U.S. patent application number 11/743707 was filed with the patent office on 2008-08-28 for methods and apparatuses for removing mercury-containing material from emissions of combustion devices, and flue gas and flyash resulting therefrom.
Invention is credited to Allen A. Aradi, Michael W. Meffert.
Application Number | 20080202396 11/743707 |
Document ID | / |
Family ID | 35462450 |
Filed Date | 2008-08-28 |
United States Patent
Application |
20080202396 |
Kind Code |
A1 |
Aradi; Allen A. ; et
al. |
August 28, 2008 |
METHODS AND APPARATUSES FOR REMOVING MERCURY-CONTAINING MATERIAL
FROM EMISSIONS OF COMBUSTION DEVICES, AND FLUE GAS AND FLYASH
RESULTING THEREFROM
Abstract
A method of removing mercury or mercury-containing material from
flue gas produced by a coal-burning main furnace includes feeding
coal, which contains mercury or mercury-containing material, to a
main furnace which produces flue gas. The method further includes
feeding the coal to an auxiliary burner which produces a slipstream
of flyash, feeding the slipstream of flyash from the auxiliary
burner into the flue gas produced by the main furnace, and
introducing a mercury-active oxidant to the coal being fed to the
auxiliary burner, the combustion air fed to the auxiliary burner,
and/or the flyash.
Inventors: |
Aradi; Allen A.; (Richmond,
VA) ; Meffert; Michael W.; (Chesterfield,
VA) |
Correspondence
Address: |
NEWMARKET SERVICES CORPORATION;c/o Thomas & Raring, P.C.
536 GRANITE AVENUE
RICHMOND
VA
23226
US
|
Family ID: |
35462450 |
Appl. No.: |
11/743707 |
Filed: |
May 3, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10991203 |
Nov 16, 2004 |
7270063 |
|
|
11743707 |
|
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Current U.S.
Class: |
110/345 ;
423/594.18; 431/12 |
Current CPC
Class: |
B01D 53/64 20130101 |
Class at
Publication: |
110/345 ; 431/12;
423/594.18 |
International
Class: |
F23J 15/02 20060101
F23J015/02; C01G 13/02 20060101 C01G013/02 |
Claims
1. A method of removing mercury or mercury-containing material from
flue gas produced by a coal-burning main furnace, the method
comprising: feeding coal which contains mercury or
mercury-containing material to a main furnace which produces flue
gas; feeding the coal to an auxiliary burner which produces a
slipstream of flyash; feeding the slipstream of flyash from the
auxiliary burner into the flue gas produced by the main furnace;
and introducing a mercury-active oxidant to at least one of the
coal being fed to the auxiliary burner, the combustion air being
fed to the auxiliary burner, and the flyash, and selectively
controlling the auxiliary burner to condition the flyash to a
combustion stage associated with a desired activity in mercury
oxidation.
2. A method of removing mercury or mercury-containing material from
flue gas produced by a coal-burning main furnace, the method
comprising: feeding coal which contains mercury or
mercury-containing material to a main furnace which produces flue
gas; feeding the coal to an auxiliary burner which produces a
slipstream of flyash; feeding the slipstream of flyash from the
auxiliary burner into the flue gas produced by the main furnace;
and introducing a mercury-active oxidant to at least one of the
coal being fed to the auxiliary burner, the combustion air being
fed to the auxiliary burner, and the flyash, and wherein the
mercury-active oxidant comprises at least one material selected
from the group consisting of inorganic oxidants, organometallic
oxidants, and organic oxidants, and further wherein the organic
oxidants include hydrogen peroxide, organoperoxides, peroxyesters,
peroxyacids, and organonitrates.
