Root Cause Analysis for Observed Increased Sedimentation in a Commercial Residue Hydrocracker

Ebullated bed vacuum residue hydrocracking is a well-established technology providing a high conversion level of low-value residue fractions in high-value light fuels. The main challenge in this technology when processing vacuum residues derived from different crude oils is the sediment formation rate that leads to equipment fouling and cycle length shortening. With the severity enhancement, the asphaltenes become more aromatic and less soluble which leads to sediment formation when the difference between solubility parameters of asphaltenes and maltenes goes beyond a threshold value. Although theoretical models have been developed to predict asphaltene precipitation, the great diversity of oils makes it impossible to embrace the full complexity of oil chemistry by any theoretical model making it impractical for using it in all applications. The evaluation of process data of a commercial ebullated bed vacuum residue hydrocracker, properties of different feeds, and product streams by intercriteria and regression analyses enabled us to decipher the reason for hydrocracked oil sediment content rising from 0.06 to 1.15 wt.%. The ICrA identified the presence of statistically meaningful relations between the single variables, while the regression analysis revealed the combination of variables having a statistically meaningful effect on sediment formation rate. In this study, vacuum residues derived from 16 crude oils have been hydrocracked as blends, which also contain fluid catalytic cracking heavy cycle oil and slurry oil (SLO), in a commercial H-Oil plant. It was found that the hydrocracked oil sediment content decreased exponentially with fluid catalytic cracking slurry oil augmentation. It was also established that it increased with the magnification of resin and asphaltene and the reduction in sulfur contents in the H-Oil feed.