Browsing by Author "Toteva V."
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Item 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.Item Biodiesel production from high free fatty acid byproduct of bioethanol production process(2022-01-01) Kokkinos N.; Theochari G.; Emmanouilidou E.; Angelova D.; Toteva V.; Lazaridou A.; Mitkidou S.Biodiesel is a reliable and promising replacement of fossil diesel. It is stable, less toxic and can be produced from sustainable resources, including a variety of raw materials. Currently, the most widely used are vegetable oils (edible and nonedible), due to their availability. The present paper considers the potential of obtaining fatty acid ethyl esters (FAEE) from corn oil, which is a byproduct of bioethanol production process. The ultimate outcome would definitely increase the profitability of the initial bioethanol production process. The biodiesel production process was implemented in two steps, due to the high content of free fatty acids of the obtained corn oil. The first step includes an acid-catalyzed esterification process and the second step comprises an alkali-catalyzed transesterification process to receive FAEE. Two different catalysts (sulfuric acid and p-toluene sulfonic acid) were utilized and compared each other in the esterification process, in order to cope with high acid number of the raw material. A comprehensive qualitative and quantitative analysis of both feedstock and biodiesel was performed using gas chromatography-mass spectrometry method. The obtained biodiesel was characterized by a significantly lower cloud point compared to the feedstock and high acid number.Item 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.Item CORRELATION BETWEEN AGING TIME PERIOD OF METAL PRECURSOR SOL - PHASE COMPOSITION AND TEXTURAL PROPERTIES OF ZIRCONIA NANOPOWDERS(2024-01-01) Mitkova E.; Stambolova I.; Stoyanova D.; Toteva V.; Dimitrov O.This article investigates the effect of the time of aging of ZrO2 powders, obtained from zirconium butoxide sols, stabilized using complexating agents on the volume phase fractions tetragonal phase (T) and baddeleyite crystalographic phase (B), pore size distribution and pore volume. It was proved that the aging time period influences ratio between these two polymorphs of zirconia. The sample Zr3d possesses the largest content of baddeleyite phase having the greatest crystallites in comparison to another two powders. The increasing of aging period leads to a gradual increase in (101) peak intensity of T phase, while all the samples are microporous regardless of the aging time. The longest time aged sample possesses higher pore volume and higher average pore diameter than the other two powders. The physico-chemical features of the prepared ZrO2 nanosized powders could be beneficial as catalysts/photocatalysts in different catalytic reactions, corrosion inhibition particles, etc.Item 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.Item Experience in Processing Alternative Crude Oils to Replace Design Oil in the Refinery(2024-06-01) Stratiev D.; Shiskova I.; Toteva V.; Georgiev G.; Dinkov R.; Kolev I.; Petrov I.; Argirov G.; Bureva V.; Ribagin S.; Atanassov K.; Nenov S.; Sotirov S.; Nikolova R.; Veli A.A comprehensive investigation of a highly complex petroleum refinery (Nelson complexity index of 10.7) during the processing of 11 crude oils and an imported atmospheric residue replacing the design Urals crude oil was performed. Various laboratory oil tests were carried out to characterize both crude oils, and their fractions. The results of oil laboratory assays along with intercriteria and regression analyses were employed to find quantitative relations between crude oil mixture quality and refining unit performance. It was found that the acidity of petroleum cannot be judged by its total acid number, and acid crudes with lower than 0.5 mg KOH/g and low sulphur content required repeated caustic treatment enhancement and provoked increased corrosion rate and sodium contamination of the hydrocracking catalyst. Increased fouling in the H-Oil hydrocracker was observed during the transfer of design Urals crude oil to other petroleum crudes. The vacuum residues with higher sulphur, lower nitrogen contents, and a lower colloidal instability index provide a higher conversion rate and lower fouling rate in the H-Oil unit. The regression equations developed in this work allow quantitative assessment of the performance of crucial refining units like the H-Oil, fluid catalytic cracker, naphtha reformer, and gas oil hydrotreatment based on laboratory oil test results.Item Extracts from coffee by-products as potential raw materials for fuel additives and carbon adsorbents(2013-11-05) Cholakov G.; Toteva V.; Nikolov R.; Uzunova S.; Yanev S.Data about coffee consumed world-wide are somewhat contradictory. A conservative estimate, suggests a number of around 8 mln tones per year. Its production involves a comparable amount of by-products, mainly pulp, husks, skins and spent coffee grounds. Thus, a sustainable coffee industry requires the development of methods for utilization of coffee by-products. Among these, the preparation of renewable fuel additives (e.g. biodiesel) and carbon adsorbents is a promising alternative to the eventual dumping of biogenic substances, harmful to the environment. Extraction of coffee by-products is the first step towards their utilization. This work presents results on laboratory extraction of spent coffee grounds (SCG) with different solvents, discussed in the context of the preparation of renewable fuel additives. The aim of the present study is to develop a procedure for extraction of coffee residues, suitable for production of biofuels and adsorbents.Item 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.Item 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.Item 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).Item 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.Item Pollutants sorbent made of cotton fabric modified with chitosan-glutaraldehyde and zinc oxide particles(2021-06-02) Toteva V.; Staneva D.; Grabchev I.The paper reports on the preparation of composite materials by modifying cotton fabric with a layer of crosslinked glutaraldehyde chitosan containing zinc oxide particles. The ability of chitosan to form complexes with zinc ions has been used to control the size, structure, and distribution of the particles on the fiber surface. The three different obtained materials have been characterized by optical and scanning electron microscopy, Fourier-transform infrared spectroscopy (FTIR), and fluorescent analysis. It has been found that the interaction of the ZnO particles with the functional groups of chitosan affects its swelling ability in water and thus determines its sorption prop-erties. The capacity of the materials to wipe water-soluble (textile reactive dye) and water-insoluble (crude oil and oil products) contaminants has been compared. The effect that the amount of zinc oxide has on the ability of the materials to remove contaminants has also been studied. The possi-bility for adsorption–desorption of the crude oil and reuse of the sorbent material has been investi-gated as well.Item Relation of the Content of Sustainable Components (HEFAs) in Blends with Hydrotreated Straight-Run Kerosene to the Properties of Aviation Fuel(2024-06-01) Dinkov R.; Stratiev D.; Andreev I.; Georgiev G.; Angelova M.; Dimitrova R.Z.; Toteva V.An expected increase in the demand for aviation transport service will result in the deterioration of the environment and human health, respectively, due to extra greenhouse gas (GHG) emissions. Concerns from EU institutions about the issue have led to legislation initiatives and, later, to development of Regulation (EU) 2023/2405 for the reduction of GHG emissions via the substitution of fossil kerosene with an increasing share of sustainable components. Hydroprocessed esters and fatty acids (HEFAs) are the most commercially acceptable sustainable alternative but their influence on aviation fuel properties needs to be further evaluated in terms of all required and extended properties, as per ASTM D1655. The main properties, together with the rarely reported upon existent gum, water separation, corrosion, and the electrical conductivity of HEFAs and their blends with fossil kerosene were quantitatively evaluated in this study. For every increase of 10% (v/v) of HEFAs, the following fuel properties improve: the freezing point decreases by 1.3 °C, the smoke point increases by an average of 3 mm, and the specific net energy increases by 0.08 MJ/kg. The acidity of HEFAs are an order of magnitude higher than that of conventional aviation fuel and, thus, close to the limit. The existent gum of the studied SAF is higher than that of fossil kerosene due to, most probably, the presence of non-evaporated residual material.Item 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.