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Chemical Engineering Science 63 (2008) 782 – 790
www.elsevier.com/locate/ces
Evaluation of mercury sorbents in a lab-scale multiphase flow reactor, a
pilot-scale slipstream reactor and full-scale power plant
Jiang Wu a,b , Yan Cao a , Weiguo Pan b , Minqiang Shen b , Jianxing Ren b , Yuying Du b , Ping He b ,
Du Wang b , Jingjing Xu b , Andy Wu a , Songgeng Li a , Ping Lu c , Wei-Ping Pan a,∗
a Institute for Combustion Science and Environmental Technology, Western Kentucky University, KY 42101, USA
b School of Energy and Environmental Engineering, Shanghai University of Electric Power, Shanghai 200090, PR China
c School of Power Engineering, Nanjing Normal University, Nanjing 210042, PR China
Received 19 September 2006; received in revised form 22 August 2007; accepted 13 September 2007
Available online 6 October 2007
Abstract
Due to its adverse effects on human health and ecosystem, mercury emission from the coal-fired utility boiler has been generating more
and more concern. Sorbent injection upstream of the electrostatic precipitator (ESP) or bag-house has been deemed one of the recommended
mature technologies to reduce mercury emission. Before a sorbent is used in practice, its mercury capture ability needs to be evaluated, but has
until recently only been demonstrated in bench-, pilot- or full-scale experiments separately. In this paper, a lab-scale multiphase flow reactor
and a pilot-scale slipstream reactor were set up and conducted such evaluation on the two scales. After that, some kinds of sorbents were
injected at a full-scale power station. The experimental results show that the lab- and pilot-scale reactor systems in this paper can provide
accurate information of sorbent evaluation under flue gas atmosphere. There was significant difference between the mercury removal efficiency
of tested sorbents, varying from 98.3% down to 23%. SO2 in the flue gas was shown to inhibit mercury oxidization and capture. The sorbents
have higher mercury capturing efficiency with higher injection rate and longer residence time when other conditions were held constant. In
the pilot-scale, four injection ports vertical to the flue gas flow direction could help improve mixture of sorbent and flue gas so that the
mercury removal efficiency became higher. The pilot-scale data can be used to predict the full-scale results. Some of the chemical and physical
mechanisms responsible for the mercury removal of the sorbents were identified.
䉷 2007 Elsevier Ltd. All rights reserved.
Keywords: Mercury; Removal efficiency; Evaluation; Mercury sorbent; Lab-, pilot- and full-scale; Prediction
1. Introduction
As reported by the U.S. Environmental Protection Agency
(EPA), the Canadian Council of Minister of Environment
(CCME) and the European Commission, the major anthropogenic source of mercury emissions, which are among the
most toxic pollutants to human health and the ecosystem, is
from coal-fired power plants (Brown, 1999; US EPA, 1998;
Pavlish et al., 2004; Keating et al., 1997). Coal contains naturally occurring mercury that varies in concentration with both
the type of coal and its place of origin. The U.S. EPA has
determined that mercury emitted from utility power plants
∗ Corresponding author. Tel.: +1 270 745 2272; fax: +1 270 745 2221.
E-mail address: wei-ping.pan@wku.edu (W.-P. Pan).
0009-2509/$ - see front matter 䉷 2007 Elsevier Ltd. All rights reserved.
