Thermodynamics extended the "no free lunch" principle to "some of the energy is unavailable to do work."
For power utilities and chemical plants:
All electricity utilities have this cycle
Heat from coal, oil, gas or
U-235 creates steam
that drives turbine.
Typical efficiency is 1/3.
3000 MW plant yields
1000 MWe electricity &
2000 MW heat at Tcold.
What happens to this heat?
Dispose of heat at Tcold to keep turbine efficiency.
1. Using external water in the condenser or
2. Using cooling towers with air to transport heat.
Both have problems, but "dry" or "hybrid" towers have the least.
In past, electricity utilities used natural bodies of water -- lakes, rivers or coasts -- to cool discharged heat. This external water is recirculated thru heat exchanger, never in contact with water in generator's closed loop. But what about heat's effect?
Water taken from lower non-circulating layer and returned to upper, stratfied layer: 5-10 C highter ⇒ 2 adverse effects.
1. Heating the upper layer decreases the amount of dissolved ("entrained") oxygen, essential to chemical processes that clean the water and sustain fish. Changing the water's temperature and oxygen content affects relative stability of fish.
2. The change in the temperature stratification of the lake can seriously affect the lake and its inhabitants.
Most suitable bodies of water have been used. Cooling towers are increasingly used. There are two kinds: "wet" or "dry" (the latter includes "hybrid").
The "wet" are cheaper but slightly affect local climate. The EPA has largely made it impossible to build these anymore.
"Dry" cooling towers use fans to move the air at greater cost. They work better than "wet" in most climates.
My summary. As anticipated growth in electricity plants occurs, "dry" towers seem to pose few problems. ... But ...
In Chemical Industry cooling towers remove heat from products and processes. The move from one-time water to recirculating decreases heat added to the source of water but not to the environment. Instead the heat goes into the atmosphere.
In contrast to power plants -- where the cooling cycle does not contact combustion products -- leaks from heat exchanges into cooling water systems raises concern:
Labels for problem:
biological oxygen demand (BOD) and
chemical oxygen demand (COD) -- the amount of organic and
non-organic materials present. E.g.
hydrocarbon leaks by failure/rupture of water tubes
particulates from dissolved solids in cooling water drifting away.
Not covered by Clean Air Acts (next lecture)
Chemical industry realizes regulations from EPA protocols are
ineffective to assess air emissions.
Contrast is between behavior of regulated utilities and companies under regulations with no developed monitoring.
Building anything new requires Environmental Impact Statement: so onerous as to undermine their effectiveness.
Indeed Congress strives to cut them back, not in a very thoughtful way.
Politics aside, These concerns focus most dramatically for proposals to building several power plants at one location for any of several reasons:
Pollution -- ever looming topic not mentioned today -- is next.