Polarity effect of pulsed corona discharge for the oxidation of gaseous elemental mercury.

The effect of polarity on the oxidation of Hg(0) was examined in the presence of O(2) via a pulsed corona discharge (PCD). The experimental result showed no difference in the energy yield of Hg(0) oxidation at both positive and negative PCDs (∼8 µg Hg Wh(-1) at following conditions: total flow rate=2 L min(-1) (Hg(0)=50 µg Nm(-3), O(2)=10%, and N(2) balance), temperature=150°C, and specific energy density=5-15 Wh Nm(-3)). This suggests that the positive PCD process used to control gaseous air pollutants may play an essential key role in Hg(0) oxidation because it consumes enough energy (∼15 Wh Nm(-3)) but an electrical precipitator could not because it consumes less energy (∼0.3 Wh Nm(-3)) to oxidize Hg(0).

Hydrogen recovery from the thermal plasma gasification of solid waste.

Thermal plasma gasification has been demonstrated as one of the most effective and environmentally friendly methods for solid waste treatment and energy utilization in many of studies. Therefore, the thermal plasma process of solid waste gasification (paper mill waste, 1.2 ton/day) was applied for the recovery of high purity H(2) (>99.99%). Gases emitted from a gasification furnace equipped with a nontransferred thermal plasma torch were purified using a bag-filter and wet scrubber. Thereafter, the gases, which contained syngas (CO+H(2)), were introduced into a H(2) recovery system, consisting largely of a water gas shift (WGS) unit for the conversion of CO to H(2) and a pressure swing adsorption (PSA) unit for the separation and purification of H(2). It was successfully demonstrated that the thermal plasma process of solid waste gasification, combined with the WGS and PSA, produced high purity H(2) (20 N m(3)/h (400 H(2)-Nm(3)/PMW-ton), up to 99.99%) using a plasma torch with 1.6 MWh/PMW-ton of electricity. The results presented here suggest that the thermal plasma process of solid waste gasification for the production of high purity H(2) may provide a new approach as a future energy infrastructure based on H(2).

Radiography simulation on single-shot dual-spectrum X-ray for cargo inspection system.

We propose a method to identify materials in the dual energy X-ray (DeX) inspection system. This method identifies materials by combining information on the relative proportions T of high-energy and low-energy X-rays transmitted through the material, and the ratio R of the attenuation coefficient of the material when high-energy are used to that when low energy X-rays are used. In Monte Carlo N-Particle Transport Code (MCNPX) simulations using the same geometry as that of the real container inspection system, this T vs. R method successfully identified tissue-equivalent plastic and several metals. In further simulations, the single-shot mode of operating the accelerator led to better distinguishing of materials than the dual-shot system.

Design and characterization of 2.45 GHz electron cyclotron resonance plasma source with magnetron magnetic field configuration for high flux of hyperthermal neutral beam.

A 2.45 GHz electron cyclotron resonance (ECR) source with a magnetron magnetic field configuration was developed to meet the demand of a hyperthermal neutral beam (HNB) flux on a substrate of more than 1x10(15) cm(-2) s(-1) for industrial applications. The parameters of the operating pressure, ion density, electron temperature, and distance between the neutralization plate and the substrate for the HNB source are specified in a theoretical analysis. The electron temperature and the ion density are measured to characterize the ECR HNB source using a Langmuir probe and optical emission spectroscopy. The parameters of the ECR HNB source are in good agreement with the theoretically specified parameters.

Demonstration of thermal plasma gasification/vitrification for municipal solid waste treatment.

Thermal plasma treatment has been regarded as a viable alternative for the treatment of highly toxic wastes, such as incinerator residues, radioactive wastes, and medical wastes. Therefore, a gasification/vitrification unit for the direct treatment of municipal solid waste (MSW), with a capacity of 10 tons/day, was developed using an integrated furnace equipped with two nontransferred thermal plasma torches. The overall process, as well as the analysis of byproducts and energy balance, has been presented in this paper to assess the performance of this technology. It was successfully demonstrated that the thermal plasma process converted MSW into innocuous slag, with much lower levels of environmental air pollutant emissions and the syngas having a utility value as energy sources (287 Nm3/MSW-ton for H2 and 395 Nm3/MSW-ton for CO), using 1.14 MWh/MSW-ton of electricity (thermal plasma torch (0.817 MWh/MSW-ton)+utilities (0.322 MWh/MSW-ton)) and 7.37 Nm3/MSW-ton of liquefied petroleum gas.

Insight into the unique oxidation chemistry of elemental mercury by chlorine-containing species: experiment and simulation.

This work investigated the oxidation chemistry of elemental mercury (Hg(0)) by chlorine-containing species produced indirectly through the gas-to-solid phase reaction between NO(x) gases and NaClO(2) powder (NaClO(2)(s)), where both experiment and simulation results were compared to clarify which species are responsible for the oxidation of Hg(0). At first, we introduced 30 ppm of NO(2) into the pack-bed reactor containing NaClO(2)(s) to produce OClO species and then injected NO and Hg(0) (260 microg/Nm(3)) to Mixer, where the concentration of NO was varied up to 180 ppm and the reaction temperature was set to 130 degrees C. We observed for the first time that the degree of Hg(0) oxidation is completely controlled by the introduced concentration of NO: for example, the oxidation efficiency of Hg(0) is drastically increased to become 100% at near 7 ppm NO, but further increasing NO concentration results in the oxidation efficiency of Hg(0) being gradually decreased. The simulation results indicated that such a propensity of Hg(0) oxidation efficiency to NO concentration can be attributed to the NO concentration-dependent Cl, ClO, and Cl(2) formation which plays a critical role in the oxidation of Hg(0).

