IL127841A - Salt purification facility comprising a vertically standing purification vessel with at least one conical area - Google Patents

Abstract

An installation for purifying particulate solids, especially a salt purification facility, comprises a vertically standing purification vessel (1) which has on top a fill aperture (10) for the solids to be purified, below an outlet aperture (11) for the purified solids and at least one conical region (12, 13). At least one feed line (30, 31) into the purification vessel (1) and at least one downwardly directed and downwardly widening nozzle (33) are provided to feed in a purification brine in counterflow to the flow direction of the solids to be purified. The at least one conical region (12, 13) of the purification vessel (1) has an angle of conical opening of 10 DEG to 30 DEG . This prevents clumping or channeling within the purification vessel, thus enhancing efficiency and prolonging uninterrupted service life without impairing the action of any downstream processing apparatus such as centrifuges.

Description

127841/3 1 ΓΙΝ win r»v»y» Jiina oy in> JMM* Salt purification facility comprising a vertically standing purification vessel with at least one conical area VA Tech Wabag AG C. 115141 127841/2 1 SALT PURIFICATION APPARATUS The present invention relates to an apparatus for the purification of particulate solids, particularly crystalline solids, ■ ' Impurities are removed from salts, e.g. sodium chloride, in salt purification apparatuses, before they are further .processed or consumed in industry. The nature of the impurities depends greatly on the production process and the salt extraction location. Known purification processes use either vacuum recrystallization or mechanical washing with a washing liquid, e.g.. water. The first process is expensive and is only used for special applications. The second process has a relatively low efficiency, because the washing, liquid is circulated several times in the purification apparatus " and consequently contains ever more already washed out impurities.

Help is provided in that said impurities are diluted in planned form or are precipitated from the brine with the' aid of chemical additives. However, the salt production costs are significantly increased by dilution and the use of chemical additives. Another reason for the limited efficiency are the salt losses resulting from the fact that part of the salt crystals is dissolved in the washing liquid.

A process and an apparatus of the present applicant known under the name SalexIRI have proved advantageous for salt purification purposes. Advantages of this process are the low operating costs, improved efficiency with regards to the attainable degree of purity of the salt and the very low salt losses.

The Salex. process is based on the countercurrent purification principle, i.e. a hydroextraction with a saturated solution, in which the impurities are removed and comminuted, dissolved salt crystals are recovered by displacement crystallization. In a very simple variant of the process the salt to be purified is filled into a conical, downwardly tapering container known as a hydroextractor . As a result of gravity the salt trickles through the container from top to bottom. In the opposite direction at least approximately pure, saturated brine solution is introduced into the hydroextractor and flows upwards along the downwardly trickling salt crystals, detaches impurities from the salt crystals and carries same upwards therewith. The purified salt is passed by the hydroextractor into a centrifuge, where the salt crystals are separated from the partly downwardly travelling brine solution.

Preferably, prior to hydroextraction, elutriation takes place in an elutriating container positioned upstream of the hydroextractor. This elutriating container also has a conical, downwardly tapering shape, so that the salt trickles through said container from top to bottom. Once again in the opposite direction an impure, saturated brine is introduced into the elutriating container, separates insoluble impurities from the salt crystals and carries them with it upwards.

Between elutriation and hydroextraction preferably a hydroclassification is performed. Hydroclassification, i.e. classification with impure brine, permits the removal of less soluble impurities, e.g. calcium sulphate. This hydroclassification generally takes place in the upper area of the hydroextractor, so that in the hydroextractor are fundamentally formed two purification areas, namely an upper hydroclassification area and a lower crystallization area, or more precisely a hydroextraction and displacement crystallization area.

In a further variant of the process, prior to elutriation, the salt crystals undergo preliminary comminution by shear comminution and/or hydrocomminution. Both hydrocomminution and shear comminution break up the salt crystal with the enclosed impurity particles at the bonding points with the impurities and release said particles.

The numerous variants of the Salex(R) process are usable not only for salts, but in general for particulate solids, particularly crystalline solids.

