Numerical modeling of a downdraft plasma coal gasifier with plasma reactions

In this paper, a 3D numerical simulation of a downdraft plasma gasifier with plasma reactions is conducted. The effects of the equivalence ratio (ER) on the syngas properties in the presence of the plasma reactions are investigated. The boundary conditions for the air plasma inlet of the gasifier are obtained from the outlet of a 10 kW microwave plasma generator. A conventional gasification analysis is carried out to validate the model. In the second part of the study, plasma reactions are added to conventional gasification equations. Mole fractions of the constituents of the syngas and temperature contours are obtained for different ER values. According to the results, with the increase of ER from 0.20 to 0.45 the lower heating value of the produced syngas decreased from 1536.6 kcal/m³ to 751.8 kcal/m³.     

Comparison tests for plasma viscosity measurements

The present study measured plasma viscosity using three different viscometers: Ostwald capillary-tube viscometer, Brookfield rotating viscometer, and scanning capillary-tube viscometer (SCTV). The plasma viscosity data obtained using Ostwald viscometer at 37 °C with the conversion constant provided by its manufacturer were in good agreement with those obtained using Brookfield viscometer at 37 °C. In addition, the plasma viscosity data obtained using SCTV were in excellent agreement with those from Brookfield viscometer. However, when the Ostwald viscometer is used for plasma viscosity measurements at the room temperature, one should be cautioned because the conversion constant provided by manufacturers may not be applicable to the room temperature as the surface tension of plasma depends on temperature, affecting the accuracy of the plasma viscosity measurement.     

The transition state of disilane plasma

The initial transition state in the plasma decomposition of disilane was investigated by measuring the electron energy in a disilane plasma, and by studying both optical emission spectroscopy and film properties.At the beginning of the discharge, the emission of SiH^* was not observed, and the electron energy in the plasma was about 10 times lower than in the steady state. These phenomena were caused by an abrupt increase of the pressure just after the ignition, followed by disilane decomposition.Under insufficient energy conditions, production of silylene is highly favoured by the disilane decomposition which gives porous hydrogenated amorphous silicon (a-Si:H) films.We shall prove the importance to shorten the initial transition period in which the plasma energy is insufficient for disilane decomposition. Keeping the gas pressure constant at the beginning of the reaction enables to avoid the depression of the plasma energy and to obtain a-Si:H films with good optoelectronic properties.     

Particle-gas mass transfer under plasma conditions

A simple analytical method is proposed for particle-gas mass transfer calculations under plasma conditions. This method, called the Z-potential method, fully accounts for the temperature variation of the gas transport properties while permitting use of the convenient isothermal expression Sh = 2.0. The Z-potential approach is also found to be extremely useful in ascertaining the Knudsen discontinuum effect on mass transfer between the plasma gas and a small particle. A predictive model for the Knudsen effect, developed by combining the Z-potential approach with the jump theory, is illustrated in detail by means of a case study on a nitrogen plasma system.     

Hydrogen production from ethanol decomposition by a microwave plasma: Influence of the plasma gas flow

This paper describes a study of molecular hydrogen production from ethanol decomposition by argon microwave discharge at atmospheric pressure. Different Ar flows (in the 0.50–1.5 L/min range) were tested while ethanol was constantly supplied at 0.22 g/h. Plasma showed a great stability throughout the whole operation range and in all cases, full ethanol conversion was obtained, the major product being hydrogen (2.1–2.5 mol per mole of ethanol). Other products were carbon monoxide, methane and acetylene with traces of some heavier molecules (e.g. diacetylene) and carbon deposits. The fact that heavier molecules are only present as traces is explained as the result of the high electron density (thus inducing multiple collisions) whereas gas flows determine the residence time of particles into the plasma and consequently the temperature, which in turn affects the different reactions. As Ar flow decreases (i.e. residence time increases), more carbon deposits (which were found to have some soot origin) are obtained.     

Characterization of metal-supported axial injection plasma sprayed solid oxide fuel cells with aqueous suspension plasma sprayed electrolyte layers

A method for manufacturing metal-supported SOFCs with atmospheric plasma spraying (APS) is presented, making use of aqueous suspension feedstock for the electrolyte layer and dry powder feedstock for the anode and cathode layers. The cathode layer was deposited first directly onto a metal support, in order to minimize contact resistance, and to allow the introduction of added porosity. The electrolyte layers produced by suspension plasma spraying (SPS) were characterized in terms of thickness, permeability, and microstructure, and the impact of substrate morphology on electrolyte properties was investigated. Fuel cells produced by APS were electrochemically tested at temperatures ranging from 650 to 750 °C. The substrate morphology had little effect on open circuit voltage, but substrates with finer porosity resulted in lower kinetic losses in the fuel cell polarization.     