3. A system for removing mercury or mercury-containing material
from flue gas produced by a coal-burning main furnace, comprising:
a supply of coal which contains mercury or mercury-containing
material; a coal-burning main furnace configured to receive coal
from the supply of coal and to produce flue gas from combustion of
the coal; an auxiliary burner configured to receive coal from the
supply of coal, generate flyash, and direct the flyash to the flue
gas of the main furnace; and a treatment device configured to
introduce a mercury-active oxidant into at least one of the coal
being fed to the auxiliary burner, the combustion air being fed to
the auxiliary burner, and the flyash, and wherein the auxiliary
burner is selectively controllable to condition the flyash to a
combustion stage associated with a desired activity in mercury
oxidation.
4. A system for removing mercury or mercury-containing material
from flue gas produced by a coal-burning main furnace, comprising:
a supply of coal which contains mercury or mercury-containing
material; a coal-burning main furnace configured to receive coal
from the supply of coal and to produce flue gas from combustion of
the coal; an auxiliary burner configured to receive coal from the
supply of coal, generate flyash, and direct the flyash to the flue
gas of the main furnace; and a treatment device configured to
introduce a mercury-active oxidant into at least one of the coal
being fed to the auxiliary burner, the combustion air being fed to
the auxiliary burner, and the flyash, wherein the mercury-active
oxidant comprises at least one material selected from the group
consisting of inorganic oxidants, organometallic oxidants, and
organic oxidants, and wherein the organic oxidants include hydrogen
peroxide, organoperoxides, peroxyesters, peroxyacids, and
organonitrates.
5. A method of removing mercury or mercury-containing material from
flue gas produced by a coal-burning main furnace, the method
comprising: feeding coal to an auxiliary burner which produces a
slipstream of flyash; generating a slipstream of flyash from the
auxiliary burner; feeding the slipstream of flyash into flue gas
produced by the main furnace; and introducing a mercury-active
oxidant into at least one of the coal being fed to the auxiliary
burner, the combustion air being fed to the auxiliary burner, and
the flyash, further comprising selectively controlling the
auxiliary burner to condition the flyash to a combustion stage
associated with a desired activity in mercury oxidation.
6. A method of removing mercury or mercury-containing material from
flue gas produced by a coal-burning main furnace, the method
comprising: feeding coal to an auxiliary burner which produces a
slipstream of flyash; generating a slipstream of flyash from the
auxiliary burner; feeding the slipstream of flyash into flue gas
produced by the main furnace; and introducing a mercury-active
oxidant into at least one of the coal being fed to the auxiliary
burner, the combustion air being fed to the auxiliary burner, and
the flyash, wherein the mercury-active oxidant comprises at least
one material selected from the group consisting of inorganic
oxidants, organometallic oxidants, and organic oxidants, and
wherein the organic oxidants include hydrogen peroxide,
organoperoxides, peroxyesters, peroxyacids, and organonitrates.
Description
[0001] The present application is a continuation of U.S. patent
application Ser. No. 10/991,203, filed Nov. 16, 2004 which is
incorporated by reference herein in its entirety.
TECHNICAL FIELD
[0002] The present disclosure relates to the removal of
mercury-containing material from emissions of combustion devices.
More particularly, the disclosure is directed to methods and
apparatuses for removing mercury-containing material from emissions
of combustion devices and to the flue gas resulting from the
removal of mercury-containing material.
BACKGROUND
[0003] Conventional coal-fired combustion devices produce emissions
that include pollutants such as mercury. Mercury vapor is a poison
of the nervous system, with chronic mercury poisoning having
potentially dire consequences. Mercury poisoning can at times be
fatal and has the characteristic of being cumulative over years of
exposure, as the body's nervous system has difficulty in purging
this element. At the levels common in the atmosphere, the
concentrations of mercury are usually safe. However, mercury can
accumulate in lakes, rivers, streams, or the like as a result of
rainfall. The mercury can then be ingested by fish, ducks, and
other wildlife. This wildlife can be destroyed by the mercury
poisoning, or the wildlife, with organic mercury molecules in them,
can be hazardous to individuals who eat them. Some conventional
systems attempt to control mercury emissions with particulate
collection devices.