doi:10.1016/j.ces.2007.09.041
should be controlled and it has set the final regulation on mercury emission from coal-fired power generation on March 15,
2005 (US Environmental Protection Agency, 2005). This decision will affect both economic and environmental aspects of the
U.S. U.S. EPA announced the Clean Air Interstate Rule (CAIR)
that will cap emissions of sulfur dioxide (SOx ) and nitrogen
oxides (NOx ) and also mercury (Hg) from coal-fired power
plants. This is a market-based cap-and-trade program, which
will reduce electric utility mercury emissions by nearly 70%
from 1999 levels when fully implemented. Sorbent injection
upstream of the ESP or bag-house is one of the recommended
methods for mercury emission control. Sorbent injected into
the flue gas ducts absorbs both of the elemental and oxidized
mercury in flue gas, then the ESP captures the sorbent and fly
ash simultaneously. However, the mercury capturing efficiency
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J. Wu et al. / Chemical Engineering Science 63 (2008) 782 – 790
of sorbents is extremely important to avoid increasing the ESP
load and to control the cost of adsorbent. Before a sorbent
is used in practice, its mercury capturing ability needs to be
evaluated. However, such evaluation has until recently only
been demonstrated in bench-, pilot- or full-scale experiments
separately (Cao et al., 2004; Wu et al., 2006a,b; Yan et al.,
2004). In this paper, a lab-scale multiphase flow reactor and a
pilot-scale slipstream reactor were set up and evaluated mercury
capture by the injection of some commercial sorbents. After
that, some kinds of sorbents were chosen to inject at a full-scale
power station to test their mercury capturing efficiency.
2. Experimental
Two phases of testing were conducted on the lab-scale multiphase flow reactor to evaluate the mercury capture efficiency of
the commercial sorbents. In the first phase, elemental mercury
generated by a special Cav-Kit䉸 , which provides a stable mercury concentration, was introduced to the lab-scale multiphase
flow reactor. An on-line Hg analyzer, semi-continuous emission
monitor (Hg-SCEM) (Kellie et al., 2004; Wu et al., 2005), was
adopted to get the quasi-real-time mercury concentration in the
flue gas. The change of the mercury concentration with sorbent
injection was monitored. The adopted Hg analyzer uses gold
amalgamation cold-vapor atomic fluorescence to measure Hg
(0) concentrations. A proprietary flue gas-conditioning system
was used to remove acid gases and reduce any Hg (2+) present
to Hg (0) for subsequently measuring total mercury. The online instrument measures Hg (0) and Hg (T) continuously by
switching from channel to channel.
The selected bituminous coal ash was injected together with
the sorbents into the lab-scale reactor so that the real working
conditions of the sorbents were simulated. The sorbent feeding and ash separation are very important for the experiments.
The feeding system was optimized and suitable transfer gas
was added so that the sorbent could be injected smoothly, and a
cyclone and inertial filter were added to remove the ash. Compressed air and simulated flue gas consisted of 9.8% of O2 ,
9.5% of CO2 and 1106 ppm of SO2 were used as the carrier
gases, respectively, for the lab-scale multiphase flow reactor.
The dimensions of this reactor are listed in Table 1.
The tubular reactor is a 0.05 m I.D. stainless steel pipe. Its
length is 1.22 m. To protect the stainless steel pipe and eliminate its effect on mercury due to possible oxidization and absorption of mercury, a 0.04 m I.D. ceramic pipe is inserted into
this stainless steel pipe. The multiphase flow reactor is heated
up by two electric furnaces. A thermocouple is inserted into
the reactor to monitor the inside temperature. A two-channel
temperature controller is utilized to control the furnaces to the
Table 1
Dimensions of lab-scale multiphase flow reactor
Stainless steel
pipe I.D. (m)
Ceramic pipe
I.D. (m)
Total
length (m)
Length of heating
section (m)
0.05
0.04
1.016
0.914
783
desired temperatures. The gaseous products flowed out the multiphase flow reactor from the outlet in the bottom end of the
stainless steel pipe, where they entered the gaseous sampling
system. The schematic of lab-scale multiphase flow reactor is
shown as Fig. 1.
In the pilot-scale slipstream testing facility, the flue gas was
directly introduced from the air pre-heater duct of utility boiler
to simulate the real flue gas atmosphere for sorbent evaluation.
The pilot-scale slipstream reactor was set up in a selected power
station in Kentucky that burns medium-sulfur bituminous coal.
The pilot-scale slipstream reactor is shown as Fig. 2. The flue
gas was taken out from the duct into the slipstream reactor and
then went back to the duct so that real flue gas was attained.
Some insulation tape was put on the surface of the duct connecting the duct and slipstream reactor. The position and thickness of the insulation tape are adjustable so that the temperature
inside the slipstream reactor can be adjusted to expected value.
