tuesday 2/21/12week 23 objective – swbat identify products of coal combustion and their effects on...
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Tuesday 2/21/12 week 23objective – SWBAT identify products of coal combustion and their effects on the environment.
HW – Read p. 89 Combustion of Fossil Fuels. Define combustion, fossil fuel, ash, ecosystem (DEJ) and answer AQ 1, 3, & 4 on p. 99 (looseleaf paper, full sentences, name & date upper right, assignment title/p. # center, no shreds, no crossing out)
BR – Summarize how electricity is produced from coal in a diagram or words.
Coal
Where does it come from?
What happens when it is burned?
Where does coal come?
Plants (mostly) and animals! The coal we burn today is from forests that died MILLIONS of years ago.
What elements make up living things?
NitrogenCarbonHydrogenOxygenPhosphorusSulfur
An Easy Way to Think of This
NCHOPS
How are pollutants formed when coal is burned?NCHOPS are released into the air.
N2 and O2 produce NO2
nitrogen dioxide
C and O2 produce CO2 and COcarbon dioxide carbon monoxide
H2 and O2 produce H2O water
O2 reacts with the other elements.
P and O2 produce P2O5 (not released into the atmosphere) phosphorus pentoxide
S and O2 produce SO2 and then SO3sulfur dioxide sulfur trioxide
Isn’t the air we breathe mostly oxygen?
NO!
Nitrogen = 78%
Oxygen = 21%
Everything else – 1%
So why is it a problem if NCHOPS go into the air?
Well here’s what happens when it rains -Nitrogen dioxide reacts with water to form nitric acid (HNO3)
Carbon dioxide reacts with water to form carbonic acid (H2CO3)
Sulfur dioxide reacts with oxygen to form sulfur trioxide. Sulfur trioxide reacts with water to form sulfuric acid (H2SO4)
NCHOPS produce acid rain!!
How can NCHOPS emissions be reduced?
Two main methods
Prevent them from being formed
Remove them from flue (smokestack) gases.
How can NCHOPS emissions be reduced?
Prevention
NO2
1. Reduce amount of extra air in the boiler. (O2 will combine with fuel rather than N2).
2. Keep temperature in burner low (also reduces plant’s efficiency).
CO
1. Keep temperature in burner high.
2. Maintain high O2 flow (form CO2, not CO)
SO2
Use coal containing less S.
Wash coal with water to remove S before burning.
How can NCHOPS emissions be reduced?
Removal from smoke stack gases
NO2
Use scrubbers (chemicals) to convert NO2 to fertilizers (costly, but removes 90% of NO2)
CO2
Scientists exploring possibility of capturing and storing underground
SO2
Use scrubbers (limestone) to convert SO2 into wet paste or dry powder - disposed of in landfill rather than released into the atmosphere
TradeoffsWhich is better?
Low burner temperature = Reduced NO2
High burner temperature = Reduced CO
Why?
What price is better? Cheaper electricity with higher emissionsExpensive electricity with lower emissions
Why?