Phase separation electrostatic precipitators

An electrostatic precipitator is a gas-solid separator in which particles suspended in a gas stream are charged and removed by electrostatic force. Since the separation force is directly applied to the particles without the need of accelerating the gas phase, an electrostatic precipitator usually requires much less hydraulic power than other separation systems. Hence, electrostatic precipitation is widely recognized as an important technique of gas-solid separation. This technique is characterized by low pressure drop, relative high... 

Only if an inert electrolyte like NaCl is added, the strong electrostatic interactions are increasingly screened and the highly expanded polyelectrolyte coils start to shrink. Eventually the unperturbed dimensions are approached at high enough concentrations of inert salt [18-20]. In such cases, phase separation occurs if this inert salt level is surpassed [21-23]. The latter phenomena has been denoted as salting out of polyelectrolytes, or alternatively, as H-type precipitation, because the concentration of inert salt required to cause precipitation of the polyelectrolyte is high and independent of the polymer concentration [23]. 

Finally, we consider the dashed curves in fig. 5.32. The curve labelled 4" represents a common situation where the solubility of the screened polyelec-trol rte is poor ix > 0.5). At low c the electrostatic contribution makes x small and the pol mier soluble, but as this contribution Is screened by salt the polyelectrolyte might precipitate at very high ionic strengths. Before this precipitation occurs, the adsorption can become very high since the surface acts as a nucleus for phase separation (through t ). Clearly, this effect Is not restricted to curve 4 it is Indicated in fig. 5.32 only once in order not to overcrowd the figure. 

The solid product, now a separate phase, can be readily captured by electrostatic precipitation or any other particulate collection device which is already normally in place for fly-ash control. 

The solubility of flexible highly charged polyelectrolytes in the presence of multivalent counterions depends on the affinity between counterions and charged groups of the polyelectrolyte. Two extreme cases can be encountered in the first one the precipitation is induced by the complexation of the polyelectrolyte with the multivalent ions, whereas in the second one the electrostatic attraction is the principal driving force for phase separation. 

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. ... 

These are prepared by drawing the distillation and combustion products from damp hardwood sawdust into a condenser fitted with an electrostatic precipitator. This removes all particulate matter from the condensate, which is collected and settled to allow separation into aqueous and tarry phases. The clear aqueous phase is the desired product. 

Most industrial liquid-liquid applications fall into the category of being more concentrated systems. We identify more concentrated systems as 4) > 0.20 by volume fraction of dispersed phase. Industrial examples include suspension and emulsion polymerization, extraction, and separations, including decantation, centrifugation, and electrostatic precipitation. Because practice is as much an art as a science, much of the industrial experience on concentrated systems is proprietary and not published, contrasting the vast amount of academic work published for dilute and clean systems. 

---