CORROSION CONTROL IN AND SELENIUM REMOVAL FROM FLUE GAS WET
SCRUBBER SYSTEMS
This application is a continuation-in-part of U.S. Patent Application Serial
No. 11/952,637, filed December 7, 2007, and of U.S. Patent Application Serial No. 12/754,683,
filed April 6, 2010, the disclosures of which are herein incorporated by reference.
COPYRIGHT NOTICE
A portion of the disclosure of this patent document contains or may contain copyright
protected material. The copyright owner has no objection to the photocopy reproduction by
anyone of the patent document or the patent disclosure in exactly the form it appears in the Patent
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whatsoever.
TECHNICAL FIELD
This invention relates to the treatment of flue gas wet scrubber processes. More
particularly, the invention relates to the method of capture of selenium from flue gases by flue
gas wet scrubber processes. The invention also relates to minimizing corrosion in flue gas wet
scrubber processes.
BACKGROUND
The demand for electricity continues to grow globally. In order to keep stride with the
growing demand, coal is being looked to as a source for its generation. At present, burning coal
produces some 50% of the electricity generated in the United States. The burning of coal in
power generation plants results in the release of energy, as well as the production of solid waste
such as bottom and fly ash, and flue gas emissions into the environment. Emissions Standards,
as articulated in The Clean Air Act Amendments of 1990 as established by the U.S.
Environmental Protection Agency (EPA), requires the assessment of hazardous air pollutants
from utility power plants.
The primary gas emissions are criteria pollutants (e.g. sulfur dioxide, nitrogen dioxides,
particulate material, and carbon monoxide). About two thirds of all sulfur dioxide and a quarter
of the nitrogen dioxide in the atmosphere is attributable to electric power generation achieved by
burning coal and other fuels.
Secondary emissions depend on the type of coal or fuel being combusted but include as
examples mercury, selenium, arsenic, and boron. Selenium chemistry is similar to sulfur
chemistry where selenium exists in flue gas as selenium dioxide and immediately converts to the
selenite ion upon absorption into the liquid stream within the flue gas wet scrubber process.
While certain chemistries have been known to successfully capture heavy metal cations, such
chemistries would not expect to be effective at reducing selenium concentrations in liquid waste
generated from flue gas wet scrubber processes.
Furthermore, because of the presence of high concentrations of halogens in the flue gas
that is transferred to the scrubber liquor, flue gas wet scrubber processes can fail from corrosion.
Recently, a metallurgy designated as 2205 alloy stainless steel has become popular in the
industry due to its low cost and high chloride resistance. Typically, these scrubbers will operate
with 10 to 12,000 ppm chloride concentration in their liquors. Unfortunately, flue gas wet
scrubbers constructed of 2205 alloy have experienced increased levels of pitting and localized
corrosion, resulting in forced, unscheduled unit shutdowns and expensive repairs.
One potential solution to the corrosion problem that has been implemented commercially
is the use of potential adjustment protection ("PAP") systems. PAP systems apply an electrical
potential across the metal surface in an effort to control and reduce corrosion. This method has
been successful, but it requires the installation of electrodes into the scrubber and the constant
application of electrical potential and current. It also suffers from being applicable to only wet
surfaces within the scrubbers.
Another solution to the problem is the operation of flue gas wet scrubbers at less than
2000 ppm chloride concentrations. While this prolongs the time between failures, it does not
completely halt corrosion. Additionally, this solution results in higher blowdown rates,
translating into higher water usage, higher wastewater treatment costs, and overall higher
operating costs.
Consequently, there remains a need for a technology that can cost-effectively remove
selenium from flue gas in flue gas wet scrubber processes. Ideally, the technology would have
the added benefit of minimizing corrosion in flue gas wet scrubber processes. The invention
described below addresses these needs.
SUMMARY OF THE INVENTION
The invention is directed toward a method for removing selenium from flue gas in a flue
gas wet scrubber process. The invention is also directed toward a method for minimizing
corrosion in a flue gas wet scrubber process. Each method comprises the steps of burning fuel,
thereby producing flue gas; and passing the flue gas into the flue gas wet scrubber process
comprising a polydithiocarbamic compound of at least one polythiocarbamic material.
In another embodiment, the method comprises the steps of burning fuel, thereby
producing flue gas; and passing the flue gas into the flue gas wet scrubber process comprising a
polymer derived from at least two monomers: acrylic-x and an alkylamine, and wherein said
acrylic-x has the following formula:
wherein X = OH and salts thereof or NHR2 and wherein R1 and R2 is H or an alkyl or aryl group,
wherein the molecular weight of said polymer is between 500 to 200,000, and wherein said
polymer is modified to contain a functional group capable of scavenging at least one metalcomprising
composition. The method may comprise a combination of the polydithiocarbamic
compound and the polymer derived from acrylic-x and alkylamine. The polydithiocarbamic
compound may be the polymer. The invention may further comprise a transition metal salt,
which may be an iron salt.
In a third embodiment, the invention is directed toward a composition of matter
comprising a polydithiocarbamic compound of at least one polythiocarbamic material; and a
transition metal salt.
In a fourth embodiment, the invention is directed toward a composition of matter
comprising a polymer derived from at least two monomers: acrylic-x and an alkylamine, and
wherein said acrylic-x has the following formula:
wherein X = OH and salts thereof or NHR2 and wherein R1 and R2 is H or an alkyl or aryl group,
wherein the molecular weight of said polymer is between 500 to 200,000, and wherein said
polymer is modified to contain a functional group capable of scavenging at least one metalcomprising
composition; and an iron salt. The composition may be comprised additionally of a
polydithiocarbamic compound of at least one polythiocarbamic material, and the polymer may be
comprised of a polydithiocarbamic compound.
BRIEF DESCRIPTION OF THE DRAWINGS
The benefits and advantages of the present invention will become more readily apparent
to those of ordinary skill in the relevant art after reviewing the following detailed description and
accompanying drawings, wherein:
FIG. 1 is a graph demonstrating the positive effects of Chemistry 1 on decreased selenium
concentration and decreased oxidation-reduction potential in the aqueous phase of a flue gas wet
scrubber process; and
FIG 2 is a graph demonstrating the positive effects of Chemistry 2 on decreased selenium
concentration and decreased oxidation-reduction potential in the aqueous phase of a flue gas wet
scrubber process.
