Cogeneration Power plants generate lots of waste heat
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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?
Cogeneration • Problem arises when the power plant is located far away from population centerscannot 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
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.
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
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
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
