Note: Descriptions are shown in the official language in which they were submitted.
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INCREASING SERVICE LIFE OF SCR CATALYST
RELATED APPLICATION DATA
[0001] This international patent application claims priority to and is a
continuation-in-part of United States Patent Application No. 13/769,686 filed
February 18, 2013 and titled "System and Method for Increasing the Service
Life
and/or Catalytic Activity of an SCR Catalyst and Control of Multiple
Emissions,"
which itself claims priority to and is a continuation-in-part of United States
Patent
Application No. 13/117,332 filed May 27, 2011 and titled "System and Method
for
Increasing the Service Life and/or Catalytic Activity of an SCR Catalyst and
Control
of Multiple Emissions," which itself claims priority to and is a continuation-
in-part of
United States Patent Application No. 12/691,527 filed January 21, 2010 and
titled
"System and Method for Protection of SCR Catalyst and Control of Multiple
Emissions," which itself claims priority to and is a non-provisional of United
States
Provisional Patent Application No. 61/171,619 filed April 22, 2009 and titled
"System
and Method for Protection of SCR Catalyst." The complete texts of these patent
applications are hereby incorporated by reference as though fully set forth
herein in
their entireties.
FIELD AND BACKGROUND OF THE INVENTION
1. Field of the Invention
[0002] The present invention relates generally to the field of emission
control
equipment for boilers, heaters, kilns, or other flue gas-, or combustion gas-,
generating devices (e.g., those located at power plants, processing plants,
etc.) and,
in particular to a new and useful method and apparatus for reducing or
preventing
the poisoning and/or contamination of an SCR catalyst. In another embodiment,
the
method and apparatus of the present invention is designed to protect the SCR
catalyst. In still another embodiment, the present invention relates to a
method and
apparatus for increasing the service life and/or catalytic activity of an SCR
catalyst
while simultaneously controlling various emissions. In yet another embodiment,
the
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present invention relates to a method and apparatus for controlling,
mitigating and/or
reducing the amount of selenium contained in and/or emitted by one or more
pieces
of emission control equipment for boilers, heaters, kilns, or other flue gas-,
or
combustion gas-, generating devices (e.g., those located at power plants,
processing
plants, etc.). In still yet another embodiment, the present invention relates
to method
and apparatus for controlling the selenium speciation in one, or both, of a
gas phase
or an aqueous phase by the addition of at least one metal additive upstream of
either
a wet flue gas desulfurization (WFGD) unit and/or a dry flue gas
desulfurization
(DFGD) unit.
2. Description of the Related Art
[0003] NO, refers to the cumulative emissions of nitric oxide (NO),
nitrogen
dioxide (NO2) and trace quantities of other nitrogen oxide species generated
during
combustion. Combustion of any fossil fuel generates some level of NO, due to
high
temperatures and the availability of oxygen and nitrogen from both the air and
fuel.
NO, emissions may be controlled using low NO, combustion technology and post-
combustion techniques. One such post-combustion technique involves selective
catalytic reduction (SCR) systems in which a catalyst facilitates a chemical
reaction
between NO, and a reagent (usually ammonia) to produce molecular nitrogen and
water vapor.
[0004] SCR technology is used worldwide to control NO, emissions from
combustion sources. This technology has been used widely in Japan for NO,
control
from utility boilers since the late 1970's, in Germany since the late 1980's,
and in the
US since the 1990's. Industrial scale SCRs have been designed to operate
principally in the temperature range of 500 F to 900 F, but most often in the
range of
550 F to 750 F. SCRs are typically designed to meet a specified NO, reduction
efficiency at a maximum allowable ammonia slip. Ammonia slip is the
concentration,
expressed in parts per million by volume, of unreacted ammonia exiting the
SCR.
[0005] For additional details concerning NO, removal technologies used in
the
industrial and power generation industries, the reader is referred to
Steam/its
generation and use, 41st Edition, Kitto and Stultz, Eds., Copyright 2005, The
Babcock & Wilcox Company, Barberton, Ohio, U.S.A., particularly Chapter 34 -
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Nitrogen Oxides Control, the text of which is hereby incorporated by reference
as
though fully set forth herein.
[0006] Regulations issued by the EPA promise to increase the portion of
utility
boilers equipped with SCRs. SCRs are generally designed for a maximum
efficiency
of about 90 percent. This limit is not set by any theoretical limits on the
capability of
SCRs to achieve higher levels of NO destruction. Rather, it is a practical
limit set to
prevent excessive levels of ammonia slip. This problem is explained as
follows.
[0007] In an SCR, ammonia reacts with NO according to one or more of the
following stoichiometric reactions (a) to (d):
4N0 + 4NH3 + 02 ¨> 4N2 + 6H20 (a)
12NO2 + 12NH3 ¨> 12N2 + 18H20 + 302 (b)
2NO2 + 4NH3 + 02 ¨> 3N2 + 6H20 (c)
NO + NO2 + 2NH3 ¨> 2N2 + 3H20 (d).
[0008] The above catalysis reactions occur using a suitable catalyst.
Suitable
catalysts are discussed in, for example, United States Patent Nos. 5,540,897;
5,567,394; and 5,585,081 to Chu et al., all of which are hereby incorporated
by
reference as though fully set forth herein. Catalyst formulations generally
fall into
one of three categories: base metal, zeolite and precious metal.
[0009] Base metal catalysts use titanium oxide with small amounts of
vanadium, molybdenum, tungsten or a combination of several other active
chemical
agents. The base metal catalysts are selective and operate in the specified
temperature range. The major drawback of the base metal catalyst is its
potential to
oxidize SO2 to S03; the degree of oxidation varies based on catalyst chemical
formulation. The quantities of SO3 which are formed can react with the ammonia
carryover to form various ammonium-sulfate salts.
[0010] Zeolite catalysts are aluminosilicate materials which function
similarly
to base metal catalysts. One potential advantage of zeolite catalysts is their
higher
operating temperature of about 970 F (521 C). These catalysts can also oxidize
SO2 to SO3 and must be carefully matched to the flue gas conditions.
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[0011] Precious metal catalysts are generally manufactured from platinum
and
rhodium. Precious metal catalysts also require careful consideration of flue
gas
constituents and operating temperatures. While effective in reducing NO,,
these
catalysts can also act as oxidizing catalysts, converting CO to CO2 under
proper
temperature conditions. However, SO2 oxidation to SO3 and high material costs
often make precious metal catalysts less attractive.
[0012] As is known to those of skill in the art, various SCR catalysts
undergo
poisoning when they become contaminated by various compounds including, but
not
limited to, certain phosphorus compounds such as phosphorus oxide (PO) or
phosphorus pentoxide (P205). Additionally, it is also well known that SCR
catalysts
degrade over time and have to be replaced periodically at a significant cost
and loss
of generating capacity. In a typical 100 MWe coal plant the downtime and cost
associated with the replacement of underperforming catalyst can be in the
neighborhood of one million US dollars or more.
[0013] More particularly, as the SCR catalysts are exposed to the dust
laden
flue gas there are numerous mechanisms including blinding, masking and
poisoning
that deactivates the catalyst and causes a decrease in the catalyst's
performance
over time. The most common catalyst poison encountered when burning eastern
domestic coal (i.e., coal mined in the eastern United States) is arsenic. The
most
common catalyst poison encountered when burning western domestic coal (i.e.,
coal
mined in the western United States) is phosphorus and calcium sulfate is the
most
common masking mechanism. One method of recycling the used catalyst is the
process called regeneration washing or rejuvenation. The initial steps of the
regeneration process involve the removal of these toxic chemicals by
processing the
catalysts through various chemical baths in which the poisons are soluble.
While
this treatment process does an excellent job of removing the desired poisons
it
produces wastewater with very high arsenic concentrations.
[0014] In another situation, Powder River Basin/Lignite coal plants, any
coal/biomass co-combustion, or any coal/bone meal co-combustion or even pure
biomass combustion power plants will suffer from phosphorus contamination of
their
SCR catalysts. Furthermore, other types of fossil fuel-fired combustion
processes
can generate phosphorus levels that lead to undesirable levels of phosphorus
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contamination of an SCR catalyst. For example, fuel oil combustion processes
can,
in some instances, suffer from phosphorus levels that lead to undesirable
levels of
phosphorus contamination of an SCR catalyst. As used herein and in the claims,
the
term "fuel oil" means any type of liquid fossil fuel (e.g., liquid petroleum),
regardless
of type, number or grade, that can be combusted to produce heat.
[0015] Additionally, beyond controlling NO emissions, other emission
controls
must be considered and/or met in order to comply with various state, EPA
and/or
Clean Air Act regulations. Some other emission controls which need to be
considered for boilers, heaters, kilns, or other flue gas-, or combustion gas-
,
generating devices (e.g., those located at power plants, processing plants,
etc.)
include, but are not limited to, mercury, SON, and certain particulates.
[0016] Furthermore, in most situations, if not all, it is desirable to
remove
various SON compounds by way of either one or more wet flue gas
desulfurization
(WFGD) units or one or more dry flue gas desulfurization (DFGD) units from a
flue
gas. As is known to those of skill in the art, in conjunction with SON removal
it is
common (and now required in most instances) to also remove and/or reduce the
amount of mercury in a flue gas. One suitable method of mercury control is
mercury
oxidation and capture via the use of one or more halogen compounds to
accomplish
the aforesaid mercury oxidation and the subsequently capturing the oxidized
mercury compound (e.g., in the form of a mercuric halide). It has been found
that
when mercury control is accomplished in whole, or in part, through the use of
one or
more halogen compounds (e.g., halide salts such as calcium bromide, etc.) that
such
compounds negatively impact on the selenium speciation in the flue gas which
in
turn negatively impacts the amount of selenium that is emitted via the liquid
effluent
outflow from one or more WFGD units, and or the particulate matter produced by
one or more DFGD units that are utilized to control SON in the same flue gas
stream.
However, it should be noted that the present invention is not limited to just
the
aforementioned situation. In fact, in one embodiment the present invention
relates to
a method and apparatus for controlling, mitigating and/or reducing the amount
of
selenium contained in and/or emitted by one or more pieces of emission control
equipment for boilers, heaters, kilns, or other flue gas-, or combustion gas-,
generating devices (e.g., those located at power plants, processing plants,
etc.). In
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another embodiment, the present invention relates to method and apparatus for
controlling the selenium speciation in one, or both, of a gas phase or a
aqueous
phase by the addition of at least one metal additive at any point upstream (as
will be
detailed below) of either a wet flue gas desulfurization (WFGD) unit and/or a
dry flue
gas desulfurization (DFGD) unit. In still another embodiment, present
invention
offers a method and apparatus by which to simultaneously control at least
selenium
speciation in one, or both, of a gas phase or an aqueous phase while further
controlling at least one of gas phase phosphorus, gas phase sodium, gas phase
potassium, and/or mercury in at least one emission from a combustion process.
[0017] Given the above, a need exists for a method that provides for any
economical and environmentally suitable method and/or system to control
selenium
emission from one or more pieces of emission control equipment that are used
in
conjunction with a combustion process. Additionally, or alternatively, a need
exists
for a method to control selenium emission while simultaneously increase
catalytic life
span and/or catalytic activity of an SCR catalyst via the control of one or
more gas
phase compounds such as phosphorus, sodium, and/or potassium, and even in
some instances the further ability to control mercury emission.
SUMMARY OF THE INVENTION
[0018] The present invention relates generally to the field of emission
control
equipment for boilers, heaters, kilns, or other flue gas-, or combustion gas-,
generating devices (e.g., those located at power plants, processing plants,
etc.) and,
in particular to a new and useful method and apparatus for reducing or
preventing
the poisoning and/or contamination of an SCR catalyst. In another embodiment,
the
method and apparatus of the present invention is designed to protect the SCR
catalyst. In still another embodiment, the present invention relates to a
method and
apparatus for increasing the service life and/or catalytic activity of an SCR
catalyst
while simultaneously controlling various emissions. In yet another embodiment,
the
present invention relates to a method and apparatus for controlling,
mitigating and/or
reducing the amount of selenium contained in and/or emitted by one or more
pieces
of emission control equipment for boilers, heaters, kilns, or other flue gas-,
or
combustion gas-, generating devices (e.g., those located at power plants,
processing
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plants, etc.). In still yet another embodiment, the present invention relates
to method
and apparatus for controlling the selenium speciation in one, or both, of a
gas phase
or an aqueous phase by the addition of at least one metal additive upstream of
either
a wet flue gas desulfurization (WFGD) unit and/or a dry flue gas
desulfurization
(DFGD) unit.
