2 replies to this topic

[karthikpadman]

In a crude distillation unit, for any particular middle east crude, i would like to know the composition of naptha stabiliser offgas. Recently in our plant, we face the problem of higher offgas make for a particular crude, but the assay suggests lower yield of non-condensibles. On component analysis of offgas sample, it is found that C3 is around 55 wt%. Is it normal? What could be the reason for the difference in actual offgas yield and assay data?

[Zauberberg]

You are probably limited on condenser capacity at current/design operating pressure of the stabilizer tower. C3 is not accounted as non-condensible component in crude assays since it is normally being recovered in fractionation processes within refinery and sold as Propane/LPG etc.

What you can do is to see whether the stabilizer pressure can be increased while still having sufficient reboiler duty to maintain fractionation efficiency at higher operating pressures. This will condense more C3 in the overheads, but if the tower feed contains C1 and C2, the C3+ losses are inevitable due to phase equilibrium in the reflux drum.

Best regards,

[Padmakar Katre]

Dear,
Could you upload the unstabilized naphtha compositions (based on pure components) and D86 Distillation.What is the configuration of the CDU main fractionator ovhd section.Is there any off-gas stream from main fractionator ovhd reflux drum which will be mainly C2(-) material. What is the operating pressure of the naphtha stabilizer. If you could upload the sketch of the stabilizer section, it would be helpful or else let us know column/reflux drum pressure control loop (concern here is if it is on the coolent side outlet flow control cascadeded and the control valve opening has any margin). C3 slip of 55wt% seems quite strange. Just waiting for your comments.