The Study On Resource Utilization And Zero Discharge Of The Waste Water From Silica Production

Aiming at the situation of high energy consumption and easy fouling of freezing process for the treatment of the waste water from silica production, a new process of resource utilization and zero discharge of the waste water from silica production was proposed. The character of the new process is to impel the cooling crystallization of the high salinity waste water from the membrane separation by using the characteristic of water absorption of LiBr solution and to regenerate the LiBr dilute solution by using waste heat. The process of evaporation cooling and crystallization were studied and the cooling and mass transfer mechanism of waste water were revealed. Based on the experimental results, a model of full process simulation of the preliminary design of the new process was established, and the solving method of the model was provided. Based on the model, the optimum process parameters were obtained. The following results were obtained:(1)The improvement of driving force and the decrease of resistance can be used for the enhancement of the cooling rate of waste water. The decrease of the concentration of waste water and the improvement of the concentration of LiBr solution can be used for the enhancement of the driving force. The resistance in the liquid film between vapor and LiBr solution form the majority of the all mass transfer resistance. The key to reduce the mass transfer resistance is to enhance the agitation intensity in absorber. The formula1.91 1.45 Sh ?0.066 Re Sc was obtained by the dimensional analysis to the process.(2)The effective method to reduce the metastable zone width and to control the diameter of Na2SO4 crystal is the control of cooling rate and agitation intensity in crystallizer. The increase of the concentration of LiBr, the concentration of waste water and the agitation intesity in absorber was beneficial to the improvement of desalination rate. The desalination rate was more than 50% under the following condition: the concentration of waste water, 12%; the concentration of LiBr solution, 55%; the agitation intensity in absorber, 1500r/min.(3)The process of resource utilization and zero discharge for the silica waste water treatment was simulated and analyzed. And the optimum process parameters were obtained; the design concentration of high-salinity water of NF, 13%; the water recovery of RO,60%; the temperature difference of the cold and hot outlet stream from E01, 3 ℃; the crystallization temperature, 10 ℃; the precooling temperature, 30 ℃; the split ratio, 0.55; the temperature difference of the cold and hot outlet stream from E01, 2℃; the range of circulation quantity of LiBr is 9000~11340kg/h under the condition: the volume flow, temperature and concentration of waste water is respectively 1m3/h, 30℃ and 3%. Compared with traditional process of silica waste water treatment, the new process have the advantages of low electric consumption, zero steam consumption, the recovery of waste heat, and low cost.The research results have a guiding significance on the process of resource utilization and zero discharge of the silica waste water treatment...