Update on curtain granulation of phosphates

The TVA process for curtain granulation of ammonium polyphosphate, which was described at the 194th National Meeting of the American Chemical Society, has been modified to allow production of a variety of ammonium phosphate fertilizers. Ammonium polyphosphate, monoammonium phosphate, diammonium phosphate, and urea-ammonium polyphosphate fertilizers have been produced. In the process, wet-process orthophosphoric acid, ammonia, and, for some products, urea melt are fed to a pipe reactor to produce an ammonium phospahte or a urea-ammonium polyphosphate melt. The melt is sprayed directly from the pipe reactor onto a falling curtain of recycled fines in a granulator with specially designed internals. The melt solidifies in thin, successive layers and forms round, closely sized granules. The products have excellent physical properties and are suitable for direct application, bulk blending, or production of suspensions.