CO2 plasma in fluidized bed—DC glow discharge reactor

As a typical highly nonlinear medium, laboratory plasmas can exhibit abundant nonlinear phenomena. It is well known that the presence of negative differential conductivity can cause the system to exhibit temporal chaotic oscillations when a DC glow discharge is operated in the subnormal glow discharge regime. In addition, for a nonlinear system, the hysteresis often occurs due to the coexistence of multiple attractors. In this work, a two-dimensional plasma fluid model based on the drift-diffusion approximation is developed to study the hysteresis phenomenon of the nonlinear dynamical behaviors of the low-pressure DC glow discharge. The results demonstrate that the initial discharge conditions selected in calculations will influence the nonlinear dynamical behaviors significantly that the system exhibits. Hysteresis can be observed from the voltage waveform when the applied voltage is altered to allow the system to work between the stationary discharge regime and the oscillatory discharge regime. In the hysteresis region, the system exhibits bi-stable characteristics. Near the critical point, the dynamical behaviors of the system will jump from the stationary state to the oscillatory state under small perturbations and the reverse adjustment of control parameters will not immediately restore the original stationary state, which is a typical characteristic of the subcritical Hopf bifurcation.

Electrothermal purification is an effective method for achieving over 99.9 pct purity for graphite particles with minimal environmental impact. However, the lack of a suitable heat and electric resistivity model has hindered the scaling up of electrically heated fluidized bed (EHFB) reactors for graphite purification. In this study, three commercial natural graphite flake populations were tested in a bench-scale fluidized bed reactor at temperatures of up to 1000 °C. The experiments varied key parameters, including the graphite particle size, particle bed temperature, fluidization index, and electrode depth within the particle bed. Controlling the fluidized bed reactor at high temperatures requires an understanding of bed resistivity and how current flows throughout the EHFB system. The results show that fluidized bed resistivity decreases with temperature, with a diminished effect at higher temperatures. Smaller particles exhibit a higher resistance, likely due to a larger number of contact points required to pass current between the electrodes. In this study, a Finite Difference Method (FDM) model was developed using Visual Basic for Applications (VBA) in Excel®. Additionally, a Finite Element Method (FEM) model was created using COMSOL Multiphysics®. The FDM model assumes the current flows only radially, whereas the FEM model accounts for both radial and vertical current flow. The FDM model was validated against experimental data. Additionally, the FDM model was verified through a comparison with the FEM model. The FDM model showed good agreement with experimental resistance data and moderate agreement with power consumption, while the FEM model provided more accurate predictions by accounting for a detailed geometry and heat loss mechanisms. Achieving a uniform temperature distribution within the fluidized bed is influenced by the electrode’s contact area. Deeper immersion of the electrode enhances thermal uniformity and provides results that more closely match experimental observations.

Chemical looping combustion of Victorian brown coal using Fe-based oxygen carriers

A direct current (dc) glow discharge—surface interaction process for in situ substrate surface pretreatment, for the promotion of diamond growth on mirror polished Si(100) is reported. A key step of the pretreatment is a generation of a stable dc-glow discharge between a grounded substrate and a positively biased electrode using a CH4/H2 gas mixture. During this stage, no additional gas phase activation by a hot filament is carried out. For subsequent diamond deposition, the dc-glow discharge is switched off and the standard hot filament CVD growth conditions are applied. The nature of the deposits formed by the dc-glow discharge process and after standard diamond deposition conditions, are investigated by Raman spectroscopy and high resolution scanning electron microscopy. It is found that the properties of the films, deposited following the dc-glow discharge pretreatment, strongly depend on the pretreatment conditions: methane concentration, substrate temperature, and pretreatment time. It is suggested that the nature of the diamond precursor formed during the dc-glow discharge pretreatment is similar to that one observed after bias enhanced nucleation process.

