Note: Descriptions are shown in the official language in which they were submitted.
CA 02952392 2016-12-21
PRODUCTION OF CEMENTITIOUS ASH PRODUCTS WITH REDUCED CARBON
EMISSIONS
INTRODUCTION
[0001] The present teachings
relate to cementitious ash products. In particular, the
present teachings relate to ash produced from the combustion of carbonaceous
fuels.
, [0002] Plentiful coal reserves
in many parts of the world are sufficient, according to
some experts, to provide a majority of the world's energy needs for decades,
and perhaps for
centuries to come. At the same time, demand for cementitious materials such as
Portland cement
is expected to increase as developed countries maintain their infrastructure
and developing
countries build and maintain roads, dams, and other major constructions for
the benefit of their
citizens.
[0003] When coal is burned to
produce heat energy from combustion of
carbonaceous material, the unburned material and particulate combustion
products form an ash
with pozzolanic and/or cementitious properties. While the chemical composition
of coal ash
depends on the chemical composition of the coal, the ash normally contains a
major amount of
silica and alumina ,and significant but lesser amount of calcium.
[0004] So-called fly ash
produced from burning of pulverized coal in a coal fired
furnace or boiler is a powdery particulate matter made of the components of
coal that do not
volatize upon combustion. The ash is normally carried off in the flue gas and
is usually collected
from the flue gas using conventional apparatus such as electrostatic
precipitators, filtration
devices such as bag houses, and/or mechanical devices such as cyclones. The
burning of coal
entails the production of a large amount of coal ash, which must be dealt with
by the coal burning
facility. For example, ash from burning coal has been successfully used in
Portland cement
concrete as a partial replacement for Portland cement. Coal ash has further
been used as a
component in the production of flowable fill and as a component as stabilized
base and sub-based
mixtures. In these applications, the amount of ash used, especially as a
replacement for Portland
cement in such applications, is limited by the cementitious nature or lack
thereof of the particular
ash product.
[0005] Even though reuse of the
ash is preferred for economic reasons, in many
situations, the ash is not suitable to be used as a component of cementitious
mixtures. In many
cases, the ash must be land filled or otherwise treated as a waste product.
[0006] Emission of the
greenhouse gas, carbon dioxide, to the atmosphere
contributes to the phenomenon known as global warming. It is estimated that
the production of
cement accounts for 5 to 10 percent of the world's total carbon dioxide
emissions and as such is a
major contributor to global warming. Cement production is the largest non-
energy industrial
CA 02952392 2016-12-21
source of carbon dioxide emissions. Cement production is both a source of
combustion related
emission of carbon dioxide and a source of process related emissions of carbon
dioxide due to
the release of carbon dioxide during the calcination of limestone. It has been
estimated that if
carbon dioxide emissions from the worldwide cement production could be reduced
by 10
percent, such a reduction could accomplish about one fifth of the Kyoto
Protocol's goal for the
reduction in total carbon dioxide emissions by 5.2 percent below 1990 levels
worldwide across
all industries.
[0007] Methods
and compositions for burning coal to produce an ash product
having highly cementitious qualities would be a significant advance, because
it would both
reduce costs of waste disposal from coal burning utilities and reduce the cost
of concrete
products for needed building projects. Furthermore, methods and compositions
to reduce carbon
dioxide emissions from the production of cement would be a significant
advance, because it
would reduce the contribution from the production of cement to global warming.
SUMMARY
[0008] Methods are provided
for operating coal burning plants, cement plants, and
the like to provide a wide variety of technological and economic benefits. In
various
embodiments, use of a sorbent or combination of sorbents leads to production
of ash that
contains low levels of acid mercury and other heavy metals, while at the same
time containing
elevated levels of total heavy metal as a result of capture of heavy metal
from the coal in the ash
during combustion. To illustrate, the ash is preferably low in leachable
mercury and high in
cementitious properties in comparison to ash that is produced by burning coal
without the sorbent
or combination of sorbents. In some embodiments, use of the cementitious ash
in building
products as total or partial replacement for Portland cement results in
reduced carbon dioxide
emissions that would otherwise result form the manufacture of Portland cement.
In addition to
avoided carbon dioxide emissions from calcining of limestone to make Portland
cement and the
burning of fossil fuels to provide the energy needed to make Portland cement,
use of the sorbent
components tends to increase the efficiency of energy production from burning
of coal, further
reducing greenhouse emissions from the burning of fossil fuel to produce
energy. In various
embodiments, a variety of emission credits, including carbon dioxide, mercury,
and sulfur credits
is generated by the use of the sorbents, leading to economic advantages and an
increase in the
value of the coal burned.
[0009] Methods
and compositions are provided for treating coal and/or burning the
treated coal to produce an ash product that is highly cementitious in nature.
In some
embodiments, the cementitious nature of the ash allows for formulation of
Portland cement
concrete and similar products with up to 50% or more of the Portland cement
being substituted
by the ash product. In some embodiments, the strength activity index of
Portland type cement
2
CA 02952392 2016-12-21
products formulated with up to 50% or more ash is greater than 75% and
preferably 100% or
greater. Accordingly, in some embodiments, the ash product of the present
teachings is used as
the main cementitious material in Portland cement concretes, in stabilized
base, in sub-base
mixtures, in flowable fill (also called controlled low strength material or
CLSM), and the like.
[0010] The ash product is
made by burning coal in the presence of sorbent
components that contain a source of calcium and further contain significant
sources of silica and
alumina. In some embodiments, the components are added to coal pre-combustion
into the
furnace during combustion, and/or into flue gases preferably with a
temperature above 500 C.
The sorbent components are preferably added as an alkaline powder containing a
mixture of
components. The ash produced from combusting coal with these sorbent.
components is
generally higher in calcium content than the specifications for class F or
class C fly ash, and the
combined content of silica, alumina, and iron oxide. while significant, is
considerably below the
specifications for class F and class fly ash.
[0011] In some
embodiments, use of the alkaline powder sorbent, preferably in
combination with other sorbent components comprising a halogen compound,
result in reduced
sulfur and/or mercury emissions from the coal burning facility. In addition,
reduction of heavy
metals such as arsenic and also chloride is observed. The highly cementitious
nature of the ash
produced according to the current disclosures is believed to be.due at least
in part to its chemical
composition.
[0012] In some embodiments,
the present teachings provide a variety of cement
products such as Portland cement concrete, flowable fill, stabilized base, and
similar products in
which the conventional cement (Portland cement) otherwise used in the products
is replaced in
whole or in part with the cementitious ash product described herein. In
particular, in some
embodiments, the cementitious ash product of the current disclosure is used to
replace 40% or
.. more of the Portland cement conventionally used in such products.
DRAWINGS
[0013] The
skilled artisan will understand that the drawings, described herein, are
for illustration purposes only. The drawings are not intended to limit the
scope of the present
teachings in any way.
[0014] Figure 1 is block
diagram illustrating a non-limiting example of elements of
total capital investment for installing and maintaining a pollution control
device;
[0015] Figure 2
is a diagram illustrating a non-limiting example of various annual
costs and their interrelationships in decision making for pollution control
options
DESCRIPTION
[0016] The following
description of technology is merely exemplary in nature of
the subject matter, manufacture and use of one or more embodiments, and is not
intended to limit
3
CA 02952392 2016-12-21
the scope, application, or uses of any specific embodiments of the some
embodiments claimed in
this application or in such other applications as may be filed claiming
priority to this application,
or patents issuing therefrom. The following definitions and non-limiting
guidelines must be
considered in reviewing the description of the technology set forth herein. In
particular, although
the present disclosure will be discussed in some embodiments as reducing
industrial emissions
such as carbon dioxide, sulfur and mercury, such discussion should not be
regarded as limiting
the present disclosure to only such applications.
[0017] The
headings (such as "Introduction" and "Summary") and sub-headings
used herein are intended only for general organization of topics within the
present disclosure, and
are not intended to limit the disclosure of the technology or any aspect
thereof. In particular,
subject matter disclosed in the "Introduction" may include novel technology
and may not
constitute a recitation of prior art. Subject matter disclosed in the
"Summary" is not an
exhaustive or complete disclosure of the entire scope of the technology or any
embodiments
thereof. Classification or discussion of a material within a section of this
specification as having
a particular utility is made for convenience, and no inference should be drawn
that the material
must necessarily or solely function in accordance with its classification
herein when it is used in
any given composition.
[0018] The
citation of references herein does not constitute an admission that those
references are prior art or have any relevance to the patentability of the
technology disclosed
herein, in the event that one or more of the references, literature, and
similar materials differs
from or contradicts this application, including but not limited to defined
terms, term usage,
described techniques, or the like, this application controls.
[0019] The description and
specific examples, while indicating some embodiments
of the technology, are intended for purposes of illustration only and are not
intended to limit the
scope of the technology. Moreover, recitation of multiple embodiments having
stated features is
not intended to exclude other embodiments having additional features, or other
embodiments
incorporating different combinations of the stated features. Specific examples
are provided for
illustrative purposes of how to make and use the compositions and methods of
this technology
and, unless explicitly stated otherwise, are not intended to be a
representation that given
embodiments of this technology have, or have not, been made or tested.
[0020] Although
the present teachings will be discussed in some embodiments as
relating to coal burning facilities, such as power plants producing
electricity and cement
factories, such discussion should not be regarded as limiting the present
teachings to only such
applications.
4
CA 02952392 2016-12-21
[0021] In one
embodiment, a method of increasing the value of coal burned in a
coal burning facility is provided. The method includes combusting coal
containing mercury,
without a flue gas desulfurization device and in the presence of at least one
sorbent, to produce
heat energy, ash, and flue gases. The method further involves monitoring the
flue gases for
sulfur and mercury and adjusting the presence of sorbent to reduce at least
one of a Sulfur
emission and a mercury emission until it is in compliance with an
environmental regulation. A
monetary savings is thereby realized by avoiding the costs associated with the
flue gas
desulfurization device.
[0022] In another
embodiment, a method of operating a coal burning plant to
produce energy and waste ash involves burning coal in the presence of a
sorbent composition to
produce a waste ash having improved cementitious properties. The improved
cementitious
properties are reflected for example in a strength activity index of the waste
ash that is higher
compared to that of a waste ash produced from burning coal without the sorbent
composition.
The method further involves recovering the waste ash; in preferred embodiments
the waste ash
also has a reduced level of acid leachable mercury as compared to a waste ash
produced from
burning coal without the sorbent composition. Thereafter the method provides
for producing a
cement product from the waste ash.
