Particulate Matter
and its Removal
4/13/2015
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
Relative sizes of particles in air
Relative sizes of particles in air
PM10
PM2.5
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 24hour concentration of 150 μg/m3.
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 is 31 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.
Non-attainment areas: PM 2.5
Yesterday
http://www.airnow.gov/
Key to air quality levels
Air Quality Index
Levels of Health
Concern
Numerical
Value
Good
0 to 50
Moderate
51 to 100
Unhealthy for
101 to 150
Sensitive Groups
Unhealthy
151 to 200
Very Unhealthy
201 to 300
Hazardous
301 to 500
Meaning
Air quality is considered satisfactory, and air pollution
poses little or no risk
Air quality is acceptable; however, for some pollutants
there may be a moderate health concern for a very
small number of people who are unusually sensitive to
air pollution.
Members of sensitive groups may experience health
effects. The general public is not likely to be affected.
Everyone may begin to experience health effects;
members of sensitive groups may experience more
serious health effects.
Health alert: everyone may experience more serious
health effects
Health warnings of emergency conditions. The entire
population is more likely to be affected.
Non-attainment areas: PM 2.5
Today
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
PM 2.5 in Iowa yesterday
PM 2.5 in Iowa last year
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
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)
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
Denver, CO, (top) and Great Smokey Mountains National Park (bottom)
in good visibility and bad visibility
Cleaning up
Particulate Matter
– Control Equipment
• Gravity and Inertial Separators
• Mechanical Collectors (Cyclones)
• Scrubbers
• Electrostatic Precipitators
• Fabric Filters
Type 1:
Gravity settler
Gravity Settlers
• Gravity settlers operate by allowing the effluent gas to
expand into a large chamber. This reduces the gas
velocity and causes the particles to settle out.
• The important factors in settling chamber designs are
the surface area available for sedimentation, the
terminal settling speed of the particles and the gas flow
rate.
Archimedes’s
Archimedes’s Principle
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.
Analysis of
Forces Acting
On
a Settling
Determining
Particle
the terminal
settling
velocity of a
particle
Expressing
terminal
settling
Terminalthe
Velocity
of a Particle
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g Ap Vt2/2
The suspended weight of the particle can be expressed as
W
Since D = W,
Vt
= ( - g)g s
the above, after substituting Ap and p for particle diameter d
_______________
=

/ 4 ( - g) gd
3l CD
Stokes’s Law
Re < 1, CD = 24 /Re
Vs = g ( -g) d2
18 
Vs = g  d2
18 
Pathways
of particles
around
media
particles
A
B
C
Gravity settler
Baffle chamber
• Another type of inertial separating system causes the
gas to change direction by means of baffles. Both the
baffle chamber and the settling chamber are seldom
used in modern gas cleaning particle because they
require a large area.
• In almost very case, a cyclone would provide better
collection efficiency.
Gravity settler
Baffle
Chamber
Gravity settler
Louvre chamber
• An extension of the baffle principle, which increases the
inertial separation of particles, is the use of banks of small
baffles which split the gas flow as well as changing its
direction.
• These baffles, which are normally referred to as louvers or
chevrons, are occasionally used for dust control , but much
more commonly to catch large droplets carried over from
cooling towers or wet scrubbers and for demisting duties
generally.
Gravity settler
Industrial applications
(1)
(2)
The combination settling chamber and
cooling device has been used in the metal
refining industry to partially collect large
PM and to reduce the gas temp before
entering the final collection device
Arsenic trioxide from smelting arsenical
copper ores has often been collected in
brick settling chambers known as
“Kitchen”
Gravity settler
Industrial applications
(3) In the manufacture of various foodstuffs, simple
settlement is the first step in dust recovery,
achieved by spraying the condensed liquids into
large chambers. The effluent air is then passed to
second-stage cleaners (cyclone) and the exhaust
re-circulated to the spray chambers.
(4) Power and heating plants may employ settling
chambers upstream of multiple cyclone units.
Quite often they are used to collect large unburned
carbon particles and re-inject them into boiler
Gravity settler
Advantages
• Low cost of construction and maintenance
• few maintenance problems
• Relatively low operating pressure drops, in
the range of approximately 0.1in H2O
• Temperature and pressure limitations
imposed only by the materials of
construction used
• Dry disposal of solid particulate
Gravity settler
Disadvantages
• Large space requirement
• Relatively low overall collection
efficiencies (typical 20 - 60 %)
Type 2: Mechanical
Collectors – Cyclones
Specific types include:
• Involute cyclone separator
• Vane-axial centrifugal separator
• Large-diameter cyclones
• Small-diameter multi-cyclones
Mechanical Collectors –
Cyclones
Advantages: Good for larger PM
Disadvantages: Poor efficiency for finer PM
Difficult removing sticky or wet PM
Cyclones A LargeDiameter
Involute
Cyclone
Separator
Involute Inlets
Cyclones - A small-diameter vaneaxial centrifugal separator
Type 3: Scrubbers
Specific types include:
• Venturis
• Ejector
• Impingement and
Sieve Plates
• Mobile Bed
• Spray Towers
• Catenary Grid
• Mechanically Aided
• Froth Tower
• Condensation Growth
• Oriented Fiber Pad
• Packed Beds
• Wetted Mist Eliminators
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
Venturi Scrubbers
Type 4: Electrostatic Precipitators
Types include:
• Dry, negatively charged
• Wet-walled, negatively charged
• Two-stage, positively charged
Electrostatic Precipitators
Advantages: Good efficiency
Disadvantages: Dependent upon
resistivity of PM, cannot be used
around explosive gases
Wet Electrostatic Precipitators
Electrostatic
Plates
List of suppliers of equipment
http://www.eco-web.com/cgi-local/sfc?a=index/index.html&b=index/category/4.4.html
Type 5: Fabric Filters / Baghouses
Types include:
• Reverse air-type
• Pulse jet
Fabric Filters / Baghouses
Advantages: Good efficiency for
various sizes of particles
Disadvantages: Not to be used
around corrosive substances,
explosive gases, or sticky and
wet particles
Technology - Media Cross Section
View in "Z" direction with no cover sheet
50x magnification
•
•
•
•
View in cross-sectional direction
50x magnification
Three-dimensional placement and immobilization of functional particles
Maximization of accessibility to particles with tortuous void space
Low pressure drop
Combi media capability for particulate filtration
Growth of Fungi
On Inside of
Filter Material
Here: Aspergillus sp.
Sources
1. EPA
2. American Lung Association
3. Polk County Health Department
Assignment: Particulates
Do Problems at the end of Chapter 5
5-3, 5-5, 5-23, 5-53
Hand in by Thursday, February 10, 2010