Method and apparatus for concentrating aqueous solutions and suspensions

Abstract

1,125,234. Ammonium salts; phosphoric acid- SINCAT-SOC. INDUSTRIALE CATANESE S.p.A. 16 June; 1966 [18 June; 1965], No. 26936 / 66; Heading C1A. [Also in Division- B1] An aqueous solution or' suspension is concentrated in a vertical elongated vessel which has a section 5 of upwardly increasing crosssection, by dispersing the solution or suspension through inlet 4 into a stream of hot gas, at a temperature of 70-1100‹ C., introduced through inlet 2 and rising up through the vessel` so that there is established, in the conical section 5, a fluidized bed of droplets of solution or suspension from which Water vaporizes from the' droplets into the rising gas stream which carries the relatively concentrated droplets from the bed into a cyclone separator 8 where the required concentrate collects in the discharge end 9. The solution or concentrate is introduced into the vessel at a constriction 3 where the gases have a velocity between 20 and 100 m / sec. The included angle of the conical section 5 is preferably 6 to 9 degrees. In the case of substances or mixtures of substances of low melting point, a molten product may be obtained at the outlet of the concentrator. The process is suitable for the concentration of phosphoric acid from 30% up to 64% by weight P 2 O 5 by using gases having an inlet temperature of up to 700‹ C. Fluorine-containing impurities in wetprocess phosphoric acid are, to a great extent eliminated in the gases discharged at 10 from separator 8. The purified product acid is suitable for the production of calcium phosphate for fodder. The process may also be used for the concentration of a solution of ammonium sulphate, or a slurry of ammonium nitrate and phosphate, or a slurry comprising NH 4 H 2 PO 4 , NH 4 NO 3 and KNO 3 . The concentration of sulphuric acid and of solutions alkali metal hydroxides are briefly referred to.

