Svetoslav Nenov

University of Chemical Technology and Metallurgy | UCTM · Department of Mathematics

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 l...

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 re...

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 o...

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 ar...

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...

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 stat...

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 t...

165 crude oils with viscosity, density, and molecular weight variation in the range 0.54 – 24135cP; 0.746 – 1.016 g/cm³; 117–579 g/mol respectively were examined for viscosity prediction using eight available in the literature models and three more, developed in this work models. The best empirical model was that of Sinha et al., 2020 with % AAD (a...

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-AD TM) methods. Intercriteria analysis was employed to determine the statistically...

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 prop...

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...

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 hydrocracked and straight-run vacuum residues are scarce. For that reason, 30 str...

274 crude oils pertaining to the groups of extra light (gas condensates), light, medium, heavy, and extra heavy crude oils were characterized by true boiling point distillation, specific gravity and kinematic viscosity at 21.11 and 37.78 °C. Eight published regression empirical methods were examined for their capability of accurately predicting the...

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...

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 characteristic parameters which have an effect on viscosity. Seven publ...

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 bet...

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 alo...

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 hydrocracking on the quality of the H-Oil liquid products. 36 c...

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 experime...

10 gas oils and one deasphalted hydrocracked vacuum residue obtained from ebullated bed vacuum residue hydrocracking have been cracked in a laboratory advanced catalyst evaluation unit on a commercial fluid catalytic cracking (FCC) catalyst. It was found that the 11 secondary heavy oils obey second order reaction kinetics. The relations between gas...

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 asphaltene...

Some properties of moving least-square approximations for two concrete weight functions are investigated. The used thecnique is based on some properties of differential equations and applications of the theory of Lyapunov functions.

The goal of this short note is to prove that every b-spline curve or surface (generated by uniform knots, without multiplicity) may be defined as minimum of positive quadratic operator.

Twenty-two crude oils around the world, from which 19 are processed in the LUKOIL Neftohim Burgas (LNB) refinery, were characterized in the LNB research laboratory by measuring 67 properties. These 22 crude oils included light low sulfur, light sulfur, intermediate low sulfur, intermediate sulfur, intermediate high sulfur, heavy high sulfur, and ex...

In this short article, some properties of matrices of moving least-squares approximation have been proven.The used technique is based on singular-value decomposition and inequalities for singular-values. Some inequalities for the norm of coefficients-vector of the linear approximation have been proven.

Thirty-four heavy oils originating from the four main groups of crude oils around the world—I group: light, low sulfur (30–400 API; S ≤ 0.5% mass); II group: light sulfur (30–400 API; S = 0, 5–1.5% mass); III group: heavy, high sulfur (15–300 API; S = 1.5, 3.1% mass); IV group: extra heavy, high sulfur (150 API, S ≥ 3% mass)—were investigated for d...

A data base of 140 diesel fuels having cetane number in the range 10 ? 70 points and the physical properties: density at 15?C, and distillation characteristics according to ASTM D-86 T10%, T50%, and T90% was used to develop new procedures for prediction of diesel cetane number by application of the least squares method (LSM) using MAPLE software, a...

In this paper, we investigate the parametric curves continuous on the left hand side. Assumed that their corresponding parameters belong to their own domains which are generally different for the non-coinciding curves. Furthermore, the points of discontinuity ( if the exist) are jump points and specific to each curve. The upper estimate of Hausdorf...

A nonlinear generalized difference equation with both delays and the maximum value of the unknown function over a discrete past time interval are studied. A nonlinear boundary value problem of antiperiodic type for the given difference equation is set up. One of the main characteristics of the considered difference equation is the presence of the u...

Differential equations with “maxima” of the type L n x(t)+f(t,max [σ(t),τ(t)] x(s))=0(E) are considered, where n≥2, σ,τ are continuous functions and σ(t)<τ(t)≤t.

In this paper we consider a second order functional differential (r(t)x′ )′ + q(t)f (max x(s))= b(t), s∈[σ(t),τ (t)] containing a function f of sublinear rate and depending on the maximum of the unknown x(t) and defined on some interval taken before coming the present time t. We call this equation with “maxima”. Criteria for existence of nonoscilla...

For the classical Lotka—Volterra predator-prey system, new notion I-optimal curve ξI is introduced. This curve is disposed in the phase space of the system. The curve ξI intersects each trajectory γc of Lotka—Volterra system at least once. The points of ξI possess the following optimal property: if (m, M) ∈ ξI ∩ γc0, then after a “jump” with magnit...

The author proves that for any solution x 1 (t) to the system Mx ¨+x ˙=f(t,x), for which lim t→∞ ∥x ˙ 1 (t)∥=0, there exists a solution x 2 (t) to the system x ˙=f(t,x) such that lim t→∞ ∥x 1 (t)-x 2 (t)∥=0. Some generalizations of this result are presented. The case f(t,x)=-∇U(x) is investigated explicitly.

Some problems for impulsive (discrete) controllability of the solutions of smooth dynamical systems are presented. Rapid outside actions over the evolutionary system result in the analysis of its impulsive control. Some examples from population dynamics are discussed.

In the present paper, a class of optimization problems to impulsive control of smooth dynamical processes is investigated. Necessary and sufficient conditions for existence of optimal impulsive controllability of the initial-value problem for a dynamical system are obtained. The derived results are applied to the analysis of some classical problems...

In questo lavoro si dimostrano l'esistenza e l'unità di un flusso vettorialeX in ℝn ,n≥3, che ha le seguenti proprietà: X non ha punti stazionari in ℝn ; tutte le orbite diX sono limitate; esiste una filtrazione perX.

We deal with some problems concerning periodic solutions of perturbed dynamical systems. Sufficient conditions for the existence of periodic solution(s) of perturbed system are obtained. Moreover, we derive some properties of the set of all perturbed terms of a dynamical system under which the perturbed system has periodic solution(s). The method i...

The object of impulsive flow on a smooth manifold generated by a consistent triple is defined and some of its basic properties are proved. A theorem analogous to the classical theorem of A. J. Schwartz for impulsive flows is proved. By means of the object of impulsive flow a weak C κ -version of Pugh’s closing lemma is proved, κ∈ℕ.

The paper deals with a decomposition method for solutions of differential equations of the form x ¨+φ(t)|x| 2k-2 x=F(t)x, k=1,2,⋯. The method under consideration is based on a theorem of decomposition of stationary points of a functional on Banach space.