POWER May 2015 - 56

FUNDAMENTALS
Best Practices for Maximizing
Condenser Efficiency
Sometimes overlooked and underappreciated, a power plant condenser can
make or break your efficiency and power delivery goals. Understanding
how important a role your condenser plays is a good step toward greater
heat rate awareness.
Una Nowling, PE
A
s part of a university class on power
generation systems that I teach, I
show my students a Sankey diagram
of the energy flow of the U.S. electrical
generation system (Figure 1). Sankey
diagrams are wonderful creations, which
allow an easy visualization of a complex
set of inputs and outputs to a system, as
well as the relative impacts of these flows.
When one views the Sankey diagram created
by the U.S. Energy Information Administration
(EIA) one is immediately struck
by the large output of the graphic labeled
" conversion losses. "
Last year, one of my students raised her
hand and asked me, " So, that giant section of
the diagram is all wasted energy? "
" Yes, " I replied, " although some of it is
necessary due to thermodynamic limits. For
a typical Rankine-cycle power plant, the condenser
dumps more than 50% of the input
heat to the environment. "
" But that's horrible! " she replied, with a
rare passion from students (especially when
taking a late-night class, when many students
are somnolent). " Can't we do something
about it? "
I paused, and then nodded to her, " Perhaps
you've just found your calling. "
An e-mail from her a year later revealed
that, rather than entering my world of power
plant efficiency, she had instead taken work
designing roller coasters for a theme park
chain. Well, you can't win 'em all.
And, unfortunately, many steam power
engineers also feel as if they can't win the
battle to make their plants more efficient.
The multiple pressures of emissions regulations,
budget cuts, and competition with gas
turbines and renewables can leave Rankinecycle
power engineers feeling that efficiency
improvements are not even on the proverbial
back burner; instead, they've been put into a
plastic bag and stuck in the deep freeze.
56
Coal
16.54
Fossil fuels
25.65
Natural gas
8.73
Petroleum
0.28
Other gases
0.11
Nuclear electric power
8.27
Renewable energy
5.07
Other
0.18
Net imports of
electricity
0.18
Gross generation of
electricity
14.65
Net generation of
electricity
13.85
Energy consumed to
generate electricity
39.17
Conversion losses
24.52
Plant use 0.80
T & D losses and unaccounted for
0.95
Residential
4.75
End use
13.07
Commercial
4.57
Industrial
3.26
Transportation
0.03
Direct use
0.48
www.powermag.com
POWER | May 2015
That attitude leads to missed opportunities,
which is why this article focuses upon
one of the components that accounts for part
of the significant energy losses in our power
generation system-the condenser. You'll
learn ways in which both condenser performance
and operation could be improved to
help position a Rankine-cycle power plant to
compete more effectively within the turbulent
power generation environment most of
us face.
Condenser Fundamentals
In a typical steam power plant, steam is sent
to various stages of the turbine in order to
produce power. After the steam exits the
final stages of the turbine, where it has no
more energy to be economically converted
into power, it must be condensed back into
a liquid in order to allow it to be pumped to
the feedwater heaters, and subsequently the
boiler. In basic operation, the condenser is a
relatively straightforward device:
■ Low-energy steam or saturated steam enters
a chamber filled with rows of heat exchanger
tube banks.
■ Cooling water is passed through the inside
of the heat exchanger banks, and heat is
transferred from the steam to the cooling
water.
■ The steam condenses and is collected in the
hotwell in the bottom of the condenser.
■ The cooling water is either dumped to the
environment (in an " open-loop " system)
or circulated to cooling towers for re-use
(in a " closed loop " system).
Some power plants utilize a different
method of heat transfer, where the low-energy
steam is passed inside heat exchanger
tubes exposed to the air, and forced-draft
fans blow air over the tubes to extract heat
and condense the steam. These air-cooled
1. So much wasted energy. Although basic thermodynamic laws prevent recovery of
much of the conversion losses, as shown in this Sankey diagram of 2013 U.S. data, many opportunities
remain for improving power plant efficiency. All values are in quadrillion Btu of energy.
Source: U.S. Energy Information Administration

http://www.powermag.com

POWER May 2015

Table of Contents for the Digital Edition of POWER May 2015