DSpace Repository :: Browsing by Author "Shishkova I."

Browsing by Author "Shishkova I."

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Alternative Options for Ebullated Bed Vacuum Residue Hydrocracker Naphtha Utilization
(2023-12-01) Stratiev D.; Shishkova I.; Ivanov M.; Dinkov R.; Toteva V.; Angelova D.; Kolev I.; Tavlieva M.; Yordanov D.
The vacuum residue hydrocracker naphtha (VRHN) is a chemically unstable product that during storage changes its colour and forms sediments after two weeks. It cannot be directly exported from the refinery without improving its chemical stability. In this research, the hydrotreatment of H-Oil naphtha with straight run naphtha in a commercial hydrotreater, its co-processing with fluid catalytic cracking (FCC) gasoline in a commercial Prime-G+ post-treater, and its co-processing with vacuum gas oil (VGO) in a commercial FCC unit were discussed. The hydrotreatment improves the chemical stability of H-Oil naphtha and reduces its sulphur content to 3 ppm. The Prime-G+ co-hydrotreating increases the H-Oil naphtha blending research octane number (RON) by 6 points and motor octane number (MON) by 9 points. The FCC co-cracking with VGO enhances the blending RON by 11.5 points and blending MON by 17.6 points. H-Oil naphtha conversion to gaseous products (C1–C4 hydrocarbons) in the commercial FCC unit was found to be 50%. The use of ZSM 5 containing catalyst additive during processing H-Oil naphtha showed to lead to FCC gasoline blending octane enhancement by 2 points. This enabled an increment of low octane number naphtha in the commodity premium near zero sulphur automotive gasoline by 2.4 vol.% and substantial improvement of refinery margin. The processing of H-Oil naphtha in the FCC unit leads also to energy saving as a result of an equivalent lift steam substitution in the FCC riser.
Challenges in Petroleum Characterization—A Review
(2022-10-01) Shishkova I.; Stratiev D.; Kolev I.V.; Nenov S.; Nedanovski D.; Atanassov K.; Ivanov V.; Ribagin S.
252 literature sources and about 5000 crude oil assays were reviewed in this work. The review has shown that the petroleum characterization can be classified in three categories: crude oil assay; SARA characterization; and molecular characterization. It was found that the range of petroleum property variation is so wide that the same crude oil property cannot be measured by the use of a single standard method. To the best of our knowledge for the first time the application of the additive rule to predict crude oil asphaltene content from that of the vacuum residue multiplied by the vacuum residue TBP yield was examined. It was also discovered that a strong linear relation between the contents of C5-, and C7-asphaltenes in crude oil and derived thereof vacuum residue fraction exists. The six parameter Weibull extreme function showed to best fit the TBP data of all crude oil types, allowing construction of a correct TBP curve and detection of measurement errors. A new SARA reconstitution approach is proposed to overcome the poor SARA analysis mass balance when crude oils with lower density are analyzed. The use of a chemometric approach with combination of spectroscopic data was found very helpful in extracting information about the composition of complex petroleum matrices consisting of a large number of components.
COMMERCIAL AND LABORATORY EXPERIENCE WITH CATALYTIC CRACKING OF STRAIGHT RUN HYDROTREATED VACUUM GAS OIL AND H-OIL GAS OILS
(2022-01-01) Stratiev D.; Shishkova I.; Ivanov M.; Petrov I.; Atanassova V.; Ribagin S.; Atanassov K.; Toteva V.; Stratiev D.
This study presents for the first time an investigation of fluid catalytic cracking of 100 % H-vacuum gas oil at a commercial FCC unit. 100 % straight run hydrotreated vacuum gas oil (HTSRVGO) and 100 % H-vacuum gas oil have been cracked in the commercial LUKOIL Neftohim Burgas fluid catalytic cracking and in a laboratory confined ebbulated bed ACE catalytic cracking unit. The relations between the operating conditions of the commercial FCC unit and conversion level in both cases 100 % HTSRVGO and its blends with H-Oil VGO were investigated using intercriteria analysis. Multiple regressions were developed to quantify the effect of the operating conditions as well as quantity and quality of H-Oil VGO on conversion level in the commercial FCC unit. ACE laboratory tests with feed containing about 20 % H-Oil VGO at different catalyst-to-oil ratios and reaction temperature were performed and the results are discussed.
