Mercury Control by Injection of Activated Carbon
and Calcium-Based Sorbentc
EPA/600/A-97/011
S.V. Krishnan, Acurex Environmental Corporation, 4915 Prospectus Drive, P.O. Box 13109,
Research Triangle Park, NC 27709
Brian K. Gullett* U.S. Environmental Protection Agency, Air and Energy Engineering
Research Laboratory, Research Triangle Park, NC 27711
Wojciech Jozewicz, Acurex Environmental Corporation, 4915 Prospectus Drive, P.O. Box
13109, Research Triangle Park, NC 27709
ABSTRACT
Injection of activated carbon is among the technologies used for control of mercury (Hg)
emitted during municipal waste combustor (MWC) operation. Depending on the form of Hg
present and amount of activated carbon injected, varying levels of control have been achieved
in field units. However, under favorable laboratory conditions, we have found that calcium
(Ca)-based sorbents can be as effective as some of the activated carbons in controlling Hg
emissions.
This paper compares the capture of both elemental mercury (Hg°) and mercuric
chloride (HgCI2) vapor by different types of commercially available activated carbons and Ca-
based sorbents, including quicklime (CaO) and hydrated lime [Ca(OH)2], Comparisons were
made at two temperatures in bench-scale reactors, with other conditions remaining identical.
Our results showed that, at the lower temperature (100 °C), Ca-based sorbents capture
incoming HgCI2 as well as the activated carbons. At the higher temperature (140 °C),
activated carbons showed relatively higher capture of HgCI2 than Ca-based sorbents.
However, only activated carbons exhibited significant capture of Hg° at either temperature.
Because field measurements as well as equilibrium predictions show that Hg exists in MWC
flue gas primarily as HgCI2, the results indicate the possibility of injecting CaO or Ca(OH)2
along with activated carbons to reduce operating costs in controlling Hg emissions,
INTRODUCTION
Emissions of Hg vapor from MWCs and coal-burning utilities may present significant
health and environmental hazards. The Clean Air Act Amendments of 1990 (Title III, Section
* Author to whom correspondence should be addressed.
1
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112[b]£1 ]) require major sources to use maximum available control technology (MACT) to
reduce Hg emissions. Existing flue gas desulfurization systems have been shown to control
Hg emissions to some extent in both MWCs and coal combustors (7,2). To achieve higher Hg
removal efficiencies, however, additional systems, such as an activated carbon sorption
process (1,2), may be required.
Hg is known to exist in flue gas as either Hg° or an oxidized form [HgCI2 or mercuric
oxide (HgO)] (3). Figure 1 shows the equilibrium concentration of Hg species at 7.7% oxygen
(02), 7.7% carbon dioxide (C02), 4% water vapor (H20), 400 ppm sulfur dioxide (S02), 19.5
ppb Hg, and the balance nitrogen (N2). The results have been obtained by employing the
thermodynamic code CET89 (4). As is seen, for all three concentrations of hydrogen chloride
(HCI), Hg° exists at the higher temperatures typically found in the combustor or economizer of
a MWC or power plant. At lower temperatures, Hg exists only as HgCI2. At higher
temperatures, negligible amounts of HgO are formed. Similar equilibrium distributions of Hg
species were obtained by Schager (5) and Lancia et al. (6). Also, it can be seen from Figure
1 that, in flue gases with relatively higher HCI concentration, HgCI2 exists at relatively higher
temperatures. Moreover, the results in Figure 1 show that, even in MWC flue gases with low
HCI concentrations, Hg exists primarily as HgCI2.
Injection of activated carbon either upstream or downstream of a spray dryer (SD) has
been shown to reduce Hg emissions in both MWCs (1) and coal-fired utilities (2). Typically,
these activated carbon processes operate at injection temperatures of 100-200 °C. Provided
that equilibrium is attained rapidly by the Hg species prior to contacting activated carbon,
HgCI2 would be the dominant species at temperatures below 500 °C (see Figure 1). Non-
attainment of equilibrium by the different Hg compounds would imply the presence of Hg° at
100-200 °C. The control of Hg emissions has been found to be strongly dependent on the
form of Hg. Several tests have shown that relatively low amounts of Hg° are captured
compared to the oxidized forms (5,7). Therefore, it is necessary to understand the sorption
process as well as the mechanism of capturing both HgCI2 and Hg° by activated carbons at
these temperatures.
