Steady-state Process Research Articles

Experimental investigation of a model bulb turbine under steady state and load rejection process

With the advantages of large flow capacity, low head, and high efficiency, the tubular turbine can well meet the demand for renewable resources. To obtain its synthetic characteristics in full operating conditions, model tests on both the steady state and transient process were designed and conducted in an ultra-low head bulb turbine. The similitude criteria, model test system, and test method were introduced; experiments on comprehensive steady-state and load-rejection conditions were performed; and the results were analyzed. Based on the steady-state test, the variation of flow, torque, and axial force with respect to the rotating speed, runner blade (RB) opening, and guide vane (GV) opening were revealed. Dynamic test results showed that the closing laws of GV and RB have an obvious influence on the quality of the transient process. Orthogonal optimization was used to acquire the optimal closing scheme of GVs and RBs when the turbine undergoes full load rejection under rated head conditions. Our test results provide a sound reference for the design and operation of tubular turbine units.

A Supervised Framework for Recognition of Liquid Rocket Engine Health State Under Steady-State Process Without Fault Samples

Data-driven intelligent models have received more and more attention in liquid rocket engine (LRE) state recognition. However, due to practical limitations, the fault data are rare for model training, which results in poor testing results. To better recognize the state of LRE, we proposed a supervised recognition framework without fault samples. First, we proposed a negative sample generation method. Then, fusion recurrent convolutional neural network (FRCNN) is constructed for data fusion and feature extraction. Finally, we evaluated the recognition results with several quantization indicators. The proposed method is verified with the real monitoring data, which is obtained from the static firing tests of a certain type of LRE. Results show that the FRCNN could recognize the state of LRE with accuracy over 93% under the confidence of 96%, which shows the effectiveness of the proposed framework. And the comparison with the literature method shows the superiority of the proposed framework. In addition, it could also perform real-time monitoring for LRE, and recognize the abnormal at the initial stage of the steady state, which has practical potential in monitoring task. At last, we further discuss and analyze the generated negative sample and the proposed framework.

Mode Analysis Theory of Small Disturbance Operation Process of Power System

The power system currently has the problem that transient steady-state low-frequency oscillations after the power system suffers from small disturbances will affect the normal operation of the power grid. This paper proposes a model analysis of engineering mathematics for the power system’s small-disturbance transient low-frequency oscillations. First, this paper constructs the mathematical model and simplified model of the power system. Next, this paper calculates the initial steady state of the model and builds a linearized model. Then small disturbances are added to the model in order to simulate the transient steady-state process of a single-machine infinite-bus system under real conditions. Finally, the power system stabilizer (Power system stabilizer PSS) is designed through model analysis. Compared the transient steady-state process the PSS isn’t installed and the PSS is installed in the singlemachine infinite power system, we can get experimental results, which show that the power system can obtain a new steady state after receiving small disturbances and eliminating small disturbances in time. At the same time, the installation of PSS can effectively increase the stability of the power system and the tolerance for the existence of interference.

Векторне керування асинхронним генератором з підвищеним коефіцієнтом корисної дії

Compared to today’s dominant in autonomous wind power, a synchronous generator with permanent magnets, an induction generator (IG) with a short-circuited rotor has such significant advantages as higher reliability and lower cost. But the energy performance in IG is lower, so their improvement is an actual task. To solve this problem, along with search algorithms, systems of no-search optimization of power losses in IG are intensively developed. In these systems, the optimal magnetic flux is determined by the analytical expression obtained from the loss model. The disadvantages of the known works on this topic are that they use various simplified models of losses. Accordingly, this reduces the accuracy of optimization algorithms. The aim of the work is to build the vector control system of IG, in which, due to the optimization of the sum of major power losses, a significant increment in the efficiency of the generator is achieved. The article uses a model of power losses, which includes all the main losses in the IG of electromagnetic nature. These include ohmic losses in the stator and rotor resistances, magnetic losses in the iron and additional losses. By analytical study of the model of losses to the extremum, an expression for determining the optimal flux linking of the rotor by the criterion of minimum total losses in the generator is obtained. The application of this expression allows to increase the accuracy of loss optimization in comparison with known analogues. The procedure for determining the optimal flux uses the signals of the instantaneous component of the stator current and rotor speed and is simple for computer implementation in real time. Numerical studies of steady-state processes in the mode of operation of the generator with a constant output power P2=const for its values from 15 % to 45 % have been conducted. It is established that the efficiency increment obtained due to control with loss optimization has an extreme character with a maximum in the vicinity of the nominal speed. As P2 increases, the loss optimization zone and efficiency increment decrease. The maximum and average efficiency increment obtained in the study reach 19 % and 11 %, respectively. This shows the prospects of the proposed system of energy-efficient vector control of IG.

