Ammonium Polyphosphate Fluid Fertilizers Made from Merchant-Grade Orthophosphoric Acid

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This article discusses developing and producing ammonium polyphosphate (APP) fluid fertilizers using merchant-grade orthophosphoric acid. The Tennessee Valley Authority (TVA) developed an energy-efficient process to produce these fertilizers, which can be stored, shipped, and marketed throughout the United States. The APP fluid contains polyphosphate, allowing it to be stored at low temperatures without freezing. A demonstration-scale plant was built, and approximately 10,000 tons of 9-32-0 grade APP suspension were produced and distributed to distributors in 13 states. The article describes the process flow, chemical and physical properties of the fertilizers, their uses in mixed-grade suspensions, and storage recommendations. The operating procedures, equipment, and polyphosphate content variables are also discussed. The findings indicate that APP fluid fertilizers offer a cost-effective alternative to suspension fertilizers, particularly in regions with sub-zero temperatures.
Fertilizers, Suspensions