[0019] Accordingly, one aspect of the present invention is drawn to a
method
for increasing the active life of an SCR catalyst, the method comprising the
steps of:
(a) providing at least one iron-bearing compound to a combustion zone or flue
gas
stream of a furnace, or boiler, prior to entry of the flue gas into an SCR;
(b)
permitting the at least one iron-bearing compound to react with any gaseous
phosphorus compounds, or phosphorus-containing compounds, present in the
combustion zone or flue gas prior to the entry of the flue gas into the SCR;
(c)
providing at least one halide-bearing compound to a combustion zone or flue
gas
stream of a furnace, or boiler, prior to entry of the flue gas into an SCR,
with the
proviso that halide-bearing compound is not an iron halide; and (d) permitting
the at
least one halide-bearing compound to react with and/or oxidize any mercury
present
in the combustion zone or flue gas, wherein the method achieves an increase in
either one, or both, of a catalytic activity and/or a catalytic lifespan of at
least about
percent at an operational time of at least about 2,000 hours.
[0020] In yet another aspect of the present invention, there is provided
a
method for increasing the active life of an SCR catalyst, the method
comprising the
steps of: (i) providing at least one iron-bearing compound to a combustion
zone or
flue gas stream of a furnace, or boiler, prior to entry of the flue gas into
an SCR; (ii)
permitting the at least one iron-bearing compound to react with any gaseous
phosphorus compounds, or phosphorus-containing compounds, present in the
combustion zone or flue gas prior to the entry of the flue gas into the SCR;
(iii)
providing at least one halide-bearing compound to a combustion zone or flue
gas
stream of a furnace, or boiler, prior to entry of the flue gas into an SCR,
with the
proviso that halide-bearing compound is not an iron halide; and (iv)
permitting the at
least one halide-bearing compound to react with and/or oxidize any mercury
present
in the combustion zone or flue gas, wherein the method achieves an increase in
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either one, or both, of a catalytic activity and/or a catalytic lifespan of at
least about
percent at an operational time of at least about 3,000 hours.
[0021] In yet another aspect of the present invention, there is provided
a
method for simultaneously sequestering one or more phosphorus compounds, or
phosphorus-containing compounds, in the form of one or more less reactive iron-
phosphorus-containing compounds, and oxidizing mercury, the method comprising
the steps of: (A) providing at least one iron-bearing compound to a combustion
zone
or flue gas stream of a furnace, or boiler; (B) permitting the at least one
iron-bearing
compound to react with any gaseous phosphorus compounds, or phosphorus-
containing compounds, present in the combustion zone or flue gas to form one
or
more less reactive iron-phosphorus-containing compounds; (C) providing at
least
one halide-bearing compound to a combustion zone or flue gas stream of a
furnace,
or boiler, prior to entry of the flue gas into an SCR, with the proviso that
halide-
bearing compound is not an iron halide; and (D) permitting the at least one
halide-
bearing compound to react with and/or oxidize any mercury present in the
combustion zone or flue gas, wherein the method achieves an increase in either
one,
or both, of a catalytic activity and/or a catalytic lifespan of at least about
10 percent
at an operational time of at least about 4,000 hours.
[0022] In yet another aspect of the present invention, there is provided
a
method for simultaneously sequestering one or more phosphorus compounds, or
phosphorus-containing compounds, in the form of one or more less reactive iron-
phosphorus-containing compounds, and oxidizing mercury, the method comprising
the steps of: (I) providing at least one iron-bearing compound to a combustion
zone
or flue gas stream of a furnace, or boiler; (II) permitting the at least one
iron-bearing
compound to react with any gaseous phosphorus compounds, or phosphorus-
containing compounds, present in the combustion zone or flue gas to form one
or
more less reactive iron-phosphorus-containing compounds; (III) providing at
least
one halide-bearing compound to a combustion zone or flue gas stream of a
furnace,
or boiler, prior to entry of the flue gas into an SCR, with the proviso that
halide-
bearing compound is not an iron halide; and (IV) permitting the at least one
halide-
bearing compound to react with and/or oxidize any mercury present in the
combustion zone or flue gas, wherein the method achieves an increase in either
one,
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or both, of a catalytic activity and/or a catalytic lifespan of at least about
15 percent
at an operational time of at least about 3,000 hours.
[0023] In yet another aspect of the present invention, there is provided
a
method for sequestering one or more phosphorus compounds, or phosphorus-
containing compounds, in the form of one or more less reactive iron-phosphorus-
containing compounds while concurrently sequestering mercury, the method
comprising the steps of: providing at least one iron-bearing compound to a
combustion zone or flue gas stream of a furnace, or boiler; permitting the at
least
one iron-bearing compound to react with any gaseous phosphorus compounds, or
phosphorus-containing compounds, present in the combustion zone or flue gas to
form one or more less reactive iron-phosphorus-containing compounds; providing
at
least one halide-bearing compound to a combustion zone or flue gas stream of a
furnace, or boiler, prior to entry of the flue gas into an SCR, with the
proviso that
halide-bearing compound is not an iron halide; and permitting the at least one
halide-
bearing compound to react with and/or oxidize any mercury present in the
combustion zone or flue gas, wherein the method achieves an increase in either
one,
or both, of a catalytic activity and/or a catalytic lifespan of at least about
15 percent
at an operational time of at least about 4,000 hours.
[0024] In yet another aspect of the present invention, there is provided
a
method for controlling the selenium speciation in a flue gas and/or in at
least one
piece of emission control equipment, the method comprising the steps of:
providing
at least one metal-bearing compound to a combustion zone or flue gas stream of
a
furnace, or boiler, prior to entry of the flue gas into an SCR; and permitting
the at
least one metal-bearing compound to react with any selenium and/or selenium
compounds present in the combustion zone, flue gas, gas phase and/or at least
one
piece of emission control equipment, wherein the method permits the control of
the
selenium speciation in one or more of the gas phase and/or in the at least one
piece
of emission control equipment thereby resulting in a reduction in the amount
of
selenium emitted in a flue gas and/or from one or more pieces of emission
control
equipment.
[0025] In yet another aspect of the present invention, there is provided
a
method for simultaneously increasing the active life of an SCR catalyst and
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controlling the selenium speciation in a flue gas and/or selenium speciation
in at
least one piece of emission control equipment, the method comprising the steps
of:
providing at least one iron-bearing compound to a combustion zone or flue gas
stream of a furnace, or boiler, prior to entry of the flue gas into an SCR;
and
simultaneously permitting the at least one iron-bearing compound to react with
any
gaseous phosphorus compounds, or phosphorus-containing compounds, present in
the combustion zone or flue gas as well as any selenium and/or selenium
compounds present in the combustion zone, flue gas, gas phase and/or at least
one
piece of emission control equipment prior to the entry of the flue gas into
the SCR,
wherein the method achieves an increase in either one, or both, of a catalytic
activity
and/or a catalytic lifespan of at least about 10 percent at an operational
time of at
least about 2,000 hours while simultaneously permitting the control of the
selenium
speciation in one or more of the gas phase and/or the at least one piece of
emission
control equipment thereby resulting in a reduction in the amount of selenium
emitted
in a flue gas and/or from one or more pieces of emission control equipment.
[0026] In yet another aspect of the present invention, there is provided
a
method for controlling the selenium speciation in a flue gas and/or in at
least one
piece of emission control equipment in conjunction with a post combustion CO2
capture process, the method comprising the steps of: providing at least one
metal-
bearing compound to a combustion zone or flue gas stream of a furnace, or
boiler,
prior to entry of the flue gas into an SCR; and permitting the at least one
metal-
bearing compound to react with any selenium and/or selenium compounds present
in the combustion zone, flue gas, gas phase and/or at least one piece of
emission
control equipment, wherein the method permits the control of the selenium
speciation in one or more of the gas phase and/or in the at least one piece of
emission control equipment thereby resulting in a reduction in the amount of
selenium emitted in a flue gas, from one or more pieces of emission control
equipment and/or in at least one amine compound that is utilized in
conjunction with
the post combustion CO2 capture process.
[0027] The various features of novelty which characterize the invention
are
pointed out with particularity in the claims annexed to and forming a part of
this
disclosure. For a better understanding of the invention, its operating
advantages and
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specific benefits attained by its uses, reference is made to the accompanying
drawings and descriptive matter in which exemplary embodiments of the
invention
are illustrated.
BRIEF DESCRIPTION OF THE DRAWINGS
[0028] Figure 1 is a schematic representation of a typical fossil fuel
burning
facility with an SCR system, and which includes a system for practicing the
methods
of the present invention; and
[0029] Figure 2 is a graph illustrating one example of an increase in
catalytic
activity and/or catalytic lifespan as realized via utilization of a system and
method in
accordance with one embodiment of the present invention.
DESCRIPTION OF THE INVENTION
[0030] While the present invention will be described in terms of SCR
systems
which use ammonia as the NO reducing agent, since ammonia is frequently
preferred for economic reasons, the present invention is not limited to
ammonia
based systems. The concepts of the present invention can be used in any system
which uses an ammoniacal compound. As used in the present disclosure, an
ammoniacal compound is a term meant to include compounds such as urea,
ammonium sulfate, cyanuric acid, and organic amines as well as ammonia (NH3).
These compounds could be used as reducing agents in addition to ammonia, but
as
mentioned above, ammonia is frequently preferred for economic reasons. Some
non-ammoniacal compounds such as carbon monoxide or methane can be used as
well, but with loss in effectiveness.
[0031] Furthermore, although the present invention is described in terms
of a
mercury oxidation and capture method that utilizes a halogen compound that is
in
the form a halide salt (e.g., calcium bromide), the present invention is not
limited to
just this type of mercury oxidation and capture. Rather, any type of mercury
control
method can be utilized in conjunction with the present invention as the
present
invention, in various embodiments, seeks to control simultaneously the amount
of
gas phase phosphorus and the nature of the selenium speciation. In other
embodiments, the present invention seeks to control simultaneously the amount
of
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gas phase phosphorus, the amount of mercury and the nature of the selenium
speciation in a flue gas.
[0032] Although the present invention is described in relation to a
boiler, or a
fossil fuel boiler, it is not limited solely thereto. Instead, the present
invention can be
applied to any combustion source that generates NO regardless of whether such
a
combustion source is utilized in conjunction with a boiler, or a steam
generator. For
example, the present invention could be used in combination with a kiln, a
heater, or
any other type of combustion process that generates, in whole or in part, a
flue gas
or combustion gas containing NON. Accordingly, the description below is to be
construed as merely exemplary.
[0033] As illustrated in Figure 1, the present invention may be applied
to a
boiler installation which employs a wet flue gas desulfurization (WFGD or wet
scrubber) for removal of sulfur oxides from the flue gases, as shown in the
upper
right-hand side of Figure 1. In this configuration, the wet scrubber is
typically
preceded (with respect to a direction of flue gas flow through the system) by
a
particulate collection device (POD), advantageously a fabric filter (FF) bag
house, or
an electrostatic precipitator (ESP). If desired, there may also be provided a
wet
electrostatic precipitator (wet ESP or WESP) which may be provided as a final
"polishing" stage for fine particulate or S03. Alternatively, the present
invention may
be applied to a system which employs a spray dryer apparatus (SDA) or dry
scrubber for removal of sulfur oxides from the flue gases, as shown in the
lower
right-hand side of Figure 1. In this configuration, the SDA or dry scrubber is
typically
followed (with respect to a direction of flue gas flow through the system) by
a
particulate collection device (POD), advantageously a fabric filter (FF) or
baghouse,
an electrostatic precipitator (ESP) or even a wet electrostatic precipitator
(wet ESP).