Description

Dr. Walter Bei! Alfred Hoeppener Dr. Hans Joachim Wolff 1 &sfgr; 1 &ogr; 71 &ogr; Dr. Hans Chr. Beil lOIÖ / U Right»*,]wäJte 4 C JlIf)I Frankfurt am Main - Höchst Adelonatrafie 58 - T»L 3126 49 Our No. 12 768 SINCAT ~ Societä Industriale Gatanese SpA Palermo / Italy Method and apparatus for concentrating aqueous solutions and suspensions The invention relates to a method for concentrating aqueous solutions and suspensions by heat exchange, in which these are ! solutions and suspensions come into contact with hot gases and a device for carrying out the process. Aqueous solutions that are most commonly subjected to concentration processes include solutions of Phosphoric acid produced by wet digestion. Such methods are suitable for dilute and contaminated aqueous solutions of Phosphoric acid, which generally has a PpOc content between 25 and 32 wt., is suitable. The main methods for concentrating Phosphoric acid obtained via wet methods is based on heat exchange either through direct or indirect contact. BATH ORIGINAL 009913 / 1342 In direct contact heat exchange systems, the gases, which have been heated to a high temperature, transfer their heat to the acid. This is generally achieved by being blown into the solution or through direct contact with the solution in the spray tower. These systems are characterized by good thermal efficiency, but have the disadvantage of causing considerable PpOc losses (at least 2-3 #), which is carried away in the form of small nebula particles from &EEgr;,&Rgr;&Ogr;, and is extremely difficult to precipitate, and which even the The installation of electrostatic gas cleaners or the introduction of gas scrubbing systems at various stages is required to remove the contamination. to avoid the atmosphere. Furthermore, the P2^ deposited in the wash water cannot be released at all or only to a very small extent. recovered v / earth. The temperature reached by the concentrated phosphoric acid solution is approximately 10-150°C lower than its boiling point. This solution at atmospheric pressure. Under such conditions, the acid is highly corrosive, and therefore highly corrosion-resistant materials are required. Materials that are very expensive, such as graphite and special nickel alloys, are used. In the indirect heat exchange process, the exchange takes place through surfaces that are placed between the solution and the heating medium. are, the latter generally consisting of steam. The process can be carried out, for example, in a vacuum evaporator with pressurized circulation. carried out · Since the operating temperature is quite low due to the vacuum, non-metallic materials and linings can be used. can be used. The PgO^ yields are good, however, with this type of apparatus, the possibility of a long continuous process is limited. The manufacturing process is limited and the procedure is costly because of this. BATH ORIGINAL 009813 / 1342 to a very high degree deposit precipitates of impurities present in the acid, thereby increasing the exchange coefficient between the vapor and acid are considerably reduced. In these two types of processes, a considerable amount of acid is in circulation, resulting in a significantly slow heating process. Therefore, when changes are made to the operating conditions of the apparatus to produce acid with different concentrations, it takes a considerable amount of time to achieve the desired concentration changes. This inertia or slowness in operating the plant often presents disadvantages. In particular, if the concentrated phosphoric acid processing plant is interrupted or out of service, there is no way to further increase the phosphoric acid concentration to its maximum possible value, thereby utilizing the most favorable storage conditions and avoiding the negative consequences of such an interruption. Another difficulty in concentration, which has never been satisfactorily resolved, is the concentration of mixed and complex fertilizer slurries before granulation. As soon as the concentration process was interrupted, the slurries settled and clogged the concentrating device. Therefore, it is necessary to use more concentrated raw materials to produce these slurries. Therefore, the aims of the invention are to provide a method for concentrating aqueous solutions or suspensions by direct heat exchange of the latter with hot gases, in which a good thermal efficiency is achieved and no crusting occurs on the BAD ORIGINAL 0 0 9 8 13 / 1342 walls of the device form and therefore no blockage occurs, concentration takes place in an exceptionally short time, so that A very high output of the concentration plant is achieved, and residual gases from other processes can be used as a heat source. which would otherwise be released into the air, solutions of any concentration can be obtained up to saturation using the same device and where the concentration of the acid to be withdrawn can be changed in a very short time without changing the concentration of the feed solution needs to be changed. Furthermore, the solutions and suspensions can be heated to temperatures that are significantly lower than those achieved in direct contact. Exchange methods are applied, whereby in the case of coirosive solutions and suspensions, especially phosphoric acid solutions, a reduction in the corrosion process is achieved. Furthermore, the process yields excellent P2OC yields and promotes the formation of PCL mists. Furthermore, the process can be used to produce mixed and complex fertilizer slurries, using diluted raw materials. can be used and the diluted slurries can be concentrated until the product reaches a consistency suitable for granulation. has a suitable water content. And finally, a device can be used to carry out the procedure that is very simply constructed and very easy to operate. can be kept and is very cheap. 