19 research outputs found
Standardization of recycled plastic materials for additive manufacturing
No full textPolymer extrusion-based additive manufacturing (AM) or 3D printing is a process that creates an object from a 3D model, a feedstock polymeric material in the form of wires or pellets, and a 3D-printer equipped with an extruder. Recycled polymeric materials can be used as feedstock for this technology. This thesis aims to enhance the quality of some plastic wastes to meet the standardized thermal and mechanical properties and make them suitable for 3D printing.
In the modern manufacturing revolution, which follows the concept of "Industry 4.0", AM plays a key role as an enabling technology, allowing objects with almost any geometry to be created in a more direct way. Material extrusion-based AM can be divided into fused filament fabrication (FFF) and fused granular fabrication (FGF). FFF uses high-quality filament that is not too brittle nor too flexible and has a specific and constant diameter. Therefore, only certain materials with the appropriate mechanical properties could be processed by FFF. In contrast, the FGF method is not so limited by the variety of materials, as all industrial polymers can be found as pellets. Moreover, the preparation of feedstock for FGF eliminates the second thermal processing for wire production, which always results in the reduction of the polymer's molar mass.
The most famous polymer for 3D printing is polylactide acid (PLA). It is a biodegradable and renewable thermoplastic polyester derived from renewable sources (mainly starch and sugar). The slow degradation rate in natural environments could lead to PLA accumulation. One way to utilize PLA waste is composting. But this method is used to degrade industrial waste, where a large amount of waste is collected every day, which is not the case for PLA at present. Also recycling the scraps for AM is interesting to save costs because PLA is an expensive polymer, and the construction of composting facilities currently involves large capital investments. In addition, an analysis of the normative base of AM in the polymer sphere revealed that ISO and ASTM organizations only developed seven standards for polymers in AM, without specifying the type of polymer.
To achieve the goal of the thesis study, a series of three interrelated experiments was performed. The first experiment on accelerated thermal and hydrothermal ageing of PLA was aimed at studying the temporal dynamics of polymer degradation. Thus, it was found that hydrothermal ageing for 1344 h, which corresponds to more than 1.5 years of operation under real conditions, leads to a significant decrease in the tensile strength of PLA samples. Based on these results, PLA waste from 3D printing up to 1.5 years old from the date of printing was collected for the second experiment. This debris was mixed with pure PLA in proportions of 25%, 50% and 75%, respectively. The results of this experiment showed that a material based on pure and recycled PLA is a feasible material for FFF. In the last experiment, the properties of the mixtures received in the previous research were modified by adding titanium dioxide nanoparticles, and the samples were printed using FGF. The nanocomposite based on primary and secondary (recycled) PLA with the addition of 7% titanium dioxide nanopowder has similar thermal and mechanical properties to the primary polymer, considering the standard deviation. Finally, to ensure the quality of the received nanocomposite and the reproducibility of the properties, the quality indicators have been documented in an organization standard.
Thus, in this work, it has been experimentally proved that using recycled PLA for extrusion-based AM is a realistic and achievable task, able to produce parts with improved comparable thermal and mechanical properties to those of primary PLA.La fabricación aditiva (FA) o impresión 3D basada en la extrusión de polímeros consiste en crear capa a capa un objeto a partir de un modelo 3D, un material polimérico de partida en forma de hilo o granza y una impresora 3D dotada con extrusora. Es posible alimentar impresoras 3D con materiales poliméricos reciclados. Esta tesis tiene como objetivo mejorar la calidad de algunos residuos plásticos para conseguir unas propiedades térmicas y mecánicas estandarizadas que permitan su adecuación como material de partida para la impresión 3D.
