| In recent years, the researches on developing seawater desalination technologyhave been investigated extensively. Integrated membrane systems （IMS） have playedan important role in seawater desalination due to their special advantages and theyhave been widely applied in residential and industrial settings and in oil exploitationof offshore. The purpose of this paper is to provide fresh water and good waterresource for further seawater desalination and oilfield water injection development byIMS technology.This investigation is based on the project of offshore oilfield polymer solutionpreparation and the experiment is carried out in Jiaozhou bay. This paper focuses onthe study of integrated membrane water softening using nanofiltration （NF）technology and the influence of antiscalant on the NF process. The effect of operatingpressure, temperature, concentrated water recycle ratio on the performance of the pilotNF process, the application of dual-pass NF process, as well as the integratedmembrane system of NF-RO （Reverse Osmosis） technology were investigated,respectively.The pilot NF experiment of IMS shows that operating pressure has efficientinfluence on the product water quantity and quality than that of the feed watertemperature and concentrated water recycle ratio. With the increase of operationpressure, permeate water flux increases linearly and the rejection rate of each ion alsoincreases gradually. But the growth becomes slowly when pressure rises to a certaindegree, due to the membrane surface concentration polarization and some otherreasons. With the variation of feed water temperature, permeate water flux changesobviously while production water quality changes only slightly. Along with theincrease of concentrated water cycle ratio, the recovery of system has been improvedbut permeate water quality declined, resulting from the poor feed water quality ofmixed with concentrated water, which illustrated that a comprehensive considerationon both the recovery and production water quality and some other aspects in practicalapplication must be taken into account. The dual-pass NF process showed that the permeate water flux of the2ndpass NFmembrane can reach50to80L·m-2·h-1with the operating pressure of the1stpass NFat2.0to3.2MPa and2ndpass NF at2.5MPa, which demonstrated that dual-pass NFprocess could greatly improve the water production capacity.The integrated membrane system of NF-RO is one of the promising technologies.When the pressure of NF process is kept at3.0MPa, the better inlet water is provided,so the better NF-RO permeate is achieved at relative low operating pressure3.0MPaof RO process.With the pursuit of higher recovery, the membrane pollution becomes more andmore serious, which restricts the development and application of IMS. Theintroduction of antiscalant can be a good solution for this problem. In the experiment,we focused on the effect of antiscalant on NF process and we explored a dedicatedantiscalant to ensure good performance of the membrane, to keep a long-term stableoperation and prolong the service life of membrane and reduce the energy costs. Withthe concentration of antiscalant increasing, the production water quality grows better.When operating pressure of NF process is kept at3.0MPa, temperature of25℃,with the concentration of antiscalant is4mg·L-1, the permeate water flux is17.23L·m-2·h-1. Through the comparison of different concentration antiscalant, appropriateamount of4mg·L-1scale inhibitors can slow down fouling formation on the surface ofmembrane and reduce the production flux decline.Necessary basic data and feasibility analysis can be obtained from this research,which will provide a good guidance for seawater softening industrial application. |
PDF Full Text Request