[0034] Additionally, the present invention can be applied to any SCR
catalyst
that is adversely affected by poisoning with a phosphorus-based compound such
as,
but not limited to, H3PO4, PO or P205. As such, the present invention is not
limited to
any one type of SCR catalyst, but rather is broadly applicable to a wide range
of
SCR catalyst systems. Suitable catalyst systems for which the present
invention is
applicable include, but are not limited to, honeycomb, plate or corrugated
type
configurations.
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[0035] In
one embodiment, the present invention is directed to reducing the
rate of SCR catalyst deactivation on Powder River Basin (PRB) coal combustion
units. In another embodiment, the present invention is directed to reducing
the rate
of SCR catalyst deactivation on any type of fossil fuel-fired combustion unit
where
the fuel and/or combustion process utilized results in the generation of
undesirable
levels of gas phase phosphorus compounds that in turn result in the
accumulation of
such compounds in an SCR catalyst thereby leading to the an undesirable
increase
in the deactivation rate of such an SCR catalyst. It should be noted that
although the
present invention is described in relation to PRB coal, the present invention
is not
limited thereto. Rather, the present invention is broadly applicable to any
situation
where an SCR catalyst is poisoned by one or more gaseous phosphorus
compounds.
[0036] In
one embodiment, phosphorus in PRB coal is suspected to cause
rapid deactivation in staged combustion and other units. In another instance,
the
phosphorus in any type of fossil fuel can lead to rapid deactivation in a
fossil fuel-
fired combustion unit. While not wishing to be bound to any one theory, it is
believed
that the deactivation is suspected to be caused by the gas phase phosphorus
released via carbothermic reduction reaction. In this reaction under oxygen
deficient
conditions, phosphorus bearing compounds release gas phase phosphorus by the
following reaction:
P205 (solid phase compounds) + 30(s) ¨> 2P0(g) + 300(g).
[0037]
This gas phase phosphorus attaches to the active sites within the
catalyst causing the deactivation of the sites for NO reduction. As a result
of this
deactivation the SCR catalyst cannot carry out the NO reduction process to the
same performance level as unused catalyst.
[0038] In
one embodiment, the present invention relates to a system and
method to prevent formation of gas phase phosphorus species in the combustion
environment thus reducing, mitigating and/or eliminating the rate of SCR
deactivation. In
one embodiment, the present invention accomplishes the
aforementioned goal by the addition of at least one iron-bearing compound to
the
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PRB coal prior to combustion. Alternatively, the at least one iron-bearing
compound
of the present invention can be added to any type of phosphorus-containing
fossil
fuel (e.g., mixed with, or supplied individually from, any type of fuel oil),
or supplied to
any of the injection points discussed below with regard to the various coal
embodiments.
[0039] In another embodiment, the present invention is directed to a
system
and method designed to increase the catalytic activity and/or catalytic life
span. In
this case, the increase in catalytic activity and/or increase in catalytic
life span is
measured against a standard, or known, rate of decline in catalytic activity
and/or life
for a given a boiler, fossil fuel boiler, kiln, heater, or any other type of
device that
generates a flue gas or combustion gas containing NON.
[0040] In one embodiment, the iron-bearing compounds of the present
invention is any iron compound (e.g., an iron oxide compound) that is able to
undergo reduction in the combustion environments common to boilers, furnaces,
power plants, etc. In another embodiment, the iron-bearing compound of the
present
invention can be a water soluble, or water insoluble, iron-bearing compound.
Suitable water soluble iron-bearing inorganic compounds include, but are not
limited
to, iron (II) acetate (e.g., Fe(C2H302)2.4H20), iron (II) nitrate (e.g.,
Fe(NO3)2.6H20),
iron (III) nitrate (e.g., Fe(NO3)3.6H20 or Fe(NO3)3.9H20), iron (II) sulfate
(e.g.,
Fe504=1-120, Fe504=4H20, Fe504=5H20, or Fe504=7H20), iron (III) sulfate (e.g.,
Fe2(504)3.9H20), or mixtures of two or more thereof. Although various hydrated
forms of iron-bearing compounds are listed here, the present invention is not
limited
to just the hydrated forms listed above. Rather, if possible, any
corresponding
anhydrous form of the above listed iron-bearing compounds can also be utilized
in
conjunction with the present invention. Given this, when an iron-bearing
compound
is mentioned herein it should be interpreted to encompass both a hydrated form
or
an anhydrous form regardless of whether or not such a formula is given with
"bound
water." Suitable water insoluble iron-bearing compounds include but are not
limited
to, metallic iron, one or more iron oxides, iron carbonate, or mixtures of two
or more
thereof. Additionally, a wide range of water soluble, or water insoluble,
organic iron
bearing compounds could be utilized in conjunction with the present invention.
As
will be discussed below, the iron-bearing compound of the present invention
can be
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supplied in any desirable form including, but not limited to, powderized form,
solid
form, as an aqueous solution, as an aqueous suspension or emulsion, or any
combination of two or more different forms of iron-bearing compounds. In still
another embodiment, where two different forms of iron-bearing compounds are
supplied in conjunction with the present invention, the iron-bearing compound
supplied via each different form can be the same or different. In one
particular
embodiment, the iron-bearing compound is iron (III) oxide (Fe203), also known
as
red iron oxide or hematite. In the embodiment where iron (III) oxide is
utilized the
reactions of interest that occur in the combustion portion of a boiler or
furnace are as
shown below:
3Fe203(s) + CO(g) ¨> 2Fe304(s) + 002(g) (1)
Fe304(s) + CO(g) ¨> 3Fe0(s) + CO2(g) (2).
[0041] It should be noted that the Fe304, also known as black iron oxide
or
magnetite, of the first reaction above can also be written more accurately as
Fe0=Fe203. The FeO or iron (II) oxide, also known as ferrous oxide, which is
generated due to the reduction of Fe203 is then available to tie-up, bind
and/or
sequester any PO gas present in the combustion zone, or the flue gas, of a
boiler, or
furnace, prior to arrival at the SCR. This PO gas will then form Fe-P
compounds in
particulate phase prior to arrival at the SCR. The particulate will pass
through the
catalyst and avoid the catalyst deterioration.
[0042] In another embodiment, the present invention can utilize iron (II)
carbonate which is converted to the desired iron (II) oxide in the combustion
zone via
the reaction shown below:
Fe003(s) ¨> FeO(s) + 002(g) (3).
[0043] In still another embodiment, the present invention can utilize a
combination of one or more iron-containing compounds and one or more halide
compounds, with the proviso that the halide containing compound is not an iron
halide. Thus, in this embodiment at least one iron-containing compound is
utilized in
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conjunction with at least one non-iron halide containing compound. In still
another
embodiment, the at least one iron compound has a generic formula of AX, where
A
is equal to iron and X is either an oxide or carbonate ion, anion, group,
and/or moiety
and the at least one halide compound has a generic formula of BY where B is
any
atom, element, or cation except for iron and Y is a halide selected from
chlorine,
bromine, fluorine, or iodine.
[0044] In one embodiment, suitable halides for use in conjunction with
the
present invention include, but are not limited to, potassium bromide,
potassium
chloride, potassium fluoride, potassium iodide, sodium bromide, sodium
chloride,
sodium fluoride, sodium iodide, calcium bromide, calcium chloride, calcium
fluoride,
calcium iodide, aluminum bromide, aluminum chloride, aluminum fluoride,
aluminum
iodide, other metal halides (e.g., bromides, chlorides, fluorides and/or
iodides) with
the proviso that the metal is not iron, or any mixture of two or more thereof.
In still
another embodiment, any one or more halide compounds in accordance with the
proviso defined above can be used in combination with one or more non-halide
containing iron compounds (e.g., iron (II) carbonate). In still another
embodiment,
the present invention utilizes a combination of iron (II) carbonate with
calcium
bromide to control the amount of phosphorus in a flue gas, or combustion gas
while
concurrently permitting both the control of mercury compounds, or mercury-
containing compounds, in a flue gas, or combustion gas and the increase in
catalytic
activity and/or service life. In still yet another embodiment, the present
invention
utilizes a combination of iron (II) carbonate with calcium chloride to control
the
amount of phosphorus in a flue gas, or combustion gas while concurrently
permitting
both the control of mercury compounds, or mercury-containing compounds, in a
flue
gas, or combustion gas and the increase in catalytic activity and/or service
life. In
still yet another embodiment, the present invention utilizes a combination of
iron (II)
carbonate with either one, or both, of aluminum bromide and/or aluminum
chloride to
control the amount of phosphorus in a flue gas, or combustion gas while
concurrently
permitting both the control of mercury compounds, or mercury-containing
compounds, in a flue gas, or combustion gas and the increase in catalytic
activity
and/or service life. As used herein, mercury compounds, or mercury-containing
compounds, include, but are not limited to, any compound that contains either
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oxidized mercury, or bound elemental mercury. In still another embodiment, the
present invention is directed to concurrently permitting the control of
mercury
compounds, or mercury-containing compounds, that contain primarily, or only,
oxidized mercury.
[0045] As used herein, any iron compound suitable for use in conjunction
with
the present invention can be utilized in a hydrated or non-hydrated form. As
such,
reference to any iron compound herein by definition includes any hydrated
forms that
exists whether or not specifically mentioned by chemical formula.
[0046] As is known in the art, (see, e.g., United States Patent
Application
Publication No. 2008/0107579 the text of which is hereby incorporated by
reference
as though fully set forth herein) halide-containing compounds are utilized to
oxidize
elemental mercury present in a flue, or combustion, gas. Due to this oxidation
reaction, the halide portion of a suitable halide-containing compound permits
elemental mercury to be converted into a more favorable form for subsequent
capture, or sequestration, via one or more suitable environmental control
technologies (e.g., a wet scrubber or spray dry absorber (SDA), a flue gas
desulfurization system (FGD), a powdered activated carbon system (PAC), or a
particulate collecting system such as a fabric filter (FF) or a electrostatic
precipitator
(ESP)). In one instance, as is known in the art, the addition of one or more
suitable
halide-containing compounds also increases the amount of mercury that is
particulate-bound. Given that numerous patents and published applications
detail
the manner by which suitable halide-containing compounds permit the increased
recovery of mercury from a flue, or combustion, gas, a detailed discussion
hereof is
omitted for the sake of brevity.
[0047] In any of the above embodiments, the suitable one or more iron-
bearing compounds, and if so desired the one or more halide compounds, can be
added to the coal via one or more pulverizers. In still another embodiment,
the one
or more iron-bearing compounds, and if so desired the one or more halide
compounds, of the present invention can be added to the combustion zone of a
boiler and/or furnace via one or more suitable supply lines designed to
deliver a
powderized, solid, aqueous suspension, suspension, or aqueous solution of the
one
or more iron-bearing compounds and/or the one or more halide compounds to the
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combustion zone of a furnace and/or boiler. To this end, Figure 1 illustrates
several
embodiments of suitable design schemes for accomplishing this result.
[0048] Referring to Figure 1, there is illustrated a schematic
representation of
a typical fossil fuel burning facility, generally designated 10, with an SCR
system,
and which includes a system for practicing the methods of the present
invention. As
shown, boiler 12 is provided for extracting the heat from the combustion of a
fossil
fuel, such as coal, through combustion with an oxidant, typically air. The
heat is
transferred to a working fluid, such as water, to generate steam used to
either
generate power via expansion through a turbine generator apparatus (not shown)
or
for industrial processes and/or heating.