[0004] Mercury (elemental symbol Hg) is a metal that melts at 234K
(-38.degree. F.) and boils at 630K (674.degree. F.). As such, it
can be expected to have a high vapor pressure relative to many
metals. However, the oxidized forms Hg.sup.++ and Hg.sup.+ have
much lower vapor pressures and can be captured by flyash
particulates. It is much easier to collect the oxidized forms that
are attached to particulates with conventional particulate
collecting devices than it is to collect elemental mercury (Hg),
which can be in its vapor or gaseous form at flue gas
temperatures.
[0005] Accordingly, some conventional systems inject additives into
flue gas to oxidize the mercury prior to collection. However,
baghouses, fabric filters, electrostatic precipitators, and other
collection devices that are efficient enough to reduce the mercury
emissions to levels that may be required are very expensive.
Moreover, it is still possible for elemental mercury vapor to
escape as a gaseous vapor molecule.
[0006] Still other conventional systems utilize activated carbon
and other fine particulates to bind or absorb mercury to facilitate
removal of oxidized mercury. However, the efficiency of
electrostatic precipitators may be diminished by high carbon
content in fly ash, which results from the use of activated carbon,
and thus baghouses are required to remove carbon-containing
particles before the flue gas enters the electrostatic
precipitator. Also, flyash having a high carbon content is not
sellable, and therefore presents a disposal problem.
[0007] Since several states and the United States Environmental
Protection Agency will soon limit the emissions of mercury from
combustion devices, efficient and cost effective apparatuses and
methods for controlling emissions of mercury are desirable.
SUMMARY OF THE INVENTION
[0008] In some aspects, a method of removing mercury or
mercury-containing material from flue gas produced by a
coal-burning main furnace includes feeding coal, which contains
mercury or mercury-containing material, to a main furnace which
produces flue gas. The method further includes feeding the coal to
an auxiliary burner which produces a slipstream of flyash, feeding
the slipstream of flyash from the auxiliary burner into the flue
gas produced by the main furnace, and introducing a mercury-active
oxidant to the coal being fed to the auxiliary burner, the
combustion air fed to the auxiliary burner, and/or the flyash.
[0009] In accordance with some aspects, a system for removing
mercury or mercury-containing material from flue gas produced by a
coal-burning main furnace comprises a supply of coal which contains
mercury or mercury-containing material and a coal-burning main
furnace configured to receive coal from the supply of coal and to
produce flue gas from combustion of the coal. The system may
further include an auxiliary burner configured to receive coal from
the supply of coal, generate flyash, and direct the flyash to the
flue gas of the main furnace and a treatment device configured to
introduce a mercury-active oxidant into at least one of the coal
being fed to the auxiliary burner, the combustion air being fed to
the auxiliary burner, and the flyash.
[0010] In some aspects, a method of removing mercury or
mercury-containing material from flue gas produced by a
coal-burning main furnace comprises feeding coal to an auxiliary
burner which produces a slipstream of flyash, generating a
slipstream of flyash from the auxiliary burner, feeding the
slipstream of flyash into flue gas produced by the main furnace,
and introducing a mercury-active oxidant into at least one of the
coal being fed to the auxiliary burner, the combustion air being
fed to the auxiliary burner, and the flyash.
[0011] In various aspects, a flue gas produced by a combustion
system fueled by lignite coal, bituminous coal, or subbituminous
coal comprises a content of elemental mercury (Hg.sup.0) which does
not exceed about 7.00 .mu.g/dscm.
[0012] According to some aspects, a flue gas may be produced by
feeding coal which contains mercury or mercury-containing material
to a main furnace which produces flue gas, feeding the coal to an
auxiliary burner which produces a slipstream of flyash, feeding the
slipstream of flyash from the auxiliary burner into the flue gas
produced by the main furnace, introducing a mercury-active oxidant
to at least one of the coal being fed to the auxiliary burner, the
combustion air being fed to the auxiliary burner, and the flyash,
wherein the mercury and/or the mercury-containing material is at
least partially oxidized by the mercury oxidant, and removing
oxidized mercury from the flue gas.
