Urea ammonium sulfate granulation equipment and method

Abstract

A method and apparatus for producing urea ammonium sulfate granules. In a first fluidized bed, a first spraying liquid is sprayed, the first spraying liquid comprising a urea melt and an aqueous ammonium sulfate solution, for example, a (near) eutectic mixture. The bed temperature is lower than the crystallization temperature of the sprayed mixture. In a next compartment, the granules are fluidized to form a second fluidized bed. A second spraying liquid comprising a urea melt is sprayed into the second fluidized bed, the second fluidized bed having a bed temperature higher than the bed temperature of the first fluidized bed and lower than the crystallization temperature of the sprayed second spraying liquid.

Description

Technical Field

[0001] The present invention relates to a method for granulating urea ammonium sulfate, which is specifically used as a fertilizer. Background Art

[0002] The granulation of urea is usually carried out in a fluidized bed reactor including one or more compartments. A nucleus inlet for forming solid nuclei of the bed is provided on the inlet side of the granulator, and the bed is fluidized by fluidizing air. The nuclei gradually flow from this inlet to the particle outlet on the opposite side of the granulator. An aqueous solution of urea (urea melt) is sprayed into the fluidized bed through a sprayer on the bottom plate of the granulator. The urea melt usually has a water content of about 1 to about 5 wt%. When the water content evaporates, the urea melt deposits on the nuclei passing through and crystallizes to form particles. For this purpose, the fluidized bed should have a bed temperature that is much lower than the crystallization temperature of the urea melt, yet high enough to ensure sufficient evaporation of the water content.

[0003] The fluidizing air discharged from the granulator contains ammonia and ammonium cyanate. The increasingly strict regulations for the emission of free ammonia require the separation of the ammonia content before the air is released into the atmosphere. For this purpose, the air is usually washed with an acidic washing aqueous solution, which generally includes sulfuric acid. To meet these more stringent requirements, a washing liquid with a lower pH and a higher acid content is used.

[0004] During this washing process, ammonia is converted into ammonium sulfate, which is particularly useful as a fertilizer compound.

[0005] The scrubber also separates part of the ammonium cyanate from the exhaust gas. Depending on the pH of the washing liquid, ammonium cyanate can hydrolyze to form ammonia (NH3) and carbon dioxide (CO2). NH3 will form ammonium sulfate again.

[0006] Due to the more stringent emission requirements, more ammonia must be removed from the exhaust gas, so a lower pH is required and more sulfuric acid is used. Due to the increased availability of sulfuric acid and the lower pH, more ammonium sulfate is produced and more ammonium cyanate hydrolyzes to form ammonium.

[0007] Ammonium sulfate is generally used as a valuable component in fertilizers. Therefore, the ammonium sulfate solution can be recovered and added to the urea melt fed to the granulator. Ammonium sulfate is soluble in the urea melt, with a maximum concentration just below 20 wt%. The amounts of ammonia and ammonium cyanate in the exhaust gas result in an amount of ammonium sulfate sufficient to produce a urea-ammonium sulfate mixture having about 2 - 13 wt% ammonium sulfate. This mixed solution of ammonium sulfate and urea forms a eutectic or near-eutectic mixture. This eutectic or near-eutectic mixture has a crystallization temperature lower than the crystallization temperatures of its components. For example, the crystallization temperature of urea having about 10 wt% ammonium sulfate is up to about 15 °C lower than the crystallization point of pure urea having the same water content. Therefore, if the bed temperature is about 15 °C lower than the bed temperature for a pure urea melt having the same water content, then this ammonium sulfate / urea melt can only be granulated. Due to this low bed temperature, the water content is not sufficiently evaporated. This results in granules having a high water content, all the more so because ammonium sulfate makes the product more hygroscopic and more difficult to dry than pure urea. These relatively wet and brittle granules have a water content far higher than 0.3 wt% and tend to form lumps during storage, making them difficult to store, process, or use. In places with high air humidity, such as marine or tropical environments, the material may even become unusable as a fertilizer.

