Removal of H 2. S in air by corona discharge under continuous flow condition. Journal of Physics: Conference Series. Related content OPEN ACCESS

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1 Journal of Physics: Conference Series OPEN ACCESS Removal of H 2 S in air by corona discharge under continuous flow condition To cite this article: Hyun-Woo Park et al 2013 J. Phys.: Conf. Ser View the article online for updates and enhancements. Related content - Decomposition of Nitrogen Trifluoride Using Low Power Arc Plasma Jee-Hun Ko, Sooseok Choi, Hyun-Woo Park et al. - Design of a MT-DBD reactor for H2S control Xu CAO, Weixuan ZHAO, Renxi ZHANG et al. - Advanced oxidation technology for H2S odor gas using non-thermal plasma Tao ZHU, Ruonan WANG, Wenjing BIAN et al. This content was downloaded from IP address on 08/07/2018 at 01:06

2 Removal of H 2 S in air by corona discharge under continuous flow condition Hyun-Woo Park, Chung Hyun Lee and Dong-Wha Park* Department of Chemical Engineering and RIC-ETTP(Regional Innovation Center for Environmental Technology of Thermal Plasma), Inha University, 253 Yonghyun-dong, Nam-gu, Incheon, , Republic of Korea. dwpark@inha.ac.kr Abstract. Hydrogen sulfide (H 2 S) gas diluted in air was removed on a large scale using a newly developed wet electrostatic precipitator (Wet-EP) system under the continuous flow condition at atmospheric pressure and room temperature. Acid H 2 S is spontaneously neutralized by NaOH and KOH used as basic materials at room temperature. And then, the solid salts generated from neutralization reaction were removed by the electrostatic precipitation method using corona discharge. The experimental variables are reaction ratio between H 2 S and basic materials, reaction time and plasma input power for the removal of generated solid salts. The purpose of this work is to determine optimal operating conditions and space velocity. The removal efficiencies of H 2 S and dust were over 99% at H 2 S initial concentration of 600 ppm and the total flow rate of 2 m 3 /min. The optimal space velocities for NaOH and KOH are almost from to hr -1 at reaction time of 0.06 and seconds, respectively. In conclusion, KOH is more efficient than NaOH for removal of H 2 S. 1. Introduction Hydrogen sulfide (H 2 S) is one of the odor substances that cause air pollution. The major emission sources of H 2 S gas are biogas production process, naphtha process, landfills, sewage treatment process, food waste treatment process and coal gasification process. Human beings have a variety of symptoms such as mental stress, psychological insecurity, petulance, hysteria, hyposmia, headache, vomit and insomnia because of odor substances [1]. Conventional methods for odor control including wet scrubbing, thermal oxidation, catalyst, adsorption, active carbon, ozone oxidation and biofiltration, are limitative technically and economically for the abatment of low concentration odor substances [2-8]. In recent years, studies of H 2 S treatment using various plasma systems, such as dielectric barrier discharge, microwave, radio frequency, pulsed corona discharge, gliding arc, have been progressed [9-12]. These methods, however, have problems in large-capacity treatment. In this experiment, a novel wet electrostatic precipitator system (Wet-EP) was used to treat H 2 S on a large scale. The Wet-EP system is the combination of two methods which are wet scrubbing for the neutralization reaction of H 2 S with basic materials and electrostatic precipitation by corona discharge for the removal of generated solid salts. An ultrasonic atomizer was used for the injection of basic material solutions in order to increase the reaction surface area. The purpose of this work is the confirmation of optimal conditions to remove large amount of H 2 S under continuous flow conditions. As variables, the reaction ratio of H 2 S with basic materials, reaction time in reaction region and the plasma input power of electrostatic precipitator were controlled. Content from this work may be used under the terms of the Creative Commons Attribution 3.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI. Published under licence by Ltd 1