En la cuarta revolución industrial, o concepto de Industria 4.0, la FA tiene un papel fundamental como tecnología habilitadora, permitiendo crear objetos con casi cualquier geometría en un proceso más directo. La extrusión de material basada en FA se puede dividir en fabricación mediante fundido de filamentos (FFF) y fabricación mediante fundido de gránulos (FFG). FFF utiliza filamentos de alta calidad, ni demasiado frágiles ni demasiado flexibles con un diámetro específico y constante. Por lo tanto, solo ciertos materiales con las propiedades mecánicas apropiadas podrían ser procesados por FFF. En comparación, el método FFG no está tan limitado por la variedad de materiales, ya que todos los polímeros industriales se pueden encontrar en forma de gránulos o pellets. Además, la preparación de la materia prima para FFG excluye el segundo procesamiento térmico para la producción de hilo, que siempre resulta en una reducción del peso molecular del polímero.
El polímero más comúnmente usado para la impresión 3D es el ácido poliláctico (PLA). Es un poliéster termoplástico biodegradable y derivado de fuentes naturales (principalmente almidón y azúcar). No obstante, su degradación en ambientes naturales normales es lenta, lo que podría conducir a la acumulación de residuos de PLA en el medio ambiente. Una forma de utilizar los residuos de PLA es el compostaje, pero este método conlleva normalmente el uso de grandes instalaciones para degradar residuos que se generan en grandes cantidades, lo que no es el caso del PLA en la actualidad. Asimismo, reciclar residuos para su uso en AM es una opción que permitiría ahorrar costes, ya que el PLA es un polímero caro, y la construcción de instalaciones de compostaje implicaría afrontar grandes inversiones. Además, el análisis de la base de datos de normativas de estandarización resulta que, en el ámbito de la FA de polímeros, las organizaciones ISO y ASTM solo han desarrollado siete estándares para polímeros, sin especificar el tipo de polímero.
Para lograr el objetivo de la tesis, se realizó una serie de tres experimentos interrelacionados. El primer experimento sobre el envejecimiento térmico e hidrotérmico acelerado del PLA tuvo como objetivo estudiar la dinámica temporal de la degradación de este polímero una vez procesado en FFF. Por lo tanto, se encontró que el envejecimiento hidrotérmico durante 1344 h, que corresponde a más de 1,5 años de operación en condiciones reales, conduce a una disminución significativa en la resistencia a la tracción de las muestras de PLA. Sobre la base de estos resultados, se recogieron residuos de PLA de la impresión 3D de hasta 1,5 años de edad desde la fecha de impresión para el segundo experimento. Estos desechos se mezclaron con PLA primario en proporciones de 25%, 50% y 75%, respectivamente. Los resultados de este experimento mostraron que un material basado en PLA primario y reciclado es un material factible para FFF. En el último experimento, las propiedades de las mezclas recibidas en la investigación anterior se modificaron mediante la adición de nanopartículas de dióxido de titanio, y las muestras se imprimieron utilizando FGF. El nanocompuesto basado en PLA primario y secundario (reciclado) con la adición de nano-partículas de dióxido de titanio al 7% tiene propiedades térmicas y mecánicas similares al polímero primario, considerando la desviación estándar. Finalmente, para garantizar la calidad del nanocompuesto recibido y la reproducibilidad de las propiedades, los indicadores de calidad se han documentado en una norma de estandarización.