Reaction pathways of NO oxidation by sodium chlorite powder.

NO oxidation is an important prerequisite step to assist selective catalytic reduction at low temperatures (< 250 degrees C). If sodium chlorite powder (NaClO2(s)) can oxidize NO to NO2, the injection of NaClO2(s) can be simply adapted to NO oxidation. Therefore, we explored the reaction pathways of NO oxidation by NaClO2(s). Known concentrations of NO and NO2 in N2 balance were injected into packed-bed reactor containing NaClO2(s) at 130 degreesC. NaClO2(s) oxidized NO to NO2 which reacts again with NaClO2(s) to produce OClO. Comparison of experimental data with simulation results demonstrates that each NO2 molecule removed by the reaction with NaClO2(s) generated one OClO molecule, which also oxidized NO to NO2 with the production of ClNO and ClNO2. Using these results, we conclude that the oxidation of NO by NaClO2(s) occurred by two pathways. One is through the direct reaction of NO with NaClO(s). The other is through both the reaction of NO with OlCO produced by the reaction of NO2 with NaClO2(s) and the reaction of NO with ClO produced by the reaction of NO with OClO.

Effect of hydrogen generated by dielectric barrier discharge of NH3 on selective non-catalytic reduction process.

Plasma-assisted selective non-catalytic reduction (SNCR) has been investigated to clarify which species generated by the plasma play a crucial role in NO reduction. We find that the presence of O(2) is indispensable and only H(2) is observed to be a stable product by dielectric barrier discharge (DBD) of NH(3). As the extent of NH(3) decomposition by DBD increases, the commencement temperature of SNCR processes is lowered and the working temperature window is widened. This propensity may be attributed to the chemical reaction of H(2) with O(2) to generate OH and H radicals which make it possible to yield NH(2) radicals even at low temperature.

Oxidation of elemental mercury using atmospheric pressure non-thermal plasma.

The oxidation of gas phase elemental mercury (Hg0) by atmospheric pressure non-thermal plasma has been investigated at room temperature, employing both dielectric barrier discharge (DBD) of the gas mixture of Hg0 and injection of ozone (O3) into the gas mixture of Hg0. Results have shown that the oxidative efficiencies of Hg0 by DBD and the injection of O3 are 59% and 93%, respectively, with energy consumption of 23.7 J L(-1). This combined approach has indicated that O3 plays a decisive role in the oxidation of gas phase Hg0. Also the oxidation of Hg0 by injecting O3 into the gas mixture of Hg0 proceeds with better efficiency than DBD of the gas mixture of Hg0. These results have been explained by the incorporation of the competitive reaction pathways between the formation of HgO by O3 and the decomposition of HgO back to Hg0 in the plasma environment.

Influence of HCl on oxidation of gaseous elemental mercury by dielectric barrier discharge process.

The influence of HCl on the oxidation of gaseous elemental mercury (Hg0) has been investigated using a dielectric barrier discharge (DBD) plasma process, where the temperature of the plasma reactor and the composition of gas mixtures of HCl, H2O, NO, and O2 in N2 balance have been varied. We observe that Cl atoms and Cl2 molecules, created by the DBD process, play important roles in the oxidation of Hg0 to HgCl2. The addition of H2O to the gas mixture of HCl in N2 accelerates the oxidation of Hg0, although no appreciable effect of H2O alone on the oxidation of Hg0 has been observed. The increase of the reaction temperature in the presence of HCl results in the reduction of Hg0 oxidation efficiency probably due to the deterioration of the heterogeneous chemical reaction of Hg0 with chlorinated species on the reactor wall. The presence of NO shows an inhibitory effect on the oxidation of Hg0 under DBD of 16% O2 in N2, indicating that NO acts as an O and O3 scavenger. At the composition of Hg0 (280 microg m(-3)), HCl (25 ppm), NO (204 ppm), O2 (16%) and N2 (balance) and temperature 90 degrees C, we obtain the nearly complete oxidation of Hg0 at a specific energy density of 8 J l(-1). These results lead us to suggest that the DBD process can be viable for the treatment of mercury released from coal-fired power plants.

Application of pulsed corona induced plasma chemical process to an industrial incinerator.

Pulsed corona induced plasma chemical process (PPCP) has been investigated for the simultaneous removal of NO(x) (nitrogen oxides) and SO2 (sulfur dioxide) from the flue gas emission. It is one of the world's largest scales of PPCP for treating NO(x) and SO2 simultaneously. A PPCP unit equipped with an average 120 kW modulator has been installed and tested at an industrial incinerator with the gas flow rate of 42 000 m3/h. To improve the removal efficiency of SO2 and NO(x), ammonia (NH3) and propylene (C3H6) were used as chemical additives. It was observed that the pulsed corona induced plasma chemical process made significant NO(x) and SO2 conversion with reasonable electric power consumption. The ammonia injection was very effective in the enhancement of SO2 removal. NO removal efficiency was significantly improved by injecting a C3H6 additive. In the experiments, the removal efficiencies of SO2 and NO(x) were approximately 99 and 70%, respectively. The specific energy consumption during the normal operation was approximately 1.4 Wh/m3, and the nanopulse conversion efficiency of 64.3% was achieved with the pulsed corona induced plasma chemical process.