POWER May 2013 - 86

WATER TREATMENT
5. Low-pressure condenser BP penalty. Again, the trend to low backpressure (BP)
during the trial indicates reduced microbial growth. Source: Nalco Chemical Co.
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0.0
-0.2
-0.4
6/10/12 6/20/12
6/30/12
Prior to trial Trial period
7/10/12 7/20/12
Table 1. The economics of improved
biocide use. The biocide tests
delivered improved condenser performance
and therefore improved plant heat rate, or
reduced fuel consumption for a specified output.
Source: Nalco Chemical Co.
LP turbine
(Btu/kWh)
Pretrial (July 1-11)
During trial
(July 13-14)
Improvement
Heat rate
improvement
Generation during
trial
7/30/12
8/9/12
8/19/12
6. High-pressure condenser BP penalty. Source: Nalco Chemical Co.
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0.0
-0.2
-0.4
6/10/12 6/20/12
6/30/12
Prior to trial Trial period
7/10/12 7/20/12
The data shows that the TTD began to
improve shortly after implementing the
biocide program (Figures 3 and 4). The
design TTD is shown as a horizontal red
line, and data above the line reflect a loss
of condenser performance. During the trial
period, confidence is high that scale control
was maintained at normal conditions
and there was no change in plant air inleakage.
Therefore, the improved TTD is a
good representation of improved microbial
control. More specifically, the data reflects
effective removal and control of biofilm
production. Also, both the LP and the HP
compartments show TTD improvement,
indicating that both compartments were
experiencing significant microbial growth
prior to the trial.
86
8/29/12
Coal heat value
Coal cost
Savings during trial
Cost of chemicals
Net saving during
trial
Net annual savings
Show Me the Money
7/30/12
8/9/12
8/19/12
8/29/12
The BP penalty is calculated from many
parameters, including condenser water inlet
temperature, condenser heat duty, condenser
tube characteristics, design cooling water
flow, and the design condenser cleanliness
factor. In other words, the design backpressure
is determined assuming the condensers
are clean, with no air in-leakage, and are
operating under design conditions. The difference
between the actual turbine backpressure
and the backpressure corrected to design
conditions is the BP penalty, or performance
lost due to heat transfer degradation. Figures
5 and 6 illustrate the BP penalty trends during
the trial. Note that these trends mirror the
TTD results, thus confirming the improved
performance can accurately be attributed to
the biocide trial.
www.powermag.com
The table illustrates the summary data collected
and processed during the test period,
as well as the calculation procedure
used to estimate cost savings. Based on
the plant's data and calculations, during
the trial period of 45 days, the plant realized
savings of $215,000 in reduced fuel
consumption simply by improving cooling
water biocide control. During this same
45-day trial period, costs for the biocide
program were estimated to be approximately
$12,000, producing a net savings
of $203,000 during that 45-day trial period,
or about $1,650,000 for a full year,
assuming constant plant operations.
The impressive trial results enabled plant
staff to obtain approval for installation of a
new biocide feed system. In addition, the
chemical feed configuration will be upgraded
so that there are separate, redundant bleach
and CB70 feed pumps for each cooling tower.
The installed cost of the new system is approximately
$106,000, which is less than the
$203,000 cost savings enjoyed by only Unit
4 during the short 45-day trial period. ■
-Ryan Forbes (rjforbes@aep.com) is
environmental and chemistry supervisor
at AEP's Conesville Station. Kevin Boudreaux
(kjboudreaux@nalco.com) is an
industry technical consultant for Nalco's
Power Business Unit. Aaron Haines
(aahaines@nalco.com) is a Nalco district
representative.
POWER | May 2013
54.8
5.9
48.9
Fuel savings calculation
69.3 Btu/kWh
855,192 MWh
11,577 Btu/lb
$84/ton
$215,006
$12,000
$203,000
C
$1,650,000
M
Y
CM
MY
CY
CMY
K
HP turbine
(Btu/kWh)
32.9
12.5
20.4
Condenser vacuum (in HgA)
Condenser vacuum (in HgA)
http://www.powermag.com
POWER May 2013

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