Plasmadynamic Structure of Electrode Torches and its Influence on the Dynamics of Development of Pulsed Surface Discharge

An experimental study has been made of the plasmadynamic structure of electrode plasma torches and its influence on the dynamics of development of a high-current pulsed surface discharge with separated torches at atmospheric and low pressures. Much attention has been given to the behavior of the discharge with change in experimental conditions. Consideration has also been given to the jet properties in the outflow of a luminous substance, which manifests itself in the structural properties of photoscans. The mechanism of spatial “spreading” of the channel of the surface discharge with separated torches has been proposed.__________Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 78, No. 2, pp. 172–177, March–April, 2005.     

Pyrolysis of waste using a hybrid argon–water stabilized torch

An experimental plasmachemical reactor equipped with the novel IPP-ASCR hybrid gas–water stabilized DC torch (160 kW) has recently been started at IPP Prague for the innovative and environmentally friendly plasma treatment of waste streams with a view to their sustainable energetic and chemical valorization and to a reduction of the emission of greenhouse gases. Since the process energy is provided by direct heat transfer from plasma, gases of widely varying chemical composition may be used. The use of electrical energy also reduces the gas flows and requirements for exhaust-gas treatment, and offers control over the chemistry. Pyrolysis of biomass was experimentally studied using wood chips as a model substance. Syngas with a high content of hydrogen and CO was produced. The influence of adding CO₂ for increase of oxygen content in the reactor was investigated.     

Numerical simulation of power-engineering complex with torrefaction reactor

The paper presents a mathematical model of power-engineering complex implementing a combined technology of production of power, heat, and solid biofuels, namely, torrefied pellets. Torrefaction of fuel pellets is carried out in a thermochemical reactor by heat from exhaust gases of a gas piston power plant. The results of testing the model by experimental data and the results of calculations of the main characteristics of torrefaction, the mass and energy flows are given. The analysis results of efficiency of the power plant with a build-on thermochemical reactor are reported.     

Numerical analysis and experiments on transferred plasma torches for finding appropriate operating conditions and electrode configuration for a waste melting process

Thermal plasma characteristics of transferred plasma torches are numerically and experimentally investigated under atmospheric conditions to find the effects of operating variables and electrode arrangements on them. A control volume method and a modified SIMPLER algorithm are used for numerical analysis, and the temperature distributions of argon plasma are calculated in different torch operating conditions of a typical transferred arc torch. Transferred plasma torches are designed and fabricated, which have six different electrode arrangements, respectively, consisting of a conical rod cathode and a nozzle in the torch, and a distant anode material. The dynamic behaviors of arc voltage are measured to obtain stable arc conditions, and a similarity criterion is determined to analyze static behaviors of arc voltage. For predicting the heat transfer rate to melted material from arc column, measurements are made for the heat loss at the anode material and fractions of input power transferred to the anode. Furthermore, thermal plasma temperatures are measured by the optical emission spectroscopy of an Ar I line. As a result of the present work, an appropriate electrode configuration and operating conditions for waste melting process are presented for the optimization of transferred plasma torches.     

Possibilities of application of plasma technologies to recycle organic-containing substances: Particularities of the processes in the arc chambers of plasma torches

The processes in the arc chambers of AC plasma torches, of 1–2 MW power, with rod electrodes, designed to run on nitrogen, hydrogen, and argon, as well as with rail electrodes to work on oxidizing media, are considered. The possibility (the efficiency) of application of such plasma torches for gasification and pyrolysis of organic-containing substances in plasmochemical reactors is analyzed. A comparison of this application with the free burning arcs directly in the plasmochemical reactors is made. The advantage of the plasma torch application for these purposes is shown.     

