Granulation tower and method for producing urea-based granules

Abstract

The present disclosure provides a prilling tower comprising a vertical body, a spray device for forming droplets from a molten composition, one or more air inlets for drawing outside air into the prilling tower, one or more air outlets wherein the prilling tower comprises one or more water sprayers, the one or more water sprayers are used for spraying water drops into the external air sucked into the prilling tower through the one or more air inlets, and the one or more water sprayers are configured to be started when the relative humidity of the external air is lower than a critical value.

Description

Technical Field

[0001] This disclosure relates to the field of fertilizer production, and in particular to granulation towers. This disclosure also relates to a method for producing granules using such granulation towers. Background Technology

[0002] A granulation tower is a tall structure (some exceeding 100 meters in height) used for the production of granules, particularly fertilizer granules. A granulation tower includes a spraying device, such as a granulation drum, located at the top of the tower, which sprays small droplets of the molten composition. The droplets fall to the bottom of the tower by gravity. During the autumn season, the droplets cool and solidify into granules upon contact with the counter-current outside air.

[0003] However, it has been observed that meteorological conditions may have a negative impact on particle quality, and there is a need to develop a new granulation tower that can produce high-quality particles independently of local weather conditions. Summary of the Invention

[0004] In a first aspect, this disclosure provides a method for producing urea-containing granules in a granulation tower, the granulation tower comprising:

[0005] - Vertical body;

[0006] - A spraying device for forming droplets from a molten composition;

[0007] - One or more air inlets for drawing outside air into the granulation tower;

[0008] -One or more air outlets;

[0009] - One or more water sprayers for spraying water droplets into outside air drawn into the granulation tower via one or more air inlets, the method comprising:

[0010] a) Create an airflow of external air from one or more air inlets to one or more air outlets;

[0011] b) Using a spraying device to form droplets from a molten composition containing urea;

[0012] c) Measure the relative humidity of the outside air;

[0013] d) When the relative humidity of the outside air is below a critical value, spray water onto the airflow using one or more sprinklers; and

[0014] e) Remove the urea-containing granules formed from the droplets from the granulation tower. Attached Figure Description

[0015] The following description of specific embodiments of the system according to this disclosure is given by way of example only and is not intended to limit this description, its application, or use. In the drawings, the same reference numerals refer to the same or similar parts and features.

[0016] Figure 1 shows an embodiment of a granulation tower for performing the method according to this disclosure. Detailed Implementation

[0017] Unless otherwise defined, all terms used in disclosing this invention, including technical and scientific terms, have the meaning commonly understood by one of ordinary skill in the art to which this invention pertains. Further guidance is provided, including terminology definitions, to better understand the teachings of this invention.

[0018] All references cited in this specification are hereby considered as incorporated herein by reference in their entirety.

[0019] As used herein, the following terms have the following meanings:

[0020] Unless the context clearly specifies otherwise, the terms “a,” “an,” and “the” as used herein refer to the singular and plural referents, respectively. For example, “entrance” refers to one or more entrances.

[0021] As used herein, “about” refers to a measurable value, such as a parameter, quantity, duration, etc., meaning a variation covering the specified value and a variation of + / - 20% or less, particularly + / - 10% or less, more particularly + / - 5% or less, even more particularly + / - 1% or less, and still more particularly + / - 0.1% or less, provided that such variation is suitable for implementation in the disclosed invention. However, it should be understood that the value referred to by the modifier “about” is itself specifically disclosed.

[0022] As used herein, “comprising” and its variations and “consisting of” are synonymous with “including” and its variations or “containing” and its variations, and are inclusive or open-ended terms that specify the presence of, for example, content following a component, and do not exclude or preclude the presence of additional, unlisted components, features, elements, components, steps known in the art or disclosed therein.

[0023] The range of values ​​represented by the endpoints includes all numbers and fractions contained within that range, as well as the endpoints themselves.

[0024] Unless otherwise defined, the expressions “percentage by weight,” “%wt,” or “weight %” herein and throughout the specification mean the relative weight of the corresponding component based on the total weight of the formulation.