Commercial Investigation of the Ebullated-Bed Vacuum Residue Hydrocracking in the Conversion Range of 55-93%
(2020-12-29) Stratiev D.; Nenov S.; Shishkova I.; Georgiev B.; Argirov G.; Dinkov R.; Yordanov D.; Atanassova V.; Vassilev P.; Atanassov K.
The LUKOIL Neftohim Burgas vacuum residue hydrocracking has increased the vacuum residue conversion from 55 to 93% as a result of a proper feed selection, optimal catalyst condition, and the use of a Mo nanodispersed catalyst. It was found that the feed colloidal instability index estimated from the feed saturates, aromatics, resins, and asphaltenes (SARA) data negatively correlated with the conversion. Correlations based on the use of the nonlinear least-squares method, which relates the density to the aromatic structure contents for the straight run and hydrocracked vacuum residues, were developed. Intercriteria analysis was applied to evaluate the relations between the different properties of the straight run and the hydrocracked vacuum residual oils. The density of the hydrocracked vacuum residue measured by dilution with toluene was found to strongly correlate with the conversion, Conradson carbon content, softening point, and Fraasss breaking point.
Correlations of HTSD to TBP and Bulk Properties to Saturate Content of a Wide Variety of Crude Oils
(2023-02-01) Stratiev D.; Dinkov R.; Tavlieva M.; Shishkova I.; Nikolov Palichev G.; Ribagin S.; Atanassov K.; Stratiev D.D.; Nenov S.; Pilev D.; Sotirov S.; Sotirova E.; Simeonov S.; Boyadzhieva V.
Forty-eight crude oils with variations in specific gravity (0.782 ≤ SG ≤ 1.002), sulphur content (0.03 ≤ S ≤ 5.6 wt.%), saturate content (23.5 ≤ Sat. ≤ 92.9 wt.%), asphaltene content (0.1 ≤ As ≤ 22.2 wt.%), and vacuum residue content (1.4 ≤ VR ≤ 60.7 wt.%) were characterized with HTSD, TBP, and SARA analyses. A modified SARA analysis of petroleum that allows for the attainment of a mass balance ≥97 wt.% for light crude oils was proposed, a procedure for the simulation of petroleum TBP curves from HTSD data using nonlinear regression and Riazi’s distribution model was developed, and a new correlation to predict petroleum saturate content from specific gravity and pour point with an average absolute deviation of 2.5 wt.%, maximum absolute deviation of 6.6 wt.%, and bias of 0.01 wt.% was developed. Intercriteria analysis was employed to evaluate the presence of statistically meaningful relations between the different petroleum properties and to evaluate the extent of similarity between the studied petroleum crudes. It was found that the extent of similarity between the crude oils based on HTSD analysis data could be discerned from data on the Kw characterization factor of narrow crude oil fractions. The results from this study showed that contrary to the generally accepted concept of the constant Kw characterization factor, the Kw factors of narrow fractions differ from that of crude oil. Moreover, the distributions of Kw factors of the different crudes were different.
Different nonlinear regression techniques and sensitivity analysis as tools to optimize oil viscosity modeling
(2021-10-01) Stratiev D.; Nenov S.; Nedanovski D.; Shishkova I.; Dinkov R.; Stratiev D.D.; Stratiev D.D.; Sotirov S.; Sotirova E.; Atanassova V.; Atanassov K.; Yordanov D.; Angelova N.A.; Ribagin S.; Todorova-Yankova L.