Using Neural Networks to Obtain Indirect Information about the State Variables in an Alcoholic Fermentation Process

This work provides a manual design space exploration regarding the structure, type, and inputs of a multilayer neural network (NN) to obtain indirect information about the state variables in the alcoholic fermentation process. The main benefit of our application is to help experts reduce the time needed for making the relevant measurements and to increase the lifecycles of sensors in bioreactors. The novelty of this research is the flexibility of the developed application, the use of a great number of variables, and the comparative presentation of the results obtained with different NNs (feedback vs. feed-forward) and different learning algorithms (Back-Propagation vs. Levenberg–Marquardt). The simulation results show that the feedback neural network outperformed the feed-forward neural network. The NN configuration is relatively flexible (with hidden layers and a number of nodes on each of them), but the number of input and output nodes depends on the fermentation process parameters. After laborious simulations, we determined that using pH and CO2 as inputs reduces the prediction errors of the NN. Thus, besides the most commonly used process parameters like fermentation temperature, time, the initial concentration of the substrate, the substrate concentration, and the biomass concentration, by adding pH and CO2, we obtained the optimum number of input nodes for the network. The optimal configuration in our case was obtained after 1500 iterations using a NN with one hidden layer and 12 neurons on it, seven neurons on the input layer, and one neuron as the output. If properly trained and validated, this model can be used in future research to accurately predict steady-state and dynamic alcoholic fermentation process behaviour and thereby improve process control performance.

Енергоефективна система керування автономним асинхронним генератором для віддалених поселень

Laying power lines to small settlements and farms away from towns and villages is not always cost-effective. Therefore, autonomous solar and wind energy sources are increasingly used in such settlements. In contrast to the dominant today in wind power plants synchronous generators with permanent magnets, an induction generator (IG) with a short-circuited rotor have such important advantages as higher reliability and lower cost. But the energy performance in IG is lower, so their improvement is an actual task. To solve this problem, systems of no-search optimization of power losses in IG are intensively developed. In these systems, the optimal magnetic flux is determined by the analytical expression obtained from the loss model. The disadvantages of the known works on this topic are that they use various simplified models of losses. Accordingly, this reduces the accuracy of optimization algorithms. The aim of the work is to build the vector control system of IG, in which, due to the optimization of the sum of major power losses, a significant increment in the efficiency of the generator is achieved. The article uses a model of power losses, which includes all the main losses in the IG of electromagnetic nature. These include ohmic losses in the stator and rotor resistances, magnetic losses in the iron and additional losses. By analytical study of the model of losses to the extremum, a expression is obtained to calculate the optimal flux linkage of the rotor by the criterion of minimum total losses in the generator. The application of this expression allows to increase the accuracy of loss optimization in comparison with known analogues. Numerical studies of steady-state processes in the mode of operation of the generator with a constant output power P2=const for its values from 10% to 50% have been conducted. It is established that the efficiency increment obtained due to control with loss optimization has an extreme character with a maximum in the vicinity of the nominal speed. The maximum and average efficiency increment obtained in the study reach 26% and 18%, respectively. This shows the prospects of the proposed system of energy-efficient vector control of IG.

