1. Cogeneration Power plants generate lots of waste heat Modern coal fired plants convert 38% of the energy in the coal to electricity, the other 62% is waste! Usually shed off into the environment (air, cooling pond, river, lake etc) Can have environmental consequences Can it be put to use?

2. Cogeneration Problem arises when the power plant is located far away from population centers- cannot effectively transport the heat over long distances In principle, the waste heat could be used to heat a boiler and provide steam for pace heating and cooling. Or it could be recycled to drive turbines to produce dditional electricity

3. Types of cogeneration plants Topping cycle plants - produce electricity from a steam turbine. The exhausted steam is then condensed, and the low temperature heat released from this condensation is utilized for heating. Bottoming cycle plants- produce high temperature heat for industrial processes, then a waste heat recovery boiler feeds an electrical plant. Need a high initial source of heat-metal manufacturing plants.

4. Examples The New York City steam system - district heating system which carries steam from central power stations under the streets of Manhattan to heat, cool, or supply power to high rise buildings and businesses. Another example is in use at the University of Colorado, Boulder - Total efficiency is 70% Possibility of explosions due to pipe failures exists

5. Example of Explosions The July 18, 2007 New York City steam explosion sent a geyser of hot steam up from beneath a busy intersection, with a 40-story-high shower of mud and flying debris raining down on the crowded streets of Midtown Manhattan It was caused by the failure of a Consolidated Edison 24- inch underground steam pipe installed in 1924

6. Possibilities Outside the U.S., energy recycling is more common. Denmark is probably the most active energy recycler, obtaining about 55% of its energy from cogeneration and waste heat recovery. In the US about 8% of its electricity is produced via cogeneration