OA11220A - Device for mixing and dissolving solid granules in a liquid, in particular for producing phospho-nitrogen fertilizers - Google Patents

Abstract

The invention concerns a device for mixing and dissolving in a liquid (L) solid prills or particles (G) of a substance soluble in said liquid but having a density lower than that of the liquid, and in particular for preparing a sulpho-ureic reagent corroding natural phosphates to produce phosphonitrate fertilisers. The device comprises a vat (2) containing first stirring means (A1) for driving the solid prills towards the vat (2) lower part, and second stirring means (A2) for generating in the reaction mixture a movement for dissolving the prills, in particular a shearing motion.

Description

011220 DEVICE FOR MIXING AND DISSOLVING SOLID DESGRANULES IN A SOLID LIQUID, ESPECIALLY FOR THE PRODUCTION OF PHOSPHO-NITROGENES. The invention relates to a device for mixing and dissolving in a liquid granules or solid particles of a soluble material in liquidemais whose density is lower than that of the liquid.

The device concerned is of the type two which comprises a tank comprising stirring means and at least one inlet for the liquid, an inlet for the solid granules, and an outlet for the solution. The invention relates more particularly, but not exclusively, to such a device for the production of phospho-nitrogen fertilizers, especially according to the method of EP-A-0 560 882 (WO 92 10 443).

This method exploits the attack of a natural phosphate, such as tricalcium phosphate, by a uro-urea reagent obtained by solid granular mixing or dissolution, or "prills", of urea in a solution of sulfuric acid. This suifo-ureic attack reagent is a precise eutectic composition which it is important to continuously prepare the solution in specific proportions.

The problem is made difficult by the fact that the solid solid in granules has a density of 0.6, whereas the sulfuric solution, in which the urea granules must be dissolved, has a density of 1.4. The solid granules thus have a strong tendency to float which is not favorable to dissolution or homogenization.

It is furthermore appropriate that this dissolution of the solid granules be effected as rapidly as possible, especially so that the volume of the tank is not too great for a given solution flow rate.

DUPLICATE 2 011220

The device of the invention aims to meet these conflicting requirements created by a solid density to dissolve significantly less than, especially less than half the density of the liquid.

According to the invention, a device for mixing and dissolving in a liquid granules or solidsolids of a material soluble in this liquid but having a lower density than that of the liquid, of the previously defined gen, is characterized in that the entry of the granules into the The vessel is located in a high part, above the level of the reaction mixture in this tank, and the stirring means comprise a first stirring means capable of creating a drive of the solid granules towards the lower part of the tank in the reaction mixture, and a second stirring means located in the tank at a lower level than that of the first stirring means and suitable to create in the reaction mixture a movement favorable to the dissolution of shear granules. In particular, the first and second stirring means are preferably mechanical stirring means.

The first stirring means is advantageously formed by a turbine with straight inclined blades, also known as the "saber turbine", in particular with four blades.

The second stirring means is advantageously formed by a radial turbine with straight blades, also known as the "Rushton turbine", in particular with six blades.

The Rushton turbine is located below the saber laturbine, at an appropriate distance.

The tank generally has a cylindrical shape of vertical axis and the first and second stirring means are advantageously mounted on the same vertical shaft, preferably coaxial with the tank.

DUPLICATE 3 011220

Such a device is particularly suitable for preparing a sulfoneutric reagent for attacking a natural phosphate in a plant for producing phospho-nitrogen fertilizers, according to the process of EP-A-0 560 882, in which case the granules are granules or solid urea prills and the liquid is a sulphuric solution. The invention consists, apart from the provisions set out above, in a number of other provisions which will be more explicitly stated hereinafter with reference to a preferred example of the embodiment described with reference to the accompanying drawings, but which is not at all limiting.

Figure 1, of these drawings, is a scheme of undispositif according to the invention.

Figure 2 is a vertical axial section, withpart outside, on a larger scale, of the tank of the device of Figure 1.

Figure 3 is a larger scale plan view of the saber turbine.

Figure 4 is an enlarged elevational view of the six-bladed Rushton turbine.

Figure 5, finally, is a view from above in relation to Figure 4.

Referring to Figure 1 of the drawings, there is shown a device 1 for mixing and dissolving in a liquid L solid granules G of a material solubled in liquid but having a lower density than liquid. In the example under consideration, the granulesolids G are urea granules of density 0.6, whereas the liquid L is formed by a sulfuric solution of density 1.4.