Method of calculation of steady-state processes in electrical circuits

Purpose. Development of a method for calculating established periodic processes of complex shapeMethodology. Polynomial approximation of functions, numerical methods for solving integro-differential equations, mathematical apparatus of matrix algebra, computer programming and methods of electric circuit theory are used.Findings. As a result of modification of the known method for calculating transient processes, a method has been developed that allows you to directly perform the calculation of steady-state periodic processes. This will reduce the time of computer simulation of electrical processes in linear electrical circuits. An example of using the proposed method is shown. Based on the developed method, a computer program for calculating the steady-state process in the model circuit is worked out. This example shows a 45% reduction in CPU time compared to the use of known methods.Originality. Processes in electrical circuits are described by integro-differential equations. The approximation of functions of current derivatives to time by series on orthogonal Tchebyshev’s polynomials is used in their solution.When approximating functions, Chebyshev polynomials have uniform error in the whole range of argument change. It is advantageous stand out them from a number of other orthogonal functions. The proposed method uses a polynomial approximation not of the solution function itself, but of its derivative. The function itself is obtained with the help of integration operation. This operation has a small margin of error compared to the differentiation operation. The direct calculation of the steady-state periodic process is achieved by taking the initial conditions for currents and their derivatives at the beginning of the period as the values of the same functions at the end of the period. In the proposed method, integro-differential equations of state are transformed into linear algebraic equations. A method for creating a unified system of linear algebraic equations is proposed. The solution of this system allows you to perform directly the calculation of steady-state periodic processes.Practical value The developed method opens a new possibility of using a diverse apparatus of the electric circuits theory to work with images of currents. Based on this method, a universal software package is developed for calculating steady-state periodic processes in electrical circuits of arbitrary complexity. This will reduce the CPU time for modeling complex circuits.

Economic Design of Solar-Driven Membrane Distillation Systems for Desalination

Solar-driven membrane distillation (SDMD) for desalination is a feasible method to solve water and energy resource issues. The design and operation of SDMD is different from continuous and steady state processes, such as common chemical plants, due to the intermittent and unpredictive characteristics of solar radiation. Employing the steady state and dynamic simulation models developed on the platform of Aspen Custom Modeler®, this paper presents a two-stage design approach for the SDMD systems using different types of membrane distillation configurations, including AGMD (air gap MD), DCMD (direct contract MD) and VMD (vacuum MD). The first design stage uses the steady state simulation model and determines equipment sizes for different constant-value solar radiation intensities with the objective of minimizing total annual cost. The second design stage is implemented on the SDMD systems with process control to automatically adjust the operating flow rates using the dynamic simulation model. Operated with the yearly solar radiation intensity of Taiwan, the unit production costs (UPCs) of the optimal SDMD systems using AGMD, DCMD, and VMD are $2.71, 5.38, and 10.41 per m3 of water produced, respectively. When the membrane unit cost is decreased from $90/m2 to $36/m2, the UPC of the optimal solar-driven AGMD system can be reduced from $2.71/m3 to $2.04/m3.

Non-isothermal crystallization during the molding of a viscoelastic polymer film

A steady-state non-isothermal process of forming a viscoelastic flat polymer film is considered. The polymer melt is extruded through a flat die, subjected to uniaxial stretching and at the same time air cooling, and then finally cooled down on a chill roll. It is assumed that the film is wide enough and the distance between the extruder die and the cooling roller is minimal to such an extent that the change in the width of a film in the course of longitudinal stretching can be neglected. From a rheological standpoint, a polymer melt is a viscoelastic fluid. The upper-convective Maxwell model is used, for which the viscosity and relaxation time are assumed to be temperature dependent. The mathematical model is supplemented by the equation of non-isothermal crystallization kinetics. The problem is solved by a numerical method of finite differences.