In previous investigations (8,9), we studied the sorption of Hg° by three activated
carbons, namely PC-100, FGD, and HGR. The first two are thermally activated, while HGR is
activated by elemental sulfur (S) impregnation. Our results showed that specific locations
(active sites) in PC-100 and FGD cause sorption of Hg°. However, upon exposure to heat
2
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(140 °C in N2) prior to Hg° sorption tests, the active sites were found to be either deactivated
or destroyed, thus leading to significantly lower capture of Hg°. Sorption of Hg° in HGR at
140 °C occurs primarily through the reaction of S and Hg° while at 23 °C, sorption occurs in
non-S sites residing on the external surface. Heating HGR did not cause a loss in its sorption
capacity, unlike PC-100 and FGD. In addition to tests studied by Jozewicz et al. (8) and
Krishnan et al. (9), previous studies by Gullett and Jozewicz (10) explored the effect of
surface area and porosity of activated carbons on Hg° capture. Unlike the studies on sorbent
reactivity towards Hg°, there is very little laboratory data in the literature on the capture of
HgCI2 by activated carbons. Therefore, experiments were performed as part of this study to
quantify and understand sorption of HgCI2 by activated carbons. Sorption of Hg° by these
sorbents under identical conditions was also studied for comparison with the capture of HgCI2.
Although activated carbons are injected in the temperature window of 100-200 °C with
the specific intent of Hg capture, injection of CaO or Ca(OH)2 to remove S02 emissions may
also capture Hg vapor from MWC flue gas. For instance, Hg reduction by injection of Ca(OH)2
was observed by Gullett and Raghunathan (11) in their pilot-scale unit. However, the species
of Hg captured by Ca(OH)2 in their study are unknown, as are the conditions where capture
occurred in their unit (e.g., temperature), Lancia et al. (6) investigated adsorption of HgCI2 on
Ca(OH}2 particles in a simulated MWC and observed high removal efficiencies of HgCI2 by
Ca(OH)2 particles. As part of this study, we investigated the capture of both Hg° and HgCI2 by
CaO and Ca(OH)2 at two temperatures (100 and 140 °C) to determine the feasibility of
injection of CaO or Ca(OH)2 in controlling total Hg emissions.
The sorption of Hg° and HgCI2 by PC-100, FGD, HGR, CaO, and Ca(OH)2 at two
temperatures is investigated in this study. Also, sorption of Hg° and HgCI2 by fresh and heat
treated activated carbons has been investigated in an effort to identify the active sites
participating in capturing Hg° and HgCI2.
SORBENT CHARACTERISTICS
Of the five types of sorbents tested for Hg° and HgCI2 capture, three (PC-100, FGD,
and HGR) are activated carbons. PC-100 and FGD are thermally activated carbons while
HGR is sulfur-activated with roughly 7% (by weight) S, Details on their physical
characteristics (pore size distributions, particle size ranges, pore volumes, and surface areas)
and a chemical analysis of each are given in an earlier publication (9). Reagent-grade
3
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hydrated lime supplied by Fischer Scientific was the source for Ca(OH)2. Approximately 1 g of
the Yorktown hydrated lime was calcined at 1,000 °C for 1 h in a flow of N2 to produce CaO
used in our experiments. I he Brun3U6r"Enini0tt""l eller ^BEET*^ surfscs siress Os|OH|2 3nd
CaO were 13 and 27 m2/g, respectively. Compared to surface areas of 1000 m2/g for PC-100
and HGR, and 500 m2/g for FGD, the Ca-based sorbents have an insignificant surface area.
EXPERIMENTAL APPARATUSES AND PROCEDURES
Hg° Capture Studies
The setup used for studying Hg° capture has been described in detail elsewhere
(8,9,10). In these experiments, approximately 100 mg of the sorbent was placed between
glass wool supports in a glass reactor. A flow of 200 cm3/min of N2 containing 30 ppb Hg°
was the inlet stream. An online ultraviolet (UV) detector (Ametek, Model 400) recorded the
Hg° concentration. The calibration of the UV detector and the experimental procedures have
also been explained elsewhere (8,9,10). Because an online analyzer is used to measure
breakthrough Hg° concentration, a simple mass balance yields the percentage of Hg°
captured by the sorbent.
