POWER August 2010 - 60

MERCURY REMOVAL
4. Low HCl operation. Advanced SCR catalysts demonstrate better mercury oxidizing
levels over time. Data were taken at 5 ppm HCl and 700F. Source: Cormetech Inc.
Advanced, fresh
100
80
60
40
20
Increasing catalyst potential or residence time
5. High HCl operation. Advanced SCR catalysts, at high levels of HCl (65 ppm) in the
flue gas, also exhibit improved mercury oxidizing potential over time. Data were taken at 757F.
Source: Cormetech Inc.
Advanced, fresh
100
80
60
40
20
Increasing catalyst potential or residence time
supplemented with additional testing as
needed. The net result will allow the user
to assess the best method(s) to achieve the
desired performance requirements at the
lowest total ownership cost.
Catalyst Advancements for
Increased Mercury Oxidation
We have presented many of the factors that
affect the rate and amount of mercury oxidation
in an SCR catalyst. As discussed,
two of the larger influences are halogen
content and temperature.
Mitsubishi Heavy Industries and
Cormetech have developed an advanced
catalyst tailored to oxidize mercury to
high levels under challenging conditions
involving high temperatures and low HCl
60
concentrations, both of which negatively
impact mercury oxidation across conventional
SCR catalysts.
Let's now examine the performance differences
between advanced Hg oxidation
SCR catalysts and standard SCR catalyst
products with respect to halogen content
and temperatures.
Aged Catalyst Performance. Figure
3 shows an example of actual field performance
versus predictive models for
an aged SCR catalyst at varying levels
of HCl in the flue gas. At a temperature
of approximately 690F, the percentage of
oxidized mercury at the SCR outlet measured
during actual tests on aged catalyst
ranged from 75% to 90% over a range in
flue gas HCl concentration of 10 to 25
www.powermag.com
Advanced, est. @ 16k hr
Current, fresh
Current, 16k hr
Advanced, est. @ 16k hr
Current, fresh
Current, 16k hr
Information gathered
through a combination
of significant
laboratory testing
and field data analysis
over the past
decade has resulted
in the development
of highly predictive
performance models.
ppmvd. The predicted levels of oxidized
mercury increase to >95% levels at higher
levels of HCl.
Advanced Catalyst Performance.
Figure 4 illustrates the performance of
the advanced Hg oxidation catalyst versus
standard catalyst at extremely low
HCl concentrations and moderate flue gas
temperatures (5 ppmvd and 700F). The
advanced catalyst exhibited high levels of
oxidized mercury for both fresh and aged
catalyst and shows a substantial increase
over an existing standard catalyst.
In Figure 5, the percentage of oxidized
mercury is shown, as expected, to be greater
due to the higher HCl concentration, despite
a higher temperature (65 ppmvd and
757F).
Planning for the Future
It's reasonable to assume that the performance
of mercury reduction technologies
and other co-benefits, such as we've
discussed here, will be used to set future
maximum achieveable control technology
regulations. Regardless of future limits,
we suggest that you adopt a holistic approach
for optimizing mercury reduction
that considers all the components in your
air quality control system, from the coal
pile through the stack. Only then will you
meet your goal of maximizing mercury
removal while minimizing overall system
and operating costs. ■
-Scot Pritchard (pritchardsg@
cormetech.com) is vice president,
sales & marketing for Cormetech Inc.
Masashi Kiyosawa (masashi_
kiyosawa@mhi.co.jp) is manager, environmental
equipment team, Mitsubishi
Heavy Industries, Nagasaki, Japan.
Katsumi Nochi (katsumi_nochi@mhi
.co.jp) is senior researcher, Chemical
Process Laboratory, Mitsubishi Heavy
Industries, Hiroshima, Japan.
POWER | August 2010
Oxidized Hg (%)
Oxidized Hg (%)

http://www.co.jp http://www.powermag.com

POWER August 2010

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