【作者】 徐佳；

【导师】 高从堦； 阮国岭；

【作者基本信息】 中国海洋大学 ， 海水利用技术， 2008， 博士

【摘要】 水污染和水资源短缺已成为制约社会进步和经济发展的世界性问题。海水淡化作为一种解决水资源短缺的重要战略手段,在世界范围内正发挥着越来越重要的作用。合理的预处理是海水淡化装置成功运行的决定性因素之一。以超滤代替传统预处理技术应用于海水淡化,研究不同规模超滤系统的运行状况,解决运行过程中的实际问题（膜污染等）,具有应用和理论的双重意义。本论文的研究内容以超滤作为海水淡化预处理工艺的应用研究为主,与大型海水淡化示范工程相结合,大部分实验在海水淡化现场完成,包括:实验室规模的无机陶瓷超滤膜作为海水淡化预处理工艺的初步可行性研究、有机超滤膜的现场中试试验研究,大型海水淡化示范工程的长期监测与参数优化研究、关于膜污染的临界通量研究和计算机模拟。主要内容和结论如下:1.通过胶州湾原海水直接进入系统和海水添加絮凝剂后再进入系统两种工艺,初步验证了50nm管式陶瓷膜作为海水淡化预处理工艺的技术可行性。原海水直接进入系统的最佳操作参数为:错流流速3.2m/s,操作压力0.14⁰.18MPa,料液温度25³0℃,料液pH 8⁹;FeCl3絮凝-陶瓷超滤膜工艺可有效提高通量和渗透液水质,且FeCl3最佳投加量为4.5⁶.0mg/L,pH最佳范围在4⁶;分析了海水对陶瓷膜产生的过滤阻力,并从膜污染类型角度分解过滤阻力,进行实验测定;确定40⁵0℃的0.01%NaClO溶液为最佳化学清洗方案。2.通过错流过滤模式的有机超滤膜处理胶州湾海水的中试试验,对操作参数进行优化。从最大净产水量的角度优化反冲参数,反洗周期为40min,反冲时间为30s、反冲流量是超滤产水流量2倍为优化结果。在试验范围内,高回收率-低通量（80%-60L/m2h）为优化运行参数,并通过比回收率通量PR%考察膜污染状况加以验证;超滤产水水质稳定,且满足海水淡化反渗透系统的进水要求。3.在胶州湾海域进行了超滤中试的极限试验研究,旨在考察极限条件（低温和死端过滤模式）下超滤系统（外压式、内压式以及双皮层超滤膜）处理胶州湾海水的可行性和稳定性,并简要分析并比较不同超滤膜组件的直接运行费用,为大型海水淡化示范工程提供重要数据。在无化学加强反洗（CEB）和化学清洗条件下,外压式膜组件B比内压式膜组件A的运行稳定,组件A和B的过滤阻力均小于双皮层膜组件C;组件A、B和C产水水质稳定且均满足海水淡化反渗透系统的进水要求,其中组件C的产水水质最优;CEB和化学清洗可抑制膜污染程度;从能耗和化学药品消耗两个方面表明,外压式膜组件B的直接运行年费用最低。4.对大型海水淡化示范工程的超滤预处理系统进行长达一年的监测研究,掌握其运行状况,收集和整理规模数据,并根据实际运行状况调整和优化工艺参数以确保超滤系统的稳定运行。超滤系统的全年运行监测数据表明,超滤系统的膜污染现象较严重,且温度对于膜污染和膜性能以及化学清洗效果具有显著影响,选择合适的工艺参数和化学清洗可以一定程度改善膜污染状况和恢复膜性能;超滤系统在正常运行情况下的产水水质符合RO进水要求;进料海水温度过低（5℃左右）,超滤膜的机械性能下降且膜丝污堵严重,应采用化学清洗和改善运行工况及时预防超滤膜断丝情况的发生。5.将临界通量Jcrit概念引入海水淡化领域,建立了测定Jcrit的实验方法,研究了超滤膜处理胶州湾海水的膜污染情况和最佳操作方式,考察了海水组成（天然有机物、悬浮物和无机盐）、错流流速和超滤膜截留分子量对超滤处理海水的Jcrit和膜污染产生不同程度的影响,该研究对于超滤预处理的通量设计和运行控制以减少化学清洗有重要理论指导意义。6.在已有的研究基础上,以错流过滤模式的超滤过程为研究系统,建立极坐标体系和物料衡算、粒子受力、过滤阻力数学模型,并采用Monte Carlo方法从微观角度对错流过滤的超滤膜表面聚集的溶质粒子的随机运动和受力状况进行计算机模拟,建立平衡状态的判定,得到初步模拟结果。实验结果表明,所建模型和Monte Carlo模拟的膜通量与实验值的相对误差为-0.246～1.518%;拟合出ΔP^J曲线,并得到J_crit=137.88L/m²h,为超滤系统的理论模拟奠定了基础。更多还原