HgCl2 Capture Studies
Figure 2 shows the schematic diagram of the apparatus used for studying HgCI2
capture. A diffusion vial filled with HgCI2 powder is the source of a constant supply of
gaseous HgCI2. The carrier gas is pure N2 flowing at 200 cm3/min. Depending on the
temperature of the furnace encasing the diffusion vial, varying levels of HgCI2 concentration in
the carrier gas can be obtained. In all our experiments, the HgCI2 concentration in the N2
stream was approximately 30 ppb.
While the reactor containing the sorbent is being heated, the HgClj/^ stream
bypasses the reactor. Once the desired conditions have been obtained, the three-way valve
is switched to direct flow through the reactor. At the end of a fixed duration experiment, the
three-way valve is used to divert flow away from the reactor, and each stage of the reactor is
analyzed for total Hg content. Unlike experiments performed to study Hg° capture, there is no
online analyzer for HgCI2; hence, batch operations were necessary.
In our experiments to study HgCI2 capture, three stages of sorbent were used. The first
stage, containing the sorbent under study, was exposed to 30 ppb HgCI2 in N2. The second
4
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and the third stages always contained activated carbon, PC-100, because PC-100 showed the
highest capture of HgCI2. Approximately 100 mg of sorbent was loaded in each stage and
was supported by glass wool. The latter two stages ensured that all the generated HgCI2 was
captured. At the end of a run, each stage was analyzed for total Hg. Analysis of the three
stages is necessary to obtain an accurate generation rate of HgCI2 vapor from the diffusion
vial such that the HgCI2 capture efficiency of the sorbent being evaluated (first stage) can be
obtained. The HgCI2 captured is obtained from
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RESULTS
Figure 4 shows the percentage of incoming HgCI2 (30 ppb) captured by PC-100, FGD,
HGR, Ca(OH)2, and CaO at 100 and 140 °C.
All five sorbents show relatively higher capture (>80 %) of HgCI2 at 100 °C (see Figure
4) than at 140 °C (<80%). Activated carbons PC-100 and HGR show comparatively smaller
decreases in HgCI2 captured at 140 °C, whereas activated carbon, FGD, and the two Ca-
based sorbents show significant decreases in HgCI2 captured. Lancia et al. (6) also observed
lower HgCI2 capture by Ca(OH)2 particles at higher temperatures (95% at 100 °C versus 80%
at 150 °C). Because their experimental conditions were different from ours (that is, sorbent
loading, face velocity, HgCI2 concentration, and particle physical characteristics), a direct
comparison of the capture efficiencies cannot be made.
The data in Figure 4 are replotted in Figures 5 and 6 to compare Hg° versus HgCI2
capture at 140 and 100 °C, respectively. Figures 5 and 6 show that all three activated
carbons show relatively higher capture of HgCI2 compared to Hg°. Activated carbon PC-100
after 4 h of exposure (at 140 °C) shows close to 90% capture of incoming HgCI2 compared to
approximately 80% capture of Hg°. However, for longer exposures, PC-100 continues to
capture 90% of incoming HgCI2, whereas the percentage of Hg° captured decreases
continuously. The difference between Hg° and HgCI2 captured by the other activated carbons
is far greater than that of PC-100. For instance, only 20% of incoming Hg° is captured by
FGD (at 140 °C) compared to roughly 60% of HgCI2 after 4 h of exposing FGD to each Hg
species. At the same conditions, HGR captures 60% of incoming Hg° compared to over 90%
of HgCI2 (see Figure 5).
DISCUSSION
Depending on the manufacturing process (activation with nitrous oxide (N20),
ammonia (NH3), or ZnCI2-NH4CI-C02, or heat-treated at 900 °C), activated carbon acquires
properties of a solid base (12). Reactions of gaseous 02with the surface of active carbon at
temperatures somewhat below 100 °C produce 02 complexes which on hydration can form
hydroxyl or other basic groups (13). The large internal surface areas of the activated carbons
may provide sufficient basic sites to capture the acidic HgCI2 by a chemical reaction.