009813 / 13A2 All these and many other goals can be achieved through this invention, which is a method and a device for concentration. aqueous solutions and suspensions are affected by direct contact of the latter with a hot gas stream, where the hot gas stream, which a temperature between 70 and 11000°C, is introduced into the lower part of an essentially vertical tube, which consists of the following consists: a) A lower part provided with an inlet zone for the gases} b) a constricted ™ part located above the gas inlet zone; c) a gradually widening section, which essentially has the shape of a truncated cone and is located above the narrowed part appropriate. In the constricted section, the gases reach a speed of between 20 and 100 m / sec. The solution or suspension is at height of the narrowed part into the tube, so that it is dispersed into the finest droplets by the gas flow, and as they begin to To release their water content into the gas, these droplets are carried upwards by the gas flow into a zone of the pipe where the J The speed of the current is such that it forms a swirling layer of essentially constant dimensions, in which the Concentration of the solution or suspension continues. The droplets of concentrated solution or suspension are carried through the The gas stream is carried upwards, beyond the stirred-up layer, and is separated from the gases as it leaves the pipe and then... obtained through known methods. The narrowed section, in the essentially vertical pipe, causes the hot gas stream to be given a maximum upward velocity. will, so that the gas is the solution BATH ORIGINAL 009813 / 1342 or suspension, which was introduced into the constricted part, is dispersed into the finest droplets and carried upwards. After the constricted part The gas velocity gradually decreases as a result of the widening of the tube cross-section until it reaches a value that meets the conditions. This corresponds to a constant, suspended layer of droplets being formed beneath it. The droplets are contained within this suspended layer. subjected to exceptionally close contact with the gas, so that the solution or suspension becomes concentrated within a very short time the droplets of the concentrated solution or suspension, which are now much smaller, are displaced by the gas, which has meanwhile cooled down, be carried upwards and can be easily separated from the gas at the outlet of the pipe. The thermal equilibrium of the gas-liquid mixture is reached within a very short time, which is unmatched by any of the previous methods. The results obtained using concentration methods are to be compared. The gas remains in contact with the pipe for only a few tenths of a second. Liquid. At the outlet of the device, there is a mixture of almost perfect equilibrium: The partial pressure of water in the gas is equal to the vapor pressure of the water in the outflowing solution. The accompanying drawings depict a longitudinal section of one of the preferred embodiments of the tube according to the invention. How As already mentioned above, the pipe is essentially vertical and consists of: a) a lower part 1, equipped with an inlet zone 2 for in which the gases, b) a constricted part 3, / a point 4-f aft-d«adie aqueous solution or suspension is introduced, and c) a extending part 5, which essentially has the shape of a truncated cone, wherein the cross-section 009813 / 1342 This section of pipe is essentially elliptical. A part 6, which has a uniform cross-section and through which the The residence time of the gas in the pipe can be extended, while simultaneously maintaining the gas velocity at the outlet. without being further devalued. Furthermore, the pipe can end at its upper part with a section 7, which has a narrowing cross-section ~ and through which the Gas velocity at the outlet™ This can be increased. This facilitates the separation of the droplets from the gas, especially when a device is used for separation. For example, a cyclone is used, where better results are achieved when the gases are introduced at a higher speed. become. The narrowed section 3 is positioned at a specific distance above the gas inlet zone 2 to allow the gases to flow in a regular manner. to be able to perform an upward movement before they reach the narrowed part. The pipe is dimensioned in accordance with the speed of the gas flow so that the speed of the gases in the constricted part possess a high value, which lies between 20 and 100 m / sec. and which reaches a certain value at a specific point in the expanding zone, which meets the conditions required for the formation of a suspended layer of droplets. To ensure a smooth flow of gas, all ropes of the pipe have a preference for a widening section. an essentially elliptical cross-section. 009813 / 1342 BADORtG1NAL If the truncated cone-shaped section has a round cross-section, the extension angle of the truncated cone, measured between Two drawn lines in the same plane, between 3 and 20°. If the cross-section is not round, the extension angle of the truncated cone is... such that the increase in cross-section relative to height is essentially equal to the increase achieved with a truncated cone, which a round cross-section with an expansion angle of 3-20° is achieved. In a preferred embodiment of the invention; All parts of the tube have an essentially round cross-section, while the angle of the truncated cone is between 6° and 9°. One type of tube that is particularly suitable for carrying out the method according to the invention is a Venturi tube, in which the atomizer is directed upwards and above which, if necessary, a pipe 6 with a uniform cross-section is attached, over which in turn a pipe 7 with is attached to a narrowing cross-section, as