Methods for the production of nitrogen fertilizer and nitrogen-sulfur fertilizer

A method for the production of a solid nitrogen fertilizer and a solid nitrogen-sulfur fertilizer, said method comprising the following steps:

• (i) synthesizing urea from ammonia and carbon dioxide thereby obtaining a liquid aqueous composition comprising urea;
• (ii) concentrating the aqueous composition obtained in step (i) to obtain a liquid urea melt comprising less than 5 wt % (by total weight of the melt) water, preferably comprising more than 95 wt. % (by total weight of the melt) urea;
• (iii) submitting the urea melt of step (ii) to a solidification step in a solidification section wherein the melt is converted to a particulate solid, thereby obtaining the solid nitrogen fertilizer, and recovering a gas stream comprising urea from the solidification section;
• (iv) recovering urea from the gas stream of step (iii), thereby obtaining an urea recyclate;
• (v) providing a composition comprising a sulfur compound selected from the group consisting of thiosulphate salts, (bi)sulfite salts, polysulfide salts, (bi)sulfide salts, metabisulfite salts, dithionite salts, elemental sulfur and combinations thereof, preferably selected from the group consisting of thiosulphate salts, (bi)sulfite salts, polysulfide salts and combinations thereof;
• (vi) submitting the urea recyclate of step (iv) to a concentration step and combining the composition provided in step (v) with the urea recyclate before, during and/or after the concentration step to obtain a concentrated nitrogen-sulfur stream;
• (vii) submitting the concentrated nitrogen-sulfur stream to a solidification step in a solidification section, wherein the stream is converted to a particulate solid, thereby obtaining the solid nitrogen-sulfur fertilizer.