Variability of complex oscillatory regimes in the stochastic model of cold-flame combustion of a hydrocarbon mixture

Processes of the cold-flame combustion of a mixture of two hydrocarbons are studied on the base of a three-dimensional nonlinear dynamical model. Bifurcation analysis of the deterministic model reveals mono- and bistability parameter zones with equilibrium and oscillatory attractors. For this model, effects of random disturbances in the bistability parameter zone are studied. We show that random forcing causes transitions between coexisting stable equilibria and limit cycles with the formation of complex stochastic mixed-mode oscillations. Properties of these oscillatory regimes are studied by means of statistics of interspike intervals. A phenomenon of anti-coherence resonance is discussed. This article is part of the theme issue ‘Transport phenomena in complex systems (part 2)’.

FLOATING TANK FOR TRANSPORTING OIL AND HYDROCARBONS FOLLOWING A MARITIME DISASTER

Storage of recovered oil and oily water is an important issue when it comes to maritime disasters, being a significant factor of the overall operation. Using large storage vessels is not always an option especially when the vessel is close to the shore. Currently, floating or non-inflatable tanks made of composite textile materials are used worldwide for the storage of the water/hydrocarbon mixture, regardless of the area of action (maritime or fluvial). The research carried out so far by INCDTP specialists, which consists in modelling, simulation and numerical analysis of various constructive forms and devices, led to the conclusion that for the making of a floating tank for storing water/hydrocarbon/oil mixtures, the best solution for its construction is represented by textile materials woven from high-tech yarns (p-aramid and polyamide 6.6) covered with polyurethane. The experimental model of the floating tank for the transport of oils and hydrocarbons in case of disaster was designed by INCDTP specialists and consists of five experimental models of floating materials (made of five variants of covered textile structures) and assembled in collaboration with specialists from SC CONDOR SA, in the form of a floating storage tank. The storage tank that has been created will be tested on the ground first, in order to perform all gravimetric and quality measurements

Autoignition of Reacting Hydrocarbon Mixture with Negative Temperature Coefficient Due to the Cold-Spot and Cold Chamber Wall

Autoignition of an n-heptane/air mixture was simulated in non-uniform temperature environments of a Rapid Compression Machine (RCM) and Shock-Tube (ST) with and without the presence of a cold-spot. The simulations were performed to investigate how the presence of a cold-spot and the cold boundary layer of the chamber wall may affect the ignition delay of the hydrocarbon mixture with NTC behavior. The simulations were performed using three models, (1) 3-Dimensional (3D) Computational Fluid Dynamics (CFD) model, (2) Zero-Dimensional (0D) homogenous batch reactor model by including the heat transfer model, and (3) 0D adiabatic homogenous batch reactor model. A detailed n-heptane mechanism was reduced in this work and used for 3D combustion modeling. A cold-spot critical radius of 7 mm was determined, which affects the ignition delay by more than 9%. In addition, two combustion modes were observed in the combustion chamber with a non-uniform temperature environment. With the first combustion mode, combustion starts at the high gas temperature region of the combustion chamber and quickly propagates towards the periphery of the chamber. In this combustion mode, the location of the maximum concentration of hydroxyl radical and the maximum temperature are the same. With the second combustion mode, the combustion starts at the periphery of the chamber, where the temperature is lower than the center of the chamber due to heat transfer to the cold chamber wall. The location of maximum concentration of the hydroxyl radical and maximum temperature are different with this combustion mode. The two observed combustion modes are due to the NTC behavior of the n-heptane mixture. The 0D homogenous batch reactor model (with and without heat transfer models) failed to mimic the ignition delay accurately when the second combustion mode was present. In addition, a propagating combustion has been observed in the simulation which is in agreement with some of the optical autoignition diagnostics of these hydrocarbons. This propagating combustion leads to a gradual pressure rise during autoignition, rather than a sharp pressure rise. The results of this work show that 0D homogenous batch reactor models are unable to simulate autoignition of mixtures with NTC behavior.