[0023] In another
embodiment, a method of operating a coal burning plant to
produce heat energy and waste ash involves burning coal in the presence of at
least one sorbent
that increases the amount of a heavy metal (such as mercury) in the waste ash
and that decreases
the acid leachable amount of the heavy metal in the waste ash when compared to
ash produced
by burning coal without the sorbent. The ash is then sold as an industrial raw
material. The
process creates at least one of a mercury emission credit, a carbon dioxide
emission credit, and a
sulfur dioxide emission credit. The credits are then sold or traded, creating
economic benefit.
[0024] In another
embodiment, the present teachings provide a method of
decreasing carbon dioxide emission from a coal burning cement manufacturing
facility. The
method involves burning coal in the presence of at least sorbent to create
energy, flue gas, and
ash. The ash has improved cementitious properties as reflected in the strength
activity index of
the waste ash as compared to an ash prepared from burning coal not in the
presence of the
sorbent. The energy created is then used in manufacturing cement. The ash
having cementitious
properties is then added to the cement, thus increasing the amount of said
cementitious material
produced by the cement plant without increasing the amount of limestone used
in the cement
manufacture. Carbon dioxide emissions are avoided because less limestone is
calcined per unit
of cementitious material made.
[0025j The sorbents used in
the methods of the present teachings provide the
described advantages when used as indicated in the coal burning processes. In
various
5
CA 02952392 2016-12-21
embodiments, the sorbents include alkaline powders and/or liquid compositions
containing
calcium, silica, alumina, and optionally a halogen such as bromine. Suitable
sorbent components
and compositions, as well as methods for their use are described in U.S.
Provisional Application
60/759,994 filed January 18, 2006 entitled "Sorbents for Mercury and Sulfur
Remediation" by
Douglas Comrie; in U.S. Provisional Serial No. 60/662,911 filed March 17, 2005
by Douglas
Comrie; in U.S. Provisional Application 60/742,154 filed December 2, 2005 by
Douglas Comrie;
in U.S. Provisional Application No. 60/765,944, filed February 7, 2006 by
Douglas Comrie; and
in international published application WO 2006099611 Al, based on
international application
PCT/US2006/010000 filed March 16, 2006 by Douglas Comrie.
[0026] In some
embodiments, an ash product is produced by burning coal in the
presence of sorbent components comprising calcium, silica, alumina, and a
halogen such as
bromine. The components are added as parts of one or more sorbent compositions
into the coal-
burning system. In a non-limiting example, sorbent components calcium, silica,
and alumina are
added together in an alkaline powder sorbent composition that comprises about
2 to 15% by
weight A1203, about 30 to 75% by weight CaO, about 5 to 20% by weight SiO2,
about 1 to 10%
Fe2O3, and about 0.1 to 5% by weight total alkali, such as sodium oxide and
potassium oxide. In
some embodiments, the sorbents comprise about 2 to 10% by weight Al2O3, about
40 to 70% by
weight CaO, about 5 to 15% by weight total alkalis. In some embodiments,
powder sorbent
compositions described herein contain one or more alkaline powders containing
calcium, along
with lesser levels of one or more aluminosilicate materials. A halogen
component, if desired, is
added as a further component of the alkaline powder or is added separately as
part of a liquid or
powder composition.
[0027] To make
the ash products, a carbonaceous fuel is burned to -produce heat
energy from combustion of the carbonaceous material. In some embodiments, the
carbonaceous
fuel can be coal. Unburned material and particulate combustion products form
an ash that
collects at the bottom of the furnace or is collected from the flue by
precipitators or filters, for
example a bag house on a coal burning facility. The content of the bottom ash
and the fly ash
depends on the chemical composition of the coal and on the amount and
composition of sorbent
components added into the coal burning facility during combustion.
[0028] Major
elements in coal, besides carbon, include silica, alumina, and calcium,
along with lesser amounts of iron. In addition, trace heavy metals such as
arsenic, antimony,
lead, chromium, cadmium, nickel, vanadium, molybdenum, manganese, copper, and
barium are
normally present. These non-carbon elements tend to report to the ash upon
combustion of coal.
Coal also contains significant amounts of sulfur. Upon combustion, the sulfur
in coal burns to
produce volatile sulfur oxides, which tend to escape from the coal burning
utility in gaseous
6
CA 02952392 2016-12-21
form. A major cause of acid raid is sulfur dioxide emissions. As generally
known in the art,
when sulfur dioxide is mixed with water, sulfuric acid is formed. It is
desired to remediate or
reduce the level of sulfur oxides emitted from coal burning plants.
[0029] Coal also
contains mercury. Although present at a low level, mercury tends
to volatilize during combustion and escape from the coal burning utility. Even
at the low levels
produced from the combustion of coal, the release of mercury into the
environment is undesirable
because the element is toxic and tends to accumulate in body tissues. Because
of mercury's
damaging effect on health and the environment, its release has recently come
under regulatory
control in the United States and elsewhere in the world. Whether mercury is
subject to
regulatory controls or not, it is highly desirable to reduce the amount of
mercury emitted from
coal burning utilities.
[0030] In some
embodiments, the sorbent compositions that tend to reduce or
remediate the release of mercury and/or sulfur from coal burning utilities
also have the beneficial
effect of rendering the ash produced by combustion of the fuel highly
cementitious so that it is
usable in commerce as a partial or complete replacement for Portland cement in
various cement
and concrete products. The ash produced from the coal combustion with the
current sorbent is
useful in commerce, not only for its highly cementitious nature, but also for
the fact that it
contains heavy metals resulting from the combustion of coal in a non-leaching
form in the ash.
That is, mercury, arsenic, lead and other heavy metals in the coal report to
the ash. Burning the
coal with the sorbent compositions described herein results in an ash that
has, in some
embodiments, increased levels of the heavy metals compared to coal burned
without the sorbent,
but which nevertheless contains lower levels of leachable heavy metals than
the ash produced
without the sorbents. As a result, the ash is safe to handle and to sell into
commerce, for example
as a cementitious material.
[0031] In some embodiments,
a process involves application of sorbents directly
into the furnace during combustion (addition "co-combustion") directly to a
fuel such as coal
before combustion (addition "pre-combustion"); directly into the gaseous
stream after
combustion preferably in a temperature zone of greater than 500 C and
preferably greater than
800 C (addition "post-combustion); or in any combination of pm-combustion, co-
combustion,
and post-combustion additions.
[0032] In some
embodiments, coal is burned along with other fuels in co-generation
plants. Such plants are flexible in the fuels they burn. In addition to
bituminous and sub-
bituminous coal, such facilities can also burn other fuels such as municipal
waste, sewage sludge,
pet coke, biomass (such as without limitation wood, wood chips, agricultural
waste, and/or
sawdust), scrap plastics, shredded tires, and the like. To the extent that the
fuels contain mercury
and sulfur, use of sorbents as described herein tends to mitigate or lower
emissions of sulfur
7
CA 02952392 2016-12-21
and/or mercury that would otherwise be released into the atmosphere upon
combustion. It also
produces an ash product with a highly cementitious nature. In some
embodiments, the use of
sorbents as described herein tends to mitigate or lower emissions of carbon
dioxide.
[0033] Depending
on the fuel value of the fuel being burned, the flame temperature
in such co-generation plants varies upward from about 1000 F - 1200 F (for low
value fuels or
fuels containing high proportions of low value biomass or other low-value
components) to
2700 F to 3600 F or higher (for high BTU coal or fuel mixes with a high
proportion of high
BTU coal). In some embodiments, use of sorbents of the present teachings
mitigates mercury
emissions from systems burning at relatively lower temperatures. It is
believed the alkaline
powder sorbents described herein are effective at removing oxidized mercury
from the flue
gases, and that oxidized mercury is the species predominantly formed by
combustion at the lower
temperatures.
[0034] Thus, in
some embodiments, co-generation plants burning a combination of
coal, biomass (e.g., woodchips, sawdust, plant wastes, crop wastes, animal
wastes, sludge, and
the like) and/or recyclable polymeric material (e.g. scrap rubber tires) are
treated with sorbent
compositions to achieve significant reductions in emissions of mercury and/or
sulfur, and to
produce an ash product with good cementitious qualities.
[0035] In some
embodiments, mercury emissions from the coal burning facility are
monitored. Emissions are monitored as elemental mercury, oxidized mercury, or
both.
Elemental mercury means mercury in the ground or zero oxidation state, while
oxidized mercury
means mercury in the +1 or +2 oxidation state. Depending on the level of
mercury in the flue gas
prior to emission from the plant, the amount of sorbent composition added pre-
, co-, and/or post-
combustion is raised, lowered, or is maintained unchanged. In general, it is
desirable to remove
as high a level of mercury as is possible. In some embodiments, mercury
removal of 90% and
greater is achieved, based on the total amount of mercury in the coal. This
number refers to the
mercury removed from the flue gases so that mercury is not released through
the stack into the
atmosphere. Normally, removal of mercury from the flue gases leads to
increased levels of
mercury in the ash. To minimize the amount of sorbent added into the coal
burning process so as
to reduce the overall amount of ash produced in the furnace, it is desirable
in many embodiments
to use the measurements of mercury emissions to adjust the sorbent composition
rate of addition
to one that will achieve the desired mercury reduction without adding excess
material into the
system.
[0036] In some
embodiments of burning coal or other fuels with the added sorbent
components, mercury and other heavy metals in the coal such as arsenic,
antimony, lead, and
others report to the bag house or electrostatic precipitator and become part
of the overall ash
content of the coal burning plant; alternatively or in addition, the mercury
and heavy metals are
8
CA 02952392 2016-12-21
found in the bottom ash. As such, mercury and other heavy metals are not
emitted from the
facility. In general, mercury and other heavy metals in the ash are resistant
to leaching under
acidic conditions, even though they tend to be present in the ash at elevated
levels relative to ash
produced by burning coal without the sorbent components described herein.
Advantageously,
heavy metals in the ash do not leach beyond regulatory levels; in fact, a
decreased level of
leachable heavy metal is observed in the ash on a ppb basis, even though the
ash normally
contains a higher absolute level of heavy metals by virtue of being produced
by burning with the
sorbents. Because in addition the cementitious nature of the ash is enhanced,
the ash from the
combustion (coal ash) is valuable for sale in commerce and use, for example,
as a cementitious
material to make Portland cements as well as concrete products and ready
mixes.
[0037] In some
embodiments, leaching of heavy metals is monitored or analyzed
periodically or continuously during combustion. The TCLP procedure of the
United States
Environmental Protection Agency is a commonly used method. As with mercury in
the flue gas,
the amount of sorbent, particularly of sorbent components with Si (SiO2 or
equivalents) and/or Al
(A1203 or equivalents), is adjusted based on the analytical result to maintain
the leaching in a
desired range.