Four nonlinear regression techniques were explored to model gas oil viscosity on the base of Walther’s empirical equation. With the initial database of 41 primary and secondary vacuum gas oils, four models were developed with a comparable accuracy of viscosity calculation. The Akaike information criterion and Bayesian information criterion selected the least square relative errors (LSRE) model as the best one. The sensitivity analysis with respect to the given data also revealed that the LSRE model is the most stable one with the lowest values of standard deviations of derivatives. Verification of the gas oil viscosity prediction ability was carried out with another set of 43 gas oils showing remarkably better accuracy with the LSRE model. The LSRE was also found to predict better viscosity for the 43 test gas oils relative to the Aboul Seoud and Moharam model and the Kotzakoulakis and George.
EFFECT OF COMMERCIAL ADDITIVES TO REDUCE SEDIMENT FORMATION IN THE EBULLATED BED VACUUM RESIDUE H-OIL HYDROCRACKING
(2020-01-01) Toteva V.; Stratiev D.; Shishkova I.; Nikolaychuk E.; Stanulov K.; Yordanov D.
Ten H-Oil residual oils and eleven commercial additives inhibiting the asphaltene agglomeration were explored in this work by employing two tests: hot filtration test (HFT) and asphaltene dispersant test (ADT). It was found that the tendency to form sediments from the asphaltenes in the H-Oil residual oils was different for the distinct feed blends processed in the LNB H-Oil vacuum residue hydrocracker. The performance of the additives was found to be specific to the alloyed H-Oil residual oils. The additive based on the polyisobuthylene succinimide was found to be capable of reducing the sediment content in the H-Oil residual oils produced from all feedstock blends studied in this work. The efficiency of its performance however was different for the studied residual oils being the highest for the residual oil obtained from the feedstock blend 70 % Urals/30 % El Bouri (with the highest tendency to form sediment). This additive has also good efficiency against the H-Oil residual oil obtained from the feed 100 % Urals (with lower tendency to form sediment) but diluted with the high aromatic heavy cycle oil from fluid catalytic cracking.
Empirical Modeling of Viscosities and Softening Points of Straight-Run Vacuum Residues from Different Origins and of Hydrocracked Unconverted Vacuum Residues Obtained in Different Conversions
(2022-03-01) Stratiev D.; Nenov S.; Nedanovski D.; Shishkova I.; Dinkov R.; Stratiev D.D.; Stratiev D.D.; Sotirov S.; Sotirova E.; Atanassova V.; Ribagin S.; Atanassov K.; Yordanov D.; Angelova N.A.; Todorova-Yankova L.
The use of hydrocracked and straight-run vacuum residues in the production of road pavement bitumen requires a good understanding of how the viscosity and softening point can be modeled and controlled. Scientific reports on modeling of these rheological properties for hydroc-racked and straight-run vacuum residues are scarce. For that reason, 30 straight-run vacuum residues and 33 hydrocracked vacuum residues obtained in a conversion range of 55–93% were investigated, and the characterization data were employed for modeling purposes. An intercriteria analysis was applied to investigate the statistically meaningful relations between the studied vacuum residue properties. It revealed that the straight-run and hydrocracked vacuum residues were completely different, and therefore their viscosity and softening point should be separately modeled. Through the use of nonlinear regression by applying CAS Maple and NLPSolve with the modified Newton iterative method and the vacuum residue bulk properties the viscosity and softening point were modeled. It was found that the straight-run vacuum residue viscosity was best modeled from the molecular weight and specific gravity, whereas the softening point was found to be best modeled from the molecular weight and C7-asphaltene content. The hydrocracked vacuum residue viscosity and softening point were modeled from a single property: the Conradson carbon content. The vacuum residue viscosity models developed in this work were found to allow prediction of the asphaltene content from the molecular weight and specific gravity with an average absolute relative error of 20.9%, which was lower of that of the model of Samie and Mortaheb (Fuel. 2021, 305, 121609)—32.6%.