[0008] US2013 / 0319060 teaches supplying a mixed urea / ammonium sulfate stream to the core inlet side of a granulator compartment and supplying a pure urea solution to the particle outlet side. For this mixed stream, the ammonium sulfate content is highest at the core inlet side and gradually decreases in the direction of the particle outlet of the granulator. This method is carried out with a limited amount of ammonium sulfate.

[0009] WO2017 / 007315 teaches that the ammonium sulfate content in fertilizer granules can be increased by spraying a urea slurry with a high ammonium sulfate content in a first granulator and subsequently spraying a urea solution with a low ammonium sulfate content in a second granulator. By spraying the slurry first instead of the solution, the ammonium sulfate content can be significantly increased. This system consumes significantly more ammonium sulfate compared to what can be obtained by recycling ammonium sulfate from a scrubber. In addition, a high ammonium sulfate content means a relatively low urea content and thus lower quality. SUMMARY OF THE INVENTION

[0010] It is an object of the present invention to provide a method that allows obtaining high-quality urea-ammonium sulfate granules with a lower residual water content and allows the recovery or addition of ammonium sulfate in a valuable way.

[0011] The object of the present invention is achieved by a method for producing urea ammonium sulfate granules, which uses a granulator and provides a first fluidized bed of a granule precursor material in a compartment of the granulator, and the first fluidized bed continuously moves from the core inlet of the compartment to the outlet. A first spraying liquid comprising a urea melt and an aqueous ammonium sulfate solution is sprayed into the first fluidized bed, and the first fluidized bed has a bed temperature lower than the crystallization temperature of the sprayed mixture. The granular material then moves to the next compartment, where the granular material is fluidized to form a second fluidized bed, and a second spraying liquid comprising a urea melt is sprayed into the second fluidized bed, and the second fluidized bed has a bed temperature higher than the first fluidized bed and lower than the crystallization temperature of the sprayed second spraying liquid.

[0012] The first spraying liquid generally has a lower crystallization temperature than the second spraying liquid. The first spraying liquid can be, for example, a eutectic or near-eutectic urea ammonium sulfate mixture, such as having about 1 to about 5 wt% of water and about 2 to about 15 wt% of water. Up to about 12 wt% of ammonium sulfate, such as about 5 wt% to about 12 wt% of ammonium sulfate. The second spraying liquid can be a pure urea melt, or a non-eutectic urea ammonium sulfate mixture with a crystallization temperature less than 5 °C lower than the crystallization temperature of the pure urea melt.

[0013] In this regard, a pure urea melt refers to a urea melt without a technically relevant amount of ammonium sulfate. A near-eutectic urea ammonium sulfate mixture refers to any aqueous urea ammonium sulfate solution having a crystallization temperature at least 5 °C lower, such as at least 8 °C, such as at least 10 °C, than the crystallization temperature of a pure urea melt having the same water content. Near-eutectic includes eutectic. Non-eutectic refers to any composition of an aqueous urea ammonium sulfate solution outside the near-eutectic range. The non-eutectic mixture can be, for example:

[0014] A hypereutectic mixture of a urea melt and at least 15 wt%, for example 18 wt%, such as about 20 wt% of ammonium sulfate in an aqueous solution; or

[0015] A sub-eutectic mixture of a urea melt and at most about 2 wt% of ammonium sulfate in an aqueous solution having about 1 - 5 wt% of water. If the ammonium sulfate content in the hypereutectic mixture exceeds 20 wt%, then part of the ammonium sulfate will not be dissolved but form a dispersion. If desired, such a dispersion can also be used.

[0016] The bed temperature of the first fluidized bed can be, for example, at least 5 °C lower, such as at least 10 °C lower, than the crystallization temperature of the sprayed mixture. The second fluidized bed can have a bed temperature at least 5 °C lower, such as at least 10 °C lower, than the crystallization temperature of the sprayed pure urea melt.

