| With the rapid development of the world's maritime trade, the damage caused by ballast water is becoming more and more serious. A large number of studies have showed that any single ballast water treatment method can not treat all harmful organisms in ballast water efficiently under the premise of meeting the IMO standards. Based on this background, this paper proposes a new method for the treatment of ballast water by the combination of cyclone separation, UV and US, and build the UV/US ballast water management system. This system uses cyclone separation as a primary treatment method to remove large particles and aquatic organisms in the seawater, reduce the turbidity of the seawater and so as to improve the light transmittance of the seawater. US is used as the second treatment method to destroy the cell structure of the microorganism in seawater or kill them directly, reduce the dose required for the inactivation of microorganisms by UV light and to further reduce the turbidity of seawater. UV as the last treat method to inactivate the small plankton, bacteria and viruses remained in the seawater. In order to improve the treatment efficiency of the system, system devices are designed and optimized in this paper, and the main work is as follows:(1) According to the design requirements of hydrocyclone and relevant empirical formula, completed the preliminary design of hydrocyclone structure whose processing capacity is 200m3/h. Based on the Eulerian multiphase flow model and RSM turbulence model of the FLUENT software to simulate the solid-liquid two phases flow field in cyclone. Through the numerical simulation, the influence of structural parameters and sand phase sizes to the separation performance of hydrocyclone was studied with single factor method and influence laws were obtained. The best structure parameters of hydrocyclone were obtained. Finally, the inlet structure of hydrocyclone was optimized. The results show that:compare to the two structure of Archimedes spiral inlet and tangential inlet, the tangential velocity and separation efficiency were increased visibly, and the separation property was improved.(2) According to the principle and influence factors of US treatment, the structure design of US processor was completed. Using FLUENT software to simulate the US processor and the flow field distribution in the processor was obtained. According to the directivity function of planar array transducer, the sound pressure calculation formula of(3) transducer array in three-dimensional spaces was derived. The sound field distribution in the US processor was calculated by using MATLAB software programming. The influence of structural parameters and frequency to the working performance of US processor was analyzed and the influence laws were obtained.(4) Optimized the UV sterilizer by installing guide vanes in the entry. RSM turbulence model combined with Species Transport model were developed to simulate the residence times of UV sterilizer with different guide vane's parameters and finally obtained the best parameters combination. The distribution of UV radiation intensity and dose inside the sterilizer were simulated by both FLUENT and MATLAB software and the difference between the two methods was compared and analyzed. The numerical results showed that comparing with the original UV device, the values for residence time and average radiation dose of the optimum device respectively increased.(5) A small UV/US ballast water experimental system was established, completed the algae removal experiments by US, UV and the combination of the two. Experimental figures showed that comparing with the US or UV algae removal experiments, the combination can visibly increased the removal rate of algae. Preliminarily verified the feasibility of UV/US ballast water system in ballast water treatment. |
PDF Full Text Request