[0025] In a first aspect, this disclosure provides a method for producing urea-containing granules in a granulation tower, the granulation tower comprising:

[0026] - Vertical body;

[0027] - A spraying device for forming droplets from a molten composition;

[0028] - One or more air inlets for drawing outside air into the granulation tower;

[0029] -One or more air outlets;

[0030] - One or more water sprayers for spraying water droplets into outside air drawn into the granulation tower via one or more air inlets, the method comprising:

[0031] a) Create an airflow of external air from one or more air inlets to one or more air outlets;

[0032] b) Using a spraying device to form droplets from a molten composition containing urea;

[0033] c) Measure the relative humidity of the outside air;

[0034] d) When the relative humidity of the outside air is below a critical value, spray water onto the airflow using one or more sprinklers; and

[0035] e) Remove the urea-containing granules formed from the droplets from the granulation tower.

[0036] In a second aspect, this disclosure provides a granulation tower comprising:

[0037] - Vertical body;

[0038] - A spraying device for forming droplets from a molten composition;

[0039] - One or more air inlets for drawing outside air into the granulation tower;

[0040] - One or more air outlets; and

[0041] - One or more water sprayers for spraying water droplets into outside air drawn in by one or more air inlets, wherein one or more water sprayers are configured to activate when the relative humidity of the outside air is below a critical value.

[0042] A conventional granulation tower includes a vertical body, a spraying device for forming droplets from the molten composition, one or more air inlets for drawing outside air into the granulation tower, and one or more air outlets.

[0043] As used in this article, the term "external air" refers to the air outside the granulation tower. External air can also be referred to as outdoor air.

[0044] The spraying device is located at the top of the granulation tower to maximize the distance the droplets travel and thus maximize the cooling effect of the air on the droplets. One or more air inlets and one or more air outlets create an airflow from the bottom to the top of the granulation tower. Air and droplets flow in opposite directions to maximize the cooling effect of the airflow. The air inlets may include devices for regulating the airflow through them, such as screens, louvers, or blinds. The air outlets may include devices for regulating the airflow through them, such as screens, louvers, or blinds.

[0045] A crucial parameter for granules produced by granulation towers is their compressive strength. Once produced, granules undergo numerous operations before reaching the end customer (farmer), including collection, bagging, storage, and transportation. If the granules have low compressive strength, all these operations will reduce their strength, generate dust, and ultimately turn them into powder. This is highly undesirable because granules are easier for farmers to distribute, and powder has a higher surface area, resulting in higher hygroscopicity, which further reduces granule strength. Granules with low compressive strength may also be rejected by customers and must be recycled at the production plant, causing financial losses for the manufacturer.

[0046] The compressive strength of particles can be measured using standard techniques known to those skilled in the art. For example, a suitable method is to place the particles on a support and apply gradually increasing forces to them using a device until the particles break. The force applied by the device when the particles break is the compressive strength of the particles.

[0047] In some embodiments, the urea-containing granules produced by the method according to the first aspect contain at least 70% by weight, at least 80% by weight, at least 90% by weight, at least 95% by weight, at least 98% by weight, 95% to 99.9% by weight, 95% to 99% by weight, or 98% to 99.5% by weight of urea.

[0048] In some implementations, the urea-containing granules may further contain one or more elements selected from the group consisting of potassium, phosphorus, magnesium, calcium, and sulfur.

[0049] The characteristics of the airflow entering the granulation tower depend primarily on the weather conditions at the production plant, and the air temperature and relative humidity can vary significantly over several days. For example, in Balbar, Uttar Pradesh, India, relative humidity has been observed to vary from 11 to 38% over 10 days.

[0050] As used in this article, the term "relative humidity" can be used to describe the current absolute humidity relative to the maximum humidity at a given temperature. It is defined as the ratio of the partial pressure of water vapor in the air to the saturated vapor pressure of water at the same temperature multiplied by 100, and is dimensionless.

[0051] By monitoring the relative humidity at the urea production plant and the quality of the produced granules daily, it was observed that when the relative humidity of the air entering the granulation tower was below 20%, the compressive strength of the granules decreased significantly.

