Vol 25, No 2 (2021)
Mechanical Engineering and Machine Science
Development of a welded structure and a technology for manufacturing a smoke valve casing ID 2000 for use in a blast furnace
Abstract
The aim of this work is to develop a welded structure and a technology for manufacturing a smoke valve casing ID 2000 for use in a blast furnace to substitute the previously used cast design from 35L steel. The proposed large-size structure (3742 x 3020 x 3275 mm) should provide a strong and tight connection of three thick-walled (to 40 mm) rolled shells. The development of the structure and its elements was carried out using three-dimensional modelling in the Compass-3d software. The joining zones of the shells are designed as bent transition elements with a double curvature. It was found that the use of technological allowances when bending the cylindrical shells of sectors makes it possible to obtain parts with the required accuracy (a deviation in diameter not higher than 5 mm). The rolling of the shells having a complex curved line of joining can be performed on a rectangular workpiece. A curved joining line with the sections having a length of 150-170 mm and cross-connections of 50-70 mm is cut out on the workpiece using a computerized flame-cutting machine. It was shown that the removal of the cross-connections by manual gas cutting and preparation of edges for welding can be performed only after rolling and welding of the straight joint of the shell. Techniques for fitting the double-curved segments during assembling using special hydraulic struts were elaborated. These techniques were used to develop a technology for manufacturing a welded casing structure. Due to the optimization of the casing design, its weight was reduced by 5.5% compared to that produced by casting. Using the developed technology, two valves were manufactured to replace obsolete valves at the largest blast furnace (5500 m3) in Europe "Severyanka", PJSC Severstal. The described technical solutions provided a significant reduction in the labour intensity of manufacturing the presented structure, at the same time as ensuring its high quality and optimized weight compared to that produced by casting.
iPolytech journal. 2021;25(2):148-160
148-160
Multi-factor influence on the roughness of the finished surface
Abstract
The aim of this work is to develop a novel approach for ensuring the quality of the finished surface based on a multi-factor model. The proposed model can take into account most of the machining process parameters. The main parameters include cutting conditions, dynamic stability of the cutting process, thermal effects in the cutting area. The development of a multi-factor model was based on a literature review and experimental data obtained from the cutting force analysis and colour pyrometry. The data obtained were summarised into a unified multi-factor model. We analysed the key literature sources and summarised the experimental data and findings to assure finished surface quality when controlling one of the input parameters of the machining process. It was shown that the surface quality (roughness) can be achieved by applying different machining parameters. They include the rational cutting conditions, a change in the geo m-etry of a cutting tool, reducing the relative spacial dynamic vibrations of the tool relative to the working surface of the raw part, using the methods influencing the physical and mechanical properties of the processed materials. It was established that the process dynamic stability, the cutting conditions or the chip formation process can be used as an input parameter. The proposed scheme of multi-factor influence of processing parameters on the output parameter - the surface roughness - applies to any materials under processing. The created model takes into account all input parameters of mechanical processing. It aims at the quality management of the finished surface based on the required performance characteristics of the items. Based on the proposed multi-factor scheme, we plan to create an adaptive system capable of controlling the mechanical processing based on a computer numeric control machining centre.
iPolytech journal. 2021;25(2):161-171
161-171
Power Engineering
Influence of the weight coefficients of measurements on the consistency of the assessment and calculation results of the power supply system steady-state operation conditions
Abstract
The aim of this work is to develop an improved procedure for assessing the state of power supply systems based on adjusting the weight coefficients of measurements. To this end, non-linear optimisation methods were used. The control equations and the solution of the simultaneous linear equations were performed using the Crout method. The results of the calculation of the electrical power steady-state mode were considered as a reference. The lower the difference between the evaluation and steady-state calculation results, the higher the accuracy of the overall state assessment procedure. The problem of correcting the weight factors is set and solved as a nonlinear optimisation problem, where the optimisation parameters are taken as the dispersion of the measurements. The objective function was formulated as follows: to minimise the measurement evaluation dispersions that are part of a single control equation by maximising the active power measurements dispersion in the swing bus of the power supply system. In this study, limitations in the form of equation and inequality are monitored. The problem of optimising the dispersions is solved after the first iteration of the state assessment; starting with the second iteration, the state assessment is performed with new measurement weight factors. The calculations were performed on a 6-node test circuit. The control equations are drawn from the current measurements. The measurements data on the selected control equation of the test circuit are used to calculate the target function. The accuracy of the dispersions redistribution and their extreme values are controlled by the limitations. The results showed that, when adjusting the dispersion of measurements, the power assessments at all nodes are closer to the steady-state mode calculation results.
