AC plasma torch with a H2O/CO2/CH4 mix as the working gas for methane reforming

Multi-gas AC plasma torches for gasification of organic substances

Thermal plasma processing of carbon sources using a plasma jet with high heat capacity is one of the most promising methods for the synthesis of new materials. This paper describes the low-temperature deposition of carbon nanomaterials by remote plasma-enhanced chemical vapor deposition (PECVD) in the absence of catalysts. The remote PECVD process differs from conventional and direct PECVD process in two ways: (a) only a subset of the process reactants and/or diluents are directly plasma excited; and (b) thin film deposition takes place on a substrate that is outside of the plasma glow region. In conventional CVD methods, carbon is produced from the decomposition of carbon sources such as hydrocarbons, carbon monoxide, alcohols, and so on, over a metal catalyst. The unavoidable metal species remaining in carbon nanomaterials would lead to obvious disadvantages for property characterization and application exploration. Despite sustained efforts, it is still an intractable problem to remove metal catalysts completely from carbon nanomaterials samples without introducing defects and contaminations. Good reactor design allowed to overcome problems of chemical and structural purity, and poor process robustness in terms of phase composition of product from run to run. For the synthesis of graphene materials, carbon black, carbon nanotubes, nanowires we used the thermal plasma generator which is a high current divergent anode-channel DC plasma torch. The experiment involved a simultaneous input of hydrocarbons (methane, propane, butane, acetylene) with the plasma forming gas (helium, argon, nitrogen) into the plasma torch, wherein heating and decompositions occurred in the plasma jet and in the region of the arc discharge, followed by condensation of the synthesis product on metallic surfaces. The deposition rate was varied with distance from the plasma. Consumption of carbon source, plasma forming gas and plasma torch power were changed independently from each other. For the experimental conditions the electric power of plasma torch was set up to 40 kW. Regularities of formation of carbon thread-like nanostructures and graphene in the course of hydrocarbons pyrolysis in thermal plasma without participation of catalytic particles were studied by means of electron microscopy, X-ray diffraction, IR-spectrometry and thermogravimetry. Depending on the pyrolytic synthesis parameters, different proportions of crystal carbon and soot may be obtained. It has been demonstrated that the phase composition is varied by hydrocarbons flow rate, plasma forming gas pressure and dc plasma torch power. It has been established through the experiments that carbon nucleation is volumetric and proceeds according to the model of explosive soot formation.

Powerful AC plasma torches are in demand for a number of advanced plasma chemical applications, they can provide high enthalpy of the working gas. IEE RAS specialists have developed a number of models of stationary thermal plasma torches for continuous operation on air with the power from 5 to 500 kW, and on mixture of H2O, CO2 and CH4 up to 150 kW. AC plasma torches were tested on the pilot plasmachemical installations. Powerful AC plasma torch with hollow electrodes and the gas vortex stabilization of arc in cylindrical channels and its operation characteristics are presented. Lifetime of its continuous operation on air is 2000 hours and thermal efficiency is about 92%, the electric arc length between two electrodes of the plasma torch exceeds 2 m.

The most important unit of the plasma torch mainly subjected to the thermal load of the electric arc is electrode. Tungsten, hafnium, yttrium, aluminum, copper, iron and their alloys are used as electrode materials depending on the plasma-forming gas. Copper-based alloys can be rationally used for gases containing oxygen. The experiments were performed on the three-phase alternating current vortex plasma torch with power of 120 kW working on a mixture of steam, carbon dioxide, methane and carbon tetrachloride for the following flow rates 2.9 g/s, 2.9 g/s, 1.21 g/s and 2.44 g/s respectively. The material of erosion of copper rod electrodes was sampled from water-cooled walls of electric arc plasma torch channels made of stainless steel. The sample was divided into magnetized and non-magnetic parts. According to the energy-dispersive elemental analysis the products of electrode erosion contain oxides and chlorides of copper and iron, as well as metallic copper and iron.

The article deals with a three-phase high-voltage AC plasma torch with separate supply of gases and vapours during its operation on a mixture of steam, carbon dioxide, methane and organic vapours. Increase in flow rates of organic vapours and methane leads to increase in the arc voltage drop from 875 to 1150 V and electric power from 80 to 102 kW.

