WO2020053629A1

WO2020053629A1 - Method and apparatus for the production of caustic soda prills

Info

Publication number: WO2020053629A1
Application number: PCT/IB2018/057051
Authority: WO
Inventors: Hans Rudolf Küng
Original assignee: Kueng Hans Rudolf
Priority date: 2018-09-14
Filing date: 2018-09-14
Publication date: 2020-03-19
Also published as: CN113015699A

Abstract

A plant (300, 400, 500) for the production of caustic soda prills is provided. The plant includes a prill chamber (306, 406, 506) with a spraying unit (324, 424, 524) in the form of a rotating container (302, 402, 502) therein. The rotating container has a perforated lower portion thereof which has downwardly directed bores which act as openings for the escaping liquid caustic soda jet (319, 419, 519). The lower portion may include a base which is preferably flat, but can also have a concave, convex or conical shape.

Description

METHOD AND APPARATUS FOR THE PRODUCTION OF

CAUSTIC SODA PRILLS

Cross Reference to Related Applications

This application claims the benefit of U.S. Provisional Application No. 62/558,904, filed September 15, 2017, 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

Caustic soda prills consist of water-free sodium hydroxide (NaOH) which is transferred as a melt (also called caustic soda melt) from a concentrator module, with a temperature typically between 330 and 400°C to a prill module. In the prill module drops are generated from the melt, cooled and solidified in a gaseous environment to form prills. The prills are spherical in shape and free from dust, do not agglomerate and therefore are easy to store and dose. Prills are increasingly becoming the most common product form of solid caustic soda.

Caustic soda prills in the context of the development and the importance of the chlorine alkali industry:

In the diagram of FIG. 9A, several processes used in the chlorine alkali industry are schematically displayed. Caustic soda, the source material for caustic soda prills, is obtained by means of the electrolysis of sodium chloride solutions. Apart from caustic soda which is the material of prime interest for the Invention, chlorine and hydrogen are thereby produced as well.

As the same is known in the art, we discuss neither the electrolysis nor the evaporation plants for NaOH for the production of a water-free caustic soda melt (typically 50% NaOH by weight) which forms the basis for caustic soda in solid form, nor do we discuss the processes for the production of sodium carbonate and calcium chloride. Nevertheless, the products which can be obtained through the process for the production of solid caustic soda are shown in FIG. 9B. They will be described in the following.

According to a known process, the caustic soda melt is poured into iron drums, wherein it solidifies upon cooling. This process is usually applied in situations in which no infrastructure exists for the transport and temporary storage of liquid caustic soda. At the user facilities, the solid material is dissolved and diluted to the required concentration of the NaOH solution for example in the textile industry. This is an elaborate and hazardous procedure. Nowadays it is only used for marginal quantities in the market.

Significant progress over the previously described process of pouring melts into iron drums resulted from the introduction of flake machines. Herein a rotating, internally cooled drum is immersed into a tub containing the liquid caustic soda melt. Thereby a film with a thickness of about 1 mm forms on the drum. During one revolution of the drum the film solidifies and cools to typically 60°C. Subsequently, the solidified film is scratched from the drum by a scrubber and formed into so-called flakes (also called pellets). The latter can be filled into packaging units, transported and dissolved as well as diluted to a concentration suitable for a particular application by the user. This is a significantly simpler procedure compared to pouring the melt into iron drums as described above.

One disadvantage however is the tendency of flakes to coalesce. Even more importantly, the flakes are not free-flowing. This renders the storage in silos impossible as well as the transport in containers and tanks. Fine dosing and admixing to granulate shaped products such as detergents are equally impossible.

In so-called prill plants, a product is created which is dust-free, uniformly sized and free- flowing. This has the advantage of lacking storage problems because the prills (shaped as little pearls) can be stored in silos, or filled into sacks, containers, etc., without causing clumping or dust formation. Furthermore, the prills can be dosed to a precision of grams.

Prills are therefore ideal for a large number of applications and for various branches of industry and service sectors. This includes both laboratories and large consumers. Prills are particularly suitable for applications in which caustic soda is mixed with other granulates, such as cleaning agents and detergents. This form of product formation is pioneering.

About 6 million tons of solid caustic soda have been produced in 2017. This corresponds to approximate 18‘000 tons per day. A large fraction of this quantity was marketed in the form of flakes because investment costs for state of the art prill plants are significantly larger than for flake plants. The high investment costs for state of the art prill plants are particularly uneconomical for daily production volumes below 300 tons. The reason is that state of the art prill chambers need to be dimensioned independently of the throughput which makes them too expensive for smaller production volumes.

