Electrostatic precipitation particle collection

Another device used to separate particulate and vapor phase PAHs is an electrostatic precipitator, consisting of a conducting surface to which an electric field has been applied. A corona is produced, which charges particles and allows them to collect on an oppositely-charged surface. A sorbent is placed downstream of the electrostatic precipitator to collect gaseous PAHs. The electrostatic precipitator is often referred to as an EA method (electrostatic precipitator-adsorbent). EA methods are less susceptible to sorption/desorption. The corona has the potential to destroy PAHs and create other artifacts by reactions with corona-generated ozone. ... 

Chow et al. [22] used spray drying to prepare nanosize hydroxyapatite (HA) particles. They used a nozzle to spray the acidic calcium phosphate solutiou aud an electrostatic precipitator to collect nanosize powder. Their high-resolution transmission electron microscopy (TEM) showed that the particles, some of which were only 5 nm in size, exhibited... 

Electrostatic precipitator (ESP) Collection of coal combustion fly ash requires the application of an electrostatic charge to the fly ash, which then is collected on grouped plates in a series of hoppers. Fly ash collected in different hoppers may have differing particle size and chemical composition, depending on the distance of the hopper from the combustor. The ESP ash may also be collected as a composite. 

In addition, certain devices are used for pollution control in industry. They either destroy contaminants or remove them (from an exhaust stream) so they are not emitted into the atmosphere. Several examples are provided. An electrostatic precipitator removes (collects) particles from a flowing gas, using the force of an induced electrostatic charge. It can remove fine particles such as dust and smoke from a stream of air. 

Over the years this effect was used in electrostatic precipitators to collect airborne dust in smokestacks,where the dust was collected as a solid cake. Winslow in 1949 found a similar but reversible effect with silica particles mixed in oil. The slurry stiffened when the field of around 2kVmm" was applied but became fluid again when the field was removed. In modem formulations, carbonaceous particles of diameter 3.5 pm and of resistivity 1 M lm are mixed to around 40% volume fraction in a silicone fluid of resistivity lOOTIJm. 

N2, and traces of PH, CO2, E, and S large furnaces generate off-gas at a rate of about 120—180 m /min. In most installations the off-gas is passed through a series of Cottrell electrostatic precipitators which remove 80—95% of the dust particles. The precipitators ate operated at temperatures above the 180°C dew point of the phosphoms. The collected dust is either handled as a water slurry or treated dry. Einal disposal is to a landfill or the dust is partially recycled back to the process. The phosphoms is typically condensed in closed spray towers that maintain spray water temperatures between 20 and 60°C. The condensed product along with the accompanying spray water is processed in sumps where the water is separated and recycled to the spray condenser, and the phosphoms and impurities ate settled for subsequent purification. 

Small solid particles, present in dust and grit emissions, have very low settling velocities (Table 4.4) The collection efficiencies of simple cyclones are tlierefore, as shown in Figure 17.3, relatively low. Fabric filters, electrostatic precipitators or wet scrubbers may be required to remove particles <5 pm in size with an acceptable efficiency. Therefore the cost of pollution control inevitably increases when dealing with particle size distributions skewed towards the lower end. 

Electrostatic precipitators (ESPs) remove particles by using an electrostatic field to attract the particles onto the electrodes. Collection efficiencies for well-designed. 

Fabric filters are useful for collecting particles with resistivities either too low or too high for collection with electrostatic precipitators. Fabric filters therefore may be good candidates for collecting fly ash from low-sulfur coals or fly ash containing high unburned carbon levels, which respectively have high and low resistivities, and thus are relatively difficult to collect with electrostatic precipitators. 

The development of electrostatic precipitators was based mostly on empirical work, and it has produced more than 1000 patents covering all aspects of electrostatic air cleaning. From the theoretical point of view, important milestones were papers published by Deutsch as well as White.These papers deal with the collection efficiency of the electrostatic precipitator. The most important early papers dealing with the electrical charging of particles are the ones published by Arendt and Kallmann, Pautheniet and Moreau-Hanot, and White. ... 

A very important parr of the gas-deatimg process is the removal of the collected particles from the cleaning system. This should be as controlled as possible in order to avoid particle reenrrainmenr to the gas flow. This can be accomplished in the case of liquid particles such as acid fume or tar or oil smoke. olid particles are normally removed by periodic rapping of discharge and collection electrodes. Solid particles can also be removed with the aid of water, as is done in wet electrostatic precipitators. 

Particle trajectories can be calculated by utilizing the modern CFD (computational fluid dynamics) methods. In these calculations, the flow field is determined with numerical means, and particle motion is modeled by combining a deterministic component with a stochastic component caused by the air turbulence. This technique is probably an effective means for solving particle collection in complicated cleaning systems. Computers and computational techniques are being developed at a fast pace, and one can expect that practical computer programs for solving particle collection in electrostatic precipitators will become available in the future. 

Most of the results presented in the previous chapters are based on idealized conditions. In practice, the performance of an electrostatic precipitator can be significantly influenced by the dust layers on discharge and collection electrodes i.e., dust layers may alter the electrical properties of the system. It is also possible that dust layers are not stable i.e., collected particles become loose, increasing the particle concentration in the outlet of the precipitator. These problems play a much smaller role if the surface collection electrode is continuously flushed with water. These wet elearostatic precipitators, however, cannot be used in all applications. 

The two-stage electrostatic precipitators used in light-industry applications are compact devices which can be fitted into the ventilation system. These air cleaners are normally used to clean air from dusts, smokes, and fumes in industrial workplaces. The basic features of these devices are the separate sections for particle charging and collection. The charging section consists of thin metal wires installed between grounded metal plates. The distance... 

Electrostatic precipitators are satisfactory devices for removing small particles from moving gas streams at high collection efficiencies. They have been used almost universally in power plants for removing fly ash from the gases prior to discharge. Electrostatic precipitators have the capability of fine particulate control. Resistivity plays an important role in determining whether a particle can be readily collected in this device. 

Even with proper operation of the reactor and regenerator cyclones, catalyst particles smaller than 20 microns still escape from both of these vessels. The catalyst fines from the reactor collect in the fractionator bottoms slurry product storage tank. The recoverable catalyst fines exiting the regenerator are removed by the electrostatic precipitator or lost to the environment. Catalyst losses are related to ... 

A Del Electronics, Model ESP-100A, electrostatic precipitator was used for sample collection. Cigarette smoke particles were found to give approx the same particle distribution pattern on the collection filter paper as the gunshot residue, and since the smoke stains the paper, this provided a v rapid technique for optimizing operation conditions. With a flow rate of 15cfm and a corona current of 125 uA, the residue collects primarily on a narrow band across the sample paper. Samples were collected on Whatman No 1541 filter paper which lined the inside of the sample collection tube. The presence of this paper allowed air to flow only thru the center of the tube, so particle collection was made upon the filter paper exclusively. The filter paper samples were pelletized prior to neutron activation analysis... 

A method used to dislodge ash particles collected by an electrostatic precipitator. 

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