Industrial Investigation of the Combined Action of Vacuum Residue Hydrocracking and Vacuum Gas Oil Catalytic Cracking While Processing Different Feeds and Operating under Distinct Conditions
(2023-11-01) Stratiev D.; Toteva V.; Shishkova I.; Nenov S.; Pilev D.; Atanassov K.; Bureva V.; Vasilev S.; Stratiev D.D.
Ebullated bed vacuum residue hydrocracking and fluid catalytic cracking (FCC) are among the most profitable processes in modern refining. Their optimal performance is vital for petroleum refining profitability. That is why a better understanding of their combined action and the interrelations between these two heavy oil conversion processes in a real-world refinery could provide valuable information for further performance optimization. Nine distinct petroleum crudes belonging to the extra light, light, and medium petroleum crude types were processed in the LUKOIL Neftohim Burgas refinery to study the combined performance of two processes: FCC of vacuum gas oil and ebullated bed vacuum residue H-Oil hydrocracking. The operating conditions along with the characterization data of the feeds and products of both processes were evaluated through the employment of intercriteria analysis to define the variables with statistically significant relationships. Maple 2023 Academic Edition mathematics software was used to develop models to predict the vacuum residue conversion level under different operating conditions. The plug flow reactor model with an activation energy of 215 kJ/mol and a reaction order of 1.59 was found to provide the highest accuracy of vacuum residue conversion, with an average absolute deviation of 2.2%. H-Oil yields were found to correlate with the vacuum residue conversion level and the content of FCC slurry oil (SLO), the recycling of partially blended fuel oil, a material boiling point below 360 °C, and the vacuum gas oil (VGO) in the H-Oil feed. FCC conversion was found to depend on the H-Oil VGO content in the FCC feed and the content of FCC SLO in the H-Oil feed.
INHIBITING SEDIMENT FORMATION IN AN EXTRA LIGHT CRUDE OIL AND IN A HYDROCRACKED ATMOSPHERIC RESIDUE BY COMMERCIAL CHEMICAL ADDITIVES
(2022-01-01) Stratiev D.; Shishkova I.; Tavlieva M.; Kirilov K.; Dinkov R.; Yordanov D.; Yankova L.; Toteva V.; Nikolova R.
Extra light crude oil from Kazahstan and hydrocracked atmospheric residue from a commercial ebullated bed vacuum residue hydrocracker were investigated to reduce their sediment formation rate by employing 13 commercial chemical additives. Ten of the studied additives were based on the organic acid derivatives. Asphaltene dispersion test was applied in this study to define the most appropriate chemical additive and the optimum treating rate. The additives demonstrated different performance with the distinct oils. All organic acid derivative additives were capable of suppressing the sedimentation in the hydrocracked atmospheric residue, while not all of them were effective in decreasing the sediment formation in the extra light petroleum. The phosphoric acid and poly-iso-butylene succinimide based additives were effective in suppressing the sedimentation in the hydrocracked atmospheric residue while they promoted the formation of sediments in the extra light petroleum. The additive based on 1,2,4-trimethylbenzene was ineffective in decreasing the sedimentation in the hydrocracked atmospheric residue and slightly effective in the suppression of sediment formation in the extra light petroleum.
Intercriteria Analysis to Diagnose the Reasons for Increased Fouling in a Commercial Ebullated Bed Vacuum Residue Hydrocracker
(2022-01-01) Stratiev D.; Shishkova I.; Dinkov R.; Kolev I.; Argirov G.; Ivanov V.; Ribagin S.; Atanassova V.; Atanassov K.; Stratiev D.; Nenov S.; Pilev D.; Yordanov D.
