U.S. patent application number 11/065398 was filed with the patent office on 2006-08-24 for method of applying mercury reagent with coal.
Invention is credited to Amy P. Evans, Bryan J. Jankura, Dennis K. McDonald.
Application Number | 20060185226 11/065398 |
Document ID | / |
Family ID | 36911103 |
Filed Date | 2006-08-24 |
United States Patent
Application |
20060185226 |
Kind Code |
A1 |
McDonald; Dennis K. ; et
al. |
August 24, 2006 |
Method of applying mercury reagent with coal
Abstract
A method of halogenating coal prior to combustion, wherein the
coal is treated with a halogen prior to pulverization and the
pulverized halogenated coal is delivered to a burner as fuel for a
combustion process.
Inventors: |
McDonald; Dennis K.;
(Massillon, OH) ; Evans; Amy P.; (Akron, OH)
; Jankura; Bryan J.; (Uniontown, OH) |
Correspondence
Address: |
THE BABCOCK & WILCOX COMPANY
PATENT DEPARTMENT
20 SOUTH VAN BUREN AVENUE
BARBERTON
OH
44203
US
|
Family ID: |
36911103 |
Appl. No.: |
11/065398 |
Filed: |
February 24, 2005 |
Current U.S.
Class: |
44/620 |
Current CPC
Class: |
C10L 5/366 20130101;
C10L 9/10 20130101 |
Class at
Publication: |
044/620 |
International
Class: |
C10L 5/00 20060101
C10L005/00 |
Claims
1. A method of oxidizing mercury comprising: treating a coal
comprising mercury with a compound comprising a halogen;
pulverizing the treated coal; feeding the pulverized treated coal
to a pulverized coal burner; utilizing the burner to combust the
pulverized treated coal, wherein the compound oxidizes a
substantial portion of the mercury contained in the coal during
combustion; and creating a flue gas comprising oxidized
mercury.
2. The method of claim 1 wherein the combustion occurs between
about 1050.degree. C. and about 2000.degree. C.
3. The method of claim 2, wherein at least one mercury removing
means removes a portion of the oxidized mercury from the flue gas
downstream of the burner.
4. The method of claim 3, wherein an aqueous solution comprising
the compound is admixed with the mercury containing coal.
5. The method of claim 4, wherein the aqueous solution is sprayed
on the coal.
6. The method of claim 3, wherein a solid comprising the compound
is admixed with the mercury containing coal.
7. The method of claim 3, wherein the compound is selected from the
group consisting of sodium chloride, calcium chloride, and calcium
bromide.
8. The method of claim 3, wherein about 2 ppmw to about 1200 ppmw
of the halogen is admixed with the mercury containing coal during
treatment.
9. The method of claim 3, wherein about 2 ppmw to about 30 ppmw of
the halogen is admixed with the mercury containing coal during
treatment.
10. The method of claim 3, wherein about 300 ppmw to about 600 ppmw
of the halogen is admixed with the mercury containing coal during
treatment.
11. The method of claim 8, further comprising the steps of
monitoring the concentration of mercury in the flue gas, and
regulating the rate of dispensing the compound to maintain
substantial oxidation of the mercury during combustion.
12. A method of producing oxidized mercury comprising: providing a
burner with a mercury containing coal; utilizing the burner to
combust the coal; and combusting the coal in the presence of a
compound comprising a halogen, wherein elemental mercury is
oxidized during combustion.
13. The method of claim 12, wherein the compound is added to the
coal upstream of the burner.
14. The method of claim 13, wherein a solution comprising the
compound is sprayed on the coal.
15. The method of claim 13, wherein a solid comprising the compound
is admixed with the mercury containing coal.
16. The method of claim 14, wherein the compound is selected from
the group consisting of sodium chloride and calcium chloride.
17. The method of claim 15, wherein the compound is selected from
the group consisting of sodium chloride and calcium chloride.
18. The method of claim 17, wherein the coal is pulverized prior to
combustion and the compound is added to the coal prior to the coal
pulverization.
