Cogeneration

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