Non-thermal Arc Plasma Research Articles

Experimental study on a small-scale oxygen-enriched entrained flow biomass gasifier assisted by non-thermal arc plasma

A small-scale oxygen-enriched entrained flow biomass gasifier consisting of a non-thermal arc plasma torch and a stainless steel bellows was developed. The characteristics of the non-thermal arc plasma were diagnosed. The effects of oxygen concentration and bellows length on the gasification process using rice husk powder as feedstock at a feed rate of 27.1 g/min were studied. The results show that increasing the oxygen concentration of gasifying agent and using longer bellows both lead to the improvement of cold gas efficiency, carbon conversion efficiency, and yields of H2 and CO. The cold gas efficiency of the gasifier at a bellows length of 500 mm and oxygen concentration of 34.7% is 65.8%. And benefiting from low auxiliary energy consumption, the gasifier’s energy efficiency reaches 60.5%. The non-thermal arc plasma assists the entrained flow gasification by converting part of the feedstock into activated reactants.

Plasma-modified wood sawdust waste for the removal of reactive blue II anionic dye from aqueous solution

The Removal of an anionic Reactive Blue 2 (RB2) dye in an aqueous solution was successfully achieved using a plasma-modified agricultural biomaterial waste. Sawdust from Moabi (Baillonellatoxisperma) and Sapelli (Entandrophragmacylindricum) was modified using non-thermal gliding arc plasma. The natural raw materials and plasma treated were characterized by Infrared Spectroscopy (FTIR), Thermogravimetric Analysis (TGA), Scanning Electron Microscopy (SEM), XRD, Chemical analysis by Fluorescence, Sorption Analyser, and Zetametry. Experimental parameters such as initial pH, contact time, adsorbent dose, initial RB2 concentration, and temperature were optimized. The results showed that the removal of Reactive Blue 2 dye was favorable at acidic pH conditions with the maximum capacity going from 172,85 to 200,91 mg.g-1 to 98,19 and 149,02 mg.g-1 respectively for raw and plasma-treated Sapeli and Moabi. The Avrami fractional-order kinetic provided the best fit to the experiments data and the thermodynamic adsorption data of untreated (SSB and SMB) and plasma-treated (SSM and SMM) sawdust followed an exothermic process. This work demonstrated that non-thermal plasma modified wood sawdust can be a good alternative absorbent for the removal of dye pollutants from an aqueous solution.

Non-Thermal Air Arc Plasma Assisted Biomass Gasification

A novel small-scale biomass gasification system assisted by a non-thermal air arc plasma is introduced in this paper and the gasification experiment setup, procedure and gasification results are described in detail. The results show that the production of syngas (CO and H2) is in the range of 1.14 Nm3/h to 1.46 Nm3/h during the system normal operation at plasma power consumption 120 W and biomass feed rate 3360 g/h, and the volume fraction of syngas in produced gas is in the range of 20.2% to 23.89%. The maximum cold gasification efficiency is 44.56% and the minimum specific energy consumption (defined as the ratio of plasma power consumption to the heat power content of the produced gas) of the gasification system is 2.18%, which is much lower than that of gasification system with thermal plasma.

Scaling Up of Non-Thermal Gliding Arc Plasma Systems for Industrial Applications

Scaling Up of Non-Thermal Gliding Arc Plasma Systems for Industrial Applications

Instantaneous hydrogen production from ammonia by non-thermal arc plasma combining with catalyst

Owing to the storage and transportation problems of hydrogen fuel, exploring new methods of the real-time hydrogen production from ammonia becomes attractive. In this paper, non-thermal arc plasma (NTAP) combining with NiO/Al2O3 catalyst is developed to produce hydrogen from ammonia with high efficiency and large scale. The effects of ammonia gas flow rate and discharge power on the gas temperature, electron density, the hydrogen production rate, and energy efficiency were investigated. Experimental results show that the optical emission spectrum of NTAP working with pure ammonia medium was dominated by the atom spectrum of Hα, Hβ, and molecular spectrum of NH component. Under the optimum experimental condition of plasma discharge, the highest energy efficiency of hydrogen production reached 783.4 L/kW⋅h at NH3 gas flow rate of 30 SLM. When the catalyst was added, and heated by the NTAP simultaneously, the energy efficiency further increased to 1080.0 L/kW⋅h.

