UREA PRODUCTION PLANT AND SCRUBBING SYSTEM

Abstract

A urea production plant including a synthesis and recovery section has a first evaporation section connected with the synthesis and recovery section and a first condensation section. A granulation section is connected to the first evaporation section. A scrubbing section is connected to the granulation section. A second evaporation section is connected to the scrubbing section. The second evaporation section is connected to the granulation section. A second condensation section is connected to the second evaporation section. A quenching section includes a liquid inlet for the distribution of a quenching liquid is located and connected between the granulation section and the scrubbing section and the quenching section is connected to a quenching liquid providing section and the second condensation section.

Claims

1.-12. (canceled)

13. A urea production plant, comprising: a synthesis and recovery section; a first evaporation section is connected to the synthesis and recovery section and a first condensation section; a granulation section is connected to the first evaporation section; a scrubbing section is connected to the granulation section; a second evaporation section is connected to the scrubbing section and the second evaporation section is connected to the granulation section; a second condensation section is connected to the second evaporation section; a quenching section comprising a liquid inlet for the distribution of a quenching liquid is located between and connected to the granulation section and the scrubbing section, and the quenching section is connected to a quenching liquid providing section and the second condensation section.

14. The urea production plant of claim 13 wherein the liquid inlet comprises spraying nozzles.

15. The urea production plant of claim 13 wherein the scrubbing section comprises one or more of a dust scrubber, an acid scrubber, or a cooler scrubber.

16. The urea production plant of claim 15 wherein the dust scrubber is connected with a dust scrubbing liquid providing section.

17. The urea production plant of claim 16 wherein the quenching liquid providing section comprises or is identical to the dust scrubbing liquid providing section and both the dust scrubber and the quenching section are connected to the quenching liquid providing section.

18. The urea production plant of claim 17 wherein the dust scrubber is free of a freshwater supply.

19. The urea production plant of claim 13 wherein a post processing section is connected to the granulation section.

20. A method for the preparation of urea granules, comprising: one or more synthesis and recovery steps wherein carbon dioxide is reacted with ammonia to form a solution comprising urea and water; evaporation of water from solution resulting in a first concentrated urea solution and a first water containing vapor; subjecting the first water containing vapor to a condensing step resulting in a first condensate; subjecting the concentrated urea solution to a granulation step resulting in urea granules and a urea dust containing off gas stream; subjecting the urea dust containing off gas stream to a scrubbing step resulting in an aqueous urea solution; subjecting the aqueous urea solution to a separate evaporation step resulting in a second concentrated urea solution and a second water containing vapor; conveying the second concentrated urea solution to the granulation step; subjecting the second water containing vapor to a separate condensation step resulting in a second condensate; and subjecting the second condensate and a quenching liquid to the urea dust containing off gas stream after leaving the granulation step and before entering the dust scrubbing step.

21. The method of claim 20 wherein the scrubbing step comprises one or more of a dust scrubbing step, an acid scrubbing step, or a cooler scrubbing step.

22. The method of claim 20 wherein the dust scrubbing step utilizes a dust scrubbing liquid and the dust scrubbing liquid is also used as the quenching liquid.

23. The method of claim 20 wherein the dust scrubbing step utilizes no additional fresh water.

Description

[0042] The invention is further described in the following figures. The figures are meant for illustrative purpose only and do not restrict the scope of protection. The figures are not true to scale. The arrows indicate suitable process flow directions.

[0043] FIG. 1 shows a schematic flow diagram of a plant setup/process for the preparation of urea granules,

[0044] FIG. 2 shows a schematic flow diagram of a plant setup/process for the preparation of urea granules according to the invention and

[0045] FIG. 3 shows a preferred schematic flow diagram of a plant setup/process for the preparation of urea granules according to the invention.

[0046] FIG. 1 shows the plant setup/process for the preparation of urea granules. The urea production plant comprises at least a synthesis and recovery section (1). In this section ammonia and urea are reacted to form urea. The resulting urea solution comprises typically around 50 wt. % to 80 wt. % of urea. A subsequent concentration step is necessary in order to achieve a urea solution with a water content typically below 5 wt. %. Therefore a first evaporation section (2) is connected with the synthesis and recovery section (1) and a first condensation section (6). The first evaporation section leads to a concentrated urea solution, preferably between 95 wt. % and 98 wt. % of urea and an aqueous vapor stream. The concentrated urea solution is transferred to a granulation section (3) connected with the first evaporation section (2). The granulation section (3) comprises a fluid-bed granulation section. A scrubbing section (4) is connected with the granulation section (3). The cooling air and off-gases from the granulation section are transferred to the scrubbing section (4). Dust, e.g. urea dust, and chemical vapors like ammonia, which are created or released during the granulation process, are removed in the scrubbing unit (4). Optionally, the scrubbing unit comprises at least a dust removing scrubber and an ammonia removing scrubber. A second evaporation section (5) downstream of the scrubbing section is connected with the granulation section (3). The term downstream generally refers to flowing direction of the respective liquids, vapors or gases. The scrubbing section (4), in particular the dust scrubbing section, produces an aqueous urea solution of around 30 wt. % to 60 wt. % urea. This aqueous urea solution is transferred to the second evaporation (5) section different from the before mentioned first evaporation section (2). A second condensation section (7) is connected with the second evaporation section (5). The resulting vapor phase of the second evaporation section (5) is transferred to the second condensation section (7), different from the first condensation section (6). The condensed liquid obtained in the second condensation section (7) is reused in the scrubbing unit (4), indicated by the connection between the second condensation section (7) and the scrubbing unit, e.g. as dust scrubbing liquid component. The granulated product of the granulation section (3) is further processed in the post processing section (9). This post processing section (9) comprises well known elements like e.g. sieves, crushers, flowing belts, coolers, elements necessary for the further processing and handling of the granules.

[0047] FIG. 2 shows the schematic flow diagram of a plant setup/process for the preparation of urea granules according to the invention. The basic setup indicated by the reference signs synthesis and recovery section (1), first evaporation section (2), granulation section (3), scrubbing section (4), second evaporation section (5), first condensation section (6), second condensation section (7) and post processing section (9) is identical with the setup described in FIG. 1. However, the second condensation section (7) is connected with a quenching section (8). The quenching section (8) comprising a liquid inlet for the distribution of a quenching liquid is located and connected between the granulation section (3) and the scrubbing section (4). The quenching section (8) is connected with a quenching liquid providing section (10) and the before mentioned second condensation section (7). Thereby, the condensate obtained in the second condensation section can be reused in the quenching of the granulator off-gas. In addition, the quenching section (8) is connected with the quenching liquid providing section (10). The quenching liquid providing section (10) comprises different aqueous liquid sources and related connections for process water, process aqueous liquids or fresh water.

[0048] FIG. 3 shows a preferred schematic flow diagram of a plant setup/process for the preparation of urea granules according to the invention. The principle setup is identical with the setup shown in FIG. 2. In addition, the quenching liquid providing section (10) is connected with the quenching section (8) and the scrubbing section (4), preferably with the dust scrubber. Thereby, the same liquid stream can be used as quenching liquid in the quenching section (8) and as dust scrubbing liquid in the scrubbing section (4). This setup simplifies the overall setup, thereby reducing process costs.

REFERENCE SIGNS

[0049] (1) synthesis and recovery section [0050] (2) first evaporation section [0051] (3) granulation section [0052] (4) scrubbing section [0053] (5) second evaporation section [0054] (6) first condensation section [0055] (7) second condensation section [0056] (8) quenching section [0057] (9) post processing section [0058] (10) quenching liquid providing section