The temperature inside the multiphase reactor and the residence
time of the flue gas in the reactor were controlled by adjusting
the insulation tape and use of the cooling fan. The temperature
inside the slipstream reactor kept very well, and the temperature difference between the two ends of the slipstream reactor
was around 1 ◦ C. A special feeder was designed to make the
sorbent enter the reactor easily and distribute evenly.
In the second phase of the experiments on the lab-scale
multiphase flow reactor, the reactor was taken to the power
station where the pilot-scale slipstream reactor was set up. The
flue gas was taken out directly from the air pre-heater duct of
the utility boiler and introduced into the multiphase reactor to
investigate the real flue gas atmosphere for sorbent evaluation.
The flue gas was taken out from the duct into the multiphase
5
10
8
6
9
4
7
16
3
18
17
11
19
2
12
13
14
1
15
1. Simulated flue gas
2. Regulator
4. Cavkit Box
5. Carrier gas
7. Flue gas port
8. Thermocouple
10. Feeder Controller
11.Tube flow reactor
13. Temperature controller 14. Mini cyclone
16. Mercury injection port 17. CEM analyzer
19. Computer
3. MFC
6. Flowmeter
9. Mini screw feeder
12. Electric furnace
15. Solid collection vessel
18. Conversion Unit
Fig. 1. The schematic of lab-scale multiphase flow reactor.
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J. Wu et al. / Chemical Engineering Science 63 (2008) 782 – 790
Pilot-scale Slipstream
Reactor
Lab-scale Multi-phase
Reactor
Flue Gas from Air
Preheater
A-A
A
A
reactor and returned back to the boiler duct through the pilotscale slipstream reactor. The process that introduces real flue
gas into the lab-scale multiphase reactor is shown as Fig. 2.
Several kinds of sorbents were tested at both of the two
phases on the lab-scale multiphase reactor and the pilot-scale
slipstream reactor under different residence time, sorbent injection rate and temperature. The injection system was also
optimized to improve the mixture and capturing process. The
residence time was 1–2.5 s and temperature inside the reactors was 150–170 ◦ C. Sorbent injection changed from 3.85 ×
10−5 .7.7×10−5 kg/m3 in the lab-scale, and 5.13×10−5 .2.57×
10−4 kg/m3 in the pilot-scale experiments.
Mercury Concentration,
ng / Nm3
Fig. 2. The schematic diagram of pilot-scale slipstream reactor.
12000
Start injection
Hg (T)
8000
4000
Stop injecting
0
14:24
16:48
Time (date)
19:12
Fig. 3. The history of Hg concentration changing during sorbent injection on
lab-scale multi-phase flow reactor.
3. Results and discussion
3.1. Definition of mercury adsorption efficiency
During the first phase of the lab-scale experiments on the
multiphase flow reactor, elemental mercury was introduced
with the flue gas into the multiphase flow reactor and residual Hg concentration changed during the sorbent injection. A
typical curve of mercury concentration at the lab-scale multiphase flow reactor during sorbent injection is shown as Fig. 3.
It demonstrates that the mercury concentration begins to drop
as soon as sorbent injection starts and gradually returns to the
original concentration level when sorbent injection ends; however, it is difficult to recover completely possibly because of
fine sorbent build-up on the wall of the reactor and inertial filter.
To describe the phenomena, maximum and minimum mercury
adsorption efficiency can be defined as
max = (Ci − Cmin )/Ci × 100%
(1)
and
min = (C0 − Cmin )/Ci × 100%,
(2)
where Ci is concentration of the injected mercury, Cmin is the
lowest concentration of the mercury in the flue gas after sorbent
injection, and C0 is the recovered concentration of the mercury
after ending sorbent injection. They are shown as Fig. 4.
