Almaz Uralovich Aetov

RELEVANCE of the study is determined by the need to reduce the high energy costs of pumping natural gas through main gas pipelines, a significant portion of which is associated with overcoming hydraulic resistance in the process equipment of compressor stations (CS), in particular, in gas cooling units. PURPOSE. To model and evaluate the efficiency of an energy-saving technological solution - bypassing the gas cooling units using a bypass line - in order to reduce fuel gas consumption to drive the gas pumping unit. METHODS. The process flow of natural gas at a typical compressor station was simulated using a software package for modeling technological processes. The model is based on the actual operating parameters and component composition of the gas provided by Gazprom Transgaz Kazan LLC. The Peng-Robinson equation of state was used for thermodynamic calculations. Two process flow diagrams were compared: the basic one (with gas passing through the GCU) and the alternative one (with gas cooling units bypassing). RESULTS . The simulation results showed that bypassing the gas cooling units under given temperature conditions reduces the required compressor outlet pressure by 19 kPa. This leads to a reduction in the required compressor drive power from 11.93 MW to 11.80 MW. Accordingly, the fuel gas mass flow rate decreases by approximately 0.00266 kg/s, which is equivalent to a savings of approximately 230 kg (or ~323 m³) of fuel gas per day. CONCLUSION. It has been shown that even a small reduction in energy consumption due to hydraulic optimization can yield a significant economic benefit during long-term compressor station operation. Practical implementation of this solution requires the development of operating regulations taking into account permissible temperature ranges and gas flow rates, as well as the possible modernization of shut-off valves and automation equipment.

The aim of the present study is to identify the preferred region of the thermodynamic surface for the separation of a mixture of ethyl esters of oleic and palmitic fatty acids within the framework of the authors' original method. This method is based on the concept of the dual nature of the mass transfer mechanism in supercritical fluid extraction processes for systems exhibiting type I and II phase behavior. Results are presented for the separation of a binary mixture of ethyl oleate and ethyl palmitate. The process was carried out in asymptotic proximity to the critical point of the CO2–ethyl oleate system. As a result, in one of the extract samples, an ethyl oleate concentration of 94 wt.% was achieved within a 20-minute process duration, starting from an initial content of 25.28 wt.% in the feed mixture. A comparison with the separation results obtained for the same mixture under asymptotic proximity to the critical point of the CO2–ethyl palmitate system revealed the superiority of the aforementioned conditions. The proposed separation method is not limited to the specific mixture discussed here and is proposed for the first time.

The high viscosity of biodiesel fuel, caused by the presence of saturated fatty acid esters, limits its application, particularly at low temperatures. Supercritical fluid extraction (SFE) using carbon dioxide represents a promising method for selective fractionation, enabling the removal of high-viscosity saturated components and the enrichment of the fuel with less viscous unsaturated esters. However, the rational design of such processes requires a deep understanding of the interrelationship between flow hydrodynamics, thermodynamic conditions, and mass transfer in a supercritical medium. In this work, a comprehensive computational fluid dynamics (CFD) modeling study of the fractionation process was performed for a model ethyl oleate/ethyl palmitate mixture (25.28:74.72 wt.%) in supercritical CO₂ at pressures of 11 and 14 MPa and a temperature of 40 °C. A three-dimensional model of a laboratory-scale extractor was developed using the Ansys Fluent software version 2020 R1 environment. Since the target esters are absent from the standard material database, a custom property library and compiled User-Defined Function (UDF) routines were developed. These describe the temperature dependence of density, viscosity, heat capacity, and thermal conductivity for both the individual components and their mixture using established mixing rules. The calculations employed an Eulerian multiphase model, the realizable k–ε turbulence model, and species transport equations. The modeling revealed pronounced selectivity: under the chosen thermodynamic conditions, ethyl palmitate is extracted preferentially over ethyl oleate, with this difference becoming more pronounced as pressure increases. The developed and verified CFD model deepens the fundamental understanding of hydrodynamics and mass transfer during supercritical fractionation and serves as a basis for optimizing process parameters to produce biodiesel with reduced viscosity. The regime at P = 14 MPa and t = 40 °C provides the most favorable thermodynamic and hydrodynamic conditions for the selective removal of saturated esters.

