Dry single-stage method of sodium tripolyphosphate production – technological and economic assessment

The study presents a technology of sodium tripolyphosphate (STPP) production with the use of a dry, single-stage method. The reacting substrates (concentrated wet-process phosphoric acid - WPPA and solid Na2CO3 ) are mixed with a recycled final product (STPP) in a mixer, then a „quasi-dry” mixture is calcined in a rotary kiln. Thanks to that, some stages of a classic method of STPP production are eliminated: one of the two-stage neutralization of the phosphoric acid with sodium carbonate at temperature ~80°C, filtration of the neutralised solution and its evaporation, as well as the stage of drying a solution of mono- and di-sodium orthophosphate in a spray dryer. According to the presented technical and economical analysis, the costs of STPP production using a single-stage dry method can be 10% lower compared to the classic method.