explained in the accompanying drawings. The method according to the invention can be successfully applied to the concentration of all those solutions and suspensions whose Their properties allow them to be concentrated through direct heat exchange with hot gases. In practice, the process can with all solutions and suspensions that possess sufficient heat resistance and are such that to concentrate The vapor pressure of the solution practically matches the vapor pressure of the water contained in the solution, so that "tea The dissolved substance does not evaporate along with the water during concentration. Good results are achieved, among other things, by... through 009813 / 1342 solutions of acids, such as EUPO and HpSOA, 4. Solutions of hydroxides, such as FaOH and KOH, solutions of salts, such as NapCO-z, NaHCO-*, ()2SO4, NH4NO3, NH4H2PO4, KNO3, KCl, K2SO4, Ca(NO3I2), and MgCl2 and solutions and mixtures of substances such as ammonium sulfophosphate and ammonium phosphonitrate. Quite good results are also achieved when using aqueous suspensions, such as... Suspensions consisting of the above salts and mixtures together with slurries of mixed and complex fertilizers were produced. Depending on the different solubility of the substance, which depends on the temperature and the amount of evaporated water At the end of the evaporation process, either a more concentrated or saturated solution or a suspension of the substance is obtained. saturated solution is obtained. In contrast, when the concentrator is fed with a suspension, a suspension is obtained at its outlet. with a lower water content. In the case of substances and mixtures that have a lower melting point, one can Furthermore, a molten product was obtained at the outlet of the concentrator. The temperature of the introduced gases can fluctuate within a wide range. When using a device with certain Dimensions make it possible to control both the temperature of the gases and the flow rate of the solution or suspension being supplied. change. A reduction in the flow rate of the solution or suspension, or an increase in the temperature of the gases, leads to changes in both. In some cases, a more concentrated solution or suspension is required. Therefore, it is possible to use gases with a relatively low temperature when a low flow rate of the feed solution or suspension is present, yet a satisfactory result is still desired. 0098 13 / 1342 Concentration is maintained at the outlet. In practice, good results can be achieved with gases that have an inlet temperature of not more than possess 7O0C. However, it also achieves good results with gases that have a very high inlet temperature, for example in the order of of 11000C, as well as all temperatures in between. The choice of the preferred temperature depends on the properties of the solutions or suspensions to be concentrated, as well as on the desired concentration level. When concentrating, for example of orthophosphoric acid, it is easiest to adjust the temperature of the to limit inlet gases in such a way as to prevent the formation of H₂PO₄ mists in the outlet gases. In the present process, gases can These devices can be used with an inlet temperature of up to 700°C without the formation of H₂PO₄ mist in the outlet gases. Considering the excellent thermal efficiency obtained by the present method even at temperatures below 700°C, it is therefore possible to avoid all difficulties associated with the precipitation of this mist. As a source of hot gas, it is possible, for example, to use hot air heated in a combustion chamber. It is also possible to utilize various exhaust gases from other processes that are normally released into the atmosphere. It is sufficient that these gases have a low moisture content, a sufficient temperature, and that they do not react with the solution or suspension to be concentrated. As explained above, the pipe is dimensioned such that the gases in the constricted part of this pipe have an upward velocity of between 20 and 100 m / sec. 009813 / 1342 In numerous trials of the procedure, a preferred upward velocity of 50-70 m / sec is used. The temperature of the solution or suspension at the outlet of the device is considerably lower than that achieved in other processes. Direct contact was established. This is a consequence of stripping, as the hot gas stream lowers the boiling point of the liquid by... The partial pressure of the water vapor is reduced, producing an effect similar to that achieved when a vacuum is applied. This explains why the corrosion phenomenon, especially when phosphoric acid is concentrated, is much less intense than that which as observed in the direct exchange process, and that it is therefore possible to use inexpensive materials for most of the device, such as for example, to use plastic materials. Concentrating the droplet suspension at the concentrate outlet presents no difficulties whatsoever. It can be done using standard procedures. Separation of liquid phases suspended in gas is achieved. Excellent results * are obtained, for example, when using conventional cyclones. A very interesting feature of this method is that a concentrated solution of any concentration can be obtained up to saturation. can be assumed to be a dilute solution of any concentration. The substances that would otherwise be present above a certain level Concentration can be reduced to this concentration by dehydration. BAD ORIGINAL 009813 / 1342 For example, in the case of orthophosphoric acid, starting from a dilute acid with, for example, 50 wt. P9O51, one can obtain a concentrated acid of any concentration up to 64 wt.