[0013] In accordance with various aspects, a flue gas may be
produced by feeding coal to an auxiliary burner which produces a
slipstream of flyash, generating a slipstream of flyash from the
auxiliary burner, feeding the slipstream of flyash into flue gas
produced by the main furnace, introducing a mercury-active oxidant
into at least one of the coal being fed to the auxiliary burner,
the combustion air being fed to the auxiliary burner, and the
flyash, wherein the mercury and/or the mercury-containing material
is at least partially oxidized by the mercury oxidant, and removing
oxidized mercury from the flue gas.
[0014] In some aspects, a method for increasing mercury content in
flyash from a main furnace of a coal combustion system comprises
feeding coal which contains mercury or mercury-containing material
to a main furnace which produces flue gas, feeding the coal to an
auxiliary burner which produces a slipstream of flyash, feeding the
slipstream of flyash from the auxiliary burner into the flue gas
produced by the main furnace, and introducing a mercury-active
oxidant to at least one of the coal being fed to the auxiliary
burner, the combustion air being fed to the auxiliary burner, and
the flyash. The mercury content of the flyash from the main furnace
may be greater than the mercury content of fly ash produced by a
coal combustion unit not introducing a slipstream of flyash from an
auxiliary furnace into flue gas of a main furnace.
[0015] According to various aspects, a method for increasing
mercury content in flyash from a main furnace of a coal combustion
system comprises feeding coal to an auxiliary burner which produces
a slipstream of flyash, generating a slipstream of flyash from the
auxiliary burner, feeding the slipstream of flyash into flue gas
produced by the main furnace, and introducing a mercury-active
oxidant into at least one of the coal being fed to the auxiliary
burner, the combustion air being fed to the auxiliary burner, and
the flyash. The mercury content of the flyash from the main furnace
may be greater than the mercury content of fly ash produced by a
coal combustion unit not introducing a slipstream of flyash from an
auxiliary furnace into flue gas of a main furnace.
[0016] In accordance with some aspects, a system for increasing
mercury content in flyash from a main furnace of a coal combustion
system includes a supply of coal which contains mercury or
mercury-containing material, a coal-burning main furnace configured
to receive coal from the supply of coal and to produce flue gas
from combustion of the coal, an auxiliary burner configured to
receive coal from the supply of coal, generate flyash, and direct
the flyash to the flue gas of the main furnace, and a treatment
device configured to introduce a mercury-active oxidant into at
least one of the coal being fed to the auxiliary burner, the
combustion air being fed to the auxiliary burner, and the flyash.
The mercury content of the flyash from the main furnace may be
greater than the mercury content of fly ash produced by a coal
combustion unit not introducing a slipstream of flyash from an
auxiliary furnace into flue gas of a main furnace.
BRIEF DESCRIPTION OF THE DRAWING
[0017] FIG. 1 is a diagrammatic view of an exemplary combustion
device in accordance with some aspects of the invention.
DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS
[0018] An exemplary embodiment of a combustion system is shown in
FIG. 1. An exemplary combustion system 100 may include a main
furnace 110, an electrostatic precipitator (ESP) 130, and a stack
140. The main furnace 110 may include a plurality of burners 112
and a combustion zone 114. The burners 112 may be located on the
front and/or rear walls of the main furnace 110. For clarity and
convenience, only three burners 112 are shown in FIG. 1. However,
it should be appreciated that the main furnace 110 may include, for
example, 24 to 84 burners 112 or any desired number of burners
112.
[0019] The combustion system 100 may also include a coal supply
120, a pulverizer 122, and a primary air source 124. Although only
one pulverizer 122 is shown in FIG. 1, a plurality of pulverizers
may be used, depending on the number of burners and/or the size of
the main furnace. The coal supply 120 is structured and arranged to
supply coal at a desired rate to the pulverizer 122, and the
primary air source 124 is structured and arranged to supply a
primary stream of air to the pulverizer 122. The pulverizer 122
grinds the coal to a small size appropriate for burning. The
pulverizer 122 is fluidly connected with the burners 112 via line
126.