Biofilm photobioreactors for the treatment of industrial wastewaters

A flat plate and a tubular packed-bed photobioreactor with an algal-bacterial biofilm attached onto Poraver beads carriers, a flat plate and a tubular photobioreactor with the biofilm attached onto the reactor walls, and an algal-turf reactor were compared in terms of BOD removal efficiencies, elimination capacities, and stability. A control column photobioreactor with suspended algal-bacterial biomass was also tested to compare the performance of biofilm photobioreactors with conventional algal-based processes. When the algal-bacterial biomass was immobilized onto Poraver the process never reached a steady state due to a poor homogenization in the bioreactor. When the biofilm was formed onto the reactor wall (or reactor base) the process was stable. A maximum degradation rate of 295mg BODl(-1)h(-1) was achieved in the algal-turf reactor although control experiments performed in the dark showed atmospheric O2 diffusion represented 55% of the oxygenation capacity in this system. BOD removal rates of 108, and 92mg BODl(-1)h(-1) were achieved in the tubular and flat plate biofilm reactors, respectively, compared to 77mg BODl(-1)h(-1) in the control suspended bioreactor. In addition, all biofilm photobioreactors produced an easily settleable biomass. Evidence was found that biomass attachment to the reactor's wall improved stability.     

Effect of biogenic substrate concentration on 4-chlorophenol degradation kinetics in sequencing batch reactors with instantaneous feed

Two sequencing batch reactors (SBRs) instantaneously fed with 200 mg/l 4-chlorophenol (4-CP) were operated at different feed peptone concentrations to investigate the effect of biogenic substrate (peptone) concentrations on reactor performance, yield coefficient (Y) and 4-CP degradation kinetics. One of the reactors was operated at 10 days of sludge retention time (SRT) and the other was operated at 20 days of SRT. High chemical oxygen demand (COD) removal efficiencies (90-95%) and complete 4-CP removals (detection limit was 0.05 mg/l) were observed even in the absence of peptone. Accumulation of 5-chloro-2-hydroxymuconic semialdehyde (CHMS), meta cleavage product of 4-CP, was observed, which was completely removed at the end of the reactor cycle. It was concluded that decreasing peptone concentrations did not affect 4-CP degradation profiles and Haldane equation can be satisfactorily used to predict time course variation of 4-CP concentrations. It was assumed that specialists (competent biomass) are only responsible for 4-CP degradation and its concentration was constant although peptone concentration in the feed was varied, as competent biomass grows on 4-CP only. Model developed using this assumption well tracked the experimental data. The kinetic coefficients obtained for the reactor operated at 10 days of SRT were also valid for the reactor operated at 20 days of SRT although higher degradation rates were observed due to higher steady state biomass concentrations.     

First-wall coatings for Tokamak fusion reactors

The coating of the first wall of a fusion reactor must withstand an intense neutron flux, the impact of energetic charged and neutral particles, and photons, all of which escape from the plasma. Penetration of material eroded from the first-wall coating into the plasma will have a detrimental effect on the plasma stability and energy balance. Therefore material selection for the first-wall coating of a fusion reactor represents one of the critical problem areas for the achievement of fusion power.Theoretical and experimental studies which have been conducted on the many facets of the problem are reviewed with special emphasis placed on the more critical aspects. Possible directions of future research in this area are outlined.     

Optimization and performance of atmospheric Fused Hollow Cathodes

Experimental results on the atmospheric hollow cathode plasma generation and performance, using a special configuration with tunable wall separations, are presented. The influence of the gas and type of the power used for generation on the optimum size of the cathode slit is investigated. The experimental results are in agreement with the hollow cathode model. The plasma source/plasma reactor design is of utmost importance for control of plasma-chemical kinetics. An example of the atmospheric hollow cathode plasma application for the NO_x conversion is given. The energy consumption and plasma characteristics are discussed.     

Use of electric-arc plasma for radioactive waste immobilization

We analyze the basic trends in the use of electric-arc plasma for radioactive waste decontamination. We present a scheme and performance figures of a process for a shaft-type furnace with fuel-plasma heating. We present the results of numerical and experimental investigations for a 150-kW direct-flow plasma reactor.     