3 2. Experimental setup Figure 1. The schematic diagram of the Wet-EP system to remove diluted H 2 S gas in air. Figure 1 shows the schematic diagram of the Wet-ESP system for the removal of dilute H 2 S gas in air. The flow rate of H 2 S was controlled by a mass flow controller (MFC, Sierra INC., USA) and it was mixed with air at the exit of ultrasonic atomizer at 600 ppm. The total gas flow rate of H 2 S-air mixture was controlled by a blower. A DC power supply (Plasmatech Co. Ltd., Korea) which has high voltage and low current was employed for corona discharge. This system consists of two step process. The first step is the spontaneous neutralization reaction of H 2 S with basic material solutions. The second step is the electrostatic precipitation process of generated salts and water mists by corona discharge. Gas phase H 2 S and liquid phase basic materials spontaneously reacted in chemical reaction region at room temperature and atmospheric pressure. Therefore, solid phase salts and non-reacted basic material solutions were existed in air. These are charged to negative by corona discharge so that negatively charged liquid and solid salts are precipitated at anode. The chemical reaction region was designated in a plastic pipe line with the inner diameter of m and the length of 5.2 m before electrostatic precipitator. The type of electrostatic precipitator electrodes are pin-to-plate with the electrodes gap distance of m. A cathode is composed of 256 stainless steel pins. An anode is cylindrical plate which is 0.35 m in length and m 2 in area, respectively. The inlet and outlet concentrations of H 2 S were measured by a flue gas analyzer (MK 9000, RBR Co. Ltd., Germany). Amount of dust with and without the operation of the electrostatic precipitator was analyzed using a dust analyzer (3442, KANOMAX Co. Ltd., Japan) to evaluate the removal efficiencies of H 2 S and dusts. Removal efficiencies of H 2 S and dusts were calculated as follow equations: Cin Cout H (%) 100 2S (1) Cin ( moff matm) mon dust(%) 100 (2) m m off where, η H2S and η dust (%) are the removal efficiencies of H 2 S and dust, respectively; C in and C out (ppm) are the inlet and outlet concentration of H 2 S; m on and m off (mg/m 3 ) are dust amount before and after the operation of the electrostatic precipitator; m atm (mg/m 3 ) is dust amount at atmosphere. Amount of dust at atmosphere was mg/m 3. The reaction ratio (R) of H 2 S and basic materials was calculated as follow equation: atm 2

4 . mb R (3). m w where, b (mol/min) and w (mol/min) are input molar flow rates of basic materials and H 2 S gas, respectively. In order to evaluate the economic feasibility in each operating conditions, the space velocity (SV) was calculated as follow equation: 36 H S SV 1 (hr ) 2 (4) R t where, SV (hr -1 ) is space velocity value in chemical reaction region; t (hr) is reaction time of gas at reaction region. Table 1 indicates the experimental conditions. The range of reaction ratio was from 0.24 to 4.98 and reaction time was varied from 0.01 to 0.06 second. The input power of electrostatic precipitator was controlled from 1 to 180 W. Total gas flow rate and initial concentration of H 2 S were fixed at 2 m 3 /min and 600 ppm, respectively. As basic materials, NaOH and KOH were used for the neutralization reaction of H 2 S. Table 1 Experiment conditions for the removal of H 2 S by using Wet-EP system. 3. Results and discussion Total flow rate (m 3 /min) 2 Initial H 2 S concentration (ppm) 600 Type of basic materials NaOH, KOH Reaction ratio Reaction time (sec) Plasma input power (W) Input voltage (kv) Input current (ma) Figure 2 shows the Gibb s free energy for the neutralization reaction of H 2 S with basic materials calculated by thermodynamic equilibrium calculation software (FactSage, CRCT & GTT-technologies, Canada & Germany). Gibbs free energies for all neutralization reactions have negative value at whole temperature range as shown in figure 2. Therefore, it can be occurred to spontaneous neutralization reaction at room temperature and atmospheric pressure. Since G value for neutralization reaction by KOH solution is lower than the reaction by NaOH solution, the reaction between H 2 S and KOH is expected to proceed at easier. The major products in the reaction by KOH and NaOH solution are expected to be solid salts such as Na 2 S, Na 2 S 2 and K 2 S. Figure 3 presents correlation between the removal efficiency of H 2 S and the reaction ratio. When H 2 S is reacted with KOH solution, removal efficiency is higher compared with NaOH solution. These results are in a good agreement with calculation results on Gibbs free energies in figure 2 consequently, neutralization of H 2 S is more favorable to use KOH than NaOH. In addition, the removal efficiencies are increased rapidly with increasing the reaction ratio. When the reaction ratio is 4.98, removal efficiency with KOH basic material is over 99 %. Figure 4 is calculation results on the space velocity. The space velocity has the opposite tendency with removal efficiency according to the reaction ratio. At the reaction ratio of 4.98, the space velocities for NaOH and KOH were approximately and hr -1, respectively. H 2 S removal efficiency by KOH was higher than by NaOH at all range of reaction ratio in figure 3, because G 3