The device 1 comprises a tank 2, of generally cylindrical shape, with a vertical axis and whose bottom is curved, convex towards the outside. The tank 2 is closed by a removable lid 3, in the upper part, on which are provided · an inlet 4 for the solution

Sulfuric acid L, an inlet 5 for the urea granules G, with water, and an inlet 6 for recycling a fraction of the reaction mixture M produced in the vessel 2.

The dissolution of the urea in sulfuric acid being exothermic, it is expected in the tank 2 (which is a continuously operating reactor) twoconducting cooling drums 7a, 7b. Lesserpentins, as visible in FIG. 2, comprise despires extending substantially over half of the height of the tank 2 and surround agitating means A. The coils of the coils are located radially inside the counter-blades or deflectors 8 constituted by four vertical blades, spaced 90 °, located in planes passing through the vertical axis of the tank 2. The outer vertical edge of the counter-blades The coolant provided by the coils 7a, 7b is sufficient to avoid exceeding the temperature of 90 ° C. in the tank, the threshold above which the urea incorporated in the mixture M has a tendency to grow. to decompose, as indicated in EP-A-0 560 882.

The stirring means A comprise a first stirring means A1 capable of creating a granular entrainment G towards the lower part of the tank 2 in the reaction mixture M, and a second stirring means A2 located at a level lower than that of the first medium. Al This second means A2 is able to create in the mixture M a movement favorable to the dissolution of the granules G, in particular a shearing movement.

The first and second stirring means A1, A2are mechanical and consist of two turbines of different types fixed on the same drive shaft 9caxial to the tank 2. The drive in rotation of the shaft 9 is provided by motor means 10 provided above the lid 3 on the outside of the tank.x

DUPLICATE 011220

The stirring means A1 is constituted by a turbomachine 11 with straight blades 12, whose average plane is inclined with respect to the vertical geometric axis of the shaft 9. As can be seen in FIG. 3, the width of the blades 12 can gradually decrease according to the radial direction away from the axis. The turbine 11 is located substantially midway up the tank 2. The normal level N of the reaction mixture in the tank 2 is located at a distance h1 above the mean plane of the turbine 11.This distance h1 is less than the distance H1 of The inclination of the blades 12 and the direction of rotation of the shaft 9 are such that a substantially axial and incidentally radial flow is created in the reaction mixture M as shown schematically by the arrows F on Fig.2. . The reaction mixture is moved upwardly in the outer radial zones and upwardly in the radially inward regions. This movement essentially makes it possible to aspirate the solid urea granules arriving at the inlet 5 at the top of the tank and to entrain them in the reaction mixture. This movement also makes it possible to mix the makeup liquids and their reagent already present in the tank.

In the example, the turbine 11, outbureau saber, comprises four blades 12 angularly spaced 90 °. The root of these blades is close to the outer surface of the shaft 9 and is fixed on a hub 13 wedged on this shaft. The flow created by the turbine 11 can flow in a direction parallel to the shaft 9, in the vicinity of this shaft.

The second stirring means A2 comprises a radial radiator 14 with straight blades, fixed to the lower end of the shaft 9, coaxially with the turbine 11. The radial laturbine 14, also called Rushton turbine, comprises six regularly spaced blades 15 formed by pads located in planes passing through the axis

The platelets are fixed half-height on a disc 16 which they overflow outwardly substantially over half their length. A sleeve 17 is fixed above the disc 16 at its center for mounting the turbine 14 at the end of the shaft 9. The mean plane of the turbine 14, which corresponds to the mean plane of the disc 16, is closer to the bottom of the tank 2 only from level N.

Preferably, the mean plane of the turbine 14 is located at a distance H2 from the bottom of the tank between one third and one half of the total height H of the level N above the bottom of the tank (1/3 H <H2 <H / 2).

The distance E at which the radial turbine 14 is located below the turbine 11 is chosen to obtain the best dissolution and homogenization efficiency.

By its rotation, the turbine 14 creates a shearing movement which cuts the threads of the flow created by the upper turbine 11, which nets the solid granules of urea. This shearing motion effectively dissolves the urea granules in the reagent. The movement created by the turbine 14 also makes it possible to maintain the reagent in its composition by intimately homogenizing the liquid and solid products added to the tank 2.

By designating by D the diameter of the disk 16 (FIG. 4), the blades 15 advantageously have a length 1 of the order of D / 4 and a height b of the order of D / 5.

