The LUKOIL Neftohim Burgas hybrid reformer has experienced unusual reformate octane drop from 100 down to 98.7 (research octane) and from 89 down to 87.5 (motor octane) during its eighth cycle and 16-year operation with the same catalytic system. Several hypotheses have been checked to identify the reason for the octane reduction over a period of five months. Finally, it was established that the basic nitrogen containing chemical substituting caustic to neutralize the chlorides in the crude distillation units upstream of the reformer in order to decrease the sodium content in the vacuum residue had been carried over to the reformer and subsequently poisoned its catalyst. Poisoning of the reformer catalytic system led to both octane reduction and reformate yield decrease.
It was observed in the LUKOIL Neftohim Burgas refinery that the employed 2-ethyl hexil nitrate cetane improver treating rate increased by a factor of two for the last 17 months. An analysis performed using intercriteria analysis revealed that the main culprit for cetane improver treating rate augmentation is the deterioration of the cetane index of the finished automotive diesel fuel as a result of the increased H-Oil severity of operation. The estimation of the cetane number (index) of the refinery diesel fuel employing the linear blending rule established that the high severity mode of operation of H-Oil leads to production of refinery diesel having about 1 point lower cetane index (number). The slope of enhancement of diesel fuel with magnification of cetane improver treating rate indicated that 1 point lower diesel cetane number (index) will need about 370 ppm higher cetane improver treating rate.
