POWER October 2011 - 70

MERCURY REMOVAL
above the first layer of catalyst. This gas
contains an adequate amount of ammonia
for the de-NOx process, so no halogen injection
was used during the testing.
In addition to mercury oxidation, inlet
and ammonia slip are meaand
outlet NOx
sured simultaneously in order to ascertain
the interaction between mercury oxidation
and de-NOx
intervals. The commercial ammonia (NH3
mole ratio.
injection system placed at the SCR inlet
flue was injected at the commercial NH3
NOx
at various conditions and time
)
/
Each layer of SSR catalyst is equipped
with air sootblowers, which are operated
automatically or at user-specified intervals.
The SSR is also equipped with electrical
heaters to keep the same temperature
across all catalyst layers. An induced-draft
(ID) fan and gas flow control damper is
provided at the SSR outlet in order to allow
adjustment of the amount of gas flow
through the SSR. Instrumentation is provided
in the SSR at various locations to
measure temperature, catalyst pressure
drop, and total gas flow. A local control
panel is used to provide user interface at
the SSR, and a programmable logic controller
is included for communication with
the plant distributed control system. All of
this data is acquired and stored on an hourly
basis for future trending and analysis.
Table 1 show the representative coal and
flue gas data from this testing. Based on
measurements taken during about 1,000
hours of operation, hydrochloric acid
(HCl) concentration in the flue gas was
very low (1 to 4 ppm) due to low chlorine
content (33 mg/kg) in the PRB coal, which
is a good representation case for mercury
oxidation for a low-chlorine coal-fired
power plant.
To address the primary objective of this
test program, mercury sampling was periodically
conducted at test ports throughout
the test program. The SSR is equipped
with test ports at the inlet, outlet, and an
intermediate point for performing measurements
using the Ontario Hydro Method.
Along with mercury speciation, other
measurements simultaneously recorded
include HCl concentration at the SSR inlet,
ammonia and NOx
concentration at the
SCR inlet and outlet, and total gas flow.
The mercury sampling activities in this
test program were divided into five major
events: January, April, July, and December
2006 and April 2007. Figure 4 summarizes
Hg speciation profiles at each sampling
point across the SSR.
One of the major objectives of this SSR
testing is to quantify the mercury oxidation
rate over a long period. The SSR dem70
2.
Hg0 oxidation of TRAC catalyst at the Hitachi pilot-scale test facility.
Source: Hitachi Power Systems America Ltd.
Conventional TRAC
100
90
80
70
60
50
644
680
716
Temperature (F)
3. Schematic of SSR test configuration. Source: Hitachi Power Systems America Ltd.
Boiler
De-NOx
SSR pilot
TF
1st layer
SCR
reactor
(actual)
DP
SSR
2nd layer
3rd layer
AH
fan
WFGD
DESP
Stack
752
788
TRAC
TF
ID
Control
valve
4th layer
Table 1. Coal and flue gas analysis during slipstream reactor testing.
Source: Hitachi Power Systems America Ltd.
Coal analysis
Heating value (Btu/lb as received)
Moisture (% as received)
Ash (% as received)
Sulfur (% as received)
Chlorine (ppm)
Hg (ppm)
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8,280
30%
5.2%
0.3%
33
0.1
POWER | October 2011
Inlet NOx (ppm)
O2 (% dry)
CO2 (% dry)
H2O (%)
HCl (ppm)
Flue gas analysis
260-300
2.9
15
12.6
1-4
Hg oxidation (%)
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POWER October 2011

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