A review of existing plasma torches designed for steam plasma is presented in this paper. Together, they cover the following ranges of key technical parameters: efficiency from 51 to 95%, enthalpy of the plasma from 12 to 84 MJ/kg, and the fraction of the steam in the plasma forming gas from 17 to 100%. The advantages of alternating current to produce plasma is grounded. The problems of creating of a steam plasma torch are described. The description of the experiments carried out on the AC plasma torch, during which the total flow of the plasma forming steam-air mixture and the effective value of the current remained constant ∼ 6.7 g/s and ∼ 28.4 A, respectively, and the steam content ranged from 54 to 85%, is given. With an increasing proportion of steam, the voltage increased from 1.03 to 1.59 kV, while the estimated temperature of the arc decreased from 11600 to 10200 K, which is caused by intensification of heat transfer. In all modes, there was a high efficiency of 94.3–95.3% with a significant change in the specific energy input from 8.3 to 12.4 MJ per 1 kg of plasma-forming gas.

The presented design and parameters of a three-phase AC plasma torch with the power up to 500 kW, flow rate of air 30–50 g/s (temperature up to 5000 K) could be used in different plasma chemical processes. Range of measured plasma temperature is 3500–5000 K. The paper presents investigations of the plasma torch operation modes for its application in plasma chemical technologies. Plasma chemical technologies for various purposes (processing, destruction of various wastes, including technological and hazardous waste, conversion or production of chemicals to obtain nanoscale materials, etc.) are very promising in terms of the process efficiency. Their industrial use is difficult due to the lack of inexpensive and reliable plasma torches providing the desired level of temperature, enthalpy of the working gas and other necessary conditions for the process. This problem can be solved using a considered design of a three-phase alternating current plasma torch with power of 150–500 kW with working gas flow rate of 30–50 g/s with mass average temperature up to 5000K on the basis of which an industrial plasma chemical plant can be created. The basis of the plasma torch operation is a railgun effect that is the principle of arc movement in the field of its own current field. Thanks to single supply of power to the arc, arcs forming in the discharge chamber of the plasma torch move along the electrodes under the action of electrodynamic forces resulting from the interaction of the arc current with its own magnetic field. Under the condition of the three-phase supply voltage, arc transits from the electrode to the electrode with change in the anodic and cathodic phases with frequency of 300 Hz. A special feature of this design is the ability to organize the movement of the arc attachment along the electrode, thus ensuring an even distribution of the thermal load and thus achieve long time of continuous operation of the plasma torch. The parameters of the plasma jet of the plasma torch and the single-phase three-phase plasma injector for use in a plasma-chemical unit for production of nano-dispersed materials are described in the paper.

The syngas production performance of scrap iron reacting with carbon dioxide and water steam was assessed under different operating conditions in a fixed bed oxidizer reactor. The syngas generation step is part of a novel process scheme encompassing the reutilization of iron scrap from steelmaking and the combined splitting of industrially captured carbon dioxide and steam into a syngas. At 1050 °C, a maximum volume percentage of 37 % carbon monoxide was detected in the product gas with the injection of 1 NL/min carbon dioxide. The carbon dioxide conversion was confirmed to be promoted by temperature. Subsequently, combined tests with carbon dioxide and water steam were carried out to assess the production and quality of the syngas (H2 and CO) by varying the reactants total flow rate, the iron bed mass and the reactants molar ratio. By decreasing the total reactants flow rate, the reactants splitting process was promoted and below a certain flow rate carbon dioxide splitting prevailed on that of water steam. By increasing the H2Ov/CO2 molar ratio, the splitting was enhanced for both species. In particular, for the tested flow rate the water splitting increased by 10% compared to 3.5% of the CO2 splitting. This indicated that a high H2Ov/CO2 ratio optimizes syngas production in the designed system. Finally, with H2Ov/CO2 = 6 and the optimal thermochemical syngas composition was achieved, including 41 % H2 and 12.1 % CO, being the remaining part constituted by CO2 when computed on a dry basis.

Compared with other fossil fuels, liquefied natural gas (LNG) supplies relatively clean energy because its low contribution to environmental pollution. Furthermore, while 10% of the gas energy was required for its liquefaction, the valuable high cryogenic (at ∼110 K) exergy of the LNG is wasted in many LNG receiving terminals worldwide, by uselessly cooling the seawater used for its re-vaporization. This cryogenic exergy is, however, as an excellent power source. In addition, due to the increasing concern about global climate change, the development of power system which minimizes CO2 emission is of great interest. In this paper, new cycles are proposed which integrate LNG cryogenic exergy utilization and CO2 recovery. The cycles employ both the fuel chemical exergy and LNG cryogenic exergy for power generation, they use no cooling water, and on the contrary, allow the easy removal and recovery of water and CO2 generated from combustion to thereby offer both energy saving and greenhouse gas emission mitigation. The cycles employ CO2 as the main working medium. Oxygen and fuel methane are introduced at stoichiometric ratio, and thus the turbine exhaust is merely a mixture of carbon dioxide and water steam. The LNG coldness is used to improve the power generation efficiency by (1) serving as a low temperature heat sink of the power cycle, and (2) cooling the working fluid prior to compression, to reduce compressor power consumption. Without consuming additional power, the water and extra carbon dioxide generated from combustion can be easily separated from the main stream during the exothermic process when integrated with the LNG evaporation process. Internal combustion and recuperation are adopted to increase the average heat absorption temperature. The proposed cycles are simulated using the commercial ASPEN PLUS code, and their performance is computed. The results indicate that the proposed cycles indeed reduce CO2 emissions significantly with very attractive thermal performances, able to attain thermal and exergy efficiencies of 60∼65% and 45∼53% respectively.