[0049] The raw coal 14 must be crushed to a desired fineness and dried to
facilitate combustion. Raw coal 14 is temporarily stored in a coal bunker 16
and then
transferred by means of a gravimetric or volumetric feeder 18 to one or more
coal
pulverizers 20. In the embodiment shown in Figure 1, there are six (6) coal
pulverizers, identified as coal pulverizers A - F. As is known to those
skilled in the
art, each coal pulverizer 20 grinds the coal to a desired fineness (e.g., 70
percent
through 200 mesh) and as it is ground, hot primary air from primary air fans
(not
shown) is conveyed into each coal pulverizer 20 to preheat and remove moisture
from the coal to desired levels as it is ground. The primary air is also used
to convey
the pulverized coal (PC) out of each coal pulverizer 20 and delivers it along
a
plurality of pulverized coal supply lines (one such burner line is identified
at A in
Figure 1; a single coal pulverizer 20 may supply coal through 4 to 8
pulverized coal
supply lines) to the burners 22 on the front and rear walls of the boiler 12.
Typically,
the burners 22 are located in spaced elevations on one or both of the opposed
front
and rear walls of the boiler 12, or at the corners of the boiler in
installations known as
corner-fired or tangentially-fired units (not shown). The present invention
can be
utilized in conjunction with, but is not limited solely to, single-wall fired,
opposed-wall
fired and corner- or tangentially-fired units. Typically, a single coal
pulverizer 20 only
provides coal to a single elevation of burners 22 on a wall. Thus, in the
embodiment
shown in Figure 1, the six coal pulverizers A - F supply corresponding burner
elevations A - F. However, as is known to those skilled in the art, other
pulverizer
and burner configurations are known (e.g., single pulverizers supplying
burners on
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multiple walls and/or elevations or multiple pulverizers supplying burners on
a single
elevation) and the present invention applies to any such configurations.
[0050] The combustion process begins in the burner zone 24 of the boiler
12's
furnace 26, releasing heat and creating hot flue gas 28 which is conveyed
upwardly
to the upper portion 30 of the boiler 12, across heating surfaces
schematically
indicated as rectangles 32. The flue gas 28 is then conveyed across the
heating
surfaces in the pendant convection pass 34, into the upper portion 36 of the
horizontal convection pass 38. The flue gas 28 is then conveyed through a
selective
catalytic reduction (SCR) apparatus 40 where NO in the flue gas is reduced,
and
then through primary and secondary air heater devices schematically indicated
at 42.
The air heaters 42 extract additional heat from the flue gas 28, lowering the
temperature of the flue gas, and preheat the incoming air used for combustion.
[0051] As illustrated in Figure 1, and downstream of the air heaters 42,
the
flue gas 28 undergoes further treatment for the removal of particulates and
sulfur
oxides. Two typical configurations of the downstream equipment employed to
accomplish these tasks are shown on the right-hand side of Figure 1. The first
equipment configuration in Figure 1 comprises a particulate collection device
(POD)
schematically indicated at 44, for removal of particulates from the flue gas
28, and
which may comprise in practice a fabric filter or an electrostatic
precipitator.
Downstream of the POD 44 there is provided a wet flue gas desulfurization
(WFGD)
device, also known as a wet scrubber, for removal of sulfur oxides from the
flue gas
28. The cleaned, scrubbed flue gas may (optionally) be conveyed through a wet
ESP 47 for removal of fine particulate or SO3, and then conveyed to stack 48
for
discharge to the atmosphere.
[0052] The second equipment configuration in Figure 1 comprises a spray
dryer apparatus (SDA) schematically indicated at 50, also known as a dry
scrubber,
for removal of sulfur oxides from the flue gas 28. Downstream of the SDA 50
there
is provided a particulate collection device (POD) 44, as described above, for
removal
of particulates from the flue gas 28. The cleaned, scrubbed flue gas is then
conveyed to stack 48 for discharge to the atmosphere.
[0053] The third equipment configuration in Figure 1 comprises a
circulating
dry scrubber (CDS) schematically indicated at 49, for removal of sulfur oxides
from
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the flue gas 28. Downstream of CDS 49 there is provided a particulate
collection
device (POD) 44 for removal of particulates from the flue gas 28. As in the
embodiments above, POD 44 may comprise any suitable particulate collection
device including, but not limited to, a fabric filter or an electrostatic
precipitator as
described above. The cleaned, scrubbed flue gas is then conveyed to stack 48
for
discharge to the atmosphere.
[0054] The
fourth equipment configuration in Figure 1 comprises a first
particulate removal device in the form of an electrostatic precipitator (ESP)
which is
schematically indicated at 44. ESP 44 is configured to remove fine
particulates from
flue gas 28. Downstream of ESP 44 there is provided a circulating dry scrubber
(CDS) schematically indicated at 49, for removal of sulfur oxides from the
flue gas
28. Downstream of CDS 49 there is provided a second particulate collection
device
(POD) 44 for removal of any remaining particulates from the flue gas 28. As in
the
embodiments above, POD 44 may comprise any suitable particulate collection
device including, but not limited to, a fabric filter or an electrostatic
precipitator as
described above. The cleaned, scrubbed flue gas is then conveyed to stack 48
for
discharge to the atmosphere. In
another embodiment, ESP 44 could be
interchangeably replaced with a fabric filter unit.
[0055] The
fifth equipment configuration in Figure 1 comprises a first
particulate removal device in the form of either a fabric filter or an
electrostatic
precipitator (ESP) which is schematically indicated at 44. FF/ESP 44 is
configured to
remove fine particulates from flue gas 28. Downstream of FF/ESP 44 there is
provided a spray dryer apparatus (SDA) schematically indicated at 50, also
known
as a dry scrubber, for removal of sulfur oxides from the flue gas 28.
Downstream of
SDA 50 there is provided a second particulate collection device (POD) 44 for
removal of any remaining particulates from the flue gas 28. As in the
embodiments
above, POD 44 may comprise any suitable particulate collection device
including, but
not limited to, a fabric filter or an electrostatic precipitator as described
above. The
cleaned, scrubbed flue gas is then conveyed to stack 48 for discharge to the
atmosphere.
[0056] In
order to further reduce NO emissions, some boilers 12 employ
staged combustion wherein only part of the stoichiometric amount of air is
provided
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in the main burner zone 24, with the balance of the air for combustion,
together with
any excess air required due to the fact that no combustion process is 100
percent
efficient, is provided above the burner zone 24 via over fire air (OFA) ports
52. If
staged combustion is employed in a boiler 12, due to the reduced air supplied
to the
burner zone 24, a reducing atmosphere is created in the lower portion of the
furnace
26, including the hopper region 54.
[0057] In accordance with a first embodiment of the present invention,
one or
more suitable iron-bearing compounds, and if so desired one or more suitable
halide
compounds, are added to the one or more coal pulverizers 20 prior to supplying
the
pulverized coal to the one or more burners 22. The system and apparatus for
accomplishing this desired result is also shown in Figure 1, generally
designated
100. The system 100 comprises a storage means 120 for temporarily storing the
iron-based phosphorus reduction compound, and if so desired the mercury
reducing
compound, generally designated 110; delivery means 130, 135 for conveying the
compound 110 to a desired location, including valves, seals, etc. as required;
and
control means 150, advantageously microprocessor-based control means, which
are
accessed via an operator via human operator interface (I/O) station 160, which
includes display and data collection and storage means as required. Although
not
illustrated individually, the system of the present invention can, in one
embodiment,
utilize independent storage, delivery and control means (in accordance with
those
described above) for each individual iron and/or halide compound. In still
another
embodiment, the system of the present invention can comprise one set of
storage,
delivery and control means for the iron compounds or compounds utilized herein
and
one set of storage, delivery and control means (in accordance with those
described
above) for the halide compound or compounds utilized herein.
[0058] In Figure 1, the raw coal 14 to which the iron-based phosphorus
reducing compound 110 has been added is referred to as 140. Advantageously,
the
iron-based phosphorus reducing compound 110 may be provided along with the raw
coal 14 via the feeder 18, which permits close control and measurement of the
delivery of both raw coal 14 and iron-based phosphorus reducing compound 110
into
the coal pulverizer 20. Alternatively, the iron-based phosphorus reducing
compound
110 may be provided directly into the coal pulverizer 20 and/or directly into
one or
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more individual burner lines A - F providing the pulverized coal to individual
burners
22, with suitable sealing devices against the positive pressure within the
coal
pulverizer 20 or burner lines A - F. The delivery means may be slurry-based or
pneumatic as required by the particulars of the iron-based phosphorus reducing
compound 110 and the amount and location of introduction into the flue gas 28.
An
interconnected arrangement of control or signal lines 170, 180, 190 and 195
interconnect these various devices to provide control signals, iron-based
phosphorus
reducing compound 110 level signals, and phosphorus level signals in the flue
gas
28 (from a sensor 200) to permit the introduction of the iron-based phosphorus
reducing compound 110 into the flue gas 28 to be controlled by a human
operator, or
automatically controlled. However, if a suitable, real-time sensor 200 for
measuring
levels of gaseous phosphorus in the flue gas 28 is not available, flue gas
samples
may instead be taken at the location 200 for later laboratory analysis via
suitable test
methods, which may be inductively coupled plasma - mass spectrometry (ICP-MS).
Based upon the laboratory results, a human operator could then use the
operator
interface 160 to manually input a desired set-point into control means 150 for
the
amount of iron-based phosphorus reducing compound 110 introduced into the flue
gas 28. Provided that subsequent laboratory analyses do not indicate any
significant
variation in gaseous phosphorus levels in the flue gas 28, there may be no
need for
real-time, close control of the introduction of iron-based phosphorus reducing
compound 110. Instead, the amount of iron-based phosphorus reducing compound
110 introduced into the flue gas 28 may be simply a function of boiler load or
coal
feed rate values.
[0059] In still yet another embodiment, the present invention utilizes
iron (II)
oxide. In this embodiment, the need for a reduction reaction to occur is
eliminated
and the addition points for the iron (II) oxide of this embodiment are
therefore
broader then previous embodiments. In this case, the iron (II) oxide can be
added at
any suitable point post-combustion and pre-SCR in order to tie up, bind and/or
sequester any PO gas present in the flue gas of a boiler, or furnace, prior to
arrival at
the SCR. In particular, the iron-based phosphorus reduction compound can be
supplied at one or more of the locations G through Q shown in Figure 1. More
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particularly, the iron-based phosphorus reduction compound can also be
provided
into the flue gas 28 at one or more of the following locations:
G: into or below the burner zone 24, in one or more of the front,
rear or side walls, via means separate from the burners 22;
H: into the furnace 26 at a location above the burner zone 24, in
one or more of the front, rear or side walls;
I, J:
into the furnace 26 in the vicinity of or via the OFA ports 52 on
one or both of the front or rear walls;
K: into the boiler 12 in the pendant convection pass 34;
L: into the boiler 12 in the upper portion 36 of the horizontal
convection pass 38;
M, N, 0, P: into the boiler 12 in the horizontal convection pass 38;
and/or
Q:
into the boiler 12 in the hopper region below the horizontal
convection pass 38.
[0060]
Given the above, it should be noted that in addition to the introduction
of the one or more iron-based phosphorus reduction compounds, the above-
mentioned systems, methods and/or control apparatuses and/or technologies can
also be utilized to introduce one or more halide compounds in accordance with
the
present invention as detailed above. Thus, in one embodiment, the present
invention is directed to a system whereby both one or more iron-based
compounds
and one or more halide compounds are supplied in any manner per the various
methods and/or systems described herein. In another embodiment, each type of
compound, or even each separate compound regardless of type, can be supplied
individually. In
still another embodiment, any combination of two or more
compounds regardless of type (i.e., whether an iron-based compound or a halide
compound) can be supplied together so long as the one compound does not react
detrimentally with the other compound.