According to the experimental data, max is a function of
both of the characteristics of a sorbent and the experimental
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J. Wu et al. / Chemical Engineering Science 63 (2008) 782 – 790
Ci
Ci
C0
Cmin
Fig. 4. The schematic of Hg concentration changing during sorbent injection.
conditions. For a given experimental run, a sorbent may have
different max and min . This is possibly a result of the sorbent
sticking to the wall of the reactor or sorbent accumulating in
the horizontal duct of the reactor so that the contact time of the
sorbent with the flue gas is longer than the calculated residence
time.
min can be adopted to study the mechanism of the sorbent
adsorption. When the sorbent is injected into the reactor, it will
be distributed by the aerodynamic effect and start to fly in the
reactor. The mercury inside the reactor will possibly collide
with the sorbent and adhere to the surface of the sorbent, and the
mercury will be oxidized not depending on the characteristics
of the sorbent. The mercury on the sorbent surface will enter
the sorbent inside or just adhere to the surface. This process is
physical and/or chemical sorption, and it can be called flying
adsorption. On the other hand, some sorbent may collide with
the horizontal tube or the wall of the reactor and stick on its
surface and accumulate. The accumulated sorbent will go on
adsorbing mercury as soon as there is a chance since it has more
mercury capturing capability after flying adsorption. This is the
main reason why the mercury concentration could not recover
its original level even after ending sorbent injection for some
time. It will take a very long time for this recovering process.
The yielding mechanism of the difference between max and
min will be described in a separated paper. This paper focuses
on max , and it will be called mercury removal efficiency in
this paper.
During the second phase of experiments on the lab-scale
reactor and experiments on the pilot-scale slipstream reactor,
elemental and oxidized mercury in the flue gas are both introduced into the reactors, and their concentration dropped during the sorbent injection and recovered gradually when sorbent
injection was ended. The specific process is shown in Fig. 5.
The relevant definition of mercury adsorption efficiency is also
applied to the second phase of testing.
3.2. Mass balance calculation
During sorbent injection, mercury was introduced into the
multiphase flow reactor and it would be adsorbed by the injected
sorbent and would stay in bottom container, horizontal tube,
cyclone or went out together with the flue gas. This process is
so complex that mercury mass balance calculation needs to be
conducted to help understand mercury transportation.
The sorbent was injected together with the selected representative bituminous coal fly ash from a power station at a ratio of 4.4:1000, so the mercury in the ash is also a mercury
source in the material balance calculation. The compressed air
785
or simulated flue gas was believed to be mercury-free. The ash
in the horizontal tube was found to be so little that it could
be ignored. Although there was a bottom container and minicyclone to collect the ash, a part of ash still escaped with the
flue gas, so the ratio of injected ash to the sum of bottom ash
and cyclone ash was adopted as a reference.
Based on the above analysis, the mercury mass balance was
calculated as
MHg,
input
= CHg,
gas phase, introduced
× Minjected
MHg,
output
= CHg,
+ YHg,
in ash
ash ,
(3)
gas phase, introduced
+ (YHg,
× (1.0 − ) × Q × t
in bottom ash
× Mbottom
ash
in cyclone ash
× Mcyclone
ash )/(Mbottom ash
ash ) × Minjected ash ,
(4)
+ Mcyclone
R = MHg,
× Q × t + YHg,
output /MHg, input ,
(5)
where the flow rate Q was 8.33 m3 /s and injected ash was
0.05 kg.
The calculated mercury mass balance results for 18 experimental runs of sorbent injection tests show that the recovery
of mercury ranged from 90% to 110%; so the experimental
data are acceptable. On the other hand, most of them are under
100%. This is possibly because the little ash together with the
injected sorbent escaping with the flue gas was fine and contained more mercury; however, such ash entered the exhaust
and was lost to the atmosphere.
During the second phase of experiments on the lab-scale
reactor and experiments on the pilot-scale slipstream reactor,
the ash collected at the bottom and cyclone was insufficient to
analyze the mercury concentration in it; so the mercury mass
balance was not calculated for these experiments.
3.3. Sorbent adsorption efficiencies under different injection
conditions
Different sorbents were injected under varying conditions on
the lab-scale multiphase flow reactor. The residence time was
1–2.5 s, temperature inside the reactors was 150–170 ◦ C, and
sorbent injection rate was 3.85 × 10−5 .7.7 × 10−5 kg/m3 . In
the first phase, compressed air and simulated flue gas were used
as carrier gases in the multiphase flow reactor and real flue gas
was introduced into the reactor during the second phase.
