Modeling of Gravitational Wet Scrubbers with Electrostatic Enhancement

Abstract

Conventional gravitational wet scrubbers, which generally perform removal of fine particles with low efficiency, cannot meet new standards for pollution emissions. One way of improving the collection efficiency of fine particles is to impose additional electrostatic forces upon particles by means of particle-charging, or droplet-charging, or even opposite-charging of particles and droplets. A Monte Carlo method for population balance modeling is presented to describe the particle removal processes of gravitational wet scrubbers with electrostatic enhancement, in such a way that the grade collection efficiency and particle size distribution are calculated quantitatively. Numerical results show that, the grade collection efficiency of submicron particles is only ca. 5 % in conventional wet scrubbers. However, it reaches ca. 25 % in particle-charging wet scrubbers, ca. 70 % in droplet-charging wet scrubbers, and even above 99 % in opposite-charging wet scrubbers. Furthermore, population balance modeling is used to optimize the operational parameters of the droplet-charging wet scrubbers by means of the quantitative comparison of the grade collection efficiency. It is found that the operational parameters that are beneficial to the high-efficiency removal of fine particles are faster gas velocity, slower droplet velocity, larger liquid-to-gas flow ratio, larger charge-to-mass ratio of droplets, smaller geometric mean diameter and smaller geometric standard deviation of droplets.

Integration of a nonmetallic electrostatic precipitator and a wet scrubber for improved removal of particles and corrosive gas cleaning in semiconductor manufacturing industries

“…Apart from the voltage applied to the chargers, the experimental conditions were kept constant at a flow rate of 2 m/sec, a liquid-to-gas ratio of 3.6 L/m 3 , and a voltage of 12 kV applied to the collection plates (460 mm). The collection efficiency with only the scrubber operation was approximately 80-95% at 1-10 mm; however, the efficiency was dramatically decreased to 20% at 0.1-0.3 mm because particles of <0.01 and >5 mm are effectively captured by droplets due to Brownian diffusion and inertial impaction, respectively; most wet scrubbers have low efficiency for intermediately sized particles in the range of 0.1-1 mm (Zhao and Zheng, 2008). However, when voltages of 8 and 12 kV were applied to the charger and collection plates, respectively, the collection efficiency was increased from 20% to 65% in the size range showing the lowest efficiency with the scrubber, and the efficiency for particles larger and smaller than this size range was increased to >80%, even to almost 100%, for particles of >1 mm.…”

“…To increase the efficiency of the scrubber for ultrafine particles, researchers have examined the use of an electrostatic precipitator (ESP) that collects particles from moving air using the force of an induced electrostatic charge onto a wet scrubber. The resulting removal efficiency was found to be >90% in terms of either the number or mass concentration (Bologa et al, 2009;Hwang et al, 2004;Jaworek et al, 2006;Tsai et al, 1997;Zhao and Zheng, 2008). Despite these successes, the use of general ESPs to remove particles in corrosive exhaust gases has relied on expensive anticorrosive metallic materials, such as Inconel (Special Metals Corporation, New Hartford, NY) and Hastelloy C (Haynes International Inc., Kokomo, IN) alloys, to maintain their performance (Bayless et al, 2004;Kim et al, 2010a).…”

“…These plumes raise public concerns about the effects of particulates on human health and atmospheric visibility and prompted the U.S. Environmental Protection Agency (EPA) to regulate the opacity of plumes to <20% (Du et al, 2007;Sivastava et al, 2004). Although gravitational wet scrubbers have high removal efficiency for soluble corrosive gases, they also have technical limitations, such as requirements for high power and large installation space due to the high pressure drop needed to remove ultrafine particles (Allen and Santen, 1996;Huang et al, 2007;Tsai et al, 2005;Zhao and Zheng, 2008). To increase the efficiency of the scrubber for ultrafine particles, researchers have examined the use of an electrostatic precipitator (ESP) that collects particles from moving air using the force of an induced electrostatic charge onto a wet scrubber.…”

Estimation of the radioactive aerosols capture in accidental sequences of nuclear power plants

“…Interception takes place when aerosol particle radius is larger than distance between the streamline followed by the aerosol particle and the surface of the obstacle (in the present case, the water droplets). Lots of expressions are available in the open literature and, many of them have been tested in the present work, for instance the Zhao and Zheng's correlation [Zhao, 2008], Slinn's correlation [Flagan, 1988], etc.…”

“…A simple expression is the one proposed by Zhao and Zheng [Zhao, 2008], in which the collection efficiency produced by interception is modeled by next expression Another expression to the interception mechanism, a little bit elaborated, is the proposed by Slinn among other authors [Zhao, 2006] Finally the selected correlation was the one proposed by Jung and Lee's [Jung, 1998] …”