FLUIDIZED BED GRANULATION

Abstract

A fluidized bed reactor includes at least one granulation compartment with one or more air inlets, and at least one scrubber for cleaning air from the granulator, such as a wet scrubber and/or a dry scrubber. The reactor comprises a return line for recycling cleaned air leaving the scrubber to the air inlets of the granulation compartment.

Claims

1. A fluidized bed reactor comprising: at least one granulation compartment with one or more air inlets; at least one scrubber coupled to the granulation compartment configured to receive and clean air from the granulation compartment; and a return line from an outlet of the air scrubber to the one or more air inlets.

2. The fluidized bed reactor according to claim 1, wherein the return line comprises a compressor, a cooler and an expander coupled consecutively in a flow direction of the recycled air flow.

3. The fluidized bed reactor according to claim 1 comprising reheating means for reheating air recycled to the granulation compartment.

4. The fluidized bed reactor according to claim 1 and further comprising a fluidized bed after-cooler and/or a bulk flow cooler coupled to the granulation compartment to receive granules from the granulation compartment.

5. The fluidized bed reactor according to claim 3, wherein the reheating means include a heat exchanger with one or more flow channels for recycled air thermo-conductively contacting air flow leading to the after-cooler.

6. The fluidized bed reactor according to claim 4 and further comprising an air return line configured to recycle air leaving the after-cooler to the air inlets of the granulation compartment.

7. The fluidized bed reactor according to claim 4, comprising an air return line configured to recycle air leaving the after-cooler to air inlets of the after cooler.

8. The fluidized bed reactor according to claim 4 and further comprising an air return line coupling air from the after-cooler to the compressor.

9. A method for the production of granules using a fluidized bed reactor comprising: injecting air into at least one granulation compartment with one or more air inlets; cleaning air from the granulator with at least one scrubber; and wherein air leaving the scrubber is at least partly recycling air from the scrubber to the one or more air inlets of the granulation compartment.

10. The method according to claim 9, and further comprising compressing at least a part of the air leaving the scrubber.

11. The method according to claim 10, and further comprising cooling at least a part of the compressed air.

12. The method according to claim 11, and further comprising decompressing at least a part of the cooled compressed air before the air is recycled back to the one or more air inlets.

13. The method according to claim 12, wherein decompressing includes separating NH3, CO2 and NH4OCN from condensate recovered with the decompressing.

14. The method according to claim 11 and further comprising recycling part of the compressed air to sprayers as atomization air.

15. The method according to claim 12 and further comprising recycling part of the compressed air to sprayers as atomization air.

16. The method according to claim 13 and further comprising recycling part of the compressed air to sprayers as atomization air.

Description

BRIEF DESCRIPTION OF THE DRAWING

[0021] Aspects of the invention will be elucidated with reference to the accompanying drawing.

[0022] FIG. 1: shows schematically an exemplary embodiment of a fluidized bed reactor;

[0023] FIG. 2: shows schematically a second exemplary embodiment of a fluidized bed reactor.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

[0024] FIG. 1 shows a fluidized bed reactor 1 comprising a granulation compartment 2 holding a bed 3 of solid nuclei. The granulation compartment 2 is provided with inlets 4 for fluidization air in an air chamber 5 below a grid floor 6 carrying the bed 3. Sprayers 7 on the grid floor 6 are used for spraying urea liquid into the bed 3. The sprayed urea liquid crystallizes on the nuclei to form granules.

[0025] Downstream the granulation compartment 2 the fluidized bed reactor 1 comprises an after-cooler 10. During the granulation process granules are gradually moved from the granulation compartment 2 to the after-cooler 10. In the after-cooler 10 cool fluidization air is blown via air inlets 11 below a grid 12 floor carrying a bed 13 of the granules. The after-cooler 10 may for example include one or more fluidized bed after-coolers and/or one or more bulk flow coolers. Stepwise cooling with one or more intermediate coolers followed by a final cooler is also possible.

[0026] Used fluidization air is discharged from the granulation compartment 2 and led to a wet scrubber 16. The fluidization air contains dust and other pollutants, which are to be removed in the wet scrubber.

[0027] A return line 17 recycles air leaving the wet scrubber 16 to the air inlets 4 of the granulation compartment 2. When the air leaves the wet scrubber 16, the air is saturated with water. In flow direction the return line 17 successively comprises a compressor 19, a cooler 20 and an expander 21, driven by a motor 22. The recycled air is first compressed in the compressor 19, then cooled in the cooler 20 and finally decompressed in the expander 21 before it re-enters the granulation compartment 2. During this process the air is dried and condensed water absorbs most of the pollutant content.

[0028] In the cooler 20 and the expander 21 the air is significantly cooled. Therefore, the air is first re-heated before it is recycled to the air inlets 4 of the granulation compartment 2. Part of the air is re-heated in an air heater 23 in the return line 17 downstream the expander 21. Optionally, reheating can be limited or even excluded by using uncleaned air from the compressor, which is still warm. Another part of the air is re-heated in an air-to-air heat exchanger 24 with flow channels 26 for recycled air being thermo-conductively connected to air flow channels 27 leading to the after-cooler 10.

[0029] It is also possible to transport part of the air, or all of the air, from the compressor directly to the heater 23. This is indicated in FIG. 1 by the dashed line 28. Since this air is not cooled, the energy consumption of the air heater 23 will be lower.

[0030] Also air leaving the after-cooler 10 is loaded with dust and must be treated in a wet scrubber 30 or any other suitable air cleaning device before the air is withdrawn by a fan 31 and vented to the atmosphere. This air does not contain ammonia or ammonium cyanate.

[0031] FIG. 2 shows an alternative embodiment similar to the embodiment of FIG. 1 but with a return line 35 recycling cleaned air from the wet scrubber 30 of the after-cooler 10 to the compressor 19. Air from the wet scrubber 30 of the after-cooler 10 is mixed with the recycled cleaned air coming from the wet scrubber 16 of the granulation compartment 2 and the two joint gas flows are jointly treated and recycled.

[0032] 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 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.