World Academy of Science, Engineering and Technology 44 2008
The Characteristics of Catalysts for Mercury
Oxidation in Thermal Power Plants
Jung-Bin Lee, Seung-Min Lee, and In Young Lee
II. EXPERIMENTAL STUDY
Abstract—The effects of the mercury oxidation on SCR
A. Catalysts
SCR Catalyst: Three species of commercial SCR
catalysts are prepared by obtaining from Korea, Japan and
Germany. SCR catalysts are composed of V2O5–based TiO2.
The structure of the TiO2 is the anatase type and the range of
vanadate concentration is 0.5~1.2%.
catalysts, Pt catalyst and Cu oxide catalyst supported on heavy oilfired fly ash(HOFA) have been studied in simulated flue gas of
thermal power plant. Substantial differences were observed in the
reaction of the mercury oxidation according to the samples. Two
species of SCR catalysts with 1.1% ~ 1.2% of vanadate showed
about 90% oxidation rate, while the other with 0.5% of vanadate was
about 40%. The mercury oxidation increased with further increasing
HCl concentration of flue gas. In addition, the rates of oxidation of Pt
and Cu oxide were above 80%, while they showed a weak
dependence of HCl concentration.
Pt/HOFA: This catalyst is prepared by impregnation of
support with on heavy oil-fired fly ash (HOFA).
CuO/HOFA: For comparison, Cu-based oxide catalyst is
selected. This catalyst is produced by solid state ion
exchange method using ball mill.
Keywords—Mercury, catalysts, SCR, oxidation.
I. INTRODUCTION
B. Apparatus
The reactor consisted of a vapor-phase elemental mercury
generator (VICI Metronics Inc.), a micro- reactor placed in
inside of an electrically heated oven and an on-line mercury
analyzer. The simulated flue gas consisted of 15% CO2 , 5%
O2, 150ppm NO, 500ppm SO2 and 1.8% H2O and 30 μg/m3
Hg0, balanced with N2 at 350°C. The flow rate is 1.2 l/min.
Mercury analyzer (Mercury/DM-6B, Nippon Instruments
Corporation) was used for measuring the mercury
concentration of Hg0 and Hg+2 in the simulated flue gas.
A
TMOSPHERIC mercury is a global problem with many
natural and anthropogenic emission sources. The coalfired power plant known to the major anthropogenic source of
mercury emissions[1]. Mercury exists in three forms in coalfired flue gas: elemental (Hgo), oxidized (Hg2+), and particlebound (Hg(p)). Hg2+ and Hg(p) are relatively easy to remove
from flue gas using typical air pollution control devices such
as electrostatic precipitators (ESPs) and wet-FGD.
Hgo, however, is difficult to capture, since it is insoluble in
water. Thus, among the technologies being considered for
mercury reduction in coal-fired power plant the combination
of a SCR and a wet scrubber is available to remove Hgo; the
SCR catalyst oxidizes Hgo to Hg2+, and the oxidized mercury
is subsequently absorbed by the scrubber system [2]. Oxidation
catalysts studied to date fall into one of three groups: SCR
catalysts, carbon-based catalysts, and metals and metal oxides
[3]
. Selective Catalytic Reduction (SCR) has been a welldeveloped and commercialized technology for controlling
emissions of NOx from power plant [4]. It is well known that
increasing the emissions of Hg2+ allows for high Hg emission
reduction because Hg2+ or Hg2+-derived species such as HgCl2
can be removed in downstream equipment such as ESPs and
wet-FGD systems. Therefore, the co-benefit of increased Hg2+
through the SCR catalyst is very important to the overall
control of mercury emissions from coal-fired power plant [5].
In the present study, the performances of the SCR catalysts
for the oxidation of mercury are compared with those of Pt
and Cu oxide. Also, the effect of HCl on the mercury
oxidation has been studied in the simulated flue gas.
FLOW
FLOW
H
N
S
N N
N
N
O
A
V
N
FUR
C
FLOW
FLOW
P
Simulated
Gas
FLOW
Reactor
MI
MOISTUR
SYRINGE
A
Mercury
ANAL
Analyzer
H
Mercury
Fig. 1 Schematic diagram of experimental apparatus
III. DISCUSSION
A. SCR Catalysts
The catalytic oxidation of mercury significantly increased
with increasing HCl concentration up to 10ppm. As can be
seen in Fig. 2, the SCR catalysts with 1.1% ~ 1.2% of
vanadate show about 90% of the mercury oxidation at
Authors are with Korea Electric Power Research Institute, Daejeon, Korea
(phone: 82.42.865.5271; e-mail: [email protected]).
256
World Academy of Science, Engineering and Technology 44 2008
IV. CONCLUSION
10ppm of HCl, while the other with about 0.5% of vanadate
is under 40%. It has been found that the amount of vanadate
has the greatest effect with the mercury oxidation. Besides
the amount of vanadate, the mercury oxidation rate is known
to be affected by the physicochemical properties such as pore
size distribution of TiO2, and the structure of V2O5 on the
catalyst surface.
The characteristics of the mercury oxidation over SCR
catalysts, Pt catalyst and Cu oxide catalyst supported on
heavy oil-fired fly ash(HOFA) have been investegated in this
study. The rates of mercury oxidation on SCR catalysts
significantly increase with increasing the amount of vanadate.
Also, it is found that the mercury oxidation rates of the SCR
catalysts more depend on HCl concentration than those of
Pt/HOFA and CuO/HOFA.
100
M ercu ry Ox id atio n (% )
90
80
REFERENCES
SCR #1(1.2%vanadate)
70
[1]
SCR #2(1.1%vanadate)
60
SCR #3(0.5%vanadate)
[2]
50
40
[3]
30
[4]
20
[5]
10
0
5
10
15
20
HCl conc.(ppm)
Fig. 2 Effect of HCl concentration on the SCR catalysts for the
mercury oxidation
B. Pt and Cu Oxide
The oxidation of Hg0 over Pt with HOFA supporter was
compared with that of CuO/HOFA in Fig. 3. The behaviors of
Pt/HOFA and CuO/HOFA are qualitatively similar to those of
the SCR catalysts. The maximum mercury oxidation rate is
about 98% of CuO/HOFA. The catalytic mercury oxidation is
increased with increasing HCl concentration up to 10ppm as
the SCR catalysts. However, their oxidation rates are less
dependence of HCl concentration than the SCR catalysts.
100
90
H g O x i d a t i o n (% )
80
70
60
50
1.0%CuO/HOFA
40
1.0%Pt/HOFA
30
20
10
0
5
10
15
20
HCl conc.(ppm)
Fig. 3 Effect of HCl concentration on Pt/CuO catalysts for the
mercury oxidation
257
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