axis of the first or second mixing container.

As a result, depending on the application, either a flow around the central longitudinal axis of the respective mixing container can be supported by appropriate arrangement of the inlet opening. Alternatively, the inlet opening can be directed against the flow generated by an agitator in the respective mixing container, and the outlet opening can also be directed either in or against a direction of flow within the respective mixing container.

In a development of the invention, the inlet opening of the first mixing container is connected to a raw material feed, in particular to a feed for urea melt, and the outlet opening of the second mixing container is connected to a device for further processing the mixture, in particular to a pastillation device.

In a development of the invention, the first mixing container and the second mixing container are each provided with an agitator.

In a further development of the invention, the first mixing container, the second mixing container, the through-line and/or the connecting line have a double-walled structure, with gaps formed by means of the double-walled structure are designed for the passage of heating or cooling media. When processing melts, in particular urea melts, the melt can be kept in the flowable state or heated within the mixing container and also within the pressure equalization line and the connecting line.

In addition, in a further development of the invention, it can be provided that the first and/or the second mixing container have external thermal insulation.

In addition, it can be provided in a further development of the invention that the intermediate spaces are connected to a heating device for the heating medium. Such heating devices are also referred to as trace heating.

The invention also relates to a system with a device according to the invention, the system having a base material feed, the system having a first metering device for a first substance to be mixed with the base material, and a second metering device for a second substance to be mixed with the base material, the system having a line with a pump arranged in its course for transferring the finished mixture from the second mixing container to a pastillating device for pastillating the mixture, with a return line being provided for partially returning the mixture to the second mixing tank, which is fed into this second mixing tank below or above the fluid level opens out and wherein the pastillating device has a rotating and perforated drum and a rotating cooling belt.

Using such a system, melts in particular can be mixed and then pelletized. The system according to the invention is particularly suitable for pastillating a urea melt, a first substance and a second substance being admixed to the urea melt. This is of great advantage, especially in the production of fertilizers. Inside the mixing container, the melt can be kept in a good flowable state, so that a very even mixture can be produced with the two substances supplied. In the liquid state, the mixture of the melt and the at least two admixed substances is then fed to the pastillation device. The return line makes it possible to maintain a comparatively high flow rate within the feed line, so that there is no risk of the melt partially solidifying in the connecting line. The melt is fed to the pelletizing device in the liquid state but at a temperature which is only slightly above its solidification temperature. This makes it possible to produce qualitatively high-quality pastilles, which solidify essentially immediately after being deposited in the form of liquid melt droplets on the cooling belt and thus essentially retain their almost spherical droplet shape on the cooling belt.

The problem on which the invention is based is also solved by a method for admixing a first substance and a second substance to a basic substance to form a mixture, the method for admixing having the following features: A basic substance, in particular a urea melt, is supplied to a first mixing container , the first substance to be mixed is fed to the base material in the first mixing tank to form an intermediate mixture, the intermediate mixture from the first mixing tank is fed to the second mixing tank, the second substance to be mixed is fed to the intermediate mixture in the second mixing tank to form the mixture, with the supply the intermediate mixing stage from the first mixing tank into the second mixing tank using gravity by means of a connecting line between the mixing tanks located below the fluid level in the mixing tanks.

By using gravity to transport the intermediate mixing stage from the first mixing container to the second mixing container, a sufficient mixing time and thus the production of a very uniform mixture can be ensured both in the first and in the second mixing container.

The base material is advantageously a melt, in particular a urea melt.

Fig. 1

eine teilweise geschnittene Seitenansicht einer erfindungsgemäßen Vorrichtung,

Fig. 2

eine schematische Ansicht des ersten Mischbehälters der Vorrichtung der Fig. 1 von oben,

Fig. 3

eine abschnittsweise Schnittansicht des Behälters der Fig. 2 und

Fig. 4

eine schematische Darstellung einer erfindungsgemäßen Anlage zum Herstellen eines Harnstoffdüngers aus einer Harnstoffschmelze.

