Study on the Effects of Pellets and Carrier Gas on Characteristics of Silent Discharge Process

Transcription

1 Study on the Effects of Pellets and Carrier Gas on Characteristics of Silent Discharge Process Yong-Hwan Lee, Won-Sok Jung, Jae-Woo Chung, Yu-ri Choi, Moo-Hyun Cho, and Won Namkung School of Environmental Science & Engineering and Pohang Accelerator Laboratory Pohang University of Science and Technology 1

2 Table of Contents 1. Introduction 2. Principle of Silent Discharge Process 3. Experimental Setup 4. Experimental Results and Discussion 5. Conclusion 2

3 Introduction(I) Health and Environmental Impacts of NOx Ground level ozone (smog) The Primary Sources of NOx Industrial/ Commercial/ Residential 19 % Utilities 27 % Acid rain Water quality deterioration Particles Global warming All Other Sources 5 % Toxic chemicals Visibility impairment Motor Vehicles 49 % 3

4 Introduction(II) Conventional NOx Emissions Control Technologies Lowering combustion temperatures Careful air/fuel control during combustion Reducing the nitrogen content of fuels Injection of water or steam Advanced NOx Emission Control Technologies NOx Catalysts Selective Catalytic Reduction Plasma Technology Combined Systems (Plasma + Catalyst) 4

5 Combined Systems for Reducing NOx Plasma process Catalytic process NOx N 2, O 2 NO NO 2 NO 2 N 2, O 2 Discharge electrode Copper tape NO x Pyrex Glass or alumina bead (N 2, O 2 ) 5

6 Principle of Silent Discharge Process Microdischarge formation Electron multiplication Space charge formation Duration 1-10 ns Ionization Filament radius 0.1 mm Peak Current Density Total charge 0.1 A A/cm pc Dissociation and excitation Ionic & excited species Electron density Electron energy Gas temperature cm ev o C Chemical reactions 6

7 The Silent Discharge Reactor & Experimental Apparatuses Gas outlet Discharge electrode Copper film tape Pyrex tube Teflon cap Gas inlet 7

8 Experimental Setup of Silent Discharge Process X 1000 probe X 100 probe 8

9 Typical Charge-Voltage Plot in Air and Argon Voltage (kv) Argon Air -21 Charge (uc) 9

10 Typical NO and NO 2 Conversion Trend in Silent Discharge Process Concentration (ppm) Input gas: Air (O 2, N 2 ) + NO e + O 2 e + O( 3 P) + O( 3 P, 1 D) (1) e + N 2 e + N( 4 S) + N( 4 S, 2 D) (2) Dissociation energy: O 2 < N 2 At a low electron kinetic energy, O + NO + M NO 2 + M (3) O + O 2 + M O 3 + M & O 3 + NO NO 2 + O 2 (4) Energy density (J/L) NO NO2 At a high electron kinetic energy, N + O 2 NO + O (5) 10

11 NO 2 Production Trend with Air Flow (Blank Test) 70 Blank test - 35C 60 Concentration (ppm) LPM 10 LPM 15 LPM 20LPM Energy density (J/L) 11

12 Effects of Carrier Gas on NO Conversion 300 Concentration (ppm) Air-NO Air-NO2 Ar-NO Ar-NO Energy density (J/L) Experimental condition Glass bead 2 mm(dia.), Flow rate: 10 l/min 12

13 Effects of Initial Concentration and Bead Type on NO Conversion Rate NO conversion rate (%) Energy density (J/L) 200 ppm-glass 200 ppm-alumina 300 ppm-glass 300 ppm-alumina 400 ppm-glass 400 ppm-alumina Experimental condition Diameter: 2 mm, Flow rate: 6.7 l/min 13

14 Effects of Bead Size on NO Conversion Rate 80 NO conversion rate (%) glass 4mm glass 3mm glass 2mm alumina 2mm alumina 3mm Energy density (J/L) Experimental condition Initial concentration: 300 ppm, Flow rate: 5.4 l/min 14

15 Effects of Flow Rate on NO Conversion NO conversion rate (%) Energy density (J/L) Conversion rate (%) Energy density (J/L) 5LPM(1.2sec) 8.6LPM(0.7sec) 10LPM(0.6sec) 12LPM(0.5sec) 20LPM(0.3sec) 10lpm 15lpm 25lpm 22.3lpm 20lpm 13lpm Experimental condition Initial concentration: 400 ppm, Glass bead (4mm) Discharge electrode: 35 mm, Coarse Experimental condition Initial concentration: 400 ppm, without beads Discharge electrode: 35 mm, Coarse 15

16 Conclusions 1. The NO conversion rate increased with decreasing initial concentration. 2. Dielectric materials affected the conversion efficiency of NO. The NO conversion rate in the alumina bead filled reactor was lower than that in the glass bead filled reactor. 3. There was an optimum bead size for obtaining the maximum NO conversion. 4. The optimum flow rate existed for the highest NO conversion in the various operating conditions. The optimum flow rate was approximately 10 l/min in the reactor filled with 4 mm glass beads in diameter. 5. In case of using the reactor without beads, the highest NO conversion rate was obtained at the flow rate of 15 l/min. 16