DETAILED DESCRIPTION OF THE INVENTION
While the present invention is susceptible of embodiment in various forms, there will
hereinafter be described a presently preferred embodiment with the understanding that the
present disclosure is to be considered an exemplification of the invention and is not intended to
limit the invention to the specific embodiment illustrated.
It should be further understood that the title of this section of this specification, namely,
"Detailed Description of the Invention," relates to a requirement of the United States Patent
Office, and does not imply, nor should be inferred to limit the subject matter disclosed herein.
The present invention documents the unexpected results obtained from the use of certain
chemistries, which unexpectedly reduced selenium concentration nearly ten-fold in water phase
blowdown of a flue gas wet scrubber process. While not wishing to be bound by a particular
mechanism, through the addition of the chemistries within the flue gas wet scrubber process, the
chemistries have the opportunity to capture the selenite before it has a chance to further oxidize
to selenate. Selenate is difficult to remove from the water phase.
Additionally, the chemistries have also proved to be advantageous in minimizing
corrosion in flue gas wet scrubber systems. Particularly, the chemistries have helped minimize
corrosion in flue gas wet scrubber systems that are constructed of 2205 alloy. It was
unexpectedly found that these chemistries, when circulated in a flue gas wet scrubber process
with flue gas wet scrubber liquor, reduced the oxidation-reduction potential ("ORP") within the
flue gas wet scrubber process. The reduction of ORP reduces the tendency for corrosion.
Examples showing the reduction are provided below.
It is important to note that, while ORP is not exactly the same as corrosion potential, the
two numbers track each other. ORP is an indication of the oxidative or reductive nature of the
environment. Corrosion potential is the oxidative or reductive nature at the surface of a specific
metal. Therefore, the corrosion potential generally reflects the ORP, but the two values are not
the same. However, the ORP trend would typically indicate the corrosion potential trend.
Hence, an observed reduction in ORP is expected to result in a reduction in corrosion potential.
For the invention at hand, it was unexpected to see the addition of the chemistries, chelating
agents for heavy metal removal, to result in a reduction in ORP value and thereby a reduction in
corrosion rate.
In an embodiment, the flue gas wet scrubber process comprises a wet flue gas
desulfurizer process.
In an embodiment, the flue gas wet scrubber process employs equipment comprising
2205 alloy.
In an embodiment, the fuel is selected from the group consisting of coal, reclailmed coal,
natural gas, industrial waste, a gasified waste product, biomass, and any combination thereof.
Chemistry 1:
Chemistry 1 is a water-soluble ethylene dichloride ammonia polymer having a molecular
weight of from 500 to 10,000, which contains from 5 to 55 mole% of dithiocarbamate salt
groups. Chemistry 1 may additionally comprise a transition metal salt, which may be an iron
salt. The positive effects of Chemistry 1 on both reduction of selenium in the aqueous phase and
reduction in oxidation-reduction potential are shown in FIG. 1. The ethylene dichlorideammonia
polymers are prepared by the reaction of ethylene dichloride and ammonia. The
starting ethylene dichloride-ammonia polymers generally have a molecular weight range of 500-
100,000. In a preferred embodiment the molecular weight is 1,500 to 10,000, with the most
preferred molecular weight range being 1,500 to 5,000. The copolymer of this invention is
produced using methods presented in U.S. Patent Nos. 4,731,187; 5,500,133; or 5,658,487 that
are examples of said copolymers available for use in the claimed invention. The copolymer is
produced by the reaction of the polyamines or polyimines with carbon disulfide to produce
polydithiocarbamic acid or its salts. Such reaction is preferably carried out in a solvent such as
water or alcohol at a temperature of from 30° and 100°C for periods of time ranging between 1
and 10 hours. Good conversion is obtained at temperatures between 40° and 70°C for 2 to 5
hours. These reaction conditions apply to the modification of ethylene dichloride-ammonia
polymers described previously.
The mole % of dithiocarbamate salt groups in the finished polymer generally is within the
range of 5 to 55%. The preferred range is 20 to 55 mole %, with the most preferred range being
about 30 to 55 mole %.
The salts include but are not limited to alkaline and alkali earth such as sodium, lithium,
potassium or calcium. The chemistry may include at least one transition metal salt, which may
be an iron salt.
The scrubber processes currently used in the industry include spray towers, jet bubblers,
and co-current packed towers as examples. These types of air quality control devices
("AQCDs") are provided as examples and are not meant to represent or suggest any limitation.
The water-soluble copolymer may be added to virgin limestone or lime slurry prior to addition to
the scrubber, the recirculation loop of the scrubber liquor, or the "low solids" return to the
scrubber from the scrubber purge stream.
Typically, the copolymer is applied at a ratio of 1:1 to 2000:1 weight copolymer to weight
of selenium being captured. The preferred ratio is from 5:1 to 1000:1 and the most preferred
range is from 5:1 to 500: 1.
In general the polydithiocarbamic acid compounds may be introduced into the scrubber
and thereby into the scrubber liquor via several routes. The following will serve as just some of
the variations that are available to introduce the compounds into the scrubber liquor. The
scrubber liquor is defined as the water-based dispersion of calcium carbonate (limestone) or
calcium oxide (lime) used in a wet flue gas scrubber ("FGS," also known as a wet flue gas
desulfurizer, or "FGD") to capture SOx emissions. The liquor may also contain other additives
such as magnesium and low-molecular weight organic acids, which function to improve the
sulfur, capture. One example of such an additive is a mixture of low-molecular weight organic
acids known as dibasic acid ("DBA"). DBA consists of a blend of adipic, succinic, and glutaric
acids. Each of these organic acids can also be used individually. In addition, another lowmolecular
weight organic acid that can be used to improve sulfur capture in a wet scrubber is
formic acid. Finally, the scrubber liquor will also contain byproducts of the interaction between
the lime or limestone and sulfur species, which leads to the presence of various amounts of
calcium sulfite or calcium sulfate. The scrubber liquor includes but is not limited to the make-up
liquor, return liquor, the reclaimed liquor, virgin liquor and liquor injected directly into flue
gases.