Further advantages and features of the invention result from the claims and the following description of preferred exemplary embodiments of the invention, which are explained below with reference to the figures. Individual features of the different exemplary embodiments can be combined with one another in any way without going beyond the scope of the invention. In the drawings show:

1

a partially sectioned side view of a device according to the invention,

2

a schematic view of the first mixing container of the device 1 from above,

3

a partial sectional view of the container of FIG 2 and

4

a schematic representation of a system according to the invention for producing a urea fertilizer from a urea melt.

one inside 1 The device according to the invention, shown partially in section, for admixing a first substance and a second substance to a base substance to form a mixture has a first mixing container 12 and a second mixing container 14 . The two mixing containers 12, 14 have the same basic shape and the same volume and are also arranged at the same height above a machine frame 16. However, within the scope of the invention, the mixing containers 12, 14 can certainly have different basic shapes and different volumes. Both mixing containers 12, 14 are each provided with an agitator 18, which is shown only schematically and which can be driven by a motor 20 in each case. The two mixing containers 12, 14 each have a cylindrical shape with a bulging bottom. The agitator extends parallel to the central longitudinal axis of the mixing container 12, 14 and a drive shaft of the agitator lies on the central longitudinal axis 22, 24 of the respective mixing container 12, 14. The mixing container 12 has an inlet opening 26 for admitting a base substance. For example, a urea melt is introduced into the first mixing container 12 via the inlet opening 26 . The first mixing container 12 has an outlet opening 28 . In the illustrated embodiment, the outlet opening 28 is opposite the inlet opening 26 and is also arranged at the same level as the inlet opening 26 . However, such an arrangement of the outlet opening 28 relative to the inlet opening 26 is not mandatory. According to the invention, however, the outlet opening 28 must be below a fluid level that is reached in the first mixing container 12 during operation.

The first mixing container 12 also has a pressure equalization opening 30 which is arranged above the outlet opening 28 and which must be above a fluid level within the first mixing container 12 during operation.

The second mixing container 14 is constructed identically to the first mixing container 12 and has an inlet opening 32 for letting in an intermediate mixture stage from the first mixing container 12 and an outlet opening 34 for letting out the finished mixture. The outlet opening 34 is arranged opposite the inlet opening 32 and at the same height as the inlet opening 32, although this is not mandatory, as has already been explained with reference to the first mixing container 12.

The second mixing vessel 14 also includes a pressure equalization port 36 located above the inlet port 32 and the outlet port 34 . In operation, the Pressure compensation opening 36 should be above a fluid level in the second mixing container 14 and the outlet opening 34 should be below a fluid level in the second mixing container 14 .

The pressure equalization openings 30, 36 are at the same height and are connected to a pressure equalization line 38.

The outlet opening 28 of the first mixing container 12 and the inlet opening 32 of the second mixing container 14 are at the same level and are connected to a connecting line 40 . Within the scope of the invention, it is not absolutely necessary for the outlet opening 28 of the first mixing container 12 and the inlet opening 32 of the second mixing container 14 to be at the same level. However, it is essential that the connecting line 40 lies below a fluid level in the first mixing container 12 and below a fluid level in the second mixing container 14 over its entire length. As a result, the inlet opening 32 of the second mixing container 14 must also be below a fluid level in the second mixing container 14 . A transport of fluid from the first mixing container 12 into the second mixing container 14 and optionally from the second mixing container 14 into the first mixing container 12 can thereby take place by means of gravity.

In the first mixing container 12, a fluid level provided during operation is indicated with the reference numeral 42. In the second mixing container 14, a fluid level present during operation is indicated with the reference numeral 44. The two fluid levels 42, 44 are practically at the same level or at least at a similar level, since the two mixing containers 12, 14 communicate with one another via the connecting line 40.

If, during operation of the device according to the invention, a base material is fed in via the inlet opening 26 of the first mixing container 12 , for example a urea melt, the fluid level 42 in the first mixing container 12 will rise slightly. The slightly increased liquid pressure at the outlet opening 28 of the first mixing container 12 causes the fluid in the first mixing container 12, which forms an intermediate mixing stage, to be transported via the connecting line 40 into the second mixing container 14, so that the fluid levels 42, 44 equalize again .