iPolytech journal. 2021;25(2):172-182
172-182
Mathematical modelling of the CHP plant-10 power unit No 5 of “Baikal Energy Company” LLC to assess the efficiency of its modernisation
Abstract
The work aims to study the effect of changes in the drain scheme of the low-pressure regeneration on the energy and economic efficiency of the CHP plant-10 power unit No 5 of “Baikal Energy Company” LLC. In this study, we used a mathematical model of the power unit adjusted to the measurements results. The mathematical modelling of the power unit was performed using the “Computer-assisted programming system” application package. The created matematical model of the heat and power plant was tailored to the current state of the study object according to the three-stage identification procedure of the mathematical model parameters. We proposed a cycle arrangement under which three streams of the low-pressure drainages were redirected to the pump suction of the low-pressure heater. The improved mathematical model of the power unit allows the calculation of the parameters of both the existing and proposed cycle arrangements. According to the calculations, the temperature difference between the main condensate after the low-pressure heater 1 and the investigated drains after mixing is minimal and amounts to 3.2 °C. The suggested modernisation increases the energy efficiency of the power unit by 0.007% under the nominal operating conditions of the existing and proposed thermal circuit. In addition, the specific standard fuel consumption for electric generation is reduced by 0.052 g.s.s.f./kWh. The operating costs to implement the proposed engineering solutions amounted to 34,191 roubles. Considering the annual power plant extensive consumption factor, the payback period of the proposed modernisation will be 5.5 months. The savings for the first operation year are estimated at 18,423 roubles, based on the rate of return and depreciation expenses. The proposed approach combines mathematical modelling of operating power plants with a technique of increasing the efficiency of technical decision-making. The proposed versatile approach can be used for the modernisation of CHPs and other plants.
iPolytech journal. 2021;25(2):183-195
183-195
Estimation of power consumption when trapping finely-dispersed particles in a separator with coaxially-arranged pipes
Abstract
This article sets out to estimate power consumption when trapping finely-dispersed particles of silicon dioxide using a separator with coaxially-arranged pipes, as well as the efficiency of such an installation. To this end, a numerical simulation of the movement of a gas flow with finely-dispersed particles of silicon dioxide through a separator with coaxial pipes was carried out in the ANSYS Fluent software. During the experiments, the inlet gas flow rate varied from 5 to 10 m/s, while the width and height of the rectangular slit ranged 2.1-8.7 and 10-30 mm, respectively. It was shown that the maximum efficiency of collecting finely-dispersed silicon dioxide particles and the minimum power consumption required for pumping the gas flow through the installation largely depends on the formation of a stable vortex structure in the interpipe space. The research showed that the optimal inlet gas flow rate equals 7.5 m/s. At this rate, the efficiency of particle collection corresponds to higher rates with a devia tion of ± 6%. In this case, the pressure loss is 1.74 times lower than that at higher rates. In order to achieve an efficiency of at least 90% with the height of the rectangular slit from 10 to 30 mm, the Stokes numbers must correspond to values of more than 50. The power consumption required for pumping a gas containing silicon dioxide particles through a separator equipped with coaxial pipes comprises from 1.9 to 31.2 W at the inlet gas flow rate of 7.5 m/s. In this case, the parameters of the rectangular slit are as follows: width - from 2.1 to 8.7 mm, height - from 10 to 30 mm. The use of separators with coaxially-arranged pipes in technological lines based on plasma technologies can become an alternative to installations for fine gas purification.