Another addition point for the polydithiocarbamic compounds of this invention to the wet
scrubber is via the "low solids" liquor return. A portion of the liquor is usually continuously
removed from the scrubber for the purpose of separating reaction byproducts from unused lime
or limestone. One means of separation that is currently used is centrifugation. In this process the
scrubber liquor is separated into a "high solids" and "low solids" stream. The high solids stream
is diverted to wastewater processing. The low solids fraction returns to the wet scrubber and can
be considered "reclaimed" dilute liquor. The polydithiocarbamic acid compounds of this
invention can conveniently be added to the reclaimed low solids stream prior to returning to the
scrubber.
Another feed liquor found in the operation of a wet flue gas desulfurizer is called "virgin
liquor." Virgin liquor is the water-based dispersion of either lime or limestone prior to exposure
to flue gas and is used to added fresh lime or limestone while maintaining the scrubber liquor
level and efficiency of the wet FGD. This is prepared by dispersing the lime or limestone in
water. Here the polydithiocarbamic acid compounds can be added either to the dispersion water
or the virgin liquor directly.
Finally, some wet scrubber installations use scrubber liquor and/or water (fresh or
recycled) injected directly into the flue gas prior to the scrubber for the purpose of controlling
relative humidity of the flue gas or its temperature. The excess liquid is then carried into the wet
scrubber. Here also are two potential addition points for the introduction of the
polydithiocarbamic acid compounds of the present invention.
The addition of the polydithiocarbamic acid compounds can be made in any of these
locations, wholly or fractionally (i.e. a single feed point or multiple feed points), including but
not limited to the make-up water for the lime or limestone slurry or the scrubber liquor.
Chemistry 2 :
A. Composition
The present disclosure provides for a composition comprising a polymer derived from at
least two monomers: acrylic-x and an alkylamine, wherein said acrylic-x has the following
formula:
wherein X = OR, OH and salts thereof, or NHR2 and wherein R1 and R2 is H or an alkyl or aryl
group, wherein R is an alkyl or aryl group, wherein the molecular weight of said polymer is
between 500 to 200,000, and wherein said polymer is modified to contain a functional group
capable of scavenging one or more compositions containing one or more metals.
The metals can include zero valent, monovalent, and multivalent metals. The metals may
or may not be ligated by organic or inorganic compounds. Also, the metals can be radioactive
and nonradioactive. Examples include, but are not limited to, transition metals and heavy metals.
Specific metals can include, but are not limited to: copper, nickel, zinc, lead, mercury, cadmium,
silver, iron, manganese, palladium, platinum, strontium, selenium, arsenic, cobalt and gold.
The molecular weight of the polymers can vary. For example, the target species/application for
the polymers can be one consideration. Another factor can be monomer selection. Molecular
weight can be calculated by various means known to those of ordinary skill in the art. For
example, size exclusion chromatography, as discussed in the examples below can be utilized.
When molecular weight is mentioned, it is referring to the molecular weight for the
unmodified polymer, otherwise referred to as the polymer backbone. The functional groups that
are added to the backbone are not part of the calculation. Thus the molecular weight of the
polymer with the functional groups can far exceed the molecular weight range.
In one embodiment, the molecular weight of the polymer is from 1,000 to 16,000.
In another embodiment, the molecular weight of said polymer is from 1,500 to 8,000.
Various functional groups can be utilized for metal scavenging. The following phraseology
would be well understood by one of ordinary skill in the art: wherein said polymer is modified to
contain a functional group capable of scavenging one or more compositions containing one or
more metals. More specifically, the polymer is modified to contain a functional group that can
bind metals.
In one embodiment, the functional group contains a sulfide containing chemistry.
In another embodiment, the functional group is a dithiocarbamate salt group.
In another embodiment, the functional groups are at least one of the following :alkylene
phosphate groups, alkylene carboxylic acids and salts thereof, oxime groups, amidooxime
groups, dithiocarbamic acids and salts thereof, hydroxamic acids, and nitrogen oxides.
The molar amounts of the functional group relative to the total amines contained in the
unmodified polymer can vary as well. For example, the reaction of 3.0 molar equivalents of
carbon disulfide to a 1.0:1.0 mole ratio acrylic acid / TEPA copolymer, which contains 4 molar
equivalents of amines per repeat unit after polymerization, will result in a polymer that is
modified to contain 75 mole % dithiocarbamate salt group. In other words, 75 % of the total
amines in the unmodified polymer has been converted to dithiocarbamate salt groups.
In one embodiment, the polymer has between 5 to 100 mole % of the dithiocarbamate salt
group. In a further embodiment, the polymer has from 25 to 90 mole % of the dithiocarbamate
salt group. In yet a further embodiment, the polymer has from 55 to 80 mole % of the
dithiocarbamate salt group.
Monomer selection will depend on the desired polymer that one of ordinary skill in the art
would want to make .
The alkylamines may vary in kind.
In one embodiment, the alkylamine is at least one of the following: an ethyleneamine, a
polyethylenepolyamine, ethylenediamine (EDA), diethylenetriamine (DETA),
triethylenetetraamine (TETA) and tetraethylenepetamine (TEPA) and pentaethylenehexamine
(PEHA).
The acrylic-x monomer group can vary as well.
In another embodiment, the acrylic-x is at least one of the following: methyl acrylate,
methyl methacrylate, ethyl acrylate, and ethyl methacrylate, propyl acrylate, and propyl
methacrylate.
In another embodiment, the acrylic-x is at least one of the following: acrylic acid and salts
thereof, methacrylic acid and salts thereof, acrylamide, and methacrylamide.
The molar ratio between monomers that make up the polymer, especially acrylic-x and
alkylamine can vary and depend upon the resultant polymer product that is desired. The molar
ratio used is defined as the moles of acrylic-x divided by the moles of alkylamine.
In one embodiment, the molar ratio between acrylic-x and alkylamine is from 0.85 to 1.5.
In another embodiment, the molar ratio between acrylic-x and alkylamine is from 1.0 to
1.2.
Various combinations of acrylic-x and alkylamines are encompassed by this invention as
well as associated molecular weight of the polymers.
