Study On The Superheated Steam Drying Characteristics And Drying Technology Optimization Of Porphyra Haitanensis

Porphyra haitanensis is a purple plant, which grows in shallow sea with large varieties. Because of high moisture content and great difficulty of storage and preservation, dehydration has become an important method of processing. Superheated steam drying (SSD) technology was applied to Porphyra haitanensis drying in this paper. The SSD characteristic of Porphyra haitanensis was studied and kinetic models of SSD were established correspondingly. Meanwhile, effects of drying parameters on main quality of Porphyra haitanensis were investigated. At last, the optimal parameters of SSD were determined. The optimal parameters could provide an important theory for industrial production of SSD on Porphyra haitanensis.1. SSD characteristic of Porphyra haitanensisInfluence of drying parameters including steam temperature, steam velocity, initial moisture content and Porphyra haitanensis thickness were researched by SSD.The best Blanching temperature was85℃and time was30s.Drying characteristic of SSD for Porphyra haitanensis was consistent with the general properties of drying. The SSD process was divided into three stages which were preheated phase, constant-speed and speed-down phase according to drying rate. The higher steam temperature, the more obvious of the change of material temperature and the shorter the dehydration time became. It could obviously increase drying time and dehydration rate of constant-speed phase by increasing the thickness. The quicker steam velocity, the shorter drying time was. However, effect of steam velocity was not obvious as both steam temperature and material thickness. Initial moisture content had great influence on drying process. As decreasing of the initial moisture content, the drying time reduced.The changes of moisture content were studied in this paper and kinetic models of SSD were established. The drying course was consistent with Page model. Ln(-LnMR)=-2.9816-0.11213X1+0.0846X2-0.3591X3+(1.3826-0.3787X1+0.0659X2+0.0685X3)Lnt. By the experiment verification, the actual value fitted well with the model predictive value. The kinetic model could be used to predict the moisture change in drying processing.2. Effect of SSD parameters on Porphyra haitanensisShrinkage, Rehydration, the change of color and Polysaccharide content as evaluation, the effect of SSD steam temperature, steam velocity and Porphyra haitanensis thickness on the quality of Porphyra haitanensis were analysed. It could provide the important theory for recommendation optimization. Taking dehydration quality of Porphyra haitanensis and energy consumption into account, the best ranges were that the steam temperature was110-120℃, the thickness was5-10mm and the steam velocity was1.0-1.5m/S。3. SSD technology optimization of Porphyra haitanensis.The effect of steam temperature, steam velocity and thickness on Retention volume rate and Polysaccharide content were studied by response surface methodology (RSM). Regression models of Retention volume rate and Polysaccharide content were established. The optimal parameters were obtained by analysis both of single factors and double factors response surface analysis. The results showed that the actual value fitted well with the model predictive value. It could be used to predict the change of Retention volume rate and Polysaccharide content. The two regression modes respectively were: Y1=28.62-3.36X1-1.13X3-2.09X12-2.09X22-2.26X32Y2=4.12-0.44X1+0.29X2+0.25X3-0.3X12-0.6X32At last, the optimal parameters were that the steam temperature was119℃, material thickness was6mm and steam velocity was1.2m/s.4. Comparison of Superheated Steam Drying and Hot Air Drying (AD) on energy utilizationHeat transfer capacity of drying medium and the heat took away by exhaust were studied. At the same time, economic analysis was researched by a hypothesis. The results showed that efficiency of drying was improved and drying time was reduced by SSD. The heat took away by SSD was less than AD and Energy consumption of SSD was far less than that of AD. The temperature of exhaust of SSD was high and could be recovered by condensation methods and energy recovery was up to84.8%. The energy needed of hot air drying was6.5times as much as superheated steam drying.