The high viscosity of biodiesel fuel, caused by the presence of saturated fatty acid esters, limits its application, particularly at low temperatures. Supercritical fluid extraction (SFE) using carbon dioxide represents a promising method for selective fractionation, enabling the removal of high-viscosity saturated components and the enrichment of the fuel with less viscous unsaturated esters. However, the rational design of such processes requires a deep understanding of the interrelationship between flow hydrodynamics, thermodynamic conditions, and mass transfer in a supercritical medium. In this work, a comprehensive computational fluid dynamics (CFD) modeling study of the fractionation process was performed for a model ethyl oleate/ethyl palmitate mixture (25.28:74.72 wt.%) in supercritical CO2 at pressures of 11 and 14 MPa and a temperature of 40 °C. A three-dimensional model of a laboratory-scale extractor was developed using the ANSYS Fluent software environment. Since the target esters are absent from the standard material database, a custom property library and compiled User-Defined Function (UDF) routines were developed. These describe the temperature dependence of density, viscosity, heat capacity, and thermal conductivity for both the individual components and their mixture using established mixing rules. The calculations employed an Eulerian multiphase model, the realizable k–ε turbulence model, and species transport equations. The modeling revealed pronounced selectivity: under the chosen thermodynamic conditions, ethyl palmitate is extracted preferentially over ethyl oleate, with this difference becoming more pronounced as pressure increases. The developed and verified CFD model deepens the fundamental understanding of hydrodynamics and mass transfer during supercritical fractionation and serves as a basis for optimizing process parameters to produce biodiesel with reduced viscosity. The regime at P=14 MPa and t=40 °C provides the most favorable thermodynamic and hydrodynamic conditions for the selective removal of saturated esters.

The isobaric heat capacity of samples of industrial molybdenum-containing industrial water runoff formed in the course of epoxidation at the Public Joint Stock Company “Nizhnekamskneftekhim” (Niznnekamsk) is analyzed. The effect of emulsification on the properties of industrial water runoff samples is investigated. The regularities of the change in the drain structure depending on the dilution rate and the ultrasonic modes of ultrasonic action are established. It is shown that emulsification affects the heat capacity of weakly diluted wastewater insignificantly.

The emergence of jumpwise increases and decreases in the isobaric heat capacity of the ternary mixture of ethanol, rapeseed oil, and heterogeneous catalyst Al₂O₃, which are components for obtaining biodiesel fuel, is substantiated theoretically. Temperature ranges of melting, dissolution, and chemical reaction are revealed.

Rapeseed oil transesterification reaction with ethanol under supercritical fluid conditions was performed either in the presence of catalysts or without them. The catalysts were Al₂O₃ and AlOOH, obtained after Al₂O₃ hydrothermal processing, and CaO/Al₂O₃ and CaO/AlOOH, obtained after permeation. The obtained product was measured for dynamic viscosity and density. Based on these data, kinematic viscosity was calculated. Biodiesel fuel was separated via centrifugation to extract more viscous ethyl esters of saturated fatty acids and unreacted triglycerides in order to comply with the standards for biodiesel fuel. Analyses have found that the maximum content of obtained ethyl esters of fatty acids in a reaction product before separation is reached, in the case of using the CaO/AlOOH catalyst, is in the amount of 93.34% by mass; and none of the samples’ kinematic viscosity values comply with the standards for biodiesel fuel. Performing centrifugation allowed us to reduce viscosity and increase biodiesel fuel concentration to reach the EN14214 standard requirements. Also, a significant deterioration of the initial catalysts’ strength after the singular experiment has been observed: Al₂O₃ by 22.4%, AlOOH by 13.89%, CaO/Al₂O₃ by 25.13%, and CaO/AlOOH by 17.27%.