Browsing by Author "Shishkova I.K."

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    Commercial Ebullated Bed Vacuum Residue Hydrocracking Performance Improvement during Processing Difficult Feeds
    (2023-03-01) Georgiev B.E.; Stratiev D.S.; Argirov G.S.; Nedelchev A.; Dinkov R.; Shishkova I.K.; Ivanov M.; Atanassov K.; Ribagin S.; Nikolov Palichev G.; Nenov S.; Sotirov S.; Sotirova E.; Pilev D.; Stratiev D.D.
    The Urals and Siberian vacuum residues are considered difficult to process in the ebullated bed hydrocracking because of their increased tendency to form sediments. Their achievable conversion rate reported in the literature is 60%. Intercriteria analysis was used to assess data from a commercial vacuum residue hydrocracker during processing blends from three vacuum residues: Urals, Siberian Light, and Basra Heavy. The analysis revealed that the main contributors to conversion enhancement is hydrodemetallization (HDM) and the first reactor ΔT augmentation. The increase of HDM from 40 to 98% and the first reactor ΔT (ΔT(R1)) from 49 to 91 °C were associated with a vacuum residue conversion enhancement of 62.0 to 82.7 wt.%. The developed nonlinear regression prediction of conversion from HDM and ΔT(R1) suggests a bigger influence of ΔT(R1) enhancement on conversion augmentation than the HDM increase. The intercriteria analysis evaluation revealed that the higher first reactor ΔT suppresses the sediment formation rate to a greater extent than the higher HDM. During processing Basrah Heavy vacuum residue, a reduction in hydrodeasphaltization (HDAs) from 73.6 to 55.2% and HDM from 88 to 81% was observed. It was confirmed that HDM and HDAs are interrelated. It was found that the attainment of conversion of 80 wt.% and higher during processing Urals and Siberian Light vacuum residues is possible when the HDM is about 90% and LHSV ≤ 0.19 h−1.
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    Comparison of empirical models to predict viscosity of secondary vacuum gas oils
    (2021-08-01) Stratiev D.S.; Nenov S.; Shishkova I.K.; Dinkov R.K.; Zlatanov K.; Yordanov D.; Sotirov S.; Sotirova E.; Atanassova V.; Atanassov K.; Stratiev D.D.; Todorova‐yankova L.
    This work presents characterization data and viscosity of 34 secondary vacuum gas oils (H‐Oil gas oils, visbreaker gas oils, and fluid catalytic cracking slurry oils) with aromatic content reaching up to 100 wt.%. Inter‐criteria analysis was employed to define the secondary VGO charac-teristic parameters which have an effect on viscosity. Seven published empirical models to predict viscosity of the secondary vacuum gas oils were examined for their prediction ability. The empirical model of Aboul‐Seud and Moharam was found to have the lowest error of prediction. A modifica-tion of Aboul‐Seoud and Moharam model by separating the power terms accounting for the effects of specific gravity and average boiling point improves the accuracy of viscosity prediction. It was discovered that the relation of slope of viscosity decrease with temperature enhancement for the secondary vacuum gas oil is not a constant. This slope increases with the average boiling point and the specific gravity augmentation, a fact that has not been discussed before.
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    Crude slate, FCC slurry oil, recycle, and operating conditions effects on H-Oil® product quality
    (2021-06-01) Stratiev D.S.; Shishkova I.K.; Dinkov R.K.; Petrov I.P.; Kolev I.V.; Yordanov D.; Sotirov S.; Sotirova E.N.; Atanassova V.K.; Ribagin S.; Atanassov K.T.; Stratiev D.D.; Nenov S.
    This paper evaluates the influence of crude oil (vacuum residue) properties, the processing of fluid catalytic cracking slurry oil, and recycle of hydrocracked vacuum residue diluted with fluid catalytic cracking heavy cycle oil, and the operating conditions of the H-Oil vacuum residue hydroc-racking on the quality of the H-Oil liquid products. 36 cases of operation of a commercial H-Oil® ebullated bed hydrocracker were studied at different feed composition, and different operating con-ditions. Intercriteria analysis was employed to define the statistically meaningful relations between 135 parameters including operating conditions, feed and products characteristics. Correlations and regression equations which related the H-Oil® mixed feed quality and the operating conditions (reaction temperature, and reaction time (throughput)) to the liquid H-Oil® products quality were developed. The developed equations can be used to find the optimal performance of the whole refinery considering that the H-Oil liquid products are part of the feed for the units: fluid catalytic cracking, hydrotreating, road pavement bitumen, and blending.
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    Empirical models to characterize the structural and physiochemical properties of vacuum gas oils with different saturate contents
    (2021-07-01) Stratiev D.S.; Shishkova I.K.; Dinkov R.K.; Petrov I.P.; Kolev I.V.; Yordanov D.; Sotirov S.; Sotirova E.; Atanassova V.; Ribagin S.; Atanassov K.; Stratiev D.D.; Nenov S.; Todorova‐yankova L.; Zlatanov K.
    Inter‐criteria analysis was employed in VGO samples having a saturate content between 0.8 and 93.1 wt.% to define the statistically significant relations between physicochemical properties, empirical structural models and vacuum gas oil compositional information. The use of a logistic function and employment of a non‐linear least squares method along with the aromatic ring index allowed for our newly developed correlation to accurately predict the saturate content of VGOs. The empirical models developed in this study can be used not only for obtaining the valuable structural information necessary to predict the behavior of VGOs in the conversion processes but can also be utilized to detect incorrectly performed SARA analyses. This work confirms the possibility of predicting the contents of VGO compounds from physicochemical properties and empirical models.
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    Evaluation of the different compatibility indices to model and predict oil colloidal stability and its relation to crude oil desalting
    (2021-08-01) Shishkova I.K.; Stratiev D.S.; Tavlieva M.P.; Dinkov R.K.; Yordanov D.; Sotirov S.; Sotirova E.; Atanassova V.; Ribagin S.; Atanassov K.; Stratiev D.D.; Todorova-Yankova L.; Nenov S.
    Thirty crude oils, belonging to light, medium, heavy, and extra heavy, light sulfur, and high sulfur have been characterized and compatibility indices defined. Nine crude oil compatibility indices have been employed to evaluate the compatibility of crude blends from the thirty individual crude oils. Intercriteria analysis revealed the relations between the different compatibility indices, and the different petroleum properties. Tetra-plot was employed to model crude blend compatibility. The ratio of solubility blending number to insolubility number was found to best describe the desalting efficiency, and therefore could be considered as the compatible index that best models the crude oil blend compatibility. Density of crude oil and the n-heptane dilution test seem to be sufficient to model, and predict the compatibility of crude blends.