Unwanted particles - agenda
• Pollution particles
– Air pollution: combustion sources, industrial
sources, resuspension sources, natural sources
– Fun particle deposition facts
– Fun lung facts
Particulate pollution sources
• Examples of large industrial stationary sources of
particles?
• Examples of mobile sources of particles?
• Examples of small stationary sources of particles?
• Examples of small residential sources of particles ?
• Examples of resuspension sources of particles?
• Examples of natural sources of particles?
Particle formation mechanisms
• Primary- particles emitted from source
• Secondary – particles form after rxn in
atmosphere
• In source, how can particles form?
– From vapor condensing
– From mechanical production of ‘fines’
• Particles have distribution with size AND
chemistry
Fun particle deposition facts
• Particle capture mechanisms – overview
• Impaction
• Interception
• Diffusion
Fun lung facts
• Once the particles get out, what happens
when we breath them in?
• For a great tutorial, and more details on
lung deposition go to
http://www.aerosols.wustl.edu/aaqrl/Courses/CYCOPCRESP/index.html
Click on respiratory deposition
Important take home message
• The particles in the size range most likely to
escape particle collection are the ones that
will reach the alveolar (pulmonary) region
of the lung
• Bonus! Particles in this size range from
some sources such as incinerators and coal
fired power plants are also likely to be
enriched in toxic metals
Brief history of air regulation
• Pre 1955 – no regulation (!) just keep neighbors happy
• 1955 – Air Pollution Control Act
– Various fed agencies were authorized to investigate cause/effect
relationships
– States and local governments are responsible for maintaining and
improving air quality within their own jurisdiction (this is
important, still holds) Transport is a big issue for states; they sue
each other!
• 1963 – Clean Air Act, more research at fed. Level, more
funds to state and local governments to improve air
pollution control
More historical stuff
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1963 act amended many times
Major amendments 1967
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Establishment of air quality control regions (AQCRs)
Development of specific mandated air quality control criteria
and control technologies
Adoption of National Ambient Air Quality Standards (NAAQS)
to protect public health and welfare
Requirements for State Implementation Plans (SIPs) to ensure
air quality meets NAAQS
Further development of crazy system of acronyms
Particles regulated as total suspended particles (all
particles less than 55 microns), vague…
Poor particles, who will care about them?
The particles in more detail?
• 1987, EPA changed the NAAQS to have separate standards
for TSP and PM10
• PSD (prevention of significant deterioration in attainment
areas) regulation was changed to reflect ONLY PM10 in
1993 (figuring all the bigger stuff will settle out, and not
make us sick anyways)
• PM2.5, regulations proposed but not yet in place
• National Regulations for PM10:(states can be higher)
– PM 10 Annual average concentration = 50 micrograms/m3
– 24 hour average standard 150 micrograms/m3
How are the regs related to the
controls at the source?
• Permits!
• Local authorities require permit for operation
• In 1990, CAA established national operating permits in
addition to local permits
• Permit sets emission limits
• Some types of permits (sulfur emissions for example are
traded)
• Permits designed to bring area into compliance or to
maintain attainment with standards
• Someone at state/local agency figures this out…
Two types:
• Permit to Construct (PTC)
– Not required at federal level unless it’s a major source
• Permit to Operate (PTO)
– Specifies maximum allowed emissions rates
– Exactly how facility will be operated
– How certification of compliance will be determined
(operators police self with penalties for not doing what permit says)
• Compliance proved via stack testing, other testing,
calculations (there’s no way it could escape over the
fence!) including mass balances, etc..
Particle control technologies
• No one magic bullet, often combo of separators is
needed
• Brainstorm on what phenomena can be used to
eliminate particles at the source
– Big particles (resuspension dust, greater than 20
microns)
– Smaller particles (1 to 10 microns)
– Nanoparticles
Control design approach from
intro to ChE perspective
Basic technologies to remove particles
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Electrostatic precipitators – Zap it!
Filters – Suck it!
Scrubbers – Wash it!
Cyclones – Fling it!
Tradeoffs? Costs, lifetimes, maintenance,
efficiency, appearance (just kidding… sort
of)
ESPs
• Applies electrical force to get particles out of gas stream
• ESPs can handle large volumetric flow rates
– Low pressure drops
– High efficiencies
• Downsides?
– Not cheap
– Inflexible to changes in the process (designed for certain efficiency
on certain sized particles)
Filters
• In industry, typically: baghouse filters, looks like bank of really big
socks!
• Air carrying dust particles is forced through a cloth bag. As air passes,
dust accumulates on cloth, leaving air cleaner. Dust is periodically
removed by shaking or reversing air flow
• Goods – filters have high efficiencies, can handle lots of different
kinds/sizes of dusts
• Bad – costly, and limited to dry, low temperature conditions
Scrubbers
• Impacts and intercepts dust particles via collisions with water droplets
• Solid particles can be separated from water stream, or whole stream
can be treated in some other way before discharge (or if you live where
there are no water regulations, and you are not nice..)
• Goods – can scavenge some gases too (mass transport!), high
efficiencies
• Bads – costly, and you have a wastewater stream to deal with
Cyclones
• Simplest is no turning, gravity settling, great for
big chunks
• More sophisticated: cyclones use centrifugal force
to fling large particles out towards wall of tube
• Goods – not as expensive, great for large particles,
easy to maintain
• Bads – efficiency poor for small particles (where
inertia does not dominate particle motion)
• Cyclones often used as pre-cleaners
http://www.aerosols.wustl.edu/aaqrl/Courses/CYCOPCRESP/index.html
Click on “Learning about cyclones”