Coal From where does it come? What happens when it is burned?
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Transcript of Coal From where does it come? What happens when it is burned?
Coal
From where does it come?
What happens when it is burned?
From where does coal come?
Plants and animals!
Of what elements do plants and animals consist?
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
What happens to these compounds when it rains?NCHOPS produce acid rain.
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)
How can NCHOPS emissions be reduced?
Two main methods
Prevent them from being formed
Remove them from flue gases.
How can NCHOPS emissions be reduced?
Prevent them from being formed
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
Keep temperature in burner high.
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?
Remove them from flue 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
TradeoffsWhat Temperature is Better?
Low Temperature = Reduced NO2
High Temperature = Reduced CO
Why?
What Price is Better? Cheaper electricity with higher emissionsExpensive electricity with lower emissions
Why?