High-performance anode of lithium ion batteries with plasma-prepared silicon nanoparticles and a three-component binder

The crystalline silicon nanoparticles coated with an amorphous silicon layer was prepared by continuously pyrolysing the mixture of silane and hydrogen in a non-thermal arc plasma reactor. The hydrogen in the gas mixture effectively controls the thickness of the amorphous silicon layer and further improves the electrochemical performance of the silicon anode. The mechanism of the hydrogen was investigated by experiments. At the same time, a three-component polymer binder was concocted and introduced to tolerate the volume expansion of silicon effectively. Combining the silicon nanoparticles prepared at the optimal conditions with the novel polymer binder, the resulting silicon anode exhibits excellent electrochemical performance of 2120 mAh g−1 at 400 mA g−1 after 100 cycles.

In situ synthesis of nitrogen-doped graphene nanoflakes using non-thermal arc plasma

A non-thermal arc plasma process was developed for the in situ synthesis of nitrogen-doped graphene nanoflakes (N-GNFs), which used CH4/C2H4 as the carbon precursor and N2 as both the plasma gas and nitrogen precursor. N-GNFs with nitrogen-doping levels of 1%–3% (atomic percentage) were fabricated in the pressure range of 100–400 kPa. The effect of pressure and carbon precursor on product characteristics was investigated. It was found that a higher pressure favored the N-GNFs with high nitrogen-doping levels and high yield but it aggravated the curling of nanoflakes and reduced the nanoflake size, resulting in increased defects and a lower specific surface area. The nitrogen configuration was mainly determined by the carbon precursor, where pyrrolic N predominated in the N-GNFs synthesized from CH4, while the level of graphitic N was markedly higher when C2H4 was used. Correlations between the product properties and experimental parameters indicate that the variation of the plasma parameters induced by pressure changes and the hydrogen-poor/rich environment (depending on the carbon precursor) were the main factors affecting the product characteristics.

Simple synthesis of ultrafine amorphous silicon carbide nanoparticles by atmospheric plasmas

An atmospheric non-thermal arc plasma source based on magnetically stabilized gliding arc discharge was developed for the continuous preparation of ultrafine amorphous silicon carbide (a-SiC) nanoparticles via hexamethyldisilane decomposition. Results showed that the as-synthesized products were a mix of a-SiC nanoparticles and free carbon excess. The average particle size of nanoparticles was about 9 nm, and there were abundant functional groups and oxidized overlayers on the surface of the nanoparticles. Photoluminescence properties revealed the a-SiC nanoparticles had strong blue-green light emission under the excitation of 340–420 nm, which was possibly related to the surface functional groups, oxidized overlayers and quantum confinement effect due to ultrafine size. Correlations between the arc current and the crystal structure of the product indicated that the low input energy favored the synthesis of a-SiC nanoparticles, while the high input energy promotedthetransition from amorphous structure to β-SiC.

Synthesis of ultrafine silicon carbide nanoparticles using nonthermal arc plasma at atmospheric pressure

AbstractIt remains a significant challenge for the scalable production of ultrafine silicon carbide (SiC) nanoparticles with sizes smaller than 10 nm. In this work, a novel process based on atmospheric nonthermal arc plasma was proposed for the continuous synthesis of ultrafine SiC nanoparticles. This low‐cost and scalable technique allows preparation of SiC nanoparticles with small size (5–9 nm) and narrow size distribution via hexamethyldisilane (HMDS) decomposition in an argon/hydrogen plasma environment. The as‐synthesized products were carbon‐rich β‐SiC nanoparticles with plentiful functional groups on the surface. The addition of hydrogen in plasma gas can tune the product characteristics, such as decreasing particle size, improving crystallinity, and reducing carbon and oxygen contents. Moreover, the as‐prepared β‐SiC nanoparticles had a high band gap (around 2.5 eV), and their photoluminescence peak showed an obvious blueshift relative to that of bulk β‐SiC, which was mainly attributed to the quantum confinement effect induced by their ultrafine size. According to the spectral information of arc plasma, the formation of SiC nanoparticles in the plasma was discussed.