Nitrogen dc discharges are investigated at a constant pressure of 3 Torr and a variable discharge current of 17–100 mA. Optical emission spectroscopy is employed to detect the excited species at four axial positions far from the cathode (25, 75, 125 and 175 mm) and to determine the rotational and translational temperatures and the vibrational distribution functions (VDFs) of the B 3Πg and C 3Πu states of the nitrogen molecule. A semiempirical level-to-level collisional–radiative model is used for the modeling of the collisional and radiative processes and the processing of data. It provides detailed information on the processes occurring in the dc discharge, calculates the nitrogen emission spectra, predicts the translational and rotational temperatures, the VDFs in the ground and electronic excited B 3Πg (vB = 0–17) and C 3Πu (vC = 0–4) states together with the corresponding vibrational temperatures TV, TB and TC. Theoretical emission spectra and VDFs of the B 3Πg and C 3Πu states are also in good agreement with the experimental ones. The main processes responsible for the VDFs are also established.

The presented results are concerned with the shape of Balmer alpha line emitted from a low pressure DC glow discharge with aluminum (Al) and copper (Cu) hollow cathode (HC) in pure H2 and Ar‐H2 gas mixture. The analysis indicates that the line profile represents a convolution of Gaussian profiles resulting from different collision excitation processes.

99/00352 Modeling of gasification behavior in freeboard of fluidized bed gasifier

Co-combustion of biomass and gaseous fuel in a novel configuration of fluidized bed: Combustion characteristics

Influence of CO2-laser mixture composition on the distribution of energy in nitrogen spectrum

Hydrodynamics of a reactor for thermocatalytic oxidation of sewage sludge

CFD-DEM simulation of fluorination reaction in fluidized beds with local grid and time refinement method

We have examined the dynamics of dust in collisionless and collisional electrode sheaths of dc and rf glow discharges. The charge of the dust particles, the various forces, oscillation frequencies, damping effects and energy potential extrema are calculated. In the rf sheaths the dust particle charge is negative in the whole sheath, while in the dc sheaths the dust particle charge is positive in a major part of the sheath. Collection of dust leads to changes in the dust and plasma potentials and to a reduction in the maximum dust particle size that can be levitated. Close to the electrode there will be a dust-free zone.

This paper focuses on how the electron temperature and other plasma properties affect optical emission and CO2 conversion in CO2 plasma. Such plasma-mediated reactions can enable efficient CO2 reuse. We study CO2 and CO plasmas generated by inductively coupled radiofrequency power (30–300 W) at low pressures (6–400 Pa). By varying the argon admixture, we can study the effect of the electron temperature, Te, on the conversion and emission properties using optical emission spectroscopy, mass spectrometry, and electrical probe measurements. Importantly, we can observe several parameters simultaneously: Te, CO2 conversion, chemiluminescence from CO2, and dissociation products and optical emission from several atomic and CO transitions and from the C2 Swan system. On the basis of these results, we establish a correlation between Te, the CO2 conversion, and the optical emission spectra. A low Te enhances CO2 conversion and Swan band emission. In contrast with published studies, our results show that the CO2 and C2 vibrations are not in local equilibrium. This means that the vibrational temperatures of CO2 and C2 should differ.

Fossil hydrogen with reduced [formula omitted] emission: Modeling thermocatalytic decomposition of methane in a fluidized bed of carbon particles

Fluidized beds are widely used in many industrial fields such as petroleum, chemical and energy. In actual industrial processes, spherical inert particles are typically added to the fluidized bed to promote fluidization of non-spherical particles. Understanding mixing behaviors of binary mixtures in a fluidized bed has specific significance for the design and optimization of related industrial processes. In this study, the computational fluid dynamic–discrete element method with the consideration of rolling friction was applied to evaluate the mixing behaviors of binary mixtures comprising spherocylindrical particles and spherical particles in a fluidized bed. The simulation results indicate that the differences between rotational particle velocities were higher than those of translational particle velocities for spherical and non-spherical particles when well mixed. Moreover, as the volume fraction of the spherocylindrical particles increases, translational and rotational granular temperatures gradually increase. In addition, the addition of the spherical particles makes the spherocylindrical particles preferably distributed in a vertical orientation.