# &Rgr;&rgr;^&dgr; ernaH»en* while according to previous methods in general No acid was obtained that had a concentration greater than 50-55 wt. PpOc. This wide concentration range can be achieved with the same device by simply changing the feed parameters, for example the The flow rate of the diluted solution is obtained. The exceptionally high speed of the concentration process allows to achieve very high performance with a relatively small concentrator. Considering the exceptional simplicity of the With this design, the cost of the system is significantly lower for a given production capacity than the cost of a conventional system. Attachment. Other advantages of this concentrator include its ease of use and simple commissioning. Due to its simplicity The handling of the process can easily be automated. Another very significant advantage of the exceptional speed of the concentration process lies in the ability to control the concentration. to rapidly change the solution at the outlet. By changing the flow rate of the introduced dilute solution within a In a very short time, i.e. on the order of a few minutes, the desired change in concentration of the solution at the outlet is obtained. In the case of phosphoric acid, it is particularly advantageous to rapidly change the concentration of the outflowing solution.* If the Processing plant for concentrated 009813 / 1342 If phosphoric acid production is interrupted for any reason, the most favorable storage conditions can be achieved by producing concentrated acid. utilize this capacity and thereby avoid the poles that would otherwise cause an interruption of the system. The storage capacity of a storage tank The calculated value based on the weight of PgO is increased by approximately 50% when using acid with a weight of 64% instead of acid with a weight of 50%. PpOc» due to the higher content and greater density of an acid with 64 wt.^. The stripping process according to the invention has a further advantage when concentrating phosphoric acid. During concentration, a larger amount of fluorine, which originates from impurities in the phosphorite, is removed. When concentrating 30% phosphoric acid, which contains 2 wt. of fluorine compounds expressed as F to 50 wt. P?O(-), approximately 70-75% of the fluorine is removed by the above method, whereas with the previously used direct exchange method, this is generally not the case. More than 50% fluorine can be removed. By concentrating the acid to a PgOc content of 64% by weight, 90% fluorine can be removed. become. Removing larger quantities of fluorine is particularly interesting when the concentrated phosphoric acid is intended for a specific use. is, in which only a low fluorine content is permitted, particularly for the production of bicalcium phosphate for animal feed. This makes it possible to to simplify or even avoid the treatment for removing fluoride. Furthermore, the recovery of fluorine from the gases is much simpler than in other direct exchange processes. According to these latter methods... The process involves the fluorine compounds, dhHJ and Si?, sucrose with water and one of the H^PO^ levers. BATH ORIGINAL -U- Precipitation, which hinders the recovery of fluorine from the precipitated solution, for example in the form of fluorides or alkali fluorosilicates, due to the presence of phosphoric acid. Since the exhaust gases obtained according to the inventive process do not contain phosphoric acid mist, the recovery of fluorine is much easier. Another very interesting feature of this concentration process is that there is neither much time for the formation of crusts on the walls of the apparatus, which would disrupt its operation, nor does the apparatus become clogged. This is a consequence of the highly kinetic system within the apparatus. The present process therefore makes it possible to concentrate fertilizers into slurries, for example, slurries obtained by dissolving phosphorite in one or more mineral acids, such as HNO₃ and H₃PO₄., and subsequent treatment with ammonia, or it allows slurries of ternary fertilizers obtained by adding potassium salts to these slurries to be concentrated. Starting from dilute solutions containing, for example, 40-50 wt. water, it is possible to obtain concentrated slurries containing, for example, 0.5-10 wt. water and thus suitable for granulation. The following examples serve to illustrate the present invention. Baispiel 1t This example concerns the concentration of a 24 solution. The concentrator consists of a vertical Yenturi tube that narrows. Part of an inner diameter * / or on r:h2ü3tfiungs·.··., which are treated with ammonia with one or more mineral acids, such as E^PO. or mixtures thereof with H2SO-. or HNO,, were, Q0nf*3 / 1?42 BATH ORIGINAL It has a diameter of 214 mm and a height of 500 mm. The atomizer's expansion angle is 7°. Above the Venturi tube is a A section of pipe with a constant diameter of 500 mm was attached. The resulting ammonium sulfate suspension is then processed by the The gases are separated in a cyclone 8 and collected at the outlet 9 of the cyclone, as shown in the accompanying drawing. They leave the cyclone at 10. The gases consist of air that has been heated to a temperature of about 650°C. Its flow velocity is approximately 2,210 m³ / h. Its sluice velocity in the constricted section is approximately m / sec. At the outlet of the The atomizer's velocity is approximately 5 m / sec. The solution, which is poured in at the level of the constricted part of the Venturi tube, exhibits the following: Composition in wt.