Prebreakdown stage of a surface discharge fired by a pulse in the air at atmospheric pressure

Results of investigation of a high-current plane pulsed surface discharge with separated torches fired in the air at atmospheric pressure are presented. The dynamics of ignition and development of the discharge in the prebreakdown stage has been considered. The main parameters of the plasma in the prebreakdown stage (the stage of intense prebreakdown glow) have been determined by spectroscopic methods and the influence of the dielectric material of a substrate on the plasma parameters has been analyzed. It has been established that the duration of an intense prebreakdown glow depends on the experimental conditions. A physical pattern of formation of an intense prebreakdown glow is proposed.__________Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 78, No. 1, pp. 178–185, January–February, 2005.     

面向等离子体材料钨中氘/氦滞留行为的研究进展

作为面向等离子体材料,钨(W)在服役的过程中不仅受到等离子体造成的高能热负荷的作用,还受到高束流粒子如氘(D)、氚(T)、氦(He)等的轰击和D-T聚变反应产生的高能中子的影响.W中D、T、He的滞留和起泡,仍是聚变堆装置中有待解决的关键问题之一.综述了D、T和He的滞留行为及其气泡形成与辐照条件之间的关系,简要评述了W的服役性能和强化机理.通过降低W中D/He滞留量、抑制气泡的形成可有效改善W的服役性能.深入研究D/He滞留行为与辐照缺陷之间的相互作用关系,进而构建D/He的宏观热脱附行为与其微观状态之间的对应关系,为寻找合适途径来改善W的服役性能提供理论支撑.     

面向等离子体材料钨中氘/氦滞留行为的研究进展

作为面向等离子体材料,钨(W)在服役的过程中不仅受到等离子体造成的高能热负荷的作用,还受到高束流粒子如氘(D)、氚(T)、氦(He)等的轰击和D-T聚变反应产生的高能中子的影响。W中D、T、He的滞留和起泡,仍是聚变堆装置中有待解决的关键问题之一。综述了D、T和He的滞留行为及其气泡形成与辐照条件之间的关系,简要评述了W的服役性能和强化机理。通过降低W中D/He滞留量、抑制气泡的形成可有效改善W的服役性能。深入研究D/He滞留行为与辐照缺陷之间的相互作用关系,进而构建D/He的宏观热脱附行为与其微观状态之间的对应关系,为寻找合适途径来改善W的服役性能提供理论支撑。     

基于半纤维素和木质素的水凝胶研究进展

作为“生物炼制”的原料,木质纤维素中的纤维素成分可为人类生产生物燃料和化学品,但其中的半纤维素和木质素成分未能有效利用.由于高分子骨架上含有大量亲水性基团,半纤维素和木质素可以转化为用途广泛的水凝胶材料.这样不仅可消除环境污染,减少资源浪费,还可以有效地降低纤维素生物燃料或者化学品的成本.综述了基于半纤维素和木质素的水...     

Analysis of high-frequency processes in an electric-discharge chamber of a three-phase plasma torch at high working gas pressure

The paper deals with electrophysical processes in an electric-discharge chamber of a three-phase AC plasma torch with nitrogen as working gas. The frequency characteristics of voltage pulsations depending on current, gas mass flow rate, power, and pressure are obtained. Photos of arc burning processes in the plasma torch discharge chamber at different parameters are presented. It is shown that two arcs burn simultaneously in the plasma torch chamber and the third one either extinguishes or arises. These investigations might be useful when creating various technological processes by applying three-phase AC plasma torches operating on inert gases.     

