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

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

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

(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 )

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

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 .

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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

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.

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

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

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 .

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

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

室内空气速度分布 18

（三）风压作用下的自然通风 19

风洞模型实验 20

风洞模型实验 21

A Typical continuous-feed mass-fired municipal Combustor

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 .

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 .

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 .

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 .

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

Ⅳ Minimizing volumetric flow rate and pressure drop Q Power

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

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

Ⅴ Efficiency, penetration, nines Q1C1 Q2C2 Q0C0 Q3C3

Ⅴ Efficiency, penetration, nines In the terms of penetration

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 .

This Lecture and the Next Lecture Chapter 7 Page 160~196 Page 202~205 The Next Lecture: Chapter 8 Page 209~246

Exerciser Page 203, 7.5 Page 204, 7.12 Page 205, 7.19, 7.21

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