1. Air Pollution Control Engineering
Prof. Jiakuan Yang
Huazhong University of Science and Technology

2. Lecture 7-1 General ideas in air pollution control
Ⅰ Three alternatives for air pollution control
Ⅱ Air pollution control systems and equipment
Ⅲ Fluid velocities in air pollution control equipment
Ⅳ Minimizing volumetric flow rate and pressure drop
Ⅴ Efficiency, penetration, nines

3. Ⅰ Three alternatives for air pollution control
(1) improve dispersion
Basic idea
Improving the dispersion of our emission and thereby diluting the pollutants and lower the concentration near the ground level where people often exist .
Threshold value

4. (1) improve dispersion For example
In a sparely populated area, the pollutant emissions are eliminated by natural removal mechanisms and without causing any damage to the neighbors.
In a densely populated world, dispersion is not a satisfactory approach .
For example
The population density is 1 person/km2
The population density is 29,000 persons/km2 ( Manhattan )

5. h H c (1) improve dispersion ① Tall stack Problem
the ground-level concentration h H c

6. For example: Acid-rain controversy
(1) improve dispersion
① Tall stack
It will certainly decrease all the ground-level concentration near the stack, but it may increase some concentration far from stack with a tall stack .
For example: Acid-rain controversy
SO2 ultimately comes to ground , mostly with rain or snow for far away from the tall stack .
Raising the emission point of stack, may raise the concentration far downwind .

7. 2001 年 度二 氧 化 硫 浓 度 区 域 分 布

8. 2001 年 度 全 国 将 水 pH 值 分 布

9. Example 1, predictive control scheme
(1) improve dispersion
② Intermittent control schemes
Example 1, predictive control scheme
down wind
morning exercise
6:30 ~ 8:00 A.M.
Stack
A fire-electric plant
Opening center-park

10. Temperature Inversion
(1) improve dispersion
② Intermittent control schemes
Temperature Inversion h T
Before 9:00 A.m. Shut off the production and stringent control of stack emission.

11. Example 2, observation control system Oxygenated motor fuels: CO
(1) improve dispersion
② Intermittent control schemes
Example 2, observation control system
Homes wood stoves: PM10
Oxygenated motor fuels: CO

12. (1) improve dispersion
③ relocate the plant
The emission source should be far away from populated areas. Such as residential areas, commercial centers .

13. Reduce emission by process change , pollution prevention
Basic idea
Cleaner production, from raw material, old process, old technology, changed into a cleaner process, to prevent pollution.
water-based paints
Coal is replaced by natural gas as a home or business fuel .

14. (3) Use a downstream pollution control device
tailpipe
end-of the pipe control device

15. Ⅱ Designing air pollution control systems and equipment
Run cost
Efficiency
Control device
Blower
stack
Fluid velocities
Hood
Collected pollutant
Emission source
Resource recovery and ultimate fate of pollutants
Reduce emission

18. 室内空气速度分布 18

19. （三）风压作用下的自然通风 19

20. 风洞模型实验 20

21. 风洞模型实验 21

24. A Typical continuous-feed mass-fired municipal Combustor

27. Resource recovery
If the pollutant is valuable material or a fuel , it may be more economical to collect and use it than to discard it.
Generally, reclamation or recovery is economical only if the concentrations are high enough in waste stream .

28. The ultimate fate of pollutants
Most organic compounds will burn.
Most particulate pollutant , e. g . fine dusts, to be captured and placed in a landfill.
Hazardous wastes disposal cost is higher .

29. Ⅲ Fluid velocities in air pollution control equipment
Almost all industrial-sized flows of air or gases are turbulent .
40 to 60 ft/s (≈12 to 18 m/s )
velocity
cost of pumping
Diameter
Cost of the pipe
Minimize sum of pumping cost and capital cost of pipes and ducts .

30. Ⅳ Minimizing volumetric flow rate and pressure drop
In the air pollution control system , fan or blower is the power source that propels the gas stream through the control device and the associated ductwork and exhaust stack .

31. Ⅳ Minimizing volumetric flow rate and pressure drop
Page 171
n = molar flow rate
R = universal gas constant
T1 = inlet absolute temperature
k = heat capacity ratio = 1.4 for air and most waste gases
η= fan or blower efficiency
P1 = inlet absolute pressure of the fan
P2 = outlet absolute pressure of the fan

32. Ⅳ Minimizing volumetric flow rate and pressure dropQ
Power

33. Ⅴ Efficiency, penetration, nines
Downstream control device C0 C1
Q0C0
Q1C1
Q0C0
Mass flow rate of contaminant into the device
Q1C1
Mass flow rate of contaminant out of the device

34. Ⅴ Efficiency, penetration, nines
90%
99%
99.9%

35. Ⅴ Efficiency, penetration, nines
Q1C1
Q2C2
Q0C0
Q3C3

36. Ⅴ Efficiency, penetration, nines
In the terms of penetration

37. Ⅵ Homogeneous and non-homogeneous pollutants
CO, SO2 are homogeneous
Every CO molecule is identical to every other CO molecule .
Particles are not homogeneous
different particle with various sizes .

38. This Lecture and the Next Lecture
Chapter Page 160~196
Page 202~205
The Next Lecture:
Chapter Page 209~246

39. Exerciser
Page 203,
Page 204,
Page 205, , 7.21

40. DISCUSSION Topics about Air pollution: Introducing yourself
Interesting news or information about air pollution your
having read or heard
Your opinions on this Air Pollution course
Your suggestions for Chinese Air Pollution
Other familiar issues about Air Pollution