METHOD FOR PRODUCING A FERTILIZER

Abstract

A method for producing a fertilizer that comprises urea and/or at least one ammonium compound may involve obtaining ammonia as an impurity in the production process, and photocatalytically decomposing the ammonia by irradiation with UV radiation. Further, an apparatus for producing fertilizer granules that comprise urea and/or at least one ammonium compound may include a plant section having a fertilizer granulator configured to produce the fertilizer granules, a supply line configured to pass a urea melt or a concentrated urea solution to the plant section, a UV lamp arrangement that is proximate the supply line and is configured to irradiate with UV radiation the urea melt or the concentrated urea solution flowing in the supply line.

Claims

1.-15. (canceled)

16. A method for producing a fertilizer that comprises at least one of urea or an ammonium compound, the method comprising: obtaining ammonia as an impurity in the production of the fertilizer; and decomposing the ammonia photocatalytically by irradiation with UV radiation.

17. The method of claim 16 comprising producing fertilizer granules in a granulation process.

18. The method of claim 16 comprising producing urea-containing fertilizer granules in a granulation process.

19. The method of claim 18 comprising producing the urea-containing fertilizer granules by fluidized bed granulation.

20. The method of claim 16 comprising destroying photocatalytically ammonia contained in an offgas stream.

21. The method of claim 16 comprising destroying photocatalytically ammonia that is bound or dissolved in a urea melt or in a concentrated urea solution.

22. The method of claim 21 comprising irradiating the urea melt or the concentrated urea solution with UV radiation on a transport path to a fertilizer granulator.

23. The method of claim 22 wherein the urea melt or the concentrated urea solution is irradiated with UV radiation at a low spatial and/or temporal distance or immediately prior to addition to the fertilizer granulator.

24. The method of claim 16 wherein the UV radiation has a wavelength in a range from 170 nm to 350 nm.

25. The method of claim 16 wherein the UV radiation has a wavelength in a range from 185 nm to 254 nm.

26. The method of claim 16 comprising photocatalytically decomposing the ammonia predominantly into nitrogen and water.

27. The method of claim 16 wherein the irradiation occurs by way of a UV lamp arrangement disposed proximate a supply line via which a urea melt or a concentrated urea solution is passed to a fertilizer granulator.

28. An apparatus for producing fertilizer granules that comprise at least one of urea or an ammonium compound by the method of claim 16, the apparatus comprising: a plant section having a fertilizer granulator in which the fertilizer granules are produced; a supply line configured to pass a urea melt or a concentrated urea solution to the plant section; and a UV lamp arrangement disposed proximate the supply line, wherein the UV lamp arrangement is configured to irradiate with UV radiation the urea melt or the concentrated urea solution flowing in the supply line.

29. The apparatus of claim 28 wherein the UV lamp arrangement comprises a UV-LED lamp.

30. The apparatus of claim 28 wherein at least in a region in which the UV lamp arrangement is disposed, the supply line is configured to be transmissive for UV radiation.

31. The apparatus of claim 28 wherein in a region in which the UV lamp arrangement is disposed, the supply line includes a window that is transmissive for UV radiation.

Description

[0052] The invention is described in more detail below with an exemplary embodiment, with reference to the drawing. The drawing, which is not to scale and does not limit the invention to the embodiments shown therein, shows:

[0053] FIG. 1: a simplified schematic representation of a method for granulating fertilizer granules, more particularly urea-containing fertilizer granules, according to one exemplary embodiment of the present invention;

[0054] FIG. 2: a schematic enlarged detail view of the supply line for urea melt in the region of the UV lamp, in partial longitudinal section.

[0055] Reference is made below to FIG. 1. The representation is highly schematically simplified, and represents only those functional structural units of the fertilizer granule production plant that are important in the context of the method of the invention. The plant comprises a granulator 10, which in the exemplary embodiment is a fluidized bed granulator. The fundamental construction of a fluidized bed granulator 10 of this kind has already been elucidated above and, moreover, is known per se from the prior art, and so this construction is not described more closely in detail once again here. The granulator 10 here is represented schematically as a plant section having a working space in which the fluidized bed granulation takes place. To generate a fluidized bed, the plant comprises a first supply line 11 for fluidizing air to the granulator 10. Arranged in this line 11 is a first blower 12, which conveys the fluidizing air to the granulator 10.

[0056] The plant further comprises a second supply line 13 for atomizing air to the granulator, and in this line as well there is a fan 14 disposed, which conveys the atomizing air to the granulator. The purpose of the atomizing air is to supply the spray nozzles (not represented here) with air by means of which the melt is finely atomized and sprayed into the granulator. A heat exchanger 15 may optionally be provided in this line 13 in order to preheat the atomizing air.