Although this process and the hydroextractor used for it give good results, it is constantly necessary to shut down the apparatus, because the hydroextractor becomes clogged. The reason for this is that the salt crystallizes in the hydroextractor to larger lumps. Therefore channels are formed in the hydroextractor, which have a greater flow than the remaining areas within the container, so that the liquid fraction of the salt entering the centrifuge and flowing out of the centrifuge is too high.

In addition, other processes and apparatus are known, which are based on a countercurrent principle.

Thus, DE-A-1, 294, 344 describes an apparatus for the continuous washing out of the mother liquor from solids, in which the washing liquid is passed from bottom to top, whilst the solid to be purified is fed in at the top and as a result of gravity sinks downwards through the washing liquid and is drained off via a discharge opening. It is necessary for the washing liquid to pass through the solid as uniformly as possible and the solid must sink slowly. To achieve this, use is made of a vertically standing, cylindrical purification vessel, having in its lower part an insert in the form of a settling area for the solids. The discharge area of the vessel below the settling area has a conical design. The washing liquid feed issues at a limited distance above or below said settling area in the purification vessel. In this process only a small part of the washing liquid rises upwards and displaces the mother liquor. The larger part flushes the removed solid particle layer towards the discharge opening. This process has a low efficiency, because the solid particles are deposited on the insert and crystallize to form larger lumps.

EP-A-98,637 also discloses an apparatus for the purification of solids in a countercurrent . The purification vessel comprises a cylinder, which is subdivided by means of intermediate plates into several, vertically superimposed mixing chambers. These mixing chambers can be interconnected by means of controllable valves, so that each portion of the solids column can be intermixed in planned manner with the rising washing liquid. This apparatus is relatively complicated and also has a low efficiency, because a remixing of the solids to be purified takes place with the washing liquid as a result of the turbulence produced.

US-A-5, 068, 092 describes a process and a device for the purification of sodium chloride by means of salt water and magnesium chloride brine in countercurrent. The purification vessel is cylindrical, having two areas with different diameters. The upper area has a larger diameter than the lower area. The transition zone between the said areas and the discharge area is conical. Both areas have feed openings for the countercurrent brines and into the upper area are introduced magnesium chloride brines having a higher magnesium chloride content than in the lower area. Once again in the case of this apparatus there is a risk of a non-uniform flow in the two directions.

In contrast DE-A-1 ' 963 ' 599 discloses a method and a device for dissolving and separating individual components from mixtures of solids, in particular a device for the enrichment of magnesium sulphate in sulphite liquor by dissolving out magnesium sulphate from kieserite. The kieserite which is fed into a conical purification container is kept in the floating bed by way of a solution fluid flowing oppositely to the gravitational force. With this, larger parts of the kieserite fall downwards and may be drawn off. In order to achieve the floating bed, the speed of the supplied solution fluid is regulated depending on the aperture angle of the container and the density and size of the solid particles. The aperture angle of the conical container is smaller than 60°, in a preferred embodiment example it is 50°.

US-A-3 ' 892 ' 539 describes a crystallization device in which oversized crystals fall from a floating bed into a lower area, where they are reduced in size by ultrasound and are again transported upwards to the floating bed by the brine, where as seeds they serve the further crystallization. This lower area is formed conical and comprises an aperture angle of 2° to 54° .

GB-A-261'085 discloses a crystallization device in which a nutrient solution is led upwards through the device in a constant flow. The crystals produced in a floating bed are drawn off downwardly. In one embodiment form the device is formed conical in order to ensure an efficient as possible discharge of the produced crystals. With this, the cone has a maximum aperture angle of 60°.

In contrast to the three last mentioned devices, with the purification of crystalline solids, in particular with the purification of salt, there should be achieved a uniform flow, distributed over the whole surface, of the solids downwards and of the salt brine upwards, so that there is no back-mixing of the solids and the salt brine and a hydroextraction and displacement crystallization takes place.

The problem of the present invention is therefore to provide an apparatus for the purification of particulate solids, which obviates the aforementioned disadvantages.

