TranThiMinhPhuong TV pdf I Study of New Electrostatic Precipitators Student Thi Minh Phuong Tran Advisor Chuen Jinn Tsai Institute of Environmental Engineering National Chiao Tung University ABSTRACT[.]
Study of New Electrostatic Precipitators StudentǺThi-Minh-Phuong Tran AdvisorǺChuen-Jinn Tsai Institute of Environmental Engineering National Chiao Tung University ABSTRACT Many previous experimental and numerical modeling studies have been conducted to improve the performance of the electrostatic precipitators (EPs) which are used widely in industries to control particulate matter emissions In this study, two new types of EPs, wireon-plate electrostatic precipitator (WOP-EP) and multipoint-to-plane electrostatic precipitator (MPP-EP) were investigated for the control fine and nanosized particles with the advantages of low pressure drop and high particle collection efficiency In conventional EPs, the discharge wires are placed in between two grounded collection plates In the present new WOP-EP, discharge wires are placed directly on the surface of a dielectric plate to replace one of the collection plates The new WOP-EP was designed and tested at the aerosol flow rate of 15 and 30 L/min for reducing particle contamination on discharge wires, prolonging the operation time and facilitating the cleaning of the collection plate In addition, two configurations of the MPP-EPs were also tested at the aerosol flow rate of 30 and 40 L/min to remove nanoparticles and sub-micron particles Furthermore, in order to develop better understanding of the experimental results, the numerical model for predicting the voltage-current (V-I) characteristic of EPs was developed Eulerian and Lagrangian numerical methods were adopted as well to predict the collection efficiency of particle with diameter dp ≤ 100nm and dp> 100nm, respectively I Test results show that when the WOP-EP was initially clean at the applied voltage of +18kV, the total collection efficiency ranged from 90.9-99.7 % and 98.8-99.9% for particle electrical mobility diameter of 16.5 to 1870 nm at the aerosol flow rate of 30 and 15 L/min (residence time of 0.36 s and 0.72s), respectively Numerical results for the particle collection efficiency show good agreement with experimental results for particles with the diameter of 70-400nm, and over-predict the collection efficiency for particles below 70nm and above 400nm The disagreement is maybe due to the partial charging effect, the influence of the dielectric plates, and very low concentration of large particles as well as the ion quenching phenomenon, respectively Whereas in MPP-EPs, the collection efficiency ranged from 96.2–99.4% and 95.5– 97.6% at applied voltage of +16kV and the flow rate of 30 L/min for MPP-EP2 and MPPEP1, respectively Simulated results for particle collection efficiency are in reasonable agreement with the experimental data for the particle diameter of 19.5-100nm, and underestimation of the collection efficiency occurs for particles above 100nm which needs to be improved in future studies Present WOP-EP and MPP-EPs could be used as efficient particle removal devices and the present model could facilitate the design and scale-up of these EPs to control fine and nanosized particles Keywords㸸wire-on-plate EP, multipoint-to-plane EP, electrostatic precipitator, air pollution control device II ACKNOWLEDGEMENT I first would like to express my gratitude to my advisor Prof Chuen-Jinn Tsai for his consistent help, support and many useful comments, remarks through the learning process of this master thesis Their guidance helped me in all the time of research and writing of this thesis I could not have imagined having better advisor for my Master study Secondly, I would like to thank all my labmates, Ms Students, PhD students and Postdocs in Nanoparticle and Air quality laboratory for their invaluable comments and big help during the time when I am studying and working over here, institute of environmental engineering, NCTU I would also like to thank all professors in IEV, NCTU for their valuable knowledge that I gained during years My thanks to SCI, OIA, staffs from library and IEV officers