The bottom of the tank 2 has a knockout orifice 18 provided with a strainer 19 (FIG 2). Pumping means 20 are connected to the orifice 18 to extract from the tank 2 the sulfo-urea attack reagent constituted by a solution of urea in a solution of sulfuric acids. A line 21 (FIG. 1) directs this reagent to another unit of the kneader type (not shown)

DUPLICATA 7 011220 in which a phosphate rock is attacked by the reagent, according to the method of EP-A-0 560 882.

A fraction of the reagent pumped by the means 20, the fraction whose flow rate is controlled by a valve 22, is recycled in the tank 2 by being returned, by a channel 23, to the inlet 6. As illustrated in FIG. Inlet 6 of the recycling comprises a tubing 24 equipped with a plunger without a nozzle. The inlet 4 of the sulfuric solution L is also provided with a plunger 10. The tank 2 is equipped with gauges or equivalent means (not shown) intended to control the parameters of the process such as temperature, composition of the reaction mixture, etc.

The motor means 10 comprise a gearbox 15 whose external dimensions appear in FIG. 2, while the motor drive and belts are encrypted in 10a. In this same Fig.2, one can see avent V in the upper part of the tank.

For its fixing, the tank 2 comprises supports 20 located in the upper part of its outer cylindrical wall, slightly below the lid 3, and regularly spaced apart.

The outer diameter of the blades of the turbineradiale 14 is smaller than the outer diameter of the blades 12 of the saber turbine 11, and in particular is approximately equal to 2/3 of this diameter. As an example of non-limiting embodiment, the outer diameter of the blades of the turbine 14 is about 1 m, while that of the blades of the turbine 12 is about 1.5 m. The inner diameter of the tank 2 is about 3 m. The counter-blades 8 project inwardly over a radial distance of about 0.3 m and the two coils 7b, 7a have a diameter of turns of about 1.8 m and 2 m. The height of the bottom tank 35 to the base of the lid is about 3.7 m, the normal N level being about 3.25 m above the bottom.

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The operation of the device results from the above explanations.

In normal operation, the sulfuric acid arrives at the inlet 4 and the solid granules of urea, with water, arrive through the inlet 5 in the tank 2, from above, in specific proportions.

A fraction of the reactant pumped at the outlet 18 is ejected from the inlet 6 in the upper part of the tank.

The saber turbine 11, driven in rotation by the shaft 9, creates the axial movement already evoked duréactif, which makes it possible to suck the solid granules in the reaction mixture and to prevent these granulesne remain on the surface because of their much lower density. This movement also makes it possible to mix the additional liquids and the reaction mixture already present.

In the event of an incident on this turbine 11, the solid urea granules float on the surface of the much denser reagent, and there is no longer any active production with the desired composition. A first consequence of such an incident is a rise of the level N of the tank with a stop of the production.

The lower turbine 14 with radial blades creates a shearing movement that dissolves efficiently in the reaction mixture the solids granules, driven down by the movement due to laturbine 11. This turbine 14 also makes it possible to maintain the reactivity to its composition by thoroughly homogenizing the liquid and solid products added to the tank 2.

In the event of an incident on this turbine 14, the solid granules of urea are no longer completely dissolved and then form thick and viscous blocks which can suck up the suction strainer 19 of the pump 22 and / or raise the level N of the tank, also leading to a cessation of production.

In both cases of incident on the turbine 11 and / or the turbine 14, an imbalance of the balance sheets

Thermal DUPLICATE 9 011220 occurs and a change in the activity of the reagent. also occurs with very serious consequences on the finished product (production stoppage, product that does not correspond to the desired title ...). The following example and counter-examples help to clarify the comments above.

EXAMPLE

In a reactor as described above, with a capacity of 10,000 liters, 1100 liters of 92% sulfuric acid are introduced. The agitation is then started at 50 rpm. 4.0685 tons of urea are then introduced by maintaining, by cooling, the temperature of the mixture below 80 ° C. (so as not to transform the urea into biurea). When the operation is completed, the temperature regulation is started at 65 ° C (at plus minus 2 ° C). 178.3 liters of water are then introduced to obtain a "stock" consisting of the reagent as defined above: 3.6 moles of urea-1 mole of sulfuric acid-1 mole of water. In this same reactor is then introduced together 6.7315 t / h of granules d'urea, 1820 1 / h sulfuric acid and 295.38373 1 / h water. Upon reaching a filling level of 7,500 liters, it is possible to export 7,312 m 2 / hr of the reagent to the phosphate reactor.