In one embodiment, the acrylic-x is an acrylic ester and the alkylamine is PEHA or TEPA
or DETA or TETA or EDA. In a further embodiment, the molar ratio between acrylic-x and
alkylamine is from 0.85 to 1.5. In yet a further embodiment, the molecular weight can
encompass ranges: 500 to 200,000, 1,000 to 16,000, or 1,500 to 8,000. In yet a further
embodiment, the acrylic ester can be at least one of the following: methyl acrylate, methyl
methacrylate, ethyl acrylate, and ethyl methacrylate, propyl acrylate, and propyl methacrylate,
which is combined with at least one of the alklyamines, which includes PEHA or TEPA or
DETA or TETA or EDA. In yet a further embodiment, the resulting polymer is modified to
contain the following ranges of dithiocarbamate salt groups: 5 to 100 mole %, 25 to 90 mole %,
55 to 80 mole %.
In another embodiment, the acrylic-x is an acrylic amide and the alkylamine is TEPA or
DETA or TETA or EDA. In a further embodiment, the molar ratio between acrylic-x and
alkylamine is from 0.85 to 1.5. In yet a further embodiment, the molecular weight can
encompass ranges: 500 to 200,000, 1,000 to 16,000, or 1,500 to 8,000. In yet a further
embodiment, the acrylic amide can be at least one or a combination of acrylamide and
methacrylamide, which is combined with at least one of the alklyamines, which includes PEHA
or TEPA or DETA or TETA or EDA. In yet a further embodiment, the resulting polymer is
modified to contain the following ranges of dithiocarbamate salt groups: 5 to 100 mole %, 25 to
90 mole %, or 55 to 80 mole %.
In another embodiment, the acrylic-x is an acrylic acid and salts thereof and the
alkylamine is PEHA or TEPA or DETA or TETA or EDA. In a further embodiment, the molar
ratio between acrylic-x and alkylamine is from 0.85 to 1.5. In yet a further embodiment, the
molecular weight can encompass ranges: 500 to 200,000, 1,000 to 16,000, or 1,500 to 8,000. In
yet a further embodiment, the acrylic acid can be at least one or a combination of acrylic acid or
salts thereof and methacrylic acid or salts thereof, which is combined with at least one of the
alklyamines, which includes TEPA or DETA or TETA or EDA. In yet a further embodiment, the
resulting polymer is modified to contain the following ranges of dithiocarbamate salt groups: 5
to 100 mole %, 25 to 90 mole %, or 55 to 80 mole %.
Additional monomers can be integrated into the polymer backbone made up of
constituent monomers acrylic-x and alkylamine. A condensation polymer reaction scheme can
be utilized to make the basic polymer backbone chain. Various other synthesis methods can be
utilized to functionalize the polymer with, for example, dithiocarbamate and/or other non-metal
scavenging functional groups. One of ordinary skill in the art can functionalize the polymer
without undue experimentation.
Moreover, the composition of the present invention can be formulated with other
polymers such as those disclosed in U.S. Patent No. 5,164,095, herein incorporated by reference,
specifically, a water soluble ethylene dichloride ammonia polymer having a molecular weight of
from 500 to 100,000 which contains from 5 to 50 mole % of dithiocarbamate salt groups. In one
embodiment, the molecular weight of the polymer is from 1500 to 10,000 and contains 15 to 50
mole % of dithiocarbamate salt groups. In a preferred embodiment, the molecular weight of the
polymer is from 1500 to 5000 and contains 30 to 55 mole % of dithiocarbamate salt groups.
Also, the composition of the present invention can be formulated with other small molecule
sulfide precipitants such as sodium sulfide, sodium hydrosulfide, TMT-15® (sodium or calcium
salts of trimercapto-S-triazine; Evonik Industries Corporation 1721 1 Camberwell Green Lane,
Houston, TX 77070, USA), dimethyldithiocarbamate and diethyldithiocarbamate.
B. Dosage
The dosage of the disclosed polymers for use may vary. The calculation of dosage
amounts can be done without undue experimentation.
Process medium quality and extent of process medium treatment are a couple of factors
that can be considered by one of ordinary skill in the art in selecting dosage amount. Ajar test
analysis is a typical example of what is utilized as a basis for determining the amount of dosage
required to achieve effective metals removal in the context of a process water medium, e.g.
wastewater.
In one embodiment, the amount of modified polymer of the invention capable of
effectively removing metals from contaminated waters is preferably within the range of 0.2 to 2
moles of dithiocarbamate per mole of metal. More preferably, the dosage is 1 to 2 moles of
dithiocarbamate per mole of metal contained in the water. According to one embodiment of the
invention, the dosage of metal removal polymer required to chelate and precipitate 100 ml of 18
ppm soluble copper to about 1ppm or less was 0.01 1 gm ( 11.0 mg) of polymer. The metal
polymer complexes formed are self-flocculating and quickly settle. These fiocculants are easily
separated from the treated water.
In the context of applying the polymer to a gas system, such as a flue gas, the polymer
can be dosed incrementally and capture rates for a particular metal, e.g. such as mercury, can be
calculated by known techniques in the art.
C. Methods of Use
The present disclosure also provides for a method of removing selenium from a medium
containing selenium which comprises the steps of: (a) treating said medium containing metals
with a composition comprising a polymer derived from at least two monomers: acrylic-x and an
alkylamine, wherein said acrylic-x has the following formula:
wherein X = OR, OH and salts thereof, or NHR2 and wherein R1 and R2 is H or an alkyl or aryl
group, wherein R is an alkyl or aryl group, wherein the molecular weight of said polymer is
between 500 to 200,000, and wherein said polymer is modified to contain a functional group
capable of scavenging one or more compositions containing one or more metals; and (b)
collecting said treated metals.
The compositions as described above are incorporated into this section and can be applied
within the claimed methodologies encompassed by this invention.
Mediums containing selenium can vary and include at least one of the following
wastewater streams, liquid hydrocarbonaceous streams, flue gas streams, flyash, and other
particulate matter. Various processing steps can be coupled with metals removal, including, but
not limited to filtration steps and/or air quality control devices, e.g. baghouses and electrostatic
precipitators and other air quality control devices.
Mediums containing a liquid phase medium/a medium containing a liquid phase are one
target for the claimed invention.
In one embodiment, the medium is a process stream containing water, e.g. wastewater or
wastewater from a power plant or industrial setting (power plant, mining operation, waste
incineration, and/or manufacturing operation).
In another embodiment, the medium is a liquid hydrocarbonaceous stream common in
petroleum refining processes or petrochemical processes. Examples include streams from these
processes that contain petroleum hydrocarbons such as petroleum hydrocarbon feedstocks
including crude oils and fractions thereof such as naphtha, gasoline, kerosene, diesel, jet fuel,
fuel oil, gas oil vacuum residual, etc or olefinic or napthenic process streams, ethylene glycol,
aromatic hydrocarbons, and their derivatives.
