Problems with the hydrocracking vacuum tower
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I entered the data provided on site, and the simulation results showed that the temperature at the bottom of the tower was more than 40 degrees higher than the actual value on site. What’s going on here?
Are the yield of bottom oil and the distillation curve consistent as well?
Since there are no specific data available for the feed to the vacuum tower, a back-calculation simulation method was used; the material balance was determined based on the calibration report. The yield is consistent, and the distillation curve is also specified to be the same
Generally, there are few data points for the heavy oil at the bottom of the tower, so the calculation accuracy is not high enough.
During the pro2 processing, 98% of the distillation point is used as the final value, while the values above 98% are determined through extrapolation; it’s not clear whether this could be a factor that has an impact.
It’s possible that the feed has not yet reached an equilibrium state, but you treated it as being in equilibrium during your simulation. This is just my speculation; if the problem remains unresolved, feel free to post it here for further discussion
There is nothing wrong with your simulation. The next steps you need to take are: (1) to determine whether the analysis of the heavy oil ROIL is correct, that is, whether there is an excess in its concentration; (2) to verify whether the temperature measurements are accurate. Your reboiler has been designed as a baffled thermosyphon, and the location of the temperature measurement points used for comparison does have an impact, but this impact generally doesn’t reach 40 degrees. In fact, if the difference were 40 degrees, the bottom temperature at the site would be 327 degrees, which is even lower than your feed temperature.