This paper addressed the effect of copper acetate on the combustion characteristics of anthracite depending on the fractional composition of fuel and additive introduction method. Anthracite was impregnated with 5 wt% of Cu(CH3COO)2 by mechanical mixing and incipient wetness impregnation. Four anthracite samples of different fraction with d < 0.1 mm, d = 0.1–0.5 mm, d = 0.5–1.0 mm, and d = 1.0–2.0 mm were compared. According to EDX mapping, incipient wetness impregnation provides a higher dispersion of the additive and its uniform distribution in the sample. The ignition and combustion characteristics of the modified anthracite samples were studied by thermal analysis and high-speed video recording of the processes in a combustion chamber (at heating medium temperature of 800 °C). It was found that copper acetate increases anthracite reactivity, which was evidenced by decreased onset temperature of combustion (ΔTi) by 35–190 °C and reduced ignition delay time (Δτi) by 2.1–5.4 s. Copper acetate reduces fuel underburning (on average by 70%) in the ash residue of anthracite and decreases the amount of CO and NOx in gas-phase products (on average by 18.5% and 20.8%, respectively). The mechanism for activation of anthracite combustion by copper acetate is proposed.
The effect of the addition of different amounts of metal-rolling production waste (metal scale in amount of 1–10 wt%) on combustion characteristics of low-reactive solid fuels (anthracite and semi-coke) was studied. XRD analysis of the metal scale identified Fe3O4 and Mn3O4 phases along with a cubic Fe phase. The characteristics of ignition and combustion of the samples were studied via thermal analysis and high-speed video recording at heating medium temperatures of 600–800 °C (with 100 °C step) using a combustion chamber. It was experimentally found that the addition of a metal scale, regardless of its weight content, increases the fuel reactivity, as evidenced by the drop in temperature of the onset of intense oxidation (ΔTi) by 2–32 °C and the decrease in the ignition delay time (Δτi) by 0.2–2.2 s. The metal scale additive also increases the fuel combustion rate, which was evidenced by the maximum rate of oxidation (Δwmax) increasing by 0.1–2.0 wt%/min and, hence, the temperature of the end of oxidation (ΔTf) reducing by 13–68 °C. Due to combustion intensification, the carbon content in ash decreased by 55 rel% on average. The amount of CO and NOx contained in gas-phase combustion products diminished as well.
The pyrolysis processing of waste tires is a promising technology for obtaining products with high marginality. One of the possible methods of solid pyrolysis product utilization is its combustion for energy production, but this is complicated by poor reactivity and sulfur emissions. The combustion of char together with more reactive fuels could solve this problem. The current study is devoted to the combustion characteristics of waste tires pyrolysis carbon residue mixed with biomass: pine sawdust and peat. The oxidation characteristics in thermal analyzer conditions were found to change insignificantly. In contrast, 15 wt% of peat and sawdust additives was found to decrease ignition delay times in realistic conditions of combustion at 800 ◦C by 42 and 78%, respectively, while the SO2 emissions also dropped by 73 and 52%, respectively. The extra sulfur was found to be contained in ash residue in the form of CaS and CaSO4. While increasing peat concentration from 5 to 15 wt% was found to have almost no effect, the same increase for sawdust resulted into an almost proportional decrease in ignition delay times. The results obtained could be used for the integration of waste tires pyrolysis char mixtures with peat or sawdust into the energy sector.
Utilization of phenol-containing pyrolysis water (PW) formed as the by-product of biomass pyrolysis is challenging issue due to large number of various organic substances in its composition. Combustion of PW as part of coal-water fuel (CWF) is effective, but poorly studied solution, which allows to neutralize all contaminants. Current study is devoted to the ignition and combustion characteristics of CWF droplets with PW and 3 fractions obtained in different temperature ranges—<100, 100–150 and 150–200 °C. The PW was obtained by separation and sedimentation from industrial biochar-producing facility. The waste of coal facility was used as a solid component of CWF. The ignition and combustion of CWF was studied via the combustion chamber in the temperature range 500–800 °C as well as a CWF with distilled water as a reference sample. The use of PW resulted into an increase in CWF reactivity, which was reflected in a reduction in the ignition delay time (up to 50% at 500 °C and up to 90% at 800 °C) and the minimum ignition temperature (by 6.9% on average). The most prominent effect was observed for CWF with PW fraction obtained in temperature range 150–200 °C, the least—for fraction < 100 °C. The heating value of CWF due to substitution of distilled water on different PW fractions was increased by 0.1–1.4 MJ/kg. According to material and energy balances, the 16.2 wt% of PW should be used for CWF to ensure energy-sufficiency of the pyrolysis facility. Obtained results provide technical background for integration of such technology into pyrolysis technological cycle.
Актуальность: замена в существующих двигателях внутреннего сгорания с различными конструкциями впрыска и системами зажигания дизельного топлива парогазовыми продуктами пиролиза, что позволяет замеcтить для производства электроэнергии дорогое топливо пиролизным газом, полученным из биомассы, вторичных продуктов древесно-перерабатывающих предприятий и муниципальных твердых отходов. Целью данного исследования является оценка эффективности сжигания парогазовых продуктов пиролиза в двигателе внутреннего сгорания, конструктивно предназначенного для использования дизельного топлива, для возможности применения данной системы. Объекты: четырехтактные дизельные двигатели внутреннего сгорания V-образной компоновки цилиндров с турбонагнетателем и без него, работающие на парогазовых продуктах пиролиза древесных отходов. Методы: численные исследования на основе математических алгоритмов систем дизельных двигателей внутреннего сгорания без наддува и с турбонаддувом с использованием методов теплового баланса. Результаты. Разработана математическая модель и программа теплового расчета четырехтактного двигателя внутреннего сгорания с V-образным расположением цилиндров с непосредственным впрыском парогазовых продуктов пиролиза древесины в камеру сгорания с системой турбонаддува и без нее. Проведен анализ влияния частоты вращения коленчатого вала, количества цилиндров на мощность, крутящий момент, удельный расход топлива. Показано, что увеличение количества цилиндров при одном и том же рабочем объеме двигателя внутреннего сгорания приводит к росту мощности, крутящего момента, при этом снижается удельный расход парогазовых продуктов пиролиза. Отмечено, что сжигание парогазовых продуктов пиролиза в двигателе внутреннего сгорания приводит к увеличению температуры выхлопных газов относительно сжигания дизельного топлива. Для двигателя с турбонаддувом увеличение температуры выхлопных газов составляет около 50 °С, без турбонаддува - около 100 °С. Установлено, что в четырехтактном дизельном двигателе внутреннего сгорания при сжигании пиролизного газа, получаемого из древесных отходов, для выработки одинакового количества электрической энергии необходим массовый расход в 7,5-8,6 раз больше, чем дизельного топлива. Выявлено, что дизельный двигатель с турбонагнетателем более экономичен и эффективен, чем силовой агрегат без нагнетателя. При частоте вращения 3000 мин-1 для 12-ти цилиндрового двигатель с турбонагнетателем экономия расхода пирогаза составляет 11,9 %, эффективная мощность и крутящий момент на 10,0 % выше, чем у двигателя без турбонагнетателя. Одним из наиболее доступных на данный момент для сжигания пиролизного газа является четырехтактный дизельный двигатель V12 с турбо-наддувом отечественного производства ЯМЗ 845.10 с рабочим объемом 25,86 л, максимальной мощностью 537 кВт (730 л.с.), максимальным крутящим моментом 2788 Н·м при частоте вращения 1500-3000 мин-1.
The results of experimental studies of carbon materials, which are formed in the plasma of a direct current (DC) arc discharge initiated in open air from the asphaltenes of different origins, extracted from the natural asphaltite and from the oil of the Sredne-Ugutskoye Oilfield, are presented. The influence of the initial asphaltene composition on the composition and properties of the resulting carbon materials is analyzed. The initial asphaltenes and the samples of the carbon materials are characterized by the methods of X-ray diffraction, differential thermal analysis, X-ray fluorescence analysis, IR-Fourier spectroscopy, laser diffraction, transmission and scanning electron microscopy. The changes in the composition and structure of the asphaltenes are determined before and after their plasma treatment and the hypotheses are put forward concerning the chemical processes causing the changes in the molecular structure of the samples. As a result of plasma treatment of asphaltenes (100 A, 30 s), it was shown that graphitization occurs, as well as oxidation, and a decrease in sulfur content. Moreover, nanotubes and nano-onions have been detected using electron microscopy. Petroleum asphaltenes after plasma treatment give a less thermostable carbon material, but with a lower content of heteroatoms, and with a large amount of sulfur in the composition of sulfoxide structural fragments. This method is shown to be a promising technology for processing the petroleum feedstock enriched with heavy asphaltene components for the manufacture of carbon nanomaterials: nanotubes, nano-onions and polyhedral graphite.
Environmentally friendly conversion of waste and energy carriers into useful and energy-efficient products is one of the forefront areas worldwide. In this paper, we propose a new method for obtaining carbon nanomaterial and hydrogen-enriched synthesis gas by electric arc gasification of pyrolysis oil in an open-air environment without pollutant emissions. As initial samples, we used petroleum (as reference sample) and pyrolysis oil – liquid pyrolysis products of wood waste (pine sawdust), waste tires and oil sludge recycling. The choice of materials was caused by the search for new approaches to waste conversion, which will allow to obtain environmentally friendly energy and to reduce carbon footprint of various production cycles. The synthesis gas formed by electric arc gasification contained hydrogen in an amount exceeding 50 vol%. The carbon material was represented by nanosized objects with a graphite-like structure and characteristics similar to carbon black, which acted as a solid-phase product.
The paper presents an analysis of the results of an experimental study of carbon materials obtained in a direct-current arc plasma from asphaltenes isolated from light oil of the Sredneugutskoye field and combined heavy oil from Venezuelan fields, as well as asphaltenes isolated from natural asphaltite. The influence of the composition of initial asphaltenes on the composition and properties of carbon materials obtained as a result of plasma treatment has been studied. The parent asphaltenes and carbon materials synthesized from them have been examined using a set of instrumental methods: X-ray diffraction, thermogravimetric analysis, energy-dispersive X-ray fluorescence analysis, Fourier-transform IR spectroscopy, X-ray photoelectron spectroscopy (XPS), transmission and scanning electron microscopy, and laser diffraction. Changes in the composition and structure of the obtained materials after plasma processing of asphaltenes have been established. It is shown that this method can be considered promising for processing not only petroleum material, but also oil industry waste enriched in resin–asphaltene components.
В работе представлены результаты экспериментальных исследований порошковых материалов, полученных в плазме дугового разряда постоянного тока, инициированного в открытой воздушной среде. Согласно результатам анализа продукта методами рентгеновской дифрактометрии в составе продукта синтеза идентифицируется графитоподобная углеродная фаза, фаза кубического молибдена и две фазы карбида молибдена Mo2C и Mo1,2C0,8. Согласно результатам растровой микроскопии в продукте идентифицируется микроразмерная и наноразмерная составляющие, продукт состоит из 52 ± 16 вес.% молибдена, 36 ± 18 вес. % углерода, 4 ± 1 вес. % кислорода и менее чем 1 вес. % других химических элементов. Согласно данным просвечивающей электронной микроскопии углеродная составляющая представлена графитоподобной матрицей, в которую погружены частицы молибдена и карбида молибдена. В работе проведены испытания полученного порошка карбида молибдена в качестве носителя катализатора в составе водородной топливной ячейки.
In this paper, we propose a method to manufacture tantalum carbide in open air by igniting a direct current arc discharge in a graphite crucible containing a mixture of raw materials: tantalum and carbon. Carbon burns to form carbon monoxide and carbon dioxide, which serve as a gaseous medium for the synthesis process. Using experimental and analytical procedures, we have obtained the necessary parameters — current, arcing time, and mass of the raw material — to produce the NaCl-type cubic phase of tantalum carbide. Micron- and submicron-sized tantalum carbide crystals are identified in the synthesis products. The combustion parameters of the resulting tantalum carbide are determined by differential thermal analysis. The proposed synthesis method is easier to implement, more energy-efficient, and less time-consuming than the current techniques
Synthesis of high-entropy carbides (HEC) requires high temperatures that can be provided by electric arc plasma method. However, the formation temperature of a single-phase sample remains unknown. Moreover, under some temperatures multi-phase structures can emerge. In this work, we developed an approach for a controllable synthesis of HEC TiZrNbHfTaC5 based on theoretical and experimental techniques. We used Canonical Monte Carlo (CMC) simulations with the machine learning interatomic potentials to determine the temperature conditions for the formation of single-phase and multi-phase samples. In full agreement with the theory, the single-phase sample, produced with electric arc discharge, was observed at 2000 K. Below 1200 K, the sample decomposed into (Ti-Nb-Ta)C, and a mixture of (Zr-Hf-Ta)C, (Zr-Nb-Hf)C, (Zr-Nb)C, and (Zr-Ta)C. Our results demonstrate the conditions for the formation of HEC and we anticipate that our approach can pave the way towards targeted synthesis of multicomponent materials.