[0038] In some
embodiments, the present teachings provides a method for reducing
the amount of oxidized mercury in flue gases that are generated by combustion
of mercury-
containing carbonaceous fuel such as coal while at the same time producing and
cementitious ash
product. The method comprises burning the fuel in the presence of an alkaline
powder sorbent
wherein the powder sorbent comprises calcium, silica, and alumina. While the
fuel is burning, a
level of mercury (oxidized, elemental, or both) is measured in the flue gases
downstream from
the furnace. The measured mercury level is compared to a target level and, if
the measured level
is above the targeted level, the amount of powder sorbent added relative to
the amount of fuel
being burned is increased. Alternatively, if the measured level is at or below
the target level, the
rate of sorbent addition can be decreased or maintained unchanged.
[0039] In some
embodiments, a method for reducing sulfur and/or mercury in the
flue gases produced by the combustion of coal in the furnace of a coal burning
facility involves
injecting a powder composition into the furnace during combustion. The powder
composition is
an alkaline sorbent composition that contains an alkaline calcium component as
well as
significant levels of silica and alumina. In a non-limiting embodiment, the
powder composition
comprises 2 to 50% of an aluminosilicate material and 50 to 98% by weight of
an alkaline
powder comprising calcium. In some embodiments, the alkaline powder comprises
one or more
of Portland cement, cement kiln dust, lime kiln dust, and sugar beet lime,
while the
aluminosilicate material contains one or more selected from the group
consisting of Calcium,
rnontmorillonite, sodium montmorillonite, and kaolin. The powder composition
is added to the
9
CA 02952392 2016-12-21
coal at a rate of about 0.1 to about 10% by weight, based on the amount of
coal being treated
with the sorbents for a batch process, or on the rate of coal being consumed
by combustion for a
continuous process. In some embodiments, the rate is from 1 to 8% by weight, 2
to 8% by
weight, 4 to 8% by weight, or about 6% by weight. In some embodiments, the
powder
composition is injected to the fireball or furnace during combustion and/or is
applied to the coal
under ambient conditions, prior to its combustion. The temperature at the
injection point is
preferably at least about 1000 F or higher. For some low value fuels, this
corresponds to
injection into or close to the fireball.
[0040] In some
embodiments, the present teachings proVide novel sorbent
compositions comprising about 50 to 98% by weight of at least one of Portland
cement, cement
kiln dust, lime kiln dust, sugar beet lime, and 2 to 50% by weight of an
aluminosilicate material.
In some embodiments, the compositions further comprise a bromine compound, for
example, as
a bromide, such as calcium bromide. Use of the sorbents during the coal
burning process as
described herein tends to lessen the amount of harmful sulfur and mercury
products emitted from
the facility, while at the same time producing an ash that is environmentally
acceptable (e.g.
leaching of heavy metals is below regulatory levels and is lower than in ash
produced by burning
the coal without the sorbent components) and highly cementitious in nature so
that the ash serves
as a complete or partial (greater than 40%, preferably greater than 50%)
replacement for Portland
cement in cementitious mixtures and processes for their use.
[0041] In some embodiments,
sorbent components are added as part of a single
composition, and/or as separate components onto the fuel pre-combustion, into
the furnace co-
combustion. and/or into the convective pathway post-combustion. For example,
it is convenient
to add the alkaline components containing calcium together with the silica and
alumina as a
single composition. When used, a halogen compound such as a bromine compound
is provided
as part of the single composition or as a separate composition.
[0042] In some
embodiments, a dual system is used wherein calcium, silica, and
alumina are added in a powder sorbent, while bromine or other halogen(s) is
added in a liquid
sorbent. The method of the present teachings provides coal ash and/or fly ash
containing
mercury at a level corresponding to capture in the ash of at least 90% of the
mercury originally in
the coal before combustion. In some embodiments, the mercury level is higher
than in known fly
ashes due to capture of mercury in the ash rather than release of mercury into
the atmosphere.
Fly ash produced by the process contains up to 200 ppb mercury or higher; in
some embodiments
the mercury content of the fly ash is above 250 ppb. Since the volume of ash
is normally
increased by use of the sorbents (in some embodiments, the volume of ash about
doubles), the
increased measured levels of mercury represent significant capture in the ash
of mercury that
without the sorbents would have been released into the environment. The
content in the fly ash
CA 02952392 2016-12-21
of mercury and other heavy metals such as lead, chromium, arsenic, and cadmium
is generally
higher than in fly ash produced from burning coal without the added sorbents
or sorbent
components.
[0043] A process
for making the coal ash involves burning coal in the presence of
added calcium, silica, and alumina, and preferably in the further presence of
a halogen such as
bromine. In some embodiments, ash is- prepared by burning coal in the presence
of sorbents or
sorbent components described herein. In some embodiments, the mercury in the
coal ash is non-
leaching in that it exhibits a concentration of mercury in the extract of less
than 0.2 ppb when
tested using the Toxicity Characteristic Leaching Procedure (TCLP), test
Method 1311 in "Test
Methods for Evaluating Solid Waste, Physical/Chemical Methods," EPA
Publication SW-846 ¨
Third Edition. It is normally observed that fly
ash from burning coal with the sorbents described herein has less leachable
mercury than ash
produced from burning coal without the sorbent, even though the total mercury
content in ash
produced from the sorbent treated coal is higher by as much as a factor of 2
or more over the
level in ash produced by burning without the sorbents. To illustrate, typical
ash from burning of
PRB coal contains about 100-125 ppb mercury; in various embodiments, ash
produced by
burning PRB coal with about 6% by weight of the sorbents described herein has
about 200-250
ppb mercury or more.
[00441 In some
embodiments, the present teachings provide a hydraulic cement
product containing Portland cement and from 0.1% to about 99% by weight, based
on the total
weight of the cement product, of a coal ash or fly ash described above.
[0045] In some
embodiments, the present teachings provide a pozzolanic product
comprising a pozzolan and from 0.01% to about 99% by weight, based on the
total weight of the
pozzolanic product of the ash described above.
[0046] The present
teachings also provide a cementitious mixture containing the
hydraulic cement described above.
[0047] In some
embodiments, a cementitious mixture contains coal ash described
herein as the sole cementitious component; in some embodiments, the ash is a
total replacement
for conventional cements such as Portland cement. The cementitious mixtures
contain cement
and optionally aggregate, fillers, and/or other admixtures. The cementitious
mixtures are
normally combined with water and used as concrete, mortars, grout, flowable
fill, stabilized base,
and other applications.
[0048] Sorbent
compositions of the present teachings contain components that
contribute calcium, silica, and alumina, preferably in the form of alkaline
powders. In some
embodiments, the compositions also contain iron oxide, as well as basic
powders based on
sodium oxide (Na2O) and potassium oxide (K20). In a non-limiting example, the
powder sorbent
11
CA 02952392 2016-12-21
contains about 2-10% by weight A1203, about 40-70% CaO, about 5-15% SiO2,
about 2-9%
Fe2O3, and about 0.1-5% total alkalis such as sodium oxide and potassium
oxide. The
components comprising calcium, silica, and alumina and other elements if
present, are combined
together in a single composition or are added separately or in any combination
as components to
the fuel burning system. In some embodiments, use of the sorbents leads to
reductions in the
amount of sulfur and/or mercury released into the atmosphere. In various
embodiments, use of
the sorbent compositions leads to the removal of mercury, especially oxidized
mercury. In
addition, the compositions reduce the amount of sulfur given off from
combustion by a virtue of
their calcium content.
[0049] Advantageously, the
sorbent compositions contain suitable high levels of
alumina and silica. It is believed that the presence of alumina and/or silica
leads to several
advantages seen from use of the sorbent. To illustrate, it is believed that
the presence of alumina
and/or silica and/or the balance of the silica/alumina with calcium, iron, and
other ingredients
contributes to the low acid leaching of mercury and/or other heavy metals that
is observed in ash
produced by combustion of coal or other fuels containing mercury in the
presence of the
sorbents.
[0050] In some
embodiments, it is observed that use of the sorbent compositions
during combustion of coal or other fuel leads to the formation of a refractory
lining on the walls
of the furnace and on the boiler tubes. It is believed that such a refractory
lining reflects heat in
the furnace and leads to higher water temperature in the boilers. In some
embodiments, it is also
observed that use of the sorbent results in reduced scale formation or
slagging around the boiler
tubes. In this way, use of the sorbents leads to cleaner furnaces, but more
importantly improves
the heat exchange between the burning coal and the water in the boiler tubes.
As a result, in
some embodiment's use of the sorbents leads to higher water temperature in the
boiler, based on
burning the same amount of fuel. Alternatively, it has been observed that use
of the sorbent
allows the feed rate of, for example, coal to be reduced while maintaining the
same power output
or boiler water temperature. In an illustrative embodiment, use of a sorbent
at a 6% rate results
in combustion of a coal/sorbent composition that produces as much power as a
composition of
the same weight that is all coal. It is seen in some embodiments that use of
the sorbent, which is
normally captured in the fly ash and recycled, actually increases the
efficiency of the coal
burning process, leading to less consumption of fuel. Advantageously in such a
process, the fly
ash, which is normally increased in volume by virtue of the use of the
sorbent, is recycled for use
in Portland cement manufacture and the like, it having an improved
cementitious nature and low
heavy metal leaching.
[0051] As noted, in some
embodiments, the components of the sorbent composition
are provided as alkaline powders. Without being limited by theory, it is
believed that the alkaline
12
CA 02952392 2016-12-21
nature of the sorbent components leads at least in part to the desirable
properties. described
above. Sources of calcium for the sorbent compositions of the present
teachings include calcium
powders such as calcium carbonate, limestone, calcium oxide, calcium
hydroxide, calcium
phosphate, and other calcium salts. It is understood that industrial products
such as limestone,
lime, slaked lime, and the like contribute major proportions of such calcium
salts. As such, they
are suitable components for the sorbent compositions of the present teachings.
[0052] Other
sources of calcium include various manufactured products. Such
products are commercially available, and some are sold as waste products or by-
products of other
industrial processes. In some embodiments, the products further contribute
either silica, alumina,
or both to the compositions of the present teachings. Non-limiting examples of
industrial
products that contain silica and/or alumina in addition to calcium include
Portland cement,
cement kiln dust, lime kiln dust, sugar beet lime, slags (such as steel slag,
stainless steel slag, and
blast furnace slag), paper de-inking sludge ash, cupola arrester filter cake,
and cupola furnace
dust. These and other materials are combined to provide alkaline powders or
mixtures of
alkaline powders that contain calcium, and preferably also contain silica and
alumina. In some
embodiments, various pozzolanie materials are used.
