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?