Fluidized bed granulation

Abstract

Method and fluidized bed reactor for the production of granules, such as granules of urea or ammonium nitrate. The fluidized bed reactor comprises at least one granulation compartment with air inlets, and an air moving device downstream of the granulation compartment, e.g., downstream of at least one scrubbers. The air moving device is configured to draw air through said at least one air inlet into at least one granulation compartment.

Claims

1. A fluidized bed reactor comprising: a) at least one granulation compartment with one or more air inlets; b) at least one after-cooler compartment downstream of and integrated with the at least one granulation compartment; c) a single scrubber downstream of the granulation compartment; d) a single exhaust duct configured to provide a single exhaust stream from the at least one after-cooler compartment directly to the scrubber; e) at least one air moving device downstream the scrubber; wherein the granulation compartment is configured to draw air through said one or more air inlets into the granulation compartment; and, wherein the at least one air moving device has sufficient capacity to create a vacuum exceeding the total pressure drop between the air inlets and the air moving device.

2. The fluidized bed reactor according to claim 1, wherein the air moving device comprises one or more exhaust fans for discharging air.

3. The fluidized bed reactor according to claim 1, wherein the fluidized bed reactor comprises three granulation compartments.

4. The fluidized bed reactor according to claim 1, wherein the fluidized bed reactor comprises two after-cooler compartments.

5. A method for producing urea-based or ammonium nitrate-based granules using a fluidized bed reactor comprising at least one granulation compartment having one or more air inlets, at least one after-cooler compartment downstream of and integrated with the at least one granulation compartment and a bed of ammonium nitrate-based or urea-based granules, a single scrubber downstream of the granulation compartment, a single exhaust duct configured to provide a single exhaust stream from the at least one after-cooler compartment directly to the scrubber, and at least one air moving device downstream the scrubber; the method comprising: drawing air in the at least one granulation compartment through the one or more air inlets using the at least one air moving device; fluidizing the bed of granules with the drawn in air in the granulation compartment; spraying the granules with a granulating liquid; transferring the sprayed granules to the after-cooler; cooling the sprayed granules.

6. The method of claim 5, wherein drawing air in the at least one granulation compartment includes creating a pressure drop between the one or more air inlets and an air exhaust below 800 mm water column.

7. The method of claim 5, wherein the method further comprises: stripping air in the scrubber thereby separating dust particles from stripped air; and, recycling the dust particles to the at least one granulation compartment via one or more ducts.

8. The method according to claim 5, wherein the pressure drop over the granulation compartment is at most 500 mm water column.

9. The method according to claim 5, wherein drawing air in the at least one granulation compartment includes creating a pressure drop between the at least one air inlet and an air exhaust of between 10 and 100 mbar.

10. The method according to claim 9, wherein the pressure drop is between 10 and 80 mbar.

11. The method according to claim 5, wherein drawing air in the at least one granulation compartment includes creating a pressure drop over the granulation compartment of between 10 and 60 mbar.

12. The method according to claim 5, wherein the bed of granules includes urea-based granules.

13. The method according to claim 5, wherein the urea-based granules are selected from the list consisting of urea, urea ammonium nitrate, urea ammonium sulphate and urea doped with elemental sulphur.

14. The method according to claim 5, wherein the bed of granules include ammonium nitrate-based granules.

15. The method according to claim 14, wherein the ammonium nitrate-based granules are selected from the list consisting of ammonium nitrate and calcium nitrate.

16. The method according to claim 5, wherein drawing air in the at least one granulation compartment includes creating a pressure drop between the one or more air inlets and an air exhaust below 750 mm water column.

17. The method according to claim 5, wherein drawing air in the at least one granulation compartment includes creating a pressure drop between the at least one air inlet and an air exhaust of less than about 80 mbar.

18. The method according to claim 9, wherein the pressure drop is less than about 75 mbar.

19. The method according to claim 5, wherein drawing air in the at least one granulation compartment includes creating a pressure drop over the granulation compartment of less than about 50 mbar.

