Granulation of urea phosphate from urea and merchant-grade phosphoric acid

A process for the direct production, from wet-process phosphoric acid containing the congeneric impurities thereof therein and urea, of granular urea phosphate fertilizers having a predetermined closely controlled particle size range and excellent handling characteristics including relatively high granular crushing strength, said granular urea phosphate being eminently suitable, either alone or in homogeneous admixture with urea, for soil surface application agronomic particles, which process comprises the steps of:

• (1) introducing into reactor means predetermined quantities of wet-process phosphoric acid and urea to effect a resulting slurry therein of urea phosphate, said predetermined quantities of said acid and said urea proportioned in said resulting slurry to effect a urea:H.sub.3 PO.sub.4 mole ratio of about 1:1;
• (2) mechanically agitating said slurry in said reactor means and introducing thereinto near the bottom portion thereof a stream of sweep air, the relative volume of said sweep air to the relative volume of said urea phosphate slurry ranging from about 4.0:1 to about 10:1, and being sufficient to physically remove from about 50 percent to about 70 percent of the free water in said urea phosphate slurry;
• (3) subsequently removing from said reactor means at least a portion of the resulting dehydrated urea phosphate slurry material and introducing same into granulator means, together with recycled fines from a later-mentioned sizing step and predetermined quantities of additional sweep air introduced beneath the resulting granulation bed in said granulator means, said additional sweep air being in volumetric proportions to said granules in said granulator means ranging from about 10:1 to about 20:1 and being sufficient to remove substantially all of the remaining free moisture in said urea phosphate slurry introduced thereinto;
• and
• (4) removing at least a portion of essentially dry granular urea phosphate product from said granulator means and introducing same into drying, cooling, and sizing means wherefrom product size material is obtained and undersize as well as crushed initially oversize material is recycled to said granulator means;
• said process characterized by the fact that at least about 99 percent of the free water present in said urea phosphate slurry formed in said reactor means is removed physically via sweep air introduced into both said reactor means and said granulator means and substantially no external heat energy is expended therein for such purposes.