WO2020254863A1

WO2020254863A1 - Process and apparatus for cooling of free-flowing granulate, in particular, caustic soda prills

Info

Publication number: WO2020254863A1
Application number: PCT/IB2019/055200
Authority: WO
Inventors: Hans Rudolf Küng
Original assignee: Kueng Hans Rudolf
Priority date: 2019-06-20
Filing date: 2019-06-20
Publication date: 2020-12-24
Also published as: CN113939704A

Abstract

Process and apparatus for cooling free-flowing granulate is provided in which the granulate trickles from top to bottom by gravity in a fixed container with movable cooling surfaces attached internally.

Description

PROCESS AND APPARATUS FOR COOLING OF FREE-FLOWING GRANULATE, IN PARTICULAR, CAUSTIC SODA PRILLS

Cross Reference to Related Applications

This application claims the benefit of U.S. Provisional Application No. 62/687,280, filed June 20, 2018, the content of the entirety of which is explicitly incorporated herein by reference and relied upon to define features for which protection may be sought hereby as it is believed that the entirety thereof contributes to solving the technical problem underlying the invention, some features that may be mentioned hereunder being of particular importance.

Copyright & Legal Notice

A portion of the disclosure of this patent document contains material which is subject to copyright protection. The Applicant has no objection to the facsimile reproduction by anyone of the patent document or the patent disclosure as it appears in the Patent and Trademark Office patent file or records, but otherwise reserves all copyright rights whatsoever. Further, no references to third party patents or articles made herein is to be construed as an admission that the present invention is not entitled to antedate such material by virtue of prior invention.

Background of the Invention

Processes and apparatus for cooling granulates play an important role in a wide range of granular products in chemical and process engineering.

The present invention therefore refers to a wide range of applications in laboratories, in the chemical and food industries, in the packaging of plastics and others, in particular the cooling of caustic soda prills, which will be treated as an example below.

Sodium caustic prills are sodium hydroxide produced from anhydrous melt in a spray tower as described in the international patent application PCT/IB2018/057051. It is this fine, spherical and free-flowing granulate that is produced from the spray tower at 160°C, for example. The granulate is then cooled down to below 60°C. The granulate comes out of the spray tower at a temperature of about 160°C. The method and the apparatus are the subject of this invention.

The special materials and processes involved in prilling plants are well worth the comparatively high investment costs incurred initially. The advantage lies mainly in the fact that prills can be stored, saving considerable manpower costs at the bagging station. This is because with prills there is no wastage in storage and handling. These tiny pearls can be accurately metered to the nearest milligram, stored in silos and filled in bags or containers, with no tendency to form lumps or create dust. Caustic soda prills are universally applicable, but of particular interest when mixing of caustic soda with other granular materials is required, for example in the manufacture of detergents and cleansers.

The development of such dust-free product in a free-flowing form redefined the market for concentrated alkalis.

In 2018, 6 million tons of caustic soda were produced, and the trend is rising. Of these, about 4 million tons were in the form of flakes and only about 2 million tons in the form of prills. This is despite the fact that the latter product form has decisive advantages over flakes. Prills are a fine granulate, dust-free, free-flowing and can therefore be dosed precisely to the gram. They can easily be added to other fine products such as detergents and cleaning agents, which is typically not possible with flakes. A further advantage is that prills can be stored in silos and transported as bulk (i.e. in a tank truck). On the other hand, flakes have to be packed in plastic bags in a complex process so that they can be transported, because otherwise they would "bake together" in larger containers. The disadvantage is that prior art equipment for the production of prills incurs higher investment costs than equipment for the production of flakes. This is particularly important for plants with a production capacity of less than 300 tons per day. However, there is a great need for such plants.

The task and object of this invention is to provide a process and apparatus for cooling the prills at considerably lower investment costs than the prior art.

The following prior art is known:

According to current practice and the prior art, the prills are cooled in so-called drum coolers 100. Referring to FIG. 1, an aggregator 100 is shown from the outside. Referring to FIG. 2, the inside view of the Drum Cooler 100 with the water flowed through cooling tubes 102 is shown.

Drum coolers 100 prove to be reliable in operation and prevent unwanted abrasion of the product and the associated formation of dust. However, such drum coolers 100 are voluminous, heavy and have many construction elements such as support rings, housing seals etc. and are therefore very expensive to manufacture. This means that a drum cooler 100 is too expensive for use in prill systems, especially for smaller production plants as are in demand today. In concrete terms, plants with a production capacity of less than 300 tons of prills per 24 hours can no longer be operated economically. On the market, however, there is a demand for plants with, for example, a production capacity of 150 tons of prills per day (in 24-hour operation).