Plasma pyrolysis and gasification of carambola leaves using non-thermal arc plasma

Soil pollution (heavy metals and organic matter) is becoming more and more serious, phytoremediation has rapidly become a highly important method to deal with this problem. Therefore, the treatment and disposal of hyperaccumulators have been a topic of concern. In this paper, carambola leaves are selected as feedstock considering that carambola is a potential hyperaccumulator. A series of tests were performed to discuss 6 main influencing factors on total gas yield and metal fixing using a non-thermal arc plasma setup, to investigate the feasibility of plasma treatment of hyperaccumulator and provide a new method to utilize the harvested hyperaccumulator. The maximum total gas yield reached approximately 85% at an airflow rate of 3 L/min, the processing time of 7 min, discharge power of 29.95 W with the addition of water (water: sample = 1:1). A reducing or inert carrier gas or the addition of some specific inorganic additives at optimal conditions were in favor of increasing metal fixing efficiency. However, the effects of these factors usually have two sides, and some factors may have conflicting effects between gas yield and metal fixing, and. It is necessary to optimize these factors for achieving the desired goal. The obtained solid products exhibit the potential to fix metals and act as activated carbon.

Characteristics of non-thermal AC arcs in multi-arc generator**Project supported by the National Natural Science Foundation of China (Grant Nos. 11875295 and 11535003), Provincial Science and Technology Major Project of Anhui Province, China (Grant No. 17030801035), and Key Program of 13th Five-year Plan, CASHIPS, China (Grant No. KP-2017-25).

To obtain large-volume non-thermal arc plasma (NTAP), a multiple NTAP generator with three pairs of electrodes has been developed. The arc plasma characteristics, including dynamic process, spatial distribution, and rotation velocity in the discharge zone, were investigated by high speed photograph and image processing methods. The results showed that the dynamic behaviors and spatial distribution of the arc plasma were strongly related to the electrode configuration. A swirl flow of multi-arc plasma was formed by adjusting the electrode configuration, and a steady luminance area was clearly observed in the center of the discharge zone. Moreover, the size of the luminance area increased by decreasing the gas flow rate. The electrical connection in series could be formed between/among these arc columns with their respective driving power supplies in the multi-arc dynamic evolution process. An approximately periodical process of acceleration and deceleration of the arc rotation velocity was observed in the multi-arc generator with swirl flow configuration. In general, the mean velocity of arc rotation was higher in the multi-arc generator with swirl flow configuration when a pair of electrodes driven by a power supply were opposite to each other rather than adjacent.

Reforming of biogas using a non-thermal, gliding-arc, plasma in reverse vortex flow and fate of hydrogen sulfide contaminants

Biogas is being produced everyday around the world due to land filling of organic wastes. Reforming of biogas to hydrogen rich gas offers a green source of energy. This work demonstrates reforming biogas into hydrogen rich gas via a non-thermal gliding arc plasma stabilized in a reverse vortex flow with very low and competitive specific energy requirement. Parametric tests determined the individual effects of power input (140-300 W), steam to carbon ratio (0.0–3.0), and equivalence ratio (0.1–0.7) on reformer performance. Factorial tests identified optimal operating condition based on minimizing the specific energy requirement, determined to be 184 kJ/mol H2 or 1.91 eV/H2 molecule, significantly below the value for conventional steam reforming of methane, 3.37 eV/H2 molecule produced. The optimum operating conditions were found at an equivalence ratio of 0.11, a steam to carbon ratio of 0.14, and an input plasma power of 160 W, resulting in methane conversion of 48.8%, hydrogen yield of 23.4%, hydrogen selectivity of 47.8%, and an efficiency of 25.3%. Hydrogen sulfide as a common contaminant in landfill gas has detrimental effects on downstream facilities. The reactor was also evaluated on synthetic biogas containing hydrogen sulfide at low concentration (21 ppm). About 5.7% of the sulfur input to the system was partitioned to the dry outlet reformate stream with the remainder captured as sulfate in a downstream impinger or recovered as a solid of unknown molecular structure deposited on tubing surfaces between the reformer and the impinger. This reforming technology offers potential to be deployed as a lightweight compact portable system for on-site applications such as landfills, and depending on available fuels, in mobile applications such as ships.