The intercriteria analysis developed on the base of intuitionistic fuzziness and index matrices was applied to evaluate processing data of the LUKOIL Neftohim Burgas H-Oil ebullated bed vacuum residue hydrocracker with the aim of revealing the reasons for increased fouling registered during the 3rd cycle of the H-Oil hydrocracker. It was found that when the ratio of the δT of the 1st reactor to the δT of the 2nd reactor gets lower than 2.0, an excessive H-Oil equipment fouling occurs. The fouling was also found to be favored by processing of lower Conradson carbon content vacuum residual oils and increased throughput and depressed by increasing the dosage of the HCAT nanodispersed catalyst. The fouling in the atmospheric tower bottom section is facilitated by a lower aromatic content in the atmospheric tower bottom product. The addition of FCC slurry oil not only increases aromatic content but also dissolves some of the asphaltenes in the atmospheric residual hydrocracked oil and decreases its colloidal instability index. The fouling in the vacuum tower bottom section is facilitated by a higher saturate content in the VTB. Surprisingly, it was found that the asphaltene content in the VTB depresses the fouling rate. No relation was found of the sediment content in the hydrocracked residual oils measured by hot filtration tests and by the centrifuge method to the equipment fouling of the H-Oil hydrocracker.
OPTIMIZATION OF THE OXIDATIVE DESULPHURIZATION OF HEAVY GAS OIL
(2020-01-01) Toteva V.; Stanulov K.; Shishkova I.; Stratiev D.
The investigation of production and application of environmentally friendly fuels has intensified because of the legislation requiring an increased control of the greenhouse gas emissions. Stringent rules have been introduced to decrease the sulphur content of the liquid fuels to an ultra-low level, which in turn makes the desulphurization technologies development an important research goal. The hydrodesulphurization (HDS) is the current industrial method for fuels sulphur removal. The objective of the present study is to decrease the sulphur content of heavy gas oil by oxidation-extraction desulphurization which is one of the alternative methods which are aimed at. An adequate mathematical model is developed on the ground of a planned experiment approach which describes the effect of a number of factors (a temperature, contact time, and a peroxide-to-formic acid molar ratio) on the rate of sulphur content decrease. The optimal values of the variables are found to provide sulphur decrease in the heavy gas oil raffinates of up to 87 %. The process is monitored by FTIR and NMR spectroscopy, and gas chromatography equipped with sulphur chemiluminescence detector (SCD).
Petroleum Crude Slate, Catalyst Properties and H-Oil VGO Properties Effects on a Commercial FCC Unit Performance
(2021-01-01) Stratiev D.; Shishkova I.; Petrov I.; Yordanov D.; Toteva V.
The performance of the commercial LUKOIL Neftohim Burgas fluid catalytic cracking unit (LNB FCCU) during processing 24 blends of straight run vacuum gas oils originating from 16 petroleum crudes and an imported atmospheric residue and employment of four catalysts was evaluated. It was found that the nature of the petroleum crudes processed in the ratios employed had no effect on the LNB FCCU performance. Instead, the content of the H-Oil vacuum gas oil (VGO) and its quality quantified by Kw-characterization factor was found to control the LNB FCCU conversion level. Based on the LNB FCCU commercial data a regression was developed quantifying the effect of equilibrium catalyst activity, H-Oil quality, and quantity in the fluid catalytic cracking (FCC) feed, and catalyst-to-oil ratio on the level of conversion. The regression was used to evaluate the impact of catalyst activity and catalyst-to-oil ratio, that is known to be a function of catalyst Δ coke selectivity, on the FCC conversion.
Prediction of Molecular Weight of Petroleum Fluids by Empirical Correlations and Artificial Neuron Networks
(2023-02-01) Stratiev D.; Sotirov S.; Sotirova E.; Nenov S.; Dinkov R.; Shishkova I.; Kolev I.V.; Yordanov D.; Vasilev S.; Atanassov K.; Simeonov S.; Palichev G.N.