Referring now to FIGs. 3 and 4, a much more cost-effective alternative to cooling free- flowing granules is shown schematically. The material to be cooled (prills or any free-flowing granulate) flows through the apparatus 300, 400, which essentially consists of a fixed container 302, 402 and also fixed cooling surfaces 304, 404, by the effect of gravity. In the example in FIG. 3, the granulate to be cooled flows into the tubes forming the cooling surface 304, 404, the coolant, usually water, flows around the tubes. In the example of FIG. 4, it is the other way round, but the principle is the same.

However, tests with caustic soda prills have shown that the heat transfer efficiency in the 300, 400 units is low compared to the rotary drum cooler 100 described above and there is a risk of bridging and clogging. Conclusion: the procedure according to FIGs. 1 and 2 is associated with too high investment costs for the plant whereas the procedure and the plants 300, 400 according to FIGs. 3 and 4 have insufficient operational reliability.

What is needed therefore is a process and apparatus for cooling free-flowing granulates, such as prills, which meet the requirements of operational safety, protection of the product against abrasion and dust formation, prevention of blockages and air ingress, and which can be manufactured at considerably lower costs.

What is needed is a way of improving the economical operation of even smaller prill systems not previously practical. This means that a wide range of market requirements can be covered.

Still further, what is needed is an effective way of manufacturing the majority of the 6 million tons of caustic soda in the form of prills, the preferred product form.

Summary of the Invention

A process for cooling free-flowing granulate is provided including at least the step of the granulate trickling from a top to a bottom by gravity in a fixed container with cooling surfaces attached internally, in which these cooling surfaces move with respect to the fixed container.

By calculations and analogy tests, it was surprisingly found that in a system with cooling surfaces through which the material to be cooled trickles by gravity along the cooling surfaces from top to bottom, the heat transfer efficiency, i.e. the heat transfer coefficient, is substantially increased when the cooling surface is moved impulsively or reciprocated. Apparently, this results in more intensive contact between the granulate and the cooling surface and even better mixing in the granulate layers and thus improved heat transfer. It is an object of the invention to provide a process and apparatus for cooling free-flowing granulates, in particular prills which meet the requirements of operational safety, protection of the product against abrasion and dust formation, prevention of blockages and air ingress, and which can be manufactured at considerably lower costs as a further decisive feature.

It is another object of the invention to provide a way of improving the economical operation of even smaller prill sy stems possible in the first place. This means that a wide range of market requirements can be covered.

It is another object of the invention to provide an effective way of manufacturing the majority of the 6 million tons of caustic soda no longer in the form of flakes, but in the form of prills, the preferred product form.

It is another object of this invention to provide a process and apparatus for cooling the free-flowing granulate more efficiently and therefore at considerably lower investment costs than the prior art.

It is another object of the invention to produce dust free and free-flowing NaOH prills.

In another object, the invention can be adapted to make smaller prills (macro- or micro prilling technology).

Brief Description of the Figures

FIG. 1 is an exterior view of a prior art apparatus with fixed head, product inlet, and rotary drum with race rings, gear rim and gear.

FIG. 2 is an interior view of the rotary drum from FIG. 1 with cooling pipes fixed to it, cooling water inlet and outlet pipes in the center.

FIG. 3 is a cross-sectional view of a prior art granulate cooler with the product flowing through the tubes and the cooling medium outside.

FIG. 4 is a cross-sectional view of a prior art granulate cooler, where the product irrigates the cooling tubes from the outside and the cooling medium flows in the cooling tubes.

FIG. 5A is a sketch of a granulate cooler with movable cooling surfaces according to the present invention.

FIG. 5B is a top view of the drive of the granulate cooler of FIG. 5 A.

FIG. 5C is a schematic cross-sectional view of the cooler of the invention.

FIG. 5D is a schematic top view of the spiral form of the heat exchanger tubes of the invention.

FIGs. 6 A and 6B are cross-sections of heat exchanger tube configurations that can be used in FIG. 5A. FIG. 6A is a schematic view of heat exchanger tubes arranged vertically to each other, creating unfavorable inactive zones.

FIG. 6B shows a preferred arrangement of heat exchanger tubes with optimized material flow and heat transfer.

