Sources of Air Pollution : Sources of Air Pollution AP Control
January 22, 2003
Slide2 : Transport, Dilution, Alteration
Sources : Sources If we are focusing on specific pollutant, then we can narrow down the list of sources.
Otherwise, air pollution sources include anything that releases anything to the air.
Power plants – electricity production
Factories, refineries
Painting
Cars and trucks
All buildings – cleaning products, heating, cooking,…
All people
This is no help at all! So let’s look at some of the prominent pollutant species. Which are ….?
US Federal Legislation : US Federal Legislation Clean Air Act (1963)
1st time federal government took charge
Clean Air Act Amendments (1970)
Identified Criteria Pollutants for which standards needed to be created.
TSP (total suspended particles), SO2, CO, NO2, O3, lead
Mandated the development of performance regulations for sources to allow urban areas to meet these standards.
Identified Hazardous Air Pollutants and declared “no standard was applicable” for these.
More Legislation : More Legislation Clean Air Act Amendments (1990)
Established a safety standard for acceptable risk of cancer of 1 in 100,000.
189 substances listed as Hazardous Air Pollutants (HAPs), up from the 7 that were listed in 1970 (beryllium, mercury, asbestos, vinyl chloride, benzene, and PCBs)
The sources of these 189 HAPs need to reduce emissions by 90% by the year 2003.
Several subsequent revisions have been made to the standards for the Criteria Pollutants.
New ozone standard
PM2.5 added to the list
Slide6 : 1997 US National Emission Estimates 116% 78% 70% 65% 1.7% 3.1 20.4 87.5 23.5 19.2 0.004 HAPs not Criteria Pollutants million short tons/yr % of 1970 ????
O3
PM2.5
????
Why do we have pollution growth? : Why do we have pollution growth? OK, so emissions control regulations are typically set on a per source activity basis.
X mg/mile of CO per vehicle
Y g/min of PCDD per stack
Are there other options?
What has really changed? : What has really changed? From 1970 to 1997
US population
30% increase
Economic activity per person
80% increase
Motor vehicle use, 400% increase
Emissions per economic activity
Huge decreases
Way to go engineers!
Effects of regulations on pollution growth : Effects of regulations on pollution growth This would be an example of an emissions control regulation.
Example of regulatory effects : Example of regulatory effects
OK, back to source types. : OK, back to source types. For all the criteria pollutants (except O3), greater 75% of the emissions originates from combustion.
O3 is a secondary pollutant, that needs NOx and VOCs and sunlight to be created.
VOCs come from combustion and evaporation.
Other pollutants from industry.
Evaporative VOC Sources (a.k.a., fugitive emissions) : Evaporative VOC Sources (a.k.a., fugitive emissions) Can you all name the most common?
Paint
Oil-based vs water-based
Cleaning
Degreasing, dry cleaning, …
Fuel
Building material
???
VOCs are a diverse group of compounds, so why group them together?
Vapor pressure, reactivity,…
Combustion : Combustion What do we burn?
Fossil fuels
Gasoline, diesel, jet fuel, propane, natural gas, coal, fuel oil
Biomass
Wood
Let’s define combustion:
Webster says, “Combustion: n 1. The process of being or causing to be on fire, 2. A rapid chemical, esp. oxidation, the produces light and heat.”
Combustion (engineering text) : Combustion (engineering text) Combustion is a chemical conversion process.
Molecules that have significant internal chemical energy (the fuel) are converted by an oxidant (typically, O2 in air) to a lower energy molecule.
“Energy in” = “energy out”
The loss of internal energy from the fuel to the product must be balanced by energy release, which is mostly thermal energy (a.k.a. heat).
The chemical reaction. : The chemical reaction. + + We use the heat generated from this reaction to warm our homes, cook our food, help us move around, generate our electricity, and create many products we use daily.
ABCs of combustion : ABCs of combustion Most effective fuels are those fuels which have the highest internal energy.
