Macro-characteristics and micro-mechanisms of Na2SO4 precipitation dissolved by KNO3 molten salt in a continuous supercritical water system,Water Research

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Macro-characteristics and micro-mechanisms of Na2SO4 precipitation dissolved by KNO3 molten salt in a continuous supercritical water system
Water Research ( IF 11.4 ) Pub Date : 2024-06-03 , DOI: 10.1016/j.watres.2024.121869
Peng Feng ₁ , Donghai Xu ₁ , Youwei Zhi ₁ , Bing He ₁ , Shuzhong Wang ₁ , Yaling He ₁ , Yang Guo ₁

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This work aims to explore the ability of molten salt to solve salt deposition in supercritical water (SCW) related technologies including supercritical water oxidation and supercritical water gasification, with KNO3 and Na2SO4 as examples. In the pure KNO3 solution, the two-phase layering of high-density KNO3 molten salt (settling at the reactor bottom) and low-density saturated KNO3-SCW salt solution (flowing out at the top outlet of the reactor) was formed in a kettle-reactor with about 6.5 ratio of depth to inner diameter, thereby improving the accuracy of measured solubilities. The precipitation macro-characteristics of mixed KNO3 and Na2SO4 in SCW were investigated under different feed concentration conditions. The results showed that Na2SO4 deposition on the reactor sidewall could be reduced by more than 90 % when the mass ratio of KNO3 to Na2SO4 in the feed was only 0.167. No visible salt deposition was observed on the sidewall when the ratio was 0.374. All solid deposited salts were converted into the liquid molten salt as the ratio reached 3.341, and thus could easily flow out of the reactor, without plugging. ‘Molten salt dissolution’ mechanism may provide a more plausible explanation for mixed KNO3 and Na2SO4 in SCW. In addition, the precipitation micro-mechanisms of mixed KNO3 and Na2SO4, and the critical conditions of avoiding sidewall deposition and reactor plugging were proposed. This work is valuable for overcoming the salt deposition problem in SCW-related technologies.

中文翻译：

连续超临界水体系中KNO3熔盐溶解Na2SO4沉淀的宏观特征和微观机制

本工作旨在探讨熔盐解决超临界水（SCW）相关技术中盐沉积的能力，包括超临界水氧化和超临界水气化，以KNO3和Na2SO4为例。在纯KNO3溶液中，在反应器内形成高密度KNO3熔盐（沉降在反应器底部）和低密度饱和KNO3-SCW盐溶液（从反应器顶部出口流出）的两相分层。釜式反应器的深度与内径之比约为6.5，从而提高了溶解度测量的准确性。研究了不同进料浓度条件下 KNO3 和 Na2SO4 混合溶液在 SCW 中的沉淀宏观特性。结果表明，当进料中KNO3与Na2SO4的质量比仅为0.167时，反应器侧壁上的Na2SO4沉积可减少90%以上。当比率为0.374时，在侧壁上没有观察到可见的盐沉积。当比例达到3.341时，所有固体沉积盐都转化为液体熔盐，因此可以很容易地流出反应器，不会堵塞。 “熔盐溶解”机制可能为 SCW 中混合 KNO3 和 Na2SO4 提供更合理的解释。此外，还提出了KNO3和Na2SO4混合沉淀的微观机制，以及避免侧壁沉积和反应器堵塞的临界条件。这项工作对于克服超临界水相关技术中的盐沉积问题具有重要意义。

更新日期：2024-06-03

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