The first mixing container 12 has a lid in which an insertion opening 46 is provided for mixing in a first substance. For example, an additive or another substance can be introduced into the base material, specifically the urea melt, in the first mixing container 14 via the introduction opening 46 . Solids may need to be preheated. The first Fabric is preferably introduced continuously via the insertion port 46 . As a result, an intermediate mixture of the base material and the first material is produced within the first mixing container.

The second mixing container 14 also has a lid with an insertion opening 48 through which a second substance can be admixed. The second substance passes through the introduction opening 48 into the second mixing container and is mixed there with the intermediate mixture stage, which consists of the base substance and the first substance and has reached the second mixing container 48 via the connecting line 40 . After the second substance has been mixed in, the finished mixture is present within the second mixing container 14 and can then be removed via the outlet opening 34 . The device according to the invention works continuously. During operation, base material is thus continuously supplied via the introduction opening 26, the first substance is continuously supplied via the inlet opening 46 and the second substance is continuously supplied via the inlet opening 48, and the finished mixture can be continuously removed via the outlet opening 34.

Sufficient mixing time can be ensured both within the first mixing container 12 and within the second mixing container 14 because the fluid is transported from the first mixing container 12 into the second mixing container 14 by the influence of gravity via the connecting line 40 . This ensures a particularly uniform mixture of the first material with the base material for producing an intermediate mixture and then of the second material and the intermediate mixture in the second mixing container. The agitators 18 provided in each mixing container 12, 14 support the production of a particularly uniform mixture.

Each of the mixing containers 12, 14 has a further outlet opening 50 at its bottom. This further outlet opening 50 is provided, for example, for completely emptying the mixing container 12, 14 as part of an inspection or as part of a shutdown of the device. The connecting line 40 is provided with branches and can also, like the pressure compensation line 38, be provided with a shut-off valve. During operation of the device, however, both the pressure equalization line 38 and the connecting line 40 should be open in order to allow pressure equalization between the mixing containers 12, 14 and fluid transport between the two mixing containers 12, 14.

The two mixing containers 12, 14 are each double-walled, so that an intermediate space 52 is formed in which a heating medium or cooling medium can be transported. If by means of the device according to the invention a mixture of a If urea melt and two other substances are produced, a heating medium is applied to the intermediate space 52 in each case in order to ensure that the melt does not already partially solidify within the mixing container 12, 14. The pressure-equalizing line 38 and the connecting line 40 are each double-walled, so that the heating medium can also heat the pressure-equalizing line 38 and the connecting line 40 . The connection pieces of the inlet opening 26, the outlet opening 28, the inlet opening 32 and the outlet opening 34 are each double-walled in order to be able to heat them and to prevent the melt from solidifying in these areas, which could cause deposits to form. Solids may need to be preheated.

A heating medium is fed into the intermediate space 52 via a heating line 54, for example.

The representation of 2 shows the first mixing container 12 in a view from above, with the mixing container 12 only being partially indicated by dashed lines in order to also be able to show components lying underneath the lid.

It is only indicated schematically in 2 the agitator 18. The intermediate space 52, which completely surrounds the mixing container 12, can be clearly seen. The inlet opening 26 and the outlet opening 28 can also be seen.

The inlet opening 26 is provided with an angled piece of pipe 56 which deflects the melt entering through the inlet opening 26 by 90° and thereby introduces it into the interior of the first mixing container 12 approximately tangentially to the central longitudinal axis 24 .

The pipe section 56 has, in the representation of 2 in the clockwise direction. Depending on the direction of rotation of the agitator 18 about the central longitudinal axis 24, the melt flowing in via the inlet opening 26 and the pipe section 56 supports a flow movement of the melt about the central longitudinal axis 24 or is directed against this flow direction. The intermediate mixture stage produced in the first mixing container 12 is removed through the outlet opening 28 . In order to ensure that the mixing is as thorough as possible and that there is sufficient mixing time within the first mixing container 12 , the piece of pipe 56 is aligned with a direction of flow that prevails in the mixing container 12 . In the representation of 2 would rotate the agitator 18 clockwise and thus also cause a flow movement within the mixing container 12 in the clockwise direction.

