Sudden abnormality in benzene content in rich and poor crude benzene streams
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Some time ago, the benzene content in the lean gas at our plant suddenly rose to around 0.7 (it had always been below 0.4 before), while the benzene content in the rich gas increased to over 1.7 (it had always been around 1.5 previously). Yet, the benzene content in the gas after passing through the benzene washing tower remained zero. None of the other process parameters changed; the testing instruments, procedures, and reagents also remained unchanged. The only change was that the desulfurization unit underwent major maintenance. What could be the reason for this? Could it be that stopping the desulfurization process has an impact on it, or are other components mixing into the washing oil, resulting in a falsely high benzene content in the oil? I hope experienced experts can provide a detailed explanation. Thank you!
Personally, I think it’s better to first check the instruments for detecting low-oil and benzene-rich conditions.
It’s fine if the benzene content behind the main gas tower is zero; higher benzene levels in the lean and rich oils don’t affect the recovery of crude benzene from the gas, so it’s not a major issue. As for high levels in either the lean or rich oils, check whether the temperatures in the tube furnace and the debenzing tower are too low, as this could affect the debenzing process
For about 10 days, the benzene content in the lean fuel was around 0.7, while it was around 1.7 in the rich fuel. Now it has basically returned to normal levels: the benzene content in the lean fuel is over 0.4, and that in the rich fuel is between 1.4 and 1.5. In the laboratory, different people are responsible for testing the benzene content in both lean and rich fuels on a daily basis.
The top temperature of the benzene removal tower is 93–94, while the bottom temperature is 176–177. The temperature of the rich oil entering the benzene removal tower is 181–182. The process parameters have not been adjusted; previously, the benzene content in the lean oil was around 0.4. The rich oil contains about 1.5% benzene, while the gas after the tower has no benzene at all. Afterwards, the lean oil has a high benzene content of 0.7%, and the rich oil’s benzene content rises to around 1.7%; yet the gas after the tower still has no benzene. It’s impossible for the benzene content in the lean oil to be so high while that in the gas after the tower remains zero. Could there be other reasons for this abnormally high benzene content in the lean oil?
No matter what the circulation volume is, it is impossible for the gas downstream of the tower to have zero benzene content; we need to take a look at the testing process. In particular, please compare the oil washing circulation volume, the benzene content in the rich and lean oils, as well as the benzene content in the gas before and after the tower – can these values be correlated with the product output? To verify the accuracy of the test.
Sulfur has an impact on the absorption of crude benzene; information can be found online
All process adjustments are made on the basis of accurate testing results; therefore, it is first necessary to check whether the testing of benzene content in the gas exiting the tower is accurate
It is very difficult to achieve zero benzene content in the residue after distillation; however, the high benzene content in the oil-rich fraction is caused by the high benzene content in the oil-poor fraction, which indicates that the benzene removal efficiency is poor. The poor benzene removal effect may be caused by changes in the quality of the circulating oil, resulting in low benzene removal efficiency.