iPolytech journal. 2021;25(2):196-206
196-206
Improving the waste utilisation efficiency of combined heat and power plants by increasing the performance of dry-ash output units
Abstract
The study aims to improve the efficiency of waste utilisation from the coal-fired power industry based on an analysis of the dry-ash output unit operating at the Novo-Irkutsk Combined Heat and Power Plant, JSC “Irkutskenergo”. The unit was tested under various operating conditions of steam generating blocks following the standard methods adopted at the enterprise. The tests showed that the station steam generating block No. 3 (with a steam load of 409.2 t/h and an electrostatic precipitator efficiency of 90.46%) provided an ash supply efficiency of 7.10 t/h. When the ash is supplied from the steam generating block No. 4, operating at a steam load of 421.8 t/h and an electrostatic precipitator efficiency of 94.72%, the ash supply efficiency amounts to 9.19 t/h. Under the simultaneous operation of the steam generating blocks No. 3 and 4 at a steam load of 397.6 and 380.7 t/h, respectively, and an electrostatic precipitator efficiency of 90.46 and 94.72%, respectively, the unit efficiency was 14.23 t/h. As a result, limitations in the unit operation were identified. Thus, the airspeed in the pneumatic ash pipeline during ash transporting was 8.0-8.5 m/s, which facilitated the operation of the dry-ash output unit in a pulsed cycle. It was, therefore, recommended to increase the airspeed by accelerating the flow rate through the jet pump or by using a smaller diameter pipe. The conducted analysis showed that the efficiency of the dry-ash output unit depends mainly on the steam capacity of steam generating blocks, as well as on the flue gas cleaning efficiency in the steam generator electrostatic precipitators. The obtained results were used to determine the technical state, efficiency and reliability of the dry-ash output unit of the Novo-Irkutsk Combined Heat and Power Plant.
iPolytech journal. 2021;25(2):207-219
207-219
Evaluation of the effect of wind-operated power plants on the total inertia of an electric power system
Abstract
This paper is aimed at determining the effect of a variable number of Type 4 wind turbines in the total generation of the corresponding electric power system on the parameters of an asynchronous regime of such a system. Processes occurring in an electric power system were simulated using an all-mode real-time simulation complex of electric power systems constituting a multi-processor software and hardware system. A model of an electric power system was developed, which, in addition to conventional power sources, included a wind-operated power plant combining a variable number of Type 4 wind turbines. The automatic control system of the simulated wind-operated power plant comprised a control loop (in terms of active power and voltage) equipped with an additional regulator of virtual inertia. An analysis of changes in the parameters of the asynchronous regime using a virtual inertia algorithm showed that the time of its advancement along the protected line was reduced maximally by 0.1 s. However, the time of the first cycle of asynchronous motion between two generators in the post-emergency regime increased by 2 times. Thus, for a wind-operated plant with a capacity of 100 MW, the time of asynchronous motion was 0.36 sec and 0.74 sec without using and when using a virtual inertia algorithm, respectively. It was experimentally confirmed that an increase in the power of a wind-operated power plant leads to a decrease in both the time of advancement of the asynchronous regime and the time, during which conventional generators transit from the synchronous regime. The latter was evidenced by the effect of Type 4 wind turbines on the value of total inertia, which ranged from 8.746 to 5.478 s. A study of the virtual inertia algorithm confirmed its impact on the electromechanical transient processes in power systems. The most favourable effect was noted at a virtual inertia value of 2 s and a wind-operated power plant capacity of 100 MW.
iPolytech journal. 2021;25(2):220-234
220-234
Metallurgy
On the question of using solid electrodes in the electrolysis of cryolite-alumina melts. Part 3. Electric field distribution on the electrodes
Abstract
The aim of this work is to identify the theoretical limitations of molten salts electrolysis using solid electrodes to overcome these limitations in practice. We applied the theory of electric field distribution on the electrodes in aqueous solutions to predict the distribution of current density and potential on the polycrystalline surface of electrodes in molten salts. By combining the theoretical background of the current density distribution with the basic laws of potential formation on the surface of the electrodes, we determined and validated the sequence of numerical studies of electrolytic processes in the pole gap. The application of the method allowed the characteristics of the current concentration edge effect at the periphery of smooth electrodes and the distribution of current density and potential on the heterogeneous electrode surface to be determined. The functional relationship and development of the electrolysis parameters on the smooth and rough surfaces of electrodes were established by the different scenario simulations of their interaction. It was shown that it is possible to reduce the nonuniformity of the current and potential distribution on the initially rough surface of electrodes with an increase in the cathode polarisation, alumina concentration optimisation and melt circulation. It is, nonetheless, evident that with prolonged electrolysis, physical and chemical inhomogeneity can develop, nullifying all attempts to stabilise the process. We theoretically established a relationship between the edge effect and roughness and the distribution of the current density and potential on solid electrodes, which can act as a primary and generalising reason for their increased consumption, passivation and electrolytic process destabilisation in standard and low-melting electrolytes. This functional relationship can form a basis for developing the methods of flattening the electric field distribution over the anodes and cathodes area and, therefore, stabilising the electrolytic process. Literature overview, laboratory tests and theoretical calculations allowed the organising principle of a stable electrolytic process to be formulated -the combined application of elliptical electrodes and the electrochemical micro-borating of the cathodes. Practical verification of this assumption is one direction for further theoretical and laboratory research.
