CN111774006A

CN111774006A - Fluidized bed granulator

Info

Publication number: CN111774006A
Application number: CN202010673988.3A
Authority: CN
Inventors: 王威; 王濛光
Original assignee: Green Granulation Co ltd
Current assignee: Green Granulation Co ltd
Priority date: 2012-08-08
Filing date: 2013-08-08
Publication date: 2020-10-16
Also published as: CN103657519A; NL2009297C2

Abstract

Fluid bed granulator (1) comprising one or more compartments (2, 3, 4), said one or more compartments (2, 3, 4) having a floor (12), said floor (12) having openings for supplying a fluidizing medium and a plurality of sprayers (21). The atomizer is connected to a source of granulation liquid and is configured to spray the liquid in one or more spray zones (29), the one or more spray zones (29) being adjacent to one or more non-spray zones (30) of the fluidized bed.

Description

Fluidized bed granulator

The application is a divisional application of Chinese patent application with the application date of 2013, 8.8.8, the application number of 201310442474.7 and the name of 'fluidized bed granulator'.

Technical Field

The present invention relates to a fluidized bed reactor and a method for producing granules, such as urea or ammonium nitrate granules, which are commonly used as fertilizers.

Background

US4,619,843 discloses a method for preparing solid particles by feeding a urea solution into a fluidized bed of solid nuclei. The liquid solidifies on the core to form the particles. The crystallization of urea generates heat which is removed by evaporation of the water and by the air acting as a fluidizing agent.

To alleviate the problem of caking during storage of the urea granules, the water content in the final granules should be low, e.g. below 0.25% of the total weight of the granules.

To produce drier granules, the residence time in the granulator may be increased, for example by using a higher bed height. However, this requires a higher pressure of the fluidizing air and thus higher energy consumption.

Alternatively, the water content may be reduced by atomizing the urea solution into finer droplets. This requires more air to atomize the urea solution and is therefore more energy intensive.

A lower water content in the final granulate can also be achieved by spraying a more concentrated urea solution. For example, EP-A0289074 teaches the use of solutions having a urea content of from 70 to 99.9% by weight. However, the use of a urea concentrate with a lower water content reduces the cooling effect of the water evaporation. As a compensation for this problem, the cooling effect of the air should be enhanced by the higher flow velocity of the air for fluidization. Thus, this option also results in higher energy consumption.

Disclosure of Invention

It is an object of the present invention to provide a fluid bed granulator and a process which do not require high energy consumption to produce dry granules.

The object of the invention is achieved by a fluid bed granulator comprising one or more compartments having a floor with an opening for supplying a fluidizing medium and a plurality of sprayers connected to a source of granulation liquid, e.g. an aqueous urea solution. The sprayers are configured to spray liquid in one or more spray zones adjacent to one or more non-spray zones of the fluidized bed. By establishing a non-spray zone in the compartment outside the range of the nebulizer, the nuclei will swirl downward until they swirl back up with the flow generated by the nebulizer.

Surprisingly, it has been found that this uneven distribution of the atomizer results in particles having a very low water content, while keeping the overall energy consumption of the process low. The moisture content of the granules produced using the granulator of the present invention may be well below 0.3 wt%, or even well below 0.25 wt% of the total weight of the granules.

In one embodiment, the sprayers are spaced at non-uniform distances from each other. Optionally, the sprayers are arranged in clusters (cluster), wherein the shortest distance between sprayers in a cluster is less than the shortest distance between two clusters. Good results can be obtained when the clusters extend in parallel in the main flow direction of the core. The primary flow direction is the horizontal direction of the nuclei from the inlet to the outlet of the granulator without the swirl imparted by the fluidizing medium. In such a configuration, the distance between the parallel clusters may be, for example, about 0.5 meters to about 1 meter, while the distance between the sprayers in the clusters may be, for example, about 0.1 meters to about 0.4 meters. The distance between clusters may be, for example, about 2-3 times the distance between sprayers within a cluster. Other distances may also be used if desired. Alternatively or additionally, non-spray areas outside the scope of the sprayer may be created by orienting the sprayer in different directions (e.g., away from each other). In this case, the sprayers may be distributed uniformly or non-uniformly.

In one embodiment, the density of sprayers in at least one compartment is at least 7 sprayers per square meter, and the density of each sprayer cluster is at least 25 sprayers per square meter. Optionally, the granulator comprises: a first compartment having a nebulizer density of at least 9 nebulizers per square meter and a density of at least 29 nebulizers per square meter per cluster of nebulizers in the first compartment; and at least one additional compartment having a nebulizer density of at least 7 nebulizers per square meter and a density of at least 25 nebulizers per square meter per cluster of nebulizers. Other configurations may also be used if desired.