[0017] The urea-ammonium sulfate mixture sprayed in the first compartment has a relatively low crystallization temperature. If, for example, the water content in the mixture is 2.5 wt%, and the ammonium sulfate content is about 10.5 wt%, the crystallization temperature is 111 °C. If the water content is 5 wt%, and the ammonium sulfate content is about 10 wt%, the crystallization temperature is 103 °C. The bed temperature in the first compartment should be lower than this temperature, for example, about 95 °C - 100 °C.

[0018] In the second compartment, the sprayed liquid is non-eutectic, for example, pure urea melt, so the crystallization temperature of the sprayed material is higher. For example, if the water content in the urea melt is 2.5 wt%, the crystallization temperature of the urea melt is 124 °C. If the water content is 5 wt%, the crystallization temperature is 118 °C. The bed temperature in the second compartment should be lower than this crystallization temperature, but can be substantially higher than the bed temperature in the first compartment, for example, about 105 °C - 112 °C. This bed temperature is high enough to produce granules with an acceptably low residual moisture content. To prevent the melting of the urea-ammonium sulfate layer of the granules in the second compartment, the bed temperature should be lower than the melting point of urea-ammonium sulfate, which is 121 °C, where the urea-ammonium sulfate has 0% water content.

[0019] The movement of the intermediate granular material from the first compartment to the second compartment will generally occur in the form of a continuous flow.

[0020] The first compartment and the second compartment can be parts of the same granulator or different granulators. Optionally, additional granulation compartments can be present between the two compartments and / or before the first compartment and / or after the second compartment. For example, if the sprayed liquid in the second compartment is a sub-eutectic urea-ammonium sulfate, a sprayed liquid of pure urea melt can be used in a third granulator compartment to further process the granules.

[0021] Although the temperature of the sprayed melt is substantially higher than its crystallization temperature, the bed temperature of the fluidized bed should be substantially lower than this temperature. Outside the range of the sprayer, the bed temperature of the fluidized bed is substantially uniform. The bed temperature should be measured outside the spray area above each sprayer. For example, the bed temperature can be measured at a certain distance above the fluidized bed. The bed temperature is controlled by controlling the flow rate and temperature of the fluidizing air. Heat is also dissipated through the evaporation of the water present in the urea melt. In addition, the temperature can be controlled by recycling the granules of the rejected particulate material that is too small in size and / or too large in crushed size.

[0022] In this regard, the particulate precursor material is any particulate material in the first fluidized bed. The intermediate particulate material is any particulate material in the second fluidized bed. Both are mixtures of granules at different stages of granulation.

[0023] In a specific embodiment, the average residence time of the intermediate granular material in the second fluidized bed is controlled to produce final granules having a residual moisture content of at most 0.3 wt%. The average residence time in the second fluidized bed can be, for example, about 10 - 15 minutes, but can be more or less if desired.

[0024] A suitable source of ammonium sulfate is to use the wash liquor from a scrubber that is used to wash the exhaust discharged from the granulator. The wash liquor is typically an aqueous solution of sulfuric acid, which converts ammonium cyanate and ammonia from the exhaust into ammonium sulfate in the aqueous solution. Such wash liquor can be collected and mixed with the urea melt to produce the desired mixture. Optionally, the concentration of ammonium sulfate can first be adjusted to a solution containing, for example, about 1 to 5 wt% water. Additionally or alternatively, other sources of ammonium sulfate can also be used.

[0025] To meet increasingly stringent environmental regulations, a low pH wash liquor can be used, such as having a pH below 5, for example below 3. The lower the pH, the higher the ammonium sulfate content in the final wash liquor, specifically due to the hydrolysis of cyanate esters at low pH values.

[0026] The volume ratio of the urea ammonium sulfate sprayed in the first compartment to the urea melt sprayed in the second compartment is, for example, between 1:2 and 2:1, for example about 1:1.