Description

BRIEF DESCRIPTION OF THE DRAWING

(1) FIG. 1: shows an exemplary fluidized bed reactor setup according to the invention. This system has being realized by Yara International ASA in a semi-industrial pilot plant (SIPP) in Sluiskil, The Netherlands.

(2) FIG. 2: shows a pressure graphs of the pressure in a fluidized bed reactor setup with two ventilators in different operational modes.

DETAILED DESCRIPTION OF THE ILLUSTRATIVE EMBODIMENT

(3) FIG. 1 shows an exemplary embodiment of a fluidized bed reactor 1 for the production of urea granules, or ammonium nitrate granules. The fluidized bed reactor 1 as shown in the figure comprises three granulation compartments 2, 3, 4 for granulation and two after-cooler compartments 5, 6 for subsequent cooling and drying the granules.

(4) The first granulation compartment 2 of the fluidized bed reactor 1 comprises an inlet 7 for the supply of nuclei. Opposite to the inlet 7 is a first passage 8, leading to the second compartment 3. The second compartment 3 comprises a second passage 9 opposite to the first passage 8 and leading to the third compartment 4. The third compartment 4 comprises an outlet 10 opposite to the second passage 9. As a result, the nuclei can flow from the inlet 7 to the outlet 10 in a straight flow path.

(5) The fluidized bed reactor 1 comprises a floor 12 made of a grid which supports a bed 13 of nuclei and which permits the passage of ambient fluidization air, supplied from a space 14 below the grid floor 12. Air inlets can for example be located at a side wall of the space 14 below the grid 12 and/or in the bottom of that space 14. In case the ambient air is relatively cold, for example during winter, the air can be preheated by heaters 15 in or upstream the space 14. The heated air fluidizes the bed 13 of nuclei.

(6) The space 14 below the grid floor 12 is divided into compartments 17, 18, 19 in line with the compartments 2, 3, 4 above the grid floor 12. In each of the compartments 2, 3, 4 the grid floor 12 of the fluidized bed reactor 1 is provided with clusters of air-assisted sprayers 21 projecting above grid floor 12. The sprayers 22 are fed with a flow of liquid product (e.g. urea or ammonium nitrate) (F1) and a flow of pressurized air (F2), and spray an aqueous solution of urea or ammonium nitrate into the fluidized bed 13. In the granulator compartments 2, 3, 4, the water of the sprayed urea or ammonium nitrate solution evaporates and urea crystallizes on the nuclei, which grow to form granules.

(7) The after-cooler is integrated into the fluidized bed reactor and comprises a fluidized bed cooler with a grid floor IT supporting a bed 13 of freshly produced granules and a space 20, 21 below the grid floor in line with the compartments 5 and 6 above the grid floor 12, also supplied with a heater 23 for the supply of air fluidizing and drying the bed 13.

(8) The after-cooler is provided with an outlet 24 for discharging the dried and cooled granules. Subsequently (not shown), undersized and oversized granules are separated from granules of the desired size, which are discharged for storage. The oversized granules can be crushed to finer particles, which can be recycled together with the undersized particles.

(9) Air and air borne dust particles are discharged from the granulator compartments 2, 3, 4 and the after-cooler compartments 5 and 6 via one or more air ducts 25 to at least one scrubbers 28. In the schematic drawing of FIG. 1 a single scrubber is shown. Separate scrubbers may be used for treating air from the granulation compartments and air from the cooler, respectively. The scrubber may be a wet scrubber.

(10) In the scrubber 28 the air is stripped. Separated dust particles can be recycled to the granulator compartments 2, 3, 4 via one or more ducts 27. Clean air leaves the scrubber 28 via a discharge duct 29 comprising an exhaust fan 30.

