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The hamper is built from eco-friendly bamboo and includes two slide out laundry bins with handles, and a workable table top for folding laundry or storing items.

1. 113/08/11 1
Electrostatic Precipitator (ESP)
•Electrical migration
•Electrical mobility
•Corona discharge
•ESP theory
•Charging mechanisms
•Ash resistivity
•Flue gas conditioning
•Power consumption
Positive Negative
Republican Democrat
Love Hate
Ying Yang
Man Woman
Hell Heaven
Cation Anion
War
Peace
Attraction Repel

6. 113/08/11 6
Single Particle Motion
Want to be great athletes? Study aerosol science & engineering
because you surely need to know how to control particle
movement in the air!

9. 113/08/11 9
L
HV
V
x
TS

Q: Can it be vertical?
Q: Can we make the acceleration > g?
Horizontal Elutriator
(settling chamber, spectrometer)

10. 113/08/11 10
Positive Corona Negative Corona
+
-
+
-
+
+ -
+
+
+
-
-
+
-
+
-
+
-
-
-
+
+
Corona Discharge
Step 1
Step 2
Step 3
Step 4
Collection Plate Collection Plate
Electron
Molecule
Particle
Electrode
Electrode
Q: How can we generate charges?
Ozone generation - http://www.mtcnet.net/~jdhogg/ozone/ozonation.html

12. Electrostatic precipitator
modeling and simulation

13. HOW ESP WORKS
Generally, the processes of electrostatic
precipitator are known as three main stages:
particle charging, transport and collection.
Main process of ESP

14. To characterize all these stages
determines to take a great number of basic
phenomena into account from a physical
point of view when they occurred.
• Introduction
These are stages interacted that originated
from the complexity of the processes of
precipitator.

15. Schematic of wire-plate ESP
Fig.1 Schematic of wire-plate electrostatic
precipitator
• Introduction

16. Mechanism of ESP
Fig. 2 Mechanism of electrostatic precipitator
• Introduction

17. 2.2.2 PROCESS OF Particle
charging
Particle charging is the first and foremost
beginning in processes.
• Introduction
As the voltage applied on precipitator reach
threshold value, the space inside divided
into ionization region and drift region.

18. The electric field magnitude around the
negative electrode is so strong that the
electrons escape from molecule.
Under the influence of electric field, the
positive ions move towards the corona, while
the negative ions and electrons towards the
collecting plates.
• Introduction

19. 2.2.3 Particle transport
In the moving way, under the influence of
electric field, negative ions cohere and charge
the particles, make the particles be forced
towards collecting-plate as well as Fig.2
shows.
• Introduction

20. 2.2.4 Particle collection
As soon as the particles reach the plate,
they will be neutralized and packed by the
succeeded ones subsequently. The
continuous process happens, as a result,
particles are collected on the collecting
plate.
• Introduction

21. • Research and design in ESP
modeling
The numerical model describes in time
and space the relevant processes that are
involved in transport, charging, migration and
collection of fly ash. To represent the
complete processes, the model is therefore
structured into several modules.

22. The model here is organized into
the following three sections:
1. electric field and discharge processes
2. particle charging
3. particle collection

23. 3.1 electric field and discharge
processes
The particle collection in electrostatic
precipitators is largely dominated by the
distribution of the electric field in the inter-
electrode space.

24. In the absence of particles, neglecting the
transport gas velocity and by assuming that
the magnetic field due to the corona current
is negligibly small.
Electronical conditions are described by
next three equations :

25. 2
0
e
V


 
2
0
( )
e e
V    
VE

(1)
(2)
(3)
Here V is the electric potential, is the space-
charge density, is the permittivity of free
space and E is the electric field.
e

0


26. Here, we adopt equations (4) (5) (6) to
describe the electric field distribution with the
initial and boundary conditions.











m xxy
xxy
m xxy
xxy
SaSmS
SaSmS
SxSmSy
SxSmSy
VyxV
}
)2/cos()/cosh(
)2/cos()/cosh(
ln{
}
)2/cos(]2/)2(cosh[
)2/cos(]2/)2(cosh[
ln{
),(
0





27. V( x, y) means the electric potential of
the position (x, y), V
0 is the initial potential
on the wire, Sx is distance between
collecting plate and wire, Sy is half length of
the two nearest wires ,a is the radius of
particle, when x, y means the coordinates
direction, shown as Fig.3.

