Integrated process for urea and melamine production

Abstract

In an integrated process for urea and melamine production, urea is produced in a urea plant ( 12 ) comprising a high pressure urea synthesis section ( 15 ) and a urea recovery section ( 16 ) for separating urea from a carbamate aqueous solution, and melamine is produced in a melamine plant ( 11 ) wherein off-gases resulting as byproducts of the melamine synthesis are discharged therefrom at a pressure of at least 2 bar and recycled to the high pressure urea synthesis section ( 15 ).

1 . Integrated process for urea and melamine production, wherein urea is produced in a urea plant comprising a high pressure urea synthesis section and a urea recovery section for separating urea from a carbamate aqueous solution, and melamine is produced in a melamine plant wherein off-gases resulting as by-products of the melamine synthesis are discharged therefrom at a pressure of at least 2 bar and recycled to said high pressure urea synthesis section, the process being characterized in that it further comprises the steps of: 
 feeding said off-gases coming from said melamine plant to an off-gas condensation section;    feeding said carbamate aqueous solution coming from said urea recovery section to said off-gas condensation section;    condensing said off-gases with said carbamate aqueous solution in said off-gas condensation section obtaining a concentrated carbamate aqueous solution;    feeding the so obtained concentrated carbamate aqueous solution to said high pressure urea synthesis section.    
   
   
       2 . Process according to  claim 1 , characterized in that said off-gas condensation section is operated at a pressure substantially equal to the pressure of said off-gases.  
   
   
       3 . Process according to  claim 1 , characterized in that said carbamate aqueous solution coming from said urea recovery section is directly fed to said off-gas condensation section.  
   
   
       4 . Process according to  claim 1 , characterized in that it further comprises the step of: 
 compressing said carbamate aqueous solution coming from said urea recovery section to a pressure substantially corresponding to the operating pressure of said off-gas condensation section, previous to feeding it in such a section.    
   
   
       5 . Process according to  claim 1 , characterized in that said concentrated carbamate aqueous solution is directly fed to said high pressure urea synthesis section.  
   
   
       6 . Process according to  claim 1 , characterized in that it further comprises the step of: 
 compressing said concentrated carbamate aqueous solution coming from said off-gas condensation section to a pressure substantially corresponding to the operating pressure of said high pressure urea synthesis section, previous to feeding it in such a section.    
   
   
       7 . Integrated plant for urea and melamine production, wherein urea is produced in a urea plant ( 12 ) comprising a high pressure urea synthesis section ( 15 ) and a urea recovery section ( 16 ) for separating urea from a carbamate aqueous solution, and melamine is produced in a melamine plant ( 11 ) comprising a melamine synthesis section ( 13 ) wherein off-gases resulting as by-products of the melamine synthesis are discharged therefrom at a pressure of at least 2 bar and recycled to said high pressure urea synthesis section ( 15 ), the plant being characterized in that it further comprises: 
 an off-gas condensation section ( 17 ) arranged between said the plant ( 11 ) for melamine production and said plant ( 12 ) for urea production and in fluid communication with said melamine synthesis section ( 13 ), said urea recovery section ( 16 ) and said high pressure synthesis section ( 15 ).    connecting means ( 37 ) for feeding said off-gases coming from said melamine synthesis section ( 13 ) to said off-gas condensation section ( 17 );    connecting means ( 38 ) for feeding said carbamate aqueous solution coming from said urea recovery section ( 16 ) to said off-gas condensation section ( 17 ), wherein said off-gases are condensed with said carbamate aqueous solution obtaining a concentrated carbamate aqueous solution;    connecting means ( 31 ) for feeding the so obtained concentrated carbamate aqueous solution to said high pressure urea synthesis section ( 15 ).    
   
   
       8 . Plant according to  claim 7 , characterized in that it further comprises a first compressor section ( 18 ), arranged between and in fluid communication with said urea recovery section ( 16 ) and said off-gas condensation section ( 17 ) for compressing said carbamate aqueous solution coming from said urea recovery section ( 16 ) to a pressure substantially corresponding to the operating pressure of said off-gas condensation section ( 17 ).  
   
   
       9 . Plant according to  claim 7 , characterized in that it further comprises a second compression section ( 19 ), arranged between and in fluid communication with said off-gas condensation section ( 17 ) and said high pressure urea synthesis section ( 15 ) for compressing said concentrated carbamate aqueous solution coming from said off-gas condensation section ( 17 ) to a pressure substantially corresponding to the operating pressure of said high pressure urea synthesis section ( 15 ).