This problem is solved by an apparatus for the purification of particulate solids, particularly crystalline solids.

The apparatus according to the invention can not only be used for the purification of sodium chloride, but .. also for purifying all particulate solids, especially crystalline solids, which can be separated from impurities according to the same principle.

In the case of the apparatus according to the invention, by simple constructional measures lump and/or channel formation within the purification vessel is prevented. Within the solid bed formed by the solid to be purified there is consequently no formation of flow channels where there is a higher' speed than in the remaining areas of the purification vessel. The solids to be purified, as a result of gravity and due to the shape of - the purification vessel, flow uniformly, i.e. with approximately the same speed, over the entire vessel cross-section and in a comparatively slow manner downwards towards the discharge opening, the purification brine flowing round all areas thereof. The purification brine flows ■ at least approximately uniformly upwards. As a result of the special shape of the purification container solids, which are initially in the hydroclassification area, cannot pass via a channel directly to the discharge opening without having been purified by a certain residence time in the crystallization area. In addition, in the crystallization area the purification brine flows at least approximately in turbulence-free manner round the solids to be purified.

The efficiency, particularly the degree of purity, is improved and the number of uninterrupted operating hours of the apparatus is increased, because the purification vessel clogging risk is reduced.

It is important for the functionality of the purification apparatus, that no channel formation can take place in the purification container. In particular, the purified purification brine must not pass from above, via a channel and downwards to the discharge opening, because the pure brine would consequently be contaminated in the lower area of the purification container.

Essential to the invention is the finding that this can be ensured by an appropriate choice of the shape of the purification vessel 1, without any special mechanical flow regulators having to be installed within the purification vessel. The special shape of the purification vessel, i.e. the small cone aperture angle of 10 to 30°, allows a uniform, constant flow in both flow directions and prevents the formation of lumps and channels. The maximum attainable cone aperture angle is dependent on the characteristics of the inner walls of the purification vessel, the fluidization rate, the particle size and the cohesion of the solids to be purified. Furthermore it is advantageous with hydro-extraxction to introduce the salt brine at that location where the relative speed of the solid, defined by the vector sum of the solid speed and the salt brine speed, is smaller than the speed of fluidization. In this way fluidization and thus channel formation is prevented.

It is also advantageous with the apparatus according to the invention that mechanical flow regulators are no longer prescribed within the purification vessel. Such flow regulators are only partly effective, lead to turbulence and an irregular flow of the solid and the brine, are usually ■ fault-prone and difficult to replace in an already installed purification apparatus. A preferred embodiment of the apparatus according to the invention consequently has no built-in baffles or flow regulators.

Admittedly the prior art purification vessels also have conical areas, but they are generally provided for creating a very short transition from an intrinsically circular cylindrical vessel to a narrowed discharge opening. However, purification vessels which have a substantially conical shape, should provide a maximum vessel volume for a minimum overall height. The cone aperture angle has therefore been optimized in accordance with these criteria and in both embodiments is 50 to 60°.

Embodiments of the invention are described in greater detail hereinafter relative to the drawings, wherein show: Fig. 1 a diagrammatic representation of the purification apparatus with the purification vessel according to the invention; Fig. 2 a further embodiment of a purification vessel according to the invention; Fig. 3 a diagrammatic representation of the SalexiR) process of the present applicant and Fig. 4 a third embodiment of a purification vessel according to the invention." Fig. 1 shows an apparatus for the purification of crystalline solids, in this case a salt purification apparatus, which is preferably operated according to the Salex(R) process. A purification vessel 1, also known as a hydroextractor, is positioned in vertically standing manner and has at the top a filling opening 10, as well as a brine overflow 15, and at the bottom a discharge opening 11. In this embodiment the discharge opening leads to a centrifuge 2 and there is preferably a controllable discharge valve 20 in the transition area. In place of a centrifuge it is also possible to use other separating devices, e.g. a belt filter.