[0061]
Furthermore, given the above, the reduced iron, or iron (II) oxide, of the
present invention is able to remove the gas phase phosphorus in the form of
iron-
phosphorus alloys which upon coming in contact with the over fire air from
iron-
phosphorus oxide compounds. This significantly reduces the amount of gas phase
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phosphorus accumulation in an SCR catalyst. Another advantage of the present
invention is that through addition of iron a significant portion of any
phosphorus
present will be iron-bound. Iron-bound phosphorus compounds are less leachable
thereby minimizing the transfer of phosphorus to an SCR catalyst. Furthermore,
phosphorus associated with and/or bound to an iron compound (e.g., an iron
oxide)
is more stable than phosphorus that is associated with and/or bound to a
calcium
compound (e.g., calcium oxide). Given this, the present invention is, in one
embodiment, directed to the situation where a majority of the phosphorus
present in
the combustion and/or flue stream is sequestered in a suitable iron-phosphorus-
oxygen-containing compound thereby substantially reducing the amount of
calcium/phosphorus/oxygen-containing compounds that are able to react with
SON.
This in turn substantially reduces the amount of gaseous phosphorus that is
produced in the combustion and/or flue gas stream by restricting the amount of
calcium/phosphorus/oxygen-containing compounds that are present in the
combustion and/or flue gas stream to react with various SO x compounds
resulting in
the unwanted production of gaseous phosphorus compounds, or phosphorus/oxygen
compounds, that can lead to the undesired poisoning of an SCR catalyst.
[0062] In still another embodiment, the iron-bearing compound and the
halide
compound of the present invention can be added via separate compounds or can
be
added via the same compound and can be supplied in any suitable manner,
including the manner detailed in the Figure 1. Suitable iron-bearing compounds
include, but are not limited to, powderized, solid, aqueous (be it an aqueous-
based
suspension or aqueous-based emulsion) and/or water soluble or water insoluble
forms of iron-bearing compounds including, but not limited to, metallic iron,
one or
more iron oxides, iron carbonate, iron (II) acetate (e.g., Fe(C2H302)2-4H20),
iron (II)
nitrate (e.g., Fe(NO3)2.6H20), iron (III) nitrate (e.g., Fe(NO3)3.6H20 or
Fe(NO3)3-9H20), iron (II) sulfate (e.g., Fe504=1-120, Fe504=4H20, Fe504=5H20,
or
Fe504=7H20), iron (III) sulfate (e.g., Fe2(504)3.9H20), iron (II) bromide
(e.g., FeBr2),
iron (III) bromide (e.g., FeBr3, Fe2Br6, or FeBr3=6H20), iron (II) chloride
(e.g., FeCl2,
FeC12=2H20, or FeC12=4H20 FeBr2), iron (III) chloride (e.g., FeCI3, Fe2CI6,
FeC13-21/2H20, or FeC13=6H20), iron (II) iodide (e.g., Fe12 or Fe12.4H20),
iron (III)
iodate (e.g., Fe(I03)3), or mixtures of two or more thereof. Although various
hydrated
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forms of iron-bearing compounds are listed here, the present invention is not
limited
to just the hydrated forms listed above. Rather, if possible, any
corresponding
anhydrous form of the above listed iron-bearing compounds can also be utilized
in
conjunction with the present invention. Given this, when an iron-bearing
compound
is mentioned herein it should be interpreted to encompass both a hydrated form
or
an anhydrous form regardless of whether or not such a formula is given with
"bound
water." Suitable halide compounds include, but are not limited to, potassium
bromide, potassium chloride, potassium fluoride, potassium iodide, sodium
bromide,
sodium chloride, sodium fluoride, sodium iodide, calcium bromide, calcium
chloride,
calcium fluoride, calcium iodide, aluminum bromide, aluminum chloride,
aluminum
fluoride, aluminum iodide, other metal halides (e.g., bromides, chlorides,
fluorides
and/or iodides) with the proviso that the metal is not iron, or any mixture of
two or
more thereof. If an existing skid is used then one or more aqueous reagents
can be
pumped via positive displacement pumps from a storage tank to the one or more
coal feeders where the reagent is sprayed on the coal as the coal passes on a
feeder belt upstream of the pulverizers. In this instance, if so utilized the
one or
more halide compounds are chosen to be soluble in water, or an aqueous-based
solvent. Suitable halides soluble halides include, but are not limited to,
potassium
bromide, potassium chloride, potassium fluoride, potassium iodide, sodium
bromide,
sodium chloride, sodium fluoride, sodium iodide, calcium bromide, calcium
chloride,
calcium iodide, aluminum bromide, aluminum chloride, aluminum iodide, or any
mixtures of two or more thereof. In still another embodiment, other transition
metal
halides (e.g., bromides, chlorides, fluorides and/or iodides) that are not
iron halides
can be utilized so long as such compounds are, in this embodiment, soluble in
water,
or an aqueous-based solvent.
[0063] In one embodiment, the present invention is advantageous in that
it is
applicable to both existing SCRs (retrofits) and new SCRs. Additionally, the
present
invention can be applied to plants that utilize biomass as a fuel source. In
one
embodiment, implementation of the present invention can be accomplished in a
cost-
effective manner utilizing low cost hardware designed to supply the necessary
iron
compound to a combustion process. The present invention also does not affect
the
current design of boilers and SCRs.
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[0064] In one embodiment, the amount of iron compound, or compounds,
utilized in conjunction with the present invention varies depending upon the
phosphorus content in the coal to be burned. In one embodiment, the present
invention is directed to a method and system whereby a stoichiometric excess
one or
more iron compounds are supplied to any point prior to an SCR. While not
wishing
to be bound to any one theory, it has been found that by supplying a
stoichiometric
excess of iron upstream of an SCR, the catalytic activity and/or catalytic
lifespan of
an SCR catalyst can be unexpectedly increased. As can be seen from the graph
of
Figure 2, the addition of a stoichiometric excess of one or more iron-based
compounds not only protects the SCR catalyst from poisoning via various
phosphorus compounds but also increases both the catalytic activity and
catalytic
lifespan over a period of at least about 2,000 operational hours.
[0065] Regarding Figure 2, Figure 2 is a graph plotting the original
expected
deactivation for a catalyst without the addition of the iron-bearing compound,
or
compounds, of the present invention versus the actual deactivation of a
catalyst with
the addition of an iron-bearing compound of the present invention versus the
observed deactivation of a catalyst without the addition of the iron-bearing
compound, or compounds, of the present invention. The y-axis of the graph of
Figure 2 is catalytic activity in decimal terms where 0.9 is equivalent to 90
percent
activity as measured when compared to unused virgin catalyst as determined
using
any suitable method for determining catalytic activity known to those of skill
in the
art. The x-axis of the graph of Figure 2 is the number of operational hours
that the
catalyst in question is exposed to the average operational conditions of a 100
MWe
coal plant.
[0066] Given the above, in one embodiment the present invention achieves
either one, or both, of an increase in catalytic activity and/or an increase
in catalytic
lifespan via the use, introduction and/or delivery of one or more iron-based
compounds. In one embodiment, an increase in either one, or both, of catalytic
activity and/or catalytic lifespan of at least about 10 percent is achieved at
an
operational time of at least about 2,000 hours versus the catalytic activity
and/or
catalytic lifespan of a given catalyst when subjected to similar operational
conditions
but not subjected to a supply of one or more iron-based compounds as disclosed
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herein. As would be apparent to those of skill in the art, various known
methods are
available to measure the baseline catalytic activity as well as the catalytic
activity of
various catalysts, including SCR catalysts. As such, a detailed discussion
herein is
omitted for the sake of brevity.
[0067] In another embodiment, the present invention achieves an increase
in
either one, or both, of catalytic activity and/or catalytic lifespan of at
least about 10
percent is achieved at an operational time of about 2,000 hours, an increase
of at
least about 12.5 percent is achieved at an operational time of about 2,000
hours, an
increase of at least about 15 percent is achieved at an operational time of
about
2,000 hours, an increase of at least about 17.5 percent is achieved at an
operational
time of about 2,000 hours, an increase of at least about 20 percent is
achieved at an
operational time of about 2,000 hours, an increase of at least about 22.5
percent is
achieved at an operational time of about 2,000 hours, an increase of at least
about
25 percent is achieved at an operational time of about 2,000 hours, an
increase of at
least about 27.5 percent is achieved at an operational time of about 2,000
hours, or
even an increase of at least about 30 percent is achieved at an operational
time of
about 2,000 hours versus the catalytic activity and/or catalytic lifespan of a
given
catalyst when subjected to similar operational conditions but not subjected to
a
supply of one or more iron-based compounds as disclosed herein. Here, as well
as
elsewhere in the specification and claims, individual numerical values can be
combined to form additional and/or non-disclosed ranges.
[0068] In still another embodiment, the present invention achieves an
increase
in either one, or both, of catalytic activity and/or catalytic lifespan of at
least about 10
percent is achieved at an operational time of about 2,500 hours, an increase
of at
least about 12.5 percent is achieved at an operational time of about 2,500
hours, an
increase of at least about 15 percent is achieved at an operational time of
about
2,500 hours, an increase of at least about 17.5 percent is achieved at an
operational
time of about 2,500 hours, an increase of at least about 20 percent is
achieved at an
operational time of about 2,500 hours, an increase of at least about 22.5
percent is
achieved at an operational time of about 2,500 hours, an increase of at least
about
25 percent is achieved at an operational time of about 2,500 hours, an
increase of at
least about 27.5 percent is achieved at an operational time of about 2,500
hours, or
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even an increase of at least about 30 percent is achieved at an operational
time of
about 2,500 hours versus the catalytic activity and/or catalytic lifespan of a
given
catalyst when subjected to similar operational conditions but not subjected to
a
supply of one or more iron-based compounds as disclosed herein. Here, as well
as
elsewhere in the specification and claims, individual numerical values can be
combined to form additional and/or non-disclosed ranges.
[0069] In
still yet another embodiment, the present invention achieves an
increase in either one, or both, of catalytic activity and/or catalytic
lifespan of at least
about 10 percent, at least about 12.5 percent, at least about 15 percent, at
least
about 17.5 percent, at least about 20 percent, at least about 22.5 percent, at
least
about 25 percent, at least about 27.5 percent, or even at least about 30
percent is
achieved at an operational time of about 3,000 hours versus the catalytic
activity
and/or catalytic lifespan of a given catalyst when subjected to similar
operational
conditions but not subjected to a supply of one or more iron-based compounds
as
disclosed herein. In still yet another embodiment, the present invention
achieves an
increase in either one, or both, of catalytic activity and/or catalytic
lifespan of at least
about 10 percent, at least about 12.5 percent, at least about 15 percent, at
least
about 17.5 percent, at least about 20 percent, at least about 22.5 percent, at
least
about 25 percent, at least about 27.5 percent, or even at least about 30
percent is
achieved at an operational time of about 3,500 hours, about 4,000 hours, about
4,500 hours, about 5,000 hours, about 6,000 hours, about 7,000 hours, about
7,500
hours, about 8,000 hours, about 9,000 hours, about 10,000 hours, about 11,000
hours, about 12,000 hours, about 13,000 hours, about 14,000 hours, about
15,000
hours, or even about 16,000 hours versus the catalytic activity and/or
catalytic
lifespan of a given catalyst when subjected to similar operational conditions
but not
subjected to a supply of one or more iron-based compounds as disclosed herein.
Here, as well as elsewhere in the specification and claims, individual
numerical
values can be combined to form additional and/or non-disclosed ranges.
[0070] As
is known to those of skill in the art, the phosphorus content of coal
can be determined by various known methods. Thus, in this instance, the
present
invention is not limited to any one range of iron compounds that are utilized.
Instead,
an excess stoichiometric ratio is utilized. In
one embodiment, the excess
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stoichiometric ratio of iron to phosphorus is in the range of about 2.5:1 to
about 10:1,
or from about 3:1 to about 9:1, or from about 3.5:1 to about 8:1, or from
about 4:1 to
about 7.5:1, or from about 5:1 to about 7:1, or from about 5.5:1 to about
6.5:1, or
even about 6:1. Here, as well as elsewhere in the specification and claims,
individual range values can be combined to form additional and/or non-
disclosed
ranges.