[0053] Sugar beet
lime is a solid waste material resulting from the manufacture of
sugar from sugar beets. It is high in calcium content, and also contains
various impurities that
precipitate in the liming procedure carried out on sugar beets. It is an item
of commerce, and is
normally sold to landscapers, farmers, and the like as a soil amendment.
[0054] Cement
kiln dust (CKD) generally refers to a byproduct generated within a
cement kiln or related processing equipment during Portland cement
manufacturing,
[0055] Generally,
CKD comprises a combination of different particles generated in
different areas of the kiln, pre-treatment equipment, and/or material handling
systems, including,
for example, clinker dust, partially to fully calcined material dust, and raw
material (hydrated and
dehydrated) dust. The composition of the CKD varies based upon the raw
materials and fuels
used, the manufacturing and processing conditions, and the location of
collection points for CKD
within the cement manufacturing process. CKD can include dust or particulate
matter collected
from kiln effluent (i.e., exhaust) streams, clinker cooler effluent, pre-
calciner effluent, air
.. pollution control devices, and the like.
[0056] While CKD
compositions will vary for different kilns, CKD usually has at
least some cementitious and/or pozzolanic properties, due to the presence of
the dust of clinker
and calcined materials. Typical CKD compositions comprise silicon-containing
compounds,
such as silicates including tricalcium silicate, dicalcium silicate; aluminum-
containing
compounds, such as aluminates including tricalcium aluminate; and iron-
containing compounds,
such as ferrites including tetracalcium aluminoferrite. CKD generally
comprises calcium oxide
13
CA 02952392 2016-12-21
(CaO). Exemplary CKD compositions comprise about 10 to about 60% calcium
oxide,
optionally about 25 to about 50%, and optionally about 30 to about 45% by
weight. In some
embodiments, CKD comprises a concentration of free lime (available for a
hydration reaction
with water) of about 1 to about 10 To, optionally of about 1 to about 5%, and
in some
embodiments about 3 to about 5%. Further, in some embodiments, CKD comprises
compounds
containing alkali metals, alkaline earth metals, and sulfur, inter alia.
[0057] Other
exemplary sources for the alkaline powders comprising calcium, and
some further comprising silica and alumina, include various cement-related
byproducts (in
addition to Portland cement and CKD described above). Blended-cement products
are one
suitable example of such a source. These blended cement products typically
contain mixes of
Portland cement and/or its clinker combined with slag(s) and/or pozzolan(s)
(e.g., fly ash, silica
fume, burned shale). Pozzolans are usually silicaceous materials that are not
in themselves
cementitious, but which develop hydraulic cement properties when reacted with
free lime (free
CaO) and water. Other sources are masonry cement and/or hydraulic lime, which
include
mixtures of Portland cement and/or its clinker with lime or limestone. Other
suitable sources are
aluminous cements, which are hydraulic cements manufactured by burning a mix
of limestone
and bauxite (a naturally occurring, heterogeneous material comprising one or
more aluminum
hydroxide minerals, plus various mixtures of silica, iron oxide, titania,
aluminum silicates, and
other impurities in minor or trace amounts). Yet another example is a pozzolan
cement, which is
a blended cement containing a substantial concentration of pozzolans. Usually
the pozzolan
cement comprises calcium oxide, but is substantially free of Portland cement.
Common
examples of widely-employed pozzolans include natural pozzolans (such as
certain volcanic
ashes or tuffs, certain diatomaceous earth, burned clays and shales) and
synthetic pozzolans (such
as silica fume and fly ash).
[00581 Lime kiln dust (LKD)
is a byproduct from the manufacturing of lime, LKD
is dust or particulate matter collected from a lime kiln or associated
processing equipment.
Manufactured lime can be categorized as high-calcium lime or dolomitic lime,
and LKD varies
based upon the processes that form it. Lime is often produced by a calcination
reaction
conducted by heating calcitic raw material, such as calcium carbonate (CaCO3),
to form free lime
CaO and carbon dioxide (CO2). High-calcium lime has a high concentration of
calcium oxide
and typically some impurities, including aluminum-containing and iron-
containing compounds.
High-calcium lime is typically formed from high purity calcium carbonate
(about 95% purity or
greater). Typical calcium oxide content in an LKD product derived from high-
calcium lime
processing is greater than or equal to about 75% by weight, optionally greater
than or equal to
about 85% by weight, and in some cases greater than or equal to about 90% by
weight. In some
lime manufacturing, dolomite (CaCO3=Mg003) is decomposed by heating to
primarily generate
calcium oxide (CaO) and magnesium oxide (MgO), thus forming what is known as
dolomitic
14
CA 02952392 2016-12-21
lime. In LKD generated by dolomitic lime processing, calcium oxide can be
present at greater
than or equal to about 45% by weight, optionally greater than about 50% by
weight, and in some
embodiments, greater than about 55% by weight. While LKD varies based upon the
type of lime
processing employed, it generally has a relatively high concentration of free
lime. Typical
amounts of free lime in LKD are about 10 to about 50%, optionally about 20 to
about 40%,
depending upon the relative concentration of calcium oxide present in the lime
product
generated.
[0059] Slags are
generally byproduct compounds generated by metal manufacturing
and processing. The term "slag" encompasses a wide variety of byproduct
compounds, typically
comprising a large portion of the non-metallic byproducts of ferrous metal
and/or steel
manufacturing and processing. Generally, slags are considered to be a mixture
of various metal
oxides, however they often contain metal sulfides and metal atoms in an
elemental form.
[0060] Various
examples of slag byproducts useful for some embodiments of the
present teachings include ferrous slags, such as those generated in blast
furnaces (also known as
cupola furnaces), including, by way of example, air-cooled blast furnace slag
(ACBFS),
expanded or foamed blast furnace slag, pelletized blast furnace slag,
granulated blast furnace slag
(GBFS), and the like. Steel slags can be produced from basic oxygen
steelmaking furnaces
(BOS/B0F) or electric arc furnaces (EAF). Many slags are recognized for having
cementitious
and/or pozzolanic properties, however the extent to which slags have these
properties depends
upon their respective composition and the process from which they are derived,
as recognized by
the skilled artisan. Exemplary slags comprise calcium-containing compounds,
silicon-containing
compounds, aluminum-containing compounds, magnesium-containing compounds, iron-
containing compounds, manganese-containing compounds and/or sulfur-containing
compounds.
In some embodiments, the slag comprises calcium oxide at about 25 to about
60%, optionally
about 30 to about 50%, and optionally about 30 to about 45% by weight. One
example of a
suitable slag generally having cementitious properties is ground granulated
blast furnace slag
(GGBFS).
[0061] As
described above, other suitable examples include blast (cupola) furnace
dust collected from air pollution control devices attached to blast furnaces,
such as cupola
arrester filter cake. Another suitable industrial byproduct source is paper de-
inking sludge ash.
As recognized by those of skill in the art, there are many different
manufactured/industrial
process byproducts that are feasible as a source of calcium for the alkaline
powders that form the
sorbent compositions of the present teachings. Many of these well known
byproducts comprise
alumina and/or silica, as well. Combinations of any of the exemplary
manufactured products
and/or industrial byproducts are also contemplated for use as the alkaline
powders of certain
embodiments of the present teachings.
CA 02952392 2016-12-21
[00621 In some
embodiments, desired treat levels of silica and/or alumina are above
those provided by adding materials such as Portland cement, cement kiln dust,
lime kiln dust,
and/or sugar beet lime. Accordingly, it is possible to supplement such
materials with
aluminosilicate materials, such as without limitation clays (e.g.
montmorillonite, kaolins, and the
like) where needed to provide preferred silica and alumina levels. In some
embodiments,
supplemental aluminosilicate materials make up at least about 2%, and
preferably at least about
5% by weight of the various sorbent components added into the coal burning
system. In general,
there is no upper limit from a technical point of view as long as adequate
levels of calcium are
maintained. However, from a cost standpoint, it is normally desirable to limit
the proportion of
more expensive aluminosilicate materials. Thus, the sorbent components
preferably comprise
from about 2 to 50%, preferably 2 to 20%, and more preferably, about 2 to 10%
by weight
aluminosilicate material such as the exemplary clays.
[0063] In some
embodiments, an alkaline powder sorbent composition contains one
or more calcium-containing powders such as Portland cement, cement kiln .dust,
lime kiln dust,
various slags, and sugar beet lime, along with an aluminosilicate clay such
as, without limitation,
montmorillonite or kaolin. In some embodiments, the sorbent composition can
contain sufficient
SiO2 and Al2O3 to form a refractory-like mixture with calcium sulfate produced
by combustion
and with mercury and other heavy metals such that the calcium sulfate is
handled by the particle
control system of the furnace and mercury and heavy metals are not leached
from the ash under
acidic conditions. In some embodiments, the calcium containing powder sorbent
contains by
weight a minimum of 2% silica and 2% alumina, preferably a minimum of 5%
silica, and 5%
alumina. In some embodiments, the alumina level is higher than that found in
Portland cement,
that is to say higher than about 5% by weight and, in some embodiments, higher
than about 6%
by weight, based on Al2O3.
[0064] In some embodiments,
the sorbent components of the alkaline powder
sorbent composition work together with optional added halogen (such as
bromine) compound or
compounds to capture chloride as well as mercury, lead, arsenic, and other
heavy metals in the
ash, render the heavy metals non-leaching under acidic conditions, and improve
the cementitious
nature of the ash produced. As a result, emissions of mercury, other heavy
metals such as
arsenic, sulfur, and chlorine are mitigated, reduced, or eliminated, and a
valuable cementitious
material is produced as a by-product of coal burning.
[0065] Suitable
aluminosilicate materials include a wide variety of inorganic
minerals and materials. For example, a number of minerals, natural materials,
and synthetic
materials contain silicon and aluminum associated with an oxy environment
along with optional
other cations such as, without limitation, Na, K, Be, Mg, Ca, Zr, V, Zn, Fe,
Mn, and/or other
anions, such as hydroxide, sulfate, chloride, carbonate, along with optional
waters of hydration.
16
CA 02952392 2016-12-21
Such natural and synthetic materials are referred to herein as aluminosilicate
materials and are
exemplified in a non-limiting way by the clays noted above.