At least one feed line 30, 31 for a purification brine issues into the purification vessel 1. Preferably each feed line 30, 31 is connected to a purification brine receiver 3, 3'. The purification brine is brought into the purification vessel 1 in the known manner and way, wherein a uniform as possible distribution of the salt brine over the whole cross section of the purification vessel 1 is to be obtained. For example nozzles directed downwardly are present or horizontally running tubes, whose surfaces are provided with several exit openings, are arranged in the cross section of the purification vessel 1.

In the embodiment shown in Fig. 1 the purification vessel 1 has a lower, a central and an upper area 12, 13, 14. In this embodiment the central area 13 corresponds to the hydroclassification area where a hydroclassification takes place, whilst the lower area 12 corresponds to the crystallization area where a hydroextraction and displacement crystallization take place. The solid to be purified and comprising individual particles in the operating state fills both areas in the form of a fixed or solid bed, shown in dotted line form in fig. 1. Above the solid bed F is located in the operating state the brine S, which has already flown through the crystallization area and/or hydroclassification area and is now drained off via the brine overflow 15.

Preferably there are feed lines 30, 31 for a purification brine in both the lower and central areas 12, 13. Into the two areas it is possible to introduce different purification brines with different degrees of purity. With the purification of solids, the best results are obtained when the feed lines 30, 31 open into the purification vessel at well defined locations. For the feed line 31 into the hydroclassification space 13, it applies that this feed line should feed the purification brine at that height of the purification vessel, where the vector sum of the solid speed and of the brine speed, due to the feed quantity of the purification brine, becomes greater than the fluidization speed. In contrast the feed line 30 leads the purification brine into the crystallization space 12 at that height where the vector sum of the solid speed and the brine speed is smaller than the fluidization speed.

The upper area 14 of the purification container is conical or cylindrical, the cylindrical variant being shown in fig. 1. It passes into the central area 13, which in the same way as the lower area is conical, the central and lower areas 12, 13 preferably forming a common cone with a constant pitch. The lower end of the cone is formed by the discharge opening 11. The diameter of the discharge opening 11 is preferably at least twenty times the average particle size of the solid to be purified. At least one of the conical areas and preferably at least the lower area 12, is provided on the inner walls with smooth, non-corroding surfaces. They are preferably made from polished, stainless steel or are plastic-coated.

The cone aperture angle a of the lower area 12 is 10 to 30°. For an average fluidization rate of (0.01 to 1) x 10"2 m/s, it is preferably approximately 15 to 20° or 15 to 25°, depending on the type of solid. The height of the lower area 12 must be sufficient to ensure that the salt to be purified can spend sufficient time in this area to be effectively purified.

The embodiment shown in fig. 2 has a purification container 1, which is substantially conical and tapers to the discharge opening 11 dimensioned as in the embodiment shown in fig. 1. Here again the cone aperture angle a is 10 to 30°, preferably approximately 15 to 25°. Thelower area 12, which essentially forms the crystallization area, has a smaller angle than the upper area 13, which essentially comprises the hydroclassification area.

Other, not shown purification container shapes are possible and it must be ensured that all walls diverging from the vertical direction of the purification vessel to be filled with the solid bed preferably always have an angle of 10 to 30°, so that there can only be a uniform flow and lump and channel formation is prevented.

By means of figs. 1 and 3 the operation of the present purification apparatus is made clear. Contaminated solid material, here salt, is filled by means of the filling opening 10 into the purification vessel 1 and as a result of gravity drops downwards to the discharge opening 11. By means of the at least one feed line 30, 31 a purification brine, here at least approximately saturated salt water is so passed into the purification vessel 1 that the salt water flows in the opposite direction to that of the contaminated salt, i.e. from bottom to top. Preferably the purification brine is pumped by means of the feed lines and uniformly distributed, downwardly directed nozzles 33 widening conically towards the discharge opening into the purification vessel 1.