iPolytech journal. 2021;25(2):235-251
235-251
Research into the chemical composition of refinery slag from silicon production for its efficient recycling
Abstract
The aim was to investigate the chemical composition of refinery slag obtained during silicon production in order to identify approaches to its further recycling. Research samples were collected from the slag remained after oxidation refining at the JSC Silicon (AO Kremny), RUSAL (Shelekhov, Irkutsk Oblast). The methods of X-ray phase, X-ray fluorescence, metallographic and scanning electron microscopy were employed to investigate the chemical composition of the samples. It was found that the refinery slag under study includes such basic components as elemental silicon, its carbide and oxide, as well as elemental carbon. It was shown that silicon carbide is the product of incomplete reduction, resulting from melting silica-containing ores in a smelting furnace. According to the conducted X-ray fluorescent analysis, the samples also contain (wt %): Ca - 7.40; Al - 3.80; Fe - 0.30; Ba - 0.19; K - 0.14; Na - 0.09; Sr - 0.09; Mg - 0.08; Ti - 0.05; S - 0.02. Calcium and aluminium are present in the slag mostly in the form of oxides. Complex oxides of an anor-thite type were also found: CaO Al2O3 2SiO2. The refinery slag under study also features insignificant amounts of other metal oxides, which are released from the furnace slag forming during the smelting process. The slag produced by oxidation refining during crystalline silicon production is a technogenic raw material containing valuable components. Due to the significant content of silicon in the refinery slag (from 42% to 65%), the existing methods applied to recycle such an industrial material were analysed in terms of additional silicon extraction or production of commercial silicon-containing products, which are in demand in various industries.
iPolytech journal. 2021;25(2):252-263
252-263
Improving the efficiency of the carbothermal reduction of red mud by microwave treatment
Abstract
In this work, we studied the effect of microwave treatment of red mud briquettes containting more than 48% of Fe on the process of iron reduction under various conditions of heat treatment. Research samples were collected from red mud formed during the production of alumina from bauxite at the Ural Aluminum Smelter. The chemical composition of mud samples was examined by X-ray fluorescence analysis. The composition of initial mud and that of agglomerates obtained after treatment in microwave and muffle furnaces was studied using the X-ray diffraction method. Phase transitions and structural changes occurring under the effect of heating were studied by scanning electron microscopy. The experimental briquettes comprising red mud and charcoal were treated at 850°C and 1000°C in a microwave furnace (under the frequency of 2.45 GHz and the power of 900 W). For reference, briquettes of analogous composition were heat-treated in a muffle furnace under the same conditions. It was found that, under the conditions of microwave heating to 1000°C for 10 min, hematite is completely reduced to metallic iron after the addition of wustite. An analysis of the m i-crostructure of the samples after microwave treatment showed that the particles of metallic iron in the as-obtained pellet-agglomerates have a larger size than in those after conventional thermal heating in a muffle furnace. The metallized phases of reduced iron at the end of heat treatment in a microwave furnace create a stable durable body of agglomerates. The evidence-based parameters of the process can become a basis for designing a technology for recycling such an industrial material as red mud. The obtained high-strength pellets from red mud with a high content of reduced iron (up to 85%) may be used as an alternative charge material for ferrous metallurgy. The proposed technology for recycling red mud into pellet-agglomerates can be applied in various industries to reduce environmental impact on the production areas of alumina plants.
iPolytech journal. 2021;25(2):264-279
264-279