6
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In a previous investigation (9), we observed that sorption of Hg° by thermally activated
carbons PC-100 and FGD occurred via a combination of physisorption and chemisorption at
specific active sites. These active sites were either deactivated or destroyed when the
activated carbons were exposed to a flow of N2 at 140 °C for 4 h (heat-treated) resulting in
lower sorption of Hg°. In the current study, we compared the sorption of HgCI2 with sorption
of Hg° by fresh and heat-treated PC-100. Figure 7 shows the amount of Hg (Hg° and HgCI2)
sorbed by 100 mg of fresh and heat-treated PC-100 after 4 h of exposure to 30 ppb of either
Hg° or HgCI2 at 140 °C. The result is expressed as milligrams of Hg per gram of PC-100.
Figure 7 shows that heat-treatment lowers the sorption of Hg° (roughly by 50%), but does not
affect sorption of HgCI2. This is indicative of different sorption sites for Hg° and HgCI2, which
likely leads to the differences in Hg° and HgCI2 sorption seen in Figures 5 and 6. The basic
sites causing the capture of HgCI2 are not affected by heat treating the activated carbon. On
the other hand, the oxygen functional groups suspected of capturing Hg° (9) are either
depleted or deactivated.
Ca(OH)2 captures high amounts of incoming HgCI2 at 100 °C and moderate amounts at
140 °C (see Figures 4, 5, and 6). At 100 °C, Ca(OH)2 captures close to 90% of incoming
HgCI2. Compared to the activated carbons, Ca(OH)2 used in this study has very little surface
area [500 to 1,000 m2/g for the activated carbons compared to 13 m2/g for Ca^HJJ. Despite
the comparative lack of an internal structure, Ca(OH)2 captures similar amounts of HgCI2 as
the three activated carbons at 100 °C. At 140 °C, Ca(OH)2 captures HgCI2 in amounts similar
to activated carbon, FGD. In the experiments of Lancia et al. (6), similar removals of HgCI2 by
Ca(OH)2 were observed. At both temperatures, however, we found Ca(OH)2 to capture
negligible amounts of Hg° (see Figures 5 and 6). Tanabe et al. (14) have classified CaO to
be a solid superbase. Therefore, in spite of the lack of a large surface area like activated
carbons, the superbasic property of Ca(OH)2 [assuming Ca(OH)2 to have superbasic
properties similar to CaO] causes high capture of HgCI2. The superbasic property of the Ca-
based sorbents, however, does not lead to capture of Hg° to the extent of the activated
carbons.
Thermodynamic predictions obtained in this study as well as studies of Hall et al. (3,
15) and Schager (5) suggest that Hg would most likely be present as HgCI2 in a MWC flue
gas. Bloom et al. (16), based on measurements from actual coal combustor sites, report that
much of the Hg in flue gas appeared to be in the oxidized form. From the high percentage of
7
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HgCI2 capture by CaO and Ca(OH)2 seen in this study, injection of Ca-based sorbents would
likely prove beneficial in capturing high amounts of total Hg in a MWC under favorable
conditions.
Dry scrubbing by spray dryer absorption (SDA) is used in several hundred MWCs and
hazardous waste incinerators (HWIs) (17, 18). Spray dryer plus fabric filter (SD/FF) systems
have shown moderate to high removals of Hg (19). Felsvang et al. (19) report 30 to 50% Hg
removal by SDA systems in MWCs. Gullett and Raghunathan (11) have also shown that
injection of Ca(OH)2 can control Hg emissions in a coal-fired pilot-plant study. Data obtained
from the U.S. Environmental Protection Agency's (EPA's) Biomedical Waste Incineration
(BWI) study (20) show, however, that dry Ca(OH)2 injection/FF- or SD/FF-equipped plants do
not control Hg. Tests at Camden County MWC (1) have shown Hg control ranging from 20 to
90 % without carbon injection. To achieve consistently high Hg control, activated carbon
injection was necessary. Factors which could probably affect Hg control by dry Ca(OH)2
injection are the process conditions -- temperature, Hg species, and physical characteristics of
Ca(OH)2. Although equilibrium calculations predict Hg to be present as HgCI2 in a BWI flue
gas, the apparent contradictions posed by the EPA BWI study (20) emphasize the need for
field speciation.