Por lo tanto, en este trabajo, se ha demostrado experimentalmente que el uso de PLA reciclado para AM basado en extrusión de polímeros es técnicamente viable, siendo posible producir piezas con propiedades térmicas y mecánicas comparables o mejoradas a las del PLA primario
MINIMIZATION OF TOXIC EMISSIONS DURING BURNING LOW-GRADE FUEL AT KAZAKHSTAN THERMAL POWER PLANT
No full textThis paper presents new results of computational experiments on the implementation of Overfire Air (OFA) technologies using an example of a combustion chamber of the BKZ-75 boiler of the Shakhtinskaya power plant (Shakhtinsk, Kazakhstan) burning high-ash Karaganda coal. The effect of mass air flow through special nozzles located above the burner level on the flow aerodynamics, temperature fields, concentration fields of carbon monoxide CO and nitrogen NO over the entire volume of the combustion chamber was studied. The studied characteristics were compared for various percentages of supplying additional air through OFA injectors: OFA is 0% (basic version), 10% and 18 %. It was shown that the installation of OFA injectors leads to a change in the field of the total velocity vector, temperature, and concentrations of carbon oxides and nitrogen. An increase in the percentage of air supplied through OFA injectors to 18% leads to a decrease in the concentrations of carbon monoxide CO by about 36% and nitrogen oxide NO by 25% compared with the base case. The obtained results will optimize the process of burning pulverized fuel in the combustion chamber of the BKZ-75 boiler, increase the efficiency of fuel burnout, reduce harmful emissions and introduce OFAtechnology at other coal-burning thermal power plants
Manufacture and Characterization of Polylactic Acid Filaments Recycled from Real Waste for 3D Printing
No full textThis paper studies the thermal, morphological, and mechanical properties of 3D-printed polylactic acid (PLA) blends of virgin and recycled material in the following proportions: 100/0, 25/75, 50/50, and 75/25, respectively. Real waste, used as recycled content, was shredded and sorted by size without a washing step. Regular dog-bone specimens were 3D printed from filaments, manufactured in a single screw extruder. Thermogravimetric analysis indicated that adding PLA debris to raw material did not significantly impact the thermal stability of the 3D-printed samples and showed that virgin and recycled PLA degraded at almost the same temperature. Differential scanning calorimetry revealed a significant reduction in crystallinity with increasing recycled content. Scanning electron microscopy showed a more homogenous structure for specimens from 100% pure PLA, as well as a more heterogeneous one for PLA blends. The tensile strength of the PLA blends increased by adding more recycled material, from 44.20 ± 2.18 MPa for primary PLA to 52.61 ± 2.28 MPa for the blend with the highest secondary PLA content. However, this study suggests that the mechanical properties of the reprocessed parts and their basic association are unique compared with those made up of virgin material
3-D MODELING OF HEAT AND MASS TRANSFER PROCESS DURING THE COMBUSTION OF SOLID FUEL IN A SWIRL FURNACE
No full textIn this work, a comprehensive study of thermal processes and aerodynamic and concentration characteristics of the combustion chamber of the boiler BKZ-75 of the Shakhtinskaya thermal power plant (Kazakhstan) are presented. A comparison of the characteristics of the combustion processes for two cases is given for the direct-flow method of supplying the mixture - the burners are located on opposite-side walls and the swirl-air mixture supplying method - burners with a swirl angle of the air mixture flow and their inclination to the centre of symmetry of the boiler by 30 degrees. The research results allow us to determine the optimal technological parameters of the studied object, to improve the methodology for the numerical study of heat and mass transfer processes in high-temperature and chemically reacting flows in the presence of turbulence, and also develop appropriate technological solutions for installing burner devices (direct-flow or swirl) in the studied combustion chamber
Numerical investigation of heat and mass transfer processes in the combustion chamber of industrial power plant boiler. Part 1, Flow field, temperature distribution, chemical energy distribution
No full textIn the present paper, the furnace chamber of the BKZ-160 boiler ofAlmaty TPP-3 (Kazakhstan) has been calculated.
