Production process for producing water-absorbent polymer particles and belt dryer

A production process for production of water absorbing polymer particles, where the production process has the following process steps:

• polymerizing (S1) an aqueous monomer solution or suspension for production of an aqueous polymer gel (S2),
• drying (S3) the aqueous polymer gel in a belt drier with a conveyor belt (400), by accommodating the aqueous polymer gel on the conveyor belt (400) and conveying the polymer gel on the conveyor belt (400) in a conveying direction (C) of the conveyor belt (400),
• crushing and/or grinding (S4) the dried polymer gel to give water-absorbing polymer particles, where, for drying (S3):
• the belt drier has a drier setup (101) in the interior (101i) of which the conveyor belt (400) is guided, wherein
• drying air in the interior (101i) of the drier setup (101) is conducted in countercurrent (C′) counter to the conveying direction (C) and the interior of the drier setup (101) is kept at a reduced pressure (p_U) relative to the ambient pressure (p_A) outside the drier setup (101), and the interior (101i) has a pressure zone (DZ), wherein, in line with conveying direction (C):
• a first internal pressure is formed as inlet pressure at a polymer gel inlet (100A) in at least one of the pressure zone (DZ) with a first pressure differential (ΔpA) from an ambient pressure (p_A), and
• a second internal pressure is formed as outlet pressure at a polymer gel outlet (100B) in the at least one pressure zone (DZ) with a second pressure differential (ΔpB) from an ambient pressure (p_A), where
• the second pressure differential (ΔpB) is smaller than the first pressure differential wherein
• the pressure zone (DZ) in the interior (101i) of the drier setup (101) or a pressure zone subregion (DZT1, DZT2) of the pressure zone (DZ) is bounded by means of a transverse wall (QWa, QWe, QWi) oriented at right angles to the conveying direction of the conveyor belt.