[0052] For urea granules containing at least 95% by weight and manufactured in Bapulara, Uttar Pradesh, India, the weight should be at least 18.5 kg / cm². -2 The compressive strength is considered satisfactory. However, for some particles produced at relative humidity below 20%, as low as 13 kg·cm⁻¹ was measured. -2 The compressive strength.

[0053] To address this problem, it was discovered that a water sprayer could be installed inside the granulation tower near one or more air inlets. The water sprayer is configured to spray water droplets into the outside air drawn into the granulation tower through one or more air inlets, and the water sprayer is configured to activate when the relative humidity of the outside air is below a critical value.

[0054] By spraying water droplets into the airflow entering the granulation tower, the relative humidity of the airflow increases, and the compressive strength of the particles increases.

[0055] In some implementations, the granulation tower includes more than one air inlet and at least one water sprayer for each air inlet. The granulation tower can be very large, up to at least 100 m high and at least 20 m in diameter, and has a very high daily output, at least 3,000 metric tons of urea granules per day. A single air inlet may not be sufficient to generate enough airflow to cool all the granules. Therefore, the granulation tower may include more than one air inlet. To ensure that the relative humidity of the air inside the granulation tower is relatively uniform across the cross-section of the granulation tower, it may be advantageous for each air inlet to include at least one water sprayer configured to spray water droplets into the airflow entering the granulation tower through the air inlet. Depending on the size of the air inlet and the spraying capacity of the water sprayer, the granulation tower may include more than one water sprayer for each air inlet.

[0056] In some implementations, one or more water sprayers are located inside the granulation tower. Positioning the water sprayers inside the granulation tower can be advantageous, as it ensures that all water sprayed by the sprayers is captured by the airflow heading towards the outlet.

[0057] In some implementations, the granulation tower includes one or more fans for drawing air into the granulation tower. To create airflow inside the granulation tower, some granulation towers rely on natural ventilation formed by inlets and outlets. However, some towers may include one or more fans to aid in creating ventilation and / or increase natural ventilation.

[0058] In some implementations, one or more air outlets are located above the spraying device. To maximize the airflow and cooling effect inside the granulation tower, one or more air outlets may be located near the top of the granulation tower.

[0059] In some implementations, one or more air inlets are located at a height of up to 20% or up to 10% of the total height of the granulation tower. To maximize the airflow and cooling effect within the granulation tower, one or more air inlets are typically located near the bottom of the granulation tower.

[0060] In some embodiments, the spraying device is a granulation barrel. A granulation barrel is a device, typically with a conical design, whose walls include multiple through-holes. A molten composition is continuously fed into the interior of the granulation barrel, and the barrel rotates continuously. Rotation causes the melt to flow against the barrel wall and pushes it through the through-holes, thereby forming molten droplets.

[0061] In some implementations, one or more sprayers are configured to increase the relative humidity of the outside air drawn into the granulation tower to at least 20%. For a urea plant in India that produces urea granules containing at least 98% by weight of urea, it has been found that a critical relative humidity of about 20 is needed to obtain granules with satisfactory compressive strength.

[0062] The critical values ​​for each plant and each product can depend on many factors, such as the size of the tower, the composition of the granulated product, and the plant's productivity. The critical values ​​for each product and plant can be determined through a series of experiments and observations.

[0063] In some implementations, one or more water sprayers are connected to a water source. The water source may vary depending on the local conditions of the plant and the availability of different water sources. In some implementations, the water source is a process condensate stream. Process condensate refers to the water stream produced by a plant (particularly a urea production plant) by condensing a gas stream containing water vapor. Connecting a water source to one or more water sprayers produces water with very low impurity levels, which can be an advantage because any impurities contained in the water source could contaminate the particles and / or the gas stream leaving the granulation tower.