The article discusses a new method for producing synthesis gas using an ac electric arc. The relationship between the electrical parameters and the energy characteristics of the process was established: with an increase in carbon dioxide concentration in the electrode zone, the hydrogen concentration increases. This leads to an increase in the plasma torch power, which can be used to adjust the chemical process.

This series of articles is devoted to the study of high-power AC plasma torches with different designs, purposes, and characteristics that allow the operation of a certain type of plasma generator in wide power and pressure ranges. The first part is devoted to the investigation of AC plasma torches with a specific purpose, that is, the initiation of an arc of a powerful PT. This paper describes the design features of a PT in detail, its characteristics, the parameters of the plasma stream, such as temperature, and heat content. The features of operation and various options of auxiliary plasma torch injectors that provide ignition of the main arc in the electric-discharge chamber are considered as well.

The paper is devoted to investigation of electrophysical processes in the electric discharge generated by a three-phase AC plasma torch when using a high pressure inert working gas. AC plasma torch design with end electrodes intended for work on inert gases at pressures up to 81 bar is studied. Current-voltage characteristics for different gas flow rates and pressures are presented. Physical processes characteristics of the arising voltage ripples which depend on various working parameters of the plasma torch have been investigated. Arc burning processes in the electric discharge chamber of the three-phase AC plasma torch at various working parameters were photographed.

This paper studies the anode region of an eroding anode with a nonstationary arc-root attachment. High-current free-burning short as well as long arcs at atmospheric pressure are investigated. A technique to study the anode region of the arc is suggested. An anode moving perpendicular to the arc axis was used for estimating parameters of the anode jets at a given moment of their development. The mechanism of current transfer in the anode region is considered on the basis of electrophysical and optical-spectroscopic investigations of the arc attachment traces and plasma parameters both of the anode jet and arc column. The anode jet was found to be of importance in the stationary arc operation. The near-anode plasma parameters depend on the effect of the cathode jet. In short arcs (L/sub a//spl sim/2 mm), the plasma temperature at the anode exceeds 20000 K, while in long arcs (L/sub a/>50 mm), it falls below 7000 K. At plasma temperature T/sub a/>11000 K, the total arc current in the anode region is transferred through the arc plasma, while at lower temperatures, both the arc column and the anode jet take part in the current transfer.

Formation of carbon oxides during tobacco combustion: Pyrolysis studies in the presence of isotopic gases to elucidate reaction sequence

Radio-frequency (RF) inductively coupled plasma (ICP) torches using a supersonic nozzle have many industrial materials processing applications and have also been proposed as novel electrothermal plasma thrusters for space propulsion. The gas injection method in plasma torches plays an important role in both gas heating dynamics and overall discharge stabilization. Here, we investigate reverse vortex gas injection into a supersonic ICP torch for RF powers up to 1 kW, argon mass flow rates between 15 and 180 mg s−1, and plasma torch pressures from ∼270 Pa to ∼50 kPa. In this configuration, gas is injected tangentially just upstream of the nozzle inlet. This produces a bidirectional vortex flow field where gas first spirals upwards along the outer edge of the plasma torch walls, before then reversing direction at the torch end and spiralling back down through the central plasma region towards the nozzle exit. Results are compared to a more conventional forward vortex configuration where gas is instead injected tangentially from the upstream end of the torch, and which forms a unidirectional vortex that spirals towards the downstream nozzle. While performance is similar for gas flows below 80 mg s−1, we show that at higher mass flow rates both the effective torch stagnation temperature and thermal efficiency can be increased by almost 50% with reverse vortex injection. Considering that the measured RF antenna-plasma power transfer efficiency is similar for both configurations, this enhancement occurs because of the unique bidirectional vortex flow field which leads to reduced gas-wall heat losses and consequently an increased enthalpy flow leaving the torch.