The atomizer may for example be an atomizer or a hydraulic atomizer, such as an air-assisted hydraulic atomizer. Combinations of these types of sprayers may also be used. One suitable type of sprayer is disclosed, for example, in US4,619,843.

When the solution is sprayed into the granulator compartment, the solution may for example have a temperature substantially above the crystallization point. If the solution is a urea solution, the solution may be sprayed, for example, at a temperature of at least about 120 deg.C, or at least about 130 deg.C, or at least about 135 deg.C. If the solution is an ammonium nitrate solution, the solution may be sprayed, for example, at a temperature of at least about 160 ℃ or at least about 170 ℃ or at least about 180 ℃. The solution may be sprayed, for example, at a hydrostatic pressure of 1.5-6bar (e.g., 2-4bar) or other suitable pressure. The ejected droplets can, for example, have an average droplet size of about 20 to about 120 μm (e.g., about 30 to about 60 μm).

For urea granulation, a highly concentrated solution may be used, e.g. with a urea content of at least 90 wt%, e.g. at least 95 wt%, of the total weight of the urea solution.

The water content of the urea solution is generally low, for example less than 5 wt% of the total weight of the urea solution, for example less than 3 wt% of the total weight of the urea solution. If the water content is below 2.5 wt%, the solution is usually referred to as urea melt (melt).

The urea solution may also contain additives, such as formaldehyde and/or urea-formaldehyde condensates (condensation), as granulation aids for reducing the rate of urea crystallization and as anti-caking agents to prevent caking of the formed granules. The atomized droplets adhere better to the urea nuclei if, for example, 0.1 to 3% of formaldehyde, based on the total weight of the urea solution, is added to the aqueous urea solution. Other suitable additives may also be used.

For ammonium nitrate granulation, Mg (NO3)2 and aluminium sulphate, for example together with NaOH, are examples of suitable additives.

The cores may be fed to the granulator through one or more inlets at the inlet side of the granulator. The nuclei may be fed continuously, or fed and processed in batches.

The core may have any suitable average particle size prior to being subjected to the granulation process, typically about at least 0.2mm, or at least 0.5mm, typically up to 6 mm.

The core may have any suitable composition. In general, these nuclei may mainly comprise the same material as the crystallization granulation liquid (in particular, crystalline urea), but nuclei having a different composition from the crystallization granulation liquid may also be used.

Usually, air is used as fluidizing agent. However, other suitable fluidizing gases may be used. For prilled urea, the flow velocity of the fluidising gas in the fluidised bed may for example be in the range of from about 1 to 8 m/s, such as at least about 2 m/s and/or up to about 3 or 4 m/s. For prilling ammonium nitrate, the flow velocity of the fluidising gas in the fluidised bed may for example be in the range of from about 1 to 8 m/s, for example at least about 2 m/s and/or up to about 3.5 or 4.5 m/s. The fluidizing gas can enter the pelletizer at any suitable pressure (e.g., 300-900 mm water, such as 400-600 mm water) and at any suitable temperature (but preferably below about 140 ℃ or below about 110 ℃).

For urea granulation, the temperature in the compartment of the granulator may for example be between 90-120 ℃, for example between 100-106 ℃. For ammonium nitrate granulation, the temperature in the compartment of the granulator may be, for example, between 110-140 ℃, for example between 125-130 ℃. Typically, the temperature in the first compartment is lower due to the backflow of recycled material. This can be compensated for by using a higher density nebulizer in the first compartment.

The fluidized bed may, for example, have a bed height of 1.5m or less (e.g., about 1m or less).

The treated granules are typically discharged continuously or batchwise through one or more outlets of the granulator. The treated particles typically have an average particle size of from about 2 to about 4mm, but the average particle size can be smaller or larger if desired. The moisture content of the granules can be kept well below 0.3 wt%, for example well below 0.25 wt% of the total weight of the granules.

Particles having a particle size above a given limit may be separated from the effluent. Optionally, the granules may be crushed and then recycled to the granulator, for example together with granules of too small a particle size and/or material separated from the air discharged from the granulator.

The granulator may have one or more granulator compartments arranged in series and/or in parallel. In a particular embodiment, the granulator has at least two, e.g. three or more compartments arranged in series.

The floor of the granulator compartment provides an inlet for the fluidizing agent. To this end, the floor may be, for example, a grid located above the air source.