FIG. 7 is a schematic view, for comparison purposes, laying out the prill and cooling systems of the prior art and of the system according to the present invention superimposed on one another, showing the order of magnitude of the dimensions.

FIG. 8 is a top view of two alternate arrangements of the heat exchanger of the invention.

FIG. 9 is a top view of still another alternate arrangement of the heat exchanger of the invention.

Detailed Description of the Preferred Embodiment

The following description is not intended to limit the scope of the invention in any way as it is exemplary in nature, serving to describe the best mode of the invention known to the inventors as of the filing date hereof. Consequently, changes may be made in the arrangement and/or function of any of the elements described in the exemplary embodiments disclosed herein without departing from the spirit and scope of the invention.

The practical implementation of this know-how takes place in a process and apparatus as shown in simplified form in the sketch according to FIGs. 5A and 5B. It consists of a fixed container 501 in which the cooling surface, i.e. the heat exchanger 502, is accommodated. The heat exchanger 502 is attached to the central tube 503, through which the cooling water enters and exits via flexible hoses 509 and which is moved forward and backward by quarter turns with drives 507, for example.

The material to be cooled enters via feed 504 at the top and exits via exit sluice 505. Level control 508 ensures that the entire cooling surface is in contact with the product and is therefore essentially 100% effective. This is in contrast to the drum cooler described above, where only approx. 30% of the cooling tubes are immersed in the product because the drum is only partially filled. In order to achieve a comparable cooling effect with the apparatus of the present invention, only approx. 30% of the cooling surfaces of a conventional drum cooler have to be installed in the apparatus of the present invention. Although the invention is applicable to many types of free-flowing granulate, in a concrete example of a prill plant for 150 tons of prills per 24 hours (150T/D), 24 stacked layers of spirally wound cooling tubes with a diameter of 40 millimeters at a distance of 52.3 to 60 millimeters form the cooling surface of approximately 54 m². The plant has an outside diameter of 1.6 meters, a total height of 3 meters and a weight of 3000 kilograms. Referring to FIG. 7 (which shows roughly to scale, on the left, the system of the invention and on the right, a prior art cooler), a drum cooler for the same performance has a diameter of 2 meters, a length of 10 meters and a weight of 15000 kilograms. As should be clear, the size difference is enormous.

Apart from the considerably lower weight, the apparatus according to the invention does not consist of complicated mechanical components, so that the manufacturing costs are a fraction of those of drum coolers. Using the example of a plant with a capacity of 150 tons per day, manufacturing costs for the plant of the invention of approximately 150,000 USD are to be expected, whereas manufacturing costs of approximately 500,000 USD for a drum cooler with comparable capacity are to be expected.

In one embodiment, the apparatus 500, 710 according to invention enables the cooling of 6'250 kg caustic soda prills 510 from 160 to 60°C in an hour. A cross-section of the apparatus 500, 710 is shown schematically in FIG. 5A. It consists of a fixed tank 501 and an internal mobile heat exchanger 502 which is attached to the rotating central tube 503. The cooling medium, in this case water, is supplied and discharged through this central tube 503. The central tube 503 is suspended from the axial/radial bearing 506, which is guided by supports 512 below tank 501. The free-flowing granulate510 to be cooled flows via feed 504 (which may be in form of a tube) into the upper part of container 501, is distributed over the entire cross-section of heat exchanger 502, trickles through heat exchanger 502 under the influence of gravity and is cooled to 60°C and below 60°C respectively. The outlet sluice 505 is controlled by control system 508 in such a way that the heat exchanger 502 is always fully charged with free-flowing granulate 510 so that the entire exchange surface of the heat exchanger 502 is used.

Using at least two hydraulic cylinders 507, the central tube 503, and thus the heat exchanger 502, is moved forwards and backwards (i.e., reciprocated) by about 45°, typically approx. 6 times per minute. In an alternate embodiment, the reciprocation can be so rapid, impulsive and of short duration and distance (not 45° but only perhaps 2°) that the heat exchanger 502 essentially vibrates. In still an alternate embodiment, the reciprocation can be in the vertical direction over a short distance. As described above, this results in more intensive contact between the free-flowing granulate 510 and the heat exchanger 502 surface and better flow, avoiding bridging and blockages. The following specific indications of sizes refer to an example ofhow the present invention can be realized. Of course, many different sized and proportions can be used to better suit a particular application.