The results obtained in our study indicate that Ca-based sorbents like CaO and
Ca(OH)2 are effective in controlling only HgCI2 and that activated carbons are needed to
control Hg°. Therefore, high removal of Hg is possible by application of Ca-based sorbents
[similar to results of Felsvang et al. (19) and Gullett and Raghunathan (11)) in flue gases
containing a significant portion of HgCI2and at temperatures below 140 °C. In situations
where both Hg° and HgCI2 are present in significant fractions, CaO or Ca(OH)2 may be
injected along with activated carbons. Such processes where hydrated lime is injected along
with activated carbon (the "Alka/Sorb" and "Sorbalit" processes) are used for treating waste-
to-energy, HWI, and BWI combustion gases (20,21). Careful sampling of the Hg compounds
in a flue gas, accompanied by the results obtained from bench-scale tests of the type reported
in this study, would allow sorbent selection for optimum control of Hg from flue gases where
the bulk of Hg capture occurs in baghouses or electrostatic precipitators (ESPs).
A possible cost optimization in controlling Hg emissions if HgCI2 sorption by activated
carbons leads to lower Hg° sorption would be to carefully "stage" the injection of Ca-based
sorbents and activated carbons. By injecting Ca-based sorbents before activated carbon,
8
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most of the HgCI2 would be captured, leaving only Hg° to be captured by activated carbon.
Therefore, only limited amounts of activated carbon would be necessary to capture the
remaining Hg, leading to potential cost reduction.
SUMMARY AND CONCLUDING REMARKS
Thermodynamic predictions obtained from this study, as well as others including field
data, have shown that Hg exists primarily as Hg° and HgCI2. The capture of Hg° and HgCI2 at
100 and 140 °C by three types of activated carbons and two Ca-based sorbents was
investigated in this study.
In general, all five sorbents studied here showed higher capture of HgCI2 at 100 °C.
The effect of temperature on HgCI2 capture was significant for activated carbon FGD and the
two Ca-based sorbents, CaO and Ca(OH)2. Lowering the temperature had only a small effect
on HgCI2 capture by activated carbons PC-100 and HGR.
Of the two species of Hg investigated, HgCI2 was found to be captured with greater
efficiency than Hg° by all the sorbents studied. Since HgCI2 is acidic, it is captured by the
basic sites in the activated carbons. The basic sites in activated carbon arise due to the
manufacturing process. Despite the lack of surface area in CaO and Ca(OH)2 compared to
the activated carbons, similar amounts of HgClz were captured by both. This is because CaO
is a solid superbase and the mechanism is not surface-limited.
The active sites where Hg° and HgCI2 are sorbed in activated carbons were found to
be different. This was concluded based on our studies comparing sorption of Hg° and HgCI2
by fresh and heat-treated PC-100, Whereas the sorption of Hg° decreased on heat-treating
PC-100 (possibly due to loss of oxygen-related functional groups), HgCI2 sorption was
unaffected.
The high percentage capture of HgCI2 by CaO and Ca(OH)2 indicates that, where
HgCI2 is present in significant amounts in MWC flue gas, dry injection of CaO or Ca(OH)2
could possibly control Hg emissions at favorable process conditions. Where both Hg° and
HgCI2 exist in significant fractions, staged injection (Ca-based followed by activated carbon)
may reduce Hg removal costs. Staging would eliminate competition for HgCI2 between Ca-
based sorbents and activated carbons. Future bench-scale experiments are planned to
investigate simultaneous sorption of Hg° and HgCI2 by activated carbons to study the
feasibility of such a process.
9
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ACKNOWLEDGEMENTS
The authors would like to acknowledge the equipment support provided by Richard E.
Valentine (EPA/AEERL) and the experimental assistance provided by Lisa Adams (Acurex
Environmental Corp.).
REFERENCES
1. D.M. White, W.E. Kelly, M.J. Stucky, J.L. Swift, and M.A. Palazzolo, "Emission Test
Report, Field Test of Carbon Injection for Mercury Control at Camden County Municipal
Waste Combustor," EPA-600/R-93-181 (NTIS PB94-101540): Research Triangle Park,
NC, September 1993.
2. J.G. Noblett, Jr., F.B. Meserole, D.M. Seeger, and D R. Owens, "Control of Air Toxics
from Coal-fired Power Plants Using FGD Technology," In Proceedings: 1993 S02
Control Symposium, Vol. 3, p. 60-1, EPA-600/R-95-015c, February 1995.