In another embodiment, additional chemistries, flocculants and/or coagulants can be
utilized in conjunction with the chemistry encompassed by this invention. The chemistries
applied to a medium containing metals can vary, including, the addition of at least one of the
following: cationic polymers, anionic polymers, amphoteric polymers, and zwitterionic
polymers.
In another embodiment, the method of this invention further comprises an additional
treatment to the process stream with a complexing amount of a water soluble ethylene dichloride
ammonia polymer having a molecular weight of from 500 to 100,000 which contains 5 to 50
mole % of dithiocarbamate salt groups to form a complex of these metals, e.g. heavy metals. In a
further embodiment, the molecular weight of the polymer is from 1500 to 10,000 and contains 15
to 50 mole % of dithiocarbamate salt groups. In a preferred embodiment, the molecular weight
of the polymer is from 1500 to 5000 and contains 30 to 55 mole % of dithiocarbamate salt
groups.
In another embodiment, the polymer treatment and additional treatment are added in a
ratio of 1:1.
Mediums containing a gas phase medium/a medium containing a gas phase are another
target for the claimed invention. In addition, processes containing a liquid and/or gas phase
medium are encompassed by this invention as well.
In another embodiment, the medium is part of a heat generating system, e.g. a flue gas
stream.
In another embodiment, the heat generating system is at least one of the following: a
combustion system; a power plant combustion system; a coal combustion system; a waste
incineration system; a kiln; a kiln for mining or cement operations; and an ore processing system.
In another embodiment, the method of this invention further comprises applying an oxidizing
agent to a heat generating system. In a further embodiment, the oxidizing agent is applied prior to
said polymer treatment.
In a yet a further embodiment, a multiphase treatment protocol for a process involves
treating a gas and a liquid, e.g., one or more metals in a gas such as mercury and one or more
metal in a liquid. This can involve the polymer treatment and additional treatment as described
above.
In yet a further embodiment, the oxidizing agent is at least one of the following: a
thermolabile molecular halogen, calcium bromide, or a halogen containing compound.
In yet a further embodiment, this invention further comprises applying an oxidizing agent to the
flue gas; optionally wherein said oxidizing agent oxidizes a target species at a temperature of
500°C or greater or a temperature where the oxidant is capable of oxidizing molecular mercury
that exists in a process that generates mercury; optionally wherein said target species is elemental
mercury or derivatives thereof; and optionally wherein said oxidizing agent is at least one of the
following: a thermolabile molecular halogen, calcium bromide, or a halogen containing
compound. Mercury oxidant methodologies are described in US Patent Nos. 6,808,692 and
6,878,358, which are herein incorporated by reference.
In another embodiment, the polymer treatment occurs at a temperature 300°C or below,
preferably 250 °C or below.
The invention is illustrated by the proceeding descriptions and the following examples
are not meant to limit the invention unless otherwise stated in the claims appended hereto.
EXAMPLES
The foregoing may be better understood by reference to the following examples, which
are intended to illustrate methods for carrying out the invention and are not intended to limit the
scope of the invention.
It should be understood that various changes and modifications to the presently preferred
embodiments described herein will be apparent to those skilled in the art. Such changes and
modifications can be made without departing from the spirit and scope of the invention and
without diminishing its intended advantages. It is therefore intended that such changes and
modifications be covered by the appended claims.
Chemistry 1: Examples 1-6
Example 1
A sample of scrubber water that was treated by vacuum filter. The objective was to
remove mercury. The sample was investigated for mercury removal using design of experiments
with two variables pH and dosage.
The results showed that mercury levels of less than 0.5 ppb in the treated water was
achieved at various pHs at a reasonable product dosages. This work demonstrated that the
product did achieve mercury capture from wet FGD liquors. The lower detection limit of the
analytical method was 0.5ppb.
The results are as follows:
aDTCP is a polydithiocarbamic compound of the present invention
bFlocculant is commercially available from Nalco Company and is a very high molecular,
30mole% anionic latex polymer.
Example 2 :
A 2L solution was prepared by dissolving 6.7 mg of sodium selenite, Na2Se0 3*5H20 , 14
mL of 0.141M Hg(N0 3)2 and 18.4g of calcium chloride, CaCl2*2H 0 . The resulting solution
had measured concentrations of 0.037mM selenium, 1.04mM mercury and 63mM calcium
chloride dehydrate.
The results are shown in the table below.
The zeolite was a spent commercial catalyst. The fly ash sample was obtained from a
coal-fired power plant. The fly ash sample was composed of 93% ash content with 6%> residual
carbon and 1% residual sulfur. These results clearly show that neither fly ash nor zeolites
significantly reduce the ionic mercury content.
Example 3:
A synthetic FGD scrubber liquor was prepared by dissolving 12.58g of calcium chloride
dihydrate, CaCl2*2H20 , in 400mL of deionized water. The resulting solution was 214mM in
calcium chloride dihydrate leading to 15,000ppm chloride and 8560ppm calcium in solution.
The solution was split into two equal portions. To 200mL of solution was added 164m of
0.6ImM mercury nitrate solution to yield a solution containing 130mg/L of ionic mercury. This
solution was treated with 27.4g of calcium sulfate dihydrate or 18 weight percent. The solution
was mixed and split into two portions. The smaller portion, 75g total, was treated with the
polydithiocarbamic acid compound at a 5:1 product to mercury weight ratio. The
polydithiocarbamic acid compound product was a 30%> active water miscible solution. The two
portions were agitated separately with a magnetic stir bar for 12 hours. After which time, the
suspension was filtered using a Pall Life Sciences GN-6 Metricel 0.45m membrane filter (P/N
63069). The filtrate was analyzed for mercury.
A second portion, 200g, of calcium chloride dihydrate solution was treated with 82mI of
0.61mM mercuric nitrate solution to yield a solution containing 78.3m of ionic mercury. Again
this solution was treated with 27.4g of calcium sulfate, dihydrate to yield a slurry containing 18%
by weight. As before, this sample was split into two solutions, the minor portion, 75g, was
treated with the polydithiocarbamic acid compound product at a 5:1 product weight to mercury
weight ratio. After further mixing for 12 hours using a magnetic stir bar, the dispersions were
filtered using a Pall Life Sciences GN-6 Metricel 0.45m membrane filter (P/N 63069). The
filtrate was analyzed for mercury.
