Electrostatic Precipitators Pdf
In low resistance dust layers, the corona current is readily passed to the grounded collection electrode. The remainder recombines with ammonia to add to the space charge as well as increase cohesiveness of the ash. Aerosol Science and Technology. The energized electrodes create ions that collide with the particles and apply the electrical charge to the particles contained in the incoming gas stream.
The migration velocities of small particles are especially affected by the reduced electric field strength. Enhances space charge effect.
At the time of Cottrell's invention, the theoretical basis for operation was not understood. Reduced operating voltage and current levels with high spark rates.
Thus, lower power current readings are noted with relatively high voltage readings. The figure to the right shows the effect of temperature and moisture on the resistivity of a cement dust. Sufficient electrical force component retaining collected dust.
Particles that exhibit high resistivity are difficult to charge. Improvements for decreased emissions and improved efficiency. The table below summarizes the characteristics associated with low, normal and high resistivity dusts.
Results for Fly Ash A in the figure to the left were acquired in the ascending temperature mode. From Wikipedia, the free encyclopedia.
Cottrell, Art of separating suspended particles from gaseous bodies, U. The first portable electrostatic air filter systems for homes was marketed in by Raytheon. Negligible voltage drop across dust layer. The ability to control two different types of power supplies adds a unique dimension to the product line.
As the dust layer builds up, and the electrical charges accumulate on the surface of the dust layer, the voltage difference between the discharge and collection electrodes decreases. Another problem that occurs with high resistivity dust layers is called back corona. This is easily remedied by making sure that the wires themselves are cleaned at the same time that the collecting plates are cleaned. The effects of relatively small amounts of acid vapor can be seen in the figure below and to the right. The strength of this electric field depends on the resistance and thickness of the dust layer.
As voltage is increased from small amounts e. The primary difference between the two classifications is the method by which the collector plates are cleaned. Therefore, a relatively weak electric field, of several thousand volts, is maintained across the dust layer. Volume conduction, or the motions of electrical charges through the interiors of particles, depends mainly on the composition and temperature of the particles.
For more information, upholstery techniques illustrated pdf see the box More About Electrostatic Precipitators. Electrostatic Precipitator Delivers Maximum Efficiency. Electrostatic precipitators can be used to sample biological airborne particles or aerosol for analysis. Wet Electrostatic Precipitators for Utility Applications.
Collected dust particles with low resistance do not adhere strongly enough to the collection plate. The controls sense this surge as a spark.
An official website of the United States government. Volume conduction also involves ancillary factors, such as compression of the particle layer, particle size and shape, and surface properties. Discharge electrodes are energized by a single transformer-rectifier T-R set power supply. These properties can be measured economically and accurately in the laboratory, using standard tests. The dust layer breaks down electrically, producing small holes or craters from which back corona discharges occur.
In high-resistance dust layers, the dust is not sufficiently conductive, so electrical charges have difficulty moving through the dust layer. American inventions Filters Chemical equipment Pollution control technologies Air pollution control systems Particulate control Gas technologies Solid-gas separation. Reduced electrical force component retaining collected dust, vulnerable to high reentrainment losses.
Higher voltages can be required in order for corona generation to begin. The characteristic is termed moderate resistivity. The particles take on the charge of the collection electrode, bounce off the plates, and become re-entrained in the gas stream. The same thing is believed to occur in laboratory measurements.
The third, and generally most common problem with high resistivity dust is increased electrical sparking. The operational theory was developed later in Germany, with the work of Walter Deutsch and the formation of the Lurgi company. The operation of Research Corporation is funded by royalties paid by commercial firms after commercialization occurs. Thus, attractive and repulsive electrical forces that are normally at work at normal and higher resistivities are lacking, and the binding forces to the plate are considerably lessened. The collection plates or pipes provide the collection surfaces for the charged particulate matter.
Electrostatic Precipitators (ESPs)
Parallel plate geometry is used in laboratory measurements without corona generation. One solution, suggested by several manufacturers, is to wash the collector plates in a dishwasher. Other indicators of performance are the spark rate, primary current, primary voltage, inlet gas temperature, gas flow rate, rapper operation, and number of fields in operation.
Another stainless steel electrode weight sits on top of the sample direct contact with the dust layer. These particles slowly leak their charge to grounded plates and are retained on the collection plates by intermolecular adhesive and cohesive forces. Experimental data lacking to substantiate which of these is predominant. In other projects Wikimedia Commons.
Electrostatic Precipitators (ESP)
Also, raising or lowering the temperature can decrease cement dust resistivity for all the moisture percentages represented. Modifies resistivity depends upon injection temperature. Not to be confused with Electrofiltration. Increases ash cohesiveness. The charged particles are then attracted to collector plates carrying the opposite charge.
The intent of the organization was to bring inventions made by educators such as Cottrell into the commercial world for the benefit of society at large. Consequently, electrical charges accumulate on and beneath the dust layer surface, creating a strong electric field.
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