On an Israeli phosphate ("31.1% ZIN of P2O5") it is then possible to produce 15.35 tons / hour of phospho-nitrogen fertilizer (finished product also referred to as USP) by mixing 5 t / h of phosphate with 7.312 m 2 / h reagent (ie 10.35 t / h reagent at 65 ° C) in accordance with the teaching of EP-A-0 560 882, or WO 92 10443.

EXAMPLES 1 / The reactor above is equipped with a saber blade alone, placed at a distance Ξ1 from the bottom of the tank equal to 1/3 (1/3) of the height of the tank. This blade ensures a movement from bottom to top of the liquid.

This movement allows urea granules (prills) to decirculate from the surface of the mixture to the interior of the vessel, however, in view of the kinetics of dissolution of these same granules in a sulfo-urea reagent as defined. above, it becomes necessary to increase the residence time of these pellets in the tank and thus to lower the production (and thus the introduction of raw materials) flow rates of the finished product (USP). this rate reduction operation is not carried out, undissolved granules pass into the feed liquid of the reactive / phosphate mixer and / or suck up the suction of the pump In all cases the reagent is no longer in the chemical equilibrium conditions as described in EP-A-0 560 882 (WO92 10443), there is an alteration of the attack level of the phosphate and thus a finished product not in accordance with the subject of the patent application.

It should be noted that it is not possible industrially to enlarge the size of the tank (thermal balance, stirrer size, etc.). 2 / The reactor above is equipped with a Rushton turbine only, installed at a height H2 equal to half the height of the reactor. It does not create enough vertical movement to squeeze the pellets into the mixture; the operation therefore stops at the stage of the "foot of tank" without allowing to constitute léeactive. Urea gets wet and then clumps into a ball that dissolves after a very long time (when the pump suction is not blocked before).

The foregoing explanations show that the combination of the two turbines 11 and 14 coaxially mounted on the same shaft, according to the particular arrangement of the invention, makes it possible to obtain particularly interesting results for. the pump, size

DUPLICATE 11 011220 dissolution of a solid product in a liquidideensity significantly higher than that of the solid product of

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Claims (10)

• · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · 1. A device for preparing a sulfur-urea reagent for the attack of a natural phosphate, in a plant for the production of phospho-nitrogen fertilizers, by mixing and dissolving, in a liquid (L) formed by a sulphuric solution, solid urea granules (G) whose density is lower than that of the liquid, comprisinga cylinder (2) of cylindrical shape with a vertical axis, with a base, comprising stirring means (A) and provided at least with an inlet (4) for the liquid (L), an inlet (5) for the solid granules, and an outlet (18) for the solution, characterized in that the inlet (5) of the granules in the tank (2) is located in the upper part, above the level (N) of the mixture in this tank, and that the stirring means (A) comprise a first stirring means (A1) capable of creating a drive of the solid granules (G) towards the bottom of the tank (2), and a second stirring medium (A2) located in the tank at a lower level than the first stirring means tion (Al) and to create in the mixture a movement favorable to the resolution of the granules, in particular a shearing movement. 2. Device according to claim 1, characterized in that the first and second stirring means (A1, A2) are mechanical stirring means. 3. Device according to claim 2, characterized in that the first stirring means (Al) is formed by a turbine (11) with inclined straight blades (12), also known as "saber turbine". 4. Device according to claim 3, characterized in that the turbine (11) has four blades. DUPLICATE Modified keel •••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••. »13 01 1 220 5. Device according to claim 3 or 4, characterized in that the second stirring means (A2) is formed by a radial turbine (14) with straight blades (15), also known as "Rushton turbine". 6. Device according to claim 5, characterized in that the radial turbine (14) with straight blades has six blades. 7. Device according to claims 3 and 5, characterized in that the two turbines (11,14) are mounted on the same vertical shaft (9), the turbineradiale (14) being located below the saber turbine (11), at a suitable distance (E). 8. Device according to claim 7, characterized in that the outer diameter of the blades of the turbineradiale (14) is less than the outer diameter despales (12) of the saber turbine (11), in particular equal to about 2/3 of this diameter . 9. Device according to claim 7, characterized in that the average plane of the radial turbine (14) issatitué at a distance (H2) of the bottom of the tank betweenentre third and half of the total height (H) ofLevel (N ) above the bottom of the tank (1/3 H <H2 <H / 2). 10. Device according to one of the preceding claims, characterized in that an inlet (6) is provided in the lid (3) of the tank for the recycling of a fraction of the reaction mixture (M) made in the tank. DUPLICATE MODIFIED SHEET