The experimental results in the first phase show that different
sorbents have different mercury removal ability, ranging from
98.3% to 23.0%. A part of the experimental results is shown as
Table 2. It demonstrates that, compared with compressed air,
simulated flue gas inhibited the mercury removal efficiency. It
was possibly because SO2 in the simulated reduced mercury
oxidization and capture. On the other hand, longer residence
time and higher injection rate help improve the mercury removal. The temperature inside the multiphase flow reactor also
has effect on the mercury adsorption efficiency, and sorbent has
higher mercury adsorption efficiency at lower temperature.
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J. Wu et al. / Chemical Engineering Science 63 (2008) 782 – 790
Mercury Concentration, ng / Nm3
786
20000.00
start injection
HgT
Hg (0)
15000.00
10000.00
start injection
5000.00
stop injection
stop injection
0.00
19:12
21:36
0:00
2:24
Time (date)
Fig. 5. The changing history of Hg concentration during sorbent injection in flue gas.
Table 2
Experimental results on the lab-scale multiphase flow rate
Injected sorbent
Carrier gas
Temperature inside
the reactor (◦ C )
Residence time (s)
Sorbent injection rate
(∗ 10−5 kb m3 )
Hg (0) adsorption
efficiency (%)
A1
A1
A1
Compressed air
Simulated flue gas
Simulated flue gas
150
150
150
1
1
2.5
3.85
5.78
7.70
84.1
77.6
82.1
B1
B1
Compressed air
Simulated flue gas
150
150
1
2.5
3.85
7.70
32.9
50.1
C1
C1
Compressed air
Compressed air
150
170
1
1
3.85
5.13
98.3
97.0
Fig. 6. Hg adsorption at difference SO2 in the flue gas.
According to the data in Table 2, we can get Hg adsorption efficiencies at different SO2 concentration in the flue gas
and at different residence time. They are shown in Figs. 6
and 7. The mercury adsorption efficiency of the sorbent C1
changed much when the SO2 concentration changed from
2 ppm in the air to 1000 ppm. For sorbent A1, its mercury
adsorption efficiency reduced from 84.1% to 77.6% when
the SO2 concentration changed from 2 ppm in the air to
1106 ppm in the simulated flue gas even the injection rate was
increased from 3.85 × 10−5 to 5.78 × 10−5 kg/m3 . When residence time increased to 2.5 s and injection rate increased to
7.7 × 10−5 kg/m3 , the mercury adsorption of sorbent A1 in the
simulated flue gas was still lower than that in the compressed
air. It shows that SO2 has big inhibition on mercury adsorption
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J. Wu et al. / Chemical Engineering Science 63 (2008) 782 – 790
787
Fig. 7. Hg adsorption at difference residence time.
Hg adsorption efficiency
120
100
C1
E
B
(%)
80
60
40
20
0
Hg (T) at flue gas
Hg (0) at flue gas
injection condition
Hg (0) at compressed air
Fig. 8. Hg adsorption efficiencies at different injection conditions.
ability. The mercury adsorption efficiency of sorbent B1 increased much when residence extended from 1.0 to 2.5 s;
however, there was little mercury adsorption efficiency change
of sorbent A1 when residence time changed. This is possibly
due to different physical and chemical characteristics of the
sorbents.
In the second phase, real flue gas from the utility duct was
introduced into the multiphase flow reactor. The experimental
data were compared with that in the first phase, and the results
are shown in Fig. 8. The temperature inside the reactor was
170 ◦ C, the residence time was 1.0 s, and the sorbent injection rate was 5.13 × 10−5 kg/m3 . It was shown that different
types of sorbents have different mercury removal efficiency.
This was possibly due to different physical and chemical characteristics of the sorbents. The typical SEM (scanning electron microscopy) results for sorbent C1 are shown as Fig. 9.
