Production of granular ammonium polyphosphate from wet-process phosphoric acid

An improved process for preparing granular substantially dust-free ammonium polyphosphate of a particle size distribution eminently suitable for subsequent bulk blending with other fertilizer values or eminently suitable for use in production of liquid or suspension fertilizers, which process consists essentially of the steps of:

• (a) simultaneously supplying a stream of anhydrous ammonia to the common pipe section of an enlarged pressurized pipe reactor;
• (b) simultaneously supplying a stream of phosphoric acid to the cross section of said pipe-cross reactor, said phosphoric acid having a P.sub.2 O.sub.5 content in the range from about 50 percent to about 58 percent by weight and a free water content ranging from about 10 percent to 22 percent by weight;
• (c) contacting said anhydrous ammonia introduced into said common pipe section of said enlarged pressurized pipe reactor at said cross section of said enlarged pressurized pipe reactor therewith, at a temperature sufficiently high so that additional water is not necessary for continuous operation;
• (d) subsequently introducing the reaction product resulting from contacting said anhydrous ammonia and phosphoric acid into a vapor tube extension of said enlarged pressurized pipe reactor to ensure continued intimate contact therebetween;
• (e) subsequently discharging from the downstream end of said vapor tube extension a spray of particles of molten material into the upper end of arm inclined rotating drum wherein is maintained a bed of rolling discrete particles of ammonium polyphosphate and on to the rapidly moving granules of substrate maintained therein such that the granules of substrate or seed recycle are increased in size by accretion as the sprayed particles solidify quickly onto the surfaces of said substrate;
• withdrawing the resulting ammonium polyphosphate material from the lower end of said inclined rotating drum;
• (f) introducing said withdrawn material into cooling means;
• (g) withdrawing the resulting cooled material from said cooling means;
• (h) introducing said material withdrawn from said cooling means into sizing means;
• (i) returning particles of pedetermined size from said sizing means into the upper end of said drum;
• and
• (j) withdrawing from said sizing means granular particles of ammonium polyphosphate as product;
• said process characterized by the fact that the proportion of the P.sub.2 O.sub.5 as polyphosphate, of the granular product withdrawn from step (j) supra is substantially equal to the proportion of the P.sub.2 O.sub.5 as polyphosphate of the melt exiting said vapor tube extention of said pipe reactor in step (d) supra;
• and said process being further characterized by the fact that the weight percent P.sub.2 O.sub.5 withdrawn from step (j) supra is substantially equal to the weight percent P.sub.2 O.sub.5 in the melt exiting said vapor tube extension in step (d) supra.