Представлены результаты экспериментальных исследований, посвященных получению углеродных наноматериалов в плазме дугового разряда постоянного тока, инициированного в открытой воздушной среде. Показано, что для получения квазидвумерных углеродных наноструктур заявленным безвакуумным электродуговым методом можно использовать в качестве катализатора отходы твердосплавного инструмента. Сделан вывод о совместимости процесса синтеза углеродных наноструктур и электродуговой переработки отходов на основе вольфрама и кобальта.
Актуальность исследования обусловлена возрастанием потребления нефтепродуктов и увеличением количества нефтяных отходов и остатков, в составе которых могут содержаться значительные количества высокомолекулярных гетеросодержащих компонентов асфальтенов и смолы. Стоит отметить, что асфальтены слабо подвержены биоразложению. Традиционно во многих странах способом утилизации нефтесодержащих отходов является способ их захоронения, но такой способ утилизации нежелателен, так как требует использования новых земельных участков и в конечном счете может нанести вред окружающей среде. В связи с этим возникла необходимость в поиске нового способа утилизации нефтяных отходов с возможностью получения из них ценных продуктов, которые могут быть применены в различных областях промышленности и хозяйственной деятельности, что в конечном итоге увеличит глубину переработки нефти.
Dry reforming of methane (DRM), to produce synthesis gas, is one of the most important chemical reactions used for the industrial production of hydrogen and leads to the synthesis of hydrocarbons (liquid fuels) and other valuable products. A cost-effective alternative to active and stable noble metal DRM catalysts, with comparable catalytic performance, can be composite materials based on nickel, cobalt and transition metal carbides. In this line, the present work proposes a non-standard way to obtain dry reforming catalysts of Ni, Co and Ni-Co-modified tungsten carbide (WC) produced by an electric arc method. Different amounts of nickel, cobalt and their mixtures were deposited on tungsten carbide by deposition-precipitation with NaOH (DP) and incipient wetness impregnation (IWI) methods. The resulting materials were characterized by N2 adsorption-desorption, transmission electron microscopy, energy dispersive spectroscopy, X-ray diffraction and X-ray photoelectron spectroscopy, and their performance was evaluated in DRM. The composition and preparation method of catalysts predetermined their structural, textural and electronic properties, playing a decisive role in their activity for DRM. DP-prepared 20%Ni/WC material remained resistant to oxidation, both that of the active metal (nickel) and of the tungsten carbide, as well as to coking during DRM. This sample proved to be the most active and stable among all studied materials. Possibly, the resistance to oxidation and coking was due to a more efficient implementation of the oxidation/(re)carbonization cycle on the surface of this catalyst.
The results of experiments on plasma processing of the samples of high-molecular fraction of the asphaltenes emitted from the asphaltite representing natural bitumen are reported. The asphaltite, according to its structure and properties, can serve as an analog of heavy oil residues of oil refining. The asphaltenes are treated with the plasma of an arc discharge in a laboratory reactor in ambient air. The structure and properties of the resulting carbon materials are determined by the methods of X-ray diffractometry, thermogravimetric analysis, differential scanning calorimetry, IR-spectroscopy, X-ray fluorescent analysis and laser diffraction. It is found out that during plasma processing of asphaltenes a mixture of gases consisting mainly of H2 and CH4 with CO2, CO, NO, SO2, H2S impurities is formed, and an polydisperse carbon material is formed with the structure of graphite, containing the elements present in the initial asphaltite forms: vanadium, nickel, iron, calcium, aluminum, sulfur, silicon and chlorine. The optimum modes of the arc reactor performing the plasma processing of asphaltenes (30 s and current 100 A), allowing to achieve the maximum yield of hydrogen and graphite-like material, are defined.
The paper reports the results obtained in the experimental studies of the oxidation behavior of powders based on carbon fibers (graphite) and carbides of metals of groups IV and V of the periodic table, including high-entropy carbide (HEC) TiZrNbHfTaC5. The materials were synthesized by vacuum-free electric arc method using X-ray fibrous amorphous carbon and metal oxides as a starting material. X-ray diffractometry of the synthesis products identified graphite, titanium, zirconium, niobium, hafnium, and tantalum carbides, and HEC TiZrNbHfTaC5. Scanning electron microscopy of the synthesis products showed carbon fibers with the surface modified by the above-mentioned carbides. Differential thermal analysis was performed to determine the parameters of the oxidation process of these materials; the main difference between the synthesized materials is the oxidation rate, with the lowest one demonstrated by the high-entropy carbide containing material.
In this paper, we report the experimental results obtained in slag waste processing by direct current arc discharge initiated in ambient air. The method does not employ vacuum and gas equipment, therefore increasing the energy efficiency of processing. Plasma processing of coal slag was performed at different arc exposure times: 5, 10, 15, 20, and 25 s. The obtained materials contained a significant amount of graphite, which was removed through combustion. The micropowder based on silicon carbide and aluminum nitride was obtained and then sintered by spark plasma. The bulk ceramic samples based on silicon carbide with the hardness of ~10.4 GPa were finally fabricated.
Ultra-refractory micropowder of the Hf-Ta-C system was synthesized using a DC atmospheric plasma electric arc discharge. The synthesis was carried out under the conditions of burning a DC arc discharge in an air environment due to the formation of a protective autonomous atmosphere from carbon dioxide and carbon monoxide gases. Hafnium and tantalum oxides and X-ray amorphous carbon were used as precursors. The main advantages of this method are simplicity of implementation, short time of the synthesis process, relatively low specific energy costs (less than 300 kJ / g), as well as the availability of equipment used for experiments. The results of studies have shown the possibility of synthesizing tantalum and hafnium carbides by the developed method. However, the product also contains phases of graphite and metal oxides, which is a disadvantage at this stage and a subject for further research.
Патент № 2780072 C1 Российская Федерация, МПК C08J 11/10 (2006.01) B29B 17/00 (2006.01) C01B 32/324 (2017.01). УСТРОЙСТВО ДЛЯ ПЕРЕРАБОТКИ РЕЗИНОВОЙ КРОШКИ ИЗНОШЕННЫХ АВТОМОБИЛЬНЫХ ШИН : № 2022102140 : заявл. 28.01.2022 : опубл. 19.09.2022 / Губин В.Е., Ларионов К.Б., Пак А.Я., Янковский С.А., Болатова Ж., Васильева Ю.З. ; заявитель ТПУ. – 14 с. : ил. – Текст : электронный. Губин В. Е. и др. УСТРОЙСТВО ДЛЯ ПЕРЕРАБОТКИ РЕЗИНОВОЙ КРОШКИ ИЗНОШЕННЫХ АВТОМОБИЛЬНЫХ ШИН. – 2022.
Kvashnin A.G., Nikitin D.S., Shanenkov I.I., Chepkasov I.V., Kvashnina Y.A., Nassyrbayev A., Sivkov A.A., Bolatova Z., & Pak, A.Y. Large‐Scale Synthesis and Applications of Hafnium–Tantalum Carbides // Advanced Functional Materials. – 2022. – P. 2206289. DOI: 10.1002/adfm.202206289 (Q1, IF: 19.924)
Comprehensive theoretical and experimental studies are performed to discover a new way of synthesis of Hf-Ta-C coatings. Here, an evolutionary search for stable crystal structures in the ternary Hf-Ta-C system with subsequent selective large-scale experimental synthesis of coatings using a unique plasma dynamic experimental setup is performed. Optimization of the experimental process allows us to perform selective synthesis of coatings made of hafnium–tantalum carbides with predefined stoichiometry, crystal structure, and properties. Along with more than 70 compounds, the Hf-Ta-C system belongs to ternary and quaternary carbides of group IV and V transition metals, and this study opens the door to synthesis of a large number of functional coatings composed of other carbides including high-entropy carbides.
The results of experimental studies demonstrating the possibility of obtaining boron-carbide powder by treating a mixture of carbon and amorphous boron containing a small amount of boron oxide with DC arc discharge plasma are presented. A feature of the applied nonvacuum electric-arc method for the synthesis of boron carbide is its implementation in an open air environment due to achievement of the effect of screening the reaction zone with gaseous oxide and carbon dioxide. In this case, the initial reagents are heated to the required temperatures by a DC arc discharge plasma burning in the immediate vicinity of the initial-material mixture in the cavity of the graphite crucible. The resulting material contains particles of boron carbide with a size in the submicron range, which are characterized by the “shell–core” type structure. The scheme of the discharge circuit of a laboratory reactor with horizontal arrangement of electrodes and an indirect supply of thermal energy to the initial reagents described in the paper makes it possible to significantly increase the content of the boron-carbide phase and reduce the content of the graphite impurity phase.
A method for producing titanium carbide with the use of charcoal, vegetable oil, and titanium dioxide powder as initial reagents is described. A feature of this method is that it is implemented in a hollow cathode direct current arc discharge with the effect of shielding the reaction volume from atmospheric oxygen by gases generated in the arc discharge. The possibility of obtaining a synthesis product consisting of a graphite phase and a cubic phase of titanium carbide is shown. In this case, according to scanning electron microscopy data, microsized objects were identified in the synthesis product, the morphology of which corresponded to the structure of charcoal, and the chemical composition, together with X-ray diffraction data, indicated the presence of a titanium carbide phase.
The paper presents the results of the experimental studies addressing the production of silicon carbide from glass waste by electric arc plasma processing. A feature of the method is the possibility of its implementation without the use of vacuum equipment. It is possible due to the effect of self-shielding of the reaction volume from atmospheric oxygen. This approach significantly simplifies the design of the electric arc reactor and its performance. After plasma processing of various types of glass waste (such as bottle glass, window glass, medical glass, quartz glass, parts of worn-out scientific and industrial equipment), silicon carbide based material was produced. Silicon carbide was obtained from a mixture of various glass waste at a current 200 A, where blend was first purified from unbound carbon and then was consolidated by spark plasma sintering at 1800 °C and 60 MPa pressure for 10 min. As a result, a ceramic bulk sample was fabricated from a mixture of glass waste of various origin. Such sample was characterized with hardness of 14.8 GPa, and attained density of 92.5 %. Despite a possible increase in the density due to impurities and inhomogeneities, the hardness of the fabricated sample is comparable to that of other silicon carbide based materials, including commercial ones. Since the hardness of the produced silicon carbide based material is comparable to that of commercial materials, the use of glass waste of various origin could be feasible for synthesis of silicon carbide based powders.
We proposed an efficient method toward the synthesis of higher tungsten boride WB5–x in the vacuumless direct current atmospheric arc discharge plasma. The crystal structure of the synthesized samples of boron-rich tungsten boride was determined using computational techniques, showing a two-phase system. The ab initio calculations of the energies of various structures with similar X-ray diffraction (XRD) patterns allowed us to determine the composition of the formed higher tungsten boride. We determined the optimal parameters of synthesis to obtain samples with 61.5% WB5–x by volume. The transmission electron microscopy measurements showed that 90% of the particles have sizes of up to 100 nm, whereas the rest of them may have sizes from 125 to 225 nm. Our study shows the possibility of using the proposed vacuumless method as an efficient and inexpensive way to synthesize superhard WB5–x without employing resource-consuming vacuum techniques.
The physicochemical characteristics of the carbon material produced by methane conversion in UHF discharge plasma are determined. The material is characterized by high carbon content (99.4 wt %); the calorific value is 32.7 MJ/kg; and the packing density is 25.5 kg/m3. According to X-ray phase analysis, the crystalline content of the sample is ~43%. Morphologically, it consists of spherical agglomerates (no larger than 20 μm) composed of numerous nanoparticles. The mean particle size is 80–120 nm; the specific surface is 51.2 m2/g; and the mean pore volume is 0.25 cm3/g.
This paper presents results of an experimental study concerned with vacuumless arc discharge synthesis of ultrafine molybdenum carbide-based materials. We have found discharge circuit parameters that ensure an essentially complete conversion of starting molybdenum. The synthesis product contained micron-sized crystals and graphene-like carbon structures, with molybdenum carbide nanoparticles embedded in them. We present preliminary results on the catalytic activity of the synthesized materials, without modification with precious metals.
Waste tires rubber utilization is one of the most important problems worldwide that affects environmental and energy aspects. In this work, we propose a method for obtaining ultrafine carbon product, as well as mixture of methane and synthesis gas, which is based on the generation of an electric arc plasma in an open-air environment. During arcing the resulting gas flow screens the reaction zone, which prevents the oxidation of the feedstock and synthesis products. This approach allows avoiding a vacuum and gas equipment as a part of a plasma reactor, which greatly simplifies its design and reduces the specific energy consumption. As a result of a series of experiments, two types of products were obtained: 1) ultrafine carbon powder containing micro and nanoscale objects with a graphite-like structure; 2) a mixture of gases, which contains up to 27, 15, and 3 vol% of methane CH4, hydrogen H2 and carbon monoxide CO, respectively.