[0066] In
aluminosilicate materials, the silicon tends to be present as tetrahedra,
while the aluminum is present as tetrahedra, octahedra, or a combination of
both. Chains or
networks of aluminosilicate are built up in such materials by the sharing of
1, 2, or 3 oxygen
atoms between silicon and aluminum tetrahedra or octahedra. Such minerals go
by a variety of
names, such as silica, alumina, aluminosilicates, geopolymer, silicates, and
aluminates. However
presented, compounds containing aluminum and/or silicon tend to produce silica
and alumina
upon exposure to high temperatures of combustion in the presence of oxygen
=
[0067] In some embodiments,
aluminosilicate materials include polymorphs of
Si0eA1203. For example, silliminate contains silica octahedra and alumina
evenly divided
between tetrahedra and octahedra. Kyanite is based on silica tetrahedra and
alumina octahedra.
Andalusite is another polymorph of Si02-A1203.
[0068] In some
embodiments, chain silicates contribute silicon (as silica) and/or
aluminum (as alumina) to the compositions of the present teachings. Chain
silicates include
without limitation pyroxene and pyroxenoid silicates made of infinite chains
of SiO, tetrahedra
linked by sharing oxygen atoms.
[0069] Other
suitable aluminosilicate materials include sheet materials such as,
without limitation, micas, clays, chrysotiles (such as asbestos), talc,
soapstone, pyrophillite, and
kaolinite. Such materials are characterized by having layer structures wherein
silica and alumina
octahedra and tetrahedra share two oxygen atoms. Layered aluminosilicates
include clays such =
as chlorites, glauconite, illite, polygorskite, pyrophillite, sauconite,
vermiculite, kaolinite,
calcium montmorillonite, sodium montmorillonite, and bentonite. Other examples
include micas
and talc.
[0070] Suitable
aluminosilicate materials also include synthetic and natural zeolites,
such as, without limitation, the analcime, sodalite, chabazite, natrolite,
phillipsite, and mordenite
groups. Other zeolite minerals include heulandite, brewsterite, epistilbite,
stilbite, yagawaralite,
laumontite, ferrierite, paulingite, and clinoptilolite. The zeolites are
minerals or synthetic
materials characterized by an aluminosilicate tetrahedral framework, ion
exchangeable "large
cations" (such as Na, K, Ca, Ba, and Sr) and loosely held water molecules.
[0071] In some
embodiments, framework or 3D silicates, aluminates, and
aluminosilicates are used. Framework aluminosilicates are characterized by a
structure where
Slat tetrahedra, A104 tetrahedra, and/or A106 octahedra are linked in three
dimensions. Non-
limiting examples of framework silicates containing both silica and alumina
include feldspars
such as albite, anorthite, andesine, bytownite, labradorite, microcline,
sanidine, and orthoclase.
[0072] In some
embodiments, the sorbent powder compositions are characterized in
17
CA 02952392 2016-12-21
that they contain a major amount of calcium, preferably greater than 20% by
weight based on
calcium oxide, and that furthermore they contain levels of silica, and/or
alumina higher than that
found in commercial products such as Portland cement. In some embodiments, the
sorbent
compositions comprise greater than 5% by weight alumina, preferably greater
than 6% by weight
alumina, preferably greater than 7% by weight alumina, and preferably greater
than about 8% by
weight alumina.
[0073] Coal or
other fuel is treated with sorbent components at rates effective to
control the amount of sulfur and/or mercury released into the atmosphere upon
combustion. In
some embodiments, total treatment levels of the sorbent components ranges from
about 0.1% to
about 20% by weight, based on the weight of the coal being treated or on the
rate of the coal
being consumed by combustion. When the sorbent components are combined into a
single
composition, the component treat levels correspond to sorbent treat levels. In
this way a single
sorbent composition can be provided and metered or otherwise measured for
addition into the
coal burning system. In general, it is desirable to use a minimum amount of
sorbent so as not to
overload the system with excess ash, while still providing enough to have a
desired effect on
sulfur and/or mercury emissions. Accordingly, in some embodiments, the
treatment level of
sorbent ranges from about 1% to about 10% by weight and, in some embodiments,
from about 1
or 2% by weight to about 10% by weight. For many coals, an addition rate of 6%
by weight of
powder sorbent has been found to be acceptable.
[00741 The powder sorbents
containing calcium, silica, and alumina as described
herein are generally effective to reduce the amount of sulfur in gases emitted
from the coal
burning facility. In some embodiments, for reduction of sulfur emissions,
methods of the present
teachings can provide calcium in the sorbent components at a molar ratio of at
least 1:1, and
preferably above 1:1, measured against the moles of sulfur in the fuel (such
as coal) being
burned. If it is desired to avoid production of excess ash, the amount of
calcium delivered by
way of the sorbent can be limited to, say, a maximum molar ratio of 3:1, again
measured against
sulfur in the coal.
[0075] In some
embodiments, the amount of mercury released is also mitigated,
lowered, or eliminated by use of such sorbents even without additional
halogen. It is believed
that the sorbents are effective at removing oxidized mercury in systems where
the flame
temperature is as low as 1000 F. However, in some embodiments, including some
in which the
flame temperature is considerably higher than 1000 F, methods of the present
teachings can =
include treating the coal with sorbent compositions that contain a halogen
compound. The use of
the halogen compound along with the alkaline powder sorbent tends to reduce
the amount of
unoxidized mercury in the gases of combustion.
[0076] Sorbent
compositions comprising a halogen compound contain one or more
18
CA 02952392 2016-12-21
organic or inorganic compounds that contain a halogen. Halogens include
chlorine, bromine, and
iodine. Preferred halogens are bromine and iodine. The halogen compounds are
sources of the
halogens, especially of bromine and iodine. For bromine, sources of the
halogen include various
inorganic salts of bromine including bromides, bromates, and hypobromites. In
some
embodiments, organic bromine compounds are less preferred because of their
cost or availability.
However, organic sources of bromine containing a suitably high level of
bromine are considered
within the scope of the present teachings. Non-limiting examples of organic
bromine compounds
include methylene bromide, ethyl bromide, bromoforrn, and carbonate
tetrabromide. = Non-
limiting inorganic sources of iodine include hypoiodites, iodates, and
iodides, with iodides being
preferred. Organic iodine compounds can also be used.
[0077] When the
halogen compound is an inorganic substituent, it is preferably a
bromine or iodine containing salt of an alkaline earth element. Exemplary
alkaline earth
elements include beryllium, magnesium, and calcium. Of halogen compounds,
particularly
preferred are bromides and iodides of alkaline earth metals such as calcium.
Alkali metal
bromine and iodine compounds such as bromides and iodides are effective in
reducing mercury
emissions. But in some embodiments, they are less preferred as they tend to
cause corrosion on
the boiler tubes and other steel surfaces. In some embodiments, the sorbents
added into the coal
burning system contain essentially no sodium salts of either bromine or iodine
compounds.
[0078] In some
embodiments, sorbent compositions containing halogen are
provided in the form of a liquid or of a solid composition. In some
embodiments, the halogen-
containing composition is applied to the coal before combustion, is added to
the furnace during
combustion, and/or is applied into flue gases downstream of the furnace. When
the halogen
composition is a solid, it can further contain the calcium, silica, and
alumina components
described herein as the powder sorbent. Alternatively, a solid halogen
composition is applied
onto the coal and/or into the combustion system separately from the sorbent
components
comprising calcium, silica, and alumina. When it is a liquid composition it is
generally applied
separately.
[0079] In some
embodiments, liquid mercury sorbent comprises a solution
containing 5 to 60% by weight of a soluble bromine or iodine containing salt.
Non-limiting
examples of preferred bromine and iodine salts include calcium bromide and
calcium iodide. In
some embodiments, liquid sorbents contain 5-60% by weight of calcium bromide
and/or calcium
iodide. For efficiency of addition to the coal prior to combustion, in some
embodiments, it is
preferred to add mercury sorbents having as high level of bromine or iodine
compound as is
feasible. In some embodiments, the liquid sorbent contains 50% or more by
weight of the
halogen compound, such as calcium bromide or calcium iodide.
[0080] To further
illustrate, some embodiments of the present teachings involve the
19
CA 02952392 2016-12-21
addition of liquid mercury sorbent directly to raw or crushed coal prior to
combustion. For
example, mercury sorbent is added to the coal in the coal feeders. Addition of
liquid mercury
sorbent ranges from 0.01 to 5%. Higher treatment levels are possible, but tend
to waste material,
as no further benefit is achieved. Preferred treatment levels are from 0.025
to 2.5% by weight on
a wet basis. The amount of solid bromide or iodide salt added by way of the
liquid sorbent is of
course reduced by its weight fraction in the sorbent. In some embodiments,
addition of bromide
or iodide compound is at a low level such as from 0.01 % to 1% by weight based
on the solid.
When a 50% by weight solution is used, the sorbent is then added at a rate of
0.02% to 2% to
achieve the low levels of addition. For example, in some embodiments, the coal
is treated by a
= 10 liquid sorbent at a rate of 0.02 to 1%, preferably 0.02 to 0.5
% calculated assuming the calcium
bromide is about 50% by weight of the sorbent. In some embodiments,
approximately 1%, 0.5%,
or 0.25% of liquid sorbent containing 50% calcium bromide is added onto the
coal prior to
combustion, the percentage being based on the weight of the coal. In some
embodiments, initial
treatment is started at low levels (such as 0.01% to 0.1%) and is
incrementally increased until a
desired (low) level of mercury emissions is achieved, based on monitoring of
emissions. Similar
treatment levels of halogen are used when the halogen is added as a solid or
in multi-component
compositions with other components such as calcium, silica, alumina, iron
oxide, and so on.
[0081] When
used, liquid sorbent is sprayed, dripped, or otherwise delivered onto
the coal. In some embodiments, addition is made to the coal or other fuel at
ambient conditions
prior to entry of the fuel/sorbent composition into the furnace. For example,
sorbent is added
onto powdered coal prior to its injection into the furnace. Alternatively or
in addition, liquid
sorbent is added into the furnace during combustion and/or into the flue gases
downstream of the
furnace. Addition of the halogen containing mercury sorbent composition is
often accompanied
by a drop in the mercury levels measured in the flue gases within a minute or
a few minutes; in
some embodiments, the reduction of mercury is in addition to a reduction
achieved by use of an
alkaline powder sorbent based on calcian, silica, and alumina.
[0082] In some
embodiments, the present teachings involve the addition of a
halogen component (illustratively a calcium bromide solution) directly to the
furnace during
combustion. In some embodiments, the present teachings provides for an
addition of a calcium
bromide solution such as discussed above, into the gaseous stream downstream
of the furnace in
a zone characterized by a temperature in the range of 2700 F to 1500 F,
preferably 2200 F to
1500 F. In various embodiments, treat levels of bromine compounds, such as
calcium bromide
are divided between co-, pre- and post-combustion addition in any proportion.