The exactitude of petroleum fluid molecular weight correlations affects significantly the precision of petroleum engineering calculations and can make process design and trouble-shooting inaccurate. Some of the methods in the literature to predict petroleum fluid molecular weight are used in commercial software process simulators. According to statements made in the literature, the correlations of Lee–Kesler and Twu are the most used in petroleum engineering, and the other methods do not exhibit any significant advantages over the Lee–Kesler and Twu correlations. In order to verify which of the proposed in the literature correlations are the most appropriate for petroleum fluids with molecular weight variation between 70 and 1685 g/mol, 430 data points for boiling point, specific gravity, and molecular weight of petroleum fluids and individual hydrocarbons were extracted from 17 literature sources. Besides the existing correlations in the literature, two different techniques, nonlinear regression and artificial neural network (ANN), were employed to model the molecular weight of the 430 petroleum fluid samples. It was found that the ANN model demonstrated the best accuracy of prediction with a relative standard error (RSE) of 7.2%, followed by the newly developed nonlinear regression correlation with an RSE of 10.9%. The best available molecular weight correlations in the literature were those of API (RSE = 12.4%), Goosens (RSE = 13.9%); and Riazi and Daubert (RSE = 15.2%). The well known molecular weight correlations of Lee–Kesler, and Twu, for the data set of 430 data points, exhibited RSEs of 26.5, and 30.3% respectively.
Prediction of Refractive Index of Petroleum Fluids by Empirical Correlations and ANN
(2023-08-01) Palichev G.N.; Stratiev D.; Sotirov S.; Sotirova E.; Nenov S.; Shishkova I.; Dinkov R.; Atanassov K.; Ribagin S.; Stratiev D.D.; Pilev D.; Yordanov D.
The refractive index is an important physical property that is used to estimate the structural characteristics, thermodynamic, and transport properties of petroleum fluids, and to determine the onset of asphaltene flocculation. Unfortunately, the refractive index of opaque petroleum fluids cannot be measured unless special experimental techniques or dilution is used. For that reason, empirical correlations, and metaheuristic models were developed to predict the refractive index of petroleum fluids based on density, boiling point, and SARA fraction composition. The capability of these methods to accurately predict refractive index is discussed in this research with the aim of contrasting the empirical correlations with the artificial neural network modelling approach. Three data sets consisting of specific gravity and boiling point of 254 petroleum fractions, individual hydrocarbons, and hetero-compounds (Set 1); specific gravity and molecular weight of 136 crude oils (Set 2); and specific gravity, molecular weight, and SARA composition data of 102 crude oils (Set 3) were used to test eight empirical correlations available in the literature to predict the refractive index. Additionally, three new empirical correlations and three artificial neural network (ANN) models were developed for the three data sets using computer algebra system Maple, NLPSolve with Modified Newton Iterative Method, and Matlab. For Set 1, the most accurate refractive index prediction was achieved by the ANN model, with %AAD of 0.26% followed by the new developed correlation for Set 1 with %AAD of 0.37%. The best literature empirical correlation found for Set 1 was that of Riazi and Daubert (1987), which had %AAD of 0.40%. For Set 2, the best performers were the models of ANN, and the new developed correlation of Set 2 with %AAD of refractive index prediction was 0.21%, and 0.22%, respectively. For Set 3, the ANN model exhibited %AAD of refractive index prediction of 0.156% followed by the newly developed correlation for Set 3 with %AAD of 0.163%, while the empirical correlations of Fan et al. (2002) and Chamkalani (2012) displayed %AAD of 0.584 and 0.552%, respectively.
Role of Catalyst in Optimizing Fluid Catalytic Cracking Performance during Cracking of H-Oil-Derived Gas Oils
(2021-03-23) Stratiev D.; Shishkova I.; Ivanov M.; Dinkov R.; Georgiev B.; Argirov G.; Atanassova V.; Vassilev P.; Atanassov K.; Yordanov D.; Popov A.; Padovani A.; Hartmann U.; Brandt S.; Nenov S.; Sotirov S.; Sotirova E.