The two-stage technology of porous carbonaceous material obtained via pyrolysis in inert medium with subsequent activation by steam is well known. While steam could be a suitable substance for pyrolysis as well, single-staged technology for waste tire recycling is yet to be developed. A comparative analysis of the characteristics of the carbonaceous materials obtained by the single-staged steam pyrolysis of waste tires was carried out, which could provide a theoretical background for the development of such technology. The steam pyrolysis was performed in a tubular reactor in an overheated steam medium (500°C with 5 kg/h mass flow rate). The technical characteristics of the obtained samples were evaluated in the context of their potential for further application as absorbent and raw material for rubber production according to Chemical Abstracts Service No. 1333–86-4. The composition and physico-chemical properties of the obtained samples were studied using BET and thermogravimetric analysis, atomic emission, transmission and scanning electron microscopies, Raman, X-ray diffraction, and photoelectron spectroscopies. The results revealed that the structure and properties of all obtained carbonaceous material samples were similar. The samples consisted of amorphous carbon (with a disordered graphite lattice) and contained a significant amount of metal oxides. According to experimental data, zinc was present in the form of ZnO with a binding energy of 1022.4 eV, while sulfur was observed in the form of sulfide and oxysulfide with binding energies of 161.8 and 163.2 eV, respectively. According to electron microscopy, the morphology of samples was represented by a set of spherical agglomerates comprising nanosized particles. According to the BET analysis of the samples, the specific surface area varied in the range between 52.0 and 66.0 m2/g and the pore volume values were within a range of 0.53–0.87 cm3/g, while the average pore size varied from 412 to 527 Å.
The paper shows the feasibility of synthesizing micro- and nano-sized particles of binary metal carbides (Me–C) and high-entropy carbide (HEC) TiZrNbHfTaC5 by vacuum-free electric arc method. The method is based on the effect of self-shielding of the reaction volume from atmospheric oxygen by carbon monoxide CO, which is generated during arcing in air. The synthesis results in a solid solution with a NaCl-type carbide with a cubic lattice, which simultaneously contains atoms of titanium, zirconium, niobium, hafnium, tantalum, and carbon. The lattice parameter of the HEC TiZrNbHfTaC5 phase is ∼4.532 Å that is in line with the known data on this compound. The synthesis product contains micro-sized particle agglomerates of transition metal carbides. The synthesis products also contain nano-sized particles with a shell-core structure, in which the core can consist of metal carbide (TiC, ZrC, NbC, HfC, TaC) or HEC TiZrNbHfTaC5, and the shell is a graphite phase.
The paper presents experimental studies on the synthesis of materials based on molybdenum carbide, which can be used as a catalyst for hydrogen production by water splitting. We successfully carried out experiments to scale up the process, namely, the amount of the synthesized product was increased by 4 times with the same parameters of the experimental setup. In this case, the specific energy decreases taking into account the increase in the mass of the product. The energy intensity of the material obtained has been reduced from 520 kJ/g to 130 kJ/g.
This work presents the results revealing the possibility of obtaining a cubic phase of silicon carbide with features of a biomorphic structure. Renewable plant raw materials were used as a source of carbon, in particular, pyrolyzed sawdust, which is a waste of a timber enterprise. Silicon dioxide powder was used as a source of silicon. The synthesis was realized using DC arc discharge plasma initiated in an open air. In this case, the oxidation of the synthesis products was prevented due to the effect of the reaction volume self-shielding from atmospheric oxygen. It was possible due to the generation of protective gaseous medium predominantly consisting of carbon dioxide and monoxide. The dependences of the product phase composition on the supplied energy and composition of initial components were established. The synthesis product was characterized by a significant excess of carbon, which was a caused by the erosion of the electrodes. After removal of chemically unbound carbon from synthesis product by annealing in an atmospheric furnace at 850 °C, obtained powder was sintered by the spark plasma sintering method. In the result, a bulk ceramic sample was obtained in which the only one crystalline phase of silicon carbide with a lattice parameter of 4.359 Å was identified.
The slow pyrolysis is a viable technology for the production of different solid products. However, its effective implementation requires utilization of material flows occurring in gaseous and liquid phases. Because liquid products of slow pyrolysis, typically referred to as bio-oil, are just by-product, their combustion characteristics are poorly studied. Current article presents the comprehensive experimental studies of the technical conditions of the slow pyrolysis bio-oil retrieved at commercial pyrolysis facility. The studies cover the composition and physicochemical properties of bio-oil, spraying characteristics, droplet ignition and combustion, and analysis of gas-phase combustion products. The bio-oil sample had relatively high density (ρ = 1180 kg/m3) and dynamic viscosity (184.16 mPa s). The pour (Tpp = 7 °C) and flashpoint (Tfp = 133 °C) were also high. The lower heating value was 25.01 MJ/kg. The majority of properties was consistent with requirements of ASTM 7544, while viscosity, pour point, and ash content were not. The study on bio-oil spraying was carried out using hydrodynamic setup equipped with pneumatic mechanical nozzle and cross-correlation camera. The fuel jet had a homogeneous structure with an average droplet diameter exceeding 0.2 mm. Ignition and combustion were studied using combustion chamber with varying the heating medium temperature in the range of 400–800 °C with a 50 °C step. The ignition delay and total combustion times of the bio-oil sample were exponentially decreasing with increasing heating medium temperature. In the temperature range of 400–500 °C, the thermal transformation proceeded in the oxidation mode, while at temperatures above 500 °C, the flame with periodic formation of microexplosions was observed.
The results of spraying characteristics of alcohol-coal-water slurries are presented. It has been experimentally proved that the lowest viscosity value of the studied slurries varies from 54 to 329 mPa s. The density value of alcohol-coal-water slurries decreases to 1130 kg m−3 when the content of isopropyl alcohol in the fuel composition is 8 wt %. The largest value of jet spraying angle corresponds to alcohol-coal-water fuel with an isopropyl alcohol content of 8 wt %. The number of sufficiently large droplets decreases in comparison with a typical two-component coal-water fuel. The calorific value of alcohol-coal-water slurries rises when the third liquid fuel component is introduced into the composition of coal-water fuel.
The technical characteristics of liquid hydrocarbons obtained by steam pyrolysis of the used automobile tires were studied as well as the features of their combustion process. Steam pyrolysis of ground tires was carried out in a tubular reactor using superheated steam with 500 °C temperature and 5 kg/h mass flow rate. The obtained characteristics were compared with a traditional liquid fuel oil. The technical characteristics were determined via the standard analytical methods. An ignition and a combustion of liquid hydrocarbon samples were carried out in the combustion chamber at different temperatures of heating medium Tg = 450–700 °C. Gas-phase combustion products were analyzed using a flow-through gas analyzer. It was found that liquid hydrocarbons were characterized by a low pour point (− 43 to − 52 °C) and calorific value comparable to traditional fuel oil (40.56–43.30 MJ/kg). In addition, the studied samples of liquid hydrocarbons were characterized by a lower ignition delay time (by 56%, on average) and flame burning time (by 30%, on average). Combustion process of the studied samples (including traditional fuel oil) was accompanied by the formation of micro-explosions. The liquid hydrocarbons obtained by pyrolysis of used tires were found to be suitable fuel for energy equipment in many aspects superior to traditional liquid fuel. Results presented could be used to involve liquid by-products of steam pyrolysis of different Russian used tires into energy industry.
In the modern realities of the energy market, the use of coal-water slurries with liquid industrial waste is a promising way to solve several problems (economic, environmental and energy). This article presents the results of experimental studies of the characteristics of spraying and ignition of promising coal-water slurries. Lignite, water and liquid pyrolysis products of wood waste were used as fuel components. It was found that substitution of 10% of coal with liquid pyrolysis products of wood waste decreases the dynamic viscosity of the fuel by 3.2 times in comparison with two-component coal-water fuel. Density for all the slurries studied (changes in the mass of the components: coal – from 40 to 50%; water – from 40 to 50%; pyrogenetic liquid – from 0 to 10%) differs by no more than 22%. Introduction of liquid pyrolysis products of wood waste into the coal-water fuel composition significantly changes the jet structure. Its characteristic parts – core, middle and peripheral zones – increase. The number of droplets with high velocities (30–40 m/s) increases significantly. The average size of fuel droplets in the jet decreases by 5–12% in comparison with two-component coal-water fuel. Ignition delay time of a single droplet of slurry at oxidizer temperature 1273 K increases by 23% in comparison with two-component coal-water fuel when 10% of coal is replaced by liquid pyrolysis products. In the case of water substitution with the same amount of the third component, the ignition delay time at an oxidizer temperature of 1273 K decreases by 26%. The most preferred of the studied coal-water fuels, from the point of view of application in the energy sector, are those in which water is replaced by the same amount of liquid pyrolysis products of wood waste.
Experimental results of the influence of thermal preparation of coal-water slurries on their rheological properties and spraying characteristics are presented. The slurry density was found to increase by 14% at a temperature of 293 K with the substitution of water in coal-water fuel with a similar by weight amount of pyrogenetic water (no more than 25%). Preliminary thermal preparation of coal-water slurries up to 333 K reduces its density by 7%. The experimental results showed that the greatest influence of thermal preparation of the studied slurries on their dynamic viscosity is characteristic of the temperature range from 293 to 323 K. At such temperature values, a decrease in the slurry viscosity is by 17–20% in comparison with two-component coal-water fuel. Preheating of slurries before spraying, in the temperature range from 293 to 333 K, makes it possible to increase the jet spraying angle by 21–29% compared to conventional two-component coal-water fuel at a temperature of 293 K. The velocity of droplets of the investigated coal-water fuels in the range of changes in their initial temperature from 293 to 333 K varies slightly. The difference is no more than 5%. Increase in the pyrogenetic water concentration in coal-water fuel of more than 25% by weight is impractical for lignite due to the dramatic increase in its viscosity. In the studied range of the third component concentration of the slurry, increase in the average size of fuel droplets is about 8%. Preheating of CWF before spraying can significantly reduce the average size of the droplets. The changes are 5–9% in comparison with coal-water slurry at a temperature of 293 K. Thermal preparation of slurries, according to the results of thermal imaging studies of coal-water fuel jet, affects the thermal contour of the jet and the geometry of its temperature zones.
Coal-water slurries have been actively studied during the last decade due to the fact that much less oxides of sulfur, nitrogen and carbon are formed during their combustion in furnaces of power boilers compared to coal. The main problem that hinders the widespread implementation of such fuels in the energy sector is their long (up to 30–40 s) ignition delay times. Significant (up to 56%) reduction of the ignition delay time is possible when a small (up to 8% by weight) amount of available and relatively inexpensive liquid combustible organic compounds is added to the suspension. The purpose of this work is to substantiate the possibility of significant reduction of the ignition delay times of coal-water fuels by introducing a third component into the coal – water suspension – isoamyl, isopropyl or ethyl alcohol in relatively small (from 3 to 8% by weight) concentrations. Mechanism, characteristics and conditions of ignition of the studied rather promising fuel compositions have been established by the results of experimental studies of ignition process of multicomponent coal-water fuel droplets based on lean coal with alcohol additives in a medium of oxidizer (still air) heated to high temperatures (from 873 K to 1273 K) with recording of heating, ignition and combustion processes by a high-speed video camera (shooting speed up to 105 frames per second). Experiments have shown that stable ignition delay time of the studied suspensions based on lean coal decreases by 11–56% with an increase (from 3 to 8%) in the mass concentration of one of the alcohols in the composition of coal-water fuel at the initial characteristic size of droplets from 1.0 to 2.5 mm. Each studied composition was compared with conventional coal-water fuel burned under similar conditions. Increase in the mass concentration of alcohol in the composition of coal-water fuel reduces the value of the flash point by 27–30%. The viscosity of alcohol-coal-water fuels increases by 7.0 to 40% when the researched alcohols are added to the coal-water slurry. Influence of mass concentration of isoamyl, isopropyl and ethyl alcohols in the composition of coal-water fuel on the characteristics of initiation of ignition and combustion processes established in experiments justifies the possibility of sufficiently effective application of such three-component suspensions in the power industry. Necessary and sufficient conditions for the ignition of alcohol-coal-water fuel droplets have been established based on a mathematical model and experimental data. Increase in the cost of such fuels has been analyzed in comparison with conventional coal-water slurry. It has been shown that the most attractive from the energy and economic points of view is coal-water fuel with isoamyl and isopropyl alcohols in the composition. The obtained results are of significant practical value, as they illustrate the possibility of achieving optimal ignition and combustion conditions for promising multicomponent coal-water suspensions with alcohol additives in the furnaces of boiler plants.
Experimental studies of the steam pyrolysis of oil sludge were performed using a flow-type pilot plant with 300 kg/h capacity (raw material) to obtain energy-valuable products, such as liquid hydrocarbons (30.4 wt%), semi-coke (39.6 wt%), non-condensable gas-phase compounds (26.5 wt%), and bitumen (3.5 wt%). The pyrolysis process was conducted at a temperature of 650 ° C and with a steam flow rate of 150 kg/h. Liquid hydrocarbons were considered a target product. Comprehensive studies of their physicochemical characteristics, atomization process, droplet ignition, and combustion were carried out. The studied sample had physicochemical characteristics similar to traditional fuel oil (calorific value—42.6 MJ/kg, sulfur content—0.8 wt%). The jet spraying angle was 25° in view of the improved rheological properties of the test sample, with a homogeneous jet structure and a predominant droplet diameter of no more than 0.4 mm. The flame combustion process was accompanied by the formation of microexplosions, the frequency and intensity of which depended on the temperature of the air (Tg = 450–700 °C). This study, in view of its applied nature, is of interest in the design of new installations and technological systems for hydrocarbon pyrolysis.
