Outlet-Air Relative-Humidity Feedback for Adaptive Binder Delivery During Pulsed Fluidized-Bed Agglomeration of Soy Protein Isolate

Fine soy protein isolate (SPI) powders exhibit poor handling and reconstitution properties, while excessive liquid loading can destabilize fluidized-bed agglomeration. This study evaluated an outlet-air relative humidity (RH)-triggered binder-diversion strategy during pulsed fluidized-bed agglomeration of SPI. Atomization pressure (0.5, 1.0, and 1.5 bar), nominal binder pump setting (3.8, 4.7, and 5.6 mL·min−1), and operating mode (continuous spraying or RH-triggered control at a 70% set point) were investigated. Under continuous spraying, outlet RH showed an overall increase throughout the 30 min process. RH-triggered operation maintained outlet RH near the set point after threshold attainment by reducing the spray duty cycle to 0.67–0.96. This corresponded to 102.6–131.0 mL of sprayed water per run, approximately 4–33% less than continuous spraying at the same nominal pump setting. Compared with continuous spraying, RH-triggered operation produced a lower mean final moisture content in all nine conditions, a higher mean process yield in seven conditions, higher D50 values in all conditions, and a lower mean particle size span in seven conditions. Agglomeration reduced the packing-derived CI and HR and shortened wetting time relative to raw SPI, whereas the effects of RH-triggered operation on flow indices, wetting time, and dispersibility depended on atomization pressure and effective binder delivery. Because the feedback action changed both cumulative binder addition and spray history, the observed product differences represent the performance of the complete RH-triggered control strategy rather than an independent effect of RH stabilization. The findings demonstrate the feasibility of outlet-RH-based adaptive binder delivery during pulsed fluidized-bed agglomeration of SPI.