Producing fertilizer granules with a defined size distribution

Abstract

A fluid-bed granulator system for producing fertilizer granules with a defined size including a fluid-bed granulator, a first cooler externally connected with the fluid-bed granulator or forming an internal part of the fluid-bed granulator, and a product screen connected with the first cooler. The product screen includes an exit for on-size particles; an exit for oversized particles and an exit for undersized particles. The exit for undersized particles is connected to the fluid-bed granulator and the exit for oversized particles is connected to the fluid-bed granulator via one or more crushers. The exit for on-size particles is connected to a first splitter. The first splitter is connected to the fluid-bed granulator and a post processing unit. A particle size analyzer is located between the fluid-bed granulator and the product screen.

What is claimed is: 
     
         1 . A fluid-bed granulator system for producing fertilizer granules with a defined size, comprising:
 a fluid-bed granulator,   a first cooler externally connected to the fluid-bed granulator or forming an internal part of the fluid-bed granulator,   a product screen connected to the first cooler wherein the product screen comprises:
 an exit for on-size particles, 
 an exit for oversized particles, and 
 an exit for undersized particles; 
 wherein the exit for undersized particles is connected to the fluid-bed granulator and wherein the exit for oversized particles is connected to the fluid-bed granulator via one or more crushers; 
 wherein the exit for on-size particles is connected to a first splitter and wherein the first splitter is connected to the fluid-bed granulator and a post processing unit; and 
   a particle size analyzer located between the fluid-bed granulator and the product screen.   
     
     
         2 . The fluid-bed granulator system of  claim 1 , wherein the product screen comprises an exit for large on-size particles and an exit for small on-size particles. 
     
     
         3 . The fluid-bed granulator system of  claim 2 , wherein the product screen comprises three inner screen meshes, the three inner screen meshes having corresponding decreasing mesh sizes. 
     
     
         4 . The fluid-bed granulator system of  claim 3 , wherein the mesh sizes of the inner screen meshes is in the range of 0.1 mm to 10 mm. 
     
     
         5 . The fluid-bed granulator system of  claim 1 , wherein
 the first splitter; and/or   the exit for oversized particles via the crusher; and/or   the exit for undersized particles;   are ingoing connected with a second splitter, wherein an output of the second splitter is connected to recycle inlets of the fluid-bed granulator.   
     
     
         6 . The fluid-bed granulator system of  claim 5 , wherein the particle size analyzer is electronically connected to the first splitter and/or the second splitter. 
     
     
         7 . The fluid-bed granulator system of  claim 6 , wherein the particle size analyzer is electronically connected to the first splitter and/or the second splitter via a processing and control unit. 
     
     
         8 . The fluid-bed granulator system of  claim 5 , wherein the fluid-bed granulator comprises a perforated plate and wherein the perforated plate comprises, in the direction of flow, a growing zone and a cooling zone. 
     
     
         9 . The fluid-bed granulator system of  claim 5 , wherein the fluid-bed granulator comprises a perforated plate and wherein the perforated plate comprises, in the direction of flow, a first growing zone and a first cooling zone, a second growing zone and a second cooling zone. 
     
     
         10 . The fluid-bed granulator system of  claim 8 , wherein the first splitter and/or the second splitter are connected to the growing zone and/or the cooling zone via recycle inlets. 
     
     
         11 . The fluid-bed granulator system of  claim 9 , wherein the first splitter and/or the second splitter are connected to the first growing zone and/or the second growing zone via the recycle inlets. 
     
     
         12 . The fluid-bed granulator system of  claim 7 , wherein the first splitter and/or the second splitter are electronically connected to the processing and control unit and wherein the processing and control unit is electronically connected to the particle size analyzer. 
     
     
         13 . The fluid-bed granulator system of  claim 5 , wherein the second splitter is connected to the first splitter; and/or
 the exit for oversized particles via the crusher; and/or   the exit for undersized particles; and   wherein the second splitter is connected to the recycle inlets of the fluid-bed granulator and wherein the recycle inlets are connected to one or more growing zones and/or cooling zone.   
     
     
         14 . The fluid-bed granulator system of  claim 5 , wherein the product screen comprises four inner screen meshes with a decreasing mesh size or five inner screen meshes with a decreasing mesh size. 
     
     
         15 . The fluid-bed granulator system of  claim 14 , wherein the product screen is connected to:
 a third splitter and a fourth splitter connected to the fluid-bed granulator and the post processing unit; and   wherein the third splitter and the fourth splitter are controlled via a processing and control unit.   
     
     
         16 . A method for a particle size controlled granulation of urea containing particles comprising:
 conveying seed granules into a fluid-bed granulator;   granulating said seed granules and receiving product granules;   conveying said product granules to a first cooler that one of externally connected with the fluid-bed granulator or forming an internal part of the fluid-bed granulator and configured to receive pre-cooled product granules;   conveying said pre-cooled product granules into a product screen comprising:
 an exit for oversized particles; 
 an exit for undersized particles; and 
 an exit for on-size particles; 
 wherein the exit for on-size particles is connected to a first splitter and wherein the first splitter is connected to the fluid-bed granulator and a post processing unit; 
   conveying the undersized particles into the fluid-bed granulator;   conveying the oversized particles into a crusher and receiving crushed particles;   conveying the crushed particles into the fluid-bed granulator; and   conveying the on-size particles via the first splitter to the fluid-bed granulator and/or the post processing unit, wherein   a.) the size of product granules or pre-cooled product granules is measured by a particle size analyzer and the obtained product granules size or pre-cooled product granules size is compared to a predefined value, wherein the predefined value defines a lower particle size threshold value, and   b.) the amount of on-size particles conveyed to the fluid-bed granulator is increased, when the size of the product granules drops below the predefined value.   
     
     
         17 . The method of  claim 16 , wherein the product screen comprises an exit for large on-size particles and an exit for small on-size particles. 
     
     
         18 . The method of  claim 16 , wherein the size of the product granules or pre-cooled product granules is measured by the particle size analyzer and the obtained product granules size or pre-cooled product granules size is compared to a second predefined value, wherein the second predefined value defines an upper particle size threshold value and the amount of undersized particles and/or crushed particles is increased, when the size of the product granules is above the predefined second value. 
     
     
         19 . The method of  claim 16 , wherein the undersized particles and/or crushed particles and/or on-size particles are introduced via recycle inlets into one or more growing zones and/or cooling zone. 
     
     
         20 . A urea granulation plant comprising the fluid-bed granulator system of  claim 1 .