Reforming of CH4 and CO2 by Combination of Alternating Current-Driven Nonthermal Arc Plasma and Catalyst

An experimental plasma reforming reactor for conversion of CH4–CO2 to synthesis gas (syngas) has been developed, in which the plasma is generated by a nonthermal arc plasma torch with simple and compact structure. The effects of total flux of feed gases and the molar ratio of CH4/CO2 on syngas production, selectivities of H2 and CO, and energy conversion efficiency were investigated. It is proven that this kind of plasma is an effective way to reforming of CO2–CH4 with energy conversion efficiency of 5.25 mmol/kJ and energy efficiency of 81%. Moreover, the heat generated by the plasma can be fully utilized to activate catalyst.

Dimensionless factors for an alternating-current non-thermal arc plasma

A gliding arc discharge, as a source of warm plasma combining advantages of both thermal and cold plasmas, would have promising application prospects in the fields of fuel conversion, combustion enhancement, material synthesis, surface modifications, pollution control, etc. In order to gain insight into the features of an alternating-current gliding arc discharge plasma, three dimensionless factors, i.e., the extinction span (ψ), current lag (δ), and heating lag (χ) factors are proposed in this letter based on the measured waveforms of the discharge voltage and current in an AC gliding arc discharge plasma. The influences of the driving frequency of the power supply (f) on these three dimensionless parameters are investigated experimentally with the explanations on the physical meanings of these factors. The experimental results show that a higher value of f would lead to the lower values of ψ and δ, as well as a higher value of χ. These experimental phenomena indicate a lower threshold ignition voltage of the discharges, a lower current-growth inertia of the gliding arcs and a larger relative thermal inertia of the plasmas with increase the driving frequency of the power supply in the operating parameter range studied in this letter.

Study of Non-Thermal DC Arc Plasma of CH4/Ar at Atmospheric Pressure Using Optical Emission Spectroscopy and Mass Spectrometry**supported by National Natural Science Foundation of China (Nos. 11035005, 11475174, 50876101) and USTC-NSRL Association Funding (No. KY2090130001)

Non-thermal C/H/Ar plasmas are widely applied to carbonaceous material production and processing. In this work, plasma parameters and gaseous species of the atmospheric non-thermal C/H/Ar plasmas produced by an atmospheric-pressure DC arc discharge generator in CH4/Ar were investigated. The voltage-current characteristics were measured for different CH4/Ar ratios. Optical emission spectroscopy was employed to analyze the electron excitation temperature, gas temperature and electron density under various discharge conditions. The hydrocarbon molecules produced in the CH4/Ar plasmas were detected with photoionization mass spectrometry. The optical spectral results demonstrated that the electron excitation temperature was 0.4-1 eV, the gas temperature was 2800-4200 K and the electron density was in the range of (5-20)×1015 cm−3. The mass spectrum indicated that a variety of unsaturated hydrocarbons (C2H4, C3H6, C6H6, etc.) and several highly unsaturated hydrocarbons (C4H2, C5H6, etc.) were produced in the non-thermal arc plasmas.

Gasification of corn cob using non-thermal arc plasma

With high quality syngas consisting almost completely of H2 and CO, and solid carbon residues with high quality, the plasma treatment technology of biomass has been widely studied with the purpose of generating hydrogen. In this paper, the plasma gasification process of corn cob using non-thermal arc plasma was investigated after comparing various components of biomass, combining the physical truth of agricultural waste. The gas yield can reach 79.0% of the biomass feed without drying conditions at a discharge power of 25.2 W when using nitrogen as carrier gas with energy cost from the decomposition of corn cob is 5328 kJ/kgH2. Meanwhile, carbon conversion rate of 82.9%, CO selectivity of 39.9% and a ratio of H2/CO greater than 1.5 are obtained. It is found that different carrier gases have different impacts upon the reforming performance, and air is more beneficial for higher gas yield and CO selectivity. Besides, the presence of moisture is conducive to improve the gas yield, especially the production of hydrogen, carbon conversion rate and the molar ratio of H2/CO. Also, the varying tendencies of the gas products over the time at different experiment parameters are also discussed. Finally, the results of residual solid products were analyzed.