[0027] The urea ammonium sulfate used in the first compartment can, for example, include a water content of at most 5 wt%. Optionally, it includes, for example, about 0.4 wt% to 0.8 wt% of an additive. The urea melt used in the second compartment can, for example, include a water content of at most 10 wt%, for example at most 5 wt%, and optionally up to 1.5 wt%, for example between 0.4 wt% and 0.8 wt% of an additive. Suitable additives for the urea ammonium sulfate mixture and for the urea melt include formaldehyde, aluminum sulfate, micronutrients, and other hydrocarbon granulation additives or mixtures thereof. In a specific embodiment, the urea ammonium sulfate for the first compartment includes aluminum sulfate as a granulation aid, while the urea melt includes formaldehyde.

[0028] The core can be any suitable natural or synthetic composition, such as soil, sand, biodegradable plastic, or different types of fertilizers. It is specifically useful to reject and recycle undersized urea granules and crush oversized urea granules produced from previous production. The core can, for example, have an average particle size up to 80% smaller than the average particle size of the final granules.

[0029] If the spraying liquid in the second fluidized bed is pure urea melt, the method produces granules that comprise particulate particles having a core covered by a first layer comprising urea ammonium sulfate and an outer second layer comprising urea substantially free of ammonium sulfate. The outer urea layer effectively coats the urea ammonium sulfate layer and inhibits the hygroscopic characteristics.

[0030] The disclosed method can be effectively implemented in a granulation apparatus comprising a first compartment and a second compartment, the first compartment having a sprayer connected to a source of a near-eutectic mixture of urea and an aqueous solution of urea ammonium sulfate, and the second compartment connected to a source of pure urea melt or a non-eutectic urea ammonium sulfate mixture as disclosed above.

[0031] The present disclosure further relates to a granulation apparatus, optionally as disclosed above, comprising a scrubber and a separator, the scrubber for scrubbing the exhaust gas from the granulator, and the separator having an inlet connected to a discharge line for the used scrubbing liquid from the scrubber. This discharge line for the used scrubbing liquid is connected to a supply line for supplying fresh urea melt.

[0032] In a specific embodiment, the separator has an outlet connected to a feed line for supplying the sprayer, e.g., in the first granulator compartment for spraying a mixture of urea melt and ammonium sulfate solution.

[0033] In a specific embodiment, the scrubber comprises:

[0034] A first scrubber compartment having a first sprayer and an inlet for the granulator exhaust gas;

[0035] A second scrubber compartment having a second sprayer, the second scrubber compartment being located downstream of the first scrubber compartment,

[0036] A first water collection reservoir for collecting the used scrubbing liquid from the first scrubber compartment and partially from the second scrubber compartment;

[0037] A first circulation loop for returning the scrubbing liquid from the first water collection reservoir to the first sprayer;

[0038] A second water collection reservoir for collecting partially used scrubber liquid from the second scrubber compartment;

[0039] A second circulation loop for returning the scrubbing liquid from the second water collection reservoir to the second sprayer;

[0040] Wherein, the second circulation loop is connected to an acid source. Thus, the washed urea is concentrated in the first circulation loop. An acid is added to the second circulation loop to limit the chemical reaction between the urea content and the acid. The first scrubber compartment and the second scrubber compartment can be separated, for example, by means of a demister (such as a woven mesh or a grid mesh).

[0041] All percentages mentioned in the present disclosure are weight percentages relative to the total weight of the corresponding composition. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] The present invention will now be further explained with reference to the accompanying drawings.