[0071] In another embodiment, the amount of iron compound, or compounds,
utilized in conjunction with the present invention is within a given range
when the
coal utilized is Powder River Basin/Lignite coal. In this embodiment, the
amount of
the iron compound, or compounds, to Powder River Basin/Lignite coal is
expressed
as the amount of iron compound, or compounds, (hereinafter referred to as just
"iron" in only this instance) in pounds for every 1,000 pounds of coal. In one
embodiment, the amount of iron compound, or compounds, utilized is in the
range of
about 5 pounds of "iron" per 1,000 pounds of coal to about 20 pounds of "iron"
per
1,000 pounds of coal. In another embodiment, the amount of iron compound, or
compounds, utilized is in the range of about 5.5 pounds of "iron" per 1,000
pounds of
coal to about 17.5 pounds of "iron" per 1,000 pounds of coal, or from about 6
pounds
of "iron" per 1,000 pounds of coal to about 15 pounds of "iron" per 1,000
pounds of
coal, or from about 7 pounds of "iron" per 1,000 pounds of coal to about 12.5
pounds
of "iron" per 1,000 pounds of coal, or from about 7.5 pounds of "iron" per
1,000
pounds of coal to about 10 pounds of "iron" per 1,000 pounds of coal, or even
from
about 8 pounds of "iron" per 1,000 pounds of coal to about 9 pounds of "iron"
per
1,000 pounds of coal. Here, as well as elsewhere in the specification and
claims,
individual range values can be combined to form additional and/or non-
disclosed
ranges.
[0072] In another embodiment, where both an iron-based compound and a
halide compound as defined above are utilized, the amount of iron-based
compound,
or compounds, as compared on a weight basis to the amount of one or more
halide
compounds is in the range of about 95 weight parts iron based compound, or
compounds to about 5 weight parts halide compound, or compounds. In another
embodiment, the weight ratio of iron-based compound, or compounds, to halide
compound, or compounds, is in the range of about 95:5 to about 75:25, or from
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about 93.5:6.5 to about 80:20, or from about 92:8 to about 82.5:17.5, or from
about
91:9 to about 85:15, or even from about 90:10 to about 87.5:12.5. Thus, in one
embodiment, the amount of the one or more halide compounds, if so utilized,
can be
calculated based on any of the above stated iron-based compound, or compounds,
amounts via the ratios disclosed in this paragraph. Here, as well as elsewhere
in the
specification and claims, individual range values can be combined to form
additional
and/or non-disclosed ranges.
[0073] In another embodiment, the injection rate of the one or more
halide
compounds, if so utilized in conjunction with the present invention, for
controlling
mercury in a flue gas, or combustion gas, is based on a non-limiting example
of a
100 MWe coal power plant. In this case, the injection rate for the one or more
halide
compounds, if in solution, is in the range of about 0.25 gallons per hour to
about 10
gallons per hour, or from about 0.5 gallons per hour to about 5 gallons per
hour, or
even from about 1 gallon per hour to about 4 gallons per hour. In another
embodiment, regardless of power plant or combustion plant size, the one or
more
halide compounds are supplied at any rate to a flue gas, or combustion gas,
sufficient to yield a concentration of halide (e.g., bromide, chloride or
iodide) between
about 10 ppm to about 200 ppm, or from about 25 ppm to about 175 ppm, or from
about 50 ppm to about 150 ppm. It should be noted that depending upon the
emissions control technology in place on the device generating the flue gas,
or
combustion gas, it may be desirable to use a lower halide concentration in
order to
prevent any type of detrimental effects to such downstream emissions
technology.
In one embodiment of such an instance the concentration of halide is between
about
ppm to about 125 ppm, or from about 25 ppm to about 100 ppm, or from about 50
ppm to about 75 ppm. Here, as well as elsewhere in the specification and
claims,
individual range values (even from different embodiments) can be combined to
form
additional and/or non-disclosed ranges.
[0074] In light of the above, one of skill in the art would recognize
that the
amount of one or more iron, or iron-based, compounds necessary to supply the
desired amount of iron to a flue gas, or combustion gas, in accordance with
the
process of the present invention will vary depending upon the size of the
device
generating such flue gas, or combustion gas. The same can be said of the one
or
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more halide compounds. That is, one of skill in the art would recognize that
the
amount of one or more halide compounds necessary to supply the desired amount
of
halide to a flue gas, or combustion gas, in accordance with the process of the
present invention will vary depending upon the size of the device generating
such
flue gas, or combustion gas. Thus, the present invention is not limited to any
specific
rate or range of supply.
[0075] In another embodiment, for a 100 MWe coal power plant the amount
of
halide solution (25 weight percent solution) supplied to the flue gas, or
combustion
gas, is in the range of about 0.25 gallons per hour to about 6 gallons per
hour, or
from 0.5 gallons per hour to about 5 gallons per hour, or even from 1 gallon
per hour
to about 4 gallons per hour. Here, as well as elsewhere in the specification
and
claims, individual range values can be combined to form additional and/or non-
disclosed ranges. However, as is noted above, the present invention is not
limited to
solely these supply rates. Rather, any supply rate can be used in order to
achieve
the desired concentration of halide.
[0076] As would be apparent to one of skill in the art, other additional
factors
can impact the amount of iron-based, iron-bearing and/or iron compounds
supplied
in connection with the various embodiments of the present invention. Such
additional factors include, but are not limited to, the amount and/or type of
phosphorus present in the coal, or other combustible fuel; the size and/or
output of
the boiler, heater, kiln, or other flue gas-, or combustion gas-, generating
device; and
the desired stoichiometric ratio to be achieved; the type and/or manner of
combustion, the type and/or arrangement of any applicable equipment or
structure.
[0077] In another embodiment, the one or more iron compounds and/or the
one or more halide compounds utilized in conjunction with the present
invention can
be of any particle size and/or particle geometry. Suitable particle geometries
include, but are not limited to, spherical, platelet-like, irregular,
elliptical, oblong, or a
combination of two or more different particle geometries. As would be apparent
to
those of skill in the art, each different compound, or even the same compound,
can
be supplied in the form of one or more particle geometries. In one embodiment,
the
one or more iron compounds and/or the one or more halide compounds of the
present invention, if water soluble, can be supplied in solution form, either
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independently or together so long as the active components to be delivered to
the
flue, or combustion, gas do not adversely react. In such an instance, a
solution
concentration of at least about 15 weight percent of one or more water soluble
iron
compounds and/or one or more water soluble halide compounds is utilized. In
another embodiment, a solution concentration of at least about 20 weight
percent, at
least about 25 weight percent, at least about 30 weight percent, at least
about 35
weight percent, at least about 40 weight percent, at least about 45 weight
percent, or
even at least about 50 weight percent of more of the one or more water soluble
iron
compounds and/or the one or more water soluble halide compounds is utilized in
conjunction with the present invention.
Here, as well as elsewhere in the
specification and claims, individual range values can be combined to form
additional
and/or non-disclosed ranges. As would be appreciated by those of skill in the
art,
the solution concentration of any one or more water soluble iron compounds
and/or
the one or more water soluble halide compounds should not, in one embodiment,
exceed the solubility amount, respectively, for the one or more iron compounds
and/or the one or more halide compounds.
[0078] In
still another embodiment, the one or more iron compounds and/or
the one or more halide compounds of the present invention can be supplied in a
powdered form, a solution form, an aqueous suspension form, or a combination
of
two or more thereof. In the case of an aqueous suspension, the one or more
iron
compounds and/or the one or more halide compounds utilized in conjunction with
the
present invention should have a suitable particle size. Additionally, even
absent the
desire to place the one or more iron compounds and/or the one or more halide
compounds of the present invention into an aqueous solution, the one or more
iron
compounds and/or the one or more halide compounds should have a suitable
particle size that facilitates a higher degree of reactivity when placed into
contact
with a flue, or combustion, gas. In one embodiment, both of these conditions
can be
met, whether individually or in combination, by one or more iron compounds
and/or
one or more halide compounds where at least about 95 percent of the particles
have
a particle size of less than about 400 pm (microns), where at least about 95
percent
of the particles have a particle size of less than about 350 pm (microns),
where at
least about 95 percent of the particles have a particle size of less than
about 300 pm
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(microns), where at least about 95 percent of the particles have a particle
size of less
than about 250 pm (microns), where at least about 95 percent of the particles
have a
particle size of less than about 200 pm (microns), or even where at least
about 95
percent of the particles have a particle size of less than about 175 pm
(microns).
Here, as well as elsewhere in the specification and claims, individual range
values
can be combined to form additional and/or non-disclosed ranges.
[0079] Although not limited hereto, a suitable iron compound for use in
conjunction with the present invention is iron (II) carbonate available from
Prince Agri
Products (a subsidiary of Phibro Animal Health Corporation located in
Ridgefield
Park, New Jersey). This iron (II) carbonate is a powdered compound where at
least
about 95 percent of its particles are less than 200 pm (microns) in size.
Additionally,
the concentration of iron (II) carbonate in this product is about 80 percent
by weight
with substantially all of the remaining 20 weight percent being non-reactive
in light of
the use here. A suitable halide compound for use, if so desired, in
conjunction with
the present invention is calcium bromide available from Tetra Chemical
(located in
The Woodlands, Texas).
[0080] In the instance where one or more aqueous suspensions is/are
utilized
in conjunction with the present invention, such aqueous suspension(s) can
further
comprise a suitable amount of one or more anti-settling, suspension,
thickening or
emulsification agents. Suitable anti-settling, suspension, thickening or
emulsification
agents include, but are not limited to, sodium polyacrylates, carbomers,
acrylates,
and inorganic thickening agents. Other suitable anti-settling, suspension,
thickening
or emulsification agents are known to those of skill in the art and as such a
discussion herein is omitted for the sake of brevity. In another embodiment, a
suitable suspension or emulsification can be achieved via agitation and does
not
necessarily require the use of one or more anti-settling, suspension,
thickening or
emulsification agents. In another embodiment, a combination of one or more
anti-
settling, suspension, thickening or emulsification agents can be utilized in
combination with agitation.
[0081] In still another embodiment, the one or more iron compounds and/or
the one or more halide compounds of the present invention should independently
have a purity of at least about 50 weight percent, at least about 55 weight
percent, at
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least about 60 weight percent, at least about 65 weight percent, at least
about 70
weight percent, at least about 75 weight percent, at least about 80 weight
percent, at
least about 85 weight percent, at least about 90 weight percent, at least
about 95
weight percent, or even at least about 99 weight percent or higher. Here, as
well as
elsewhere in the specification and claims, individual range values can be
combined
to form additional and/or non-disclosed ranges.
[0082] As for the portion of the one or more iron compounds that is not
"an
iron compound," such impurities should be non-reactive in the environments
present
in conjunction with the present invention. Alternatively, if reactive, such
impurities
should either be easily captured, removed and/or sequestered, or should not
add
significantly to any further contamination of any catalyst downstream. In
still another
embodiment, the amount of phosphorus-containing compound impurities in any of
the one or more iron compounds and/or the one or more halide compounds that
are
utilized in conjunction with the present invention should independently be
less than
about 5 weight percent, less than about 2.5 weight percent, less than about 1
weight
percent, less than about 0.5 weight percent, less than about 0.25 weight
percent,
less than about 0.1 weight percent, or even less than about 0.01 weight
percent.
Here, as well as elsewhere in the specification and claims, individual range
values
can be combined to form additional and/or non-disclosed ranges. In still yet
another
embodiment, the amount of phosphorus-containing compound impurities in any of
the one or more iron compounds and/or the one or more halide compounds that
are
utilized in conjunction with the present invention should be zero. That is, in
this
embodiment the one or more iron compounds and/or the one or more halide
compounds that are utilized in conjunction with the present invention should
independently be free from any phosphorus-containing compounds.
[0083] While not wishing to be bound to any one theory, it is believed
that the
present invention exploits various preferential reactions between phosphorus
compounds, or phosphorus-containing compounds, to sequester various phosphorus
compounds, or phosphorus-containing compounds that are detrimental to an
increased active, or service, life of an SCR catalyst. Thus, the reactions
discussed
herein are to be construed as non-limiting in that other additional reactions
may be
occurring in the combustion and/or flue gas stream.