The thermal characteristics of the process were studied in the form of the distribution of temperature fields and
chemical energy, and the aerodynamics of the combustion chamber was also calculated. The type of fuel, its
elementary and fractional composition, exerts the greatest influence on the course of heat-mass exchange processes
and aerodynamics. The computational experiment was carried out with two models of particle size distribution: a
polydisperse fuel flame (the particle diameter varies from 10 to 120 μm) and monodisperse fuel flame (particle size
identical and equal to dp = 60 μm). Based on the results of the computational experiments, the main regularities in
the distribution of heat fluxes in the combustion chamber volume and flow aerodynamicswere obtained. It is shown
that the greatest thermal load falls on the central region of the walls of the combustion chamber and the location of
the burner devices, which is typical for both mono- and polydisperse fuel flames. The temperature data obtained
as a result of the computational experiment showed better convergence with the empirical data obtained directly
at TPP-3. Aerodynamics of the flow for the two selected models of particle size distribution has insignificant
differences, but how they affect other characteristics of the process is one of the following tasks in view of the
authors. It should be noted that the calculation of the polydisperse fuel flame takes much more calculation time
Computer Technologies of 3D Modeling by Combustion Processes to Create Effective Methods of Burning Solid Fuel and Reduce Harmful Dust and Gas Emissions into the Atmosphere
No full textUsing numerical methods, studies have been carried out to determine the effect of the introduction of the technology of two-stage combustion of high-ash Karaganda coal on the main characteristics of heat and mass transfer processes in the furnace of the BKZ-75 boiler at Shakhtinskaya TPP (Kazakhstan). Various regimes of supplying additional air into the combustion space, the volume of which varied from 0% (traditional basic version) to 30% of the total volume of air required for fuel combustion, have been investigated using 3D computer modeling methods. The performed computational experiments made it possible to obtain the distributions of the total velocity vector, temperature fields, concentration fields of carbon monoxide CO and nitrogen dioxide NO2 over the entire volume of the furnace and at the outlet from it. The introduction of the two-stage combustion technology made it possible to optimize the combustion of high-ash coal, since in this case there is an increase in the temperature in the torch core and a decrease in it at the outlet from the furnace, which has a significant effect on the chemical processes of the formation of combustion products. Based on the results obtained, it can be concluded that an increase in the percentage of air supplied through additional injectors to 18% leads to a decrease in the concentrations of carbon monoxide CO by about 36%, and nitrogen dioxide NO2 by 25% compared to the base case. A further increase in the volume of additional air leads to a deterioration in these indicators. The results obtained will make it possible to optimize the combustion of low-grade fuel in the furnace of the BKZ-75 boiler, increase the efficiency of fuel burnout, reduce harmful emissions into the atmosphere, and introduce a two-stage combustion technology at other coal-fired TPPs
Визначення оптимальної температури окислення неізотермічних впорскувань рідких палив з використанням моделювання на основі статистичного розподілу крапель за розмірами
No full textSingle-hole injections of liquid hydrocarbon fuels (isooctane and dodecane) under high turbulence have been investigated using direct numerical simulation based on the statistical model considering the droplets’ atomization, distribution, and combustion. The study objects are the heat and mass transfer processes during atomization and combustion of liquid fuels injections within the combustion chambers of thermal engines. The temperature and carbon dioxide concentration distributions of the fuel-air mixture, the distributions of the droplets, their velocities, and the Sauter mean radius within the isooctane and dodecane oxidation in the engine’s combustion space were obtained. An investigation of the oxidizer’s initial temperature influence on the droplets’ atomization and combustion processes showed that the optimal temperature for both fuels is 900 K. The obtained modeling results were confirmed in good agreement with theoretical and experimental data.
Thanks to the integrated use of approaches from statistical theory, numerical algorithms and 3D computer modeling techniques, the results obtained are distinguished by high accuracy, efficiency in reducing computational resources, scientific novelty in the type of droplet atomization and suitability for practical application for technological solutions not only for single-hole, but also for multi-hole injections of liquid fuels and studying the jet-to-jet interaction phenomena.
