Seiji Kanazawa

NO/sub x/ removal by a pipe with nozzle-plate electrode corona discharge system

The effects of additional gas composition on the corona discharge characteristics in a pipe with nozzle electrode system and the NOx removal characteristics for flue gases are experimentally investigated. The additional gas consists of a mixture of Na+O/sub 2/+NH/sub 3/ and a small amount of Ar or CO/sub 2/, and is introduced to the flue gas stream from the pipe electrode through the corona discharging zone at the tip of nozzles. The results show that corona discharge characteristics and modes are significantly influenced by the composition of the additional gas mixture. Both NO/sub x/ reduction rate and energy yield of NO/sub x/ removal increase with decreasing corona discharge input power. NO reduction rate and energy yield can be optimized by the type of the additional gas mixture and the flow rates. >

Decomposition of toluene by streamer corona discharge with catalyst

Abstract The improvement in the decomposition of volatile organic compounds was investigated by combining discharge plasma with photocatalyst (TiO2). A DC streamer corona plasma reactor combined with photocatalyst pellet layer was developed. It was found that the combination of the plasma and TiO2 was effective for improving toluene decomposition when the streamers cover the surface of the pellet layer.

Oxidation and Reduction Processes During NOx Removal with Corona-Induced Nonthermal Plasma

In this paper, the NO-to-NO2conversion in various gaseous mixtures is experimentally investigated. Streamer coronas are produced with a dc-superimposed high-frequency ac power supply (10–60 kHz). According to NOxremoval experiments in N2+NOxand N2+O2+NOxgaseous mixtures, it is supposed that the reverse reaction NO2+O→NO+O2may not only limit NO2production in N2+NOxmixtures, but also increase the energy cost for NO removal. Oxygen could significantly suppress reduction reactions and enhance oxidation processes. The reduction reactions, such as N+NO→N2+O, induce negligible NO removal provided the O2concentration is larger than 3.6%. With adding H2O into the reactor, the produced NO2per unit removed NO can be significantly reduced due to NO2oxidation. NH3injection could also significantly decrease the produced NO2via NH and NH2- related reduction reactions. Almost 100% of NO2can be removed in gaseous mixtures of N2+O2+H2O+NO2with negligible NO production.

Measurements of the velocity field of the flue gas flow in an electrostatic precipitator model using PIV method

Abstract In this paper, results of use of the PIV method to measure the flow field in a wire-plate type ESP model are presented. The results show that the PIV method is well suited to investigate the flow field in ESP models, in particular the characteristics of secondary and reversal flows, which increase the flow turbulence. The PIV investigation of the near-collecting electrode region shows the importance of the secondary flows, the velocity of which is several tens of cm/s. This means that the secondary flows can have a great impact on the motion and precipitation of small particles, mainly those in the submicron range.

Time dependence of NO/sub x/ removal rate by a corona radical shower system

In this paper, the effects of flow rate of treatment gas and additional gas on the corona current-voltage characteristics and NO/sub x/ removal characteristics, and the operational time dependence of the corona characteristics and NO/sub x/ removal characteristics are investigated experimentally in a corona radical shower system. The corona current-voltage characteristics have two modes which have a significant influence on NO/sub x/ removal characteristics. The threshold value of the gas flow rate ratio of treatment gas to additional gas is about 8. The hysteresis of corona current-voltage characteristics is observed in this system. For longer operational time, corona current and NO/sub x/ removal rate significantly changes with time. When the operation of the apparatus starts at relatively low applied voltage, the corona current under constant applied voltage increases with time. It takes a maximum value at an operational time and then decreasing with time, finally settles down to a constant value. At this condition, high NO/sub x/ removal rate NO/sub x/ removal efficiency can be achieved. >

NO removal characteristics of a corona radical shower system under DC and AC/DC superimposed operations

In this paper, the effects of operating applied voltage modes on the corona discharge morphology and NO removal characteristics from air stream are experimentally investigated. By applying a DC superimposed high frequency AC voltage, a uniform streamer corona can be generated, which is also less sensitive to electrodes mis-arrangements. Hermstein glow can be transferred to streamer by applying a DC superimposed AC power supply if the peak to peak voltage is larger than 1.0 kV at the voltage change rate of 0.2 kV//spl mu/s. A significant amount of NO removal is observed under streamer corona. While for Hermstein glow the removal is negligible.

Control of flow stabilized positive corona discharge modes and NO removal characteristics in dry air by C02 injections

Abstract In this paper, the effects of C0 2 injection rate on the flow stabilized positive DC corona discharge in dry air are experimentally investigated. As an example of chemical reactions induced by different corona modes, NO removal is also studied in gaseous mixtures of N 2 +O 2 +CO 2 +NO x at atmospheric pressure and in room temperature. The transition between glow and streamer can be controlled by C0 2 on and off injection. 95% of NO can be removed under streamer corona discharge with an energy yield of about 12.5–25g(NO)/kWh. However, for glow corona discharge, the NO removal is negligible.

Electrification of a pipe wall during powder transport

Abstract The inner surface potential of an insulating pipe is measured in a cascade flow system during powder transport. The influence of the pipe material and the powder flow trajectory inside the pipe on the charge of pipe wall is studied experimentally. A bipolar charge distribution on the surface of a pipe wall is observed for the transport of industrial granules.

Submicron particle agglomeration and precipitation by using a bipolar charging method

Abstract The collection efficiency of modern electrostatic precipitators (ESP) is very high except for that of submicron particles. To improve the collection efficiency of fine particles, it is considered to use an electrostatic agglomeration technique. This technique is to produce larger particles by collision of oppositely charged fine particles under Coulomb force. In this paper, a two-stage ESP with a bipolar charging section is proposed and the fundamental characteristics of agglomeration and precipitation of submicron particles are studied. The ESP consists of a bipolar charging section and an electric field section. Smoke particle trajectories are observed and particle size distributions are measured with the charging voltage and the electric field strength as parameters. Moreover, particle charges are calculated by using a corona field calculation method and theoretical particle trajectories are compared with experimental results. As a typical result, 0.3−1 μm particles decrease to only 18% (75% without bipolar charging), while 1−5 μm particles increase to about 82% (25% without bipolar charging). The mean diameter of smoke particles with electrostatic agglomeration increases two times compared to that of non-agglomerated particles. The collection efficiency for submicron particles is about 80% under an optimum condition.

Laser Flow Visualization and Velocity Fields by Particle Image Velocimetry in an Electrostatic Precipitator Model

AbsractAlthough improving electrostatic precipitator (ESP) collection of fine particles (micron and submicron sizes) remains of interest, it is not yet clear whether the turbulent flow patterns caused by the presence of electric field and charge in ESPs advance or deteriorate fine particle precipitation process. In this paper, results of the laser flow visualization and Particle Image Velocimetry (PIV) measurements of the particle flow velocity fields in a wire-to-plate type ESP model with seven wire electrodes are presented. Both experiments were carried out for negative and positive polarity of the wire electrodes. The laser flow visualization and PIV measurements clearly confirmed formation of the secondary flow (velocity of several tens of cm/s) in the ESP model, which interacts with the primary flow. The particle flow pattern changes caused by the strong interaction between the primary and secondary flows are more pronounced for higher operating voltages (higher electrohydrodynamic numbernehd) and lower primary flow velocities (lower Reynolds number Re). The particle flow patterns for the positive voltage polarity of the wire electrodes are more stable and regular than those for the negative voltage polarity due to the nonuniformity of the negative corona along the wire electrodes (tufts).