[0083] In some
embodiments, various sorbent components are added onto coal prior
to its combustion. The coal can be particulate coal, and is optionally
pulverized or powdered
according to conventional procedures. In a non-limiting example, the coal is
pulverized so that
CA 02952392 2016-12-21
75% by weight of the particles passes through a 200 mesh screen (a 200 mesh
screen has hole
diameters of 75 Am). In some embodiments, the sorbent components are added
onto the coal as a
solid or as a combination of a liquid and a solid. Generally, solid sorbent
compositions are in the
form of a powder. If a sorbent is added as a liquid (usually as a solution of
one or more bromine
or iodine salts in water), in some embodiments, the coal remains wet when fed
into the burner.
In some embodiments, a sorbent composition is added onto the coal continuously
at the coal
burning facility by spraying or mixing onto the coal while it is on a
conveyor, screw extruder, or
other feeding apparatus. In addition or alternatively, a sorbent composition
is separately mixed
with the coal at the coal burning facility or at the coal producer. In some
embodiments, the
sorbent composition is added as a liquid or a powder to the coal as it is
being fed into the burner.
For example, in some embodiments, the sorbent is applied into the pulverizers
that pulverize the
coal prior to injection. If desired, the rate of addition of the sorbent
composition is varied to
achieve a desired level of mercury emissions. In some embodiments, the level
of mercury in the
flue gases is monitored and the level of sorbent addition adjusted up or down
as required to
maintain the desired mercury level.
[0084] In some embodiments, levels of mercury and/or sulfur emitted
from the
facility are monitored with conventional analytical equipment using industry
standard detection
and determination methods. In some embodiments, monitoring is conducted
periodically, either
manually or automatically. In a non-limiting example, mercury emissions are
monitored once an
hour to ensure compliance with government regulations. To illustrate, the
Ontario Hydro method
is used. In this known method, gases are collected for a pre-determined time,
for example one
hour. Mercury is precipitated from the collected gases, and the level of
elemental and/or
oxidized mercury is quantitated using a suitable method such as atomic
absorption. Monitoring
can also take more or less frequently than once an hour, depending on
technical and commercial
feasibility. Commercial continuous mercury monitors can be set to measure
mercury and
produce a number at a suitable frequency, for example once every 3 to 7
minutes. In some
embodiments, the output of the mercury monitors is used to control the rate of
addition of
mercury sorbent. Depending on the results of monitoring, the rate of addition
of the mercury
sorbent is adjusted by either increasing the level of addition; decreasing it;
or leaving it
unchanged. To illustrate, if monitoring indicates mercury levels are higher
than desired, the rate
of addition of sorbent is increased until mercury levels return to a desired
level. If mercury
levels are at desired levels, the rate of sorbent addition can remain
unchanged. Alternatively, the
rate of sorbent addition can be lowered until monitoring indicates it should
be increased to avoid
high mercury levels. In this way, mercury emission reduction is achieved and
excessive use of
sorbent (with concomitant increase of ash) is avoided.
[0085] Mercury is monitored in the convective pathway at suitable
locations. In
some embodiments, mercury released into the atmosphere is monitored and
measured on the
21
CA 02952392 2016-12-21
clean side of the particulate control system. Mercury can also be monitored at
a point in the
convective pathway upstream of the particulate control system. Experiments
show that as much
as 20 to 30% of the mercury in coal is captured in the ash and not released
into the atmosphere
when no mercury sorbent is added. In some embodiments, addition of mercury
sorbents
described herein raises the amount of mercury capture to 90% or more. Mercury
emissions into
the atmosphere are correspondingly reduced.
[0086] In some
embodiments, sorbent components or a sorbent composition is
added more or less continuously to the coal before combustion, to the furnace
during
combustion, and/or to the convective pathway in the 1500 F to 2700 F zone as
described above.
In some embodiments, automatic feedback loops are provided between the mercury
monitoring
apparatus and the sorbent feed apparatus. This allows for a constant
monitoring of emitted
mercury and adjustment of sorbent addition rates to control the process.
[0087] In some
embodiments, mercury and sulfur are monitored using industry
standard methods such as those published by the American Society for Testing
and Materials
(ASTM) or international standards published by the International Standards
Organization (ISO).
An apparatus comprising an analytical instrument is preferably disposed in the
convective
pathway downstream of the addition points of the mercury and sulfur sorbents.
In some
embodiments, a mercury monitor is disposed on the clean side of the
particulate control system.
Alternatively or in addition, the flue gases are sampled at appropriate
locations in the convective
pathway without the need to install an instrument or monitoring device. In
various embodiments,
a measured level of mercury or sulfur is used to provide feedback signals to
pumps, solenoids,
sprayers, and other devices that are actuated or controlled to adjust the rate
of addition of a
sorbent composition into the coal burning system. Alternatively or in
addition, the rate of
sorbent addition can be adjusted by a human operator based on the observed
levels of mercury
and/or sulfur.
[0088] The ash
produced by burning coal in the presence of the sorbents described
herein is cementitious in that it sets and develops strength when combine with
water. The ash
tends to be self-setting due its relatively high level of calcium. The ash
serves alone or in
combination with Portland cement as a hydraulic cement suitable for
formulation into a variety
of cementitious mixtures such as mortars, concretes, and grouts.
[0089] The
cementitious nature of ash produced as described herein is demonstrated
for example by consideration of the strength activity index of the ash, or
more exactly, of a
cementitious mixture containing the ash. As described in ASTM C311-05,
measurement of the
strength activity index is made by comparing the cure behavior and property
development of a
100% Portland cement concrete and a test concrete wherein 20% of the Portland
cement is
replaced with an equal weight of a test cement. In the standard test, strength
is compared at 7
22
CA 02952392 2016-12-21
days and at 28 days. A "pass" is considered to be when the strength of the
test concrete is 75%
of the strength of the Portland cement concrete or greater. In some
embodiments, ashes of the
present teachings exhibit of strength activity of 100% to 150% in the ASTM
test, indicating a
strong "pass." Similar high values are observed when tests are run on test
mixtures with other
than an 80:20 blend of Portland cement to ash. In some embodiments, a strength
activity index
of 100% to 150% is achieved with blends of 85:15 to 50:50, where the first
number of the ratio is
Portland cement and the second number of the ratio is ash prepared according
to the present
teachings. In particular embodiments, the strength development of an all-ash
test cementitious
mixture (i.e., one where ash represents 100% of the cement in the test
mixture) is greater than
50% that of the all-Portland cement control, and is preferably greater than
75%, and more
preferably 100% or more, for example 100 ¨ 150%. Such results demonstrate the
highly
cementitious nature of ash produced by burning coal or other fuel in the
presence of the sorbent
components described herein.
[0090] Because
the ash resulting from combustion of coal according to the present
teachings contains mercury in a non-leaching form, it is available to be sold
into commerce.
Nan-limiting uses of spent or waste fly ash or bottom ash include as a
component in a cement
product such as Portland cement. In some embodiments, cement products contain
from about
0.1% up to about 99% by weight of the coal ash produced by burning
compositions according to
the present teachings. In some embodiments; the non-leaching property of the
mercury and other
heavy metals in the coal ash makes it suitable for all known industrial uses
of coal ash.
[0091] The
hydraulic cement product containing ash according to the present
teachings is combined in some embodiments with aggregates to form a ready mix
compound.
The ready mix compound is sold to consumers or provided to contractors, who
mix the ready mix
with water and form a variety of concrete products such as sidewalks, curbs,
streets, pillars,
culverts, pipes, and the like. The set concrete constructions are the product
of hydration of ready
mixes that contain coal ash according to the present teachings.
[0092] In some
embodiments, the present teachings provides a hydratable or
settable concrete composition made by adding water to any of the cement
products or concrete
products noted above.
[0093] Coal ash according
to the present teachings is used in Portland cement
concrete (FCC) as a partial or complete replacement for Portland cement. In
some embodiments,
the ash is used as a mineral admixture or as a component of blended cement. As
an admixture,
the ash can be total or partial replacement for Portland cement and can be
added directly into
ready mix concrete at the batch plant. Alternatively, or in addition, the ash
is inter-ground with
cement clinker or blended with Portland cement to produce blended cements.
[0094] Class F
and Class C fly ashes are defined for example in U.S. Standard
23
CA 02952392 2016-12-21
ASTM C 618. The ASTM Standard serves as a specification for fly ash when it is
used in partial
substitution for Portland cement. It is to he noted that coal ash produced by
the methods
described herein tends to be higher in calcium and lower in silica and alumina
than called for in
the specifications for Class F and Class C fly ash in ASTM C 618. However, it
is observed that
fly ash according to the present teachings is highly cementitious, allowing
for substitutions or
cutting of the Portland cement used in such cementitious materials and
cementitious materials by
50% or more. In some applications, the coal ash resulting from burning coal
with sorbents
described herein is sufficiently cementitious to be a complete (100%)
replacement for Portland
cement in such compositions.
[0095] To further
illustrate, the American Concrete Institute (ACT) recommends that
Class F fly ash replace from 15 to 25% of Portland cement and Class C fly ash
replace from 20 to
35%. It has been found that coal ash produced according to the methods
described herein is
sufficiently cementitious to replace up to 50% of the Portland cement, while
maintaining 28 day
strength development equivalent to that developed in a product using 100%
Portland cement.
That is, although in some embodiments, the ash does not qualify as Class C or
Class F ash
according to ASTM C 618, it nevertheless is useful to formulate high strength
concrete products.
[0096] Coal ash
made according to the present teachings can also be used as a
component in the production of flowable fill, which is also called controlled
low strength
material or CLSM. ' CLSM is used as self leveling, self compacting back fill
material in place of
compacted earth or other fill. The ash described herein is used in some
embodiments as a 100%
replacement for Portland cement in such CLSM materials. Such compositions are
formulated
with water, cement, and aggregate to provide a desired flowability and
development of ultimate
strength. For example, the ultimate strength of flowable fill should not
exceed 1035 kPa (150
pounds per square inch) if removability of the set material is required. If
formulated to achieve
higher ultimate strength, jack hammers may be required for removal. However,
when it is
desired to formulate flowable fill mixes to be used in higher load bearing
applications, mixtures
containing a greater range of compressive strength upon cure can be designed.
[0097] Coal ash
produced according to the methods described herein is also usable
as a component of stabilized base and sub base mixtures. Since the 1950's
numerous variations ,
of the basic lime/fly ash/aggregate formulations have been used as stabilized
base mixtures. An
example of the use of stabilized base is used as a stabilized road base. To
illustrate, gravel roads
can be recycled in place of using ash according to the composition. An
existing road surface is
pulverized and re-deposited in its original location. Ash such as produced by
the methods
described herein is spread over the pulverized road material and mixed in.