[0064] In some implementations, the granulation tower includes a device for measuring the relative humidity of the outside air. This inclusion of a device for measuring the relative humidity of the outside air can be advantageous for granulation tower operation and for rapid response to changes in weather conditions. This ensures that operators of the granulation tower can respond quickly to changes in relative humidity and immediately activate the spray system when the relative humidity falls below a critical value. Technicians are familiar with several methods for measuring the relative humidity of air. For example, a combination of a wet-bulb thermometer and a dry-bulb thermometer can be used to measure the relative humidity of air, such as the humidity of the air outside the granulation tower. By reading the temperatures indicated by these two thermometers, the relative humidity of the air can be calculated.

[0065] In another aspect, this disclosure provides a method for producing granules using a granulation tower according to the second aspect, the method comprising the following steps:

[0066] a) Creates an airflow of external air from one or more air inlets to one or more air outlets;

[0067] b) Using a spraying device to form droplets from the molten composition;

[0068] c) Measure the relative humidity of the outside air;

[0069] d) When the relative humidity measured in step c) is below a critical value, spray water using one or more sprinklers; and

[0070] e) Remove the particles formed from the droplets from the granulation tower.

[0071] Step a) of the method is to form an airflow from one or more inlets to one or more outlets. The airflow can be natural ventilation. The speed and flow rate of natural ventilation can depend on many factors, such as the height difference between one or more inlets and one or more outlets, the combined surface area of ​​the inlets, and the combined surface area of ​​the outlets. Mechanical devices (such as air pumps or fans) included in the granulation tower can also be used to form or increase the airflow. An airflow is required to cool the molten droplets.

[0072] In some implementations, the airflow velocity is at least 500,000 m. 3 / h or at least 900,000 m 3 / h.

[0073] Step b) of the method involves forming droplets from the molten composition using a spraying device of the granulation tower. Droplets can be formed by pushing or forcing the molten composition through a surface including through-holes (such as a granulation tank or nozzle). The size of the droplets depends directly on the through-holes.

[0074] In some embodiments, the molten composition is a urea melt containing at least 95% by weight of urea.

[0075] Step c) of the method is to measure the relative humidity of the outside air. Step c) can be performed continuously during production. It can be performed before step a) and / or step b). Measuring the relative humidity of air (such as outside air) is a well-known task for technicians. Different systems can be used to perform this task. For example, a combination of a wet-bulb thermometer and a dry-bulb thermometer can be used to measure the relative humidity of the air.

[0076] Step d) of the method involves spraying water using one or more sprayers when the relative humidity measured in step c) is below a critical value. To obtain high-quality granules, the relative humidity inside the granulation tower must be maintained above a specific critical value. This critical value can depend on several factors, such as the composition of the product produced in the granulation tower, the size of the produced granules, and the location of the granulation tower. For example, in Uttar Pradesh, India, a plant producing urea containing at least 98% by weight granules found critical relative humidity values ​​of 18 to 25, 18 to 22, or 20.

[0077] In some implementations, water spraying is initiated when the relative humidity measured in step c) is below 22, 20, or 18.

[0078] Step e) of the method involves removing particles formed from droplets from the granulation tower. Once the particles have reached the bottom of the granulation tower, they are moved for further processing and storage. When the particles reach the bottom of the granulation tower, they may only be partially solid. For example, the core of the particle may still be partially liquid.

[0079] An example of further processing is a coating step. In some embodiments, the method includes applying a coating agent to the granules removed from the granulation tower. Urea granules can be coated with a coating agent to improve some properties of the granules. For example, urea granules can be coated with neem oil. In some embodiments, the coating agent is neem oil. In some embodiments, the method includes coating the granules removed from the tower in step e) with at least 200 ppm neem oil, with 200 ppm to 500 ppm neem oil, with 300 ppm to 500 ppm neem oil, or with 300 ppm to 400 ppm neem oil.

[0080] In some embodiments, the molten composition used in step b) contains at least 90% by weight of urea.

[0081] In some embodiments, the molten composition used in step b) comprises at least 70% by weight, at least 80% by weight, at least 90% by weight, at least 95% by weight, at least 98% by weight, 95% to 99.9% by weight, 95% to 99% by weight, or 98% to 99.5% by weight of urea.