28. Fig. 3 Sketch of precipitator geometry and
computed grid

29. )
22
()(
31
0
24
00
0000
0
2
0
y
y
x
x
d
E
d
E
yy
V
xx
V 
















 (5)
)(2
/)()(
22
00
22
31
2
24
2
0
yx
yxxy
dd
ddVVdVVd
V




(6)
and V
0 mean the charge density and
electric potential at the position as Fig.3
shown.


30. 3.2 particle charging
The field charging refers to the local
distorsion caused near the particle surface by
the difference in dielectric constants.
This process continues until the particle goes
up to the saturation charge, which produces
an electric field on particle surface equal and
opposite to the external field.

31. Equation (7) is chosen to describe the
model of particle charging :
2
0 0
12
2
r
s
r
q R E





(7)
Where is the relative dielectric constant
and E
0 is the external field, q
s and R are the
particle charge and radius.
r


32. 3.3 particle collection
This module simulates in detail the boundary
layer near the collecting plates and the
interchange that take place.
Here, we choose equation (8) to describe
particle collection .

33. ))(exp(
0
x
v
yw
f
a
CC 

 (8)
C is the particle density, C
0
is the entry density of
particle, a is the unit collecting area in the flow
way, f is area of ESP cross section, when w
means particle velocity towards plate and v is the
velocity moving to outlet.

34. 4 Simulation results and analysis
According the above analysis of the
mechanism and modeling of ESP, we design
a simple ESP simulation platform which is
based on Scilab .

35. Fig.4 Simulation Platform

36. Fig.5 Input Interface

37. Fig.6 Distribution of electric field Ex
Simulation of electric field

38. we can find that around the wires, Ex get a
largest value, when at the connecting way
of two wires, Ex is no more than zero. The
cause of this distribution is the potential, at
the connecting way of wires, nearly zero.
Ex is decreased regularly from the wire at
the coordinate line x, but larger when close
to the collecting plate.

39. Fig.7 Distribution of electric field Ey
Simulation of electric field

40. Fig.8 Particle density distribution in ESP
Simulation of particles density
distribution

41. From Fig.8, we see the particles density
distribution obviously. The density reaches the
largest value at the entry of the ESP under the
influence of electric wind. The value of density
gets smallest near the wire at the direction to
collecting plate.

42. Simulation of deposit density
Fig.9 Distribution of deposit density

43. Fig.9 shows us the deposit density, along the
collecting plate deposit density is decreased
definitely, since as time go on, the particle is
collected by the plate continuously. So at the
later part, the deposit density is lower, and
reasonable.

44. • CONCLUSION
we construct a numerical model of
electrostatic precipitator and design base on
Scilab. The simulation results of these
processes are according with laboratory
experimental tests to obtain physical
information and useful validations.

45. 113/08/11 45
Electrical Migration
•Coulomb’s law
–Statcoulomb (stC): the charge that causes a repulsive force of 1 dyne when 2 equal charges are separated by 1 cm (3.3310
-10
C)
–Unit charge: 4.8 10
-10
stC (1.610
-19
C)
2
21
r
qq
KF
EE E
F
q
E
 (q=ne)
Electric Field

46. 113/08/11 46
Millikan Experiment
(Robert Millikan,
US, 1868-1953;
Nobel Prize
Laureate, 1923)
Hinds, Aerosol Technology, 1999
http://nobelprize.org/nobel_prizes/physics/laureates/1923/millikan-bio.html

47. 113/08/11 47
Electrical Mobility
•Terminal velocity in an electrical field
(electrical migration velocity/drift velocity)
c
TEp
C
Vd
qE
3

 qEB
d
qEC
wV
p
c
TE 
3

qB
d
qC
E
V
Z
p
cTE

3
(force balance)
DEFF
(for Re < 1)
Q: What is the physical meaning of electrical mobility?
Q: When does a particle have a higher mobility?
May the force be with the particles!
Q: Difference between cyclone
and ESP in terms of forces
acting on the system?
What’s the effect?

48. 113/08/11 48
1 2 3
1 2 3
(20) (12) (8)
Turbulent Flow with Lateral Mixing Model
Electrostatic Precipitator

49. 113/08/11 49
•Deutsch-Anderson Equation
R
dtV
R
dtRV
N
dN
TETE
22
2



)
2
exp(
)(
0
R
tV
N
tN
TE










Q
AV
P
cTE
exp11
A
c/Q: Specific Collection Area (SCA)
• Turbulent flow: uniformly mixing
• Perfect Collection
•The fraction of the particles
removed in unit time = the ratio of
the area traveled by drift velocity in
unit time to the total cross-section
Q: How to increase the efficiency?