Optionally, the granulator may comprise an aftercooler, such as a fluid bed cooler, which receives the discharged granules from the granulator compartment. An aftercooler may for example be used to cool the particles to a temperature of about 40 ℃.

The granulator according to the invention is particularly suitable for use in a process for producing granules, wherein the granulation liquid is sprayed to the compartments in spray zones of the fluid bed alternating with non-spray zones.

Each spray zone may be generated, for example, by a cluster of sprayers. In the spray zone, the granulation liquid flows upwards. The non-spray area is not within the confines of the sprayer and allows the nuclei to flow downward. It has been found that the nuclei flow faster through the spray zone, so that less new solution settles on the nuclei each time they pass through the spray zone. A thinner solution layer allows for better evaporation of water. In the non-spray zone, the nuclei flow downward and are recirculated to the spray zone. As a result, the nuclei pass through the spray area many times. Each time they pass through the spray area, they collect an additional coating of spray solution. Finally, this results in particles of the desired size with a lower residual moisture content. As a result, the mean residence time of the nuclei in the granulator can be reduced, and the fluidized bed level can thus be kept low, which in turn requires a lower fluidizing air pressure and lower energy consumption.

The process may for example be carried out as a continuous process in which the material of the fluidised bed is moved in a flow direction from one or more inlets to one or more outlets of the pelletiser, the spray zone being parallel to the flow direction.

Good results can be obtained if the method is carried out in such a way that the shortest distance between two sprayers located on opposite sides of the non-spraying zone is at least half the height of the fluidized bed contained in the respective compartment.

Drawings

Exemplary embodiments of a granulator according to the present invention will be described below with reference to the accompanying drawings.

FIG. 1: showing a cross-section of a granulator according to the present invention along the flow direction;

FIG. 2: a cross-section perpendicular to the flow direction of the granulator of figure 1 is shown;

FIG. 3: there is shown a plan view of the pelletizer of figure 1.

Detailed Description

Fig. 1 shows an exemplary embodiment of a granulator for producing urea granules or ammonium nitrate granules. The granulator 1 is divided into three compartments 2, 3, 4 for granulation and a compartment 5 for subsequent cooling and drying of the granules.

The first compartment 2 of the granulator 1 comprises an inlet 7 for supplying a core (core). Opposite the inlet 7 is a first passage 8, the first passage 8 leading to the second compartment 3. The second compartment 3 comprises a second channel 9 opposite the first channel 8 and leading to the third compartment 4. The third compartment 4 comprises an outlet 10 opposite the second channel 9. As a result, nuclei can flow from the inlet 7 to the outlet 10 along a straight flow path, which is indicated by arrow a in fig. 1.

The granulator 1 comprises a bottom plate 12 made of a grid (grid), the bottom plate 12 supporting a bed 13 of nuclei and allowing the passage of a fluidizing agent (for example air) supplied from a space 14 below the grid bottom plate 12 and preheated by a heater 15 in the space 14. The heated air fluidizes the bed of nuclei 13.

The space 14 below the grid base 12 is divided into compartments 17, 18, 19 corresponding to the compartments 2, 3, 4 above the grid base 12. In each compartment 2, 3, 4, the grate base plate 12 of the granulator 1 has a cluster of air-assisted sprayers 21, which air-assisted sprayers 21 project above the grate base plate 12. The sprayer 21 sprays the aqueous urea solution into the fluidized bed 13. In the granulator compartments 2, 3, 4, the water in the sprayed urea solution evaporates and the urea crystallizes on the nuclei, which grow to form granules.

Aftercooler 5 is a fluidized bed cooler having a grid floor 22 supporting a bed 23 of freshly produced particles and a space below grid floor 22 having a heater 24 to supply air to fluidize and dry bed 23.

Air and air-borne dust particles are discharged from the granulator compartments 2, 3, 4 and the aftercooler 5. The air may be stripped (stripped), for example in a scrubber tower and/or cyclone or similar separator. The separated dust particles may be recycled to the granulator.

The aftercooler 5 has an outlet 26 for discharging the dried and cooled particles. Subsequently, the undersized and oversized particles are separated from the desired sized particles, which are discharged and stored. Oversized particles may be crushed into smaller particles that may be recycled with undersized particles.

