POWER July 2015 - 42

ENVIRONMENTAL ISSUES
Table 3. Wet FGD stack PS-11 correlation test models. Source: Altech PCME
Confidence
Model
Linear
Polynomial
Logarithmic
Exponential
Power
Correlation
coefficient
>0.85
?
0.989 Yes
0.988 Yes
0.852 Yes
0.769 No
0.98 Yes
interval
half range < 10% ?
7.30% Yes
9.30% Yes
25.75% No
24.99% No
7.32% Yes
cally found at EGUs due to the elevation of the
plant. Of greater significance was the 181 WS
exhaust gas temperature at the measurement
location (350F to 400F), which is much higher
than wet FGD stack temperatures (typically
around 122F) and must be taken into account.
Results from a Plant with Sorbent
Injection
Given limited empirical particle size distribution
data at wet FGD outlets, FGD removal efficiency
versus particle size and the spread in
the reported volume means of calcium hydroxide
sorbent particles (one supplier reports this
as 5.48 microns when measured with optical
methods and 4.27 according to a measurement
Tolerance
interval
half range <25% ?
23.00% Yes
24.70% Yes
81.20% No
146.80% No
24.80% Yes
Note: NA = not applicable: criterion applies only to polynomial model.
technique based on Stokes Law of Sedimentation,
and another has published a volume mean
from optical methods much like a coal fired
EGU ESP outlet, that is to say 2 microns), it is
not known how much the use of hydrated lime
sorbent injection at FGD inlets influences particle
size distribution at the FGD outlet. However,
it is clear that PM CEMS instruments can
detect sorbent carryover and may serve as a
means to optimize sorbent use and minimize
carryover based on data from wet FGD EGU
stacks operating in this manner.
In one such plant the site had a PCME 181
WS PM CEMS providing real-time particulate
data, though it had not yet been correlated
versus a gravimetric reference method.
Min/max
within
allowable
range?
NA
Yes
NA
NA
NA
Does
model
meet all
criteria?
Yes
Yes
No
No
Yes
9. Opacity and flow data. When the
hydrated lime injection was turned off on Nov.
9, 2012, PM concentration as measured by the
PCME 181 WS decreased by approximately 7
mg/m3. Source: Altech PCME
■ PCME 181WS outout, mg/Am3 ■ Hypothetical lime
concentration due to carry over, mg/Am3
■ Stack opacity, % ■ Stack flow volume
45
40
35
30
25
20
15
10
5
100,000,000
90,000,000
80,000,000
70,000,000
60,000,000
50,000,000
40,000,000
30,000,000
20,000,000
10,000,000
8/11/12 9/11/12 10/11/12 11/11/12 12/11/12 13/11/12
Plant abatement included a seasonally operated
SCR, an ESP, a wet FGD, and hydrated
lime sorbent injection prior to the FGD inlet.
Review of data from this site shows that
when the hydrated lime injection was turned
off on November 9, 2012, PM concentration
as measured by the PCME 181 WS decreased
by approximately 7 mg/m3 (see Figure 9).
Load and flow velocity were steady during
this interval, though opacity did decrease
somewhat. However, other similar decreases
in opacity that occurred during intervals with
sorbent injection did not show decreases in
PM readings from the 181 WS. This would
seem to indicate that sorbent carryover was
approximately 7 mg/m3, though the 181 WS
had not been correlated to Method 5 yet, so
its calibration was in question.
Recommendations
An optical PM CEMS can be applied to
wet FGD stacks for meeting environmental
compliance requirements created by consent
decrees with state or local regulators, CAA
Title V CAM plans, and MATS PM limits.
PM CEMS may also be a way for a wet FGD
EGU to gain relief from inlet opacity reporting
requirements if local and state regulatory
authorities are agreeable to the idea.
PM CEMS may also have process control
benefits in wet FGD stacks that inject hydrated
lime at the FGD inlet because they should
be able to detect sorbent carryover. Finally,
use of PM CEMS as a PM CPMS relieves a
source from difficulties associated with creating
elevated particulate levels during a PS11
correlation test. ■
-John Brown (johnb@pcme.com) is
PCME sales manager for Altech PCME.
CIRCLE 18 ON READER SERVICE CARD
42
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mg/Am3 or % opacity
Stack flow volume (SCFH)
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