Plasma reforming of bio-ethanol for hydrogen rich gas production

Hydrogen production from ethanol by non-thermal arc discharge was investigated in a novel miniaturized plasma reactor. It is observed that ethanol–water mixture was converted into hydrogen, carbon monoxide and other products. The V–I characteristic was recorded by an oscilloscope to study the effect of discharge on the ethanol reforming. In the experiments, ethanol–water mixture entered the reaction chamber through a special gas–liquid spray nozzle for a quick evaporation and a rapid mixing with air at room temperature. Assisted by a Laval nozzle electrode, non-thermal arc plasma can improve the performance of ethanol reforming. It is found that the maximum conversion rate of ethanol was 90.9% at O/C=1.4, S/C=1.2 and ethanol flow rate=0.05g/s, and the maximum hydrogen yield was 40.9% at O/C=1.4, S/C=1.2 and ethanol flow rate=0.10g/s. The ethanol reforming process produced little coke and nitrogen oxide which was less than 10ppm in the supersonic/subsonic plasma working condition.

Renewable hydrogen from ethanol by a miniaturized nonthermal arc plasma-catalytic reforming system

Ethanol–water mixtures were reformed directly into H2-rich gas without extra heat source with conversion rates of 69.8% and 88.0% by nonthermal arc plasma and plasma-catalytic reactors, respectively. The plasma reactor consists of a Laval nozzle electrode and a central electrode. The ethanol, water and air mixtures were mixed by a spray nozzle, and then introduced into the Laval nozzle. In terms of energy efficiency, the optimal reforming condition was determined to be O/C ∼ 0.5 and S/C ∼ 1.0 with an ethanol input rate of ∼0.10 g s−1. Furthermore, it is also found that applying Ni/γ-Al2O3 catalyst just at the downstream of the discharge region contributed to a better conversion extent and a higher hydrogen production rate, while the power consumption increased slightly, thus the specific energy required for hydrogen production reduced from 68.5 to 40.1 kJ mol−1 at O/C = 0.44, S/C = 1.28 and inlet ethanol = 0.10 g s−1. This reforming technology has promising prospects not only for low-cost hydrogen generation and efficiency improvement for inner combustion engine, but also for many other potential chemical applications, such as nanophase material preparation and solar fuel cell manufacturing.

A Study on Magnetism-Driven Gliding Arc Discharge

The diameter of non-thermal arc plasma is one of the main parameters that determine the current density of arc, so as to the temperature and the density of electrons. The imagines of gliding arc discharge driven by magnetism at atmosphere are captured observed and its dimension is measured by commercial CCD. The diameter projecting in the direction of motion of the arc (diameter in positive direction) is attained. And the relationship between diameter and current, magnetic field is analyzed, too.

Alternating current-driven non-thermal arc plasma torch working with air medium at atmospheric pressure

This work is devoted to the investigation of the discharge characteristics of high-frequency alternating current (ac) plasma torch working with air medium using electrical and spectroscopic techniques. A simple structure and compact ac plasma torch associated with a resonance power supply allows the generation of low power discharges (lower than 1 kW) with high voltage and low current. The discharge shows a negative resistance characteristic, and its curve shifts up with gas flow increased. The effects of power on the emission intensity of NO (A 2Σ+ → X 2Π), OH (A 2Σ → X 2Π, 0–0), N2(C 3Πu → B 3Πg), Hα and O and their spatial distributions in plasma jet axial direction were investigated. It has been found that the emission intensities of NO, OH, N2, Hα and O rise with an increase in power dissipation. With increasing axial distances of plasma jet from nozzle exit, the emission intensity of OH increases and then decreases, while the emission intensities of other species decrease sharply. The vibrational temperature is much higher than the gas temperature, which demonstrates the ac-driven arc discharge deviation from thermal equilibrium plasma.