The results are shown below.
It is clear from this example that the polydithiocarbamic acid compound of this invention
removes the ionic mercury from the liquid phase. The gypsum solids for the above samples were
submitted for TGA (Thermogravimetric Analysis) in order to observe any decomposition or
release of mercury. All the thermographs were identical exhibiting only the loss of associated
and bound water between room temperature and 170°C. Above this temperature no further
decomposition could be observed. This indicates that once the complex is formed, it does not
decompose under normal FGD scrubber operation.
Example 4 :
A general stock solution was prepared containing 0.214M calcium chloride dihydrate by
dissolving 220g of CaCl2*2H20 in 7L of deionized water. To this was added 7 m of 61mM
mercury nitrate solution to yield a solution containing 136 mg/L. This solution was divided into
two portions. The first portion was mixed with enough calcium sulfate dihydrate to yield slurry
at 18% by weight-dispersed solids. The second portion was mixed with enough calcium sulfate
dihydrate to yield a 21% by weight slurry.
Organic acids are used in many wet FGD scrubbers to improve the SOx removal
efficiency as well as the limestone or lime utilization. In most cases, a by-product stream known
in the industry as Dibasic Acid or DBA is the product of choice. DBA is a mixture of adipic acid
(aka hexanedioic acid), succinic acid (aka butanedioic acid) and glutaric acid (aka pentaedioic
acid). For the purposes of this example, a "synthetic" DBA was prepared using an equal molar
ratio of adipic and succinic acids. The adipic acid can be obtained from Mallmckrodt Chemicals,
Cat No. MK180159. The succinic acid can be obtained from J.T. Baker, reagent grade, Cat. No.
JT0346-5. The solutions were spiked with the equal molar ratio acids to produce 332 and
lOOppm total acid concentrations.
The polydithiocarbamic acid compound of the current invention was added at a product to
mercury weight ratio of 4.5 :1 and 1:1 respectively with or without the synthetic DBA present in
the slurry. The order of addition was kept to the following: synthetic DBA then the
polydithiocarbamic acid compound of this invention. Once the various additives have been
introduced into the slurry, it is mixed for an additional 15 to 20 minutes with a magnetic stir bar.
After this time, the slurry is filtered using a Pall Life Sciences GN-6 Metricel 0.45 m membrane
filter (P/N 63069). The filtrate is subsequently analyzed.
The results are shown in the table below:
DTCP is the polydithiocarbamic acid compound of this invention. See above for the
definition of synthetic DBA, aka "Syn DBA".
The results in the table above clearly show that the presence of organic acids in the
scrubber liquor does not interfere with the performance of the polydithiocarbamic acid compound
of this invention regarding complexing mercury in the liquid phase. The results also confirm that
the copolymer interacts with and removes ionic mercury from the liquid phase to below 500 parts
per trillion.
Example 5:
Three additives were tested in a bench-scale wet scrubber with a gas flow of 1-cfm. One
additive, TMT-15 is currently used to control mercury emissions from incinerators. The
polydithiocarbamic acid compound, sodium salt used is an embodiment of the claimed invention.
The bench-scale unit allows for the use of a simulated flue gas composed of S0 2, NOx,
HC1, C0 2, oxygen and nitrogen. Moisture is controlled by exposing a portion of the oxygen,
carbon dioxide, and nitrogen to water saturators. The flue gas composition used in the study
consisted of 15-25 mg/Nm HgCl2, 12% C0 2, 3% 0 2, lOOOppm S0 2, 15ppm HC1, no NOx, the
balance nitrogen. The flow rate was 28 L/min. The sorbent solution or scrubber liquor was
maintained at a temperature of 55°C and consisted of lOOmM sodium chloride, and lOmM
sodium sulfate (initial concentration) with a pH of 5.0. The sulfite concentration was controlled
at 5mM by the addition of hydrogen peroxide to the sorbent solution. The pH of the scrubber
liquor was maintained by the addition of NaOH. In each case, the appropriate amount of additive
was introduced into the scrubber liquor just prior to the injection of 0.5mM HgCl2 as a solution of
0.5mM HgCl and after the system had reached equilibrium.
The bench-scale scrubber uses a bubbler type gas contactor. The gas contact vessel sits
on top of the scrubber liquor reaction vessel so that the liquor returns to the reactor vessel via
gravity drainage. The liquor is recirculated into the scrubber via a recirculation pump to maintain
a constant liquid/gas ratio. The pH is monitored both in the scrubber and in the reaction vessel.
The pH of the reaction vessel is maintained by addition of sodium hydroxide solution. The
reaction vessel is mixed via magnetic stirring. A flow-through cell and spectrophotometer was
used to monitor sulfite concentration in the scrubber liquor via a modification of a method
reported by M.W. Scoggins, Analytical Chemistry, 42(9), 1091 (1970). The results were used to
automatically control the addition of hydrogen peroxide so as to maintain the target sulfite
concentration. Oxidized mercury is added to the gas by passing a portion of the dry nitrogen gas
through a mercury diffusion cell. About 5% of the total mercury introduced in this way was
elemental. Two separate CVAAS (Cold Vapor Atomic Adsorption Spectroscopy) instruments
monitored respectfully the flue gas inlet and the scrubber outlet. The mercury re-emissions were
calculated as follows:
Average re-emission = [average elemental Hg outlet] -[average elemental Hg inlet]
The results are shown in the table below:
Additive Hg re-emissions, m / m
None 2.05
0.05 mM TMT-15 1.70
0.022mM DEDTCb with 15mM Ca+2 1.05
0.05 mM Polydithiocarbamic acid, sodium salt <0.01
bdiethyldithiocarbamate, sodium salt
It is clear from these bench-scale results that the polydithiocarbamic acid compound of
the current invention successfully controls the re-emission of mercury from a wet FGD and does
so more efficiently than the current art.
Example 6 :
A study was undertaken at a commercial site consisting of a 512 MW boiler equipped
with cold-side electrostatic precipitator ("ESP") and a flue gas wet scrubber process comprised of
limestone forced oxidation ("LSFO") wet FGD system. The boiler fired high-sulfur sulfur
bituminous coal. Samples of the LSFO wet FGD liquor were collected during the demonstration
under the noted conditions and analyzed for total selenium. The results are presented in the table
below as well as FIG. 1.