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[0084] In
another embodiment, the present invention is direct to a system and
method for the injection of iron carbonate, another suitable iron compound, or
a
blend of one or more iron compounds and one or more non-iron-containing halide
compounds with coal in the furnace in order to replenish the active catalytic
sites on
the surface of SCR catalyst with Fe active sites while simultaneously
achieving
mercury oxidation. In one instance, the injection material is a blend of iron
carbonate
(about 90 percent by weight) and a non-iron-containing halogen compound (e.g.,
calcium bromide 10 percent by weight). As is known to those of skill in the
art, any
iron that is present in coal ash (including but not limited to PRB coal ash)
is not
catalytically active as it bonds, or is bonded, with various silicates and/or
aluminates
in the coal combustion process. In PRB coal more than 90 percent of total iron
occurs as a bonded mineral meaning that it is mostly trapped in glassy silica
and/or
alumina compounds during the combustion process thereby making it unavailable
for
any other chemical reaction.
Thus, the present invention, by injecting iron
separately, provides "free" iron that, while not wishing to be bound to any
one theory,
is believed to settle onto and/or be deposited onto the surface of fly ash
which
makes it available for further chemical reactions.
[0085]
This blended material that contains "free" iron as defined above can
then provide iron for increasing the catalytic activity and/or catalytic
lifespan of the
DeN0x catalyst while, if so provided, the halogen portion of the one or more
halide
compounds of the present invention acts to aid, or achieve, mercury oxidation.
While not wishing to be bound to any one theory, is believed that when the fly
ash
gets deposited on the surface of SCR catalyst the iron on the surface of fly
ash or
iron deposited on catalyst as a result of the injection process provides sites
onto
which ammonia and NO can react to form N2 and water. As the iron is injected
continuously at a low rate of injection, any active iron sites that become
depleted are
replaced by new iron sites at a reasonable rate thereby allowing for the
extension
and/or increase of catalytic lifespan and/or catalytic activity when compared
to
similar untreated catalyst as explained in detail above. The halogen portion
of the
halide compound, or compounds, oxidizes elemental mercury into its oxidized
form
and makes it easier for removal by a downstream wet or dry scrubber, or with
PAC
injection.
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[0086] While not wishing to be bound to any one example, data to support
this
invention is supplied from a long-term injection test of iron carbonate at a
100 MWe
coal power plant. Before exposure of the catalyst to the combustion flue gas,
the
catalyst analysis by XRF technique showed negligible iron present both on the
surface and in the bulk of catalyst. After approximately 2,000 hours of
operation and
injection of FeCO3 a catalyst sample is obtained and analyzed by XRF. This
sample
shows 0.35 percent Fe on the surface and 0.13 percent Fe in bulk. Previously
used
catalyst (no FeCO3 injection from the same site) had 0.26 percent Fe on
surface and
0.06 percent Fe in bulk after 11,000 hours of operation. Baseline testing
prior to the
injection of iron carbonate indicates that the SO3 concentration is less than
1 ppm in
flue gas at the outlet of air heater. After 8,000 plus hours of operation the
SO3
concentration is measured at the air heater outlet and is about 2.6 ppm. This
proves
that iron injection into the furnace is indeed reaching the SCR. The increase
in SO3
concentration can be related to the presence of iron on catalyst surface,
since Fe is
also a good catalyst for conversion of SO2 to S03.
[0087] As noted above, Figure 2 illustrates catalyst performance with and
without iron injection. The upper line plot (the one with the lower case "Xs")
is the
originally expected catalyst deactivation curve. This catalyst is expected to
last for
about 16,000 hours of operation. The lower plot (diamonds) illustrates the
actual
performance for this catalyst. The catalyst actually lasts for only 6,800
hours of
operation due to phosphorus deactivation. The middle line (triangles)
illustrates the
performance of a catalyst subjected to at least the iron compound injection of
the
present invention. The catalyst in this example is not new when it is
installed but is
regenerated catalyst with 15 percent lower initial activity than virgin
catalyst.
[0088] Thus, in one embodiment, the present invention provides additional
sites for the DeN0x reaction by injection of one or more iron-bearing
compounds
thereby making it possible to significantly improve the life and/or catalytic
activity of
an SCR catalyst beyond presently accepted, or believed, time spans. When
utilized,
the one or more halide compounds of the present invention provide a halogen
component that permits for increased mercury oxidation and makes possible
mercury removal downstream by any suitable technology (e.g., AQCS equipment).
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[0089] In
another embodiment, the present invention seeks to at a minimum
control the amount of gas phase selenium and/or the nature of the selenium
speciation in at least one of the flue gas or an aqueous environment found in
one or
more emission control devices (e.g., a WFGD) via the addition of at least one
metal
compound at any point described herein with regard to the aforementioned iron-
bearing compound. In yet another embodiment, the present invention relates to
a
method and apparatus for controlling, mitigating and/or reducing the amount of
selenium contained in and/or emitted by one or more pieces of emission control
equipment for boilers, heaters, kilns, or other flue gas-, or combustion gas-,
generating devices (e.g., those located at power plants, processing plants,
etc.) via
the addition of at least one metal compound at any point described herein with
regard to the aforementioned iron-bearing compound. In
still yet another
embodiment, the present invention relates to method and apparatus for
controlling
the selenium speciation in one, or both, of a gas phase or a aqueous phase by
the
addition of at least one metal (e.g., an aluminum metal additive, or a
transition metal
additive such as iron, nickel, zinc, copper or other transition metal)
additive upstream
of either a wet flue gas desulfurization (WFGD) unit and/or a dry flue gas
desulfurization (DFGD) unit (i.e., also known as semi-dry flue gas
desulfurization
units which include, but are not limited to, spray dry absorbers (SDAs),
circulating
dry scrubbers (CDSs), etc.). Given this, in Figure 1 when the "term" SDA is
utilized it
should be viewed as encompassing all types DFGD units.
[0090] In
another embodiment, the present invention seeks to at a minimum
control the amount of gas phase selenium and/or the nature of the selenium
speciation in at least one of an amine-based post combustion CO2 capture
processes. In various amine-based post combustion CO2 capture processes the
amine utilized therein will start to degrade due to being subjected to SO2,
002, heat,
02, and other degradation products. Due to the large amine volume, or
inventory,
needed for a post combustion CO2 capture process, the amine degradation volume
is very large and requires the amine to be regenerated to make operation more
economical. This is generally done via a thermal reclaimer, which creates a
large
volume of thermal sludge and/or waste product. It has been observed that the
selenium, due to the recirculation process, present in the inlet gas is
removed by the
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process in the thermal sludge of the thermal reclaimer (this will happen for
all amines
with thermal reclaiming). Due to the nature of the thermal reclamation
process, it
concentrates the removed products from the circulating solution such as
selenium.
This makes the thermal sludge a hazardous waste and is an additional problem
to be
resolved when these processes are commercialized. When selenium is discovered
in a waste stream, the post combustion 002 capture process may be required to
shut down until the selenium issue is resolved. By tying up the selenium
upstream of
the post combustion 002 capture process via the addition of one or more metal
additives of the present invention, this permits allow the continued operation
of 002
capture processes without concern of concentrated selenium-containing wastes.
[0091] Suitable metal compounds include water soluble or water insoluble
compounds, be they inorganic or organic compounds, of iron, aluminum, nickel,
zinc,
copper, or mixtures of two or more thereof. Suitable iron-bearing compounds
include, but are not limited to, powderized, solid, aqueous (be it an aqueous-
based
suspension or aqueous-based emulsion) and/or water soluble forms of iron-
bearing
compounds including, but not limited to, metallic iron, one or more iron
oxides, iron
carbonate, iron (II) acetate (e.g., Fe(02H302)2.4H20), iron (II) nitrate
(e.g.,
Fe(NO3)2.6H20), iron (III) nitrate (e.g., Fe(NO3)3.6H20 or Fe(NO3)3.9H20),
iron (II)
sulfate (e.g., Fe504 120, Fe504=4H20, Fe504=5H20 or Fe504=7H20), iron (III)
sulfate (e.g., Fe2(504)3.9H20), iron (II) bromide (e.g., FeBr2), iron (III)
bromide (e.g.,
FeBr3, Fe2Br6 or FeBr3=6H20), iron (II) chloride (e.g., Fe0I2, Fe012=2H20 or
Fe012=4H20 FeBr2), iron (III) chloride (e.g., Fe0I3, Fe2016, Fe013.21/2H20 or
Fe013=6H20), iron (II) iodide (e.g., Fe12 or Fe12.4H20), iron (III) iodate
(e.g., Fe(103)3),
or mixtures of two or more thereof. Suitable aluminum-bearing compounds
include,
but are not limited to, powderized, solid, aqueous (be it an aqueous-based
suspension or aqueous-based emulsion) and/or water soluble or water insoluble
forms of aluminum-bearing compounds including, but not limited to, metallic
aluminum, aluminum acetate (e.g., Al(02H302)3), aluminum bromate (e.g.,
Al(Br03)3.9H20), aluminum bromide (e.g., AlBr3, Al2Br6, AlBr3.6H20 or AlBr3.1
5H20),
aluminum chloride (e.g., AlC13, A12016 or A1013.6H20), aluminum fluoride
(e.g., AlF3,
AlF3=31/2H20 or AlF3.1-120), aluminum hydroxide (e.g., Al(OH)2), aluminum
iodide
(e.g., AII3, AI216 or A113.6H20), aluminum nitrate (e.g., Al(NO3)3.9H20),
aluminum
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oxide (e.g., A1203, A12034-120 or A1203-3H20), aluminum sulfate (e.g.,
Al2(SO4)3 or
Al2(SO4)3-1 8H20), or mixtures of two or more thereof. Suitable nickel-bearing
compounds include, but are not limited to, powderized, solid, aqueous (be it
an
aqueous-based suspension or aqueous-based emulsion) and/or water soluble or
water insoluble forms of nickel-bearing compounds including, but not limited
to,
metallic nickel, nickel acetate (e.g., Ni(C2H302)2 or Ni(C2H302)2-4H20),
nickel
bromate (e.g., Ni(Br03)2-6H20), nickel bromide (e.g., NiBr2 or NiBr2-3H20),
nickel
carbonate or basic nickel carbonate (e.g., NiCO3, 2NiCO3-3Ni(OH)2-4H20 or
zaratite), nickel chloride (e.g., NiCl2 or NiCl2-6H20), nickel fluoride (e.g.,
NiF2), nickel
hydroxide (e.g., Ni(OH)2 or Ni(OH)2-XH20), nickel iodate (e.g., Ni(103)2 or
Ni(103)2-4H20), nickel iodide (e.g., Ni12), nickel nitrate (e.g., Ni(NO3)2-
6H20), nickel
oxide (e.g., NiO), nickel sulfate (e.g., Ni504, Ni504-7H20 or Ni504-6H20), or
mixtures of two or more thereof.