The representation of 3 shows the area of the inlet opening 26 on the first mixing container 12 in more detail and in a sectional view. The pipe section 56 angled by 90° connects to the inlet opening 26 . The inlet opening 26 bridges the intermediate space 52 which, as has already been described, is heated by means of a heating medium. The intermediate space 52 also continues up to a connecting flange 60 . The piece of pipe 62 between the connecting flange 60 and the inlet opening 26 can also be heated by means of the heating medium. This prevents the supplied melt from solidifying in this area.

The representation of 4 shows a system for pastillating a melt, in particular a urea melt, the system having a device 10 according to the invention for admixing a first substance and a second substance to a base substance. Plant 70 is used to produce urea fertilizer. The urea fertilizer can be removed downstream of the plant in the form of solidified pastilles. The lozenges then consist of a mixture of urea with at least a first and a second substance, the first and the second substance being admixed in the device 10 .

As has already been explained, a urea melt is supplied to the first mixing container 12 via the introduction opening 26 and mixed there with a first substance which is supplied via the introduction opening 46 . Starting from the first mixing container 12 , the intermediate mixture stage consisting of the urea melt and the first substance reaches the second mixing container 14 and is mixed there with a second substance that is fed in via the introduction opening 48 . The finished mixture is removed from the second mixing container 14 at the outlet opening 34 and fed to a grinding unit 74 by means of a pump 72 . In the milling unit 74, a particle size of the mixture, which forms a dispersion of the urea melt and the first material and the second material, can be reduced. Alternatively, the grinding unit 74 can also be omitted.

Starting from the grinding unit 74, the mixture is then fed to a pastillating device 76 via a further connecting line. The pastillation device 76 has a rotating, perforated drum 78 and a nozzle bar, which conveys the mixture against the perforated drum 78 from the inside. The perforated drum produces melt droplets which are then deposited on a circulating cooling belt 80 . After being deposited, the deposited product droplets solidify on the cooling belt 80 to form lozenges and can then be removed from the cooling belt 80 as solid lozenges.

A return line 82 leads from a branch 84 back to the second mixing container 14 . Through this return line 82, the finished mixture can reach the branch 84 not only to the pastillation device 76, but back again into the second mixing container 14. On the one hand, this makes it possible to circulate a larger quantity of the mixture in the connecting line and the return line 82 . This can ensure, for example, that the mixture, which consists of a dispersion of a melt and other substances, does not separate again within the connecting line or partially solidify. In addition, the mixing device 10 can continue to be operated even if the pastillating device 76 is temporarily stopped, for example.

Claims (14)

1. Device for admixing at least one first substance and one second substance to a flowable base substance for forming a mixture by means of a continuous mixing operation, in particular for admixing a first substance and a second substance to a urea melt for forming a dispersion, wherein the device for admixing has the following features:

   a the device (10) for mixing has at least one first mixing vessel (12) and one second mixing vessel (14),

   b the first and second mixing vessels (12, 14) have in each case one inlet opening (26, 32), in each case one introduction opening (46, 48) for admixture of the first substance and second substance, respectively, in each case one outlet opening (28, 34) and in each case one pressure-equalization opening (30, 36), each of the mixing vessels (12, 14) having at its base a further outlet opening (50), which is intended for complete emptying of the mixing vessels (12, 14),

   wherein

   c the first mixing vessel and the second mixing vessel are each provided with a stirrer,

   d the pressure-equalization openings (30, 36) of the first and second mixing vessels (12, 14) are connected to one another by means of a pressure-equalization line (38) or are open to the surroundings, wherein, during the operation of the device, the pressure-equalization openings (30, 36) are situated above fluid surfaces (42, 44) present in the mixing vessels, and