for helping me during these years Last but not least, I take this opportunity to thank my family for their unconditional love and support they gave me during entire process I will be grateful forever for your love III TABLE OF CONTENTS ACKNOWLEDGEMENT III TABLE OF CONTENTS IV LIST OF FIGURES VI LIST OF TABLE IX LIST OF SYMBOLS X INTRODUCTION 1.1 Wire-on-plate EP 1.2 Multipoint-to-plane EP LITERATURE REVIEW 2.1 2.1.1 V-I characteristic 2.1.2 Experimental studies on WIP-EP for particle control 2.2 Multipoint-to-plane EP 2.2.1 V-I characteristic 2.2.2 Experimental studies on MPP-EP for particle control 10 2.3 Wire-in-plate EP Numerical model for predicting collection efficiency of EPs 14 METHODS 16 3.1 Experimental method 16 3.1.1 EP configurations 16 3.1.2 Particle collection efficiency experiment 17 3.2 Numerical method 19 3.2.1 Calculation domain 19 3.2.2 Electric Field and Ion Concentration Distribution 20 3.2.3 Charged Particles Concentration Distribution-Particle Collection Efficiency 24 IV RESULTS AND DISCUSSION 28 4.1 Wire-on-plate EP 28 4.1.1 V-I characteristics 28 4.1.2 Particle collection efficiency 29 4.2 Multipoint-to-plate EPs 33 4.2.1 V-I characteristics 33 4.2.2 Particle collection efficiency 36 CONCLUSIONS 40 RECOMMENDATIONS FOR FUTURE STUDY 41 REFERENCES 42 V LIST OF FIGURES Fig 1.1 Wire-plate EP configuration: (a) Conventional wire-in-plate EP (b) Present idea wire-on-plate EP Fig 1.2 The schematic diagram of a MPP-EP Fig 2.1 Electric potential distribution of wet EP (Lin et al,.2010b) Fig 2.2 Ion concentration distribution of wet EP (Lin et al,.2010b) Fig 2.3 Voltage-current relationships of the positive corona for two difference wires (Goo and Lee ,1997) Fig 2.4 V-I characteristic curves of EP (Huang and Chen, 2003) Fig 2.5 Particle collection efficiency as a function of discharge voltage and flow velocity (Marek et al., 2005) Fig 2.6 Aerosol penetration through EP as a function of aerosol size under different applied voltages (Huang and Chen, 2002) Fig 2.7 Comparison of aerosol penetration through difference wires versus particle size for a given corona current (Huang and Chen, 2002) Fig 2.8 The electric field distribution between electrodes of a single PP-EP (Arrows represent electric filed lines) (Balek and Cervenka, 2010) Fig 2.9 The electric field distribution along y-direction of a single PPEP with d = cm, a = 0.045 mm (Abdel-Salam et al., 2007) Fig 2.10 V-I characteristics of MPP-EP (Le et al., 2013) 10 Fig 2.11 The MPP-EP with needle-type discharge electrode investigated by Kim et al (2000) and Mermelstein et al (2002) 10 Fig 2.12 The MPP-EP with saw-type discharge electrodes investigated by Huang and Chen, 2001 11 Fig 2.13 Applied voltages versus collection efficiencies (Huang and Chen, 2001) 11 VI Fig 2.14 Flow rates versus collection efficiencies (Huang and Chen., 2001) 11 Fig 2.15 The wet electrocyclone with saw-type discharge electrodes are used investigated by Lin et al., 2013 12 Fig 2.16 Typical V-I characteristics and collection efficiencies of MPP-EP, wire-to-plate EP and flate-to-plate EP (Lin et al., 2012b) 12 Fig 2.17 Typical V-I characteristics and collection efficiencies for various discharge electrode designs (a) Spiked band electrode a=60mm, (b) pipe and double-spike electrode a=100mm (RDE 1), (c) pipe and double-spike electrode a=180mm (RDE 2)(Jedrusik and Swierczok, 2004) 13 Fig 3.1 Schematic diagram of the present WOP-EP 16 Fig 3.2 The schematic diagram of the MPP-EP 1,2 17 Fig 3.3 Schematic diagram of the experimental setup 17 Fig 3.4 Calculation domain and grid (a) WOP-EP, (b) MPP-EP1 20 Fig 3.5 Scheme of needle tip 22 Fig 4.1 V-I characterstics derived from theoretical, numerical and experimental data 28 Fig 4.2 (a) Electric potential distribution and (b) Ion concentration distribution 29 Fig 4.3 Experimental collection efficiency at face velocity of 0.50m/s 30 Fig 4.4 Experimental collection efficiency at face velocity of 0.25m/s 30 Fig 4.5 Comparison of particle collection efficiency between numerical and test results 33 Fig 4.6 The comparison of V-I curve with positive corona between experimental results and prediction 34 Fig 4.7 (a) Electric potential