Progress in waste utilization via thermal plasma

As the world races toward its urban future, the quantity of wastes, one of the vital by-products of an enhancement in the standards of living, is exponentially rising. The treatment of wastes employing plasma is an upcoming area of research and is globally used for the simultaneous processing of diverse wastes coupled with the recovery of energy and materials. Ground-breaking and cost-effective thermal plasma technologies with high efficiencies are a prerequisite for the growth of this technology. This paper delivers an evaluation of the fundamentals such as the generation and characteristics of the thermal plasma along with the various types of wastes treatable by thermal plasma and the related issues. Furthermore, the authors discuss different types of advanced technologies as well as the material and energy recovery techniques and their present status worldwide, at lab-scale and industrial scale. The application of different thermal plasma technologies is discussed as a means to promote this technology into alternative applications, which require higher flexibility and greater efficiency. Mathematical modeling studies are also assessed with an objective to derive ideal conditions and permissible limits for the reactors and to test a variety of waste materials. A strategy to improve the feasibility and sustainability of waste utilization is via technological advancement and the minimization of environmental effects and process economics. This paper sheds light on diverse areas of waste utilization via thermal plasma as a potentially sustainable and environmentally friendly technology.     

Employing plasma as catalyst in hydrogen production

A novel approach in hydrogen production via reforming of hydrocarbons that will use catalytic properties of non-equilibrium plasma gas discharge is presented. CH₄/CO₂ mixtures are heated to a temperature of 900°C, so that mixture will have approximately 80% of the energy required for thermal reforming. Preheated mixtures are then processed in a Pulsed Corona Discharge type plasma source and the catalytic effect of a non-equilibrium plasma is observed for promotion of hydrogen generation.     

Investigation of hydrogen plasma interaction withmetal hydride

The correlation between phase composition hydride forming alloysZr-V-Fe and Zr-V-Fe-B-O, their hydrogen sorption characteristics, and electrotransfercharacteristics, in the gas phase of alloy-hydrogen systems under gas discharge burning in planarmagnetron whose cathode was covered with a powder metal hydride layer, has been established.It has been shown that the balance of gas discharge particles is primarily determined by thepeculiarities of the discharge plasma interaction with metal hydride.     

Plasma-controlled chemistry in plasma reforming of methane

Plasma is receiving attention as a prospective tool for the reforming process of obtaining synthesis gas and hydrogen. Although many reports on plasma-induced reforming have been introduced, detailed correlations between the reaction paths and plasma parameters remain unclear. Therefore, to figure out the relative role and dominance of plasma-controlled chemistry in the reforming process, we investigate diverse reaction paths in reforming CH₄. The arc column length is proposed as a universal process parameter of the plasma-reforming process, and a rationale to support the proposition is provided As a result, the dependence of the reforming process on the arc column length is explained. Three different reaction regimes, defined according to the arc column length and plasma chemistry in each regime, are addressed. The arc column length controls the thermal environment of the reaction and activates different reaction pathways depending on its length. This concept of control also enables the discovery of efficient ways of reforming. The increase in thermal efficiency by controlling the arc column reveals possibilities for optimizing the plasma-induced reforming process.     

燃气轮机等离子点火系统实验研究

现代燃气轮机以其体积小、重量轻、运行可靠、机动性好、自动化程度高、单机功率大、维护简单等优点已经广泛应用于航空、船舶、电力、铁路、石油和天然气输送等诸多工业领域。控制燃气轮机的点火和燃烧过程将直接关系到整机的工作可靠性和经济性。特别是在高空燃气轮机上,缩短     

等离子体NOx脱除技术概述

等离子体NOx脱除技术作为一种脱硝新工艺,受到世界各国的广泛关注.在叙述了等离子体脱硝的的两种反应机理、等离子体NOx脱除的主要方法(电子束照射法、高压脉冲电晕法、高压直流电晕法、介质阻挡放电法和介质填充床放电法)和等离子体脱硝的反应器结构的基础上,指出了等离子体脱硝方法中的不足,并对等离子体脱硝技术做了展望.     