   e the outlet opening (28) of the first mixing vessel (12) and the inlet opening (32) of the second mixing vessel (14) are connected to one another by means of a connecting line (40), wherein, during the mixing operation of the device (10), the connecting line (49) is open and the outlet opening (28) of the first mixing vessel (12) and the inlet opening (32) of the second mixing vessel (14) and also the connecting line (40) are situated below the fluid surfaces (42, 44) in the mixing vessels (12, 14), so that fluid can pass from the first mixing vessel (12) into the second mixing vessel (14) under the effect of gravitational force.
2. Device for admixing according to Claim 1, characterized in that
   the first mixing vessel (12) and the second mixing vessel (14) in each case have a substantially identical basic shape with substantially the same volume and are arranged at substantially the same height.
3. Device for admixing according to Claim 1 or 2, characterized in that
   the outlet opening (28) of the first mixing vessel (12) and the inlet opening (32) of the second mixing vessel (14) are arranged at substantially the same height.
4. Device for admixing according to one of the preceding claims, characterized in that

   a the inlet openings (26, 32) and/or the outlet openings (28, 34) of the first and second mixing vessels (12, 14), within the mixing vessels (12, 14), in each case transition into an angled tube piece (56, 58), preferably into a tube piece which is angled away by an angle of 90°, and

   b the central planes of the angled tube pieces (56, 58) are in each case oriented substantially perpendicularly to a central longitudinal axis (24) of the first or second mixing container (12, 14) .
5. Device for admixing according to Claim 4, characterized in that

   a openings of the angled tube pieces (56, 58) that form the inlet opening or the outlet opening within the mixing vessels (12, 14) in each case face in the same tangential direction as seen parallel to the central longitudinal axis (24) of the first and of the second mixing vessel (12, 14), respectively.
6. Device for admixing according to one of the preceding claims, characterized in that

   a the inlet opening (26) of the first mixing vessel (12) is connected to a base-substance feed, in particular to a feed for urea melt, and

   b the outlet opening (34) of the second mixing vessel (14) is connected to a device for further processing of the mixture, in particular to a pastillation device (76), to a granulating device or to a device for producing flakes.
7. Device for admixing according to one of the preceding claims, characterized in that

   a the first mixing vessel (12), the second mixing vessel (14), the pressure-equalization line (38) and/or the connecting line (40) have/has a double-walled construction,

   b intermediate spaces formed by means of the double-walled construction are configured for passing-through of heating or cooling media.
8. Device for admixing according to Claim 7, characterized in that

   a the first and/or second mixing vessel (12, 14) have/has external heat insulation.
9. Device for admixing according to either of Claims 7 and 8, characterized in that

   a the intermediate spaces are connected to a heating device for the heating medium.
10. Installation having a device for mixing according to one of the preceding claims, characterized in that

    a the installation has a base-substance feed,

    b the installation has at least one first dosing device for a first substance to be admixed to the base substance and has at least one second dosing device for a second substance to be admixed to the base substance,

    c the installation has a line with a pump (72) arranged in the course thereof for transferring the finished mixture from the second mixing vessel (14) to a pastillation device (76) for pastillation of the mixture, to a granulating device or to a device for producing flakes.
11. Installation according to Claim 10, characterized in that
    provision is made of a return line (82) for returning the mixture into the second mixing vessel (14), which return line opens out into said second mixing vessel (14) preferably above the fluid surface.
12. Installation according to Claim 10 or 11, characterized in that
    the pastillation device (76) has a rotating and perforated drum (78) and a circulating cooling belt (80) .
13. Method for admixing at least one first substance and at least one second substance to a base substance for forming a mixture by means of a continuous mixing operation using a device according to one of Claims 1 to 9, wherein the method for admixing has the following features:

    a a base substance is fed to a first mixing vessel (12),

    b the first substance for admixture is fed to the base material in the first mixing vessel (12) for forming an intermediate mixture stage,

    c the intermediate mixture stage from the first mixing vessel (12) is fed to the second mixing vessel (14),

    d the second substance for admixture is fed to the intermediate mixture stage in the second mixing vessel (14) for forming the mixture,

    characterized in that
    e the feeding of the intermediate mixture stage from the first mixing vessel (12) into the second mixing vessel (14) is realized, utilizing gravitational force, by means of a connecting line (40) between the mixing vessels (12, 14), which connecting line is open during mixing operation and is situated below the fluid surfaces (42, 44) in the mixing vessels (12, 14).
14. Method according to Claim 13, wherein the method has the following feature:
    a the base substance is a melt, in particular a urea melt.

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