57. 113/08/11 57
Q: An ESP that treats 10,000 m
3
/min of air is
expected to be 98% efficient. The effective
drift velocity of the particles is 6.0 m/min. (a)
What is the total collection area? (b) Assuming
the plates are 6 m high and 3 m long, what is
the number of plates required?
6 m
3 m
Internal Configuration: self-review

58. 113/08/11 58
Charging Mechanism: Diffusion Charging
•Random collisions between
ions and particles









kT
tNecd
e
kTd
n
iipp
2

1ln
2
2
2

Q: Does q depend on time?
Does q depend on d
p?
The total number of charges on a particle
(c
i ~ 2.410
4
cm/s)
neq
The total charges on a particle
Use esu, not SI units.

59. 113/08/11 59
Charging Mechanism: Field Charging
•Bombardment of ions in the presence of a strong field

eZ 1
eZ

4

2
3
i
i
2

























tN
tN
e
Ed
n
i
ip




Total number of charges by field charging
Q: Is the charging rate dependent on
particle size? On field strength? On time?
On material?
Aerosol Technology, Hinds, W. C., John Wiley & Sons, 1999.
















e
Ed
n
p
s
4

2
3
2


Saturation charge (Z
i ~ 450 cm
2
/stV•s)

60. 113/08/11 60
Comparison of Diffusion & Field Charging
Q: Does collection efficiency
increase as particle size increase
(because of a higher number of
charges)?
dp (um) n
diff n
field n
total Z
diff Z
FieldZ (stC•s/g)
0.01 0.10 0.02 0.12 0.66 0.10 0.76
0.02 0.30 0.06 0.36 0.49 0.11 0.60
0.05 1.1 0.40 1.50 0.31 0.12 0.43
0.1 2.8 1.6 4.38 0.23 0.13 0.36
0.2 7 6.5 13.2 0.18 0.17 0.35
0.5 21 40 61.2 0.15 0.30 0.45
1 48 161 209 0.16 0.52 0.68
2 108 646 754 0.16 0.98 1.14
5 311 4035 4346 0.18 2.34 2.52
10 683 16140 16824 0.20 4.61 4.80
20 1490 64562 66052 0.21 9.16 9.37
50 4134 403510 407644 0.23 22.78 23.0
Nit = 10
7
s/cm
3
= 5.1
E = 5 KV/cm
T = 298 K

61. 113/08/11 61
Typical fly ash
size distribution
Q: If the ESP is used to collect the
fly ash, how will the particle size
distribution at ESP outlet look like?

62. 113/08/11 62
Resistivity/Conductivity
•Impact of particles’ resistivity on ESP’s performance:
•Factors: temperature, composition
•Flue gas conditioning
10
9
- 10
10
ohm-cm is desired
Q: How does resistivity affect an ESP’s performance?

63. 113/08/11 63
Effects of sulfur content and temperature on resistivity
Q: Is S in coal good or bad?

64. 113/08/11 64
Water spray for cement kiln dust
Flue Gas Conditioning

65. 113/08/11 65
Effective drift velocity as a function of resistivity by measurement
Use the same Deutsch-Anderson Equation with new w
e
.
Q: Estimate the total collection area required for a 95% efficient fly-ash ESP
that treats 8000 m
3
/min. The ash resistivity is 1.6×10
10
ohm-cm.

66. 113/08/11 66
Good for moderate
collection efficiency
(90% ~ 95%)

67. 113/08/11 67
High Efficiency ESP (>95%)
Matts-Ohnfeldt Equation

















k
e
C
w
Q
A
exp1
Use k = 1 for fly ash
k = 0.5 or 0.6 for
industrial category
Rule of Thumb
• Below 95%, use Deutsch-Anderson Equation
• Above 99%, use Matts-Ohnfeldt Equation
• Between them, use an average
Q: In designing a high
efficiency ESP, a smaller
drift velocity is to be used.
Why?

68. 113/08/11 68
Power Consumption
avgCC VIP
C
C
e
A
kP
w
Power density ~ 1-2 W/ft
2









Q
kP
C
exp1
•Corona power
•Drift velocity
•Efficiency vs. Corona Power
k = 0.55 for P
c
/Q in W/cfs up to 98.5%

69. 113/08/11 69
Quick Reflection