STUDY OF CONVERTER WITH FIFTEEN ZONE REGULATION VOLTAGEAND ACTIVE-INDUCTIVE LOADS

Analysis of the electromagnetic processes is organized beside this article in electric circuit with semiconductor commutator. Mathematical model is created for analysis electro-magnetic processes in semiconductor converter with width pulsed regulation of the output voltage. The broughted graphs, which reflect the electromagnetic processes in electric circuit. Method much parametric functions was used when performing calculation. The mathematical model of the converter is created for fifteen zoned regulations of the output voltage. Article is devoted to the development of a method of multi-parametric modulating functions by means of working out of new mathematical models and definition of functions and the algorithmic equations for the analysis on sub- system components of electromagnetic processes in electric circuits of variable structure with sinusoidal, direct and pulsing voltage. Introduction of functions with discrete parameters in the algorithmic equations for analysis of processes in circuits with semiconductor commutators simplifies modeling on subsystem components. The mathematical model of steady-state processes and transients in electric circuits of semiconductor converters of modulation type with multi-channel zonal use of phase and line voltages of a three-phase network of power supplies is developed. The mathematical model of electric circuits of thyristor shapers of electro-discharge pulses for the analysis and the matching of capacitors charging modes with decrease several times of electric resistance of technological load is also created. The obtained results have a great value for development theoretical electrical engineering in a direction of simplification of calculations of electromagnetic processes in electric circuits with semi-conductor converters of the electric power. The Electromagnetic processes in electric circuit under width-pulse regulation possible to analyse with use the algorithmic equations multivariable function, which argument are a system parameters semiconductor commutator, signal of control, phases to network of the power supply and time. Introduction multivariable function with discrete parameter in algorithmic equations of the analysis formed and connecting processes in electric circuit of the variable structure allows to reflect change of this structure under system components, simplifying modeling and analysis of such processes to account of the generalization of the got equations. Except specified correlations and diagrams designed model allows to analyse forms of the output voltages and current of the separate power modules.

PROBLEMS OF FREE ROLLING OF THE PILGER HEAD AND WAYS OF THEIR SOLUTION

A feature of the process of hot pilgring rolling of pipes is the presence of an under-roll of the rear end of the sleeve, which forms the so-called pilger head, which is due to the presence of a front support on the sleeve from the mandrel head of the feeding apparatus. Pilgerghead refers to the technologically inevitable loss of metal in the pilger mill, especially when rolling thin-walled (D / S = 12.5 - 40) and especially thin-walled (D / S > 40) pipes. At the same time, when rolling thick-walled pipes (D / S = 6-12.5), in practice, the methods of butt-end rolling of sleeves and free rolling of the pilger head are used, and the latter is used quite limited and only as an addition to the butt-to-butt rolling method of the last sleeve in a batch or in case of disturbance this process. The presence of a pilger head is one of the main factors of increased metal consumption at pilgrim mills. The analysis of the problems of the process of free rolling of the pilger head is carried out and the ways of their solution are proposed. One of the main problems of this process is the impossibility of its use when rolling out thin-walled (D / S = 12.5-40) and especially thin-walled (D / S > 40) pipes, which is due to the peculiarities of removing the pipe from the mandrel using a gate device and a feeder.To solve this problem, a new technology has been proposed, which provides for rolling the pilger head to such a wall thickness at the end, which ensures the removal of thin-walled (D / S = 12.5-40) and especially thin-walled (D / S > 40) pipes from the mandrel. New solutions have been proposed to reduce the displacement of the roll along the mandrel in the first rolling cycles of the pilger head, the theoretical study of which made it possible to recommend a method of reducing the speed during its rolling in comparison with the steady-state process by 40-50%, as the simplest and most effective. Two new methods have been proposed for removing the pipe from the mandrel after full or partial rolling of the pilger head, the first of which is distinguished by the simultaneous convergence of the upper and lower gates, and the second - by holding the rolling by the press dies. To hold the mandrel ring at the mandrel head, two new solutions have been proposed, according to the first, permanent magnets are mounted in the ring, according to the second, both halves of the ring are connected using Belleville springs, which create the necessary adhesion to the mandrel.

