1. Particle Control Technologies
Lecture notes adapted from
Prof. Dr. Benoit Cushman-Roisin
Thayer School of Engineering at Dartmouth

2. Design Criteria
Design of a system which remove solid or liquid particulate matter from a gaseous medium
Chacacteristics of gaseous medium and particulate matter to consider in the design:
Size T,P,Q,
Chem. Composition Chem. Composition
Resistance Pressure Drop PM
Control
Device

3. Collection Efficiency
Considering the wide range of size of particulates, efficiency will be different for each size.
The overall efficiency (h) can be calculated on a basis of total number (or mass) of particles
Generally regulations are written based on mass, and efficiencies are calculated on mass basis.

4. Collection Efficiency
Efficiencies calculated on mass basis:
h: overall collection efficiency (fraction)
Mi: total mass input rate (g/s or equivalent)
Me: total mass emission rate (g/s or equivalent)
Li: particulate loading in the inlet gas to the device (g/m3)
Le:particulate loading in the exit gas stream, (g/m3)

5. Collection Efficiency
When the particulate size distribution is known, and the efficiency of the device is known as a function of particle size, the overall collection efficiency can be calculate:
where
hj: collection efficiency for the jth size
mj: mass percent of particles in the jth size

6. Example 3.1 from the book

7. PM Control Devices Gravity Settler Cyclones ESP Filters and Baghouses
Wet Scrubbers

8. Settling Chamber
Efficient for particles with diameter of mm (depending on its density)
Velocity through chamber < m/s (to prevent reentrainment) V H L

9. Settling Chamber Settling time < transit time through chamberv H L
Settling time < transit time through chamber
t = H/vt = L/v 
Settling chambers are cheap to build and operate but not preferred due to their large space requirement

10. Settling Chamber Dp (um) Vt (m/s) Required Area 0.1 8.6 (10)-7 3 km2
Assuming unit density sphere at STP, vt and chamber Lw are tabulated below: Assumed flow rate Q = 150 m3/min
Dp (um)
Vt (m/s)
Required Area
0.1
8.6 (10)-7
3 km2
0.5
1.0 (10)-5
0.25 km2
1.0
3.5 (10)-5
71000 m2 5
7.8 (10)-4
3200 m2 10
3.1 (10)-3
810 m2

11. Settling Chamber Baffled Settling Chamber
Large particles can not make sudden direction change and settle into dead space of chamber
Baffle chambers are used as precleaners

12. Cyclones :

13. Cyclones :

14. Cyclone Geometry

15. Cyclone Geometry

16. Cyclone Theory

17. Cyclone Theory

18. Cyclone Theory

19. Cyclone Theory

20. Collection Efficiency

21. Collection Efficiency
(i) increase Vt (expensive, since DP a Vt2, as we will see in the next slides

22. Collection Efficiency

23. Collection Efficiency

24. Pressure Drop
K: a constant depends on cyclone configuration and operating conditions. Theoretically K can vary considerably but for air pollution work with standard tangential-entry cyclones values of K are in the range of 12 to 18
Cyclone pressure drops range from about 0.5 to 10 velocity heads (250 to 4000 Pa)

25. Cyclone Analysis

26. Example

27. Example Conventional Type (No:3) N=(1/H) (Lb+Lc/2) = (1/0.5)(2+2/2)=6
Vi=Q/WH =150 /(0.25*0.5) =1200 m/min 20
Vi=20 m/s

28. Example
Calculate efficiency for each size range witch dpc = 5.79 um:

29. Example 4.5

30. Example 4.5

31. Example 4.5

32. ESP

33. ESP

35. ESP Geometry

36. ESP Theory

37. Corona Power vrs Efficiency

38. ESP Theory

39. ESP THEORY

40. ESP Theory

41. ESP Theory

42. ESP Theory

43. ESP Theory

44. ESP Theory

45. ESP Theory

46. ESP Theory

47. ESP Theory

48. ESP Theory

49. Efficiency

50. Efficiency

51. Effect of Resistivity

52. Resistivity
Resistivity (P) is resistance to electrical conduction and can vary widely
P of a material is determined experimentally by establishing a current flow through a slab (of known geometry) of the material
P = (RA/L)=(V/i)(A/L) [ohm-cm]
R:resistance, ohm
A: area normal to the current flow, cm2
L:path length in the direction of current flow, cm,
V: voltage, i: current, A

53. Resistivity

54. Resistivity

55. Sparking

56. Internal Configuration
Internal configuration design is more art than science
The even distribution of gas flow through the ducts is very important to the proper operation of an ESP
The number of ducts (Nd) is equal to one less than the number of plates (n-1)
Nd = Q/uDH (eq 5.15)
u: linear gas velocity (m/min)
D Channel width (plate separation), m
H: plate height, m

57. Internal Configuration
At the start of the design, use 5.15 to estimate Nd by assuming a value for H and choosing representative values of u and D

58. Typical Values for the Fly-Ash ESP
Parameter
Range of Values
Drift velocity
1-10 m/min
Channel (Duct) Width, D
15-40 cm
Specific Collection Area Plate area/Gas Flow
m2/(m3/min)
Gas velocity u
m/s
Aspect Ratio (R)
Duct Length/Plate Height
Corona Power Ratio Pc/Q
W/(m3/min)
Corona Current Ratio (Ic/A)
mA/m2
Plate area per electrical set As m2
Number of electrical sections
2-6
Table 5.1

59. Internal Configuration
The overall length of the precipitator (Lo)
Lo=NsLp + (Ns-1)Ls + Len +Lex
Lp:: length of plate
Ls: spacing between electrical sections ( m)
Len: entrance section in length (several meters)
Lex:exit section in length (several meters)
Ns: number of mechanical fields
Ns ranges between 2 and 6.
Ns=RH/Lp R is the aspect ratio

60. Internal Configuration
When the numbers of ducts and sections have been specified, the actual collection area (Aa) can be calculated as:
Aa=2HLpNsNd
During the design process several plate sizes and numbers of ducts are tried until one combination is found such that Aa is equal to the required collection area.

61. Collection Efficiency vrs Particle Diameter

62. An Example

63. Example

64. Example

65. POWER REQUIREMENT

66. POWER REQUIREMENT
k: an adjustable constant in the range of for we in ft/sec and Pc/A in W/ft2

68. Problem 5.10
Provide a reasonable design for a 99.4% efficient ESP treating 30,000 m3/min of gas. The dust has a resistivity of 7.1 (10)10 ohm-cm. Specify the total plate area, channel width, number and size of plates, number of electrical sections (total and in the direction of flow), and total corona power to be supplied, and estimate the overall dimensions.

69. SOLUTION

70. SOLUTION

71. SOLUTION

72. SOLUTION

74. Video Demonstration on Electrostatic Precipitation