Refining of metallurgical-grade silicon by inductive plasma

A new process combining inductive plasma torch and electromagnetic stirring of molten silicon in a cold crucible has been developed to refine upgraded metallurgical silicon. The addition of reactive gases to the plasma leads to volatilisation of impurities at the liquid silicon surface. The concentration of boron impurities decreased from 15 ppmw in the raw material to less than 2 ppmw after the plasma treatment. The most volatile form of boron was BOH, which was obtained by simultaneous treatment with oxygen and hydrogen. The limitation in boron volatilisation is due to the formation, at high oxygen flow rate, of a silica layer at the surface of the molten silicon, which results in a dramatic drop of the volatilisation rate. In contrast to boron, the concentration of phosphorus was reduced by only a factor of two, although the remainder seems to be electrically neutral. Thermodynamic studies suggest that phosphorus could be trapped as phosphate in combination with metallic impurities. Cells made of material produced using this technique exhibited a conversion efficiency of 12.4%.     

等离子体技术转化煤的应用

介绍等离子体的发生机理和等离子体技术在煤炭转化领域的应用,包括煤的热解、气化、液化、发电及煤的脱硫脱硝等,介绍该技术的应用研究现状、存在问题及发展前景,指出等离子煤转化是一种高效、洁净的技术,在煤化工等领域具有巨大的应用空间。     

等离子体脱碳氢研究

文章综述了等离子体技术在脱除汽车尾气上的应用，主要总结了国内外用等离子体技术处理HC化合物的反应原理和装置，最后对该技术的前景和应用作总结。     

On efficiency of plasma gasification of wood residues

High temperature plasma gasification of wood is evaluated for the production of a fuel gas (syngas) for combined heat and power production. The advantages of plasma by comparison with existing thermochemical processes are in the high heating value gases, process control and the lower energy consumption per unit of output. From one kilogram of 20% moisture wood it is possible to obtain 4.6-4.8 MJ of electricity (net of electricity input) and 9.1-9.3 MJ of thermal energy when using wood with average elemental composition and with a LHV energy content of 13.9 MJ, when using a combined Brayton and Steam cycle generating plant. Experimental data from an air plasma gasification plant using alternating current (AC) plasma torches was integrated with a thermodynamic model showing that the chemical energy in the produced syngas was 13.8-14.3 MJ kg⁻¹ with a power input of 2.2-3.3 MJ kg⁻¹.     

Atmospheric pressure microwave plasma source for hydrogen production

Nowadays hydrogen is considered as a clean energy carrier and fuel of the future. That is why the interest in production and storage of hydrogen is still increasing. One of the promising technology is using microwave plasma for hydrogen production. In this study we propose two types of an atmospheric pressure microwave plasma source (MPS) for hydrogen production via methane conversion. The first one was a nozzleless waveguide-supplied coaxial-line-based. The second one was a nozzleless waveguide-supplied metal-cylinder-based. They can be operated with microwave frequency of 2.45 GHz and power up to a few kW with a high gas flow rates (up to several thousands l/h). We present experimental results concerning electrical properties of the MPS, plasma visualization, spectroscopic diagnostics and hydrogen production. The experiment was carried out with methane flow rate up to 12,000 l/h. An additional nitrogen or carbon dioxide swirl flow was used. The absorbed microwave power was up to 5000 W. Our experiments show that MPSs presented in this paper have a high potential for hydrogen production via hydrocarbon conversion.     

等离子发生器燃烧过程的数值研究

用湍流扩散燃烧的简单概率密度函数模型对等离子发生器燃烧流场进行了数值模拟。其中概率密度分布采用函数,使用RNG湍流模型得到了流场各参数同平均混合分数,混合分数脉动均方值的关系图及等离子发生器内部温度、压力、速度、密度、湍动能及各种燃烧产物等一系列湍流燃烧流场的特性参数分布,为研究燃烧室等离子强化燃烧机理奠定了基础。     

Hydrogen production by low-temperature plasma decomposition of liquids

The paper shows, that a low-temperature plasma initiated in liquid media in interelectrode discharge gap is able to decompose hydrogen containing organic molecules resulting in obtaining gaseous products with volume part of hydrogen higher than 90% (up to gas chromatography data). Tentative assessments of energy efficiency, calculated with regard for hydrogen and feedstock heating value and energy consumption, have shown efficiency factor of 60–70%, depending on the source mixture composition. Theoretical model calculations of discharge current and voltage have been performed; the values are in good accordance with experimental data.