【Abstract】 Water pollution and shortage has become a critical and serious challenge to society progress and economy development in the world. As an important strategic solution to water shortage, seawater desalination has been playing an increasingly momentous role. The desired performance of seawater desalination systems is guaranteed by appropriately designed pretreatment to face the varying seawater quality. It is of great theoretic and practical importance to focus on Ultrafiltration (UF) as an alternative replacement of conventional pretreatment system prior to seawater desalination. Prior to perform Ultrafiltrtion as the pretreatment, laboratory studies, pilot testing and demonstration, and membrane fouling in the filtration process should be considered. Most of the work is conducted on the desalination site and combined with demonstration seawater desalination plant which includes the feasibility studies of ceramic UF membrane and pilot testing of organic UF membrane as a pretreatment prior to seawater desalination on the laboratory scale and pilot scale respectively, the long-period investigation on demonstration seawater desalination plant and optimal performance, the studies of critical flux to minimize the membrane fouling in UF process and computer simulation on cross-flow UF process. The results are shown as follows:⑴Evaluation of the primary technical feasibility of 50nm monolith ceramic UF membrane as pretreatment prior to seawater desalination on the laboratory scale by feeding raw seawater and seawater with coagulant. The results from experiments on ceramic membrane performance including permeate flux and solute removal indicate that the optimal cross-flow velocity, TMP, feed temperature and pH are 3.0～3.5m/s, 0.14～0.18MPa, 25～30℃and 8～9, respectively; the optimum coagulation conditions were 4.5～6mg/L at pH 4～6; the optimum foulant cleaning was 1% NaClO at 40~50℃.⑵The main purposes of pilot testing of organic UF membrane treating seawater on cross-flow mode are to find the optimum filtration and backwash duration, backwash flow rate, recovery and flux. Based on maximum net product volume, performance of the UF system is good with the following conditions: backwash durationτ=30 s, filtration duration t=40 min, and backwash flow rate is 1800L/h. The operation of the UF system in high recovery-low flux mode (80%-60L/m2h) might be the best and should be adopted. The UF permeate has 100% of turbidity below 0.01NTU and 95% of the SDI15 below 3.0, which satisfies the requirement of SWRO feed water.⑶Pilot testing of organic UF membrane treating seawater in critical conditions of low feed temperature and dead-end mode mainly investigates the performance of inside-out and outside-in UF modules, evaluates the stability of dual-active layer of UF membrane as seawater desalination pretreatment, and analyses the direct operational cost. In filtration process, TMP increases rapidly and membrane fouling is obvious when inside-out module A is operated on designed flux and regular backwash; performance of outside-in module B is better than A with respect to stable TMP and flux, but there is more serious membrane fouling observed when module B is operated at up to 120% each designed flux. Membrane fouling can be controlled effectively by CEB with NaClO or NaClO/HCl, and CEB period of 16h is the optimal parameters. Permeate quality of both module A and B can meet the requirement of SWRO feed despite the variation of the raw seawater quality. The intrinsic resistance of dual-active layer module C is higher than module A and B; in module C, TMP is the highest and permeability is the lowest of all the modules investigated, but the permeate quality is best of all the testing modules. According to the consumption of energy and chemical reagents, the direct operational cost of module B is the lowest.⑷By monitoring the performance and adjusting the process parameters of UF system in the large-scale demonstration seawater desalination plant for one year, the data indicate that the membrane fouling is significant. It is also observed that the feed temperature affects membrane fouling and permeability, and membrane fouling can be reduced to some extent by chemical cleaning and operating at optimum conditions. The quality of UF permeate can satisfy the requirement of SWRO feed water, with turbidity and SDI15 in the range of 0~ 0.02NTU and 2.1~3.5, respectively. When feed temperature is low (about 5℃), mechanical properties of UF membrane may become poor and weak and therefore, rupture. It might be prevented by cleaning and optimum operating condition.⑸The concept of“Critical Flux”(Jcrit) is introduced into the field of seawater desalination, and used to investigate the membrane fouling and the optimal operational mode. A natural flux method is proposed to measure Jcrit which is proved feasible, accurate and easy to operation. By analyzing type of Jcrit in UF treating seawater, it is assumed that the membrane fouling cannot be avoided despite the operating conditions, but can be minimized. The seawater main components (NOM, suspended matter and inorganic salts), cross-flow rate and MWCO of UF membrane have different effects on Jcrit and membrane fouling. Under sub-critical conditions, operating the system on different modes including constant flux, constant pressure and natural flux mode results in the stable performance of UF treating seawater and the trends of flux and TMP have nearly no change. Comparing with different operating modes, natural flux mode has a good performance with the lowest total resistance, and it is the best choice of all the investigated operating modes.⑹By using Monte Carlo, a different point of view of microcosmic to simulate the particle random displacement and force situation in the condition of cross-flow UF process can be provided. It can relate microcosmic parameters (the dimensionless center-to-center separation between two particles scaled by the particle radius, s, and volume fraction,φ) and measuring parameters (flux and TMP). The results indicate that the relative error of flux between Monte Carlo simulation and experimental measurement is in the range of -0.246~1.518%. From fitting the curve ofΔP~J, Jcrit is estimated to be 137.88L/m2h.更多还原