Tairo Ito

Reduction of NO/sub x/ from combustion flue gases by superimposed barrier discharge plasma reactors

NO/sub x/ reduction from combustion flue gases by superimposed barrier discharge plasma reactors is experimentally investigated. The experiments are conducted for applied voltages from 0 to 28 kV, flue gas rates from 0.5 to 2 L/min, ammonia mixture concentrations from 0.7 to 2.65 stoichiometry, and applied voltage phase differences from 0/spl deg/ to 180/spl deg/, where two 60-Hz AC power supplies are used. The results show the following: (1) NO/sub x/ reduction rate decreases with increasing discharge power for surface discharge operations, however, NO/sub x/ reduction rate increases with increasing discharge power for silent and superimposing discharge operating modes; (2) NO/sub x/ reduction rate increases with increasing discharge power, gas flow rate and ammonia stoichiometry under in-phase operations; (3) NO/sub x/ reduction rate for out-of-phase operations is much higher compared with in-phase operations, however, NO/sub x/ reduction rate has an optimum condition on ammonia stoichiometry, discharge power, and gas flow rate; and (4) energy efficiency of NO/sub x/ reduction increases with increasing ammonia mixture and gas flow rate and decreases with increasing discharge power.

Destruction of volatile organic compounds in air by a superimposed barrier discharge plasma reactor and activated carbon filter hybrid system

The superimposed barrier discharge and activated carbon filter hybrid systems are used to remove toluene and trichloro-ethylene (TCE) from air streams. The superimposed barrier discharge consists of silent and surface discharges. Experiments are conducted for the gas flow rate from 1 to 10 L/min., applied power from 0 to 7 W and toluene and TCE initial concentration from 0 to 2,000 ppm for 60 Hz AC applied voltage conditions. Discharge byproducts are measured by FTIR, GC and TLV VOC detector. The results shows that: (1) toluene decomposition rate monotonically increases with increasing applied power; (2) approximately 90% of toluene is removed by plasma reactors alone and up to 98% is removed by hybrid systems; (3) TCE removal rate by hybrid system is 90% and up to 50% is removed by a discharge reactor alone; (4) the pressure drop of the reactor and carbon filter increase with increasing gas flow rate; (5) TCE decomposition to form CO/sub 2/, H/sub 2/O and Cl/sub 2/ and except CO/sub 2/ and H/sub 2/O these discharge byproducts are absorbed in activated carbon filters; (6) no COCl/sub 2/, HCl, CO, NO/sub x/ and O/sub 3/ are observed in a discharge byproducts for the present range of experiments; and (7) the energy yield for toluene decompositions is up to 30 g/kWh, and up to 15 g/kWh for TCE decompositions.

Simultaneous removal of aerosol particles, NOx and SO2, from incense smokes by a DC electrostatic precipitator with dielectric barrier discharge prechargers

In this paper, electrostatic precipitators (ESPs) under positive corona discharge operation with and without wire-rod and wire-quadrupole type barrier discharge prechargers were tested for simultaneous removal of submicron particles, NOx and SO2. High dielectric constant ferro-electric materials and hard glass were used as the barrier for barrier discharge type precharger. The results show that aerosol particles, NOx and SO2, were simultaneously removed by DC positively biased wire-plate ESPs, and that the particle collection efficiency was improved by an addition of wire-quadrupole type barrier discharge precharger in front of the wire-plate ESP. The addition of the prechargers, however, had little effect on the overall removal efficiencies of NOx and SO2.

Suppression of particle deposition onto downstream wall in an AC Electrostatic Precipitator with neutralisation

Electrostatic Precipitators (ESPs) are used to decontaminate polluted environment around the tunnels. A conventional ESP has high collection efficiency but still has a problem in that its downstream walls are polluted due to particle deposition. The experiments carried out in this study have focused on how the particle deposition can be prevented by neutralising the gases. The collection efficiency as a function of particle diameter and the amount of deposited particles on the wall were studied on three types of the ESP: the universal ESP under DC operating mode (DCESP), the ESP under AC operating mode (ACESP) and the ACESP with gas-neutralising equipment (ACESP with neutralisation). Electrostatic field intensity and ion concentration were also measured to understand the state of neutralising the gases. The ACESP, an invention of the authors, prevents particle re-entrainment. The ACESP with neutralisation, which not only prevents the particle re-entrainment but also decreases the charge amount of the downstream gases, was most effective in decreasing the amount of deposited particles.