5 value of reaction by KOH was lower than by NaOH at room temperature in figure 2 Due to these results, reaction by KOH was more progressed easily than reaction by NaOH. Figure 2. Gibb s free energy calculation result of neutralization reaction of H 2 S and basic materials. H 2 S removal efficiency was confirmed at fixed reaction ratio and controlled the reaction time in the reaction region. Figure 5 shows the removal efficiency of H 2 S according to the reaction time. Length of plastic pipe line was adjusted in order to control the reaction time. The reaction time was varied from 0.01 to 0.06 second at the fixed reaction ratio of NaOH and KOH with Although the removal efficiency with NaOH is sharply decreased as decreasing the reaction time, it with KOH is gradually decreased as decreasing the reaction time. Therefore, it is revealed that KOH has faster neutralization reaction rate and higher chemical activity than NaOH. Figure 6 shows the space velocity according to the reaction time. The difference of space velocity between NaOH and KOH cases is reduced with increasing the reaction time. On the other hands, the difference of space velocity by NaOH and KOH is reduced increasing the reaction time. The reason is that the difference of H 2 S removal efficiency by NaOH and KOH is decreased due to sufficient reaction time. The space velocities for NaOH and KOH were about and hr -1 at the reaction time of 0.06 and seconds, respectively. Therefore, KOH is more effective than NaOH for neutralization of H 2 S. Figure 3. Removal efficiency of H 2 S according to the reaction ratio variation. Figure 4. Space velocity calculation results according to the reaction ratio variation. 4

6 Figure 5. Removal efficiency of H 2 S according to the reaction time. Figure 6. Space velocity calculation results according to the reaction time. Since large amount of solid salts, un-reacted solution and water mists were generated by neutralization reaction of H 2 S with basic materials, the electrostatic precipitator was used to remove them. Figure 7 indicates the removal efficiency of dust according to the plasma input power which was varied from 1 to 180 W. Dust was mostly removed above 30 W. The removal efficiencies are fairly similar each other in figures 7 (a) and (b) for NaOH and KOH, respectively. Amount of exhausted dust was mg/m 3 at the input power of 180 W after electrostatic precipitation by corona discharge in both cases. It is very similar with the dust content in atmosphere of mg/m 3. Because the amount of exhausted dust without the electrostatic precipitation was over than 140 mg/m 3, the removal efficiencies of dust were over 99% when the input power exceeded 40 W. Therefore, large amount of H 2 S gas and dust can be removed simultaneously at room temperature and atmospheric pressure under continuous flow condition using the Wet-EP system. 4. Conclusion Figure 7. Removal efficiencies of dust according to the plasma input power with (a) NaOH and (b) KOH solutions. A large amount of H 2 S gas diluted in air was removed in the Wet-EP system by neutralization reaction and electrostatic precipitation under continuous flow condition. NaOH and KOH were used for neutralization reaction with H 2 S gas, and they were spontaneously reacted at room temperature and atmospheric pressure. The removal efficiency of H 2 S was 99% at the highest reaction ratio of The KOH reacts with H 2 S more effectively than NaOH, due to relatively low Gibbs free energy. For 5

7 high removal efficiency, optimal conditions of H 2 S removal reaction by NaOH and KOH were reaction ratio of 4.98 in both cases, reaction time of 0.06 and seconds, respectively. Under these conditions, the values of space velocity by NaOH and KOH were and hr -1. The input power of plasma was required about 40 W in order to remove dusts completely. In conclusion, H 2 S contained contaminant of 2 m 3 /min can be efficiently removed by using the low power of 40 W in Wet-EP system. Acknowledgments This work was supported by the Regional Innovation Center for Environmental Technology of Thermal Plasma (ETTP) at Inha University designated by MKE (2013). References [1] S.S. Shiffman, E.A. Sattely Miller, M.S. Suggs and B.G. Graham 1995 Brain Res. Bulletin [2] W. H. Cheng, M. S. Chou, W. S. Lee and B. J. Huang 2002 J. Env. Eng [3] Y. I. Matatov-Meytal and M. Sheintuch 1997 Ind. Eng. Chem. Res [4] Z. H. Huang, F. Kang, Y. P. Zheng, J. B. Yang and K. M. Liang 2002 Adsorp. Sci. & Tech [5] S. W. Baek, J. R. Kim, and S. K. Ihm 2004 Catal.Today [6] A. H. Wani, R. M. R. Branion, and A. K. Lau 1997 J. Env. Sci. Health A [7] J. Ruan, W. Li, Y. Shi, Y. Nie, X. Wang and T. Tan 2005 Chemosphere [8] I. Traus and H. Suhr 1992 Plasma Chemistry and Plasma Processing [9] Zhao Gui-Bing 2007 Chem. Eng. Sci [10] E. Krasheninnkov, V. D. Rusanov, S. V. Sanyuk and A. A. Fridman 1986 Zh. Tekh. Fiz [11] T. Nunnally, K. Gutsol, A. Rabinovich, A. Fridman, A. Starikovsky, A. Gutsol and R.W. Potter 2009 Inter. J. Hydro. Ener [12] S. John, J.C. Hamann, S.S. Muknahallipatna, S. Legowski, J.F. Ackerman and M.D. Argyle 2009 Chem. Eng. Sci