[0082] In some implementations, the critical value for relative humidity is 20.

[0083] Figure 1 shows the interior of a granulation tower 1 according to one embodiment of the present disclosure. The granulation tower 1 includes a vertical cylindrical body 2, an air outlet 4 located at the top of the granulation tower 1, and an air inlet 3 located at the bottom of the granulation tower 1. The granulation tower 1 also includes a granulation tank 7 for spraying urea melt and forming droplets. A device 6 for measuring the relative humidity of the outside air is attached to the outer wall of the granulation tower 1. The granulation tower 1 includes a water sprayer 5 located inside the granulation tower 1 and directly in front of the air inlet 3.

[0084] Example

[0085] Several urea granule samples were collected in April and May 2021 from a urea production plant in Bapulara, Uttar Pradesh, India, which was producing urea granules containing 95% to 99% wt% urea in a granulation tower. The relative humidity of the atmosphere at the time of sampling was recorded, and the compressive strength of the granules was measured using a single-particle loading technique, where a gradually increasing load was applied to one particle at a time (see Table 1). The compressive strength was measured for several granules, and the average values ​​of the obtained data are shown in the table below. Compressive strength is expressed in kg·cm². -2 express.

[0086]

[0087] Table 1

[0088] Subsequently, 20 nozzles were installed inside the granulation tower, near the air inlet at the bottom. The nozzles activated when the combined reading of the dry-bulb and wet-bulb thermometers indicated that the relative humidity outside the granulation tower was below 20%. The compressive strength of the granules was consistently measured to exceed 18.5 kg·cm². -2 .

[0089] Those skilled in the art will recognize that the present invention is by no means limited to the embodiments described above. Rather, many modifications and variations can be made within the scope of the appended claims.

Claims

1. A method for producing urea-containing granules in a granulation tower, the granulation tower comprising: - Vertical body; - A spraying device for forming droplets from a molten composition; - One or more air inlets for drawing outside air into the granulation tower; -One or more air outlets; - One or more water sprayers for spraying water droplets into the outside air drawn into the granulation tower via the one or more air inlets, the method comprising: a) To create an airflow of external air from the one or more air inlets to the one or more air outlets; b) Using the spraying device to form droplets from the molten composition containing urea; c) Measure the relative humidity of the outside air; d) When the relative humidity of the outside air is below a critical value, water is sprayed onto the airflow using one or more of the water sprayers; and e) Remove the urea-containing granules formed from the droplets from the granulation tower.

2. The method of claim 1, wherein the granulation tower comprises more than one air inlet and at least one water sprayer for each air inlet.

3. The method according to claim 1 or 2, wherein the one or more water sprayers are located inside the granulation tower.

4. The method according to any one of claims 1 to 3, wherein the granulation tower includes one or more fans for drawing air into the granulation tower.

5. The method according to any one of claims 1 to 4, wherein the spraying device is a granulation tank.

6. The method according to any one of claims 1 to 5, wherein the one or more water sprayers are configured to increase the relative humidity of the external air drawn into the granulation tower to at least 20.

7. The method according to any one of claims 1 to 6, wherein the one or more water sprayers are connected to a water source.

8. The method according to any one of claims 1 to 7, wherein the granulation tower further comprises means for measuring the relative humidity of the external air drawn into the granulation tower.

9. The method of claim 8, wherein the device for measuring the relative humidity of the outside air comprises a dry-bulb thermometer and a wet-bulb thermometer.

10. The method according to any one of claims 1 to 9, wherein the molten composition used in step b) comprises at least 70% by weight, at least 80% by weight, at least 90% by weight, at least 95% by weight, at least 98% by weight, 95% to 99.9% by weight, 95% to 99% by weight, or 98% to 99.5% by weight of urea.

11. The method according to any one of claims 1 to 10, wherein water spraying is initiated when the relative humidity measured in step c) is below 20%.

12. The method according to any one of claims 1 to 11, wherein the method further comprises the following steps: f) Apply the coating agent to the particles removed from the granulation tower in step e).

13. The method of claim 12, wherein the coating agent is neem oil.

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