[0043] Figure 1 An exemplary embodiment of a granulation device according to the present invention is schematically shown. DETAILED DESCRIPTION

[0044] Figure 1 A granulation device 1 is shown, which granulation device 1 includes a granulator 2 having a first compartment 3 and a second compartment 4. The first compartment 3 and the second compartment 4 include a bottom plate (not shown) having openings for the fluidizing air to pass through, and the fluidizing air is blown from a blower 6. In this exemplary embodiment, these two compartments 3, 4 include sprayers 7, 8 extending from the bottom plate and connected to an atomizing air source 9. In other embodiments, the sprayers can extend from one or more side walls and / or downward. The sprayer 7 in the first compartment 3 is connected to a separator 11, which forms a source of a eutectic or near-eutectic aqueous solution of urea ammonium sulfate, as explained below. The sprayer in the second compartment is connected to a source of urea melt. The first compartment 3 has a nucleus inlet port 12 and an intermediate particle port 13, the nucleus inlet port 12 being connected to a nucleus source, and the intermediate particle port 13 leading to the second compartment 4 on the opposite side of the first compartment 3. The second compartment 4 includes a particle outlet port 14 opposite to the intermediate particle port 13.

[0045] In use, the nuclei gradually flow from the nucleus inlet 12 of the first compartment 3 to the intermediate particle port 13. The nuclei are fluidized by the fluidizing air blown into the first compartment 3 through the openings in the bottom plate to form a first fluidized bed 16. The urea ammonium sulfate solution is sprayed into the first fluidized bed 16 through the sprayer 7 on the bottom plate of the granulator. When the water content evaporates, the urea ammonium sulfate deposits on the passing nuclei and crystallizes to form intermediate particles. The first fluidized bed 16 has a bed temperature of 95°C to 100°C, which is much lower than the crystallization temperature of the sprayed urea ammonium sulfate, yet high enough to ensure sufficient evaporation of the water content.

[0046] The core and intermediate particulate material in the first fluidized bed 16 moves continuously in the direction of the intermediate particle port 13, where it enters the second compartment 4 to form a second fluidized bed 17. Here, the sprayer 8 sprays pure urea melt into the second fluidized bed 17, which has a bed temperature of 105°C - 112°C. This temperature is lower than the crystallization temperature of the urea melt, but higher than the bed temperature of the first fluidized bed. The bed temperature is also lower than the melting point of the ammonium sulfate - urea layer on the intermediate particles (about 121°C with 0% water content). The particles leaving the second compartment 4 have a core, an inner layer of ammonium sulfate - urea, and an outer layer of urea, all of which have a residual moisture content of at most 0.3 wt%.

[0047] The exhaust gases from the first compartment 3 and the second compartment 4 are conveyed via line 21 to the wet scrubber 20. In Figure 1 the exemplary embodiment, the wet scrubber 20 includes a first scrubber compartment 22, a second scrubber compartment 23, a water separation compartment 24, and a clean air outlet 25 operably connected to a discharge pump 26. The first scrubber compartment 22 and the second scrubber compartment 23 are separated by a first knitted or wire mesh demister 27. Another demister 28 separates the second scrubber compartment 23 from the water separation compartment 24. A third demister 29 separates the water separation compartment 24 from the clean air outlet 25. A first water collection reservoir 31 is located below the first scrubber compartment 22. Below the water separation compartment 24 is a second water collection reservoir 32. The second scrubber compartment 23 is partially located above the first water collection reservoir 31 and partially above the second water collection reservoir 32. A first recirculation loop 34 returns water from the first water collection reservoir 31 to the sprayer 35 in the first scrubber reservoir 31. A second recirculation loop 36 returns water from the second water collection reservoir 32 to the sprayer 37 in the second scrubber reservoir 23. The second recirculation loop 36 is also connected to a sulfuric acid source 38 to maintain a pH below 5. The second water collection reservoir 32 also has a fresh water inlet 41. All the exhaust gases from the granulator 2 enter the scrubber via an inlet in the first scrubber compartment 22. Thus, the urea concentration will be significantly higher in the first water collection reservoir and the first recirculation loop. In the second recirculation loop with added acid, the urea concentration is significantly lower. In this way, the chemical reaction between sulfuric acid and urea is restricted.

[0048] The acidic water absorbs ammonia and ammonium cyanate and separates them from the exhaust gases entering the wet scrubber 20. Ammonia dissolves in the form of ammonium. Ammonium cyanate is unstable but tends to convert to urea or hydrolyze into ammonium and carbon dioxide. The ammonium forms ammonium sulfate with sulfuric acid.