Following
compaction, a seal coat surface is placed on the roadway. Ash according to the
present teachings
is useful in such applications because it contains no heavy metals that leach
above regulatory
24
CA 02952392 2016-12-21
requirements. Rather, the ash produced by methods of the present teachings
contains less
leachable mercury and less leachable other heavy metals (such as arsenic and
lead) than does
coal ash produced by burning coal without the sorbents described herein.
[0098] Thus, the
present teachings provides various methods of eliminating the
need to landfill coal ash or fly ash resulting from combustion of coal that
contains high levels of
mercury. Instead of a costly disposal, the material can be sold or otherwise
used as a raw
material.
[0099] In some
embodiments, use of the sorbents results in a cementitious ash that
can replace Portland cement in whole or in part in a variety of applications.
Because of the re-
use of the cementitious product, at least some Portland cement manufacture is
avoided, saving
the energy required to make the cement, and avoiding the release of
significant amounts of
carbon dioxide which would have arisen from the cement manufacture. Other
savings in carbon
dioxide emissions results from the reduced need for lime or calcium carbonate
in desulfurization
scrubbers. The present teachings thus provide, in some embodiments methods for
saving energy
and reducing green house emissions such as carbon dioxide. Further detail of
some embodiments
of this aspect of the present teachings are given below.
[00100] Portland cement is manufactured in a wet or a dry process kiln. While
the
wet and dry processes differ, both processes heat the raw material in stages.
Cement
manufacturing raw materials comprise sources of calcium, silica, iron, and
alumina, and usually
include limestone, as well as a variety of other materials, such as clay,
sand, and/or shale, for
example. The first stage is a pre-heating stage that drives off any moisture
from the raw
materials, removes water of hydration, and raises the material temperature up
to approximately
1500 F. The second stage is the calcination stage which generally occurs
between about 1500 F
and 2000 F, where the limestone (CaCO3) is converted to lime (CaO) by driving
off carbon
dioxide (CO2) in a calcination reaction. The raw materials are then heated to
a maximum
temperature of between about 2500 F to 3000 F in the burning zone, where they
substantially
melt and flux, thus forming inorganic compounds, such as tricalcium silicate,
dicalcium silicate,
tricalcium aluminate, and tetracalcium aluminoferrite. A typical analysis of
Portland cement
products shows that they contain approximately 65-70% CaO, 20% SiO2, 5% Al2O3,
4% Fe2O3,
with lesser amounts of other compounds, such as oxides of magnesium, sulfur,
potassium,
sodium, and the like. The molten raw material is cooled to solidify into an
intermediate product
in small lumps, known as "clinker" that is subsequently removed from the kiln.
Clinker is then
finely ground and mixed with other additives (such as a set-retardant, gypsum)
to form Portland
cement. Portland cement can then be mixed with aggregates and water to form
concrete.
[00101] Cement production is an energy sensitive process in which a
combination of
raw materials is chemically altered through intense heat to form a compound of
binding
properties. Cement manufacturing is the largest non-energy industrial source
of carbon dioxide
emissions. The emissions result from heating limestone, which constitutes
approximately 80%
of the feed to cement kilns. During cement production, high temperatures are
used to transform
the limestone into lime, releasing carbon dioxide into the atmosphere. In this
process, one
molecule of calcium carbonate is decomposed into one molecule of carbon
dioxide gas and one
molecule of calcium oxide.
[00102] The cement manufacturer utilizes nearly 100% of the calcium oxide
obtained
from calcinated calcium carbonate. Thus, the amount of calcium oxide in the
cement clinker is a
good measure of the carbon dioxide produced during production. In an example,
to estimate
carbon dioxide emission from cement production, an emission factor is derived
by multiplying
the fraction of lime in the cement clinker by a constant that reflects the
mass of carbon released
per unit of lime. In one example, assuming an average lime content of 64.6%
based on
recommendations of the International Panel for Climate Control, an emissions
factor of 0.138
tons of carbon per ton of clinker produced is obtained. Additional carbon
dioxide may be
released as a result of adding extra lime to make masonry cement, a more
plastic cement that
typically is used in mortar,
[00103] In cement making, carbon dioxide emissions result from energy use and
from decomposition of calcium carbonate during clinker production. Depending
on the fuel
source that provides the energy, carbon dioxide emissions may vary. For
example, the use of a
cleaner burning fuel, such as natural gas, produces less carbon dioxide
emissions than the use of
a fuel such as coal. In some embodiments, the present teachings described
above may be used in
the production of cement. In some embodiments, the use of the present
teachings in the
production of cement will reduce carbon dioxide
emissions.
[00104] In some
embodiments, the present teachings described herein, may be used
in the production of cement to produce carbon dioxide emission credits by
lowering carbon
dioxide emission in the production of cement. In some embodiments, a point
source for air
emissions, such as a cement plant or a coal-fired power plant, is brought Into
compliance with the
Kyoto protocol.
[00105] Under
the Kyoto protocol, industrialized countries are required to reduce
emissions of six greenhouse gases, including carbon dioxide, on an average by
5.2% below the
1990 levels during the first commitment period from 2008 ¨ 2012. The Kyoto
Protocol is an
attempt to halt the global increase in greenhouse gas emissions in an effort
to slow the rate of
global warming. The Kyoto Protocol sets legally binding limits on greenhouse
gas emissions in
industrial countries and envisions innovative market-based implementation
mechanisms aimed at
keeping the cost of carbon emissions low. The Kyoto Protocol envisions three
innovative
market-based flexible mechanisms; coal emissions trading, dry chemical
implementation, and
26
CA 2952392 2019-12-23
the clean development mechanism. These are to allow industrialized countries
to meet their
targets through trading emission allowances among themselves and gaining
credits for
emission-curbing projects.
[00106] An example of emission trading, the European Union is implementing its
own internal emissions trading system. The directive was approved by the
European Parliament
on June 2, 2003 and the Council on July 22, 2003. The European Union model
will be the first
multi-national emissions trading scheme in the world and may be considered an
example of the
international emissions trading under the Kyoto Protocol. Under the European
emissions trading
scheme, the European Union members states will set limits on carbon dioxide
emissions from
energy-intensive companies including steel factories, power plants, oil
refineries, paper mills,
and glass and cement manufacturing by issuing allowances as to how much carbon
dioxide these
companies are allowed to emit. Reduction below these allowable limits will be
tradable.
Companies that achieve reductions can sell them to companies that have
problems staying within
their limits for emission reduction measures that are expensive in comparison
to what a tradable
credit would cost. Any company may also increase its emissions above the limit
or allowance
that has been issued prior to acquiring more credits from the market.
[00107] The
cost of the CO2 credits is typically measured in a per ton basis; the
actual cost varies based on market conditions and geographical locations. In
some embodiments,
the present teachings as described herein produces carbon dioxide credits to a
point source that is
a cement production facility. Under an emissions trading scheme as described
above, the scheme
will induce companies to make emissions cuts where they are the cheapest,
thereby insuring that
reductions are made at the lowest possible cost to the economy and that
innovation is fostered.
Such innovation includes the present teachings as described here.
[00108] Energy
efficient seed projects in the industrial sector provide a source of
reducing the greenhouse gas emissions such as CO2 under a Clean Development
Mechanism
(CDM) scheme which is laid out under Article 12 of the Kyoto Protocol. The CDM
offers a
mechanism for developed countries to meet greenhouse gas reduction
requirements by getting
offsets from projects they fund in developing countries. To receive these
offsets known as
carbon emission reduction units, the project should demonstrate real
measurable and long-term
benefits and reductions should be additional to any of those that would occur
in the absence of
the project.
[00109] In some
embodiments, use of sorbents as described herein reduces carbon
dioxide emissions and can be used in a CDM with the receipt of carbon emission
reduction units.
In the development of the CDM, a benchmarking process may be used so that a
determination of
the amount of carbon emission reduction units that will be granted can be
measured. An example
of such benchmarking implementation is described in Ruth et al. (2000)
"Evaluating clean
27
CA 2952392 2019-12-23
development mechanism projects in the cement industry using a process step
benchmarking
approach" the U.S. Department of Energy, Lawrence Berkley National Laboratory.
[00110] To establish a CDM evaluation tool for cement
production that addresses
clinker production, raw materials and cement grinding, it may be necessary to
establish
benchmark performance values for each of the three stages. Then a project can
be compared
against the benchmark to determine the projected level of carbon dioxide
reduction the project
will accomplish.
[00111] The formula for calculating carbon emission reductions
at a cement plant is
given below. This formula takes into account only energy use at the three key
process stages:
raw material preparation, clinker production, and cement grinding. A benchmark
value is used at
each stage to measure the carbon emissions avoided.
=
C(t) = Emfq./. = (b, = X ,(t)¨ K(r))+q,=[(b, = X (t)¨ M (t))+ 0, =
X,(t)¨G(t))]
clinker producrion pew marrieds cement grinding
(1)
C(t) ¨ carbon dioxide emission reduction at the plant in year t (tonnes CO2)
Carbon contents:
mf = percentage of fuel! in total primary fuel use for year t (%)
qf = carbon content of fuel f (tonnes CO2/0.T)
q. = carbon content of electricity (tonnes CO2/kWh)
Outputs:
Xat) = output of raw material at the plant in year t (tonnes)
XK(t) = output of clinker at the plant in year t (tonnes)
X0(t) = output of ground cement at the plant in year t (tonnes)
Energy Use:
M(t) = total plant electricity use for raw materials preparation in year t
(kWh)
K(t)= total plant energy use for clinker production in year t (GJ)
G(t) - total plant electricity use for cement grinding in year t (kWh)
Benchmarks:
bm= energy benchmark for raw meal production (kWh/tonne raw meal)
bK= energy benchmark for clinker production (GJ/tonne clinker)
b0 r-= energy benchmark for cement production (kWh/tonne cement)
28
CA 2952392 2019-12-23
[00112] In the
cement production process, carbon dioxide emissions can be granted
as energy-related, referring to emissions that result from the combustion of
fossil fuel, and
process-related, referring to the emissions from the decomposition of calcium
carbonate.
Process-related emissions are not accounted for in equation (1) above because
they are not a
matter of efficiency or performance, instead they are related to the total
amount of clinker
produced and not to the technology used. These emissions can be reduced on a
per ton of
cement-basis by decreasing the amount of clinker per ton of cement (clinker-to-
cement ratio).
-The calculation above is neutral to the clinker-to-cement ratio.