The obtained research results can be applied in miscellaneous internal combustion engines development with different atomization types, which will allow us to contemporaneously settle the concerns of streamlining the combustion process, improving the completeness of fuel combustion and reducing emissions of harmful substancesЗа допомогою прямого чисельного моделювання на основі статистичної моделі, що враховує процеси розпилення, розподілу та згоряння крапель, були досліджені одноструменеві впорскування рідких вуглеводневих палив (ізооктану і додекану) в умовах високої турбулентності. Об’єктами дослідження є процеси тепломасообміну при розпиленні та згорянні впорскувань рідких палив у камерах згоряння теплових двигунів. Отримано дані про розподіл температури та концентрації вуглекислого газу в паливоповітряній суміші, розподіл крапель, їх швидкості та середній радіус Заутера в межах окислення ізооктану і додекану в камері згоряння двигуна. Дослідження впливу початкової температури окислювача на процеси розпилення та згоряння крапель показало, що оптимальна температура для обох видів палива становить 900 К. Підтверджено гарну відповідність отриманих результатів моделювання теоретичним та експериментальним даним.
Завдяки комплексному використанню підходів статистичної теорії, чисельних алгоритмів і методів комп’ютерного 3D-моделювання, отримані результати відрізняються високою точністю, ефективністю скорочення обчислювальних ресурсів, науковою новизною в типі розпилення крапель та практичною застосовністю в технологічних рішеннях не тільки для одноструменевих, але й багатоструменевих впорскувань рідких палив та вивчення явищ взаємодії струменів.
Отримані результати досліджень можуть бути використані при розробці різних двигунів внутрішнього згоряння з різними типами розпилення, що дозволить одночасно вирішувати завдання оптимізації процесу згоряння, підвищення повноти згоряння палива і зниження викидів шкідливих речови
3-D MODELING OF HEAT AND MASS TRANSFER PROCESS DURING THE COMBUSTION OF SOLID FUEL IN A SWIRL FURNACE
No full textIn this work, a comprehensive study of thermal processes and aerodynamic and concentration characteristics of the combustion chamber of the boiler BKZ-75 of the Shakhtinskaya thermal power plant (Kazakhstan) are presented. A comparison of the characteristics of the combustion processes for two cases is given for the direct-flow method of supplying the mixture - the burners are located on opposite-side walls and the swirl-air mixture supplying method - burners with a swirl angle of the air mixture flow and their inclination to the centre of symmetry of the boiler by 30 degrees. The research results allow us to determine the optimal technological parameters of the studied object, to improve the methodology for the numerical study of heat and mass transfer processes in high-temperature and chemically reacting flows in the presence of turbulence, and also develop appropriate technological solutions for installing burner devices (direct-flow or swirl) in the studied combustion chamber
Computational modeling of heat and mass transfer processes in combustion chamber at power plant of Kazakhstan
No full textIn this paper the results obtained by the method of numerical modelling of Ekibastuz coal burning in furnace of Kazakhstan Power Plant. Numerical experiment was carried out on the basis of three-dimensional equations of convective heat and mass transfer, taking into account the heat propagation, heat radiation, chemical reactions and multiphase structure of the medium to predict the influence of different water content in coal on overall furnace operation and formation of combustion products
SIMULATION OF LOW-GRADE COAL COMBUSTION IN REAL CHAMBERS OF ENERGY OBJECTS
No full textThe aim of the work is to create new computer technologies for 3D modelling of heat and mass transfer processes in high-temperature physicochemically reacting environments that will allow to determine the aerodynamics of the flow and heat and mass transfer characteristics of technological processes occurring in the combustion chambers in existing coal-fired thermal power plants of the Republic of Kazakhstan. The novelty of the research lies in the use of the latest information technologies of 3D modelling, which will enable project participants to obtain new data on complex heat and mass transfer processes when burning pulverized coal in real combustion chambers operating in Kazakhstan’s Thermal Power Plants (TPP). A numerical simulation, including thermodynamic, kinetic and threedimensional computer simulation of heat and mass transfer processes when burning low-grade fuel, will allow finding optimal conditions for setting adequate physical, mathematical and chemical models of the technological process of combustion of burning high ash coals. The computer modelling methods proposed for the development are new and technically feasible, since coal-fired power plants all over the world use all types of coal. The developed technologies will allow replacing or eliminating the conduct of expensive and labour-consuming natural experiments on coal-fired power plants
