Abstract:

To solve the problem that direct contact membrane distillation (DCMD) process presents a low distillate flux and membrane fouling, a new form of membrane distillation module has been designed in the paper. Sucrose solution was used as feed solution in the experiments. The effect of various parameters on the performance of DCMD process was investigated. The parameters included the packing density of the module Φ, the membrane aeration amount q, the concentration c and temperature T₀ of feed solution. The results indicated that with the increase of the packing density of module Φ and membrane aeration amount q, the DCMD flux increased first, then gradually decreased. Φ and q had optimal value, respectively. The DCMD flux decreased gradually with the increase of c, but increased with the increase of T₀. For a constant concentration (30%) feed, when the DCMD process ran 330 min, compared to the process without membrane aeration, membrane aeration made the initial flux J_initial increased 24.7%, the decay rate of flux ΔJ decreased more than 55.0%, the continuous running time t₀ for maintaining high flux lengthened 4 times. The hot feed of DCMD process was aerated by PVDF membrane, on the one hand, to promote the heat and mass transfer of process, thus to intensify the separation performance of process, on the other hand, to control effectively the concentration polarization of process, thus to delay the membrane fouling process. The study was helpful to promote the engineering application of DCMD technique.

Key words: direct contact membrane distillation, membrane aeration, gas-liquid flow, process intensification, heat transfer, mass transfer, membrane fouling

摘要：

针对直接接触式膜蒸馏（direct contact membrane distillation，DCMD）过程存在的膜通量小及膜污染问题，设计了一种新型结构的膜蒸馏组件。以蔗糖溶液为处理液，考察了膜组件装填密度Φ、膜曝气量q、蔗糖浓度c与温度T₀对DCMD过程的影响。结果表明：随着Φ、q的增加，DCMD过程的膜通量先增大，后逐渐降低，Φ、q均存在最优值；随着c的增加，膜通量逐渐降低；随着T₀的增加，膜通量增大；对c为30%（mass）的蔗糖溶液进行DCMD法处理330 min时，膜曝气可使DCMD的初始膜通量J_initial提升24.7%、膜通量衰减率ΔJ降低55.0%，维持高膜通量的连续运行时间t₀延长4倍。主要原因是膜曝气强化了DCMD过程的传热传质，进而强化过程的分离性能；有效控制了DCMD过程的浓差极化，进而延缓过程的膜污染进程。研究结果有利于推进DCMD的工程化应用。

关键词: 直接接触式膜蒸馏, 膜曝气, 气液两相流, 过程强化, 传热, 传质, 膜污染