The SEM analysis results show that there is bromine as well
as carbon in the sorbent C1. The main content of sorbent
B was carbon and no halogen was in the sorbent B. The
carbon mainly adsorbs the oxidized mercury. It is easy to yield
chemical bond between bromine and elemental mercury, so
bromine can help sorbent to improve elemental adsorption
efficiency. Fig. 8 demonstrates that sorbent C1 mainly adsorb
elemental mercury and sorbent B adsorb more oxidized mercury than elemental mercury, and that the sorbent C1 has much
higher mercury adsorption efficiency than that of sorbent B.
The bromine helps to improve the mercury adsorption efficiency. The sorbent E is a non-carbon based sorbent, and there
were aluminum, silicon, sulfur, chlorine, calcium, manganese,
iron, copper, and other inorganic contents instead of carbon in
it. The main mercury adsorption mechanism of the sorbent E
may be its porosity and specific surface area. At the same time,
chlorine in sorbent E helps capture and oxidize elemental mercury through chemical bond to improve the mercury adsorption
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J. Wu et al. / Chemical Engineering Science 63 (2008) 782 – 790
Fig. 9. SEM results for sorbent C1.
efficiency, so that sorbent E has higher mercury removal ability
than sorbent B. There was also chlorine in sorbent D, which can
help explain why it has high adsorption efficiency on elemental
mercury.
The sorbent has lower mercury adsorption efficiency in real
flue gas than that in the compressed air. This was possibly
because SO2 , NOx and other contents in the flue gas inhibited
the mercury capture and/or oxidization by the sorbent.
During experiments on the pilot-scale slipstream reactor, the
sorbent injection feeder was modified. Before modification, the
sorbent entered the reactor with one port vertical to the reactor
and its injection direction was same as the flue gas flow. After modification, the sorbent entered the reactor through four
ports uniformly distributed at each side of the reactor and their
injection directions were vertical to the reactor and vertical to
the flue gas flow. When the residence time, temperature inside
the reactor and injection rate were kept at 1.0 s, 170 ◦ C and
2.57 × 10−4 kg/m3 , respectively, the experimental results of
different sorbent injection before and after the sorbent injection
feeder modification were shown in Table 3. It demonstrated
that the capture efficiencies of the total mercury and elemental mercury of all the sorbents were improved at different
levels after the sorbent injection system modification. It was
possibly because the modified sorbent injection system
enhanced the mixture between the sorbent and mercury and
lengthened their contact and reaction time, which helped the
process of mercury capturing of the sorbents. On the other
hand, the mercury removal efficiency with 2.57 × 10−4 kg/m3
sorbent injection at the pilot slipstream reactor was similar
to that with 5.13 × 10−5 .7.7 × 10−5 kg/m3 at full-scale. It
may be because the aerodynamic field inside the pilot-scale
slipstream reactor needs to be further optimized to improve
the distribution of the injected sorbent and mercury capturing
process, and it is in consideration.
The changing of mercury removal efficiency with the injection rate on the pilot-scale slipstream reactor is shown in
Fig. 10. It shows that the mercury removal efficiency will
be higher when the injection rate increased; however, the increasing extent became less and less. Different type of sorbent has different mercury adsorption efficiency relative to its
own physical and chemical characteristics. For the purpose
of comparison, the Hg adsorption efficiency of standard PAC,
as derived from the literature (Withum et al., 2005) is plotted in Fig. 10 along with our experimental results. The PAC
was injected at Pleasant Prairie Power Plant (PPPP) combusting sub-bituminous coal. The shape of the PAC curve follows
the same trend as that of the data in the present paper. The
difference in magnitude of Hg removal between PAC and adsorbents C1, D and E is reflective of experimental conditions,
particularly adsorbent injection efficiency. The sorbent C1 is
carbon based and its removal efficiency on mercury total attained on the pilot-scale slipstream reactor with injection rate
of 2.57 × 10−4 kg/m3 is 49.6%. The removal efficiency of
PAC on mercury total at the full-scale power station with injection rate of 7.7 × 10−5 kg/m3 is 56.0%. The absolute difference between them is 6.4% and the relative difference is
11.4%. The injection rate is one of the reasons. The sorbent injection rate of 2.57 × 10−4 kg/m3 at the pilot-scale slipstream
reactor was around equal to 5.13 × 10−5 .7.7 × 10−5 kg/m3 at
the full scale. In fact, the removal efficiency of PAC on mercury total at the full-scale power station with injection rate of
5.13 × 10−5 kg/m3 is 50.0%, which is close to 49.6% at the
pilot scale slipstream reactor. At the same time, the coal type
and boiler operation conditions may make part contribution to
the difference.
