Regarding internal leakage in heat exchangers
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Our catalytic unit (MIP) has several liquid hydrocarbon coolers that do not leak when pressurized, but start leaking once they are installed in the system; this is quite confusing； Recently, a leak occurred in the bottom reboiler of the stabilization unit (with steam as the heat source). Oil was detected in the condensate tank at the reboiler’s outlet, so the unit was taken out of service for maintenance. During pressure testing, it was found that the reboiler had no leaks, which was quite embarrassing. After the unit was put back into operation, oil was again detected in the condensate tank at the reboiler’s outlet; however, the steam was checked and found to contain no oil at all. I would appreciate it if experts could help analyze what the problem might be
The suppression operating condition is different from the actual operating condition, right?
Is it being suppressed as required? Suppression pressure is not the operating pressure
The steam pressure in the tube side should be higher than the oil pressure in the shell side, right?
May I ask what type of reboiler the original poster is using?
By common sense, if the steam pressure is higher than that of the oil, it is difficult to explain why condensed water would contain oil. Have other ways of entering been considered? For condenser pressure testing, due to the significant differences in operating conditions (temperature), it can sometimes be difficult to detect leaks.
It is recommended that the poster conduct a leakage test or a airtightness test on the shell side, to check whether there are any leaks at the weld joints between the heat exchange tubes and the tube sheet; pressure testing alone cannot detect leaks. If there is no leakage, then it must be a problem with the heat exchange tubes; it’s necessary to check for leaks in those tubes, which is quite troublesome.
The medium in the shell side of our reboiler is condensed oil at a pressure of around 1.3 MPa, while the tube side contains steam at a pressure of 0.8–0.9 MPa. The reboiler is of the siphon type
Both the tube side and shell side have been pressurized, with the equipment supervisor personally overseeing the process on site; there are no leaks at all. I wonder where the problem lies?
Is the tube bundle U-shaped, with floating heads?
This post was last edited by Sima Xueye on 2015-12-4 09:06. First, use DCS to check the pressure in the distillation column over the recent period (the pressure at the bottom of the column), to see if there were any operations by the crew that led to abnormally high column pressure and thus caused a leak in the reboiler (this possibility is low)； Analyze again the sulfur content of the raw material or that of the absorbed oil coming from the stabilizer tower to determine whether excessive sulfur content is causing corrosion and resulting in leaks ；