[0020] A secondary air source 128 may provide a secondary air flow
to the burners 112. The secondary air source 128 may comprise
ambient air from the environment, and the air may be heated with
one or more preheaters (not shown) prior to providing the air to
the burners 112. Each burner 112 may have an adjustable secondary
air register (not shown) to control the flow of air to the
respective burner 112.
[0021] Each of the burners 112 burns its respective air/fuel
mixture in the combustion zone 114 of the main furnace 110. The
gaseous by-product of the burners 112 flows in the direction of
arrows A out of the main furnace 110, through a flue line 132,
through the ESP 132, and into the stack 140, where it is exhausted
to the atmosphere at 142. A fan (not shown) may be used to aid the
flow of the gaseous by-product in this manner. The gaseous
by-product flowing through the flue line 132 may be referred to as
flue gas The flue gas may be used to heat steam and water in
convective passes 144, as is known in the art.
[0022] The combustion system 100 may further include an auxiliary
furnace 150 comprising an auxiliary burner 152 and a combustion
zone 154. The pulverizer 122 may be fluidly connected with the
auxiliary burner 152 via line 156. As a result, a slipstream of the
same coal and air being supplied to the main furnace 110 and
burners 112 may be supplied to the auxiliary furnace 150 and
auxiliary burner 152.
[0023] The secondary air source 128 may provide a secondary air
flow to the auxiliary burner 152. The auxiliary burner 152 may have
an adjustable secondary air register (not shown) to control the
flow of air to the burner 152. The auxiliary burner 152 burns its
air/fuel mixture in the combustion zone 154 of the auxiliary
furnace 150. The gaseous by-product of the auxiliary burner 152,
including flyash, flows in the direction of the arrow B out of the
auxiliary furnace 150, through line 158, and into the flue line 132
of the main furnace 110.
[0024] The combustion system may include, for example, one or more
injection ports 170 for supplying additives to the fuel supply, the
combustion air supply, and/or the flyash of the auxiliary and/or
the main furnace 110, 150. The additives may include one or more
mercury-active oxidants such as, for example, inorganic oxidants,
organometallic oxidants, and organic oxidants. Inorganic and
organometallic oxidants that are capable of emerging active from a
flame front may be introduced to the flame of or upstream of the
burner 152 of the main and/or the auxiliary furnace 110, 150.
Organic oxidants, which are not flame stable, can be added to the
flyash of the auxiliary furnace 150 at an appropriate temperature
before the flyash is injected into the flue line 132 or they can be
added directly into the flue line 132.
[0025] In various embodiments, the inorganic and organometallic
oxidants may include compounds of Li, Na, K, Rb, Ca, Sr, Ba, Cr,
Mn, Fe, Co, Cu, Y, Zr, Mo, Ru, Rh, Pd, Sn, La, Re, Os, Ir, Pt, Ce,
and paraperiodic acid (H.sub.5IO.sub.6). For example, the
CrO.sub.3, CrO.sub.2Cl.sub.2, CrO.sub.2(OCOCH.sub.3), other
tetravalent Cr.sup.IV, pentavalent Cr.sup.V, and hexavalent
Cr.sup.VI compounds (H.sub.2SO.sub.4 and HClO.sub.4 treatment may
enhance the oxidizing power of Cr compounds), KMnO.sub.4, other
heptavalent Mn.sup.VII compounds, RuO.sub.4, PT-C, PtO, and
KIO.sub.4. The compounds may be provided in powder and/or liquid
forms, for example, hydrocarbonaceous solutions, colloidal
dispersions, or aqueous solutions.