The ignition and combustion of coal-water fuel (CWF) droplets based on pyrolysis water and its various fractions obtained in 3 different temperature ranges – less than 100, 100-150 and 150-200°C – had been investigated. The separation of pyrolysis water was carried out by the sedimentation of bio-oil obtained at industrial biochar-producing facility. The mass ratio of solid to liquid-phase components in CWF was equal to 1:1. The ignition and combustion of CWF was studied via the combustion chamber at temperatures of the heating medium varied in range 500-800°C. The characteristics of the ignition and combustion processes of the investigated fuel compositions were compared to CWF with distilled water. The use of pyrolysis water and its various fractions resulted into an increase in CWF reactivity, which was reflected in a reduction in the ignition delay time (by 39.7% on average) and the minimum ignition temperature (by 6.9% on average). The lower heating value of CWF was increased by 0.1-1.4 MJ/kg. According to the data on material and energy balances, it was determined that 16.2 wt% of pyrolysis water can be involved to ensure energy-sufficiency of the pyrolysis. The remaining pyrolysis water could be used for the chemical industry or energy complex.
The effect of metal nitrates on the activation of anthracite combustion process has been studied. Fe(NO3)2 · 9H2O and Cu(NO3)2 · 3H2O were used as nitrates in an amount of 5 wt% applied to anthracite powder (fraction less than 0.1 mm) by incipient wetness impregnation. Using scanning electron microscopy and EDX mapping, it was found that using this method of applying the additive makes it possible to achieve high dispersion and uniform distribution in the fuel composition. The characteristics of oxidation, ignition, and combustion were studied using thermal analysis methods and high-speed video recording in the combustion chamber at a temperature of 800°C. It was found that the use of metal nitrates contributes to an increase in the reactivity of anthracite as evidenced by a decrease in the temperature of the intensive oxidation beginning (ΔTi) by 23–84°C and the ignition delay time (Δti) by 0.9–2.2 seconds. The greatest effect of changing the reactivity of anthracite was recorded in the case of using copper nitrate additive. The use of nitrates also contributed to the decrease in the resulting fuel underburning (from 3.5 to 0.4 wt%) and gas-phase CO compounds (by 31–53%). At the early stages, combustion process of modified samples was accompanied by periodic formation of micro-explosions, which led to the activation and development of the particle surface.
Актуальность темы обусловлена возможностью использования такого вида топлива, как парогазовые продукты пиролиза древесных отходов, в качестве основного или вспомогательного топлива для выработки электрической энергии. Направления, связанные со снижением углеродных выбросов, позволят расширить области применения пиролиза как средства переработки промышленных отходов, сводя к минимуму их воздействие на окружающую среду.Цель: исследование вопросов повышения эффективности выработки электрической энергии на двигателях внутреннего сгорания и газотурбинных установках при работе на продуктах пиролиза древесных отходов с целью сокращения потребления невозобновляемых энергоресурсов, таких как уголь, нефть и природный газ. Объекты: установка пиролиза древесных отходов, двигатели внутреннего сгорания и газотурбинные установки, работающие на парогазовых продуктах пиролиза древесных отходов. Методы: численные методы исследования на основе математического моделирования систем и элементов двигателей внутреннего сгорания и газотурбинных установок на основе материальных и энергетических балансов. Результаты. Разработана математическая модель и программа для теплового расчета двигателей внутреннего сгорания и газотурбинных установок, сжигающих парогазовые продукты пиролиза. Проведен параметрический анализ влияния температуры выхода парогазовых продуктов из пиролизной установки на эффективность работы, электрическую мощность и температуру уходящих газов рассмотренных силовых агрегатов. Установлено, что для утилизации парогазовых продуктов пиролиза с целью получения электрической энергии наиболее эффективно применение двигателя внутреннего сгорания, работающего по термодинамическому циклу Тринклера, и газотурбинной установки, работающей по термодинамическому циклу Брайтона, при этом абсолютный электрический коэффициент полезного действия в номинальном режиме работы пиролизной установки составляет 23,34 и 22,28 % соответственно. Выявлено, что при использовании парогазовых продуктов пиролиза в качестве вспомогательного топлива к метану в объемной составляющей 25 %, снижение мощности силового агрегата ожидается не более 10 %.
Янковский С. А., Кузнецов Г. В., Мисюкова А. Д. ОБОСНОВАНИЕ СНИЖЕНИЯ ВЫХОДА ОКСИДОВ СЕРЫ ПРИ ПИРОЛИЗЕ УГЛЕЙ С ДОБАВКОЙ ОТХОДОВ ЛЕСОПИЛЕНИЯ // ХИМИЯ ТВЕРДОГО ТОПЛИВА. - 2022. - № 1 - с. 57–65
Проведены экспериментальные исследования газообразных продуктов совместного пиролиза достаточно типичных и широко используемых в России и во многих других государствах энергетических углей и древесины (опил сосновых пород древесины). Установлено, что в газообразных продуктах пиролиза всех исследованных древесно-угольных смесей значительно (на 95% при высокой доле древесной биомассы) снижается выделение оксидов серы. Предложено использование древесины в составе смесевых топлив на основе типичных энергетических углей разных марок в качестве добавки, обеспечивающей существенное снижение выхода оксидов серы в газообразных продуктах сжигания таких топлив в топках паровых и водогрейных котлов.
The paper presents the results of experimental studies on the silicon carbide powder synthesis from charcoal and silicon in plasma of DC low-voltage arc discharge in ambient air. The observed dependencies of the initial mixture composition, arc discharge duration and treatment cycles on the phase composition of synthesized products allow fabrication of the powdery product composed of two phases: graphite and cubic phase of silicon carbide. The powdery product contains crystals that correspond to the morphology of biomorphic wood-derived silicon carbide. The temperature range suitable for synthesis of powdery product with a removal of an excess of free carbon was established by the differential thermal analysis. The synthesis product consists mainly of carbon and silicon, and insignificant amount of impurities contained in the original charcoal. Oxygen is also present in the synthesis product in an amount up to 4.6 at. %, which may indicate the presence of an amorphous silicon oxide layer on the silicon carbide surface. The proposed method finally yielded the silicon carbide based powder with a lattice parameter a = 4.359 Å.
Ash accumulation is a relevant problem due to the widespread use of coal-fired power plants and a very limited number of ash utilization technologies. Plasma processing of ash is a promising method of ash valorization for production of various useful products, which is limited by high energy consumption. In the current study, a mixture of waste ash from power plant and black carbon was processed using an original direct current plasma arc experimental setup in ambient air which allows lower energy consumption due to the absence of the vacuuming system. Four types of samples at different plasma exposure times were produced and together with the initial ash were studied by thermal analysis, X-ray diffractometry and scanning electron microscopy. The X-ray diffraction analysis identified the resulting phases of graphite, silicon carbide, and aluminum nitride in the synthesis products; at the same time, at the arc discharge energy increased from 26 to 105 kJ, the intensities of the maxima that correspond to metal and nonmetal oxides in the composition of the initial ash decreased to nearly zero. To remove graphite, the processed samples were annealed at 750 °C in air and studied. It was found that the applied approach made it possible to obtain a mixture of silicon carbide and aluminum nitride powders in direct current arc plasma initiated in ambient air, which reduced the energy consumption for ash processing by electric arc.
The paper presents the results of experimental studies on the preparation of ultrafine powder materials of the tungsten-carbon system in the plasma of a direct current arc discharge initiated in ambient air. According to the results of X-ray diffractometry, transmission electron microscopy, scanning electron microscopy, and elemental analysis, the product contains microsized and nanoscale crystalline objects that are carbon graphite-like materials gC, tungsten carbides WC and W2C with a hexagonal structure, and tungsten W with a cubic structure. As a result of a series of experiments, the possibility of influencing the phase composition of the synthesis product by the amount of energy supplied, which is linearly dependent on the duration of the arc discharge, was established. In this case, tungsten oxide phases were not found in the composition of the synthesis products within the framework of the applied analytical techniques. The process of obtaining non-oxide materials during the generation of a direct current arc plasma in the presence of carbon and tungsten is possible owing to the intense generation of carbon monoxide and carbon dioxide gases, which shield the reaction volume from atmospheric oxygen. Thus, in the framework of the presented work, the possibility of controlling the phase composition of the product of vacuumless arc synthesis in the tungsten-carbon system by changing the duration of the discharge burning at a constant direct current was shown for the first time.
Газификация твердых топлив : учебное пособие / Д. В. Гвоздяков, В. Е. Губин, С. В. Лавриненко [и др.] ; Национальный исследовательский Томский политехнический университет. – Томск : Национальный исследовательский Томский политехнический университет, 2021. – 172 с. – ISBN 978-5-4387-1009-7. – EDN RCJMWX.
В учебном пособии отражены основные вопросы газификации твердых топлив. Представлен анализ влияния свойств топлив на эффективность процесса газификации и физико-химические характеристики данного процесса. Описаны современные технологии газификации, существующие и перспективные газогенерирующие установки в России и за рубежом, а также технологии выработки электрической и тепловой энергии на основе газификации твердых топлив. Отдельное внимание уделено экспериментальной реализации технологии газификации твердого топлива на Томской ТЭЦ-3: описан экспериментальный образец горновой газогенераторной установки, представлены результаты проведенных испытаний и варианты развития данной технологии. Пособие предназначено для студентов, обучающихся по направлениям 13.03.01 «Теплоэнергетика и теплотехника», 13.03.02 «Электроэнергетика и электротехника», 03.03.02 «Физика».
Vassilyeva Y. Z., Pak A. Y. SYNTHESIS OF MOLYBDENUM CARBIDE IN SELF-SHIELDING ELECTRIC ARC PLASMA //St. Petersburg Polytechnic University. Journal of Engineering Sciences and Technology. – 2021. – Т. 27. – №. 2. – С. 62.
The paper presents the results of vacuum-free electric arc synthesis of catalysts based on molybdenum carbides, which can be used for hydrogen production by electrochemical water splitting. The synthesis of carbide phases is possible due to self-shielding effect of the reaction volume during DC arcing in open-air environment. According to X-ray diffractometry data, there are two phases of molybdenum carbides in the synthesized product: Mo2C and Mo1. 2C0. 8, the phase of initial molybdenum, and the phase of graphite were identified. In a series of experiments, the authors were able to control the phase composition of the synthesis product by changing the distance between the initial reagents and the zone of initiation and combustion of the arc discharge. The estimated catalytic activity of the synthesized samples is close to the activity of catalysts based on molybdenum carbides obtained by other methods.
В работе представлены результаты экспериментальных исследований, показывающие возможность реализации безвакуумного электродугового синтеза катализаторов на основе карбидов молибдена для реакции электрохимического разложения воды. Метод позволяет вести синтез карбидных фаз при горении дугового разряда постоянного тока в открытой воздушной среде за счет достижения эффекта самоэкранирования реакционного объема. По данным рентгеновской дифрактометрии в продукте синтеза идентифицированы две фазы карбидов молибдена: Mo2C и Mo1.2C0.8, фаза исходного молибдена, а также фаза графита. В серии экспериментов удалось реализовать управление фазовым составом продукта синтеза путем изменения расстояния между исходными реагентами и зоной инициирования и горения дугового разряда. Оцененная каталитическая активность синтезированных образцов близка к активности катализаторов на основе карбидов молибдена, полученных другими методами.
Актуальность исследования обусловлены растущим потреблением карбида вольфрама в связи с его применением в различных сферах: обрабатывающая промышленность, катализ, металлургия и др. Соответственно поиск новых малозатратных методов переработки вольфрамсодержащих руд является актуальной задачей.Цель: определить параметры безвакуумного электродугового синтеза карбидов вольфрама в атмосферной плазме с использованием в качестве исходного сырья концентрата вольфрамсодержащей руды, которые обеспечивают эффект самопроизвольного экранирования реакционного объема от кислорода воздуха.Объекты: синтез карбида вольфрама в плазме дугового разряда постоянного тока из концентрата вольфрамсодержащей руды безвакуумным методом.Методы: безвакуумный электродуговой метод синтеза, рентгенофазовый анализ на рентгеновском дифрактометре Shimadzu XRD 7000s (λ=1,54060 Å), электронная микроскопия, совмещенная с рентгенофлуоресцентным энергодисперсионным анализом на базе микроскопа TESCAN VEGA 3 SBU с приставкой OXFORD X-Max 50 с Si/Li (TESCAN, Чехия).Результаты. Проведена серия экспериментов по синтезу карбидов вольфрама в дуговом разряде постоянного тока из вольфрамового концентрата руды, в результате рентгенофазового анализа полученных образцов, растровой электронной микроскопии, совмещенной с энергодисперсионным анализом химического состава полученных из рудного концентрата образцов, было установлено, что в продуктах электродуговой переработки можно идентифицировать фазы карбида вольфрама WC и W2C, при этом полная переработка исходного сырья наблюдается при длительности электродуговой обработки не менее 30 с (при энергии дуги не менее 95 кДж). Было установлено, что с увеличением времени синтеза доля W2C убывает,при этом доля карбида вольфрама WC возрастает.
