Seeking help with issues related to the operation of extractive distillation columns
Thread Content
This post was last edited by tjumilan on 2009-11-5 at 15:52. Our workshop’s extraction distillation column is used for distilling triphenyls and separating non-aromatic compounds, and we have encountered a problem; we hope experts can help solve it. The specific situation was that the liquid level in the tower bottom fluctuated significantly; under normal operating conditions it was around 60%, but it suddenly dropped to around 10%. It took an hour to bring the liquid level back to its normal level, and the instruments seemed to be functioning properly. Along with this, the pressure at the tower bottom increased, while the pressure at the tower top first decreased before also increasing later on. I would like to ask the experts: why did the liquid level suddenly fluctuate? At that time, the steam flow to the reboiler at the bottom of the tower, as well as the feed and product flow rates, were all normal, with no significant changes. Our extractant is sulfolane, which is continuously regenerated using deionized water during production. The situation may not be described in detail; if experts still have questions, please contact us within the forum
The fluctuations in the liquid level at the bottom of the tower are likely caused by fluctuations in tower pressure. If the content of light non-aromatics in the feed is high, foaming easily occurs in the sulfolane solution. This leads to the occurrence of the ‘tower collision’ phenomenon. This, in turn, causes fluctuations in tower pressure and bottom liquid level. This is one possible reason. If the design includes foam suppressant injection, the amount of foam suppressant injected can be increased. Additionally, I have a few questions: 1. You mentioned triphenyl extraction; generally, factories use single-phenyl (B) or diphenyl (BT) extraction. With triphenyl extraction, C9 heavy aromatics may accumulate in the system, affecting solvent efficiency. How do you handle this? -Is it designed with a continuous weight removal system? Is it still reformed feedstock being used, with less C9NA? 2. Is your solvent pure cyclosulfone? If different second and third additives are added, they will also have varying effects on the system. 3. Regenerate with deionized water? Does it mean steam stripping is used in the regeneration tower? Intermittent discharge of heavy components from the bottom of the tower? I don’t know how to regenerate it using desalinated water. 4. When this phenomenon occurs, can your non-aromatic and aromatic hydrocarbon products still remain qualified? . . . . . . There are still many issues if we are to make a truly reasonable and effective judgment. . .
2# Fred_bj We pre-treated the crude benzene feedstock by separating heavy components such as C9, then carried out hydrodesulfurization of the light benzene, and only after that did we proceed with triphenyl extraction. We use pure sulfolane, with some antifoam agents added intermittently. You’re right; we do use steam stripping to remove the intermediate components intermittently. Production experience shows that the solvent regeneration effect is not significant, and the pH value of the solvent is less than 7. With such large fluctuations in tower pressure, the product quality was of course unsatisfactory; at that time, the line was switched to one for producing substandard products.
The LZ process involves the hydrogenation of coke naphtha, followed by extraction. ph
upstairs, the 7 causes analysis for PH is correct; moreover, we still haven’t found a targeted solution for dealing with Cl. Regarding the second question, our reactor bottom design is not as you described. We used a solvent ratio of 7.1:1, so there should be a large amount of liquid solvent present.
I think the most likely reason is that the heating capacity at the bottom of the tower increases (the steam pressure rises); with the inlet and outlet flow rates of the tower remaining unchanged, the amount of steam rising inside the tower increases (as does the reflux ratio), resulting in a higher pressure at the bottom of the tower. Check if that’s the reason. Let’s talk about it here once we have clear results; it’s very useful for everyone to learn from it!
We experienced the aforementioned phenomenon again; it is presumed that the accumulation of non-aromatic compounds in the tower bottom increased, leading to flashing, and the reflux liquid could not flow back, which caused a sudden drop in the liquid level.
The real cause of the severe fluctuations in the tower liquid level is likely the pressure changes at the top and bottom of the tower. 2# Fred_bj
8# Old chemical engineer, new student: Has the solvent degraded so much that it can no longer perform the extraction function?