3. B. Hall, P. Schager, and 0. Lindqvist, "Chemical Reactions of Mercury in Combustion
Flue Gases," Water. Air. Soil Poll. 56, 3-14 (1991).
4. S. Gordon and B.J. McBride, "Computer Program for Calculation of Complex Chemical
Equilibrium Compositions, Rocket Performance, Incident and Reflected Shocks, and
Chapman-Jouguet Detonations," NASA SP-273; Interim Revision, 1976.
5. P. Schager, 'The Behaviour of Mercury in Flue Gases," STEV-FBT-91-20, Statens
energiverk, Goteborg, Sweden, December 1991.
6. A. Lancia, D. Musmarra, F. Pepe, and G. Volpicelli, Comb. Sci. & Tech. 93, 277-289
(1993).
7. C. Volland, "Mercury Emissions from Municipal Solid Waste Combustion," 84th Annual
Meeting and Exhibition, AWMA, Vancouver, BC, June 16-21, 1991. Paper 91-35.1.
8. W. Jozewicz, S.V. Krishnan, and B.K. Gullett, "Bench-scale Investigation of
Mechanisms of Elemental Mercury Capture by Activated Carbon," paper presented at
the Second International Conference on Managing Hazardous Air Pollutants,
Washington, D.C., July 13-15, 1993.
9. S.V. Krishnan, B.K. Gullett, and W. Jozewicz, "Sorption of Elemental Mercury by
Activated Carbons." Environ. Sci. Technol. 28. 1506-1512 (1994).
10. B.K. Gullett and W. Jozewicz, "Bench-scale Sorption and Desorption of Mercury with
Activated Carbon," paper presented at 1993 International Conference on Municipal
Waste Combustion, Williamsburg, VA, March 30-April 2, 1993.
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11. B.K, Gullett and K. "Raghunathan, 'The Effect of Sorbent Injection Technologies on
Emissions of Coal-based Metallic Air Toxics," In Proceedings: 1993 S02 Control
Symposium, Vol. 3, p. 63-1, EPA-600/R-95-015c, February 1995.
12. K. Tanabe, "Solid Acids and Bases, Their Catalytic Properties," Academic Press: New
York, 1970.
13. M. Smisek and S. Cerny, "Active Carbon. Manufacture, Properties, and
Applications," Elsevier: New York, 1970.
14. K. Tanabe, M. Misono, Y. Ono, and H. Hattori, "New Solid Acids and Bases, Their
Catalytic Properties," Elsevier: New York, 1989.
15. B. Hall, O. Lindqvist, and E. Ljungstrom, "Mercury Chemistry in Simulated Flue Gases
Related to Waste Incineration Conditions," Environ. Sci. Technol. 24(1), 108-111
(1990).
16. N.S. Bloom, E.M. Prestbo, and V.L. Miklavcic, "Fluegas Mercury Emissions and
Speciation from Fossil Fuel Combustion," paper presented at the Second International
Conference on Managing Hazardous Air Pollutants, Washington, D.C., July 13-15,
1993.
17. J.R. Donnelly and K.S. Felsvang, "Joy/Niro SDA-FGC Systems - North American and
European Operating Experience," In Proceedings: 1989 International Conference on
Municipal Waste Combustion, Vol. 4, p. 9C-39, EPA-600/R-92-052d (NTIS PB92-
174697), March 1992.
18. 0. Christiansen et al., "Control of Heavy Metals and Dioxins from Hazardous Waste
Incinerators by Spray Dryer Absorption Systems and Activated Carbon Injection," paper
presented at the Air & Waste Management Association 85th Annual Meeting, Kansas
City, MO, June 21-26, 1992.
19. K. Felsvang, R. Gleiser, G. Juip, and K.K. Nielsen, "Air Toxics Control by Spray Dryer
Absorption Systems," paper presented at the Second International Conference on
Managing Hazardous Air Pollutants, Washington, D.C., July 13-15, 1993.
20. B.J. Lerner, "Mercury Emission Control in Medical Waste Incineration," paper
presented at the 86th Annual Meeting & Exhibition, AWMA, Denver, CO, June 13-18,
1993.