The purification brine flows round the salt to be purified and as a function of the nature of the contaminating impurity particles different purification processes take place: - by elutriation (A) with impure, saturated brine insoluble impurities are separated from the salt crystals and carried upwards therewith; by hydroclassification (B) calcium sulphate and insoluble impurities are conveyed together with the purification brine upwards towards the filling opening 10/ by hydroextraction (C) soluble impurities are dissolved in the pure, saturated purification brine and conveyed on therewith; by displacement crystallization (D) , due to hydroextraction with saturated purification brine, comminuted or dissolves salt crystals are recovered.

In addition to these purification processes as the first step can be performed a shear comminution and/or hydrocomminution (A')/ so that the salt crystals with the enclosed impurities are broken open at the bonding points with the impurities.

Thus, fundamentally the impurities are conveyed upwards together with the purification brine, so that over the salt supply is formed a layer of contaminated purification brine and this is led away by means of the overflow 15. However, the purified salt flows downwards to the discharge opening 11. The purification salt fraction conveyed along with the purified salt is separated from the latter in the centrifuge 2. The centrifuged purification brine is returned by means of feed lines 30 to the purification vessel 1 in a preferred embodiment .

As a result of the apparatus according to the invention the degree of purity of the washed salt is increased, as is proved by the following examples.

Example 1 Crude salt was purified in the apparatus according to the invention according to the Salex(R1 process. The crude salt had the following composition: calcium Ca 0.350 wt . % magnesium Mg 0.050 wt sulphate S04 3.600 wt.% sodium chloride NaCl 94.273 wt.% During purification the salt to be purified passed through two purification stages. Each stage was performed in two series-connected purification apparatuses, so that the above-described purification processes were performed twice. The salt was comminuted in a hydromill between the first and second purification stages. The contaminated brine of the second, series-connected apparatus was used as the purification brine for the first purification apparatus. The purified salt had the following composition: calcium Ca 0.023 wt.% magnesium Mg 0.007 wt.% sulphate S04 0.050 wt.% sodium chloride NaCl 99.777 wt.% Example 2 Crude salt was purified in the apparatus according to the invention using the Salex(R) process, in accordance with example 1. The crude salt had the following impurities: calcium Ca 0.100 wt.% magnesium Mg 0.157 wt.% sulphate S04 0.110 wt.% The purified salt still had the following impurities: calcium Ca 0.020 wt.% magnesium Mg 0.016 wt.% sulphate S04 0.020 wt.

In addition, the crude salt with the same impurities was purified with ultrapure brine in a laboratory purification apparatus having a hydromill and in accordance with the standard testing process, which follows the purification stages adopted in the Sale'x(R) process. This testing process is used in practice to establish what proportion of impurities can be removed from the salt in an ideal case. The salt purified according to the standard testing process still had the following impurities: calcium Ca 0.020 wt.% magnesium Mg 0.017 wt.% sulphate S04 0.020 wt.% The efficiency of the purification process is in practice defined as the ratio between the fraction as a percentage by weight of an impurity removed in the purification apparatus and the fraction removed in the standard testing process.

For this example the efficiency for all three measured impurities is approximately 100%: for Ca (0.100% - 0.020%) : (0.100% - 0.20%) x 100% = 100% for Mg (0.157% - 0.016%) : (0.157% - 0.017%) x 100% = 100.7% for S04 (0.110% - 0.020%) : (0.110% - 0.020%) x 100% = 100% Example 3 Crude salt with the following impurities was purified in the apparatus according to the invention using the Salex'R! process according to example 1: calcium Ca 0.086 wt.% magnesium Mg 0.138 wt.% sulphate S04 0.100 wt.% The purified salt still had the following impurities: calcium Ca 0.019 wt.% magnesium Mg 0.016 wt sulphate S0 0.020 wt.% As in example 2, a standard testing process was performed in parallel. The salt purified according to this process still had the following impurities: calcium Ca 0.019 wt magnesium Mg 0.015 wt.% sulphate S04 0.020 wt.% Once again an efficiency of approximately 100% was obtained.

In Figure 4 there is shown a third embodiment example of the purification vessel according to the invention. The purification vessel again consists of at least, in this case exactly two sections with differing cone aperture angles a.

