Theoretical Foundations of Chemical Engineering最新文献

Modern challenges in chemical technology require effective solutions for separating bulk materials into fractions with specified granulometric characteristics. This is especially important for processes involving the handling of fine-dispersed materials, where particle separation plays a key role in improving the quality of the final product and reducing costs. The article presents a multi-vortex classifier designed for particle size fractionation. The aim of the study is to numerically investigate the influence of the geometric parameters of the classifier on its efficiency. Numerical modeling is performed in the Ansys Fluent software environment using the k–ω SST turbulence model and the Discrete Phase Model (DPM) to track particle motion in the gas flow. During the calculations, the inner pipe diameter d and the degree of rectangular slit opening k are varied. It is found that the efficiency of bulk material separation in the multi-vortex classifier is determined by the interaction of airflows through the lower opening of the inner pipe and the rectangular slits. The flow through the lower opening forms an upward current that destabilizes the vortex structure, while the flow through the rectangular slits ensures the stability of the vortices in the annular space. An increase in the inner pipe diameter d leads to a decrease in particle capture efficiency. For example, as d increases from 43 to 66 mm, the average efficiency E decreases from 79.7 to 32.1%, which is associated with the intensification of the destabilizing upward flow. This occurs because the number of rectangular slits increases from 4 to 8 (resulting in a larger total cross-sectional area of the slits), which reduces the effect of the centrifugal forces. A decrease in d contributes to the stabilization of vortices, resulting in additional pronounced efficiency peaks in the fine particle range up to 40 μm. Reducing the degree of rectangular slit opening k to values of k ≤ 20% ensures a sharp increase in particle fractionation efficiency, achieving values greater than 95% for particles with sizes >55 μm. At k ≥ 40%, a significant decrease in the classifier efficiency is observed.

In the petrochemical industry, a critical challenge is the effective control of the granulometric composition of dispersed materials to optimize reaction processes, improve the quality of final products, and reduce energy consumption. One promising approach in this field involves the development and refinement of equipment capable of achieving high selectivity in the separation of fine-dispersed powder systems. This article examines the fractionation of fine particles in an air stream using a novel multi-vortex classifier. Numerical experiments are conducted in Ansys Fluent using the k−ω SST turbulence model, which ensures accurate modeling of high velocity gradients in the vortex zones. The study aims to numerically investigate the fractionation of a solid dispersed phase in an air stream by varying the structural parameters of the multi-vortex classifier. Based on 3D models of the apparatus, 35 numerical experiments are performed, covering a wide range of adjustable parameters. The simulation analyzes the behavior of fractional efficiency for particle sizes ranging from 1 to 200 μm, identifying five characteristic points on the curve that reflect the boundary and transitional states of the separation process. It is established that increasing the vortex diameter promotes the formation of stable multivortex structures and enhances overall separation efficiency. The highest efficiency and a pronounced extremal curve shape are observed at vortex diameters of 27.5–29 mm. Power-law correlations are derived between characteristic particle sizes and flow velocity ratios, enabling the application of these results for engineering optimization of classifiers operating in petrochemical powder processing.

