Study On Nanofiltration Seawater Desalination And Its Performance Of Boron Removal

Nanofiltration membrane, as a kind membrane with low operation pressure, was used in seawater desalination by a dual-stage process to reduce the energy consumption and ensure the production to meet drinking water standards. So the dual-stage nanofiltration seawater desalination was expected to be an impotant desalination technology in future. The commercial nanofiltration membrane modular was employed to investigate the dual-stage nanofiltration process in this paper. A novel complex-dual stage NF process was also studied to sovle the boron removal problem.A single element experiment equipment was set up. Based on the feature of dual- stage nanofiltration technology and the requirement of permeate quality, FilmtecTM NF90-4040 was choosed as the experiment membrane after a testing experiment among several commercial NF membranes. The effect of pressure, temperature and flow rate on the permeate quality and scaling possibility were investigated, and the basic mass trassfer data and regular facing industry were also obtained. It was shown that the permeate TDS could be reduced below 250mg/L under a condition of 35bar, 2.46m3/h , 20℃in 1st stage and 10-30bar, 1.8m3/h in 2nd stage. The effect of TDS in feeding water on the relation of TDS in permeation and pressure was disscused at the same time.The boron removal performance of dual-stage nanofiltration seawater desalination process was initially investigated by using commercial nanofiltration elements, and the effect of pH was also studied. The concentration of boron in permeate could reach to 1 mg/L when the pH was adjusing to 10.3. A novel boron removal technology using polyols in seawater desalination process was investigated, in which sorbitol was initially used as additive. A complexation-nanofiltration process was set up and different effects were studied. The sorbitol was both added in 1st and 2nd stage and the boron could be reduced to 0.1mg/L combined with pH adjusting. The molecular simulation result shown that the better rejection was mainly caused by the change of molecular size& structure after comlextion reaction.The water and salt permeate coefficient were calculated, based on which the recurrence formulars were used to calculate the performance of industrial scale process. The effects of temperature,pressure and flow rate on energy consumption in a single stage system was investigated. Several different dual-stage NF desalination process were designed. The energy consumption was modeled and the effect of operation condition was studied. It was shown that the energy consumption of dual-stage NF desalination was low and it was a kind of economic and feasible technology.