Utilities Affect Environment

Thermodynamics extended the "no free lunch" principle to "some of the energy is unavailable to do work."
Here we discuss in the context of power utilities:

There is substantial unused heat

All electricity utilities have this cycle

Natural inefficiency of using heat 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?

Disposing of Unusable ("waste") Heat

Must dispose of heat at Tcold: efficiency of turbine generating electricity depends on it! Only two ways:

  1. Using external water in the condenser or
  2. Using cooling towers with air to transport heat.

Neither is without problems, but "dry" or "hybrid" towers seem to raise the least concerns.

Using Lakes to remove "waste" heat

Electricity utilities had long used natural bodies of water -- lakes, rivers or coasts -- to cool discharged heat. With nuclear power, the same approach was used, as long as such sources were available.

This external water is recirculated through a heat exchanger, never in contact with water in closed loop of generator. The only question is heat's effect.

Altho returned water is only 5-10 C higher, it was taken from lower non-circulating layer & returned to upper layer in a stratified lake ⇒ 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.

Cooling towers to remove "waste" heat

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

But .. Petrochemical Cooling Towers

Chemical industry widely uses cooling towers to remove heat from products and processes. Increasingly, such cooling is moving from one-time use of water to recirculating. This decreases the 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 it seems the cooling cycle does not come into contact with combustion products -- leaks from heat exchanges into the cooling water systems raises concern:

 

The most common environmental problem is hydrocarbons leaking into the cooling water from "aging" heat exchanges. This problem is characterized in terms of biological oxygen demand (BOD) and chemical oxygen demand (COD) -- the amount of organic and non-organic materials present as determined by a specific test. Examples include:

It does not seem these cooling towers are covered by Clean Air Acts -- discussed in the next lecture.

But in this century, chemical industry sees regulations coming & recognizes standard EPA protocols are ineffective in assessing air emissions.

Differing treatments illustrates the difference between regulated utilities and companies under regulations for which monitoring has not been developed.

Environmental Impact of New Power

Building anything new requires Environmental Impact Statement: so onerous as to undermine their effectiveness. Indeed Congress is making efforts to cut them back, not in a very thoughtful way. Regardless of the politics, there are valid concerns.

These concerns focus most dramatically for proposals to building several power plants at one location for any of several reasons:

    1. Economies of scale,
    2. Availability of fuel (e.g., huge coal seam),
    3. Inexpensive land not suitable for other purposes (in the eye of the developer).

  1. Construction. For a large project, a factory may be constructed to produce some parts that would be hard to transport, especially to a remote site.
  2. Boomtown syndrome. Such a large construction poses severe logistic problems. US workers aren't willing to be away from family and creature comforts for long periods. Is it sensible to create a society infrastructure that would largely vanish?
  3. Environmental effects. A large complex of power plants could have unexpected consequences. While new designs need less water, still there might be significant need, especially including the staff necessary to maintain and run the power plants.
  4. Net energy gain. Over the long term is this economically sensible?

Pollution -- ever looming topic not mentioned today -- is next.


Utilities Affect Environment
<http://www.physics.ohio-state.edu/~wilkins.5/energy/Resources/Lectures/util-environ.html>
[Friday, 15-Dec-2017 11:07:01 EST]
Edited by: wilkins@mps.ohio-state.edu on Thursday, 11-Oct-2007 09:31:13 EDT