Experts in distillation, take a look!
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Well, the diesel extracted from the bottom of the diesel tower in our residue hydrogenation unit suddenly turned brown, almost black in color, but the test results were normal – both the initial boiling point and the 95% boiling point were within normal ranges! In the initial stage, the unit was operating steadily; when the amount of material drawn from the fractionation tower to the diesel tower increased by two tons, the color deepened, and it improved again when that amount was reduced by two tons. What is going on? It had never happened before. Afterward, we conducted an investigation into the cause of the accident and ruled out the possibility of leaks in the heat exchange with heavy oil, as well as leaks in the heat exchange with light hydrocarbons. We also checked the level gauges in the distillation tower, and all of them were functioning normally. The strange thing about this issue is that the boiling range of diesel doesn’t widen after it turns black? One technician said that it might be caused by a dry plate phenomenon inside the distillation tower; I find this explanation difficult to understand. I would appreciate it if those with experience in operating distillation towers as well as those with theoretical knowledge could analyze this issue – does such a phenomenon occur in industrial production? What are the reasons for this? Is it related to the magnitude of the interrupted reflux flow and the amount of diesel extracted? Could excessive extraction of the interrupted reflux cause a dry zone between the feed section and the interrupted reflux section?
During the distillation of residue after hydrogenation, incomplete hydrogenation may occur (under normal conditions), resulting in a product containing large amounts of unsaturated hydrocarbons such as indanes. Such compounds are unstable and prone to color change, and their components are essentially similar to those of aromatics. If handled simply, antioxidants can be added. The final method is hydrogenation saturation. The color change is not a processing issue; it is a problem with the oil itself.
The original poster should provide a flowchart to help everyone analyze and respond.
Agree with the view from Floor 4; the increased extraction from the fractionation tower has caused dry plates.
During the major maintenance of our equipment, we discovered an internal leak in the tail oil and light hydrocarbons heat exchanger! The corrosion is quite severe! The change in the color of diesel, without an increase in its boiling range, can thus be explained! This post was last edited by byrant on 2007-12-12 12:02]
Your answer seems incorrect. No matter how it’s arranged, a light hydrocarbon heat exchanger does not affect the color of diesel; moreover, if light hydrocarbons leak into the diesel side, it will cause the diesel’s initial boiling point to decrease. Therefore, your answer is wrong. It should be the feed oil that leaks into the diesel side
I’m sorry, that was a mistake; it’s been corrected now. It’s caused by an internal leak in the exhaust oil and light hydrocarbons heat exchanger!
Colleagues, one must maintain a serious attitude at work. Although it is meant for discussion among everyone, there should be evidence behind the arguments; we shouldn’t lead others to rely on mere speculation, as that can be harmful:lol
Agree with the opinion on the fourth floor; additional content should be included. The diesel becomes darker and its boiling range widens; you just haven’t detected this. There won’t be much change in the 95% point, but the 98% point may change, and there is definitely a change in the dry point. Our hydrogenation unit has experienced the aforementioned issue due to internal leakage in the feed/product heat exchangers; diesel colority is more sensitive to this aspect compared to boiling range.
What was said upstairs is correct; diesel turns black, and it should change when it dries out.
It must be contaminated with something; it’s impossible to determine the exact amount just by looking at the color, so the test results appear normal