^&khgr; (NH4)2SO4 43 J* H2O 57 96 Its flow rate is approximately 1365 kg / hr and its temperature approximately 65°C. At the outlet of the cyclone, approximately... Suspension > kg / hr of the iöekag of the following composition obtained: \ (NH4 )2so4, crystallizes 25 ,4 (NH4)2so4, dissolved 35.9 H2O 38.7 However, if the concentrator is fed with approximately 1,735 kg / hr of the same solution, 1,300 kg / hr of a solution will be discharged at the outlet of the cyclone. Suspension of the following composition obtained: (HH4J2SO4, crystallized 19.05%) (HH4)2S04, solved 38.7Ji H2O 42.25 Jt 009813 / 1342 When the concentrator is fed with approximately 1,015 kg / hr of the same solution, a quantity of approximately 610 kg / hr is discharged at the outlet end of the cyclone. Std. of the suspension obtained, which has the following composition: 43.3 27.5 29.2 This example concerns the concentration of a phosphoric acid solution that was prepared using a wet method and has the following composition: (NH4 )2so4, crystallizes (NH4 )2so4, dissolved H2O Example 2: 1*2° 5 expressed as 30, in F 0 wt. CaSO4 1, - 2, 4 It Fluorine compounds, 27 0 H2SO4 g / L. The concentrator described in Example 1 is heated with air heated to 6350°C and supplied with >igr; supplied by approximately 2,160 mvhr. which was heated to 6350°C, with a flow rate The flow rate of the dilute acid solution is approximately 1.085 kg / hr and its temperature is approximately 500°C. At the outlet of the cyclone... Approximately 636 kg / hr of a solution with a PgOc content of approximately 50.9 wt. b will be obtained. The PgOc loss was less than 1 <f» und The exhaust fumes were completely free of PoOC. 009813 / 1342 Example 3: This example concerns the concentration of a phosphoric acid solution, which has practically the same composition as that of Example 2 and a PgO content of about 29.8 wt. The concentrator described in Example 1 is supplied with air heated to about 625°C at a flow rate of about 2135 m³ / h. The phosphoric acid solution has a temperature of about 5°C. This solution is fed into the concentrator at a flow rate of about 600 kg / h. At the outlet of the cyclone, about 280 kg / h of the solution is recovered, which has an IgO content of about 63.8 wt. Example 4: The fourth example concerns the concentration of a phosphoric acid solution, which has practically the same composition as that of Example 2 and a P₂O₇G content of about 30.1 wt. The concentrator described in Example 1 is supplied with air heated to about 465°C at a flow rate of about 2,340 m³ / h. The phosphoric acid solution had a temperature of about 530°C and was introduced into the concentrator at a flow rate of about 2,000 kg / h. At the outlet of the cyclone, about 1,610 kg / h of the solution, which had a P₂O₇G content of about 36.9 wt., was obtained. Example 5: This example concerns the concentration of a phosphate acid solution, which has practically the same composition as that of Example 2 and an IgOc content of e-fcwa 29.9 wt / fo. The concentrator described in Example 1 is C09813 / 13A2 The phosphoric acid solution was supplied with air heated to approximately 62°C at a flow rate of approximately 2,200 nm / hr. The material is fed into the concentrator at a temperature of approximately 500°C and at a flow rate of approximately 850 kg / h. At the outlet of the cyclone... Approximately 457 kg / hr of a solution with a PpO^ content of approximately 552 wt.$ are obtained. Example 6: This example illustrates the use of exhaust gases from other devices as a heat source. The gas to be concentrated The solution is a phosphoric acid solution that has practically the same composition as that of Example 2 and a PpO^ content of about 30.0 wt.; The gases come from a plant where nitric acid is produced by the oxidation of ammonia. They consist essentially of Air containing a very small amount of nitrogen gases. Its temperature is approximately 225°C and it flows at a velocity of approximately... 2,380 m³ / hr were introduced into the concentrator described in Example 1. The solution has a temperature of approximately 50°C and is filled into the concentrator at a flow rate of approximately 460 kg / hr. At the outlet of the cyclone, approximately 310 kg / hr of a solution with a P2O content of approximately 44.7 wt. is obtained. In contrast, the concentrator operates at approximately 308 kg / hr. are fed with a dilute solution, w*a»«l· at the outlet end of the cyclone approximately 180 kg / hr of a solution with a ?2O5" content of approximately 51.2 kg gained. 009813 / 13 4 2 Example 7: This example illustrates the concentration of a slurry of a binary fertilizer. This slurry originates from a mixture. from nitric acid and phosphoric acid, which was obtained by wet means, and in which both acids were adjusted to a pH value by the addition of ammonia. were brought from 4.2" The slurry has the following composition: N 12.30 io H0O 48.3 # P2O5 12.45 Its temperature is approximately 85°C. This slurry is transferred to the concentrator described in Example 1 at a flow rate of approximately 620 kg / hr was filled in together with air heated to approximately 6100°C, which had a flow rate of 2165 m³ / hr. On From the cyclone discharges, approximately 318 kg / hr of a molten product with the following composition was obtained: N 23.90 # P2O5 24.25 # H2O 0.5 # This slurry was then transferred to a granulation plant. Example 8t This example illustrates the concentration of a slurry of a ternary fertilizer. The slurry consists of a mixture. from NH.HgPO^, NH^NO, and KNO, &Pgr;09813 / 1342 in such proportions that a weight ratio of the fertilizer components, expressed in N / PpOc / KpO, of 1:1:1 was obtained. Its content Its density in water was approximately 43.3 g / w and its temperature was approximately 75 g / w. This slurry is fed into the concentrator described in Example 1 at a flow rate of approximately 940 kg / hr, together with Approximately 2,260 m³ / hr of a gas at 62°C is introduced. At the outlet of the cyclone, approximately 576 kg / hr of a concentrated slurry is discharged. The slurry was obtained with a water content of approximately 7.8 Ji. It was then transferred to a granulation plant. 009813 / 1342