[0049] The first recirculation loop 34 includes a branch line 42 leading to the vacuum concentration unit, which is continuously connected to a supply line 43 for urea melt, a pump 44, a heat exchanger 45, and a separator 11. In the separator 11, a concentrated aqueous solution of ammonium sulfate and urea is separated from the stream. The separated solution has an ammonium sulfate content of up to 12 wt%, a urea content of at least 80 wt%, and a water content of about 1 - 5 wt%.

[0050] This forms a eutectic or near-eutectic mixture in which all of the ammonium sulfate is dissolved. The aqueous solution is returned via a return line 47 to the sprayer 7 in the first granulator compartment 3. This return line 47 is provided with an inlet 48 for an additive such as aluminum sulfate as a granulation aid.

[0051] The separated water vapor leaves the separator 11 and leads to a vacuum condenser 49, where the water vapor is separated into water and treated air. The condensed water is returned via a return line 50 to the first water collection reservoir 31, which includes a sealed tank 51 where the water is mixed with fresh sulfuric acid. The treated air from the condenser 49 is mixed with the exhaust gas from the granulator 2 and returned to the first scrubber compartment 22.

[0052] With Figure 1 the arrangement for operation testing. The separator 11 is controlled to produce an ammonium sulfate and urea solution having 5 wt% water, up to 12 wt% ammonium sulfate, and at least 80 wt% urea. Nuclei are supplied to form a fluidized bed that continuously moves from the nuclei inlet 12 through an intermediate particle port 13 to the particle outlet 14 of the second compartment 4. The average bed temperature in the first compartment 3 is 90 °C.

[0053] In the second compartment 4, the urea melt is sprayed with a water content of 5 wt%. The spray volume of the urea melt is approximately the same as the volume of the ammonium sulfate and urea sprayed in the first compartment 3. The average bed temperature in the second compartment 4 is about 112 °C

[0054] The resulting particulate product includes nuclei coated with an inner layer of ammonium sulfate and urea and an outer urea layer. The residual water content is less than 0.3 wt%.

[0055] In an alternative embodiment, the sprayer in the second compartment may be fed from a source of a hypoeutectic mixture of urea melt with, for example, 18 - 20 wt% ammonium sulfate in an aqueous solution or a source of a eutectic mixture of urea melt with up to about 2 wt% ammonium sulfate in an aqueous solution.

Claims

1. A method for producing urea ammonium sulfate granules, using a granulator and providing a first fluidized bed of particulate precursor material in a compartment of the granulator, the first fluidized bed continuously moving from a core inlet of the compartment to an outlet; Among them, Spraying a first spraying liquid comprising a urea melt and an ammonium sulfate aqueous solution into the first fluidized bed to produce intermediate granular material, the first fluidized bed having a bed temperature lower than the crystallization temperature of the sprayed mixture; Wherein the intermediate granular material is then moved to the next compartment, where it is fluidized to form a second fluidized bed, and a second spraying liquid comprising a urea melt is sprayed into the second fluidized bed, the second fluidized bed having a bed temperature higher than the first fluidized bed and lower than the crystallization temperature of the sprayed second spraying liquid; The first spraying liquid comprises a eutectic or near-eutectic mixture of urea ammonium sulfate in an aqueous solution.

2. The method according to claim 1, wherein, The bed temperature of the second fluidized bed is maintained below the melting temperature of the dry mixture on the particulate precursor material.

3. The method according to claim 1, wherein, The bed temperature in the second compartment is 10 - 12 °C higher than the bed temperature in the first compartment.

4. The method according to claim 1, wherein The bed temperature in the first compartment is 95 - 100 °C and / or the bed temperature in the second compartment is 105 - 112 °C.

5. The method according to claim 1, wherein, Controlling the average residence time of the particulate precursor material in the second fluidized bed to produce final granules having a residual moisture content of at most 0.3 wt%.

