Crystal Growth Kinetics for Phosphorus in Wastewater by Adding CaCl2 in the Fluidized Bed Crystallizer

• Main Authors: Yang -Kai, 鄭瓊怡
• Other Authors: Wu-Chun Sheng
• Format: Others
• Language: zh-TW
• Published: 2008
• Online Access: http://ndltd.ncl.edu.tw/handle/74579446138054923081

碩士 === 立德大學 === 資源環境研究所 === 96 === In this study, fluidized-bed crystallizer (FBC) was applied to crystallize the wastewater containing KH2PO4 by adding CaCl2. The optimal operation conditions of FBC were investigated under controlling the concentrations of KH2PO4 and CaCl2 within the range of metastable region. The recirculation flow rates were varied and the operation time was lengthened to further investigate the effect of hydrodynamics on growth rate of crystal. The experimental results showed that the best crystallization conditions were illustrated as follows: pH = 10, Ca/P = 1, Ca = 10 mg/L, P = 7.8 mg/L, influent flow rate = 4.8 L/hr, recirculation flow rate = 2.4 L/hr, surface loading rate = 0.916 Kg-P/m2-hr. The results of a continuous-flow 168-hours experiment indicated that the crystallization rate reached the value 89.08 %. Furthermore, with a greater recirculation flow rate, the greater the specific energy dissipation rate (ωs) is, but the smaller the crystallization rates (G) is. Another observation phenomena was found that the greater specific weight, was the pellet the lower part the pellet would move, and the pellet should be drawn out of when their crystallization amount reaches a certain utmost value. By the study of EDS (qualitative and quantitative analysis of element for crystal) and the SEM observation of crystal surface, the result shows that the phosphate content in the crystal was about 13.316 %. The appearance of the crystal phase on the bed top appeared more round and loose, while appearing more needle-like at the bed bottom. The correlated mathematical model among G, relative saturation level (σ), and specific energy dissipation rate in the FBC was finally established: 048 . 1 501 . 0 263 . 2 03 291 . 6 r L E G s − − − = ω . From the model of the growth rate for crystallization, the conclusion can be III made that G will decrease as L or ωs increases, but will increase as r increases. The correlations can be applied in estimating the growth of crystal operation, and design of the fluidized-bed crystallizer.