Container 501 has a diameter of 1 ,600 millimeter, a cylindrical height of 1 ,800 millimeter, a cone with guide bearing for the central tube 503 at the bottom and a flat lid at the top. The whole container 501 is made of about 8 millimeter thick sheet steel.

Referring to FIG. 5C and 5D, in one embodiment, the heat exchanger 502 has an effective area of 54 square meters, formed by pipes with diameter 40/36 millimeters. The pipes are formed into 24 spirals 502’, each spiral with 6 turns. The spirals are arranged stacked. Six of them are connected in series on the water side and thus form one donut-shaped unit or group 502”. The central tube 503 is of a relatively large diameter because of the limits of bending metal tube and other than a reservoir of cooling water, is not otherwise required to be so large. Recesses 503^' provide a channel for the inlet and outlet tubes to service each subgroup 502”. The heat exchanger 502 consists of four such subgroups 502” of six spirals 502’ connected in series on the water side, each subgroup with a pipe length of 108 meters and separate cooling water inlet and outlet 516’ and 518’. In this arrangement, each subgroup 502” is serviced by separate inlet and outlets 516’ and 518’, to minimize hydraulic resistance/back pressure and improve flow while maximizing the cooling capacity of the system 500, 710 of the invention.

The arrangement of the pipes 602 is shown in more detail in cross-section in FIGs, 6A and 6B. FIG. 6A shows a less than optimal arrangement of pipes 602 where granulate can pass between the pipes 602 without touching a cooling surface thereof. FIG. 6B shows a preferred arrangement of the pipes 602, whereby in each position, the pipes 602 are offset from the previous position by a certain transverse distance y (transverse to the axis of the spiral) leaving a suitable space therebetween for the free-flowing granulate 510. The distance z between spirals 502’ is also selected to optimize contact but prevent blockages. Thus, the distance that a particle (i.e. prills or free-flowing granulate 510) must travel to the next cooling surface (which is the surface of an adjacent tube 602) is selected to be minimal such that the heat transport and cooling effect is optimized in a way that avoids blockages. As an option, every second spiral of the 24 spiral stack is "reversed", i.e. wound in opposite directions. This means that one spiral works the free-flowing granulate 510 to the outside during the reciprocal movement, and the next spiral to the inside. In other words, as one pipe of a spiral moves in one direction, it moves the surrounding free-flowing granulate to the inside and, then the direction or rotation changes, to the outside, all while the particulate trickles down under the effect of gravity. Another spiral, having an opposite spiral direction, then may be positioned to move the free-flowing granulate that have moved to the outside, generally back to the inside. This results in a "three-dimensional" movement of the free-flowing granulate 510: vertically by gravity, horizontally/tangenti ally by rotation and horizontally/radially by the reversal of the spirals, resulting in a surprisingly high heat transfer efficiency compared to prior art equipment.

In this example, 280,000 kcal per hour must be removed from the chilled goods, i.e. from the free-flowing granulate 510. With a cooling water inlet temperature of 20°C and an outlet temperature of 40°C, in one embodiment, a cooling water quantity of 14 cubic meters per hour is required. The water enters via flexible hoses 509 through an entry port 514 into the reciprocating central tube 503 and from there though manifolds 516’ to each subgroup 502” of the heat exchanger 502 and then back again though manifolds 51 8’ and an exit port 520 via the other flexible hose 509. The diameters of the entry and exit ports 514 and 520 as compared to the diameters of each of the manifolds 516’ and 518’ are not to scale. Ideally, the entry and exit ports 514 and 520 are capable of transporting four times that of an individual manifolds 516’ and 518’ which connect to one of four subgroups 502” of heat exchangers 502 in order to minimize hydraulic backpressure.

FIG. 7 shows for dimensional comparison purposes, a free-flowing granulate cooler 706 according to the prior art and the cooler 710 according to the invention fed in this example, by a prill forming device 712. Note that due to the orientation of the cooler 706, it does not take advantage of gravity as does the cooler 710 of the invention.

The invention can be summarized by the following feature sets:

1. A process for cooling free-flowing granulate including the steps of:

a. allowing granulate to trickle from a top to a bottom of a fixed container under the effect of gravity against cooling surfaces disposed within the fixed container, and

b. moving the cooling surfaces with respect to the fixed container, thereby forcing the granulate to frequently contact the cooling surfaces.