Fig. 2 shows a cross-section of the granulator 1 through a plane perpendicular to the flow direction a. In the particular embodiment shown, the sprayers 21 in the compartments are arranged in three clusters 27 with spaces 28 between the clusters 27. Each cluster 27 produces a spray area 29 by the air-assisted sprayer 21, in which spray area 29 nuclei are caused to flow upwards. The spaces 28 between the clusters 27 form non-spray areas 30 with no atomizing air, and nuclei tend to flow downward (arrows B in fig. 2) in the non-spray areas 30.

The arrangement of the sprayer 21 is shown in the plan view of fig. 3. In this exemplary embodiment, the first compartment 2 comprises 64 sprayers 21 arranged in three parallel clusters 27. In a compartment 3m wide and 2.35m long this means that the average nebulizer density exceeds 9 nebulizers per square meter. The clusters 27 in the first compartment have the same width and the same length. The middle cluster 27 comprises 3 rows of 8 sprayers each. The other two clusters each comprise 8 columns with alternately two and three sprayers, adding up to a total of 16 sprayers per cluster. For a cluster width of 0.4m and a cluster length of 1.7m, the density of sprayers in the middle cluster will exceed 35 sprayers per square meter, while the density of sprayers in the other two clusters will exceed 29 sprayers per square meter.

The second compartment 3 and the third compartment 4 have three parallel clusters 27, each cluster 27 having 18 sprayers. For a cluster width of 0.4m and a cluster length of 1.7m, the sprayer density of these clusters 27 will exceed 26 sprayers per square meter. In a compartment 3m wide and 2.35m long, this represents an average nebulizer density of over 7 nebulizers per square meter. In each cluster 27 of the second compartment 3 and the third compartment 4, the cluster 27 has six columns of three sprayers 21 each. The distance between the second and third rows and the distance between the fourth and fifth columns is greater than the distance between the other columns.

Claims

1. A fluid bed granulator (1) comprising one or more compartments (2, 3, 4) having a floor (12), said floor (12) having openings for supplying a fluidizing medium and a plurality of sprayers (21) connected to a source of granulating liquid,

wherein the atomiser is configured to inject the liquid in one or more spray zones (29) adjacent to one or more non-spray zones (30) of the fluidised bed;

wherein all the sprayers (21) are arranged in clusters (27), and

wherein the density of sprayers in at least one compartment is at least 7 sprayers per square meter and the density of sprayers per cluster is at least 25 sprayers per square meter.

2. A fluid bed granulator according to claim 1, wherein the shortest distance between adjacent sprayers in a cluster is smaller than the shortest distance between two adjacent clusters.

3. A fluid bed granulator according to claim 1 or 2, wherein the clusters (27) are parallel clusters extending in the flow direction (a).

4. A fluid bed granulator according to claim 3, wherein the distance between the parallel clusters (27) is about 0.4 to 1 meter.

5. A fluid bed granulator according to any of the preceding claims, wherein the distance between the sprayers (21) in the clusters (27) is about 0.1 to 0.4 meters.

6. A fluid bed granulator according to any of the preceding claims, wherein for at least a part of the sprayers (21), the distance between clusters (27) is 2-3 times the distance between sprayers within a cluster.

7. A fluid bed granulator according to any of the preceding claims, the granulator comprising: a first compartment (2), the density of sprayers of said first compartment (2) being at least 9 sprayers (21) per square meter, and the density of sprayers of each cluster in the first compartment being at least 29 sprayers per square meter; and at least one further compartment (3, 4), the nebulizer density of the at least one further compartment (3, 4) being at least 7 nebulizers per square meter and the nebulizer density of each cluster being at least 25 nebulizers per square meter.

8. A fluid bed granulator according to any of the preceding claims, wherein the base plate (12) is a grid base plate.

9. A fluid bed granulator according to any of the preceding claims, wherein the outlet of the granulator (1) leads to an aftercooler (5).

10. A fluid bed granulator according to claim 9, wherein the aftercooler is a fluid bed cooler (5).

11. A method of producing granules using a fluid bed granulator (1) according to any of the preceding claims,

wherein the fluidizing medium is blown into the compartment via openings in the floor (12) of the compartment, while granulation liquid is sprayed into the compartment in said spray zones (29) of the fluidized bed alternating with said non-spray zones (30).

12. A method according to claim 11, which is carried out as a continuous process in which the material of the fluidised bed is moved in a flow direction (a) from one or more inlets (7) to one or more outlets (10) of the granulator, wherein the spray zone (29) is parallel to the flow direction (a).

13. Method according to claim 12, the shortest distance between two sprayers (21) being at least half the height of the fluidized bed contained in the respective compartment (2, 3, 4) at opposite sides of the non-spraying zone (30).