(11) The exhaust fan 30 creates a pressure drop of about 10 and 100 mbar, e.g., about 75 mbar over the full flow path from the grid floor 12, 12 to the exhaust fan 30. As a result, fluidization air is sucked into the granulation compartments 2, 3, 4 via the grid floors 12 and 12. No additional blowers are provided. The difference with known systems is shown in FIG. 2. FIG. 2 shows a pressure graphs of the pressure in a system, with either a downstream ventilator active (this application, C), an upstream ventilator active (A), or both an upstream ventilator and a downstream ventilator active (B) active such that a small underpressure (0.1 to 10 mbar) is formed in the fluidized bed reactor, as disclosed in U.S. Pat. No. 5,779,945 (DSM N.V., 1998) and EP 2253374 A1 (Stamicarbon, 2010). It is obvious that in the setup according to this invention, a larger underpressure is formed in the fluidized bed reactor, typically between 10 and 60 mbar.

EXAMPLE

(12) A setup of the fluidized bed reactor according to the invention with three granulation compartments and integrated after-cooler was used for the continuous production of ammonium nitrate granules (see FIG. 1). The parameters of the experiment are summarized in the Tables 1 and 2 below. These are typical parameters for the operation of the fluidized bed reactor according to the invention.

(13) TABLE-US-00001 TABLE 1 Average material balance After After Units Start 7 hours 13.5 hours Outflow granulator kg/h 11,775 11,385 11,221 Ready product after sieving kg/h 7,660 7,520 7,380 Fines after sieving kg/h 2,782 2,388 2,784 (returned to granulator) Coarse after sieving kg/h 1,308 1,452 1,032 (to be crushed) Product after crushing kg/h 1,308 1,452 1,032 Dust at exit granulator kg/h n.m. n.m. n.m. Dust after ventilator kg/h n.m. n.m. n.m. Agglomerates kg/h 25 25 25 n.m. not measured

(14) TABLE-US-00002 TABLE 2 Process parameters Ammonium nitrate solution Temperature 178 C. Concentration 97.6 % Flow rate 5.5 m.sup.3/h Pre-pressure 2.0 ato.sup.1 Per nebulizer 1st compartment about 0.561 m.sup.3/h Number of nebulizer: 4 Per nebulizer 2th compartment about 0.360 m.sup.3/h Number of nebulizer: 5 Per nebulizer 3th compartment about 0.291 m.sup.3/h Number of nebulizer: 5 Injection air Temperature 142 C. Pressure 0.52 ato Flow rate about 1,800 Nm.sup.3/h Per nebulizer 1st compartment about 130 Nm.sup.3/h Number of nebulizer: 4 Per nebulizer 2th compartment about 130 Nm.sup.3/h Number of nebulizer: 5 Per nebulizer 3th compartment about 130 Nm.sup.3/h Number of nebulizer: 5 Fluidization air Temperature Flow rate Speed ( C.) (Nm.sup.3/h) Nm/sec 1st 78 2,471 2.02 compartment 2d 81 2,359 1.93 compartment 3d 79 2,836 2.92 compartment 4th 20 2,235 compartment 5th 18 2,299 compartment Suction 113 about 14,000 Fluidized bed Height 685 mmwk.sup.2 Temperature 1st compartment 127 C. Temperature 2d compartment 127 C. Temperature 3d compartment 130 C. Temperature 4th compartment n.m. C. Temperature 5th compartment 119 C. Temperature after granulator 119 C. Expansion room (space over the granulator compartments) Temperature 1st compartment 127 C. Temperature 2d compartment 130 C. Temperature 3d compartment 127 C. Temperature 4th + n.m. C. 5th compartment Temperature top granulator 113 C. .sup.1atmospheres of overpressure over the standard atmospheric pressure; n ato = n + 1 atm (absolute) n + 1 bar .sup.2mmwk = mm water column; 1 mmwk = 0.0981 mbar 0.1 mbar

RESERVATIONS

(15) Although the subject matter has been described in language, specific to structural features and/or methodological acts, it is to be understood that the subject matter as defined in the appended claims is not necessarily limited to the specific features or acts described above as has been held by the courts. Rather, the specific features and acts described above are disclosed as example forms of implementing the claims. The claimed subject matter is not limited to implementations that solve any or all disadvantages noted in the background.