Granular DAP and MAP Processes

MAP and DAP fertilizers are made in a granulation process from ammonia and wet-process phosphoric acid. The acid is partially neutralized in a tank reactor. Ammoniation and granulation are completed in a rotary drum. Drying, cooling and product screening complete the process238. 

In an attempt to further simplify DAP plants and reduce the recycle ratio, TVA, CROS S.A., and ERT - Espindesa have tried to use pipe reactors (also called T reactors or pipe-cross reactors) directly releasing slurry in the rotary granulator, instead of applying a preneutralization tank. CROS and ERT -Espindesa report successful operation, but experiences in several U.S. plants were disappointing because of high heat input in the granulator296. 

Approximately half of the phosphoric acid is fed to a pipe reactor that operates at N/P =1.4 and releases its product into the granulator. The remaining acid is fed into a second pipe reactor at N/P =1.1 that sprays into the dryer. Extra ammonia is introduced underneath the rolling bed in the rotary drum granulator296. 

The pipe reactor in the dryer produces MAP powder. Part of it is carried away into the cyclones of the dedusting loop. The remainder crystallizes on the DAP product. The recycle ratio of this process is lower than with a conventional preneutralizer, and fuel consumption in the dryer is also reduced296. 

Granular MAP is produced in the same types of plants as DAP. The preneutralizer is operated at an N/P ratio of 0.6, (a point of high solubility) and more ammonia is added in the granulator to increase the molar ratio to 1.0296. 

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