Effect of applied voltage frequency on NOx removal rate for a superimposing discharge reactor

Abstract We are interested in the removal technique of NO x gas exhausted from a diesel engine with the use of several electric discharge methods. Several reactors have been proposed in order to remove NO x by electric discharge. Nomura et al. have proposed the superimposing methods of surface and silent discharges. These methods suggested the usefulness for the removal of NO x and the generation of ozone. We have exhibited in this paper, the removal of NO x in dry gas similar to a gas exhausted from a diesel engine with the use of superimposing discharge methods. We present the accelerating effects of the superposition of discharges and the frequency of electric source onto the NO x removal process. The experimental results indicate a high acceleration of NO x removal rate. This high acceleration was performed by the extension of discharge space and the injection of high electric power into the reactor due to the discharge superposition and high frequency.

Modelling of the effect of electrode geometries on the corona discharge current-voltage characteristic for wire-plate electrostatic precipitators

An electrostatic precipitator (ESP) operates on the principle of electrostatic separation of dust particles after charging, hence high ion density and electric fields are required. Therefore, the corona discharge current-voltage characteristic is very important and depends on several factors: discharge electrode shape, dimensions and surface condition, gas flow properties, dust particle loading and space charge, polarity of applied voltage, etc. We present a model for the prediction of the current-voltage characteristic and experimentally validate it for round, threaded, rectangular and rigid discharge electrodes in combination with plate type collecting electrodes. The experimental validation shows good agreement for the case of the round discharge electrode. The model predicts the effect of wire diameter, plate length and gas flow temperature. For the rigid discharge electrode, of the same electrode thickness as the diameter of the round electrode, much lower corona onset voltage was observed.

A study of NO removal by packed-beads discharge reactor

Recently, air pollution has become a serious problem; photochemical smog and acid rain are typical phenomena. NO/sub x/ is a serious air pollutant and a toxic gas. In spite of an attempt to reduce the amount of NO/sub x/ emitted, the density of NO/sub x/ in the atmosphere has remained on a stable level, or even become worse. Here, the authors propose a new reactor in which the gap area is filled as a single layer of glass plates and beads. They expect that surface and silent discharges are generated simultaneously in the same space. In this paper, the removal of NO/sub x/ from a dry NO/N/sub 2/ mixed gas by barrier discharge among glass beads in the reactor is experimentally investigated. The experiments are carried out for the frequency 50 Hz, with applied voltage from 0 to 20 kV/sub pp/ and a gas flow rate from 0.4 to 1.4 L/min. The results show that the NO and NO/sub x/ removal rates with glass beads are higher than those without glass beads at the same flow rate or residence time. Thus, the new reactor in which the gap area is filled with glass beads is more effective for NO/sub x/ removal.

Investigation of two-stage type electrostatic precipitator reentrainment phenomena under diesel flue gases

One electrostatic precipitator (ESP) application is cleaning the air and increasing the visibility index in highway tunnels. The main particles found in highway tunnels are made of carbon. ESP collection efficiency of a certain particle diameter is often negative when the ESP collects carbon particles of low resistance. This means that the number of particles downstream is greater than that of the number of particles upstream of the ESP. Generally, this phenomenon is explained by the reentrainment of particles. In this work, experiments were performed to investigate the cause of the ESP negative particle collection efficiency. Experimental results show that the ESP negative particle collection efficiency is caused by a reentrainment of particles during ESP operation. The effect of gas flow velocity on the ESP collection efficiency was also investigated to clear the cause of reentrainment phenomena. The result shows that the reentrainment may depend on gas flow velocity, because the ESP collection efficiency for the larger particles increases with increasing gas flow velocity.

Phase analysis of discharge magnitude distributions inside a small void and its applications to diagnosis of deteriorating insulations

A breakdown phenomenon of electrical equipment due to the deterioration of insulation was investigated. The degree of deterioration or breakdown of the insulating system was predicted from the distribution of induced electric charges inside small voids in an insulator-the discharge magnitude distribution. This distribution was measured by a special internal-discharge pulse measurement system, which analyzes it according to the phase area of the applied AC 50-Hz voltage. This technique was used to investigate tree progression in the microvoid of PMMA (polymethyl methacrylate). The density and the growing speed of the trees are analyzed in terms of the discharge magnitude distributions.<<ETX>>

The relation between shape of particles and collection efficiency by electrostatic precipitators

Electrostatic precipitator (ESP) has been used to decontaminated polluted gases and improve the visibility index in expressway tunnels. Lots of particles in expressway tunnels are made of carbon that has low resistivity. The collection efficiency of large particles decreases due to re-entrainment phenomena. Therefore, it is important to prevent re-entrainment. In this work, we discussed the method preventing particles re-entrainment, and devised transforming shape of the agglomerated particles on the collecting electrodes.