distribution, (b) Ion concentration distribution and (c) Detail of ion concentration distribution near ground-plate, MPP-EP1, 16kV 35 Fig 4.8 (a) Electric potential distribution, (b) Ion concentration distribution and (c) Detail of ion concentration distribution near ground-plate, MPP-EP2, 16kV 35 VII Fig 4.9 3D- Electric potential distribution (a) and Ion concentration distribution (b), 16kV, MPP-EP1 36 Fig 4.10 Collection efficiency MPP-EP at the flow rates of 30 L/ and 40 L/min 37 Fig 4.11 Collection efficiency MPP-EP at the flow rates of 30 L/ and 40 L/min 38 Fig.4.12 Comparison of particle collection efficiency between numerical and experimental results at the flow rates of 30 L/ and 40 L/min 39 VIII LIST OF TABLE Table 3.1 Characteristics of the test particles 18 IX LIST OF SYMBOLS a Atip d I J(0) the radius needle tip the tip surface area of the needle the point-to-plane spacing the ion current of a electrode the current density directly under the electrode m m2 m A A/m2 J(θ) l P P0 R S T T0 V Va (V0) the current density on the ground plate the thickness of ionization layer the air pressure the standard pressure the maximum radius on the plane to which corona current flows the point-to-point spacing the air temperature the standard temperature the electric potential the applied voltage on the electrode A/m2 µm bar bar m m K K volt volt αi the empirical coefficient γ1 and γ2 regression coefficients εo θ the permittivity of air semi-apex angle of corona discharge and its shape A.sec/V.m ρi,0 the ion density on the electrode surface C/m3 A total collection area (m2) ap radius of particles (m) Cc Cunningham slip correction factor CD empirical drag coefficient Cin particle inlet concentration (#/ cm3) cin mean thermal speed of the ions (m/s) dp particle diameter (nm) Di diffusion coefficient of ions (m2/s) DB Brownian diffusion coefficient of particles E electric field strength (m2/s) (V/m) Ec corona initiating electric field (V/m) Eave average electric field strength (V/m) Ex electric field strength in x direction (V/m) Ey e f electric field strength in y direction elementary electrical charge wire roughness factor (V/m) X (A/m2) Jp Kn kc average current density at the collection plate Knudsen number constant kb Boltzmann constant J/K lw wire length Mi molecular weights of ions Mair molecular weights of air (kg/mol) Na Avogadro number 1/mol (kg/mol) Ni ion number concentration (#/m3) Np,q concentration of particles carrying q elementary charges (#/m3) Np,0,total(y) (#/m3) Q q qsat r inlet uncharged particle number concentration outlet number concentration of particles carrying q elementary charges air flow rate number of charges carried by particles saturation charge distance between particles and ions center apsoidal distance Rep particle Reynolds number reff equivalent cylinder radius (m) rc wire radius (m) Sc generation of particles with q-1 charges sx half wire to wire spacing (m) sy u up v vp wire to plate spacing air velocity in x direction particle velocity in x direction air velocity in y direction particle velocity in y direction (m) (m/s) (m/s) (m/s) (m/s) Vc corona onset voltage (V) VTE particle migration velocity (m/s) VTE,k average migration velocity of particles (m) Zi ion mobility (m2/s-V) ZP particle electrical mobility (m2/s-V) αq combination coefficient of ions for particles carrying q elementary charges (m3/s) ηtotal particle collection efficiency of the EP % λion δ mean free path of ions relative density of air (nm) Np,q,outlet(y) (m) XI (#/m3) (m/s) (C) (C) (m) (m) δr radius of the limiting sphere (m) ρair air density (kg/m3) ρi space charge density (C/m3) κd dielectric constant of particle ε0 ξ permittivity of free air striking probability electrostatic potential between the particle and the ion viscosity outlet particle number concentration of the EP with supplying high voltages outlet particle number concentration of the EP without supplying high voltages electrostatic precipitation collection efficiency of the EP collection efficiency by particle diffusion and impaction mechanism of the EP ᢥ μair Cout,ON Cout,OFF ηelec ηdiff+impa XII (F/m) (kg/m-s) #/ cm3 #/ cm3 % %