Sorbent E was chosen to conduct injection test at a power
station burning bituminous coal. The sorbent injection port
was as before ESP. The mercury concentration changing with
the sorbent injection was monitored by Hg SCEM and Ontario hydro (OH) method. The injection rate was around 7.7 ×
10−5 kg/m3 . The mercury removal efficiency was 41.4% on Hg
(0) and 35.4% on Hg (T). The result attained on the pilot-scale
slipstream reactor with injection rate of 2.57×10−4 kg/m3 was
36.1% and 46.2%. The comparison between them was shown
as Fig. 11. It demonstrates that the data of mercury removal
efficiency attained from pilot-scale slipstream reactor can be
used to predict the results at the full-scale power station. For
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J. Wu et al. / Chemical Engineering Science 63 (2008) 782 – 790
789
Table 3
Experimental data for the pilot-scale tests
Injected sorbent
Hg(VT) capture efficiency (%)
after feeder modification
Hg(VT) capture efficiency (%)
before feeder modification
Hg(0) capture efficiency (%)
after feeder modification
Hg(0) capture efficiency (%)
before feeder modification
C1
D
E
49.6
14.5
36.1
40.1
10.5
28.8
63.5
80.1
46.2
50.1
67.0
36.4
Fig. 10. The mercury removal efficiencies at different injection rates (pilot-scale).
Hg Capturing Efficiency (%)
100
90
Lab-scale with compressed air
Pilot-scale with real flue gas
Power Plant with real flue gas
Lab-scale with simulated flue gas
80
70
60
50
40
30
20
10
0
Hg (0) adsorption
Hg (T) adsorption
injection condition
Fig. 11. The mercury removal efficiencies of sorbent E at different scales.
the removal efficiency on the mercury total, the absolute difference between them is 5.3% and the relative difference is
12.8%. Considering relationship between the sorbent injection
rate (2.57 × 10−4 kg/m3 ) at the pilot scale slipstream reactor
and that at the full scale (5.13 × 10−5 .7.7 × 10−5 kg/m3 ), the
difference may be less.
Together with the comparison result between sorbent C1 injected on the pilot-scale slipstream reactor and PAC injected
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J. Wu et al. / Chemical Engineering Science 63 (2008) 782 – 790
on the full-scale power station, the predicted results are with
around 6% of absolute difference and 12% or less of relative
difference.
4. Conclusions
1. The sorbent injection tests on the lab-scale multiphase
flow reactor and pilot-scale slipstream reactor systems could
simulate the working conditions of the full-scale power plant
and provide accurate information of sorbent evaluation in the
flue gas atmosphere. The data of mercury removal efficiency
attained from pilot-scale system can be used to predict the
results at the full-scale power plant, and the relative difference
is around 12%.
2. There was significant difference between the mercury
removal efficiencies of tested sorbents, varying from 98.3%
down to 23%. It is due to different physical and chemical
characteristics of the sorbents and different reaction conditions. The halogen in the sorbent can help improve the
mercury capture efficiency. The coal type and boiler operation parameters may impact the mercury removal efficiencies.
SO2 in the flue gas may inhibit the mercury oxidation and
capturing.
3. The mercury capturing efficiency of the sorbents is affected by the injection rate, residence time and mixture between
the sorbent and flue gas. The tested sorbents had higher mercury capture efficiency with higher injection rate and longer
residence time when other conditions were held constant. At
the pilot-scale slipstream reactor, four injection ports vertical
to the flue gas flow direction could help improve mixture of
sorbent and flue gas so that the mercury removal efficiency
became higher.