[0092] Suitable copper-bearing compounds include, but are not limited to,
powderized, solid, aqueous (be it an aqueous-based suspension or aqueous-based
emulsion) and/or water soluble or water insoluble forms of copper-bearing
compounds including, but not limited to, metallic copper, copper acetate
(e.g.,
Cu(C2H302)2-Cu0-6H20 or Cu(C2H302)2-1-120), copper bromate (e.g.,
Cu(Br03)2.6H20), copper bromide (e.g., CuBr, Cu2Br2 or CuBr2), copper
trioxybromide (e.g., CuBr2-3Cu(OH)2), copper carbonate or basic copper
carbonate
(e.g., Cu2003, CuCO3-Cu(OH)2 or 2CuCO3-Cu(OH)2), copper chloride (e.g., CuCI,
Cu2C12, CuCl2 or CuCl2-2H20), copper fluoride (e.g., CuF, Cu2F2, CuF2 or
CuF2-2H20), copper hydroxide (e.g., Cu(OH)2), copper iodate (e.g., Cu(I03)2 or
Cu3(103)6=2H20), copper iodide (e.g., Cul or Cu212), copper nitrate (e.g.,
Cu(NO3)2-1-120 or Cu(NO3)2-3H20), copper oxide (e.g., Cu20, CuO, Cu02-1-120 or
Cu40), copper sulfate (e.g., Cu2504, Cu504 or Cu504-5H20), or mixtures of two
or
more thereof. Suitable zinc-bearing compounds include, but are not limited to,
powderized, solid, aqueous (be it an aqueous-based suspension or aqueous-based
emulsion) and/or water soluble or water insoluble forms of zinc-bearing
compounds
including, but not limited to, metallic zinc, zinc acetate (e.g., Zn(C2H302)2
or
Zn(C2H302)2-2H20), zinc bromate (e.g., Zn(Br03)2-6H20), zinc bromide (e.g.,
ZnBr2),
zinc carbonate (e.g., ZnCO3), zinc chloride (e.g., ZnCl2), zinc ferrate (e.g.,
ZnFe204),
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zinc fluoride (e.g., ZnF2 or ZnF2-4H20), zinc hydroxide (e.g., Zn(OH)2), zinc
iodate
(e.g., Zn(I03)2 or Zn(103)2=2H20), zinc iodide (e.g., ZnI2), zinc nitrate
(e.g.,
Zn(NO3)2-3H20 or Zn(NO3)2-6H20), zinc oxide (e.g., ZnO or Zn020/2H20), zinc
sulfate (e.g., ZnSO4, ZnSO4=6H20 or ZnSO4=7H20), or mixtures of two or more
thereof.
[0093] It should be noted that although various hydrated forms of metal-
bearing compounds are listed here, the present invention is not limited to
just the
hydrated forms listed above. Rather, if possible, any corresponding anhydrous
form
of the above listed metal-bearing compounds can also be utilized in
conjunction with
the present invention. Given this, when a metal-bearing compound is mentioned
herein it should be interpreted to encompass both a hydrated form or an
anhydrous
form regardless of whether or not such a formula is given with "bound water."
[0094] In still another embodiment, the present invention can entail the
use of
at least one kaolin-bearing compound to control gas phase sodium and potassium
compounds as described in United States Patent No. 8,303,919 the complete
disclosure and teachings of which are hereby incorporated herein by reference
in
their entirety.
[0095] Given the above, the present invention is, in one embodiment,
directed
to a method and/or apparatus that enables one to control either one, or both,
of gas
phase selenium or aqueous selenium in one or more emission control
devices/equipment for boilers, heaters, kilns, or other flue gas-, or
combustion gas-,
generating devices. While not wishing to be bound to any one theory, it is
believed
that the addition of the one or more metal-bearing compounds permits the gas
phase
and/or aqueous phase capture of selenium via modification of the selenium
speciation thereby resulting in a selenium compound having a lower solubility
in
water, or other aqueous solutions, than would otherwise occur without the
addition of
the one or more metal-bearing compounds of the present invention. As noted
above, the present invention is application to both WFGD and DFGD systems and
permits the control, mitigation, and/or reduction of selenium in, for example,
the
effluent of a WFGD, the slurry solution of a WFGD, the particulate matter
resulting
from a DFGD, etc. While not wishing to be bound to any one theory, in one
embodiment the present invention achieves a modification of the selenium
speciation
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in a gas phase and/or a liquid/aqueous phase to an oxidation state and/or
selenium
compound (e.g., including, but not limited to, an insoluble selenite compound
and/or
an insoluble selenide compound, etc.) having a low solubility (herein defined
as a
solubility of less than about 0.1 grams per 100 mL, less than about 0.01 grams
per
100 mL, less than about 0.001 grams per 100 mL, less than about 0.0001 grams
per
100 mL, less than about 1 x 10-5 grams per 100 mL, or less than about 1 x 10-6
grams per 100 mL in water at SATP); essentially no solubility (herein defined
as a
solubility of less than about 1 x 10-7 grams per 100 mL, less than about 1 x
10-8
grams per 100 mL, or even less than about 1 x 10-9 grams per 100 mL in water
at
SATP); or even practically zero solubility in water or an aqueous solution
(herein
defined as a solubility of less than about 1 x 10-1 grams per 100 mL, or less
than
about 1 x 10-11 grams per 100 mL, or less than about 1 x 10-12 grams per 100
mL,
less than about 1 x 10-13 grams per 100 mL, or less than about 1 x 10-14 grams
per
100 mL, or less than about 1 x 10-15 grams per 100 mL, or even less than about
1 x
10-16 grams per 100 mL in water at SATP), results in a lower amount of
selenium
that is able to be "emitted" and/or "leached" into a surrounding environment
(e.g., a
river, a lake, groundwater, etc.). As defined herein, SATP is known as
"standard
ambient temperature and pressure" and is defined herein to be equivalent to a
temperature of 298.15 K (i.e., 25 C or 77 F) and an absolute pressure of 100
kPa
(i.e., 14.504 psi or 0.986 atm). Here, as well as elsewhere in the
specification and
claims, individual numerical values can be combined to form additional and/or
non-
disclosed ranges.
[0096] In still yet another embodiment, the present invention's selenium
control can be accomplished with, or without, one or more of: (i) the control
of
mercury in the flue gas via mercury oxidation and capture using any suitable
mercury
control technology discussed herein; (ii) the control of one or more of gas
phase
sodium and/or gas phase sodium compounds; and/or (iii) the control of one or
more
of gas phase potassium and/or gas phase potassium compounds. In still yet
another
embodiment, the present invention utilizes at least one iron-bearing compound
to
simultaneously control gas phase phosphorus and gas phase and/or aqueous
selenium as described above. In this additional embodiment of the present
invention
the amount of iron-bearing compound that is supplied in any manner and at any
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position discussed previously can be the same amount discussed above with
regard
to the control of gas phase phosphorus. In another embodiment, the amount of
iron-
bearing compound, or other metal-bearing compound, supplied in accordance with
this embodiment of the present invention is not limited to any one amount.
[0097] In one embodiment, as is known to those of skill in the art upon
determining the selenium content of the coal to be combusted via any suitable
known method, an excess stoichiometric ratio can be utilized. In one
embodiment,
the excess stoichiometric ratio of metal (e.g., iron, aluminum, nickel, zinc
and/or
copper via the one or more metal-bearing compounds) to selenium is in the
range of
about 2.5:1 to about 10:1, or from about 3:1 to about 9:1, or from about 3.5:1
to
about 8:1, or from about 4:1 to about 7.5:1, or from about 5:1 to about 7:1,
or from
about 5.5:1 to about 6.5:1, or even about 6:1. Here, as well as elsewhere in
the
specification and claims, individual range values can be combined to form
additional
and/or non-disclosed ranges. It should be appreciated that in those
embodiments of
the present invention where an iron-bearing compound is utilized, it may not
be
necessary to add any additional iron-bearing compound in order to control,
reduce,
and/or mitigate the amount of undesirable selenium species and/or selenium
compounds in a flue gas and/or water/aqueous solution as the amount of excess
iron-bearing compound utilized for controlling the aforementioned gas phase
phosphorus can, in some embodiments, be sufficient to control the nature of
the
selenium speciation.
[0098] Turning to the other fossil fuel-related embodiments of the
present
invention, regarding these embodiments the amount of the one or more iron-
bearing
compounds of the present invention that are utilized to remove gas phase
phosphorus and/or one or more gas phase phosphorus compounds are within the
scope of the one or more ranges detailed above in connection with the various
coal-
based embodiments of the present invention. In another embodiment, the present
invention relates to a process for reducing the impact of one or more gas
phase
compounds such as phosphorus, sodium, and/or potassium compounds on the
catalytic activity of an SCR catalyst. In these embodiments, the same types of
compounds as described above with regard to the various coal embodiments
detailed above, as well as the same amounts thereof, can be utilized to
control one
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or more gas phase phosphorus, sodium, and/or potassium compounds during the
combustion of other types of fossil fuels (e.g., fuel oil). In
still yet another
embodiment, the present invention relates to the use of the various
embodiments
described above with regard to the control of one or more gas phase
phosphorus,
sodium, and/or potassium compounds, as well as the control of one or more of
mercury and/or selenium in connection with the combustion of any type of
fossil fuel
(e.g., fuel oil). Again, the types of compounds utilized to control such one
or more
gas phase compounds, mercury and/or selenium are similar to the embodiments
detailed above and apply equally to any of the other fossil fuel embodiments
of the
present invention.
[0099]
Given the above, the following embodiments of the present invention
are applicable to any of the fossil fuels described herein. In one such
embodiment,
the present invention relates to a method for controlling the selenium
speciation in a
flue gas and/or in at least one piece of emission control equipment, the
method
comprising the steps of: (a) providing at least one metal-bearing compound to
a
combustion zone or flue gas stream of a furnace, or boiler, prior to entry of
the flue
gas into an SCR; and (b) permitting the at least one metal-bearing compound to
react with any selenium and/or selenium compounds present in the combustion
zone, flue gas, gas phase and/or at least one piece of emission control
equipment,
wherein the method permits the control of the selenium speciation in one or
more of
the gas phase and/or in the at least one piece of emission control equipment
thereby
resulting in a reduction in the amount of selenium emitted in a flue gas
and/or from
one or more pieces of emission control equipment, wherein the at least one
metal-
bearing compound is selected from one or more organic iron-bearing compounds,
one or more aluminum-bearing compounds, one or more nickel-bearing compounds,
one or more copper-bearing compounds, one or more zinc-bearing compounds, or
mixtures of any two or more thereof.
[0100] In
another embodiment, the present invention relates to a method for
controlling the selenium speciation in a flue gas and/or in at least one piece
of
emission control equipment in conjunction with a post combustion CO2 capture
process, the method comprising the steps of: (I) providing at least one metal-
bearing
compound to a combustion zone or flue gas stream of a furnace, or boiler,
prior to
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entry of the flue gas into an SCR; and (II) permitting the at least one metal-
bearing
compound to react with any selenium and/or selenium compounds present in the
combustion zone, flue gas, gas phase and/or at least one piece of emission
control
equipment, wherein the method permits the control of the selenium speciation
in one
or more of the gas phase and/or in the at least one piece of emission control
equipment thereby resulting in a reduction in the amount of selenium emitted
in a
flue gas, from one or more pieces of emission control equipment and/or in at
least
one amine compound that is utilized in conjunction with the post combustion
CO2
capture process.
[0101] In still another embodiment, the present invention relates to a
method
for simultaneously increasing the active life of an SCR catalyst and
controlling the
selenium speciation in a flue gas and/or selenium speciation in at least one
piece of
emission control equipment, the method comprising the steps of: (A) providing
at
least one iron-bearing compound to a combustion zone or flue gas stream of a
furnace, or boiler, prior to entry of the flue gas into an SCR; and (B)
simultaneously
permitting the at least one iron-bearing compound to react with any gaseous
phosphorus compounds, or phosphorus-containing compounds, present in the
combustion zone or flue gas as well as any selenium and/or selenium compounds
present in the combustion zone, flue gas, gas phase and/or at least one piece
of
emission control equipment prior to the entry of the flue gas into the SCR,
wherein
the method achieves an increase in either one, or both, of a catalytic
activity and/or a
catalytic lifespan of at least about 10 percent at an operational time of at
least about
2,000 hours while simultaneously permitting the control of the selenium
speciation in
one or more of the gas phase and/or the at least one piece of emission control
equipment thereby resulting in a reduction in the amount of selenium emitted
in a
flue gas and/or from one or more pieces of emission control equipment.
[0102] While specific embodiments of the present invention have been
shown
and described in detail to illustrate the application and principles of the
invention, it
will be understood that it is not intended that the present invention be
limited thereto
and that the invention may be embodied otherwise without departing from such
principles. In some embodiments of the invention, certain features of the
invention
may sometimes be used to advantage without a corresponding use of the other
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features. Accordingly, all such changes and embodiments properly fall within
the
scope of the following claims.