According to the Invention, the investment costs of prill plants can be significantly lowered. In view of the unique advantages of the product form of prills, it is therefore expected that its market share will rise fast. In the future, the daily production volume of 18Ό00 tons of caustic soda will in large part be processed in the form of prills which is advantageous for manufacturers of prill plants, as well as of producers and users of the prills.

Process and apparatus for the production of caustic soda prills according to the state of the art:

Caustic soda is sodium hydroxide (NaOH) which has been concentrated to a virtually water-free melt and subsequently transformed to a solid product. The market favors delivery in the form of“prills”. These are little spheres with diameters in the range of millimeters, which are free from dust and free-flowing and thus suitable for packaging, storage and diverse applications.

The prills are manufactured in prill plants (see FIG. 9A) in which a caustic soda melt coming from an upstream concentration plant at a temperature of typically 330 to 400°C is shaped into fine liquid jets which transform into drops cooling down in an air stream, and finally solidifying into millimeter sized globules at around 320°C.

In a state of the art process schematically depicted in FIG. 1, liquid jets 116 are generated by introducing the melt into a fixed container 104, the bottom of which is formed as a perforated plate 106 with fine bores. This process has the disadvantage that the drops 114 formed from the liquid jet 116 have different size and are accompanied by a fog of so-called satellite drops. These suspended satellite drops absorb moisture from the cooling ambient air 112. As a result the interior of the apparatus becomes coated with a sticky layer of caustic soda and hence must be frequently cleaned, which leads to undesirable interruptions of the production and economic loss. The described process therefore has disadvantages in terms of product quality and operational readiness. In the apparatus and process 200 according to FIG. 2, liquid jet and drop formation are realized by a rotating container 202, which may have a shape of a cylinder, with lateral bores 204 in its jacket. In the following, this cylinder will also be called a spraying device, spraying module or spraying unit.

As a result of the rotation, the jets 206 are subject to a lateral momentum while the air supply 214 is essentially non-rotating. This has a beneficial effect on the drop formation. The drops 220 have substantially equal diameter, and satellite drops are not detectable. With the apparatus 200 it is thus possible to generate a uniform, dust-free and pourable product which is also known under the name of“prills”. These prills are ideal for storing, dosing and admixing to other fine-grained products such as laundry detergents and cleaning agents.

The supply 210 of ambient air 214 to the prill chamber 212 is provided from above and is dosed in such a way that the temperature inside is nowhere below the dew point. In contrast to the method of FIG. 1, the prills therefore do not absorb any humidity from the ambient air 214. As a result, high quality of the product and safe operation are guaranteed.

The apparatus 200 has, on the other hand, the following significant disadvantage: the cylinder 202 with the lateral bores 204 has to rotate at high speed, for example at 600 rpm, in order for a sufficiently thick layer of caustic soda to accumulate on its inner surface 216 and in order to accelerate the jet 206 in a way sufficient for the generation of ideal drops. In accordance with the high rotation speed, the radial velocity of the drops, i.e., the velocity towards the inner surface 216 of the prill chamber 212, is rather high, for example 7 - 8 m/sec. Since, however, the semi-liquid drops 220 must not touch the inner surface 216 of the prill chamber 212, the diameter of the latter needs to be correspondingly large, typically about 14 m.

It is precisely this requirement which makes the entire state of the art plants 200 voluminous and expensive, such that their operation is uneconomical for throughputs below 300 tons per day. As a matter of fact, the diameter of the prill chamber 212 has to be kept at typically 14 m even for smaller production volumes because of similar requirements for the particle speed. This makes the costs of such a plant too expensive in relation to its production rate.

Many producers are, however, looking for prill plants which can be economically operated also in a lower throughput range.

The procedural and economical importance of the Invention can be seen in the following context: In 2017 approximately l8‘000 tons per day of solid caustic soda have been produced worldwide, the largest fraction of which still in the form of flakes. There is a need for low investment cost prill plants for the replacement of conventional plants producing flakes.

There is a need for significant cost reductions of prill plants.

There is a need for prill plants that can be operated economically for a large range of throughput conditions, including throughputs below 300 tons per day.

