Process for producing polyphosphoric acid P3 comprising the following steps: (a) introducing, into a gas/acid contactor, a feed stream F0 of a phosphoric acid feed solution P0 and comprising at least 40% equivalent in P 2 O 5 units, (b) introducing, into the gas/acid contactor, a recirculation stream F2 of recirculated enriched phosphoric acid solution P2, (c) introducing, into the gas/acid contactor, combustion gases G1, (d) bringing into contact the feed stream F0, the recirculation stream F2 and the combustion gases G1, in order to form, on the one hand, an enriched phosphoric acid solution P1 and, on the other hand, contacted combustion gases G3, • separating the contacted combustion gases G3 from the enriched phosphoric acid solution P1, • discharging the contacted combustion gases G3 from the gas/acid contactor, and • taking the enriched phosphoric acid solution P1 out of the gas/acid contactor, (e) forming, from said enriched phosphoric acid solution P1, on the one hand, • a recirculation stream F2 of recirculated enriched phosphoric acid solution P2, in order to introduce it into the gas/acid contactor as defined in step (b) and, on the other hand, • a spray stream F1 of the enriched phosphoric acid solution P1, in order to introduce it into a combustion chamber, (f) spraying the enriched phosphoric acid solution P1 through a burning flame in the upper part of the combustion chamber in order: • to evaporate water and thus to concentrate the enriched phosphoric acid solution P1, • to polymerize the enriched phosphoric acid solution in order to form polyphosphoric acid P3 and • to form combustion gases G1, (g) separating the polyphosphoric acid solution P3 from the combustion gases G1 and • recovering the polyphosphoric acid solution P3, and • transferring the combustion gases G1 into the gas/acid contactor as defined in step (c). (a) introducing, into a gas/acid contactor, a feed stream F0 of a phosphoric acid feed solution P0 and comprising at least 40% equivalent in P 2 O 5 units, (b) introducing, into the gas/acid contactor, a recirculation stream F2 of recirculated enriched phosphoric acid solution P2, (c) introducing, into the gas/acid contactor, combustion gases G1, (d) bringing into contact the feed stream F0, the recirculation stream F2 and the combustion gases G1, in order to form, on the one hand, an enriched phosphoric acid solution P1 and, on the other hand, contacted combustion gases G3, • separating the contacted combustion gases G3 from the enriched phosphoric acid solution P1, • discharging the contacted combustion gases G3 from the gas/acid contactor, and • taking the enriched phosphoric acid solution P1 out of the gas/acid contactor, • separating the contacted combustion gases G3 from the enriched phosphoric acid solution P1, • discharging the contacted combustion gases G3 from the gas/acid contactor, and • taking the enriched phosphoric acid solution P1 out of the gas/acid contactor, (e) forming, from said enriched phosphoric acid solution P1, on the one hand, • a recirculation stream F2 of recirculated enriched phosphoric acid solution P2, in order to introduce it into the gas/acid contactor as defined in step (b) and, on the other hand, • a spray stream F1 of the enriched phosphoric acid solution P1, in order to introduce it into a combustion chamber, • a recirculation stream F2 of recirculated enriched phosphoric acid solution P2, in order to introduce it into the gas/acid contactor as defined in step (b) and, on the other hand, • a spray stream F1 of the enriched phosphoric acid solution P1, in order to introduce it into a combustion chamber, (f) spraying the enriched phosphoric acid solution P1 through a burning flame in the upper part of the combustion chamber in order: • to evaporate water and thus to concentrate the enriched phosphoric acid solution P1, • to polymerize the enriched phosphoric acid solution in order to form polyphosphoric acid P3 and • to form combustion gases G1, • to evaporate water and thus to concentrate the enriched phosphoric acid solution P1, • to polymerize the enriched phosphoric acid solution in order to form polyphosphoric acid P3 and • to form combustion gases G1, (g) separating the polyphosphoric acid solution P3 from the combustion gases G1 and • recovering the polyphosphoric acid solution P3, and • transferring the combustion gases G1 into the gas/acid contactor as defined in step (c). • recovering the polyphosphoric acid solution P3, and • transferring the combustion gases G1 into the gas/acid contactor as defined in step (c).