Three H-Oil gas oils, heavy atmospheric gas oil (HAGO), light vacuum gas oil (LVGO), heavy vacuum gas oil (HVGO), and two their blends with hydrotreated straight run vacuum gas oils (HTSRVGOs) were cracked on two high unit cell size (UCS) lower porosity commercial catalysts and two low UCS higher porosity commercial catalysts. The cracking experiments were performed in an advanced cracking evaluation fluid catalytic cracking (FCC) laboratory unit at 527 °C, 30 s catalyst time on stream, and catalyst-to-oil (CTO) variation between 3.5 and 7.5 wt/wt The two high UCS lower porosity catalysts were more active and more coke selective. However, the difference between conversion of the more active high UCS lower porosity and low UCS higher porosity catalysts at 7.5 wt/wt CTO decreased in the order 10% (HAGO) > 9% (LVGO) > 6% (HVGO) > 4% (80% HTSRVGO/20% H-Oil VGO). Therefore, the catalyst performance is feedstock-dependent. The four studied catalysts along with a blend of one of them with 2% ZSM-5 were examined in a commercially revamped UOP FCC VSS unit. The lower UCS higher porosity catalysts exhibited operation at a higher CTO ratio achieving a similar conversion level with more active higher UCS lower porosity catalysts. However, the higher UCS lower porosity catalysts made 0.67% Δcoke that was higher than the maximum acceptable limit of 0.64% for this particular commercial FCC unit (FCCU), which required excluding the HVGO from the FCC feed blend. The catalyst system containing ZSM-5 increased the LPG yield but did not have an impact on gasoline octane. It was found that the predominant factor that controls refinery profitability related to the FCCU performance is the FCC slurry oil (bottoms) yield.
SAR-AD Method to Characterize Eight SARA Fractions in Various Vacuum Residues and Follow Their Transformations Occurring during Hydrocracking and Pyrolysis
(2023-04-01) Adams J.J.; Rovani J.F.; Planche J.P.; Loveridge J.; Literati A.; Shishkova I.; Palichev G.; Kolev I.; Atanassov K.; Nenov S.; Ribagin S.; Stratiev D.; Yordanov D.; Huo J.
Model compounds were used to provide some chemical boundaries for the eight-fraction SAR-ADTM characterization method for heavy oils. It was found that the Saturates fraction consists of linear and highly cyclic alkanes; the Aro-1 fraction consists of molecules with a single aromatic ring; the Aro-2 fraction consists of mostly 2 and 3-ring fused aromatic molecules, the pericondensed 4-ring molecule pyrene, and molecules with 3–5 rings that are not fused; and the Aro-3 fraction consists of 4-membered linear and catacondensed aromatics, larger pericondensed aromatics, and large polycyclic aromatic hydrocarbons. The Resins fraction consists of mostly fused aromatic ring systems containing polar functional groups and metallated polar vanadium oxide porphyrin compounds, and the Asphaltene fraction consists of both island- and archipelago-type structures with a broad range of molecular weight variation, aromaticity, and heteroatom contents. The behavior of the eight SAR-ADTM fractions during hydrocracking and pyrolysis was investigated, and quantitative relations were established. Intercriteria analysis and evaluation of SAR-ADTM data of hydrocracked vacuum residue and sediment formation rate in commercial ebullated bed vacuum residue hydrocracking were performed. It showed that total asphaltene content, toluene-soluble asphaltenes, and colloidal instability index contribute to sediment formation, while Resins and Cyclohexane-soluble asphaltenes had no statistically meaningful relation to sediment formation for the studied range of operation conditions.
Screening and Investigation on Inhibition of Sediment Formation in a Kuwait Light Crude Oil by Commercial Additives with Some Guidelines for Field Applications
(2023-03-01) Qubian A.; Abbas A.S.; Al-Khedhair N.; Peres J.F.; Stratiev D.; Shishkova I.; Nikolova R.; Toteva V.; Riazi M.R.