Summary of the Invention

A plant for the production of caustic soda prills is provided. The plant includes a prill chamber with a spraying unit in the form of a rotating container therein. The rotating container has a perforated lower portion thereof which has downwardly directed bores which act as openings for the escaping liquid caustic soda jet. The lower portion may include a base which is preferably flat, but can also have a concave, convex or conical shape.

In one embodiment, the plant for the production of caustic soda prills has a prill chamber with a spraying unit in the form of a rotating cylinder with a perforated bottom plate having downwardly directed bores as openings for the escaping liquid caustic soda jet. The bores of the bottom plate may be concave, a convex, a flat and a conical shape. Furthermore, the bottom of the prill chamber may contain, in one embodiment, a fluidized bed which is created by air blown into the prill chamber.

An upstream concentration apparatus supplies the liquid caustic soda melt to the spraying unit by gravity. The diameter of the prill chamber is in the range of about 4 - 6 m and its height in the range of about 7 - 10 m. The present invention provides as well a method for the production of prills, wherein the rotation speed of the rotating cylinder of the spraying unit is chosen to adjust the radial velocity of the drops in the direction of the inner wall of the prill chamber to about 2.3 - 2.5 m/s.

It is an object of the Invention to replace current production plants for caustic soda flakes with prill plants in the future.

It is another object of the Invention to provide an apparatus and process which have the advantages over apparatus and process of FIG. 2 in terms of product quality and production readiness, but which can be realized at significantly lower costs.

Brief Description of the Figures FIG. 1 is a cross-sectional view of a prior art prilling system with static prilling nozzles and an open cooling air supply.

FIG. 2 is a cross-sectional view of a prior art prilling system with a rotating spraying module, horizontally escaping jets of molten caustic soda and a regulated air supply.

FIG. 3 is a cross-sectional view of a prilling system with a rotating spraying module comprising a cylinder with vertical rotational axis, vertically escaping jets of molten caustic soda and a regulated air supply.

FIG. 4 is a cross-sectional view of a prilling system with a rotating spraying module comprising a cylinder with a vertical rotational axis, vertically escaping jets of molten caustic soda, a regulated air supply and with a bottom designed as a fluidized bed.

FIG. 5 is a more detailed cross-sectional view of a prilling system with a rotating spraying module comprising a cylinder with a vertical rotational axis, vertically escaping jets of molten caustic soda, a regulated air supply and with a bottom designed as a fluidized bed.

FIG. 6A is a cross-sectional view of a spraying unit with partially domed bottom portion.

FIG. 6B is a cross-sectional view of a spraying unit with flat bottom portion.

FIG. 6C is a cross-sectional view of a spraying unit with convex conical bottom portion.

FIG. 6D is a cross-sectional view of a spraying unit with spherical bottom portion.

FIG. 7A is a perspective view of a fluidized bed.

FIG. 7B is a cross-sectional view of one variant of an air nozzle suitable to be used in the fluidized bed system.

FIG. 7C is a cross-sectional view of another variant of an air nozzle suitable to be used in the fluidized bed system. FIG. 8A is a front view of the prilling system as per FIG. 3 with gravity flow of the molten caustic soda from the top mounted concentrator to the prilling system.

FIG. 8B is a top view of FIG. 8 A.

FIG. 9A is a diagram illustrating basic processes in the chlorine-alkali industry.

FIG. 9B is a diagram illustrating products which can be obtained through the process for the production of solid caustic soda.

FIG. 10 is a comparison of typical dimensions of the device shown in FIG. 2 and the device shown in FIG. 4 and FIG.5.

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.

Referring now to FIG. 3 embodiment 300 of a prill plant comprises, a prill chamber 306, a spraying unit 302 with downwardly directed bores in the rotating container, preferably cylinder instead of the lateral bores 204 in container 202, preferably cylinder of FIG. 2. The prill chamber 306, 406, 506, 806 further contains a gaseous environment. During operation, air from the environment is continuously supplied into the prill chamber 306 via a feeder 340 while a fan 336 continuously guides air out of the prill chamber 306.

