Optimization of Wastewater Purification in a Cool Thermal Storage System

• Main Authors: Yu-Zhi Chen, 陳諭志
• Other Authors: Cheng-Liang Chang
• Format: Others
• Language: zh-TW
• Published: 2001
• Online Access: http://ndltd.ncl.edu.tw/handle/59527145805354520651

碩士 === 淡江大學 === 化學工程學系 === 89 === Purification of wastewater by freezing in a cool thermal storage process is investigated. Mathematical models of heat and mass transfer in this system are developed to describe the thickness and the solute distribution of ice as the cool-thermal storage process proceeds. A mathematical description for determining the optimum solidification thickness and operating time to remove the maximum amount of solute is presented. For the system of constant temperature of ice free surface, the optimal operating time is within off-peak period of electricity supply when the ice temperature is maintained at —20 or -40℃, and the time needed for -40℃ is shorter than the time needed for -20℃. Because of the convenience of temperature control when a specific coolant is used, it is more practical to keep the free surface temperature constant in a commercial application. For the system of constant heat flux of ice free surface, the optimal operating time is within the off-peak period when the heat flux is fixed at 4000, it is not for the case of 2000. Significant error will occur when semi-infinite domain is assumed in the case of finite depth of wastewater since the heat penetration rate is so fast such that the temperature at the bottom of the water tank won’t be able to keep constant as the freezing process proceeds. For the system of constant volumetric rate of vacuum, the suction rate is an important factor in determining the efficiency of the process. The suction rate should be kept within the range of 15000 to 20000 when the solute distribution coefficient is less the one. When the coefficient is greater than one ,the suction rate should be run within 5000 to 10000. Over the proper of range operation, the optimal operating time is a week function of suction rate.