Pneumatic separation of hulls and meats from cracked soybeans

The dehulling process of cracked soybeans was experimentally investigated in this work. The mean Sauter diameter ( d v,s) of as-received material was 2.70 mm, with an average proportion of 95% meats and 5% hulls for a moisture content of 11.8%. The true densities of hulls and meats were 1090 and 1267 kg/m 3, with d v,s of 2.11 and 2.74 mm, respectively. Hulls were mostly elutriated around 2.7–4.5 m/s and meats around 9.1–13.7 m/s. The overlap of terminal velocity profiles required a combination of pneumatic and sieving operations for optimized separation. The influence of particle concentration on continuous dehulling was investigated for three solid-to-air ratios ( W/ Q). The procedure that maximized particle separation was a sequence of pneumatic dehulling with v s = 7.4 – 9.1 m / s and W/ Q = 1.05 kg solids/m 3 air, followed by screening of lifted material with sieve ASTM no. 6 and a final pneumatic separation of small hulls and meats at v s = 3.9 − 4.1 m / s . An industrial scale pneumatic dehuller was built and tested for W = 6973 kg/h, v s = 7.6 – 8.2 m / s and W/ Q = 0.97 kg solids/m 3 air. The efficiency of the pneumatic device to remove hulls from the cracked soybean was very high, with the recovery of meats with purity around 99%.