A LABORATORY SYSTEM FOR INVESTIGATING OF FLUIDS FLOW CAPACITY THROUGH UNCONSOLIDATED SAND SAMPLES

Practically all studies of reservoir engineering involve detailed knowledge of fluid flow characteristics. The fluid flow performance in porous media is affected by pressure, flow rate, and volume of single fluid phases. Permeability is a measure of how well a porous media allows the flow of fluids through it. Permeability and porosity form the two significant characteristics of reservoir rocks. This research aimed to present the design of laboratory equipment to test the ability of fluid flow through different sandstone samples. Two sand core samples (coarse sand sample and fine sand sample) were tested. The laboratory findings measurements of porosity, saturation, total permeability, effective permeability, and relative permeability were evaluated. The laboratory tests were performed on partially saturated, unconsolidated core sand for two-phase fluid flow. The experimental work was developed for measuring the flow capacity achieved under the steady-state conditions method. Various grain sizes sands were selected as a porous medium to determine petrophysical properties and fluid flow capacity of the rock sample. Nitrogen and air were utilized as gas-phases, and, for liquid-phases, water was chosen as an injection fluid. The steady-state process method was used to determine the permeability and relative permeability of unconsolidated sands to water flow. Different flow rates were measured for different pressure gradients in a viscose flow. As the flow rate increases, the pressure difference also increased. It can be observed that there are a direct correlation and relationship between the flow rate and the pressure difference. The core plug's absolute permeability was measured using Darcy Equation. Absolute permeability does not depend on fluid characteristics but only on media properties. The sample container contains a more significant amount of sand, decrease the permeability, and therefore requires high pressure for fluid flowing within the sample.

INVESTIGATION OF LONGITUDINAL STABILITY PROCESS AT ROLLING WITH STRIP TENSION

Earlier in the works, a qualitative construction of the diagram of changes in longitudinal normal stresses in the case of thin-sheet rolling with strip tension was proposed.. On the basis of the proposed stress distribution, the internal longitudinal forces were determined in a dimensionless form. Knowing these values, it is possible to determine the average resultant longitudinal force of the plastically deformed metal during rolling with the strip tension. It is shown that the value of the mean resulting internal forces is a more stringent boundary condition for the rolling process than the equality of the angle of the neutral section to zero.In this work, the influence of the strip tension mode on the ultimate stability of the metal in the rolls was determined, as well as the limiting condition of rolling, the change in the moment in the deformation zone and the angle of the neutral section. The theoretical analysis was carried out proceeding from the solution of the equilibrium equation with the specific friction forces specified by the Coulomb model. Using the technique proposed in previous works, we studied the effect of the magnitude and mode of strip tension on the longitudinal stability of the sheet during continuous rolling. It is shown that the rear tension has a significant effect on the average resultant longitudinal internal forces, and thereby predetermines the boundary conditions of the rolling process. The boundary conditions of deformation in a steady-state process presented in this work and generally accepted in theory differ significantly, which should be taken into account when developing a technology for continuous sheet rolling.

A Parametric Investigation of Corneal Laser Surgery Based on the Multilayer Dynamic Photothermal Model.

Corneal laser surgery is a widely used method for the treatment of ocular myopia, hyperopia, and astigmatism. Although it is a well-established technique, the photothermal properties of the cornea are often overlooked, causing unexpected changes in temperature during laser irradiation. Therefore, there is a need for further investigation of the temperature response of the cornea under laser irradiation. In the present work, a photothermal corneal numerical model is presented, assuming the stratification of the cornea with laser ablation in an uncoagulated layer, a coagulated layer, a dehydrating layer, a dried layer, and a carbonized layer. The modified Pennes' bioheat transfer equation and Lambert-Beer's law are applied to simulate heat transfer in the corneal tissue during laser irradiation. And the corneal dynamic photothermal parameters are considered in the proposed model. The central surface temperature, the boundary and thickness of each layer, and the thermal damage during laser irradiation are investigated. From the model, it was found that in the steady-state process, the thickness of the coagulated layer was 2.6, 14.4, and 52.4 times larger than that of the dehydrating layer, the dried layer, and the carbonized layer, respectively. The thickness of the corneal thermal damage gradually increased, and reached a peak of 0.196 mm at about 18.2 ms. Subsequently, it sharply decreased by 0.01 mm before stabilizing. On this basis, the influence of laser intensity is investigated. The parametric investigation and analysis presented provide a theoretical basis for corneal laser surgery, which can be used to improve our understanding of laser-tissue surgery.