Phase Behavior and Composition Distribution of Multiphase Hydrocarbon Binary Mixtures in Heterogeneous Nanopores: A Molecular Dynamics Simulation Study

In this study, molecular dynamics (MD) simulation is used to investigate the phase behavior and composition distribution of an ethane/heptane binary mixture in heterogeneous oil-wet graphite nanopores with pore size distribution. The pore network system consists of two different setups of connected bulk and a 5-nm pore in the middle; and the bulk connected to 5-nm and 2-nm pores. Our results show that nanopore confinement influences the phase equilibrium of the multicomponent hydrocarbon mixtures and this effect is stronger for smaller pores. We recognized multiple adsorbed layers of hydrocarbon molecules near the pore surface. However, for smaller pores, adsorption is dominant so that, for the 2-nm pore, most of the hydrocarbon molecules are in the adsorbed phase. The MD simulation results revealed that the overall composition of the hydrocarbon mixture is a function of pore size. This has major implications for macro-scale unconventional reservoir simulation, as it suggests that heterogenous shale nanopores would host fluids with different compositions depending on the pore size. The results of this paper suggest that modifications should be made to the calculation of overall composition of reservoir fluids in shale nanopores, as using only one overall composition for the entire heterogenous reservoir can result in significant error in recovery estimations.

Evaluation and Modeling of Asphaltene Deposition in Oil Wells

Asphaltene deposition in oil wells is a challenging flow-assurance phenomenon that affects the well production, project economics, and operational safety. While asphaltene precipitation is governed by the hydrocarbon mixture thermodynamics, Asphaltene deposition is governed by the complexity of flow hydrodynamic behavior and characteristics. This study aims to evaluate and compare the performance of the existing asphaltene deposition models and improve the current theoretical understanding of the deposition phenomenon by developing better predictive asphaltene deposition model. A large experimental database is collected, including aerosol and asphaltene particles deposition in air and crude oil systems, respectively, to carry on the evaluation. The results of this study revealed that Kor and Kharrat (2017) model of transport coefficient, which accounts for both diffusional and inertial deposition mechanisms outperformed other models in matching the transport coefficient from aerosol/air data. In addition, an improved sticking probability model is proposed in this study, and curve fitted using corrected deposition flux data to obtain the model constant. The improved model is not only physically sound, i.e. SP≥1, but also it requires less input data than other models. A validation study of the improved model shows a slight over prediction of experimental data with an absolute average error of 6.8% and standard deviation of 11.4%. The significance of this work is to provide theoretical predictive tool for asphaltene deposition in pipes to enable prevention, mitigation, and management of oil field asphaltene deposition strategies.

Virtual Soft Sensor of the Feedstock Composition of the Catalytic Reforming Unit

The paper discusses a method for obtaining a matrix of individual and group composition of a hydrotreated heavy gasoline fraction in industrial conditions based on the fractional composition obtained by the distillation method according to the ASTM D86 (the Russian analogue of such a standard is GOST 2177). A method for bounds estimation of the retention index (RI) change is considered on the basis of the symmetry of the RI change range relative to its arithmetic mean. Implementation of this method is performed by simulation of individual composition of C6–C12 feedstock of the catalytic reforming unit in the software package. For this purpose, the boiling curve of individual composition of hydrocarbon mixture is converted into the corresponding curve of fractional composition. The presented technique of creating a virtual soft sensor makes it possible to establish a correct relationship between the fractional composition and the individual hydrocarbon composition obtained according to the IFP 9301 (GOST R 52714) (Russian GOST R 52714 and international IFP 9301 standards for the determination of individual and group composition of hydrocarbon mixtures by capillary gas chromatography). The virtual soft sensor is based on chemical and mathematical principles. The application of this technique on the data of a real oil refinery is shown. Obtaining accurate data by means of a virtual soft sensor on the individual composition of feedstock will make it possible to optimize the catalytic reforming process and thus indirectly improve its environmental friendliness and enrichment efficiency.