19. The method of claim 12, wherein the combustion take place
between about 1050.degree. C. and about 2000 C.
20. The method of claim 19, wherein about 2 ppmw to about 1200 ppmw
of the halogen is admixed with the mercury containing coal during
treatment.
21. The method of claim 19, wherein about 2 ppmw to about 30 ppmw
of the halogen is admixed with the mercury containing coal during
treatment.
22. The method of claim 18, wherein about 300 ppmw to about 600
ppmw of the halogen is admixed with the mercury containing coal
during treatment.
Description
FIELD AND BACKGROUND OF THE INVENTION
[0001] The present invention generally relates to combustion of
fossil fuels in a boiler or furnace, and more specifically to a
method of halogenating a fossil fuel prior to combustion to enhance
removal of mercury from flue gas.
[0002] Coal fired utility plants are necessary to satisfy the
energy needs of many countries. Heat energy derived from combusting
fossil fuels such as coal produces steam utilized to drive energy
producing turbines. A byproduct of the combustion process is a flue
or combustion gas which, after a cleaning process, exits into the
atmosphere.
[0003] Fossil fuels such as coal may contain varying levels of
mercury. Upon combustion mercury may enter the flue gas as a solid
particulate or as a gas in the vapor phase as elemental mercury or
in one of many oxidized forms. Flue gas scrubbers are readily able
to remove a substantial portion of mercury in the oxidized form,
however current scrubber technology is relatively ineffective in
removing elemental mercury from flue gas.
[0004] Environmental regulations strictly regulate flue gas
emissions for pollutants such as sulfur and nitrogen oxides, and
the U.S. EPA is considering implementing mercury emission
standards. In order to meet such proposed environmental
regulations, a need exists for a new and more effective means of
controlling mercury emissions arising from the combustion of fossil
fuels.
SUMMARY OF INVENTION
[0005] A general object of the present invention is drawn to a
method for enhancing mercury removal from flue gas. A more
particular objective of the present invention involves a method for
halogenating a fossil fuel such as coal prior to combustion to
suppress the formation of elemental mercury in the vapor phase and
favor its conversion to an oxidized form.
[0006] In a first aspect, the present invention provides a method
for halogenating a fossil fuel such as coal with chlorine or
compounds thereof. After chlorination the coal is fed to a
pulverizer which further admixes the coal and chlorine thereby more
uniformly dispersing the chlorine amongst the pulverized coal
particles. Once pulverized the coal is fed to at least one burner
and combusted in the presence of oxygen. The admixed chlorine
readily oxidizes the elemental mercury contained within the coal
during combustion, thereby suppressing formation of mercury in the
elemental form. The oxidized mercury is then removed downstream of
the burner utilizing a scrubber or other mercury removal means
readily known to one of ordinary skill in the art.
[0007] In another aspect, the invention comprises the steps of
treating mercury containing coal with a chlorine containing
compound, pulverizing the treated coal, conveying the pulverized
treated coal to a pulverized coal burner, utilizing the burner to
combust the pulverized treated coal, wherein the chlorine
containing compound oxidizes a substantial portion of the mercury
contained in the coal during combustion, and creating a flue gas
comprising oxidized mercury.
[0008] In yet another aspect, the invention comprises the steps of
providing a burner with a mercury containing coal, utilizing the
burner to combust the coal, and combusting the coal in the presence
of a halogen containing compound, wherein elemental mercury is
oxidized during combustion.
[0009] In yet another aspect a flue gas monitoring means is
utilized to monitor the mercury concentration of flue gas exiting
the boiler. The monitoring means then relays a signal to a
regulating means, which regulates the level of chlorine treatment
applied to the coal prior to pulverization in order to maximize
mercury oxidation.
[0010] In yet another aspect of the present invention a halogen
other than chlorine, such as bromine, iodine, fluorine, or
compounds thereof, may by used to halogenate the fossil fuel.