Wastewater treatment in a hybrid activated sludge baffled reactor

A novel hybrid activated sludge baffled reactor (HASBR), which contained both suspended and attached-growth biomass perfect mixing cells in series, was developed by installing standing and hanging baffles and introducing plastic brushes into a conventional activated sludge (CAS) reactor. It was used for the treatment of domestic wastewater. The effects on the operational performance of developing the suspended and attached-growth biomass and reactor configuration were investigated. The change of the flow regime from complete-mix to plug-flow, and the addition of plastic brushes as a support for biofilm, resulted in considerable improvements in the COD, nitrogen removal efficiency of domestic wastewater and sludge settling properties. In steady state, approximately 98+/-2% of the total COD and 98+/-2% of the ammonia of the influent were removed in the HASBR, when the influent wastewater concentration was 593+/-11 mg COD/L and 43+/-5 mg N/L, respectively, at a HRT of 10 h. These results were 93+/-3 and 6+/-3% for the CAS reactor, respectively. Approximately 90+/-7% of the total COD was removed in the HASBR, when the influent wastewater concentration was 654+/-16 mg COD/L at a 3h HRT, and in the organic loading rate (OLR) of 5.36kgCOD m(-3) day(-1). The result for the CAS reactor was 60+/-3%. Existing CAS plants can be upgraded by changing the reactor configuration and introducing biofilm support media into the aeration tank.     

Evaluation of potential integration of entrapped mixed microbial cell and membrane bioreactor processes for biological wastewater treatment/reuse

The challenge of biological wastewater treatment process is the design and operation of effective retention of mixed microbial cells within the reactor. Entrapped mixed microbial cell (EMMC) technology is designed to entrap the mixed microbial cells in polymeric carriers; membrane bioreactor (MBR) process utilizes membrane sheets/fibers to effectively retain the biomass in the reactor. These two biotechnologies are considered potential alternatives for conventional biological treatment/reuse because of their capability of retaining high concentration of biomass in the reactor, or in other words increasing the solid retention time (SRT). The simultaneous removal of organics and nitrogen were investigated using a modified EMMC system design. The modified EMMC system demonstrated higher organic and nitrogen removal performance due to high SRT. Compared to single-stage MBR process operated at similar conditions, the modified EMMC system was able to achieve slightly lower organic removal, comparable nitrification, and higher total nitrogen removal. One limitation in applying an EMMC only treatment process regime for potential reuse of treated wastewater is that such an operation requires the removal of pathogens and large particles if disinfection and solid/liquid separation were not followed. The major challenge of MBR process to overcome is membrane fouling, and the high energy consumption associated with fouling control. The intrinsic features of EMMC process including high SRT, low, and stabilized effluent suspended biomass concentration may significantly reduce the chance and extent of membrane fouling; while the membrane filtration can further polish the effluent quality from EMMC process. Therefore, integrating MBR and EMMC is strongly recommended because it may be a ??break-through?? for solving the membrane fouling problem and in improving effluent quality for potential reuse.     

Development of alternative plasma sources for cavity ring-down measurements of mercury

We have been exploring innovative technologies for elemental and hyperfine structure measurements using cavity ring-down spectroscopy (CRDS) combined with various plasma sources. A laboratory CRDS system utilizing a tunable dye laser is employed in this work to demonstrate the feasibility of the technology. An in-house fabricated sampling system is used to generate aerosols from solution samples and introduce the aerosols into the plasma source. The ring-down signals are monitored using a photomultiplier tube and recorded using a digital oscilloscope interfaced to a computer. Several microwave plasma discharge devices are tested for mercury CRDS measurement. Various discharge tubes have been designed and tested to reduce background interference and increase the sample path length while still controlling turbulence generated from the plasma gas flow. Significant background reduction has been achieved with the implementation of the newly designed tube-shaped plasma devices, which has resulted in a detection limit of 0.4 ng/mL for mercury with the plasma source CRDS. The calibration curves obtained in this work readily show that linearity over 2 orders of magnitude can be obtained with plasma-CRDS for mercury detection. In this work, the hyperfine structure of mercury at the experimental plasma temperatures is clearly identified. We expect that plasma source cavity ring-down spectroscopy will provide enhanced capabilities for elemental and isotopic measurements.     

Study of the Electrode Erosion in Powerful,Single-Chamber,Three-Phase Alternating-Current Plasma Torches

High Temperature - The paper compares two types of alternating-current (AC) plasma torches of different power and application that fundamentally differ in the design of the electrodes and operate...