Surprisingly, calculations and tests have revealed that with a spraying unit, wherein the bores are arranged on the bottom portion 610, 620, 630, 640 of the container, preferably cylinder, ideal drop formation can be achieved at significantly lower rotation speeds of, for example, 120 rpm. Because of the lower rotation speed and the absence of the lateral bores, the radial velocity of the liquid caustic soda jets 319, 419, 519, later transformed into prill drops 320, in the direction of the inner wall 304, 404, 504 of the prill chamber 306, 406, 506, 806 is on the order of 2.4 m/s instead of the 7.8 m/s of prior art prill plants. The diameter of the prill chamber 306, 406, 506, 806 can therefore be reduced from the prior art value of typically 14 m to about 4 - 6 m. The values given below have been calculated on the basis of a diameter of 5 m. The corresponding weights of the prill chambers amount to about 40Ό00 kg for state of the art plants and 16’OOQ kg for plants of the Invention. The resulting cost reduction is enormous.

The radial velocity of the jets towards the inner wall 304, 404, 504 of the prill chamber 306, 406, 506, 806 may vary between 1.5 m/s and 3 m/s and is chosen as a function of the diameter of the prill chamber 306, 406, 506, 806 and as a function of the number of rotations per second of the spraying unit. It is known that a radial velocity below 1.5 m/s leads to unfavorable drop formation from the liquid stream. Furthermore, radial velocity above 3 m/s would require an increase of the diameter of the prill chamber 306, 406, 506, 806 in order to avoid contact of the drops with the inner wall 304, 404, 504 prematurely.

In a preferred embodiment, the spraying unit has a diameter of about 0.4 m and rotates at about 120 rpm. This results in a radial velocity of about 2.4 m/s.

Experiments have also shown that plants according to the Invention allow for a reduced height compared to state of the art plants. Typically, the height at the level of entry 310, 410, 510, 810 to the spraying modules 324, 424, 524, 824 is reduced by about 9 m, which permits the upstream concentrator module 412, 512, 812 for the caustic soda melt to be positioned in such a way that the melt flows towards the spraying module 324, 424, 524, 824 in the prill chamber 306, 406, 506, 806 under the influence of gravity. This essentially eliminates the costs of pump and control systems for the delivery of the caustic soda melt which are required in the state of the art systems. Such pump and control systems result in significant costs for installation and maintenance in a prior art apparatus.

Referring now to FIG. 4 and in more detail to FIG. 5, embodiment 400, 500 of the Invention comprises a prill chamber 406, 506, the bottom of which is implemented in the form of a fluidized bed 414, 514. This is a known technology, which, however, has not to date been used in caustic soda prill plants. The fluidized bed technology is used for a large number of processes in the industry. For example, for the production of CaCl₂ granulate, as shown in FIG. 9A or NaCOa granulate and other substances in granulate form. Other applications are drying, heating or cooling granulates of different medias in granulate form.

Up to now, the fluidized bed process has not been used in caustic soda prilling plants, as prill chambers of state of the art technology have a large diameter, typically about 14 m. In order to properly operate, a fluidized bed requires to cover a majority of a bottom area inside a prill chamber, which is in the state of the art prill chambers distinctly larger than in prill chambers of the present invention. The use of fluidized beds in prill chambers of state of the art would therefore lead to high initial cost for a large fluidized bed. Furthermore, a proper operation of such a large fluidized bed would require a large volume flow of air in order to keep prills hovering. The creation of a sufficient large volume flow would require investment on sufficient strong ventilators and would lead to increased operation costs. In contrast, the bottom area inside the prill chamber (306, 406, 506) of the present invention is substantially smaller which makes, as a consequence, the use of a fluidized bed economically worthwhile.

According to the present invention, the fluidized bed 414, 514 is blown into from below by a part of the air flow 416, 516 introduced into the prill chamber 406, 506. The dropping prills 420, 520 are swirled about in a region 422, 522 and simultaneously partially cooled from about 230°C to l60°C.

This has at least the following positive effects:

a) The falling height of the prills 420, 520 and with it the height of the prill chamber 406, 506 can be further reduced with respect to the one of FIG. 3 since the prills are gently stopped in the fluidized bed 414, 514 and further cooled.

b) The diameter of the prill chamber 406, 506 can be further reduced, because the jets expand less in the radial direction from the rotation axis 426 of the spraying module 424, 524, 824.

c) The cooling system external to the prill chamber 406, 506 can be dimensioned smaller and thus cheaper because of the additional pre-cooling in the whirl region 422, 522.

In the following, the performance of the apparatus and process of embodiment 400, 500 schematically shown in FIG. 5 will be calculated for a diameter of the prill chamber 406, 506 of 5 meters and a height of 8 meters, which generates diameter of prills 420, 520 of about 0.5 - 1.2 mm.