С использованием техники плазменного дугового разряда постоянного тока при атмосферном давлении синтезирован микропорошок высокоэнтропийного карбида Hf Ta Ti Nb Zr C 5 . Синтез осуществлялся в воздушной атмосфере в условиях формирования защитного газового слоя из монооксида углерода. В качестве исходного сырья использованы оксидные порошки металлов TiO 2 , ZrO 2 , Nb 2 O 5 , HfO 2 и Та 2 О 5 , входящих в состав высокоэнтропийного карбида, с характерными размерами зерен 5-10 мкм. Показано, что для формирования высокоэнтропийного карбида из исходного сырья под воздействием плазмы дугового разряда необходимо время не менее 90-100 с. Преимуществом предложенного метода получения высокоэнтропийного карбидного микропорошка по сравнению с другими аналогичными методами является короткое время синтеза такого порошка с низкими энергетическими затратами (~960 кДж/г) и возможность использования для синтеза простого оборудования.
This paper presents the experimental results of metal carbides synthesis by DC arc discharge plasma in ambient air. The results indicate that the synthesis takes place in the atmosphere of CO and CO2, which are generated during the DC arcing process on graphite electrodes and that mixture of CO and CO2 prevents the reaction zone from air oxygen. The paper introduces experimentally substantiated arguments about the possibility of obtaining metal carbides by the developed arc discharge method. By the moment, the authors have already obtained silicon carbide and titanium carbide in this way.
Coal-water slurries are promising fuels for thermal power engineering despite some problems associated with their combustion in steam and hot water boilers. One of these problems is formation of sufficiently large (more than 1 mm) fuel droplets during coaxial spraying through the nozzles. The aim of this work is to substantiate efficiency of ethyl or isoamyl alcohol addition as a third component of coal-water fuels, which significantly improve atomization technology, by the results of experimental determination of distribution of coal-water slurry droplets by velocity and size in the process of coaxial spraying. Based on the results of experimental studies of atomization process of coal-water slurries prepared on the basis of lignite with addition of ethyl and isoamyl alcohol, instantaneous fields of fuel droplet velocities and sizes in a wide range (from 20 μm to 1 mm) in several cross-sections of the jet at several values of air and fuel pressure were determined using a non-contact method of jet visualization. It was experimentally established that substitution of water (no more than 3% by weight) in the composition of coal-water slurry by fairly typical alcohols leads to decrease in droplet velocities during atomization of alcohol-coal-water slurries in comparison with conventional coal-water fuel by 5–8% at air pressure of 0.28 MPa and fuel pressure of 0.3 MPa. Concentration of sufficiently small fuel droplets (up to 200 μm) increases by 13.4% and by 6.6% during atomization of alcohol-coal-water slurries with addition of ethyl and isoamyl alcohol, respectively, in comparison with conventional coal-water fuel. Influence of small additives of ethyl and isoamyl alcohol in the composition of coal-water fuel, established in experiments for the first time, on flow characteristics of the droplets after spraying proves the possibility of effective application of such three-component suspensions in thermal power engineering. The results obtained are of significant practical value, since they illustrate the possibility of ignition delay time reduction of droplets of promising three-component coal-water slurries with addition of such alcohols.
Application of liquid waste of industrial rubber goods (IRG) and waste car oil (WCO) as an additional component of coal-water fuel (CWF) was experimentally studied. It has been established that efficient introduction of liquid combustible components (LCC) into coal-water fuel prepared on the basis of long-flame coal is possible, if their concentrations in the studied slurries do not exceed 8% by weight. A further increase in the concentration of the third component causes an increase in the fuels viscosity, which significantly worsens the jet characteristics after spraying. Increase in the jet spraying angle is about 25%, but a significant number of inhomogeneities and large fragments appear in its composition. Introduction of the third component into the composition of coal-water fuel allows increasing its calorific value by 9.9–31.1%.
Coal-water fuels have been actively studied in the last decade due to the fact that when they are burned in the furnaces of steam and hot-water boilers, much less anthropogenic oxides of sulfur, nitrogen, and carbon are formed in comparison with coal. The main problem that hinders the widespread introduction of such fuels in the energy sector is long (up to 30 seconds) ignition delay times. Significant (10%-50%) reduction in the ignition delay time is possible when a small (up to 10%) amount of available and inexpensive liquid combustible organic compounds are added to the suspension. The purpose of the work is to substantiate (from the results of experimental studies) the possibility of significant reduction of the ignition delay times of coal-water fuels by introducing a third component into the suspension—isopropyl alcohol in relatively small (from 3% to 8%) concentrations. According to the results of experimental studies on the ignition process of multicomponent coal-water fuel droplets, based on long-flame coal, with addition of isopropyl alcohol in oxidizer (still air) heated to high temperatures (from 873 to 1273 K), with recording the processes of heating, ignition, and combustion by a high-speed video camera (speed of shooting up to 105 frames per second), the mechanism, characteristics, and conditions of ignition of the researched compositions of quite promising fuels were established. Experiments have shown that the delay time of stable ignition of the studied suspensions based on long-flame coal decreases by 12% to 47% with the increase (from 3% to 8%) of the mass concentration of isopropyl alcohol in the composition of coal-water fuel at the initial characteristic size of droplets from 1.5 to 3.5 mm. Each studied composition was compared with conventional coal-water fuel burned under similar conditions. The influence of mass concentration of isopropyl alcohol in the composition of the coal-water fuel on the characteristics of the initiation of ignition and combustion processes, established in the experiments, proves the possibility of effective an application of such three-component suspensions in thermal power engineering. The possibility of formation of a significantly larger quantity (about 80%) of small droplets (250-400 μm) in the flow during atomization of coal-water fuel with addition of isopropyl alcohol in comparison with the usual coal-water suspension was experimentally proved. The results are of significant practical importance because they illustrate the possibility of achieving optimum conditions for ignition and combustion of promising multi-component coal-water slurries with the addition of alcohol in the furnaces of boiler plants of large- and small-scale power engineering.
The process of slow pyrolysis of seven nut shell samples, in a nitrogen-purged atmosphere, has been studied, as well as characteristics of biochar obtained. The heat carrier with a temperature of 400–600 °C (with a step of 100 °C) was supplied indirectly using a double-walled reactor. The heating rate was 60 °C/min. At increased temperature of the heating medium, a decrease in the amount of the resulting carbon residue averaged 6.2 wt%. The release of non-condensable combustible gas-phase compounds CO, CH4, and H2, with maximum concentrations of 12.7, 14.0, and 0.7 vol%, respectively, was registered. The features of the obtained biochar sample conversions were studied using thermal analysis in inert (nitrogen) and oxidative (air) mediums at 10 °C/min heating rate. Kinetic analysis was performed using Coats–Redfern method. Thermal analysis showed that the main weight loss (Δm = 32.8–43.0 wt%) occurs at temperatures ranging between 290 °C and 400 °C, which is due to cellulose decomposition. The maximum carbon content and, hence, heat value were obtained for biochars made from macadamia nut and walnut shells. An increased degree of coalification of the biochar samples affected their reactivity and, in particular, caused an increase in the initial temperature of intense oxidation (on average, by 73 °C). While technical and elemental composition of nut shell samples studied were quite similar, the morphology of obtained biochar was different. The morphology of particles was also observed to change as the heating medium temperature increased, which was expressed in the increased inhomogeneity of particle surface. The activation energy values, for biochar conversion in an inert medium, were found to vary in the range of 10–35 kJ/mol and, in an oxidative medium—50–80 kJ/mol. According to literature data, these values were characteristic for lignin fibers decomposition and oxidation, respectively.
The ignition and combustion of anthracite modified by the addition of pyrolysis oil obtained during thermal processing of waste car tires (WCTs) had been studied. The mass fraction of WCT pyrolysis oil was varied in the range from 5 to 30 wt %. The additive was applied by the drop impregnation method. Ignition and combustion of obtained samples were carried out in a combustion chamber at temperatures of the heating medium Tg = 600–800 °C. The gas-phase combustion products were analyzed using an in-line gas analyzer. The application of WCT pyrolysis oil as a combustion modifier contributed to an increase in the reactivity of anthracite, which was expressed in a decrease in the minimum ignition temperature (by 23–104 °C) and a reduction in the ignition delay time. The high-speed video recording indicated that the combustion of both initial and modified with 5 wt % pyrolysis oil anthracite samples was realized in oxidation mode. For samples with more than 10 wt % pyrolysis oil additive, the formation of a visible flame was observed near the sample surface. With an increase in the mass fraction of the additive, the rate of combustion front propagation was increased. The application of WCT pyrolysis oil as a combustion modifier also contributed to the reduction or even the almost complete elimination of unburnt carbon content in the ash residue formed after anthracite combustion.
Under research, there is a combustion process of multicomponent coal-water fuel (CWF) that was conducted with mixing ratio of coal, pyrolysis, and technical water. The pyrolysis water was extracted through pyrolysis oil settling, where the oil was obtained from pyrolysis of wood waste. Ignition and combustion of CWF samples were carried out in a combustion chamber at heating medium temperatures (Tg = 600-1000°C, with an interim step of 50°C). Gas-phase combustion products were analyzed with a flow-line gas analyzer. Technical water in CWF composition was replaced with pyrolysis one that was acted to raise the reactive capacity. It resulted in reducing the ignition delay time τi (by an average of 25%) and the minimum ignition temperature (from 440°С to 393°С, reliance on a CWF composition). In addition, increase in flame combustion time was recorded by an average of 20%, as well as dependence on a heating medium temperature and a CWF composition. In the case when a CWF liquid-phase component was completely replaced with the pyrolysis water, the significant increase in heat value by 2.14 MJ/kg was observed. According to the data of the flow-line gas analyzer, we concluded that the CWF combustion based on the pyrolysis water was accompanied by less NOx emission (by an average of 22%) but more CO and CO2 amount (by an average of 1.4 and 1.2, respectively). It was found according to the results of the energy balance assessment that application of pyrolysis water in CWF composition leads to a decrease in fuel consumption for heat production by 16.7%.
Gasification is one of the promising technologies for the use of solid fuels in power generation, chemical industries, and a number of related areas. Despite a significant amount of theoretical and experimental work performed in Russia, one of the key factors that limits the widespread commercialization of gasification technologies is the lack of practical experience of operation under industrial conditions or those close to them. To gain experience in managing the fixed-bed coal gasification technology, in autumn 2019, specialists of Tomsk Polytechnic University, based on the Ekoenergetika 4.0 (Ecoenergy Generation) research center in Tomsk, tested Russia’s first pilot fixed-bed gasifier with a capacity of 4 t of fuel per hour, which was developed at the All-Russia Thermal Engineering Research Institute. The tests were conducted using coals of four grades of the Kuznetsk and Kansk-Achinsk basins, viz., anthracite, long-flame and lean coals, and lignite. As a result of the tests, the technical feasibility of both individual components and the gasification plant as a whole was proven. In the course of the tests, high-quality synthesis gas was obtained with a calorific value in the range 6.0–8.3 MJ/m3, which makes its use as a fuel in combined-cycle plants with the reliable and stable ash removal possible. The possibility of using the gas produced in the tests of the fixed-bed gasifier for the synthesis of liquid hydrocarbons by the Fischer–Tropsch process has been experimentally established. Further, the possibility of producing coke and semicoke in the gasifier has been proven. The assessment of the reliability of the gasification plant performed using the ANSYS software based on the test data has shown a satisfactory lifetime of the plant with the expected service life of the most stressed gasifier components of 68 000 h.
This paper examines combustion of coal and semicoke modified by 5 wt% of Cu(NO3)2, CuSO4 and Cu(CH3COO)2. The additives were introduced using the wet impregnation method. Ignition and combustion experiments were performed in a combustion chamber at temperatures of the heating medium varying from 500 °C to 700 °C. The gas-phase combustion products were analyzed using an in-line gas analyzer. It was found that, on average, the use of activating additives contributed to a reduction of the ignition delay time by 1.8 times and a decrease in the minimum ignition temperature by 54–135 °C. An increase in the heating medium temperature resulted in a significant ignition delay decrease (by ~270%). The maximum difference in the ignition delay time between the reference sample and the modified coal (3.4 s) and semicoke (10.4 s) samples was observed at 500°С while using copper nitrate. In the initial stage of combustion, formation of micro-explosions on the samples modified with copper nitrate and acetate was observed. The use of additives contributed to reducing the content of unburnt carbon in the fuel. Addition of copper salts resulted in a significant reduction in the CO production volume and better fuel oxidation to CO2.
