This paper investigated different strategies to prevent salt deposition during weak black liquor (WBL) desalination under hydrothermal liquefaction conditions based on phase behaviour analysis. Phase equilibria of model salt solutions replicating the WBL composition were studied by high-pressure differential scanning calorimetry (HP-DSC) and different strategies to induce the Type 1 salt behaviour were applied. Two strategies led to an optimised salt separation: adjusting the concentrations of Type 1 salts, NaOH and NaHS, present in the WBL, and selectively exchanging carbonate from the model salt solution by replacing it with hydroxide. These strategies were tested in PSI’s continuous salt separation test rig, considering the recovering of salts. Although increasing the concentration of the Type 1 salts (NaOH and NaSH) impacted the precipitation temperature and extent of the salts, the strategy was not able to prevent it entirely. The HP-DSC results confirmed the efficiency of carbonate replacement by hydroxide since the Type 1 behaviour was observed after exchanging 75% of the carbonate. In the presence of organics, some salt accumulation and overflow into the desalinated stream occurred, which was addressed by optimising the brine flow rate.

中文翻译：

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基于相行为分析的稀黑液连续脱盐策略的制定

本文基于相行为分析，研究了水热液化条件下弱黑液（WBL）淡化过程中防止盐沉积的不同策略。通过高压差示扫描量热法 (HP-DSC) 研究了复制 WBL 成分的模型盐溶液的相平衡，并应用了不同的策略来诱导 1 型盐行为。两种策略实现了盐分离的优化：调整 WBL 中存在的 1 型盐、NaOH 和 NaHS 的浓度，并通过用氢氧化物替代模型盐溶液来选择性地交换碳酸盐。这些策略在 PSI 的连续盐分离试验装置中进行了测试，考虑了盐的回收。尽管增加 1 型盐（NaOH 和 NaSH）的浓度会影响盐的沉淀温度和程度，但该策略无法完全阻止它。 HP-DSC 结果证实了氢氧化物取代碳酸盐的效率，因为在交换 75% 的碳酸盐后观察到了 1 型行为。在有机物存在的情况下，会发生一些盐积累并溢出到脱盐流中，这可以通过优化盐水流量来解决。