Urea granulation process

Abstract

A process of granulation of a urea melt, comprising: adding a first additive containing carboxymethyl starch to one or more first stage(s) of the granulation process, to form a carboxymethyl starch containing inner layer of urea granules, and adding a second additive containing calcium lignosulfonate to one or more second stage(s) of the granulation process, downstream said first stages, to form granules with a coating containing calcium lignosulfonate.

1 . A process of granulation of a liquid urea melt containing at least 96% wt urea, the process comprising:
 adding a first additive containing carboxymethyl starch to one or more first stage(s) of the granulation process;   performing one or more second stage(s) of the granulation process downstream said one or more first stage(s);   wherein no amount of said first additive is added to said one or more second stage(s) of the granulation process.   
     
     
         2 . The process according to  claim 1 , comprising the addition of a second additive, which is an anti-caking additive, to said one or more second stage(s) of the granulation process. 
     
     
         3 . The process according to  claim 2 , wherein the second additive provides slower nitrogen release from the granules of urea. 
     
     
         4 . The process according to  claim 2 , wherein said second additive includes calcium lignosulfonate. 
     
     
         5 . The process according to  claim 1 , wherein said one or more second stage(s) of the granulation process include the last stage of the granulation process. 
     
     
         6 . The process according to  claim 2 , wherein no second additive is added to said one or more first stage(s) of the granulation process. 
     
     
         7 . The process according to  claim 1 , wherein the first additive and optionally the second additive are added to said stages of the granulation process by mixing with a portion of the urea melt. 
     
     
         8 . The process according to  claim 1 , wherein each of said stages of the granulation process receives a portion of the urea melt mixed with the first additive and/or the second additive. 
     
     
         9 . The process according to  claim 1 , wherein:
 in the one or more first stage(s) of granulation, carboxymethyl starch is added in an amount of 0.1% to 0.8% in weight based on the amount of urea fed to said one or more first stage(s).   
     
     
         10 . The process according to  claim 4 , wherein:
 in the one or more second stage(s) of granulation, calcium lignosulfonate is added in an amount of 0.3% to 1% in weight based on the amount of urea fed to said one or more second stage(s).   
     
     
         11 . The process according to  claim 1 , wherein said first additive contains carboxymethyl starch dissolved in a urea aqueous solution. 
     
     
         12 . The process according to  claim 11 , said urea aqueous solution comprising a solution taken after the recovery section of a urea plant and/or a urea-water recycle solution from a granulation scrubber. 
     
     
         13 . The process according to  claim 1 , wherein the urea melt contains at least 97% wt urea. 
     
     
         14 . The process according to  claim 1 , wherein the granulation process is performed in a longitudinal granulator and said stages of the granulation process are distributed over the length of said granulator. 
     
     
         15 . The process according to  claim 1 , wherein the granulation process is performed in a fluid bed condition. 
     
     
         16 . A process according to  claim 1 , including:
 feeding said urea melt into a granulation environment by means of a plurality of urea inputs, wherein each of said stages of the granulation process has a respective urea input;   wherein the addition of the first additive and optionally of the second additive to the stages of the granulation process is performed by mixing the urea melt of selected urea inputs with said additives.   
     
     
         17 . The urea granular product obtainable with a process according to  claim 16 , said product including granules made of at least 96% urea with a layer containing carboxymethyl starch and a coating layer containing calcium lignosulfonate. 
     
     
         18 . The urea product according to  claim 17 , wherein the carboxymethyl starch containing layer has a thickness of 0.6 to 1.05 mm and the coating layer has a thickness of 0.1 to 0.2 mm. 
     
     
         19 . The urea product according to  claim 17 , wherein the carboxymethyl starch containing layer contains 0.1% to 0.8% in weight of carboxymethyl starch and the coating layer contains 0.3% to 1% in weight of calcium lignosulfonate.