1. Vehicle pollution control

2. An example of Gaussian dispersion case
A Chimney emits SO2 at a rate of 40 g/s. The stack diameter and height are 5 m and 150 m respectively. The stack gas velocity is 10 m/s and stack gas temperature is 140 OC. Ambient temperature is 25 OC.
The atmospheric condition is cloudy with wind speed at 2.5 m/s at 10 m and 4.3 m/s at stack height.
Calculate the ground level concentration of SO2 at 4 km downwind at plume centerline.

3. Internal combustion engine
Combustion chemistry
C8H O N2  8CO N2+ 9 H2O
For complete combustion: Air-fuel (A/F) ratio = 15:1
CO is produced from incomplete combustion HCs are produced when the flame front approaches relatively cool walls of the cylinder. NOx is produced from N2 + O2 2 NO

4. Internal combustion engine combustion cycle

6. Petrol and diesel engine:
Air-fuel ratio: higher ratio for diesel
Compression ratio: High for diesel CO HC
NOx PM
Petrol
High
Low
Diesel

7. CO and HCs control Modify engine design to improve combustion
Use of catalytic converters

8. Control of NOx emission
Generally more difficult to control, mainly to decrease combustion temperature
Retardation of spark
Decreased compression ratio
exhaust has recirculation

9. Control technologies New control technologies Alternative fuels
dual and three-way catalytic converter (NOx ->N2)
Alternative fuels
Conventional gasoline contains a mixture of paraffinic, and aromatic HC compounds
Octane rating: When combustion is too rapid, a sharp metallic noise called knock is produced. Component that reduces the knock has the octane quality.
Historically lead alkyls have been added to boost octane ratings.
In unlead gasoline, aromatic HCs are added.

10. Control technologies Reformulated gasolines and oxygenated additives
oxygenated additives such as MTBE, ETBE, methanol, ethanol (to boost the octane rating due to reducing aromatics)
- Alcohol fuels
Alcohol-gasoline blend
- Compressed and liquefied gases
Natural gas (mainly contains methane)
Liquefied petroleum gas (largely propane)
limited supply and higher exhaust reactivity

11. Control of diesel vehicle pollution in Hong Kong
Euro III standard for vehicles of 1995 and onwards
Existing ones
Taxies: LPG
Light buses: to be switched to LPG or electricity
Heavy duty: traps and/or catalytic converters

12. Stationary sources control
Tall stacks
Fuel-use changes
Fugitive emission containment
Pollution prevention
Substitution
Process equipment changes
Plant operating practices
Maintenance
Process changes
Energy conservation
“End of the pipe” control (see next pages)

13. Particle Collection Systems
Cyclone collectors
In general, collection efficiency increases with increased particle size and density, dust loading, and collector size.
Multiple tubes collectors can be used to increase collection efficiency
Cyclones are often used to control relatively large particles, and often are used in series as pre-cleaners for more efficient collectors.

14. Filtration
Fabric filters are commonly used to control particle emissions where dust loading are higher, particle sizes are small, and high collection efficiencies are needed.
Limitations include high capital costs, flammability hazards for some dusts, high space requirements, flue gas temperature limited to 285 C, and sensitivity to gas moisture.

15. Electrostatic precipitator
High collection efficiencies for all particle sizes, low operating and power requirements; But high capital costs and space requirement.

16. Wet scrubbers Open spray Tower Venturi Scrubber
Almost exclusively used to remove fine particles
Capital costs are low, but operating costs are high (energy and disposal of waste liquid)

17. Control of gas-phase emissions
More complex technologically than control of particles. Control techniques for a specific gas pollutant needs to be developed.
Combustion
Adsorption
Absorption
Direct flame incinerators

18. Control of gas-phase emissions
Thermal incineration
Additional fuel needed
Catalytic incineration

19. Control of gas-phase emissions
Adsorption
Gas pollutant being adsorbed by the surfaces of solids such as molecular sieve, activated carbons etc
Absorption
Absorbed by liquids