Notation
C
Hg (0)
Hg (2+)
Hg (T)
M
ppm
Q
R
t
Y
concentration, kg/m3
elemental mercury
oxidized mercury
mercury total
mass, kg
Parts per million
flow rate, m3 /s
ratio, %
injection duration time, s
concentration, kg/kg
Greek letter
mercury adsorption efficiency
Acknowledgments
This work was partially supported by the U.S. Department of
Energy (Cooperative Agreement No. DE-FC26-03NT41840),
Key Fund of Shanghai Science Technology Committee (Grant
No. 062312059), Shanghai Pujiang Program (07PJ14045) and
Shanghai Leading Academic Discipline Project (No. P1302).
The authors would like to thank Mr. John Smith, Martin Cohron,
and Stan Herren for their help during the setup of the reactor
systems.
References
Brown, T.D., 1999. Mercury measurement and its control: what we know,
have learned, and need to further investigate. Journal of the Air and Waste
Management Association 49 (6), 628–640.
Cao, Y., Liu, X., Liu, K.L., Yang, H., Riley, T.R., Pan, W.P., 2004. The labscale sorbent injection testing on mercury capture with follow-up solid–gas
mixture. Preparation Paper—American Chemical Society, Fuel Chemistry
49 (2), 918.
Keating, M.H., Mahaffey, K.R., Schoeny, R., Rice, G.E., Bullock, O.R.,
Ambrose, R.B. Jr., Swartout, J., Nichols, J.W., 1997. Mercury study
report to Congress, EPA-452/R-97-003 through 010’U.S. Environmental
Protection Agency. Office of Air Quality Planning and Standard and Office
of Research Development, Research Triangle Park, NC, vols. I–VIII.
Kellie, S., Duan, Y., Cao, Y., Chu, P., Mehta, A., Carty, R., Liu, K., Pan, W.,
Riley, J., 2004. Mercury emissions from a 100-MW wall-fired boiler as
measured by semi-continuous mercury monitor and Ontario hydro method.
Fuel Progressing Technology 85, 487–499.
Pavlish, J.H., Holmes, M.J., Benson, S.A., Crocker, C.R., Galbreath, K.C.,
2004. Application of sorbents for mercury control for utilities burning
lignite coal. Fuel Progressing Technology 85, 563–576.
U.S. EPA,1998. A study of hazardous air pollution emissions from utility
steam generating units: final report to Congress; EPA-453/R-98-004a. U.S.
EPA Office of Air Quality Planning and Standards, U.S. Government
Printing Office, Washington, DC.
U.S. Environmental Protection Agency, 2005. Clean air mercury rules.
Accessed on December 2005. http://www.epa.gov/mercuryrule/index.htm.
Withum, J.A., Tseng, S.C., Locke, J.E., 2005. Mercury emissions from coalfired facilities with SCR-FGD systems. DOE/NETL’s Mercury Control
Technology R&D Program Review, July 12–14, 2005.
Wu, J., Chen, B., Yang, H., Cao, Y., He, B., Wu, A., Pan, W.P., 2005.
Comparison between dry and wet based mercury SCEM. The 30th
International Technical Conference on Coal Utilization and Fuel Systems,
April 17–21, 2005.
Wu, J., Cao, Y., Li, S., Cui, H., Lu, P., Pan, W.P. 2006a. Evaluation of
mercury sorbents on a lab-scale multi-phase flow reactor and on a pilotscale slipstream reactor. 232nd ACS National Meeting, San Francisco,
CA, September 10–14, 2006.
Wu, J., Cao, Y., Wu, A., Li, S., Pan, W.P., 2006b. Evaluation of mercury
sorbents in a lab-scale multi-phase flow reactor. The 9th Annual EPA,
DOE, EPRI, EEI Conference on Clean Air, Mercury, Global Warming
and Renewable Energy. The Westin La Paloma, Tucson, Arizona, USA,
January 22–25, 2006.
Yan, R., Liang, D.T., Tsen, L., Wong, P.Y., Lee, Y.K., 2004. Benchscale experimental evaluation of carbon performance on mercury vapor
adsorption. Fuel 83, 2401–2409.