Chemical conversion process can release the most possible amount of energy.
Fuels with the most internal energy are those which have the greatest capacity to accept O2 (i.e. be oxidized).
Best fuels are those which contain least oxygen.
Best fuel is natural gas, which is mostly methane (CH4).
Methane is the most reduced (or has the greatest potential to be oxidized) form of carbon.
All fuels are carbon based – for now.
Fossil fuels usually contain just C and H and are called hydrocarbons.
Combustion of methane : Combustion of methane CH4 + air (O2 + 3.78 N2) CO2 + H2O N2 + heat 1 1 2 2 7.56 + • As the fuel changes, the number of molecules
(a.k.a. stoichiometry) will change. • This chemical reaction is called “complete combustion”. • If we combine natural gas with air does this reaction occur? NO, we need the 3 T’s.
Complete Combustion : Complete Combustion Complete Combustion is defined as complete conversion of the C in the fuel to CO2 and complete conversion of the H in the fuel to H2O.
If that was all that ever happened, the only “stuff” we would be putting into our atmosphere would be CO2, H2O, N2, and heat. Life wouldn’t be so bad, except that I would not have a job.
The 3 T’s. : The 3 T’s. Temperature
Almost all chemical reactions occur faster at higher temperatures, so if we want to have combustion occur at a desired rate we will heat the fuel and the air.
Time
Even if we heat the fuel and air, we still need to let them hang out together for a certain length of time to enable a reaction.
Turbulence
I think of a turbulent reaction as a reaction in which the fuel and air are mixed completely.
Unfortunately life isn’t perfect. : Unfortunately life isn’t perfect. Reason #1: Combustion is not always complete.
Why?
What happens if we do not have the right ratio of air to fuel (i.e., what if we are not operating at the stoichiometric mix)?
Answer: “Incomplete combustion”
What happens if we do not satisfy the 3 T’s? (Remember - Temperature, Time, Turbulence)
Answer: “Incomplete combustion”
What happens?
If we have too much fuel. : If we have too much fuel. • “too much fuel” is defined as burning rich. • You can think of it has not having enough oxygen. 1 7 5 4 + 1 CO 26.5 Result:
Not all the C is completely oxidized to CO2 and we get CO.
If we have too little fuel. : If we have too little fuel. “too little fuel” is termed burning lean.
You can think of it as having too much O2.
Result:
Heating more air than we need, means we are going to get less net energy from the reaction.
Excess O2 can also cause problems in combination with Reason #2. We will see this in 2 slides.
Do not satisfy the 3 T’s. : Do not satisfy the 3 T’s. If we do not reach the desired temperature for the desired length of time, then
we will exhaust pure fuel as well as the usual products.
we will not break all the bonds in the fuel molecule and exhaust partially combusted fuel.
If we do not create enough turbulence (a.k.a. mixing), then we will have pockets of rich burning and pockets of lean burning.
Unfortunately life isn’t perfect. : Unfortunately life isn’t perfect. Reason #2: N2 is not totally inert at the relevant temperatures.
At high temperatures (like those experienced inside a car’s engine), N2 can be oxidized by O2 to form 2 molecules of NO.
NO is pretty unstable and will pick up another oxygen molecule to form NO2.
NOx is defined as the sum of NO and NO2.
Excess O2, which occurs when you are burning lean, helps the formation of NOx
Unfortunately life isn’t perfect. : Unfortunately life isn’t perfect. Reason #3: Fuel is not always as simple as plain C and H.
Addition of sulfur (S), nitrogen (N), or even more oxygen (O) to the fuel will cause the formation of oxidized S (SO2) or oxidized N (NOx).
Things that do not burn (ex. metals) will be released as particles.
Very large fuel molecules may not be completely broken down to CO2 and will be released as soot, smoke, particles, smells, etc…
Example of large fuel molecule. : Example of large fuel molecule.