Experiments and simulation of varying parameters in cryogenic flue gas desulfurization process based on Aspen plus

The study of flue gas desulfurization is of great significance to environmental protection. With the principle that sulfur dioxide (SO2) can be liquefied with the cooling of flue gas and further be removed with gas-liquid separation, a cryogenic desulfurization process was designed based on Aspen plus. The steady state process was simulated by using appropriate property methods included in Aspen plus, and the two-stage cryogenic desulfurization test bench was set up, to carry out the cryogenic process experiments. To explore the rule of cryogenic desulfurization and determine the appropriate process parameters, the influence of temperature, pressure, concentration of SO2 and the water vapor volume fraction were analyzed. It was found that the desulfurization efficiency can be improved from 33% to 73.2% with the temperature of fuel gas decreased from −12 °C to −45 °C, and can be further improved to the maximum of 90.2% with the cryogenic pressure increased from 0.5 MPa to 2.5 MPa. The desulfurization efficiency also can increase with the increase of SO2 concentration, but decrease with the increase of the inlet temperature. Based on the simulations and the practical application in engineering project comprehensively, the more suitable operating conditions were obtained.

Force parameters of metal deformation during sheet drawing

The aim of the work. The effect of the curvature of the rounding of torus surfaces during the formation of a cylindrical product (glass) is investigated, taking into account the plastic thinning of the deformable material at the end edges of the matrix and pressing punch. Methods. The existing scheme for determining the power parameters of sheet drawing is analyzed, based on the assumption of the implementation of some abstract stress state in the material; mainly conditional tensile strength. At the same time, the possibility of forming the product without destruction determines the obvious overestimation of the stress level. A mathematical model of the volumetric stress state of the metal is being developed, which makes it possible to assess the deformation and stress state during the formation of a cold-drawn product, i. e. the folding of the sheet blank along the end radius of the rounding of the pressing punch and the steady-state process of drawing the blank into the deformation zone with successive bending/straightening of the material along the edge of the matrix are considered. The level of radial stresses during folding and stretching of sheet material is estimated, taking into account its strain hardening and thinning, which determine the forming force. The obtained results will make it possible to simulate the stress-strain state of the metal during the development of sheet drawing technology: to establish the amount of thinning, to estimate the level of radial stresses in the formation of rounding of torus surfaces along the end edges of the matrix and the pressing punch, as well as to determine the power parameters of the formation, which will prevent the destruction of the pulled part, guaranteeing obtaining high-quality products and more accurately choosing the deforming equipment.

Thermal Performance and Numerical Simulation of the 1-Pyrene Carboxylic-Acid Functionalized Graphene Nanofluids in a Sintered Wick Heat Pipe

Experimental and numerical modeling of a heat pipe included with a phase change heat transfer was developed to assess the effects of three parameters of nanofluid, heat pipe inclination angles, and input heating power. Distilled water (DW) and 1-pyrene carboxylic-acid (PCA)-functionalized graphene nanofluid (with concentrations of 0.06 wt%) were used as working fluids in the heat pipe. A computational fluid dynamic (CFD) model was developed for evaluation of the heat transfer and two-phase flow through the steady-state process of the heat pipe. It was found that inclination significantly affects the heat transfer of the heat pipe. Maximum increment of thermal performance in the heat pipe reached 49.4% by using 0.06 wt% of PCA-functionalized graphene as working fluids. The result associated with this comparison indicates that the highest deviation is less than 6%, consequently confirming that the CFD model was successful in reproducing the heat and mass transfer processes in the DW and nanofluids charged heat pipe. The results of CFD simulation have good agreement between predicted temperature profiles and experimental data.