Актуальность работы обусловлена возрастающим интересом к технологиям пиролиза биомассы для снижения углеродного следа процессов её переработки. Для повышения экономической и энергетической эффективности данных технологических решений необходимо максимально полное использование всех материальных и энергетических потоков, одним из которых является формирование жидких продуктов пиролиза (т. н. пиролизной жидкости, или бионефти).Цель: классификация и выделение технологических решений для утилизации жидких продуктов пиролиза древесной биомассы с определением уровня технической готовности. Методы: аналитический обзор тематических публикаций с использованием материалов баз данных РИНЦ, Scopus и Web of Science, уровень технической готовности оценивался согласно шкале TRL.Результаты. Идентифицированы, классифицированы и описаны основные методы утилизации пиролизной жидкости, получаемой в результате медленного пиролиза древесной биомассы. Представлен обзор технологических решений и научно-исследовательских работ в области утилизации жидких продуктов медленного пиролиза. Наиболее распространенными технологиями преобразования пиролизной жидкости с получением тепловой и/или электрической энергии являются прямое сжигание в горелках котлов и теплогенераторов, в камере сгорания газотурбинных двигателей, газификация с получением синтез-газа, а также использование в качестве топлива поршневых двигателей. Технологии получения химических продуктов и веществ разделяются на простые (получение компонент дорожного строительства, консерванта для древесины, фенолформальдегидных и омыленных смол и др.) и сложные, требующие комплексной многостадийной переработки. Установлено, что наибольшим уровнем технической готовности обладают технологии энергетического применения данного продукта, в то время как наибольшей экономической эффективностью обладают технологии химического применения, несмотря на относительно низкий уровень готовности. Коммерческие решения по утилизации пиролизной жидкости доступны в области её сжигания в горелках и дизель-генераторах.
The simultaneous pyrolysis of coal with wood was experimentally found to allow reducing concentrations of sulfur-containing substances in gases released. The objective of experimental studies is comparison of the sulphate of calcium and aluminum in the ash of coal-wood mixtures after pyrolysis of the latter in a dense “packing” of aggregate particles of these two fuels and at a few millimeters distance between particles. The 3B-grade lignite, T-grade bituminous coal and pinewood sawmill waste were chosen as feedstocks for pyrolysis experiments because they are widespread in Russia as well as many other countries. The elemental composition of all raw materials and pyrolysis residues was determined. The inorganic composition of obtained pyrolysis product in the solid phase was characterized by X-ray analysis. The content of aluminum and calcium sulfate in residue in case of simultaneous processing of coal with wood was found to be higher, compared to the processing of coal only (within the random errors of the experiment), than those established for such mixtures under conditions of dense “packing” of large masses (up to 15 g).
The purpose of this work is to experimentally determine conditions and characteristics of floating particles ignition of fuel mixtures based on coal dust with characteristic sizes of less than 80 μm and fine wood (typical sizes up to 200 μm) at various mass concentrations of fuel components. The experiments were conducted in a medium heated to high temperatures of still air (from 600 °C to 1200 °C). Record of the processes of heating of the researched fuel mixture that is quite promising for heat power engineering, their subsequent ignition and combustion was performed by a high-speed video camera (image format - 1024 × 1024 pixels, frame rate - up to 105 per second). It has been established that increase in the proportion of relatively large particles (compared to coal) of the wood component in the fuel mixture does not significantly affect the values of ignition delay times of all investigated wood-coal mixtures based on two typical grades of coal (long-flame and lean).
This paper presents results of experimental research on thermal decomposition processes of a rather common D grade steam coal (metalignitous coal) and wood. The research aims to substantiate the previously formulated hypothesis on the mechanism of sulfur oxide sequestration in the combustion products of such mixtures. The elemental composition of the reference coal and wood biomass (pine sawdust) and the ash remaining after complete thermal decomposition of the studied mixtures was analyzed. The obtained results, along with results of the X-ray phase analysis of the ash composition, showed an increase in the proportion of calcium and aluminum sulfates in solid pyrolysis products. The performed experiments substantiate that the use wood as an additive for mixed metalignitous coal fuels reduces sulfur oxide yield during their combustion in power boilers in large-scale and small-scale power generation systems. It was established that pyrolysis of two-component fuels based on the D grade coal mixed with dispersed wood biomass contributes to reducing sulfur oxide concentration in gaseous products of their thermal decomposition. This effect can be attributed to formation of calcium and aluminum sulfates in the mixed fuel ash. They are formed as a result of reactions between the coal and wood pyrolysis products that occur if the content of wood components in the mixture is from 10% to 50%.
Results of experimental studies of joint pyrolysis processes of a fairly typical and widely used in Russia and Poland 3B grade lignite and wood (sawdust of pine wood) are provided. The results were performed in order to substantiate the previously formulated hypothesis about the mechanism of suppression of sulfur oxides in the combustion products of such mixed fuels. Conclusions on the mechanism of SOx suppression were made after comparing the analysis results of the elemental composition of the initial lignite, wood, and ash remaining after the total completion of the studied mixtures pyrolysis processes, as well as X-ray phase analysis of the ash composition. It was found that the proportion of calcium and aluminum sulfates is higher in the solid pyrolysis products of mixtures of crushed coal and wood compared to the ash of homogeneous coal. Practical significance of the performed studies is that the obtained results of the experiments allow to justify the possibility of using wood as a part of mixed fuels based on 3B grade lignite as an additive that significantly reduces the yield of sulfur oxides during combustion of such fuels in the furnaces of steam and hot water boilers. It has been experimentally established that during high-temperature decomposition of two-component fuels based on 3B lignite in a mixture with fine wood biomass, the effect of reduction of sulfur oxide concentration in gaseous pyrolysis products of such mixtures is obtained due to the formation of calcium and aluminum sulfates in the ash of mixed fuels as a result of chemical reactions between gaseous and solid pyrolysis products of lignite and wood with participation of water vapor.
The goal of this paper is to simplify and reduce the cost of manufacturing tungsten carbide. The work presents the results of experimental studies that prove the possibility of synthesizing fine and ultrafine crystalline phases of tungsten carbide in the DC arc discharge plasma ignited in open air by a developed vacuumless technique. The synthesis is implemented in the process of arc discharge burning between the graphite rod (anode) placed inside the cavity of the graphite cathode in the presence of graphite and tungsten powders used as initial precursors. The cathode cavity (reaction zone) is shielded from oxygen by a stream of carbon monoxide and carbon dioxide gases, which are generated during the arc discharge burning in an open air. After studying the influence of main process parameters (parameters of the discharge circuit and graphite electrode's dimensions) and optimizing the system, the authors obtained tungsten carbide phases without impurities of oxide phases. This allows simplifying significantly the technology of tungsten carbides synthesis by excluding the stage of vacuum creation.
Electrochemical water splitting is attractive for hydrogen production, however, high cost of noble metal catalysts, such as platinum, restrict its use. Herein, molybdenum carbide nanoparticles encapsulated within carbon matrices as a high-performance and low-cost electrocatalyst for hydrogen evolution reaction (HER) were prepared by DC arc discharge plasma under ambient air conditions. According to XRD patterns the synthesized product includes molybdenum carbides (β-Mo2C and Mo1.2C0.8), molybdenum and graphite crystalline phases. The resulting material shows highly active catalytic properties with very small onset potential of −63 mV, a low overpotential of −226 mV at current density of 10 mA cm−2 and Tafel slope of 66.1 mV.dec−1 in 1.0 M KOH. The long-term HER stability test for 50 h under constant current density of 10 mA cm−2 confirmed the stability of the catalytic properties of the synthesized product. Therefore, such a method for producing Mo-based material for HER electrocatalysts is promising and can have practical application.
The paper presents the results of experimental studies on the preparation of fine powder materials of the tungsten-carbon system in a plasma of a direct current (DC) arc discharge initiated in an open-air environment. The initial reagents for the synthesis of powders containing tungsten carbide was waste of worn hard metal elements based on tungsten carbide and cobalt, which had been previously ground and subjected to oxidation. The process of obtaining non-oxide materials during the generation of a direct current arc plasma in the presence of carbon and tungsten is possible due to the intense generation of carbon monoxide and carbon dioxide gases, which shield the reaction volume from atmospheric oxygen. Synthesis products were analyzed by X-ray diffraction analysis, scanning electron microscopy and elemental analysis, tungsten carbides WC, W2C with hexagonal structure, tungsten-cobalt carbide and graphite-like materials were identified as synthesized polymorphs.
The paper represents the results of experimental studies, showing the possibility of obtaining submicron and nanoscale crystalline phases in direct current arc plasma, formed in an open air in the cavity of a graphite cathode. In the series of experiments the objects were synthesized in the presence of carbon and molybdenum powders, which were identified as particles of polyhedral graphite. The objects are characterized by the sizes of the order of ~ 100-500 nm, typical morphology and a graphite-like structure. According to the energy dispersive analysis, these objects contain on average up to 98% (mass) of carbon, up to 1% (mass) of molybdenum and up to 1% (mass) of oxygen. A feature of the applied approach is its implementation in the open air, which is possible due to the effect of self-shielding of the reaction zone from air oxygen by carbon monoxide and carbon dioxide gases. Also, the cubic molybdenum phase, the orthorhombic MO2C and hexagonal Mo1.2C0.8 phases of molybdenum carbide are identified in the synthesis product.
Предложен способ получения порошка, содержащего карбид кремния и нитрид алюминия, из золы природного угля, включающий перемешивание и помол золы в шаровой мельнице, термическую обработку в газовой среде в течение 30 минут, где порошковую смесь золы и графита в массовом соотношении 80:20 размалывают в шаровой мельнице в течение 1 часа и насыпают слоем не более 1 мм на дно катода в виде вертикально расположенного графитового стакана, генерируют дуговой разряд постоянного тока в воздушной среде соприкосновением анода в виде сплошного графитового стержня с указанной порошковой смесью при силе тока от 165 до 200 А в течение от 10 до 20 секунд, затем прерывают горение разряда, отводя анод, и после остывания катода до комнатной температуры порошковую смесь извлекают из полости катода, помещают в корундовую посуду и нагревают в атмосферной печи до 900°С, выдерживая при этой температуре в течение 30 минут, полученный порошок извлекают из печи и остужают в естественных условиях. Технический результат - сокращение времени получения порошка, содержащего карбид кремния и нитрид алюминия, из золы природного угля. 1 з.п. ф-лы, 2 ил., 1 табл., 1 пр.
The possibility of obtaining solid silicon-carbide-based ceramics from ash and slag wastes (ASWs) is demonstrated. The technological process contains three stages: (i) nonvacuum processing of the initial ASWs in dc arc discharge carbon plasma under normal atmospheric condition, (ii) cleaning of the obtained powdered material from unbound carbon by annealing in atmospheric furnace, and (iii) final spark plasma sintering of the powder. Analytical data indicate that the obtained product is a silicon-carbide-based ceramics with a density of 3.05 g/cm3 and a hardness of up to 19.9 GPa.
The results of experimental studies on the development of scientific and technical foundations of a method to obtain cubic titanium carbide in plasma of a DC arc discharge initiated in air have been presented. According to X-ray diffractometry of powder materials obtained in a series of experiments, the dependences of phase composition of the product on the duration of synthesis have been determined. Using the results of scanning electron microscopy and energy dispersion analysis, several morphological types of titanium carbide particles, which are formed as a result of uneven energy distribution in the reaction volume, have been revealed.
Silicon carbide (SiC) is a widely used material characterized by unique physical and chemical properties. In the paper, cubic silicon carbide nanowires are synthesized via the non-vacuum DC (direct current) arc discharge method. DC arc is generated between the graphite rod and the graphite crucible under ambient air conditions without any vacuum or applying special defenses to the used atmosphere equipment. According to experimental data, the percentage of silicon carbide of the total product in interval from 70 A to 100 A increases from 3.9% up to 26.7% (mass), and in interval from 130 A to 200 A of arc discharge current decreases from 26.1% down to 19.9% (mass). The silicon carbide wires are characterized by the typical core-shell SiC–SiOx structure. It is possible to control the phase composition and increase the yield of SiC by changing the arc discharge current amplitude. The optimal synthesis parameters using the DC source with the maximum current of 200 A are a current of 200 A, synthesis time of 12 s and a silicon fraction in the initial mixture not more than 25% (mass) to completely process the initial silicon into its carbide.
Исследовано получение ультрадисперсных порошковых материалов системы “вольфрам - углерод” в плазме дугового разряда постоянного тока, инициированного в открытой воздушной среде. Согласно результатам рентгеновской дифрактометрии, просвечивающей электронной микроскопии, растровой электронной микроскопии и элементного анализа в составе продукта идентифицируются микроразмерные и наноразмерные кристаллические объекты, являющиеся углеродными графитоподобными материалами gC, карбидами вольфрама WC и W2C с гексагональной структурой, вольфрамом W с кубической структурой. В результате серии экспериментов установлена возможность влияния на фазовый состав продукта синтеза количеством подведенной энергии, которое находится в линейной зависимости от длительности поддержания дугового разряда. При этом в составе продуктов синтеза фазы оксида вольфрама в пределах применяемых аналитических методик не обнаружены. Процесс получения неоксидных материалов при генерации плазмы дугового разряда постоянного тока в присутствии углерода и вольфрама возможен благодаря интенсивной генерации газов оксида и диоксида углерода, экранирующих реакционный объем от кислорода воздуха. Впервые показана возможность управления фазовым составом продукта безвакуумного электродугового синтеза в системе “вольфрам - углерод” путем изменения длительности горения разряда при неизменной силе постоянного тока.