The spraying module 424, 524, 824 typically has 1'200 - 1'300, preferably about 1 '250 downwardly oriented bores on the bottom with a diameter of about 0.5 mm. The exit velocity of the liquid jets amounts to about 5 m/sec. These parameters result in the throughput cited above of 6250 kg of prills per hour. In order to achieve a lower or higher throughput, the number of bores may be adapted accordingly.

In the event a diameter of the prills 420, 520 is dimensioned to be less than 0.5mm, the diameter of the prill chamber 306, 406, 506, 806 can be less than 5 m, e.g. 4.5m or 4m. For a preferred diameter of the prills 420, 520 of about 0.5 - 1.2 mm, it is technically possible to choose a larger diameter of the prill chamber 306, 406, 506, 806. The apparatus would work with a diameter of the prill chamber 306, 406, 506, 806 of e.g. 5.5m, 6m, or more. However, this leads to higher costs because the chamber becomes unnecessary large.

In the following portion of this description, the functionality, context and practical operational limits of the spraying unit 424, 524, 824 are described. The exit velocity of the caustic soda melt depends on the hydrostatic pressure given by the level of the melt in the spraying unit 424, 524, 824. A higher level requires a longer spraying unit. For example, a liquid column of a height of 0.8 m yields an exit velocity of about 4 m/sec; 1.25 m yields about 5 m/sec; and 1.8 m finally about 6 m/s.

We have empirically found that for a caustic soda melt with a temperature in the range between 325°C and 340°C at the entrance to the spraying module 424, 524, 824, an exit velocity on the order of 5 m/s leads to the favorable form of the product, i.e. fine grained, uniform and dust-free.

All parameters can be varied within practically determined limits.

Bores with diameters below 0.3 mm are hard to manufacture and tend to clog. For diameters above 0.7 mm, the prills become larger than desired, and their cooling requires a larger height of the prill chamber.

For exit velocities below 4 m/s, the drops become too large, and velocities above 7 m/s result in a dusty product.

From these considerations it follows that the optimized parameters are a bore diameter of in the range of about 0.3 - 0.7mm, preferably 0.5 mm and an exit velocity in the range of about 4 - 7 m/s, preferably 5 m/s.

The spraying units 424, 524, 824 are preferably equipped with exchangeable bottom plates 610, 620, 630 each having different numbers of bores such that the plant can be run under optimized conditions for varying throughputs and operational parameters. A lower number of bores than in the example above, for example 1200, 1000, 800, 500, 100, yield a lower production rate. Larger numbers of bores, such as 1300, 1500, 1700, 2000, result, on the other hand, in higher production rates. The thickness or length of the bores are typically 0.5— 2.0 mm, preferably between 0.5 - 1.0 mm.

The form of the bottom portion 610, 620, 630, 640 of the spraying unit 424, 524, 824 may be slightly concave, convex, flat, spherical or slightly conical. For concave and conical shaped bottom plates, the bores are slightly tilted toward the wall of the prill chamber with respect to the rotation axis of container, preferably a cylinder 302, 402, 502. In other words, they are downwardly oriented. The respective embodiments are depicted in FIGS. 6A - 6D. FIG. 6 A is an embodiment with a partially domed bottom plate 610. FIG. 6B is an embodiment with a flat bottom plate 620. FIG. 6C is an embodiment with a convex conical bottom plate 630. FIG. 6D is an embodiment with spherical bottom plate 640.

The concentrator 412, 512 in which the water-free NaOH melt is generated, is arranged at a height permitting the supply of the melt to the spraying module 424, 524, 824 by gravity. The throughput of the plant can therefore be regulated simply by the supply of so-called dilute caustic melt to the concentrator 412, 512.

As exemplified in FIGS. 7B and 7C, the fluidized bed 414, 514 is blown into from below by the exhaust air component 416, 516 from the prill chamber 406, 506, 806 regulated by ventilator 430 (FIG. 4), 530 (FIG. 5) through nozzles 532 (FIG. 5). The rate of air flow is controlled in such a way that the prills 420, 520 are kept hovering within a layer of a typical height of 15 - 25 cm, 20 - 50 cm, or 20 - 60 cm.