Reactors with a fluidized bed of catalysts are used in many industries, particularly oil refining, coal gasification, petrochemistry, etc. It is known that in order to prevent the entrainment of the catalyst, the reactors are equipped with devices of particle-capture systems, i.e., cyclones. However, there are significant disadvantages, particularly the removal of the catalyst. The paper proposes to reduce catalyst losses in a fluidized bed reactor by replacing cyclones with separation devices with arc-shaped elements. The article presents the design of the proposed separator. The principle of its operation is described. It is shown that under the action of inertial and centrifugal forces, particles are knocked out of the gas–dust flow towards the arc-shaped elements. In the course of numerical studies conducted in the Ansys Fluent software package, it is found that at relatively low speeds up to 1 m/s, a high separator efficiency of more than 69.2% is achieved. At a gas–dust flow velocity of more than 1 m/s, two critical particle sizes are identified, which correspond to maximum and minimum efficiency. At a gas–dust flow velocity of 2 m/s, the value of a_cr.1 = 52.4 µm (E = 99.9%), a_cr.2 = 138 µm (E = 63.7%). At a gas–dust flow velocity of 3 m/s, the value of a_cr.1 = 52.4 µm (E = 99.9%), a_cr.2 = 138 µm (E = 25.7%). As the particle size increases to a_cr.1, the efficiency increases, since the particles can be better knocked out of the structured flow. With a particle size between a_cr.1 and a_cr.2 the particles bounce off the arc-shaped elements back into the current and are carried away. When the particle size is more than a_cr.2, they randomly bounce off different arc-shaped elements and fall into the hopper due to gravity. The pressure loss in the separator is less than 58 Pa at a gas–dust flow rate of less than 1 m/s. The use of separators with arc-shaped elements in fluidized bed reactors to capture catalyst particles as an alternative to cyclone separators is an appropriate measure that significantly reduces catalyst losses.

Interest in a detailed study and simulation of the processes occurring in heat- and mass-transfer equipment is determined by the variety of designs and types of devices, as well as the variety of different ways to enhance the processes taking place in the equipment. The study of the hydrodynamics of technological media and the interaction of phases (components) in contact devices makes it possible to optimize the geometry of the designed equipment in order to enhance the efficiency of the heat- and mass-transfer processes. For simulation and analyzing of the processes taking place in technological equipment, computational fluid dynamics software systems based on finite-element analysis methods are often used, which allows obtaining velocity, concentration, temperature, and pressure distribution curves only for single-phase media. However, simulation of technological processes involves describing the hydrodynamics of multiphase media under the influencing conditions of centrifugal field and Coriolis acceleration on the nature of interaction, which today is a rather complex task requiring significant computing resources, machine time, as well as human resources. In connection with the above, it is of interest to develop an approach to simulation that combines the simplicity of analytical dependences and ensures sufficient accuracy in computations, verified by satisfactory agreement of the results obtained from the literature sources and the results of numerical studies performed using computational fluid dynamics software systems. The present paper proposes a mathematical description of the solution of a hydrodynamic problem related to determining the two-phase flow velocity in a profile nozzle of a centrifugal unit. The paper presents the basic differential equations and boundary conditions describing the flow of interacting phases in a profile nozzle.

In view of rising energy prices, energy-saving measures are becoming relevant even for small-scale plants that use relatively inexpensive energy resources (steam, water). Using computer simulation of three designs of energy-saving distillation systems for tetrachloroethylene (simple sequential separation, use of a heat pump, and mechanical steam recompression), the efficiency of heat-integration methods for small-scale production is demonstrated, and the option with the lowest total annual costs is selected. As a result of the study, it is concluded that for existing plants not optimized for energy consumption, using mechanical steam recompression from one column to heat the reboiler of another column can reduce total annual costs by 8.6%, with a payback period for the upgrade of 3.5 years. Operating expenses are reduced by 29.5% in monetary terms. For newly established plants, simultaneously optimizing the distillation-stage equipment for energy consumption and applying heat-integration methods in the form of mechanical steam recompression can reduce total annual costs by more than 23% compared with the base case.

The article presents the results of determining the mass-transfer characteristics of three membrane-type contact devices of various designs, which can be used to solve problems of detritiation of low-level aqueous waste. All devices used a single domestic tubular membrane TF-4SK, rolled into a spiral, with a hydrophobic catalyst RCTU-3SM placed around the membrane. The high efficiency of devices with a single membrane is demonstrated with much smaller weight and size parameters compared to a classic membrane-type contact device. With a fivefold increase in the vapor-gas flow rate, the mass-transfer coefficient in membrane contact devices increases up to threefold. The possibility of operation of contact devices with tubular membranes at a linear velocity of the vapor-gas flow of more than 5 m/s, which is more than an order of magnitude higher than for traditional packed contact devices, is demonstrated. The membrane contact devices presented in the article can be used to create compact, high-performance separation units for processing tritium-containing low-level aqueous waste generated during the operation of power plants.