The influence of lignocellulose on biomass pyrolysis product distribution and economics via steady state process simulation

Pyrolysis is one of the most commonly used methods for deriving renewable energy from biomass and is the first step of many thermal processes. A simulation model was developed in SuperPro Designer (SPD) to simulate the pyrolysis of biomass and its individual lignocellulosic components. The model was used to study the pyrolytic behaviours of biomass, predict product yield and to investigate the economic aspects of biomass pyrolysis. It is a more comprehensive and updated version of existing models detailing individual mechanisms during reaction. The proposed model has been verified using experimental data and counter-verified using literature-obtained experimental values. In both cases, the model predicted values within 10 % of the actual data. The model was then used to predict the pyrolysis of a matrix of 75 samples with varying cellulose, hemicellulose and lignin compositions. Results showed a clear product distribution which is heavily influenced by the biomass lignocellulosic components. Biomass with high cellulose content would lead to products rich in bio-oil, whilst hemicellulose-dominant biomass would yield products rich in bio-gas. Biomass with high proportion of lignin would result in products rich in bio-char. Economic evaluation and sensitivity analysis have shown that the lignocellulosic components collectively influence the economic performance of biomass pyrolysis.

Improving the Energy Efficiency for Propane Recovery from Natural Gas using Pinch Technology: A Case Study

Process integration (PI) techniques is an efficient approach to increase the profitability due to reduction in energy, water and raw materials consumption, reduction in greenhouse gas (GHG) emissions, and in waste generation. The PI method, pinch technology is certainly the most widely used in industrial processes. When planning a new plant or revamping an existing plant it is very important to understand and select the right process to minimize capital and operating costs. This research was directed to investigate the reduction of energy consumption in propane recovery units that process natural gas produced from wells existing in the Egyptian western desert fields. The first step was process simulation of the existing gas processing plant using AspenHysys8.3 steady state process simulation program. Next, pinch technology has been adopted in order to achieve minimum hot and cold utilities and save capital cost of the process. Target utilities were calculated using pinch analysis in the Aspen energy analyzer program. Modifications in heat exchanger network could result in savings of 8.3% in hot utility, 6.5% in cold utility of the existing plant and of 46.7% in capital cost for a grass root plant.

Secondary Reduction of Refractory Metal near Smooth Cathode during the Salt Melt Electrolysis. 3. Numerical Reproducing of Natural Experiment with the Nb Cathodic Reduction in KNaCl2–NaF–K3NbF7 Melt

In terms of the model of steady-state process of a refractory-metal ion secondary reduction with an alkali (or alkali-earth) metal formed on a smooth cathode during salt melt electrolysis, numerical reproducing of a natural experiment is carried out. The model calculations are based on the polarization measured during the cathodic reduction of Nb in chloride―fluoride melt: [Nb] = 2.4 mol %, 800°C, current density i up to 5.4 A/cm2. On a smooth cathode in the overvoltage range from 0.21 to 0.41 V (i = 0.75―1.17 A/cm2), the reduction mechanism is shown to completely change from primary to the secondary reduction. The secondary reduction zone is located inside the diffusion layer and moves away from the cathode with increasing i. Even at maximal i, this zone remains inside δ (δ is the thickness of the diffusion layer): with i = 0.96 A/cm2, the coordinate of the maximum of the secondary reduction rate xm = 0; with i = 5.4 A/cm2, xm = 0.93δ (in the experiment, the value of i at which xm ≥ δ was not achieved). At i = 5.4 A/cm2, the fraction of secondary reduction in the bulk is insignificant, ≈10−5 A/cm2. The δ vs. E curve is calculated: when E is shifted from the equilibrium value toward the negative values, |i| increased from zero and higher, whereas δ first decreased by an order of magnitude and then increased. Correspondingly, the limiting diffusion current is not constant at a constant Nb concentration in the bulk. This is the reason of uncertain limiting current on steady-state cathodic polarization curves during the electrolysis of metals in melts. A hypothesis is proposed on the dependence of the Nernst diffusion layer thickness near the cathode on the current density exceeding the limiting diffusion current density under the conditions of secondary reduction.