Claims

Patent claims:

1. A method for concentrating aqueous solutions and suspensions by direct contact with a hot gas stream, characterized in that the hot gases, at a temperature between 70 and 1100°C, are introduced into the lower part of a substantially vertical tube, comprising a) a lower part provided with an inlet zone for the gases, b) a constricted part arranged above the gas inlet zone, and c) a substantially frustoconical part arranged above the constricted part with a cross-section that increases upwards, wherein the gases travel at a velocity of approximately 20–100 m / sec in the constricted part.to achieve this, the solution or suspension is introduced into the tube at the level of the constricted part, so that it is dispersed into the finest droplets by the gas flow; these droplets, while they begin to release V / water to the gas, are carried by the gas flow into an upper zone of the tube, where a velocity prevails by which the droplets form a constant suspended layer of essentially uniform dimensions, and where the concentration of the solution or suspension continues, the k- <Hs tp--- Tröpfchen der konzentrierten - i. The solution or suspension is carried by the gas flow over the stirred-up layer to the outlet of the pipe, separated from the gases, and recovered using known methods.

2. Method according to claim 1, characterized in that the gas velocity in the constricted part is between 50 and 70 m / sec.

5. Method according to any of the preceding claims, characterized in that the concentrated solution or suspension is separated from the gases at the outlet of the pipe by a cyclone. BATH ORIGINAL 0 0 9813 / 1342 4. Gate direction for carrying out the method according to one of the preceding claims, characterized in that the device consists of a a substantially vertical pipe containing the following a) A lower part provided with an inlet zone for the gases, b) a constricted part located above the gas inlet zone and c) a substantially frustoconical part arranged above the narrowed part, with an upwardly widening Cross section.

5. Device according to one of the preceding claims, characterized in that a [description of the part with the increasing cross-section] is arranged above the part with the increasing cross-section. A pipe section with a constant cross-section is arranged.

6. Device according to one of the preceding claims, characterized in that the tube terminates at its upper end with a part, whose cross-section decreases accordingly.

7. Device according to one of the preceding claims, characterized in that the frustoconical part with the enlarging The cross-section has a substantially circular cross-section.

8. Device according to claim 7, characterized in that the expansion angle of the truncated cone section is between 6 and 9°, For SIiTCAT - Societä Industriale Catanese Sp / A., Palermo / Ital. Rec 009313 / 13U