[0011] The present invention, due to its ease of incorporation and
benefit in mercury removal, provides an important advantage over
prior art methods due to unexpected advantages and cost savings
associated with forgoing the need to install expensive mercury
vapor removal means in order to lower mercury emissions. Further,
as a single pulverizer may provide coal to numerous burners,
substantial economic savings are observed by chlorinating the coal
prior to combustion and utilizing existing piping between the
pulverizer and burners thereby forgoing the need to install
additional piping or ductwork to each burner.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] FIG. 1. is a schematic diagram of an embodiment of the
present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0013] Referring now to FIG. 1, a schematic diagram of an
embodiment of the present invention is shown. A fossil fuel, such
as coal, is provided from a coal silo onto a belt feeder, such as a
gravimetric feeder or other belt feeding apparatus. The belt feeder
in turn provides the coal to the pulverizer wherein the coal is
pulverized to a predetermined particle size.
[0014] Prior to being pulverized, preferably while the coal is on
the belt feeder or alternatively dropping into the pulverizer, the
coal is treated with a liquid or solid chlorine reagent, preferably
sodium chloride or calcium chloride. Spray nozzles located above
and/or around the belt may be provided to treat the coal with
liquid chlorine reagent prior to pulverization. Reagent flow rate
may be control manually by valves or alternatively utilize
automated means. Alternatively, reagent may be supplied to coal in
the form of solid pellets, powder, or granules utilizing a solids
feeder in place of the spray nozzle. Preferably the coal is treated
with between about 2 ppmw and 1200 ppmw of halogen, and more
preferably between about 200 ppmw and 600 ppmw, wherein ppmw refers
to pounds of halogen per one million pounds of a wet fossil fuel
such as wet coal.
[0015] Treatment comprises the steps of providing the coal with
sufficient chlorine to substantially suppress the formation of
elemental mercury vapor, and pulverizing the coal in the presence
of the chlorine reagent. During pulverization the coal and chlorine
reagent are further admixed so as to provide more uniform
distribution of chlorine amongst the pulverized coal particles.
[0016] Upon exiting the pulverizer, the treated coal particles are
fed through a series of coal pipes to a burner, wherein the coal is
combusted, preferably at a temperature between about 1050.degree.
C. and about 2000.degree. C., in the presence of oxygen. During
combustion the mercury contained within the coal oxidizes in the
presence of chlorine to favor the production of an oxidized form of
mercury, such as mercuric chloride, over elemental mercury in the
vapor form.
[0017] Resulting mercury concentration in the flue gas exiting the
boiler is decreased because scrubbers and other flue gas cleansing
means are more readily able to remove mercury in the oxidized form,
and formation of mercury in the elemental form is suppressed in
favor of the oxidized form due to the presence of a halogen such as
chlorine.
[0018] In an alternative embodiment, a single reagent storage means
is used to supply chlorine reagent to multiple belt feeders
utilizing control valves and piping that allows the treatment rate
to any belt feeder to be controlled independently of the treatment
rate to another belt feeder.
[0019] In yet another alternative embodiment, an automated means
for controlling the treatment rate may be utilized. In this
embodiment, a mercury detection means is installed in the flue gas
stack to monitor the level of mercury in the flue gas as it exits
into the atmosphere. An electronic signal is then sent to a
regulating means which conveys instructions to adjust the flowrate
of the chlorine reagent treating the coal to a level which
optimizes low mercury emissions.
[0020] In yet another embodiment, the chlorine reagent may be
replaced with another halogen reagent such as bromine, iodine,
fluorine, etc. . . . or compounds thereof.
[0021] In yet another embodiment a combination of more than one
halogen reagent may be used such as reagent mixture comprising both
bromine and chlorine, or any other number of halogen reagent
combinations incorporating more than one halogen reagent as would
be known by one of ordinary skill in the art.
[0022] While the specific embodiments of the invention have been
shown and described in detail to illustrate the application of the
principles of the invention, it will be understood that the
invention may be embodied otherwise as appreciated by one of
ordinary skill in the art without departing from the scope of the
present invention.
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