[quote=LMagic007;237900]This might seem like an ignorant question, but I cant help but wonder about the efficiency design of a power station that requires cooling towers. i.e. surely all that waste heat could be harnessed and fed back into the system somehow ? i.e. to reduce the water heating requirement to produce steam for the turbines.
There's a theoretical maximum for the efficiency of heat engines, which means that waste heat is inevitably ejected. I think the formula is
1 - Tc/Th where Tc is the heat of the steam exiting the turbine and Th is the heat of the steam after it has been heated by the furnace before it goes into the turbine. The point of using the river water to cool the steam exiting the turbine is to lower Tc and improve efficiency. CHP stations use the low grade waste heat to heat homes as well as produce electricity. Overall efficiencies can be in the order of 80% provided there's a demand for the heat. CHP stations tend to me more efficient at producing heat than electricity so they can be inefficient if used primarily to produce electricity. CHP also depends on there being buildings nearby to use the heat along with a heat distribution system.
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