In this paper, we consider the proposed method for identifying the average integral heat transfer coefficient of an axial heat pipe (ATT) coolant to a capillary—porous wick as a function of temperature. The purpose of axial heat pipes is to divert thermal energy from the heat-generating equipment and redistribute it over the surface of the radiator to ensure the regular functioning of the thermostatically controlled equipment. This problem is solved by determining the global extremum of the RMS functional of the discrepancy between the theoretical and experimental temperature field at the temperature sensor installation sites. The method of thermal balances was chosen as a method for solving the “direct” problem of heat transfer inside a heat pipe, and the gradient method of conjugate directions was chosen as an optimization method, as the most accurate method of the first order of convergence of the iterative process. As a criterion for stopping the iterative process, a superposition of errors is used that introduce incorrectness into the studied formulation of the heat transfer problem, such as systematic, error in the formulation of the “direct” heat transfer problem, etc. The resulting identified solution is compared with the classical experimental method for determining the heat transfer coefficient based on the analysis of thermal resistances of the structure.

The paper examines modern marine turbine units, which differ in terms of purpose, type, design features, materials, and working bodies. This diversity is due to the use of innovative information technologies, from the preproduction process to the final product release. It is noted that at the turbomachinery design stage it is necessary to take into account the external characteristics such as power, angular velocity, shaft torque, and efficiency, which is characterized by losses in the turbine stage, etc. It is emphasized that in an effort to reduce losses in the turbine stage, engineers resort to the creation of low-consumption partial turbines, in which the losses from partial admission ratio are significantly reduced due to changes in the design parameters. An example of such a design is a turbine with partial blading of the runner. The study object is a low-consumption centripetal turbine with partial blading of the runner with varying degrees of partial admission ratio. The study subject is the gas dynamic characteristics of the flow part of the nozzle diaphragm and the runner of a low-consumption centripetal turbine. The main objective of the study is to compare the velocity coefficients of the nozzle diaphragm and the runner of the turbine stage. It is noted that low-consumption turbines are characterized by their small size, which does not allow for a high-quality physical experiment. In the present paper the research method is numerical simulation of gas flow using computational gas dynamics. The paper presents graphical dependences of the velocity coefficients of the nozzle diaphragm and the runner as a function of u₁/C₀ at varying degrees of partial admission ratio. The unsatisfactory convergence of the velocity coefficients has been established and recommendations for improving the convergence of the gas dynamic computation have been proposed.

The paper provides a brief overview of publications in which the study of some complex technical objects is carried out by presenting their mathematical models in the form of mathematical problems, specifically linear programming (LP) problems. In particular, the following are considered: a model of mixed-integer linear programming for optimal planning of multi-plant, multi-delivery, and multi-grade petrochemical production; the problem of minimizing the use of water and wastewater in the production process of the Brazilian petrochemical industry using mass integration through the use of mathematical programming; innovations in petrochemical technologies aimed both at increasing the supply of liquefied natural gas and at solving new problems, including the need for decarbonization and adaptation to the future circular economy; a methodology for optimal short-term planning of integrated oil refining and petrochemical complexes; and spatial organization of the Chinese petrochemical industry. A method is proposed for the generalized solution of an improper linear programming problem in a normal form, in which the system of constraints/inequalities is incompatible. Potential reasons for this incompatibility include errors in the mathematical model itself and its information support, as well as real contradictions of the analyzed object, which are therefore reflected in the model. At the first stage, by solving a sequence of 0-1 mixed-integer linear programming problems, a set of vectors is formed, including the numbers of joint constraints, and at the second stage, by solving linear programming problems for each of these vectors, a generalized solution to the original problem is found, preserving the maximum power of the joint subsystem of constraints. A numerical example containing two variables and ten constraints is solved.