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真空膜蒸馏处理高矿化度矿井水试验研究

Experimental research on treatment of highly-mineralized mine water by vacuum membrane distillation

  • 摘要: 基于高矿化度矿井水在我国西部煤矿区普遍存在的现状,为实现矿井水的高效利用,提出了采用膜蒸馏处理高矿化度矿井水的技术思路,膜蒸馏技术可充分利用西部矿区丰富的低品位热源,实现矿井水的大规模低成本处理。采用疏水性聚偏氟乙烯(PVDF)中空纤维膜,在石灰-纯碱法软化处理的基础上,对真空膜蒸馏(VMD)处理高矿化度矿井水技术进行了试验研究,着重探讨了热料液温度、热侧流量和冷侧真空度等操作条件对VMD过程的影响;分析了VMD浓缩过程中膜通量、脱盐率等膜性能的变化;考察了长期运行过程PVDF膜性能的稳定性。试验结果表明,对于硬度高而碱度低的矿井水,石灰-纯碱法可有效去除其硬度成分,投加质量浓度为600 mg/L CaO和500 mg/L Na2CO3可使矿井水中硬度的去除率达到77%以上;对VMD膜通量影响的重要性由强到弱依次为冷侧真空度、热料液温度、热侧流量,本试验的最优操作条件为温度75 ℃、流量1 L/min、真空度90 kPa;维持最优操作条件,VMD浓缩过程的初始膜通量约13.4 kg/(m2·h),分别浓缩5、14.5倍时,膜通量降至初始值的81.22%和34.51%,脱盐率则始终在99.5%以上;随着VMD长期运行,膜通量逐渐下降,元素分析结果证实了膜污染和膜润湿现象,膜丝内表面的结晶主要是钙、镁硬度,Na、Cl元素的渗漏是膜润湿的重要原因;采用物理清洗干燥初期效果较好,清洗干燥后膜通量恢复至初始值的93.77%,但持续使用恢复作用逐渐降低。

     

    Abstract: Based on the status quo that high-salinity mine water generally exists in coal mining areas in western China, in order to realize the efficient use of mine water, the technical idea of treating highly-mineralized mine water by membrane distillation was put forward. The low-grade heat source can realize large-scale and low-cost treatment of mine water. In this study, a hydrophobic polyvinylidene fluoride (PVDF) hollow fiber membranes were used to treat high-mineralized mine water by vacuum membrane distillation (VMD), which was studied on the basis of softening pretreatment with CaO and Na2CO. The effect of operating conditions such as hot liquid temperature, hot side flow rate and cold side vacuum degree on the VMD process were analyzed. The changes of the membrane performance such as membrane flux and desalination rate during the VMD concentration process were analyzed. The long-term stability of the PVDF membrane performance was investigated. The test results show that for the mine water with high hardness and low alkalinity, the lime-soda ash method can effectively remove its hardness components, and adding 600 mg/L CaO and 500 mg/L Na2CO3 can make the hardness removal rate in mine water reach more than 77%; The importance of influence on the membrane flux of VMD from strong to weak is the vacuum degree on the cold side, the temperature of the hot liquid, and the flow rate on the hot side. The optimal operating conditions in this study were temperature 75 ℃, flow rate 1L/min and vacuum degree 90 kPa, the initial membrane flux of the VMD concentration process is about 13.4 kg/(m2·h). When the concentration times were 5 and 14.5, the membrane flux drops to 81.22% and 34.51% of the initial value, respectively. Simultaneously, the desalination rate was always at 99.5% or more. With the long-term operation of VMD membrane flux gradually decreased. The elemental analysis results confirmed the existence of membrane fouling and wetting. The crystallization on inner surface of membrane filament were mainly Ca and Mg hardness, and the leakage of Na and Cl elements was an important reason for membrane wetting. The initial effect of physical cleaning and drying was better. After cleaning and drying the membrane flux returns to 93.77% of the initial value, but the recovery effect continues to decrease.

     

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