Results of Example 6.
The untreated unit was burning the same fuel during this commercial test. Chemistry 1
was applied to the treated unit. Two samples were taken during different periods of the
demonstration while the technology was applied. The disclosed technology was turned off for 18
hours (i.e. Condition Additive Off shown above) prior to sampling. Then Chemistry 1 was
reapplied to obtain the final condition, i.e. additive reapplied.
As can be seen in the previous table, the untreated unit total selenium varied from 585 to
676 mg/L. The application of the disclosed technology resulted in 65% reduction of selenium in
the scrubber liquor. The efficacy of the technology is further demonstrated by the cessation of
the application of the technology resulting in an observed increase in total selenium which was
again reduced by reapplication of the technology. It is clear from these results that Chemistry 1
reduces selenium concentration in wet FGD liquor.
Chemistry 2 : Examples 7-1 1:
Example 7 :
Methyl Acrylate / Tetraethylenepentamine Polymer Backbone which is then functionalized with
a dithiocarbamate group
a . Methyl Acrylate / Tetraethylenepentamine Polymer Backbone Synthesis
Tetraethylenepentamine (TEPA) (18.275 weight %) was charged into a glass reactor
fitted with a mechanical stirrer and a condenser. While purging the headspace with nitrogen and
stirring, methyl acrylate (16.636 weight %) was added dropwise over 30 min where the
temperature was maintained between 25 - 31° C during the addition and for 1 h after the addition
was finished. Next, a second charge of TEPA (18.275 weight %) was performed and the
resulting reaction mixture was heated to 130° C. This temperature was held for ~ 3 h while
collecting the condensate in a Dean-Stark trap. At this time, the polymer melt was allowed to
cool to 120° C and then slowly diluted with deionized (DI) water (46.814 weight %) keeping the
temperature above 90° C during the dilution. The resulting -50 weight % polymer solution was
then cooled to room temperature. Weight average molecular weight of the polymer was
determined to be 7,500 using a size exclusion chromatography method and polysaccharide
standards.
b. Dithiocarbamate Polymer Preparation
The second step involved adding the methyl acrylate / TEPA polymer (35.327 weight %),
DI Water (28.262 weight %), and Dowfax 2A1 (0.120 weight %), Dow Chemical Company
Midland, MI 48674, USA, to a round bottom flask fitted with a mechanical stirrer. Next, a 50%
NaOH solution (9.556 weight %) was added to the stirring reaction mixture. Once the mixture
was heated and maintained at 40° C, carbon disulfide (17.179 weight %>) was added drop-wise
over 2 h. One hour within the carbon disulfide addition, another amount of 50% NaOH (9.556
weight %) was charged. The reaction mixture was maintained at 40° C for an additional 2 h.
Finally, the reaction was cooled to room temperature and filtered through filter paper to obtain ~
40 weight % polymeric dithiocarbamate product.
Example 8 :
Acrylic Acid / Tetraethylenepentamine Polymer Backbone which is then functionalized with a
dithiocarbamate group
a . Acrylic Acid / Tetraethylenepentamine Polymer Backbone Synthesis
Tetraethylenepentamine (TEPA) (37.556 weight %) and sulfuric acid (0. 199 weight %)
was charged into a glass reactor fitted with a mechanical stirrer and a condenser. While purging
the headspace with nitrogen and stirring, acrylic acid (14.304 weight %) was added dropwise
over 30 min where the temperature was maintained between 130 - 140° C during the addition,
allowing the exotherm from the acid base reaction to reach the desired temperature. Next the
resulting reaction mixture was heated to 160° C. This temperature was held for 4.5 h while
collecting the condensate in a Dean-Stark trap. At this time, the polymer melt was allowed to
cool to 120° C and then slowly diluted with DI water (47.941 weight %) keeping the temperature
above 90° C during the dilution. The resulting -50 weight % polymer solution was then cooled
to room temperature. Weight average molecular weight of the polymer was determined to be
4,700 using a size exclusion chromatography method and polysaccharide standards.
b. Dithiocarbamate Polymer Preparation
The second step involved adding the acrylic acid / TEPA polymer (3 1.477 weight %), DI
Water (36.825 weight %), and Dowfax 2A1 (0.1 18 weight %) to a round bottom flask fitted with
a mechanical stirrer. Next, a 50% NaOH solution (8.393 weight %) was added to the stirring
reaction mixture. Once the mixture was heated and maintained at 40° C, carbon disulfide (14.794
weight %) was added drop-wise over 2 h. One hour within the carbon disulfide addition, another
amount of 50% NaOH (8.393 weight %) was charged. The reaction mixture was maintained at
40° C for an additional 2 h. Finally, the reaction was cooled to room temperature and filtered
though filter paper to obtain ~ 35 weight % polymeric dithiocarbamate product.
Example 9 :
a . Acrylamide / Tetraethylenepentamine Polymer Backbone Synthesis
Tetraethylenepentamine (TEPA) (14.581 weight %) was charged into a glass reactor
fitted with a mechanical stirrer and a condenser. While purging the headspace with nitrogen and
stirring, a 48.6 % acrylamide solution (30.441 weight %) was added dropwise over l h during
which the desired temperature was reached and was maintained between 65 - 75° C. After the
acrylamide charge, the temperature was maintained for an additional 1 h. Next, a second charge
of TEPA (14.581 weight %) was performed and the resulting reaction mixture was heated to 160°
C while collecting the distilled water via a Dean-Stark trap. This temperature was held for ~ 4 h
while continuing to collect the condensate in a Dean-Stark trap and trapping the released
ammonia side product. At this time, the polymer melt was allowed to cool to 120° C and then
slowly diluted with DI water (40.397 weight %) keeping the temperature above 90° C during the
dilution. The resulting ~50 weight % polymer solution was then cooled to room temperature.
