Fundamental Behavior of Direct-Coupled Submicrosecond Pulse Energization in Electrostatic Precipitators

The fundamental characteristics of the direct-coupled pulse energization in electrostatic precipitators (EP's) are investigated in a test rig comprised of a coal pulverizing facility, a furnace, a gas cooling system, and an EP. The EP consisted of a corona electrode with barbed wires and a collection electrode with 300-mm duct spacing. This simulates the type of EP normally used in a coal-fired power station. The pulse-energized collection field shows a very high collection performance of more than 99 percent collection efficiency and the performance enhancement compared to the conventional dc energization, causing very severe back corona, becomes as large as H = 2.50.H is the enhancement factor in terms of the Deutsch migration velocity in the case of the very high resistivity dust of rd = 2 x 1013 ?cm at the gas temperature of Tg = 150°C. Even at the lower level of the dust resistivity at Tg = 110°C, where no back corona occurs in the dc-energized collection field, the performance enhancement is as large as H = 1.21. The mechanism of such great performance enhancement is likely to be the result of the very uniform and very intense formation of corona plasmas on the wires as a result of the very fast rise in the pulse voltage applied and a special sawtooth waveform of the operating voltage between the corona and collection electrodes.     

Separation of Small Particles Suspended in Liquid by Nonuniform Traveling Field

A study of size and charge-dependent separation of small particles in liquid using a traveling-field-type electric curtain device is made. The principle of the separation is to make use of the spatial harmonic components of the rotating traveling field produced by such a device, the first harmonic propagating in one direction, which plays a dominant role in the region distant from the electrodes, and the second harmonic propagating in the opposite direction, which becomes dominant near the electrodes. Small particles brought into this field undergo circular motion and, as a result of field nonuniformity, are repelled from the electrodes and drift in the direction of the dominant harmonics. The lighter or more charged particles are strongly repelled from the electrodes and swept by the first harmonic, while the heavier or less charged particles can approach the electrodes and are transported by the second harmonic in the opposite direction, thus enabling separation by mass and charge. First a theoretical investigation of this method is made to clarify the operation conditions for the separation, then the experimental observations of particle motion are made and scaling laws of transport velocity with the applied voltage and frequency are confirmed. Finally, an example of a cell separator design using this method is presented.     

Bipolar Structure of a Back-Discharge Field in an Electrostatic Precipitator

The current densities of positive and negative ions i+ and i- in the back-discharge field of an electrostatic precipitator (ESP) are measured with a bipolar current probe. The ratio i+/i- rises with increasing total current density i (= i+ + i-) in the streamer-mode back discharge, but it remains almost constant (10-20 percent) in the glow-mode back discharge. The probe-measured values of the back-discharge-starting current density are slightly higher in pulse charging than in dc charging. In addition, the pulse charging does not cause back discharge at a resistivity below 1013 ?cm. However, beyond 1014 ?cm the back discharge can hardly be avoided, even by pulse charging. The probe diagnosis of i+/i- in an ESP enables an approximate estimation of the charge-to-mass ratio of dust and the collection performance when i+/i-, averaged in space, is used.     

Corona Transmission Line Energized by Very Short Pulse Voltages as Applied in Electrostatic Precipitators

The corona-producing characteristics of a corona wire energized by a very short pulse voltage superposed on top of a dc base voltage are investigated in consideration of its application in electrostatic precipitators. A ``formation region' of the pulse-induced negative corona is determined in terms of a Vb - Vp domain where Vb represents the dc base voltage and Vp the pulse peak voltage. A pulse voltage propagates in a form of a traveling wave along a transmission line out of an elongated corona wire and collection plates. It produces streamer coronas and loses its energy during propagation and finally becomes inactive so as not to produce coronas. As a result, a longitudinal distribution of the ionic current shows a decay towards the end of the line. An ``effective pulse energy' We is defined as an energy to produce uniform current distribution on the entire collection plates. This value of We amounts to 0.8 J for a 200-m corona line. A ``pulse peaking' to squeeze more corona energy from the pulse after corona-induced deterioration is tested using partial and total reflections, and its effectiveness is confirmed. A matched feeder concept to enable uniform distribution of pulse power to a number of corona transmission lines is also presented.     

Inflow and outflow of agricultural chemicals in Lake Biwa

The annual pesticide inputs and outputs crossing the boundary of Lake Biwa were estimated. The inputs were calculated from continuous observations in four rivers flowing into Akani Bay, and from simultaneous observations in 65 influent rivers. The annual losses of pesticide from the watershed to Lake Biwa were 1.7% for esprocarb, 4.8% for mefenacet, 2.3% for thiobencarb, 3.7% for molinate, 9.4% for simetryn and 13.0% for isoprothiolane. The outputs from the lake were estimated from weekly observations in the Seta River. The loss of pesticides discharged downstream through the Seta River, compared with the amount applied, were estimated to be 0.9% for esprocarb, 3.2% for mefenacet, 0.5% for thiobencarb, 1.3% for molinate, 10.0% for simetryn and 5.7% for isoprothiolane. Pesticide outputs generally decreased to 30–80% of the input amounts, although simetryn was retained in the lake without substantial elimination.     

High-Efficiency Ozonizer Using Traveling Wave Pulse Voltage

The energy yield of ozone generation can be raised substantially by using a fast-rising narrow pulse voltage in combination with a transmission-line type ozonizer. The pulse voltage proceeds in the form of a traveling wave to produce very active coronas. Both wire-to-cylinder type ozonizers and parallel-strip-line-with-insulator type ozonizers are tested. The former produces streamer coronas along the wire and indicates a high ozonizer-based energy yield Yo but its volume yield Yu is very low. The latter produces pulse-induced intense-glow coronas, and indicates very high Yo and Yu. However, the energy yield based on the stored energy of the pulse-forming condenser Yc still remains low, because of poor coupling of the pulse energy with the ozonizers. The plate-type ozonizer, comprising zigzag-shaped strip-line electrodes on the insulator plates, represents one of the practical embodiments of the stripline ozonizer. The pulse-peaking method provides a possibility of enhancing the level of Yo. An improvement of the coupling method is likely to improve the level of Yc.     

Regression models for estimating storm runoff load and its application to Lake Kasumigaura

Regression models are proposed for accurate estimation of storm runoff load. Regression equations are obtained for the relationship between final cumulative load and flow during direct runoff by each storm event. The models are applied to estimate annual nutrients load by all influent rivers into the Lake Kasumigaura for a model year of average annual rainfall. The load in dry weather is calculated from observed data of all influent rivers. Total annual load for a year is the sum of loads in dry weather days and loads in wet weather days. The ratios of the load in a wet weather day to total annual loads are 29 percent for T‐N, 51 percent for T‐P, 53 percent for T‐COD, 22 percent for D‐N, 22 percent for D‐P and 30 percent for D‐COD.