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• 1963 act amended many times• Major amendments 1967

1. Establishment of air quality control regions (AQCRs)2. Development of specific mandated air quality control criteria and

control technologies3. Adoption of National Ambient Air Quality Standards (NAAQS) to

protect public health and welfare4. Requirements for State Implementation Plans (SIPs) to ensure air

quality meets NAAQS5. 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• 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.htmlClick on “Learning about cyclones”