2. The process of feature set 1 , wherein the movement is axial and reciprocal.

3. The process of feature set 1, wherein the movement is rotational and the cooling surfaces are formed as flat spirals optionally alternately wound in different directions such that, as the granulate moves vertically, the granulate is alternatively moved to the outside and then to the inside of the fixed container. The process of feature set 1, wherein the movement is rotational and the cooling surfaces are formed as nested axially wound spirals, optionally alternately wound in different directions such that, as the granulate moves vertically, the granulate is alternatively moved tangentially from one side to the other side inside of the fixed container. The process of feature set 1 , wherein the movement is a reciprocal movement through a selected angle and then reversed. The process of feature set 5, wherein the selected angle is approximately 45°. The process of feature set 5, wherein the reciprocal movement has a frequency of approximately 6 per minute. The process of feature set 1 , wherein the movement is a vertical movement. The process of feature set 1 , wherein the movement is a vibrational movement. The apparatus of feature set 1 wherein the movement is rotational, oscillating forward and backwards or slowly rotating. An apparatus for carrying out the process of feature set 1 , wherein cooling surfaces are attached to a central tube which is rotatably mounted inside the container and connected to hydraulic cylinders adapted to set the cooling surfaces in motion. The apparatus of feature set 11, wherein the cooling surfaces are disposed on hollow cylindrical walls which are optionally nested. The apparatus of feature set 11 wherein the cooling surfaces are disposed on cooling pipes. The apparatus of feature set 13 wherein the cooling pipes are formed is a flat spiral form. The apparatus of feature set 13, wherein the cooling pipes are formed in a star shape. 16. The apparatus of feature set 13, wherein the cooling pipes are formed in flat concentric circles.

17. The apparatus of feature set 1, wherein the cooling surfaces consist of tubes arranged spirally or concentrically in several layers or of hollow cylindrical plates.

18. A free-flowing granulate cooled according to the process of one of feature sets 1 to 9.

In one advantage, the invention provides a process and apparatus 500, 710 for cooling free- flowing granulates 510, such as prills, which meet the requirements of operational safety, protection of the product against abrasion and dust formation, prevention of blockages and air ingress, and which can be manufactured at considerably lower costs.

In another advantage, the invention provides a way of improving the economical operation of even smaller free-flowing granulate cooling systems 500, 710 which were not economical using the technology of the prior art. This means that a wide range of market requirements can be covered.

In another advantage, the invention provides an effective way of manufacturing the majority of the 6 million tons of caustic soda no longer in the form of flakes, but in the form of prills 510, the preferred product form.

In another advantage, the production of dust free and free-flowing NaOH prills 510 is made possible.

In another advantage, production capacity can be increased from, say 150 tons per day up to 500 tons per day (NaOH 100%).

In another advantage, the invention can be adapted to make smaller prills 510 by scaling size appropriately.

All the above information is exemplary and may therefore deviate from the values stated. This also applies to the design of the apparatus. For example, referring to FIG. 8, three alternate exemplary arrangements 800, 802, 803 of the heat exchanger of the invention include (1) six nested vertical spiral screw forms (with 24 turns) with each adjacent screw form taking an opposite direction (right hand screw and left hand screw), (2) 24 stacked, flat concentric interconnected circular pipes, and (3) six nested hollow cylindrical forms. Referring to FIG. 9, still another alternate arrangement 900 of the heat exchanger of the invention is a star-shaped form. Thus, the heat exchanger 500, 710 can be designed as nested vertical hollow cylinders 804, as nested screw forms 806 instead of flat spirals 502’ or as star-shaped horizontal tubes 900. And the direction of reciprocation of the heat exchanger may be carried out as a vertical movement instead of a horizontal rotary movement. Vertical movement can be imparted by a cam (not shown) at acts on the lower axial guide 506 to move the axis up and down.

As will be appreciated by skilled artisans, the present invention may be embodied as a system, a device, or a method.

The specification and figures should be considered in an illustrative manner, rather than a restrictive one and all modifications described herein are intended to be included within the scope of the invention claimed. Accordingly, the scope of the invention should be determined by the appended claims (as they currently exist or as later amended or added, and their legal equivalents) rather than by merely the examples described above. Steps recited in any method or process claims, unless otherwise expressly stated, may be executed in any order and are not limited to the specific order presented in any claim. Further, the elements and/or components recited in apparatus claims may be assembled or otherwise functionally configured in a variety of permutations to produce substantially the same result as the present invention. Consequently, the invention should not be interpreted as being limited to the specific configuration recited in the claims.