The height of the layer can be adjusted by a flap 534 (FIG. 5). The prills leave the fluidized bed continuously by overflow over the flap 534 (FIG. 5) and the exit lock. The flap can be flipped horizontally to permit emptying the fluidized bed 414, 514. The ambient air, the flow rate of which is controlled by the exhaust ventilator 436, 536, flows through a feeder 540 (e.g. a ring nozzle) into the prill chamber 406, 506, 806.

The relative sizes of FIGS. 1 - 4 are shown approximately to scale and illustrate typical dimensions of the respective prill chambers. A comparison of typical dimensions of prior art plants 200 with the embodiment 400, 500 of the Invention can be seen in FIG. 10 in which FIG.2 and FIG. 4 have been superimposed. The dimensions are independent of the throughput of the plants. The typical weight of a plant according to FIG. 2 is about 40Ό00 kg, one according to FIG. 3 about 16’ 000 kg, and one according to FIG. 4 about 8400 kg. This illustrates the lower investment costs of the plants of the Invention compared to prior art plants. The differences are significant so that it becomes economical to produce and apply more of the yearly production of 6 million tons of caustic soda in the form of prills.

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 explicitely 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 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

1. A plant (300, 400, 500) for the production of caustic soda prills, comprising a prill chamber (306, 406, 506) with a spraying unit (324, 424, 524) in the form of a rotating container (302, 402, 502) with a perforated lower portion thereof comprising downwardly directed bores as openings for the escaping liquid caustic soda jets (319, 419, 519).

2. The plant of claim 1 , wherein the rotating container is substantially cylindrical in form.

3. The plant of claim 1, wherein the prill chamber is substantially cylindrical in form.

4. The plant of claim 1, wherein the downwardly directed bores are substantially vertical.

5. The plant of claim 1, wherein the downwardly directed bores are disposed about 5 degrees to 60 degrees from the vertical, disposed toward an interior wall of the prill chamber.

6. The plant of claim 1 , wherein the downwardly directed bores are disposed downwardly from about 30 degrees to about 85 degrees from the horizontal, disposed toward an interior wall of the prill chamber.

7. The plant of claim 1, wherein the lower portion of the spraying unit comprises an interchangeable bottom portion.

8. The plant of the above claim, wherein the bores are disposed in the lower portion of the rotating container at least partially in a lower end of the outer most surface of the rotating container.

9. The plant of claim 1 wherein the lower portion of the spraying unit comprising the bores has a shape chosen from one of the group of shapes consisting of a concave, a convex, a flat and a conical shape.

10. The plant of claim 1, wherein the bottom of the prill chamber (406, 506) contains a fluidized bed (414, 514) into which air (416, 516) is blown.

11. The plant of claim 10, wherein the air (416, 516) is suck by a ventilator (430, 530) from air exhausting the prill chamber.

12. The plant of claim 1, wherein an upstream concentration (412, 512, 812) device supplies the liquid caustic soda melt to the spraying unit by gravity.

13. The plant of claim 1 , wherein the prill chamber (306, 406, 506) has a major diameter in the range of 4 - 15 m, preferably of 4 - 10 m, and more preferably of 4 - 6 m.

14. The plant of claim 1 , wherein the prill chamber (306, 406, 506) has a height in the range of 7 - 15 m, preferably of 7 - 10 m, and more preferably of 7 - 8 m.

15. A method for the production of prills made of caustic soda melt using the plant of claim 1, the method having the following steps:

(a) concentrating sodium hydroxide (NaOH) into caustic soda, a water-free melt, in a concentrator (412, 512, 812);

(b) preferably gravity feeding the melt at a temperature of 330 to 400°C into the rotating container or spraying unit (302, 402, 502, 324, 424, 524) within the prill chamber (306, 406, 506) in which the rotation speed of the rotating container is chosen to control a radial velocity of the liquid jets (319, 419, 519) in the direction of the inner wall (304, 404, 504) of the prill chamber (306, 406, 506) to about 2.4 m/s, thereby generating liquid jets (319, 419, 519) by introducing the melt into the container, the bottom of which is formed as a perforated plate with fine bores;

(c) driving the melt, under hydraulic pressure and centripetal force, through the bores in the rotating container, thereby creating fine liquid jets (319, 419, 519) which transform the melt into drops cooled down in a gaseous environment and an air stream within the prill chamber, solidifying the melt into millimeter sized globules at around 320°C; and

(d) at the same time, supplying ambient air to the prill chamber, dosed in such a way that the temperature inside is nowhere below the dew point.