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Published byBarbara Sutton Modified over 9 years ago
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Coal From where does it come? What happens when it is burned?
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From where does coal come? Plants and animals!
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Of what elements do plants and animals consist? Nitrogen Carbon Hydrogen Oxygen Phosphorus Sulfur
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An Easy Way to Think of This NCHOPS
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How are pollutants formed when coal is burned? NCHOPS are released into the air. N 2 and O 2 produce NO 2 nitrogen dioxide C and O 2 produce CO 2 and CO carbon dioxide carbon monoxide H 2 and O 2 produce H 2 O water O 2 reacts with the other elements. P and O 2 produce P 2 O 5 (not released into the atmosphere) phosphorus pentoxide S and O 2 produce SO 2 and then SO 3 sulfur dioxide sulfur trioxide
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What happens to these compounds when it rains? NCHOPS produce acid rain. Nitrogen dioxide reacts with water to form nitric acid (HNO 3 ) Carbon dioxide reacts with water to form carbonic acid (H 2 CO 3 ) Sulfur dioxide reacts with oxygen to form sulfur trioxide. Sulfur trioxide reacts with water to form sulfuric acid (H 2 SO 4 )
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How can NCHOPS emissions be reduced? Two main methods Prevent them from being formed Remove them from flue gases.
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How can NCHOPS emissions be reduced? Prevent them from being formed NO 2 1.Reduce amount of extra air in the boiler. (O 2 will combine with fuel rather than N 2 ). 2.Keep temperature in burner low (also reduces plant’s efficiency). CO 1.Keep temperature in burner high. 2.Maintain high O 2 flow (form CO 2, not CO) SO 2 1.Use coal containing less S. 2.Wash coal with water to remove S before burning.
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How can NCHOPS emissions be reduced? Remove them from flue gases NO 2 Use scrubbers (chemicals) to convert NO 2 to fertilizers (costly, but removes 90% of NO 2 ) CO 2 Scientists exploring possibility of capturing and storing underground SO 2 Use scrubbers (limestone) to convert SO 2 into wet paste or dry powder - disposed of in landfill rather than released into the atmosphere
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Tradeoffs What Temperature is Better? Low Temperature = Reduced NO 2 High Temperature = Reduced CO Why? What Price is Better? Cheaper electricity with higher emissions Expensive electricity with lower emissions Why?
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