Benefits, other advantages and solutions mentioned herein are not to be construed as critical, required or essential features or components of any or all the claims.

As used herein, the terms "comprises", "comprising", or variations thereof, are intended to refer to a non-exclusive listing of elements, such that any apparatus, process, method, article, or composition of the invention that comprises a list of elements, that does not include only those elements recited, but may also include other elements such as those described in the instant specification. Unless otherwise explicitly stated, the use of the term“consisting” or “consisting of’ or“consisting essentially of’ is not intended to limit the scope of the invention to the enumerated elements named thereafter, unless otherwise indicated. Other combinations and/or modifications of the above-described elements, materials or structures used in the practice of the present invention may be varied or adapted by the skilled artisan to other designs without departing from the general principles of the invention.

The patents and articles mentioned above are hereby incorporated by reference herein, unless otherwise noted, to the extent that the same are not inconsistent with this disclosure.

Other characteristics and modes of execution of the invention are described in the appended claims. Further, the invention should be considered as comprising all possible combinations of every feature described in the instant specification, appended claims, and/or drawing figures which may be considered new, inventive and industrially applicable.

Copyright may be owned by the Applicant(s) or their assignee and, with respect to express Licensees to third parties of the rights defined in one or more claims herein, no implied license is granted herein to use the invention as defined in the remaining claims. Further, vis-a-vis the public or third parties, no express or implied license is granted to prepare derivative works based on this patent specification, inclusive of the appendix hereto and any computer program comprised therein.

Additional features and functionality of the invention are described in the claims appended hereto and/or in the abstract. Such claims and/or abstract as well as referenced documents, are hereby incorporated in their entirety by reference thereto in this specification and should be considered as part of the application as filed.

Multiple variations and modifications are possible in the embodiments of the invention described here. Although certain illustrative embodiments of the invention have been shown and described here, a wide range of changes, modifications, and substitutions is contemplated in the foregoing disclosure. While the above description contains many specific details, these should not be construed as limitations on the scope of the invention, but rather exemplify one or another preferred embodiment thereof. In some instances, some features of the present invention may be employed without a corresponding use of the other features. Accordingly, it is appropriate that the foregoing description be construed broadly and understood as being illustrative only, the spirit and scope of the invention being limited only by the claims which ultimately issue in this application.

Claims

What is claimed is:

1. A process for cooling free-flowing granulate including the steps of:

2. The process of claim 1, wherein the movement is axial and reciprocal.

3. The process of claim 1, wherein the movement is rotational and the cooling surfaces are formed as flat spirals optionally alternately wound in different directions such that, as the granulate moves vertically, the granulate is alternatively moved to the outside and then to the inside of the fixed container.

4. The process of claim 1, wherein the movement is rotational and the cooling surfaces are formed as nested axially wound spirals, optionally alternately wound in different directions such that, as the granulate moves vertically, the granulate is alternatively moved tangentially from one side to the other side inside of the fixed container.

5. The process of claim 1, wherein the movement is a reciprocal movement through a selected angle and then reversed.

6. The process of claim 5, wherein the selected angle is approximately 45°.

7. The process of claim 5, wherein the reciprocal movement has a frequency of approximately 6 per minute.

8. The process of claim 1, wherein the movement is a vertical movement.

9. The process of claim 1, wherein the movement is a vibrational movement.

10. The apparatus of claim 1 wherein the movement is rotational, oscillating forward and backwards or slowly rotating.

11. An apparatus for carrying out the process of claim 1, wherein cooling surfaces are attached to a central tube which is rotatably mounted inside the container and connected to hydraulic cylinders adapted to set the cooling surfaces in motion.

12. The apparatus of claim 1 1, wherein the cooling surfaces are disposed on hollow cylindrical walls which are optionally nested.

13. The apparatus of claim 1 1 wherein the cooling surfaces are disposed on cooling pipes.

14. The apparatus of claim 13 wherein the cooling pipes are formed is a flat spiral form.

15. The apparatus of claim 13, wherein the cooling pipes are formed in a star shape.

16. The apparatus of claim 13, wherein the cooling pipes are formed in flat concentric circles.

17. The apparatus of claim 1 , wherein the cooling surfaces consist of tubes arranged spirally or concentrically in several layers or of hollow cylindrical plates.

18. A free-flowing granulate cooled according to the process of one of claims 1 to 9.