Weight average molecular weight of the polymer was determined to be 4500 using a size
exclusion chromatography method and polysaccharide standards.
b. Dithiocarbamate Polymer Preparation
The second step involved adding the acrylamide / TEPA polymer (34.004 weight %), DI
Water (36.518 weight %), and Dowfax 2A1 (0.122 weight %) to a round bottom flask fitted with
a mechanical stirrer. Next, a 50% NaOH solution (7.763 weight %) was added to the stirring
reaction mixture. Once the mixture was heated and maintained at 40° C, carbon disulfide (13.830
weight %) was added drop-wise over 2 h. One hour within the carbon disulfide addition, another
amount of 50% NaOH (7.763 weight %) was charged. The reaction mixture was maintained at
40° C for an additional 2 h. Finally, the reaction was cooled to room temperature and filtered
though filter paper to obtain ~ 35 weight % polymeric dithiocarbamate product.
Example 10:
A sample of scrubber water was treated and then allowed to settle. A supernatant sample
was taken and measured for total mercury content and then filtered for dissolved mercury
content. The objective was to remove mercury. The samples were investigated for mercury
removal relative to the dosage of Chemistry 2 in wet FGD liquors from two different coal-fired
power plants.
The results show that a mercury level of less than 0.5 ppb in the treated water was
achieved at reasonable product dosages. This work demonstrated that the polymer achieved
mercury capture from wet FGD liquors. The lower detection limit of the analytical method was
0.010 ppb. The efficient/effective action of mercury capture by Chemistry 2 can be extrapolated
to its ability to successfully prevent mercury re-emission within an operating wet FGD.
aDTCP is a polydithiocarbamic polymer of the present invention
bFlocculant is commercially available from Nalco Company and is a very high molecular,
65mole% cationic latex polymer.
Example 11:
A sample of scrubber water was treated at temperatures typical of wet FGD operations
(50°C), measured with an ORP electrode and then filtered. The objective was to investigate the
effect that Chemistry 2 has on the ORP of the liquor and selenium removal relative to the dosage.
The results show that Chemistry 2 is capable of removing selenium from wet FGD liquor.
In this case, 56% removal of selenium was achieved. This work also demonstrated that
Chemistry 2 can successfully lower the ORP of the liquor, thus reducing the tendency for
corrosion within a wet FGD scrubber. Graphical results of these tests is illustrated in FIG. 2.
DTCP is a polydithiocarbamic polymer of the present invention
All patents referred to herein, are hereby incorporated herein by reference, whether or not
specifically done so within the text of this disclosure.
In the present disclosure, the words "a" or "an" are to be taken to include both the
singular and the plural. Conversely, any reference to plural items shall, where appropriate,
include the singular.
From the foregoing it will be observed that numerous modifications and variations can be
effectuated without departing from the true spirit and scope of the novel concepts of the present
invention. It is to be understood that no limitation with respect to the illustrated specific
embodiments or examples is intended or should be inferred. The disclosure is intended to cover
by the appended claims all such modifications as fall within the scope of the claims.
CLAIMS
We claim:
1. A method for minimizing corrosion and/or removing selenium from flue gas in a flue
gas wet scrubber process, the method comprising the following steps:
burning fuel, thereby producing the flue gas; and
passing the flue gas into the flue gas wet scrubber process comprising a scrubber liquor and a
composition comprising at least one of the following:
(i) a polymer derived from at least two monomers: acrylic-x and an alkylamine, and
wherein said acrylic-X has the following formula:
wherein X = OH and salts thereof or NHR2 and wherein R1 and R2 is H or an alkyl or aryl group,
wherein the molecular weight of said polymer is between 500 to 200,000, and wherein said
polymer is modified to contain a functional group capable of scavenging at least one metalcomprising
composition; and
(ii) a polydithiocarbamic compound of at least one polythiocarbamic material.
2. The method of claim 1, wherein the flue gas wet scrubber process additionally
comprises a second composition comprising a transition metal salt.
3. The method of claim 1, wherein the flue gas wet scrubber process comprises a wet
flue gas desulfurizer process.
4. The method of claim 1, wherein the functional group is a dithiocarbamate salt group
and wherein the polymer has between 55 to 80 mole % of said dithiocarbamate salt group
5. The method of claim 1, wherein the polydithiocarbamic compound comprises 30 to
80 mole percent of dithiocarbamate salt groups.
6. The method of claim 1, wherein the polydithiocarbamic compound has a molecular
weight of 500 to 100,000 Da.
7. The method of claim 1, wherein the polydithiocarbamic compound is present in the
flue gas wet scrubber process in a weight ratio of 1:1 to 2000: 1 in relation to the selenium
content.
8. The method of claim 1, wherein the acrylic-X is acrylic acid or salts thereof and the
alkylamine is PEHA or TEPA or DETA or TETA or EDA, and wherein the molar ratio between
acrylic-x and alkylamine is from 0.85 to 1.5; and wherein the molecular weight of said polymer
is from 1,500 to 8,000; and wherein the polymer is modified to contain more than 55 mole
percent dithiocarbamic acid or salts thereof.
9. The method of claim 1, wherein the fuel is selected from the group consisting of coal,
reclaimed coal, natural gas, industrial waste, a gasified waste product biomass, and any
combination thereof.
10. The method of claim 1, wherein the flue gas wet scrubber process employs equipment
comprising 2205 alloy.
11.A composition of matter comprising:
(i) a polymer derived from at least two monomers: acrylic-x and an alkylamine, and
wherein said acrylic-x has the following formula:
wherein X = OH and salts thereof or NHR2 and wherein R1 and R2 is H or an alkyl or
aryl group, wherein the molecular weight of said polymer is between 500 to 200,000, and
wherein said polymer is modified to contain a functional group capable of scavenging at
least one metal-comprising composition; and
(ii) a transition metal salt
12. The composition of claim 11, wherein the composition additionally comprises a
polydithiocarbamic compound of at least one polythiocarbamic material.
13. The composition of claim 11, wherein the functional group is a dithiocarbamate salt
group and wherein the polymer has between 30 to 55 mole % of said dithiocarbamate salt group.
14. The composition of claim 11, wherein the acrylic-x is acrylic acid or salts thereof and
the alkylamine is PEHA or TEPA or DETA or TETA or EDA, and wherein the molar ratio
between acrylic-x and alkylamine is from 0.85 to 1.5; and wherein the molecular weight of said
polymer is from 1,500 to 8,000; and wherein the polymer is modified to contain more than 55
mole percent dithiocarbamic acid or salts thereof.
15. The composition of claim 11, wherein the transition metal salt is an iron salt.
16. The composition of claim 11, wherein the transition metal salt is a manganese salt.