Elemental mercury oxidation in an electrostatic precipitator enhanced with in situ soft X-ray irradiation

Abstract

Corona discharge based techniques are promising approaches for oxidizing elemental mercury (Hg 0 ) in flue gas from coal combustion. In this study, in-situ soft X-rays were coupled to a DC (direct current) corona-based electrostatic precipitator (ESP). The soft X-rays significantly enhanced Hg 0 oxidation, due to generation of electrons from photoionization of gas molecules and the ESP electrodes. This coupling technique worked better in the positive corona discharge mode because more electrons were in the high energy region near the electrode. Detailed mechanisms of Hg 0 oxidation are proposed and discussed based on ozone generation measurements and Hg 0 oxidation behavior observations in single gas environments (O 2 , N 2 , and CO 2 ). The effect of O 2 concentration in flue gas, as well as the effects of particles (SiO 2 , TiO 2 , and KI) was also evaluated. In addition, the performance of a soft X-rays coupled ESP in Hg 0 oxidations was investigated in a lab-scale coal combustion system. With the ESP voltage at +10 kV, soft X-ray enhancement, and KI addition, mercury oxidation was maximized.Implications: Mercury is a significant-impact atmospheric pollutant due to its toxicity. Coal-fired power plants are the primary emission sources of anthropogenic releases of mercury; hence, mercury emission control from coal-fired power plant is important. This study provides an alternative mercury control technology for coal-fired power plants. The proposed electrostatic precipitator with in situ soft X-rays has high efficiency on elemental mercury conversion. Effects of flue gas conditions (gas compositions, particles, etc.) on performance of this technology were also evaluated, which provided guidance on the application of the technology for coal-fired power plant mercury control.

Investigation of aerosol and gas emissions from a coal-fired power plant under various operating conditions

“…Also, for both positive and negative polarity, the current was higher with SXR at low voltages. Interestingly, with voltages higher than 12 kV, the currents were similar regardless of the presence of SXR, which was not reported in previous studies (Hogan, Lee, and Biswas 2004;Jing et al 2015;Kulkarni et al 2002).…”

“…However, there is no study on applying SXR to capture fine particles in coal-fired power plants. In our work, the capture efficiency of a lab-scale SXR-enhanced ESP, for which the configuration details can be found in Figure S1 in the supplemental information and in previous studies (Jing et al 2015), was tested with the undesiccated wet flue gas. Figure S2 shows the current-voltage (I-V) characteristics of the ESP with SXR.…”

Atmospheric pressure plasma corona enhanced by photoionizer for degradation of VOCs

“…SXR has more intensity than UV lamps but less intensity than x-ray, and therefore can be utilized safely and can be easily controlled by turning them on and off [13,14]. SXR generates gaseous ions, which have been widely studied for charging aerosol particles and oxidizing environmental pollutants [11,[13][14][15]. Namiki et al were the first to introduce SXR into the V/TiO 2 -ESP system to remove VOCs; they obtained approximately 70% removal efficiency of toluene with high reaction rate (8.07 × 10 −2 μmol h −1 cm −2 ), which was much faster than conventional UV lamp systems [6].…”

Mobility and Bipolar Diffusion Charging Characteristics of Crumpled Reduced Graphene Oxide Nanoparticles Synthesized in a Furnace Aerosol Reactor

“…It takes place in a wide range of processes from gas reactions and particle formation in the atmosphere 34 to particle removal in industrial or household devices. 35 The diffusion charging of particles is commonly realized by introducing particles into an environment that contains radioactive materials, where radiation generates ions that actively collide with the particles. 36 Currently, two theories exist in describing the diffusion charging of spherical particles.…”

“…In diffusion charging, bipolar/unipolar ions freely diffuse to the surface of the particles, where the charges are transferred. It takes place in a wide range of processes from gas reactions and particle formation in the atmosphere to particle removal in industrial or household devices . The diffusion charging of particles is commonly realized by introducing particles into an environment that contains radioactive materials, where radiation generates ions that actively collide with the particles .…”