Specialized software that supports existing approaches to processing images of the crystal structure of materials for analyzing transmission electron microscopy images have a lot of different digital image processing methods, but major part of it are weakly automated. Automatic algorithm is able to make the crystal structure analysis more fast and effective process. The paper considers the problem of automated processing of SAED images of transmission electron microscopy. Proposed automated image processing algorithm based on methods of adaptive binarization and Watershed segmentation allows one to determine the distances on the diffraction pattern of a material sample on the image of transmission electron microscopy. The proposed algorithm has been tested on several SAED images, distances were calculated in automatic mode and compared with the results of semi-automatic measurement in Digital Micrograph GMS 1.8 software. The analysis of the results showed high agreement in considered cases, which let us assume that proposed algorithm has good development prospects.
Патент № 2716694 C1 Российская Федерация, МПК B22F 9/14 (2006.01), B22F 9/16 (2006.01), C01B 32/949 (2017.01), C23C 14/34 (2006.01), C01G 39/00 (2006.01), B01J 19/08 (2006.01). Устройство для получения порошка, содержащего карбид молибдена : № 2019115985 : заявл. 24.05.2019 : опубл. 13.03.2020 / Пак А.Я. ; заявитель ТПУ. – 9 с. : ил. – Текст : электронный.
Изобретение относится к получению соединений с углеродом и может быть использовано в водородной энергетике. Устройство для получения порошка, содержащего карбид молибдена, содержит камеру 1 из диэлектрического материала с крышкой 2 вверху, внутри которой горизонтально и соосно размещены цилиндрические графитовые анод 9 и катод 5. На дне камеры 1 вертикально закреплены два металлических держателя 3, 4. В держателе 3 сбоку, со стороны, обращенной к центру камеры 1, выполнена выемка, в которую горизонтально вставлена закрытая торцевая часть цилиндрического полого катода 5, открытая часть которого обращена к аноду 9. Полость катода 5 предназначена для размещения цилиндрической прессовки 11 из порошка графита и молибдена до соприкосновения её круглой плоской поверхности с соответствующей поверхностью полости катода 5. В держателе 4 горизонтально выполнено сквозное отверстие с резьбой, в которое вставлен винт 6, конец которого прикреплен к середине дна металлического стакана 8, в который вставлен сплошной анод 9. Анод 9 закреплен с возможностью перемещения вдоль продольной оси при помощи винта 6, один конец которого выведен из камеры 1 и снабжен рукоятью 7. Диаметр полости катода 5 больше диаметра анода 9 от 2 до 4 раз, а глубина полости катода не меньше её диаметра. Стакан 8, в который вставлен анод 9, и держатель 3 катода 5 соединены с источником постоянного тока 10, расположенным снаружи камеры 1. Для работы устройства не требуются операции по формированию защитной газовой разряженной атмосферы, так как анод и катод расположены в камере, сообщающейся с открытым воздухом, а защитная атмосфера СО генерируется самопроизвольно непосредственно в процессе горения дугового разряда в полости графитового катода. Производительность не ограничивается скоростью расхода анода, так как прессовка из смеси графита и молибдена закладывается в полость цилиндрического графитового катода. В результате в плазме дугового разряда постоянного тока, инициированного в воздушной атмосфере при нормальных условиях, получают порошок, содержащий карбид молибдена гексагональной и орторомбической структуры. 2 ил.
Представлены результаты экспериментальных исследований по разработке научно-технических основ метода получения кубического карбида титана в плазме дугового разряда постоянного тока, инициированного в воздушной среде. По данным рентгеновской дифрактометрии порошковых материалов, полученных в серии экспериментов, определены зависимости фазового состава продукта от длительности синтеза. По данным растровой электронной микроскопии и энергодисперсионного анализа выявлен ряд морфологических типов частиц карбида титана, которые формируются в результате неравномерности распределения энергии в реакционном объеме.
Рассмотрен безвакуумный электродуговой синтез порошковых материалов в системе “углерод – кремний”. Оценена возможность управления фазовым, гранулометрическим составом и морфологией частиц продукта в процессе безвакуумного электродугового синтеза. По данным рентгеновской дифрактометрии в составе полученного продукта идентифицируется кубическая модификация карбида кремния с параметром элементарной ячейки 4,375 ± 0,016 Å; также исходный кремний и несвязанный углерод в форме графита. Показана зависимость фазового состава продукта от средней мощности дугового разряда. Определены морфологические типы полученных в серии экспериментов кристаллов карбида кремния, оценен средний размер частиц карбида кремния, изучен химический состав продукта синтеза. Применяемый безвакуумный электродуговой метод отличается отсутствием необходимости формирования защитной газовой среды внутри герметичной камеры электродугового реактора постоянного тока совмещенного типа, так как процесс проходит в атмосфере газа СО, который генерируется при горении дугового разряда в воздушной среде.
Molybdenum carbides can be used in one of the most perspective sectors−hydrogen energy. Materials based on molybdenum carbide have high catalytic activity, which allows them to be used as effective inexpensive catalysts in hydrogen generation reactions, associated with the generation and oxidation of hydrogen. One of the main approaches to the obtaining of molybdenum carbides is the electric arc method based on the synthesis of material in DC arc plasma initiated in the gap between graphite electrodes. This article presents the results of a series of experiments on the production of molybdenum carbides, using a vacuumless arc discharge method, and on the influence of energy on the phase composition of the synthesis product.
The low-temperature pyrolysis of wood briquets is investigated. A double-walled reactor permits indirect heat supply. In modeling the continuous production of semicoke from wood briquets, the process is divided into stages: preliminary heating (at 220°C, which corresponds to briquet production); low-temperature pyrolysis (temperature 350–550°C); and cooling of the semicoke in an inert medium (gaseous nitrogen). The process is exothermal. The release of H2, CH2, and CO (with maximum concentrations of 7.0, 47.6, and 31.2 vol %, respectively) is observed. These compounds are present in the hot gaseous products formed after condensation of the vapor–gas mixture. The characteristics of the semicoke produced are determined. The variability in its reactivity and morphological structure is investigated. With increase in carbonization of the semicoke samples, nonlinear increase in the calorific value is observed (from 30.04 to 33.02 MJ/kg). In addition, the morphology of the particles changes, on account of the formation of open pores and channels.
The process of anthracite and its semi-coke combustion in the presence of 5 wt.% (in terms of dry salt) additives of copper salts Cu(NO3)2 and Cu(CH3COO)2 was studied. The activating additives were introduced by an incipient wetness procedure. The ignition and combustion parameters for coal samples were examined in the combustion chamber at the heating medium temperatures (Tg) of 600–800 °C. The composition of the gaseous combustion products was controlled using an on-line gas analyzer. The fuel modification with copper salts was found to reduce the ignition delay time on average, along with a drop in the minimum ignition temperature Tmin by 138–277 °C. With an increase in Tg temperature, a significant reduction in the ignition delay time for the anthracite and semi-coke samples (by a factor of 6.7) was observed. The maximum difference in the ignition delay time between the original and modified samples of anthracite (ΔTi = 5.5 s) and semi-coke (ΔTi = 5.4 s) was recorded at a Tg temperature of 600 °C in the case of Cu(CH3COO)2. The emergence of micro-explosions was detected at an early stage of combustion via high-speed video imaging for samples modified by copper acetate. According to the on-line gas analysis data, the addition of copper salts permits one to reduce the volume of CO formed by 40% on average, providing complete oxidation of the fuel to CO2. It was shown that the introduction of additives promoted the reduction in the NOx emissions during the combustion of the anthracite and semi-coke samples.
The kinetic characteristics of the oxidation of non-food municipal MSW (MSW) were studied. Energetically valuable components of non-food MSW (sawdust, plastics, cardboard, textiles, leather, and rubber) were used as test samples. The elemental composition and technical characteristics of the test samples were determined using an elemental analyzer and standard procedures. The thermal conversion of non-food MSW was carried out using thermogravimetric analysis in the oxidation mode at a heating rate of 10 K/min in a temperature range of 25–800°C at atmospheric pressure. According to thermal analysis data (DTG curves), the process stages of the oxidation of non-food MSW, which correspond to the mono- or bimodal evolution of volatile compounds and the oxidation of the resulting carbon residue, were determined. The qualitative analysis of the gas-phase products of non-food MSW oxidation was performed by mass spectrometry, and the results were compared with the elemental composition and technical characteristics of the test samples. The activation energies of the stages of non-food MSW oxidation were calculated using the Coats–Redfern method. The maximum value of Ea (114.7 kJ/mol) was observed in a plastic sample, the decomposition of which tentatively proceeded in a single stage.
Analysis of the possibility of lumber waste disposal via combustion in a mixture with coal has been conducted. Conditions and characteristics of pellets ignition of fuel mixtures based on coal dust and grounded wood at various mass concentrations of the components have been experimentally determined. Fuel pellets were made by cold pressing on a hydraulic press. The experiments were performed in a medium of still air heated to high (from 600 °C to 800 °C) temperatures. Record of heating processes of the researched promising for thermal power engineering granules of mixed fuels, their subsequent ignition and combustion has been conducted using a high-speed video camera (image format - 1024 × 1024 pixels, frame rate - up to 100000 per second), which provides high discretization of registration results of processes characteristic times. It has been established that an increase in the proportion of wood components in the fuel granule significantly reduces values of ignition delay times of all researched mixtures based on 2B and 3B brown coal. The limit of stable ignition of such fuels has been determined. It is shown that ignition delay times of fuel pellets with characteristic sizes up to 8 mm (height) with diameter of 8 mm even at relatively low temperatures of the combustion medium do not exceed 16 s, which illustrates the promising application of such fuels even in small-scale power engineering.
In this paper, the possibility of synthesizing multiwalled carbon nanotubes (CNTs) by DC arc discharge plasma in ambient air is shown. The synthesis takes place in a graphite cathode with a crucible shape using tungsten powder as a catalyst. In the non-vacuum synthesis method the CO atmosphere is generated in the reaction zone during the arcing, preventing the products of the synthesis from oxidation. According to the X-ray diffraction analysis (XRD), the synthesized product includes more than 85 vol % of carbon crystalline phases with a graphite-like structure, a cubic tungsten phase, and two phases of tungsten carbide WC and W2C. The transmission electron microscopy data shows that the product of the synthesis contains CNTs with a relatively large number of walls (up to ~50 pcs) (MWCNTs) with a diameter of up to ~100 nm and a length of up to ~1.5 μm. It was found that crystalline objects corresponding in structure to WC tungsten carbide are identified inside CNTs.
The experimental study results of synthesizing molybdenum carbide in a plasma of a direct-current arc discharge by the vacuum-free method are presented. The influence of the current amplitude of the discharge circuit on the phase composition of the synthesis product is established. The synthesis product contains a microdimensional component and a nanosized one. The scanning electron microscopy (SEM) and X-ray diffractometry methods identified carbon fibers with a graphite structure and modified fibers containing graphite and molybdenum carbide as part of the microsized component. The nanoscale component contains clusters of particles that are a graphite matrix in which molybdenum carbide particles are immersed.
The work shows the results of the literature review of the methods for obtaining aluminium-silicon carbide - metal matrix composites (Al/SiC MMCs). This work also includes the collection, analysis, and systemization of the literature data where textual information is presented as a single lexical and semantic system and where numeral information is presented as a dimensional system. The analysis of the literature data was conducted by visual and cognitive modelling, so that methods of forming Al/SiC MMCs and operating parameters that provide the best properties of the material (maximum level of thermal conductivity and minimum level of thermal linear expansion) are determined. Compared to the literature data, the data are presented that were received in a series of tests for obtaining Al/SiC MMCs with spark plasma sintering from SiC, which was synthesized in atmospheric electric arc plasma. Within the framework of the given subject, the authors do not know any analogues of such an analysis and visualization system that allows us to analyse multivariate data, which is essential for solving issues of finding a correlation for the variety of initial parameters that characterize the process of obtaining Al/SiC MMCs and that characterize the cluster of properties for the obtained material. The comparison data are given for thermal conductivity levels of modern (aluminium) LED light devices and Al/SiC MMC samples.
The results of experimental studies indicating the possibility of obtaining molybdenum carbide crystalline phases in a dc arc discharge plasma initiated inside a hollow graphite cathode in the air gaseous atmosphere under normal atmospheric conditions are presented. According to the X-ray diffraction data, two molybdenum carbide phases are identified in the powder synthesis product: Mo1.2C0.8 and Mo2C, as well as graphite and metallic molybdenum. According to the transmission electron microscopy data, molybdenum carbide particles are in the carbon matrix and are characterized by dimensions mostly not exceeding 5–10 nm.