[0057] Additionally provided is a third supply line 16 for urea melt or concentrated urea solution to the generator 10, and a pump 17 is provided in this third supply line 16 to convey the urea melt or concentrated urea solution to the granulator 10. In the spray nozzles, not represented here, the urea melt or urea solution is mixed with the atomizing air, atomized to form fine spray droplets, and sprayed into the granulator. As a result of this spraying procedure, the urea melt or concentrated urea solution comes into contact with the granulation seeds, and accretion produces the granule particles, as already elucidated above, which are then discharged for further treatment via at least one granule discharge aperture, represented here only schematically, by way of the line 18 in the arrow direction out of the granulator 10. The offgas departs the granulator 10 in the upper region via the offgas line 19, which then leads in general to an offgas scrubber 20, in which the offgas is cleaned. In the case of dust scrubbing of the offgas, a dust-containing scrubbing solution is formed, which contains urea and can be taken off from the offgas scrubber 20 by means of a pump 22. This urea-containing scrubbing solution may subsequently be concentrated by evaporation and passed back as concentrated urea solution to the process for producing urea particles and for this purpose, for example, as indicated by the arrow 21, it can be fed into the supply line 16 which leads to the granulator 10.

[0058] For the production of fertilizer granules, the granulator 10 may be supplied not only with the urea melt or concentrated urea solution but also with further constituents such as formaldehyde, for example. In that case use is frequently made, for example, of a solution of formaldehyde (e.g., 60%), urea (25%) and water (15%) (also designated UFC 85), which can be admixed to the urea melt or concentrated urea solution via the line 23, which opens out into the line 16, after which this united mixture can be supplied to the granulator 10. The admixing of a formaldehyde-containing UFC solution of this kind is stated here only illustratively, in order to emphasize that the urea granules may contain a wide variety of constituents additional to urea. Accordingly, in the context of the present method, the admixing of formaldehyde or UFC should by no means be regarded as necessary to the invention, instead having only an elucidating, illustrative character at this point.

[0059] In accordance with the present invention, at least one UV-LED lamp 24 is arranged next to the supply line 16 which supplies the urea melt or concentrated urea solution to the granulator 10, and this UV-LED lamp 24 emits UV radiation which decomposes the ammonia dissolved in the urea melt or concentrated urea solution. This UV-LED lamp 24, as can be inferred from the representation in FIG. 1, is arranged next to the supply line 16 in spatial vicinity to the granulator 10, upstream of the granulator, shortly before the urea melt or concentrated urea solution is sprayed into the granulator 10. The effect of this is that ammonia which forms in the course of production and storage and also, possibly, in the conveying pathway taken by the urea melt to the granulator, is decomposed before the ammonia enters the granulator, and so can no longer be released in the fluidized bed granulation process within said granulator. This also prevents the ammonia reaching the offgas which is taken off from the granulator 10 via the offgas line 19. A further effect of this is that the reaction to form biuret is not promoted. By destruction of the NH.sub.3, the reaction equilibrium shifts in the direction of biuret, and so the premature removal of ammonia would cause more biuret to form. The UV lamps are preferably mounted not on the main line but instead at the feeds to the individual melt nozzles.

[0060] In practice, the urea solution ought to be divided between numerous nozzles (up to 400, for example). From the main line represented in FIG. 1, accordingly, there are individual lines to the nozzles. The nozzles are in turn arranged in groups (up to 18, for example). Each nozzle group has a dedicated feed line. There is therefore a further possibility for mounting the UV lamp(s) on the individual nozzle feed lines. This has the further advantage that the lamps can be physically mounted directly on the granulator.

[0061] The performance of the plant is regulated by the taking of the individual nozzle groups into operation. Hence the UV lamps also need only be taken into operation if that nozzle group is being utilized. This enables an energy saving and also longer durability of the UV lamps.

[0062] Reference is made below to FIG. 2, which shows a schematic, enlarged detail view of the supply line 16 for urea melt in the region of the UV lamp 24, in a partial longitudinal section. A urea melt is transported to the granulator through the supply line 16 in the direction of the arrow 28. The supply line 16 has a window 25 which is transmissive for UV radiation 27, and the UV radiation 27 emitted by the UV lamp 24 is irradiated through this window into the inside of the supply line 16. The supply line 16 is preferably coated on the inside with a reflective layer 26 which reflects the irradiated UV radiation 27, and so the UV radiation impinging on this reflective layer is reflected there, thereby intensifying the UV radiation in the supply line 16. The UV radiation 27 causes photocatalytic decomposition of the ammonia contained in the urea melt.

LIST OF REFERENCE SYMBOLS

[0063] 10 Granulator, fertilizer granulator

[0064] 11 Supply line for fluidizing air

[0065] 12 Fan for fluidizing air

[0066] 13 Supply line for atomizing air

[0067] 14 Fan for atomizing air

[0068] 15 Heat exchanger

[0069] 16 Supply line for urea melt

[0070] 17 Pump

[0071] 18 Line for discharging the granules

[0072] 19 Offgas line

[0073] 20 Offgas scrubber

[0074] 21 Arrow

[0075] 22 Pump

[0076] 23 Line for UFC

[0077] 24 UV Lamp

[0078] 25 Window

[0079] 26 Reflective layer

[0080] 27 UV radiation

[0081] 28 Arrow