6. The method according to claim 1, wherein, Washing the exhaust gas from the granulator with an aqueous sulfuric acid solution, the aqueous sulfuric acid solution converting ammonium and ammonium cyanate from the exhaust gas into ammonium sulfate in an aqueous solution, collecting the ammonium sulfate for producing the mixture.

7. The method according to claim 6, wherein, After adjusting the ammonium sulfate concentration, the aqueous solution is used to produce the mixture.

8. The method according to claim 6, wherein The aqueous sulfuric acid solution has a pH below 5.

9. The method according to claim 6, wherein, The aqueous sulfuric acid solution has a pH below 3.

10. The method according to claim 1, wherein, The eutectic or near-eutectic mixture of urea ammonium sulfate in an aqueous solution has; 1 wt% to 5 wt% of water; and 2 wt% to 15 wt% of ammonium sulfate.

11. The method according to claim 1, wherein, The eutectic or near-eutectic mixture of urea ammonium sulfate in an aqueous solution has; 1 wt% to 5 wt% of water; and 5 wt% to 15 wt% of ammonium sulfate.

12. The method according to claim 1, wherein The second spraying liquid is selected from the group comprising: Urea melt, or A urea melt and a sub-eutectic mixture of at least 15 wt% ammonium sulfate in an aqueous solution; or A urea melt and a hypo-eutectic mixture of at most 2 wt% ammonium sulfate in an aqueous solution.

13. The method according to claim 12, wherein, The second spraying liquid comprises a urea melt and a sub-eutectic mixture of at least 18 wt% ammonium sulfate in an aqueous solution.

14. Granules produced by the method according to claim 1, the granules comprising particulate particles having a core, the core being covered by a first layer comprising ammonium sulfate and an outer second layer comprising urea without ammonium sulfate or an outer second layer comprising at least 15 wt% ammonium sulfate; the granules having a residual moisture content of at most 0.3 wt%.

15. The particle according to claim 14, wherein, The outer second layer comprises at least 18 wt% ammonium sulfate.

16. A granulation device according to the method of claim 1, comprising: A first compartment (3), said first compartment (3) having a sprayer (7) connected to a source of a mixture of the first spraying liquid; A second compartment (4), said second compartment (4) having a sprayer (8) connected to a source of the second spraying liquid; A scrubber (20) for scrubbing the waste gas from the granulator; And A separator (11) having an inlet connected to a discharge line (42) for the spent scrubbing liquid from the scrubber (20); The sprayer (7) in the first compartment (3) is connected to the separator (11) to form a source of a eutectic or near-eutectic aqueous solution of ammonium sulfate and urea.

17. The granulating device according to claim 16, wherein, The discharge line (42) for the spent scrubbing liquid is connected to a supply line (43) for supplying fresh urea melt.

18. The granulation device according to claim 16, wherein, The separator (11) has an outlet connected to a supply line for supplying the sprayer (7) within the first granulator compartment (3).

19. The granulating device according to claim 16, wherein, The scrubber (20) comprises: A first scrubber compartment (22) having a first sprayer (35) and an inlet for the granulator exhaust gas; A second scrubber compartment (23) having a second sprayer (37), said second scrubber compartment being downstream of the first scrubber compartment; A first water collection reservoir (31) for collecting the spent scrubbing liquid from the first scrubber compartment and partially from the second scrubber compartment; A first circulation loop (34) for returning the scrubbing liquid from the first water collection reservoir to the first sprayer (35); A second water collection reservoir (32) for collecting a portion of the spent scrubbing liquid from the second scrubber compartment; A second circulation loop (36) for returning the scrubbing liquid from the second water collection reservoir (32) to the second sprayer (23); wherein the second circulation loop is connected to an acid source.

20. The granulation device according to claim 19, wherein, The first scrubber compartment and the second scrubber compartment are separated by a demister.

21. The granulating device according to claim 20, wherein, The demister is a woven mesh or a grid mesh.

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