electrostatic precipitator design by use of simulation models

1. The design of electrostatic precipitators by use of physical models G. Bacchiega - IRS S.r.l. – www.irsweb.it R. Sala -I. Gallimberti - P. Tronville - F. Zatti

5. Data structure Gas Flow: 3D Fluid-Dynamic Gas Flow: 2D Fluid-Dynamic Sect. 1 Laplacian Field Electric Field time loop Back Corona Glow Corona Streamer Corona Breakdown Electric Field Sect. 2 Ion Migration Particle Charging Particle Migration Space Charge Distribution Sect. 3 Particle Collection Rapping Reentrainment Process Efficiency Sect. 4

6. Fluid-Dynamic simulation 3-D Fluid-Dynamic Fluid-dynamics conditions of gas flow: stationary conditions of 3-D gas flow in the precipitator 2-D Fluid-Dynamic Fluid-dynamics conditions of gas flow: 2-D gas flow in a single cell Data structure Gas Flow: 3D Fluid-Dynamic Gas Flow: 2D Fluid-Dynamic Laplacian Field Electric Field time loop Back Corona Glow Corona Streamer Corona Breakdown Electric Field Ion Migration Particle Charging Particle Migration Space Charge Distribution Particle Collection Rapping Reentrainment Process Efficiency Sect. 1 Sect. 2 Sect. 3 Sect. 4

8. Operating parameters - characteristics FLUE GAS OPERATING CONDITIONS Gas flow (on wet) Nm 3 /h 124000 Operating temperature °C 402 Operating Pressure kPa 98.7 O 2 Concentration % vol 11.25 Relative humidity % vol 8.7 INLET PARTICLE CHARACTERISTICS Particle concentration (dry at 8% O 2 ) mg/Nm 3 4707 Furnace particles ( average diameter 0.25 micron) % in mass 4.2 Reaction particles ( average diameter 6.0 micron) % in mass 95.8 DRAFT ESP CHARACTERISTICS N° of fields 3 N° of gas passages (d = 400 mm) 19 N° of plates per field (h = 13.35 m, l = 0.5 m) 8 N° of emitting electrodes per plate (RDE type) 1

9. 3-D mesh of the ESP

10. Calculated velocity contours (central section)

11. Smoothing velocity profile See white lines and dashes (perforated plates)

12. Fluid dynamic optimization Perforated plates with variable permeability

13. Electric field section Laplacian Field electrostatic conditions defined by geometry Electric Field Time dependent electrostatic conditions defined by charge in the space Data structure Gas Flow: 3D Fluid-Dynamic Gas Flow: 2D Fluid-Dynamic Laplacian Field Electric Field time loop Back Corona Glow Corona Streamer Corona Breakdown Electric Field Ion Migration Particle Charging Particle Migration Space Charge Distribution Particle Collection Rapping Reentrainment Process Efficiency Sect. 1 Sect. 2 Sect. 3 Sect. 4

14. Modeling the electrostatic field Defines characteristics of electric discharges Defines forces over the particles Poisson equations Calculation method Potential and field: iterative FDM algorithm (Finite Differences Method) with convergence verification Electrostatic field Orthogonal embedded grid Calculation domain

17. Electric field contour in a collection cell

18. Voltage-Current characteristic

19. Discharging characterization Glow corona Stationary corona discharge Back corona Micro-discharge in the dust layer at the plates Data structure Gas Flow: 3D Fluid-Dynamic Gas Flow: 2D Fluid-Dynamic Laplacian Field Electric Field time loop Back Corona Glow Corona Streamer Corona Breakdown Electric Field Ion Migration Particle Charging Particle Migration Space Charge Distribution Particle Collection Rapping Reentrainment Process Efficiency Sect. 1 Sect. 2 Sect. 3 Sect. 4

20. Model of Glow Corona Electrons emission by positive ions collisions Molecular ionization and attachment Ions drift by electric field force Ionisation region Transport region V= 0 V dc = V

21. Glow Corona: calculation procedure Electric field distribution Ions current injection Space charge distribution Time dependent solution of transport equation Ions transport

23. Charging section Particle charging Mechanism of particle charging Data structure Gas Flow: 3D Fluid-Dynamic Gas Flow: 2D Fluid-Dynamic Laplacian Field Electric Field time loop Back Corona Glow Corona Streamer Corona Breakdown Electric Field Ion Migration Particle Charging Particle Migration Space Charge Distribution Particle Collection Rapping Reentrainment Process Efficiency Sect. 1 Sect. 2 Sect. 3 Sect. 4

24. Model of particle charging By means of the field: The particle modifies locally the electric field Ions drift and attach to the particles The process ends when the electric field created by the particle is greater then the ambient field

25. By diffusion: Thermal agitation of ions produce collisions with the particles Model of particle charging

26. Particle migration section Ionic migration Ionic migration process Particle migration Particle migration process Space charge distribution Time dependent variation of ionic and particles distribution Data structure Gas Flow: 3D Fluid-Dynamic Gas Flow: 2D Fluid-Dynamic Laplacian Field Electric Field time loop Back Corona Glow Corona Streamer Corona Breakdown Electric Field Ion Migration Particle Charging Particle Migration Space Charge Distribution Particle Collection Rapping Reentrainment Process Efficiency Sect. 1 Sect. 2 Sect. 3 Sect. 4

27. Particles migration section Fluid transport: particles are dragged by the gas in the duct Velocity v p depends not only on forces, but also on inertia Electric transport: charged particles are drifted by electric field to the plates Global instantaneous velocity

28. Rend.tot. 98.95%

29. Particles collection section Rapping-Reentrainment Conditions of particles collection: stationary simulation of dust over the plates Data structure Gas Flow: 3D Fluid-Dynamic Gas Flow: 2D Fluid-Dynamic Laplacian Field Electric Field time loop Back Corona Glow Corona Streamer Corona Breakdown Electric Field Ion Migration Particle Charging Particle Migration Space Charge Distribution Particle Collection Rapping Reentrainment Process Efficiency Sect. 1 Sect. 2 Sect. 3 Sect. 4

31. Collection and re-entrainment Mass balance of re-entrained, collected and fallen particles M in M out-ree M out-hop

32. Inlet particle size distribution Percentage by mass

33. Particle size distribution (inlet and exit)

34. Mechanical layout