[0026] In some embodiments, the compounds of manganese useful
herein as oxidants may include, but are not limited to, methyl
cyclopentadienyl manganese tricarbonyl, manganese sulfonate,
manganese phenate, manganese salicylate, cyclopentadienyl manganese
tricarbonyl, alkyl cyclopentadienyl manganese tricarbonyl, organic
manganese tricarbonyl derivatives, alkyl cyclopentadienyl manganese
derivatives, bis-cyclopentadienyl manganese, bis-alkyl
cyclopentandienyl manganese, neutral and overbased manganese
salicylates, neutral and overbased manganese phenates, neutral and
overbased manganese sulfonates, manganese carboxylates, and
combinations and mixtures thereof.
[0027] According to one embodiment, a desired manganese oxidant
source is methylcyclopentadienyl manganese tricarbonyl, available
from Afton Chemical Corporation as MMT.RTM. Gasoline Additive, or
HiTEC.RTM. 3000 Performance Additive, or GREENBURN.RTM. Fuel
Additive.
[0028] In some embodiments, an oxidatively effective amount of a
source of manganese added to a fuel or to the combustion air, for
example and without limitation, is between about 2 and 200 ppm
wt/wt percent manganese in the fuel. In various embodiments, the
effective amount of a source of manganese added is between about 5
and 50 ppm wt/wt percent manganese in the fuel. It may be used in
burners such as those found in industrial furnaces and utility
power generation furnaces. This manganese can be added to the fuel
as noted or also directly to the combustion air, or the combustion
exhaust gas stream at any time before the combustion exhaust gas
reaches the ESP. The treat rate of the additive in the combustion
exhaust gas may range between about 0.5 and 3 wt % manganese
relative to the weight of the fly ash.
[0029] The organic compounds useful herein as mercury oxidants may
include for example hydrogen peroxide, organoperoxides,
peroxyacids, peroxyesters, and/or organonitrates, and mixtures
thereof. For example, the organic compounds may include peracetic
acid, peroxytrifluoroacetic acid/boron trifluoride etherate, and/or
perbenzoic acid.
[0030] The combustion system 100 may also include a controller 190
electrically connected to at least the burners 112, the coal supply
120, the pulverizer 122, the primary air source 124, the secondary
air source 128, the auxiliary burner 152, and the injection ports
170. The controller 190 may be operated to control one or more of
the elements to which it's electrically connected so as to
condition the flyash resulting from the auxiliary furnace 150 to a
combustion stage most conducive to a desired (e.g., optimum)
activity in mercury capture. The optimum condition may resemble
that of commercially-activated carbon in porosity and
absorbability, but with lower levels of carbon. As a result, the
conditioned flyash from the auxiliary furnace 150 may in one
embodiment have a carbon content sufficiently low to avoid the need
for a baghouse to remove excessive levels of carbon particles.
Moreover, the condition of the flyash from the auxiliary furnace
150 may be highly variable, even to the extent that it may
sometimes be nonexistent.
[0031] It should be appreciated that the auxiliary burner 152 may
be fed with partial-burn coal from the main furnace 110 as an
alternative or in addition to being fed coal directly from the
pulverizer 122. It should further be appreciated that the
combustion system 100 may include a baghouse, a fabric filter, a
scrubber, and/or any other device for removing particles from the
flue gas, regardless of whether such a device is necessary to
remove a sufficient amount of mercury to reduce the mercury level
in the flue gas to at least meet a desired level.
[0032] The combustion system 100 may be embodied as any and all
internal and external combustion devices, machines, boilers,
furnaces, incinerators, evaporative burners, stationary burners and
the like, for example, power plant generators, power plant
furnaces, and the like, in which coal or a coal-containing fuel can
be combusted. The term "combustion air" includes ambient or
pressurized air or any other oxidant that is combusted with a fuel
in a combustion unit. The oxidant may be gaseous or it may be
liquid or solid or mixtures or precursors thereof. The combustion
air may be additized prior to combustion or otherwise modified to
meet or maximize the efficiencies of the combustion unit.
