Gypsum scaling in membrane distillation: Impacts of temperature and vapor flux
Gypsum scaling in membrane distillation: Impacts of temperature and vapor flux
复制标题
DOI：
10.1016/j.desal.2021.115499
复制
发表时间：
2022-03-01
期刊：
影响因子：
9.9
通讯作者：
Lin, Shihong
中科院分区：
文献类型：
--
作者：
Christie, Kofi S. S.;Horseman, Thomas;Lin, Shihong
难溶石膏（CaSO 4 &BH2; 2 H（2）O）的矿物结垢是膜蒸馏技术面临的一个长期挑战.沉淀溶液的热力学状态和由于矿物快速生长导致的通量下降点之间的潜在关系尚不清楚。本工作通过一系列实验沿着半经验模型来考察料液在料液/膜界面处的热力学状态，以评价和比较结垢临界点。这些实验是特意设计的，以消除进料温度和蒸汽流量的影响。在膜界面的沉淀溶液的热力学状态进行评估，使用饱和指数和成核能垒从溶解的离子和石膏矿物之间的化学势差，该模型是植根于已建立的传热和传质关系，并反映了用于进行实验的测试条件。该模型是建立在实验结果在一系列的操作条件下，与散装进料溶液的温度范围从50到80？(at恒定通量）和跨膜水通量范围为10至40 L m（-2）h（-1）（在恒定进料温度下）。据观察，在诱导点计算的界面饱和指数在不同的实验中是不一致的，证实了MD中的石膏结垢是由动力学而不是热力学控制的。我们还发现，温度起着更重要的作用比蒸汽流量在影响临界恢复。最后，我们还提供了理论推理，以支持实验观察，石膏结垢在MD在很大程度上是由膜表面上的异相成核。
Mineral scaling by sparingly soluble gypsum (CaSO4 & BULL;2H(2)O) is a persistent challenge to membrane distillation (MD). The underlying relationship between the thermodynamic state of the precipitating solution and the point of flux decline due to rapid mineral growth remains unclear. In this work, a series of experiments along with a semi-empirical model are executed to examine the thermodynamic state of the feed solution at the feed/mem-brane interface to evaluate and compare the critical point of scaling. The experiments were deliberately designed in a way to decouple the influence of feed temperature and vapor flux. The thermodynamic state of the precipitating solution at the membrane interface is evaluated using the saturation index and the nucleation energy barrier derived from the chemical potential difference between the dissolved ions and the gypsum mineral. The model is rooted in established heat and mass transfer relationships and reflects the testing conditions used to carry out the experiments. The model is built upon experimental results across a range of operational conditions, with the bulk feed solution temperature ranging from 50 to 80 ? (at a constant flux) and the trans-membrane water flux ranging from 10 to 40 L m(-2) h(-1) (at a constant feed temperature). It was observed that interfacial saturation index calculated at the induction point was not consistent across different experiments, confirming that gypsum scaling in MD is controlled by kinetics instead of thermodynamics. We also found that temperature plays a more important role than vapor flux in affecting the critical recovery. Lastly, we also provide theoretical reasoning to support the experimental observation that gypsum scaling in MD is largely dominated by heterogeneous nucleation onto the membrane surface.