The upper section 17 comprises an angle a of 10° to 30°, preferably 15° to 25°. The lower section 18, which has a smaller height, encompasses however a larger angle of 30° to 90°, preferably 45° to 75°. The feed line 30 for the purification brine introduced into the crystallization space in a preferably located at the transition of the lower section 18 into the upper section 17. This means that in this transition the vector sum of the solid speed andthe brine speed is equal to or smaller that the fluidization speed.

In the inside of this lower section 18, a further insert cone 16 is arranged in the middle, this comprising the angle of 10° to 30°, preferably 15° to 25° , in accordance with the invention. The angles are preferably selected such that when the insert cone comprises the angle a, the lower section 18 encompasses an aperture angle 3a. The height of the insert cone differs according to the apparatus. In one embodiment the upper edge of the insert cone 16 is flush with the transition from the upper to the lower area or it protrudes into the upper area 17. In another embodiment the upper edge ends below this transition. Its lower end is preferably flush with the lower end of the lower section 18 which blends into an exit cone 19, wherein this exit cone 19 again preferably has an aperture angle of 10° to 30°, preferably 15° to 25°.

This embodiment has the advantage that the total height of the purification vessel 1 may be reduced in size whilst maintaining the required aperture angle according to the invention.

Claims (10)

1. Apparatus for the purification of particulate solids, particularly crystalline solids, with a vertically standing purification vessel (,Ι') , which is provided at the top with a filling opening {1-0) for the solids to be purified, at the bottom with a discharge opening (,ϊί) for the purified solids and at least one conical area (1'2, Jr3T) , there being at least one feed line (-3Θ-7 3T) to the purification vessel (,!') for the supply of at least one purification brine in the countercurrent direction to the flow direction of the solids to be purified, characterized in that at least one conical area of the purification vessel J^fc " has a cone aperture angle (a) of 10 to 30°.

2. Apparatus for the purification of particulate solids, particularly crystalline solids, with a vertically standing purification vessel (¥f , which is provided at the top with a filling opening (1-0") for the solids to be purified, at the bottom with a discharge opening -1) for the purified solids and at least an upper and a lower conical area (-l-^-r—1"8)~, there being at least one feed line (-3-Οτ—3-1-) to the purification vessel IY) for the supply of at least one purification brine in the countercurrent direction to the flow direction of the solids to be purified, characterized in that the conical section ((J7') has a cone aperture angle of 10° to 30° and the lower section (18) a larger cone aperture angle, and that in the lower section J.l-8') there is arranged an insert cone (16)" which has a cone aperture angle of 10° to 30°.

Apparatus according to one of claims 1 or 2, characterized in that the cone aperture angle (a) is 15 to 25°.

4. Apparatus according to one of claims 1 or 2, characterized in that the purification vessel J.-l'f is substantially conical .

5. Apparatus according to one of claims 1 or 2, characterized in that the purification vessel (1-Γ has at least two conical areas .-^^"""KT) which have different aperture angles .

6. Apparatus according to one of claims 1 or 5, characterised in that two conical areas !^τ2~,—rS are present which are connected to feed lines (-3-0-,—3-1-) for purification brines, which are separated from one another, wherein an upper feed line r ) opens into the purification vessel J^L at a location where the vector sum of the solid speed and of the brine speed is larger than the fluidization speed, and the lower feed line (,3:07 opens where the vector sum of the solid speed and of the brine speed is smaller than the fluidization speed.

7. Apparatus according to one of the claims 1 or characterized in that at least one of the conical ar Π —-tS-) has smooth inner walls .

8. Apparatus according to claim 7, characterized in that the inner walls are plastic-coated.

9. Apparatus according to claim 7, characterized in that the inner walls are made from polished stainless steel.

10. Apparatus according to one of claims 1 or 2, characterized in that it has at least one nozzle j.33"f for the supply of at least one purification brine, which is directed downwards . Apparatus according to claim 10, characterized in that the at least one nozzle widens conically downwards. For the Applicants seemrmft