[0033] In operation, the pulverizer 122 receives a supply of coal
from the coal supply 120 and a primary flow of air from the primary
air source 124. A stream of primary air and coal is carried out of
the pulverizer 122 and fed via line 126 to the burners 112, where
the air/fuel mixture is burned in the combustion zone 114. A
slipstream of the primary air and coal is also fed to the auxiliary
burner 152 via line 156 and burned in the combustion zone 154. To
assist in the burning, a secondary flow of air from the secondary
air source 128 may be provided to the burners 112 and/or the
auxiliary burner 152. In some embodiments, about 20% of the air
required for optimum burning conditions is supplied by the primary
air source 124, with the secondary air source 128 providing the
remaining air.
[0034] In the main furnace 110, each of the burners 112 burns its
respective air/fuel mixture in the combustion zone 114. As the
burners 112 burn their respective air/fuel mixtures, a gaseous
by-product is produced. The gaseous by-product flows in the
direction of the arrows A out of the main furnace 110 and into the
flue line 132, where the flue gas may be used to heat steam and
water in convective passes 144, as is known in the art.
[0035] In the auxiliary furnace 150, the auxiliary burner 152 burns
its air-fuel mixture in the combustion zone 154. As the auxiliary
burner 152 burns its air/fuel mixture, a gaseous by-product
including flyash is produced. The flyash is directed to the flue
line 132 via line 158. The flyash resulting from the auxiliary
furnace may be additized with one or more mercury-active oxidants
such as, for example, one or more of the inorganic oxidants,
organometallic oxidants, and organic oxidants listed above. As
mentioned above, inorganic and organometallic oxidants that are
capable of emerging active from a flame front may be introduced to
the flame of or upstream of the burner 152 of the main and/or the
auxiliary furnace 110, 150. Organic oxidants, which are not flame
stable, can be added to the flyash of the auxiliary furnace 150 at
an appropriate temperature before the flyash is injected into the
flue line 132 or they can be added directly into the flue line
132.
[0036] The additized flyash from the auxiliary furnace 150 may
provide active oxidation, which facilitates the oxidation of the
mercury and subsequent capture of the oxidized mercury by the
flyash in the flue gas from the main furnace 110. The mercury-laden
flyash may then flow to and be captured by the ESP 130, where it
can be dropped into a hopper (not shown) and removed from the
combustion system 100. After exiting the ESP 130, the resulting
flue gas is directed to the stack 140, where it is exhausted to the
atmosphere at 142. In this manner, the total emission of mercury
can be dramatically reduced, or completely eliminated, relative to
a system not utilizing the stated mercury oxidant(s).
[0037] The controller 190 may be selectively operated to control
one or more of the elements to which it's electrically connected so
as to condition the flyash resulting from the auxiliary furnace 150
to a combustion stage most conducive to a desired (e.g., optimum)
activity in mercury capture. For example, the controller 190 may be
operated to control the combustion system 110 such that the final
level of elemental Hg (Hg.sup.0) in the flue gas exhausted from the
stack 140 to the atmosphere 142 does not exceed about 7.00
.mu.g/dscm when burning bituminous, sub-bituminous, and/or lignite
coal. When burning sub-bituminous coal, the final level of
elemental Hg in the flue gas exhausted from the stack 140 in one
embodiment does not exceed about 3.00 .mu.g/dscm, and when burning
bituminous, the final level of elemental Hg does not exceed about
1.50 .mu.g/dscm. In another embodiment, no detectable mercury would
remain in the flue gas exhausted from the stack 140. The present
disclosure thereby provides a method for reducing the mercury in
flue gas from a coal combustion unit.
[0038] It will be apparent to those skilled in the art that various
modifications and variations can be made to the exemplary apparatus
and method of the present disclosure without departing from the
scope of the invention. Other embodiments of the invention will be
apparent to those skilled in the art from consideration of the
specification and practice of the invention disclosed herein. It is
intended that the specification and examples be considered as
exemplary only.
* * * * *