21. J. Blumbach and L-P. Nethe, "Sorbalit - A New Economic Approach Reducing
Mercury and Dioxin Emissions," paper presented at the Air & Waste
Management Association 85th Annual Meeting, Kansas City, MO, June 21-26,
1992.
11
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Figure 7. Effect of heat-treatment (exposing sorbent to a flow of N2 at 140 °C for 4 h prior to capturing Hg)
on Hg° and HgCI 2 capture by PC-100, Figure compares Hg° and HgCk capture by 100 mg of fresh
and heat-treated PC-100 after 4 h of exposure to 30 ppb Hg° or HgCl2 in a flow of 200 cm^/min N2.
16
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_ irir7r TECHNICAL REPORT DATA
¦A hi hiti J_i~ V~ LJ, I 8 (Please read Instructions on the reverse before completi
1, REPORT NO, 2.
EPA/600/A-97/011
3. I
4, TITLE AND SUBTITLE
Mercury Control by Injection of Activated Carbon
and Calcium-based Sorbents
5. REPORT DATE
6. PERFORMING ORGANIZATION CODE
7. AUTHOR(S)
S. V. Krishnan (Acurex), B. K.Gullett (EPA/AEERL),
and W. Jozewicz (Acurex)
8. PERFORMING ORGANIZATION REPORT NO.
9. PERFORMING ORGANIZATION NAME AND AODRESS
Acurex Environmental Corporation
P, 0. Box 13109
Research Triangle Park, North Carolina 27709
10. PROGRAM ELEMENT NO.
11. CONTRACT/GRANT NO.
68-D5-0005
12. SPONSORING AGENCY NAME AND AODRESS
EPA, Office of Research and Development
Air and Energy Engineering Research Laboratory
Research Triangle Park, NC 27711
13. TYPE OF REPORT AND PERIOD COVERED
Published paper; 10/93 - 3191
14. SPONSORING AGENCY CODE
EPA/600/13
15. supplementary NOTES AEERL project officer is Brian K. Gullett, Mail Drop 4. 919/541-
1534. Presented at International Conference on Solid Waste Management: Thermal
Treatment and Waste-to-energy Technologies, Washington, DC, 4/18-21/95.
16. abstract rj-^e paper compares the capture of both elemental mercury (Hg°) and mer-
curic chloride (HgC12) vapor by different types of commercially available activated
carbons and calcium (Ca)-based sorbents, including quicklime (CaO) and hydrated
lime, Ca(GH)2. Comparisons were made at two temperatures in bench-scale reac-
tors, with other conditions remaining identical, (NOTE: Injection of activated carbon
is among the technologies used for control of mercury (Hg) emitted during municipal
waste combustor (MWC) operation. Depending on the form of Hg present and amount
of activated carbon injected, varying levels of control have been achieved in field
units. However, under favorable laboratory conditions, Ca-based sorbents can be as
effective as some of the activated carbons in controlling Hg emissions.) Study results
showed that, at the lower temperature (about 100 C), Ca-based sorbents capture in-
coming HgC12 as well as activated carbons. At the higher temperature (140 C). acti-
vated carbons showed relatively higher capture of HgCl2 than Ca-based sorbents.
However, only activated carbons exhibited significant capture of Hg° at either tem-
perature. Because field measurements and equilibrium predictions show that Hg in
MWC flue gas exists primarily as HgC12, the results indicate the possibility of in-
jecting CaO or Ca(OH)2 along with activated carbons to reduce operating costs.
17. KEY WORDS AND DOCUMENT ANALYSIS
a. DESCRIPTORS
b. 1DENTIF1ERS/OPEN ENDED TERMS
c. COSATI Field/Group
Pollution
Mercury (Metal)
Activated Carbon
Sorbents
Calcium Oxides
Combustion
Wastes
Pollution Control
Stationary Sources
Mercuric Chloride
Quicklime
Hydrated Lime
Municipal Waste Com-
bustion
13 B
07B
11G
21B
14G
18. DISTRIBUTION STATEMENT
Release to Public
19. SECURITY CLASS (This Report)
Unclassified
21. NO. OF PAGES
20. SECURITY CLASS (Thispage)
Unclassified
22. PRICE
EPA Form 2220-1 (9-73)
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