Particulate Matter and its Removal

1. Particulate Matter and its Removal

2. Particulate Matter – Overview • Can be solid or liquid particles • Usually defined in terms of PM10 and PM2.5 where the subscript refers to the diameter of the particle in microns  10 or 2.5 • Reduces visibility in the atmosphere • Causes health problems related to the respiratory system and circulatory system

3. Relative sizes of particles in air

4. Relative sizes of particles in air PM10 PM2.5

5. Particulate Matter Standards • High-volume samplers measured PM by Total Suspended Particulate Matter (TSP). TSP usually less than 25-50 μg/m3. Concentrations measured usually around 260 μg/m3 . • Based on research in the 1960s and 1970s, the human respiratory system was found to be affected by PM that was finer than what high-volume samplers measured. • A new standard based on PM10 was established using a 24-hour concentration of 150 μg/m3.

6. Particulate Matter Standards –EPA in 1997 as amended 2006 The EPA set a new stricter standard that regulated fine particulate matter (PM2.5) in 1997: 65 μg/m3 measured over a 24-hour period and 15 μg/m3 averaged over a year. The EPA announced in 2006 that it revised the level of the 24-hour PM-2.5 standard to 35 micrograms per cubic meter (µg/m3) and retained the level of the annual PM-2.5 standard at 15 µg/m3. The EPA announced the designations for nonattainment for the PM-2.5 2006 Standard, October 8, 2009. The current number of areas that violate the PM-2.5 2006 Standard is31 and the number of counties that violate is currently 120. A map of the EPA's PM2.5 designations for nonattainment can be reviewed by clicking here.

7. Non-attainment areas: PM 2.5 Yesterday http://www.airnow.gov/

8. Key to air quality levels

9. Non-attainment areas: PM 2.5 Today

10. Polk County Health Department – Polk County Air Quality Takes PM readings every 24 hours Weighted annual mean PM 2.5 = 10 μg/m3 (http://www.city-data.com/city/Des-Moines-Iowa.html) Link: http://www.airnow.gov/index.cfm?action=airnow.showmap&pollutant=PM2.5

11. PM 2.5 in Iowa yesterday

12. PM 2.5 in Iowa last year

13. Sources of PM • motor vehicles • wood burning stoves and fireplaces • dust from construction, landfills, and agriculture, mining • wildfires and brush/waste burning • industrial sources • windblown dust from open lands

14. Health Effects • Aggravates conditions such as asthma, bronchitis, emphysema • Can trigger asthma attacks • Makes it difficult to breathe • Can cause premature death in elderly people or people with heart disease and respiratory diseases • Can cause future health problems in children (such as asthma, increased illness)

15. Effects on Visibility • Most haze is not natural, it is caused by air pollution • Air pollution, especially particulate matter, scatters and absorbs light • Sulfates particles are very effective in scattering light, especially in humid conditions

16. Denver, CO, (top) and Great Smokey Mountains National Park (bottom) in good visibility and bad visibility

17. Cleaning up Particulate Matter – Control Equipment • Gravity and Inertial Separators • Mechanical Collectors (Cyclones) • Scrubbers • Electrostatic Precipitators • Fabric Filters

18. Type 1:

20. Archimedes’s Principle Archimedes’s Principle Examination of the nature of buoyancy shows that the buoyant force on a volume of water and a submerged object of the same volume is the same. Since it exactly supports the volume of water, it follows that the buoyant force on any submerged object is equal to the weight of the water displaced. This is the essence of Archimedes principle.

21. Analysis of Forces Acting On a Settling Particle Determining the terminal settling velocity of a particle

22. Expressing the terminal settling velocity of a particle Terminal Velocity of a Particle An expression for Vs from the submerged weight of the particle, W, and the fluid drag force, D The drag force on a particle is given by D = CDgAp Vt2/2 The suspended weight of the particle can be expressed as W = ( - g)g s Since D = W, the above, after substituting Ap and p for particle diameter d _______________ Vt= /4 ( - g) gd  3l CD

23. Stokes’s Law Re < 1, CD = 24 /Re Vs=g ( -g) d2 18  Vs =g  d2 18 

24. Pathways of particles around media particles

25. B A C

35. Type 2: Mechanical Collectors – Cyclones • Specific types include: • Involute cyclone separator • Vane-axial centrifugal separator • Large-diameter cyclones • Small-diameter multi-cyclones

36. Mechanical Collectors – Cyclones Advantages: Good for larger PM Disadvantages: Poor efficiency for finer PM Difficult removing sticky or wet PM

37. Cyclones - A Large-Diameter Involute Cyclone Separator

38. Involute Inlets

39. Cyclones - A small-diameter vane- axial centrifugal separator

41. Type 3: Scrubbers • Specific types include: • Venturis • Impingement and Sieve Plates • Spray Towers • Mechanically Aided • Condensation Growth • Packed Beds • Ejector • Mobile Bed • Catenary Grid • Froth Tower • Oriented Fiber Pad • Wetted Mist Eliminators

42. Scrubbers Advantages: Good efficiency, can collect (potentially explosive) gaseous pollutants as well as PM, small size Disadvantages: Requires a lot of water, generates waste stream

47. Venturi Scrubbers

48. Type 4: Electrostatic Precipitators • Types include: • Dry, negatively charged • Wet-walled, negatively charged • Two-stage, positively charged

49. Electrostatic Precipitators Advantages: Good efficiency Disadvantages: Dependent upon resistivity of PM, cannot be used around explosive gases