The precipitation of asphaltene and waxes occurs when crude oil characteristics change as a consequence of pressure, temperature variations, and/or chemical modifications, etc. The costs associated with the cleaning of deposition on the production equipment and the loss of profit opportunities can go beyond hundreds of millions of USD. Thus, there is a strong incentive to search for ways to mitigate deposit formation during the crude production process. A light crude bottom hole fluid sample from a deep well with an asphaltene deposition problem was analyzed in the laboratory. Basic data on density, viscosity, bubble point, GOR, and asphaltene onset pressure were measured at a PVT laboratory. Asphaltene characterization, as a prescreening for appropriate inhibitors, has been conducted using asphaltene phase diagrams (APD). The APD generated from two developed software programs in both Matlab and Excel codes were favorably compared with the phase behavior of other oil samples available in the literature and has shown to be an excellent match. Various test methods were used to demonstrate the asphaltene instability of the oil samples. Eleven chemical inhibitors from five global companies were screened for testing to inhibit the precipitation. The optimum concentration and the amount of reduction in precipitation were determined for all of these chemicals to identify the most suitable chemicals. Finally, some recommendations are given for the field application of chemicals.
Study of Bulk Properties Relation to SARA Composition Data of Various Vacuum Residues Employing Intercriteria Analysis
(2022-12-01) Stratiev D.; Shishkova I.; Palichev G.N.; Atanassov K.; Ribagin S.; Nenov S.; Nedanovski D.; Ivanov V.
Twenty-two straight run vacuum residues extracted from extra light, light, medium, heavy, and extra heavy crude oils and nine different hydrocracked vacuum residues were characterized for their bulk properties and SARA composition using four and eight fractions (SAR-ADTM) methods. Intercriteria analysis was employed to determine the statistically meaningful relations between the SARA composition data and the bulk properties. The determined strong relations were modeled using the computer algebra system Maple and NLPSolve with the Modified Newton Iterative Method. It was found that the SAR-ADTM saturates, and the sum of the contents of saturates and ARO-1 can be predicted from vacuum residue density, while the SAR-ADTM asphaltene fraction content, and the sum of asphaltenes, and resins contents correlate with the softening point of the straight run vacuum residues. The softening point of hydrocracked vacuum residues was found to strongly negatively correlates with SAR-ADTM Aro-1 fraction, and strongly positively correlates with SAR-ADTM Aro-3 fraction. While in the straight run vacuum residues, the softening point is controlled by the content of SAR-ADTM asphaltene fraction in the H-Oil hydrocracked vacuum residues, the softening point is controlled by the content of SAR-ADTM Aro-3 fraction content. During high severity H-Oil operation, resulting in higher conversion, hydrocracked vacuum residue with higher SAR-ADTM Aro-3 fraction content is obtained, which makes it harder and more brittle.
Validation of Diesel Fraction Content in Heavy Oils Measured by High Temperature Simulated Distillation and Physical Vacuum Distillation by Performance of Commercial Distillation Test and Process Simulation
(2022-11-01) Stratiev D.; Shishkova I.; Ivanov M.; Dinkov R.; Argirov G.; Vasilev S.; Yordanov D.
A gas chromatography high temperature simulation distillation (HTSD: ASTM D 7169), and physical vacuum distillation (ASTM D 1160) were employed to characterize H-Oil vacuum distillates, straight run vacuum distillates, and hydrotreated vacuum distillates with the aim to determine their content of diesel fraction and evaluate the possible higher extraction of diesel fraction from the heavy oils. The ASTM D 7169 reported about six times as high diesel fraction content in H-Oil heavy distillates as that reported by the ASTM D 1160 method. Performing a commercial distillation column test along with a simulation of the column operation using data of both ASTM methods and a software process simulator revealed that the HTSD is the more valid method for proper determination of the diesel fraction content in heavy oils. The software process simulation of the commercial distillation column operation suggests that the HTSD could be considered as a true boiling point distillation method for heavy oils. The separation of the diesel fraction from the H-Oil heavy distillates quantified by the HTSD could deliver oil refining profit improvement in the amount of six digits USD per year.

Browsing by Author "Shishkova I."

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