A method is presented for obtaining a material consisting mainly of carbon fibers with a graphite-like structure (Cfib) and a cubic phase of silicon carbide β–SiC using a DC arc plasma. The developed method of synthesis is characterized by a number of advantages, such as no protective gases required, easy implementation, and short duration of the operating cycle in the system (for several seconds). Judging by the data of scanning electron microscopy, the obtained silicon carbide crystals have a typical regular facetting and are characterized by a wide particle size distribution ranging from a size less than 1 μm to tens of microns. The silicon carbide crystals grow on the surface of carbon fibers, whereas their average size exhibits a decrease upon approaching the interface between the surface of graphite fiber and silicon carbide.
Патент № 2687423 C1 Российская Федерация, МПК C01B 32/921 (2017.01), C01G 23/00 (2006.01), B22F 9/14 (2006.01), B22F 9/16 (2006.01). СПОСОБ ПОЛУЧЕНИЯ ПОРОШКА НА ОСНОВЕ КАРБИДА ТИТАНА : № 2018130646 : заявл. 26.09.2018 : опубл. 13.05.2019 / Пак А.Я. ; заявитель ТПУ. – 9 с. : ил. – Текст : электронный.
Изобретение может быть использовано в неорганической химии. Способ получения порошка на основе карбида титана включает генерацию дугового разряда постоянного тока в газообразной среде между цилиндрическими графитовыми анодом и катодом. Порошковую смесь углерода и титана, взятую в атомарном соотношении Ti:C, равном 1:(1-3), помещают в полость катода, выполненного в виде вертикально расположенного стакана. Дуговой разряд поджигают в воздушной среде соприкосновением анода, выполненного в виде сплошного стержня, с порошковой смесью, расположенной на дне катода, при силе тока от 80 А до 200 А. Затем анод отводят вертикально вверх, образуя разрядный промежуток от 0,1 до 0,8 мм и поддерживая дуговой разряд в течение 2-20 с. Изобретение позволяет получить порошок на основе карбида титана в плазме дугового разряда постоянного тока, инициированного в воздушной атмосфере без создания разреженной защитной атмосферы. 4 ил., 1 табл., 3 пр.
Патент № RU 2686897 C1 Российская Федерация, МПК C01B 32/921 (2017.01), C01G 23/00 (2006.01), B22F 9/16 (2006.01), B22F 9/14 (2006.01).УСТРОЙСТВО ДЛЯ ПОЛУЧЕНИЯ ПОРОШКА НА ОСНОВЕ КАРБИДА ТИТАНА : № 2018130644 : заявл. 24.08.2018 : опубл. 06.05.2019 / Пак А.Я. ; заявитель ТПУ. – 7 с. : ил. – Текст : электронный.
Изобретение может быть использовано в неорганической химии. Устройство для получения порошка на основе карбида титана содержит цилиндрические анод и катод, выполненные из графита. Катод выполнен в виде вертикально расположенного стакана, к которому прикреплен диэлектрический держатель, в резьбовое отверстие которого вставлен винт, соединенный c одним концом анода. Другой конец анода расположен соосно катоду с возможностью продольного перемещения в полости катода для соприкосновения с порошковой смесью углерода и титана на дне катода. Анод и катод подключены к источнику постоянного тока. Изобретение позволяет получить порошок на основе карбида титана в плазме дугового разряда постоянного тока, инициированного в воздушной атмосфере без создания разреженной инертной атмосферы. 2 ил.
Патент № RU 2700596 C1 Российская Федерация, МПК C01B 32/991 (2017.01), B22F 9/14 (2006.01) . УСТРОЙСТВО ДЛЯ ПОЛУЧЕНИЯ ПОРОШКА НА ОСНОВЕ КАРБИДА ТИТАНА : № 2019111857 : заявл. 19.04.2019 : опубл. 18.09.2019 / Мартынов Р.С., Пак А.Я., Мамонтов Г.Я. ; заявитель ТПУ. – 9 с. : ил. – Текст : электронный.
Изобретение относится к неорганической химии, а именно к получению соединений с углеродом, и может быть использовано для получения порошка на основе карбида бора в металлургии, машиностроении. Устройство для получения порошка на основе карбида бора содержит диэлектрический корпус 1, на дне которого расположен цилиндрический графитовый тигель 2, в стенке которого напротив друг друга выполнены два сквозных отверстия, в которые соосно вставлены с одной стороны один конец графитового цилиндрического катода 3, а с другой стороны – один конец графитового цилиндрического анода 4. Другой конец катода 3 неподвижно закреплен на одной стенке корпуса 1 при помощи винта 6 через резьбовое отверстие. Второй конец анода 4 закреплен в держателе 7, конец которого вставлен в резьбовое отверстие в другой стенке корпуса 1. Анод 4 и катод 3 подключены к источнику постоянного тока 5. Технический результат cостоит в возможности получения порошка на основе карбида бора в плазме дугового разряда постоянного тока, инициированного в воздушной атмосфере при нормальных условиях. Поскольку графитовый депозит в процессе горения дугового разряда постоянного тока оседает на поверхности катода, сбор синтезированного порошка на основе карбида бора может быть осуществлен отдельно от него. При этом исходная порошковая смесь аморфного углерода и аморфного бора за счет размещения в отдельно стоящем тигле не оказывает влияния на величину омического сопротивления разрядного промежутка. 2 ил.
Представлены результаты исследований по получению кубического карбида титана в плазме дугового разряда постоянного тока, инициированного в открытой воздушной среде. Особенностью изложенного метода является его реализация без применения газовых или жидких защитных сред, предотвращающих окисление продуктов и исходных реагентов кислородом воздуха. По данным рентгеновской дифрактометрии в составе порошкового продукта идентифицированы графит gC, гексагональный титан alpha-Ti, кубический карбид титана TiC. Частицы TiC представлены объектами с правильной характерной огранкой и размерами от единиц до десятков микрометров.
Представлены результаты экспериментальных исследований синтеза карбида молибдена в плазме дугового разряда постоянного тока безвакуумным методом. Установлено влияние амплитуды тока разрядного контура на фазовый состав продукта синтеза. Продукт синтеза содержит микроразмерную компоненту и наноразмерную. В составе микроразмерной составляющей методами растровой электронной микроскопии и рентгеновской дифрактометрии идентифицированы углеродные волокна со структурой графита, а также модифицированные волокна, содержащие графит и карбид молибдена. Наноразмерная компонента содержит скопления частиц, представляющих собой графитовую матрицу, в которую погружены частицы карбида молибдена.
Показана возможность синтеза многостенных углеродных нанотрубок в плазме дугового разряда постоянного тока, инициированного в открытой воздушной среде. Процесс синтеза реализован в полости графитового катода, в которой в качестве катализатора присутствует порошок вольфрама. Применяемый метод реализуется за счет генерации газообразного оксида углерода СО, экранирующего реакционную зону от кислорода воздуха, предотвращая окисление продуктов синтеза. Согласно данным рентгеновской дифрактометрии синтезированные порошковые материалы содержат более чем 85 об. % углеродных кристаллических фаз с графитоподобной структурой, а также содержат кубическую фазу вольфрама, две фазы карбида вольфрама WC и W2C. Согласно результатам просвечивающей электронной микроскопии продукт синтеза содержит углеродные нанотрубки, особенностью которых можно считать относительно большое количество слоев (до ~50 шт.) при диаметре до ~100 нм и длине до ~1.5 мкм. При этом внутри углеродных нанотрубок идентифицируются кристаллические объекты, соответствующие по структуре карбиду вольфрама WC.
Изложены результаты экспериментальных исследований, свидетельствующие о возможности получения кристаллических фаз карбида молибдена в плазме дугового разряда постоянного тока, инициированного внутри полого графитового катода в воздушной газовой среде при нормальных атмосферных условиях. По данным рентгеновской дифрактометрии в порошковом продукте синтеза идентифицируются две фазы карбида молибдена: Mo1.2C0.8 и Mo2C, а также графит и металлический молибден. По данным просвечивающей электронной микроскопии частицы карбида молибдена находятся в углеродной матрице и характеризуются размерами, преимущественно не превышающими 5−10 nm.
Представлены результаты экспериментальных исследований по разработке научно-технических основ метода получения кубического карбида титана в плазме дугового разряда постоянного тока, инициированного в воздушной среде. По данным рентгеновской дифрактометрии порошковых материалов, полученных в серии экспериментов, определены зависимости фазового состава продукта от длительности синтеза. По данным растровой электронной микроскопии и энергодисперсионного анализа выявлен ряд морфологических типов частиц карбида титана, которые формируются в результате неравномерности распределения энергии в реакционном объеме.
Рассмотрен безвакуумный электродуговой синтез порошковых материалов в системе “углерод – кремний”. Оценена возможность управления фазовым, гранулометрическим составом и морфологией частиц продукта в процессе безвакуумного электродугового синтеза. По данным рентгеновской дифрактометрии в составе полученного продукта идентифицируется кубическая модификация карбида кремния с параметром элементарной ячейки 4,375 ± 0,016 Å; также исходный кремний и несвязанный углерод в форме графита. Показана зависимость фазового состава продукта от средней мощности дугового разряда. Определены морфологические типы полученных в серии экспериментов кристаллов карбида кремния, оценен средний размер частиц карбида кремния, изучен химический состав продукта синтеза. Применяемый безвакуумный электродуговой метод отличается отсутствием необходимости формирования защитной газовой среды внутри герметичной камеры электродугового реактора постоянного тока совмещенного типа, так как процесс проходит в атмосфере газа СО, который генерируется при горении дугового разряда в воздушной среде.
Molybdenum carbides can be used in one of the most perspective sectors−hydrogen energy. Materials based on molybdenum carbide have high catalytic activity, which allows them to be used as effective inexpensive catalysts in hydrogen generation reactions, associated with the generation and oxidation of hydrogen. One of the main approaches to the obtaining of molybdenum carbides is the electric arc method based on the synthesis of material in DC arc plasma initiated in the gap between graphite electrodes. This article presents the results of a series of experiments on the production of molybdenum carbides, using a vacuumless arc discharge method, and on the influence of energy on the phase composition of the synthesis product.
Non-isothermal oxidation of brown coal with 5 wt% of Cu(NO3)2, 5 wt% of Ce(NO3)3 and {2.5 wt% Cu(NO3)2 + 2.5 wt% Ce(NO3)3} additives was studied. The introduction of additives was carried out by an incipient wet impregnation method to ensure uniform distribution of cerium and copper nitrates within the structure of coal powdery samples (according to SEM and EDX mapping). The samples reactivity was studied in an isothermal oxidation regime at 200 °C (1 h) and by DSC/TGA at 2.5 °C/min heating rate. The additives implementation was found to reduce significantly the oxidation onset temperature (ΔTi = 20–55 °C), the samples oxidation delay time (Δti = 2–22 min) and overall duration of the oxidation process (Δtc = 8–16 min). The additives efficiency could be graded in accordance with the activation on the coal oxidation in the following row: Cu(NO3)2 > {Cu(NO3)2 + Ce(NO3)3} > Ce(NO3)3. According to the mass spectroscopy, the obtained row of activation correlates well with the initial temperature of the studied nitrate’s decomposition (from 190 to 223 °C). A presence of nitrates was found to change significantly the trend of heat release taking place during the oxidation of coal samples (according to DSC/TGA data). The influence of coal morphology and volatiles content in initial sample on the parameters of the oxidation process was studied as well. Activation energy (Ea) of the coal oxidation was calculated using Coats–Redfern method. Maximum decrease in Ea from 69 to 58 kJ/mol was observed for the samples with Cu(NO3)2.
The exact characteristics of the pyrolysis and combustion kinetics for Siberian bituminous coals and lignites were studied for better understanding of the fuel conversion processes. The bituminous coal samples of Kuznetskiy deposit and lignite samples of Kansko-Achinsk deposit were investigated in argon and in argon/air gas mixtures. The pyrolysis and oxidation experiments were executed at four heating rates (5, 10, 20 and 30 °C/min) under TG/DSC analyses coupled with mass-spectrometry. The activation energy for bituminous coal and lignite samples was decreased with conversion degree during oxidation. The combustion products of highest oxidation degree (CO2 and H2O) were dominated in gases released in oxidizing atmosphere. Contrariwise, activation energy was increased during pyrolysis with high content of CO, CO2, H2O, CH4, and H2 in released gases. The two isoconversional models were applied to determine the activation energy dependence on fuel samples conversion: Starink model and Ozawa iterative procedure. The mean arithmetic values of the resulted activation energy were 60 kJ/mole and 400 kJ/mole for oxidation and pyrolysis processes, respectively. These values are in good agreement with the results, presented previously for the other coals. The Starink model showed higher accuracy and lower activation energy values. The heating rate by non-isothermal oxidation and pyrolysis had the significant influence on the reaction rate because of evolution processes of the reactive surface and pore structure of the coal samples.