[00113] In the
finished grinding stages of cement production, the clinker is mixed
with additives and ground to a fine powder. These additives affect the
strength, curing time, and
other characteristics of the final concrete product. The most commonly used
cement type in the
U.S., Portland cement, has a clinker-to-cement ratio of about 95%. By
increasing the amount of
additives in the mix, which results in lowering the clinker-to-cement ratio,
less clinker is needed
so energy use in clinker production decreases per ton of cement even though
the efficiency of the
process may not have been improved. At the same time, lower clinker production
means that
less carbon dioxide is emitted from dissociating calcium carbonate during the
calcination phase
of clinker production. The cements with lower clinker-to-cement ratios are
typically known as
blended cements. Increasing the fraction of additives with respect to Portland
cement may lead
to longer curing times, but may lead to ultimately greater strength in the
final product. The use
of blended cements reduces energy consumption, as well as offers an
opportunity for improved
industrial ecology since the additives can come from waste such as fly ash. In
some
embodiments, the present teachings may be used in the production of blended
cements. In some
embodiments, the use of the present teachings in blended cements reduces the
amount of carbon
emissions from the cement-manufacturing site. In some embodiments, the use of
the present
teachings allows the cement manufacturing site to market carbon dioxide
emission credits.
[00114] The formula for evaluating carbon reductions given in equation (1) is
neutral
to the clinker-to-cement ratio. If projects that involve the production of
blended cements are to
be considered for CDM credits, then a value needs to be introduced to equation
(1) that links
clinker production and cement production. This may be done by introducing
another benchmark
value such as a benchmark clinker-to-cement ratio. For example, if the clinker-
to-cement ratio
benchmark is 0.9, then for every I ton of cement produced, 0.9 tons of clinker
will be produced
and by avoiding the production of 0.1 ton of clinker, the plant saves energy
and also eliminates
emissions from calcinations.
[00115] A link
can also be made with the raw materials preparation stage, if desired,
29
CA 2952392 2019-12-23
by introducing a benchmark raw material-to-clinker ratio. Adding these
benchmarks changes the
Equation (1) in the following way:
dx= benchmark clinker-to-cement ratio (ton clinker/ton cement)
dm= benchmark raw material-to-clinker ratio (tons raw material/ton clinker)
then new benchmark values can be calculated on a per ton of cement basis:
=d, =b, = energy benchmark for clinker production, cement basis (GJ/tons
cement)
to. = d, = dõ =b,õ =energy benchmark for raw material production, cement basis
(kWh/ton
cement)
Since the clinker share per ton of cement changes, there are reduced emissions
from the
calcinations process that must be accounted for. The carbon emissions evolved
from this process
are a fixed stoichiometric value:
qc= carbon emissions from the calcination process (tonnes CO2/ton clinker)
so equation (1) becomes:
C(t)=q1 (4-X ,(t)¨K(t)+q,-[(bõ' -X 6(0¨M (0)+(b,* -X ,(0¨G(0)]+q,..(d ,=X
0(t)¨X 0(t)¨X (t
clinker production raw materials finish grinding
calcination
[00116] There are three important differences between the two
equations: (1) the
addition of the calcination term in the second equation, (2) the modification
of benchmark values
to all be on a "per ton of cement basis," and (3) the second equation only
uses the output of
cement (XG), not that of raw materials and clinker. This example suggests that
blending cement
may lead to significant carbon emissions reductions. The savings may be much
larger than those
the energy efficiency projects may attain. Even lowering the clinker-to-cement
ratio to 0.95 to
0.90 leads to greater reduction in carbon dioxide emissions. In the equations
used above for
carbon reduction, the benchmark is given in terms of energy of carbon used. If
coal was chosen
as the benchmark for fuel, then the benchmark for kiln could be expressed in
carbon rather than
energy terms by multiplying energy benchmark by the carbon content of the
coal. Coal is the
typical fuel for cement plants worldwide. Using coal as the fuel in cement
plants may include
the use of the present teachings as described herein such that emissions from
sulfur and mercury
CA 2952392 2019-12-23
are reduced. In some embodiments, the use of the sorbent described herein on
coal that is then
used in the production of energy, cement, or other industrial processes
decreases sulfur emissions
and by decreasing sulfur emissions decreases CO2 emissions. In many industrial
point sources,
flue gas desulfurization, also known as scrubbers, are typically used on point
source emissions to
reduce sulfur.
[00117] As used
herein a scrubber can be any system that is an air pollution control
device that can be used to remove particulates and/or gases from industrial
exhaust streams, such
as for example a stack. Traditionally scrubbers have been referred to devices
that used liquid to
scrub unwanted pollutants from a gas stream. More recently, the term scrubber
can be used to
describe systems that inject a dry reagent or slurry into an exhaust stream to
scrub out acid gases.
A scrubber can be a flue gas desulfurization device.
[00118] The wet
lime/limestone scrubber is the most widely used flue gas
desulphurization system. In such
system, the flue gas passes through the flue gas
desulphurization absorber, where sulfur dioxide is removed by direct contact
with any aqueous
suspension of finely ground limestone before it is released in the atmosphere
from the point
source or a cooling tower. The byproducts of this reaction include calcium
sulfate, carbon
dioxide, and oxygen. The resulting carbon dioxide is emitted from the point
source.
[00119] In
addition, carbon dioxide is emitted in the production of the limestone that
is used in the flue gas desulfurization systems. By using this sorbent as
described herein, the
need for a flue gas desulphurization system is decreased or eliminated. . A
decrease in, or the
elimination of, flue gas desulfurization system in a power plant or industrial
site employing the
sorbent used with coal as described herein may be eligible for carbon dioxide
emissions credits
by eliminating CO2 emissions from the flue gas desulfurization system and may
be eligible for
additional carbon dioxide emissions credit from the elimination of the
additional production of
limestone to be used in the flue gas desulphurization. In a non-limiting
example, the chemical
reaction of the calcium carbonate in the limestone with the sulfur dioxide
produces calcium
sulfate, and carbon dioxide. See the following equation:
CaCO3 + SO2 CaS03 + CO240
The elimination of a mole sulfur dioxide using this reaction creates a mole of
carbon dioxide that
is emitted into the atmosphere. For every metric ton of sulfur dioxide that is
removed using this
reaction, 0.69 metric tones of carbon dioxide is emitted into the atmosphere.
[00120] In some
embodiments, methods of the present teachings involve a business
analysis for assessing the value of various proposed control systems,
including the use of
sorbents to control emissions from coal burning facilities. Following the
assessment, business
decisions are made based on the result of the analysis.
[00121] In some
embodiments, a business analysis may include an estimating
31
CA 2952392 2019-12-23
procedure that can consist of five steps: (1) obtaining the facility
parameters and regulatory options
for a given facility; (2) roughing out the control system design; (3) sizing
the control system
components; (4) estimating the costs of these individual components; and (5)
estimating the costs
(capital and annual) of the entire system.
[00122] Regulatory options are usually specified by others (generally a
regulatory authority)
and are often technology driven, typically defining allowable ways to achieve
a predetermined
emission limit. These options range from "no control' to a requirement for the
system to reach the
maximum control technically achievable. The options allowed will depend,
firstly, on whether the
emission source is a point source such as a stack or other identifiable
primary source of pollution.
Stacks are normally controlled by "add-on" devices. Probably the most
subjective part of a cost
estimate occurs when the control system is to be installed on an existing
facility. Unless the original
designers had the foresight to include additional floor space and room between
components for new
equipment, the installation of retrofitted pollution control devices can
impose an additional expense
to "shoe-horn" the equipment into the right locations.
[00123] In some embodiments, total capital investment ('[CI) includes all
costs required to
purchase equipment needed for the control system (purchased equipment costs),
the costs of labor and
materials for installing that equipment (direct installation costs), costs for
site preparation and
buildings, and certain other costs (indirect installation costs). In some
embodiments, TCI also includes
costs for land, working capital, and off-site facilities.
[00124] In some embodiments, direct installation costs include costs for
foundations and
supports, erecting and handling the equipment, electrical work, piping,
insulation, and painting.
Indirect installation costs include such costs as engineering costs;
construction and field expenses (i.e.,
costs for construction supervisory personnel, office personnel, rental of
temporary offices, etc.):
contractor fees (for construction and engineering firms involved in the
project); start-up and
performance test costs (to get the control system running and to verify that
it meets performance
guarantees); and contingencies. Contingencies is a catch-all category that
covers unforeseen costs that
may arise, such as possible redesign and modification of equipment, escalation
increases in cost of
equipment, increases in field labor costs, and delays encountered in start-up.
Contingencies are not the
same thing as uncertainty and retrofit factor costs.
[00125] In a non-limiting
example, the elements of total capital investment 100 are displayed
in Figure 1. The total capital cost 100 can be divided into two types of
investments, Total Depreciable
Investment 101 or Total Non-Depreciable Investment 102. The Total Non-
Depreciable Investment
102 would include costs for land 105. Note that the sum of the purchased
equipment cost 108, direct
installation costs 109, site preparation 110, buildings costs 111, and
indirect installation costs 112,
comprises the "battery limits" cost 103. Specifically, the total direct costs
106 of the "battery limits"
cost could include costs for the primary control device 113, auxiliary
equipment (including duct work)
114, instrumentation 115. sales tax 116, freight 117, foundations and supports
118, handling and
32
CA 2952392 2019-12-23
erection 1 19, electrical 120, piping 121, insulation 122 and painting 123.
The total indirect costs 107
of the ''battery limits" cost could include costs for engineering 124,
construction and field expenses
125, contractor fees 126, start-up 127, performance test 128 and contingencies
129. The indirect
installation cost 112 is typically factored from the sum of the primary
control device 113 and auxiliary
equipment costs 114. The direct installation 109 costs is typically factored
from the purchases of
equipment costs 108. The site preparation cost is usually required only at
"grass roots" or "greenfield"
installations. Unlike the other direct 106 and indirect costs 107. costs for
the buildings 111 are not
factored from the purchased equipment cost 108. Rather. they are sized and
costed separately. The
cost for land 105 is normally not required with add-on control systems. This
would mainly apply to
control systems installed in existing plants, though it could also apply to
those systems installed in
new plants when no special facilities for supporting the control system (i.e.,
off-site facilities 104)
would be required. Off-site facilities 104 include units to produce steam,
electricity, and treated water;
laboratory buildings; and railroad spurs, roads, and other transportation
infrastructure items. Pollution
control systems do not generally have off-site capital units dedicated to them
since pollution control
devices rarely consume energy at that level. However, it may be necessary -
especially in the case of
control systems installed in new plants - for extra capacity to be built into
the site generating plant to
service the system. Note, however, that the capital cost of a device does not
include utility costs, even
if the device were to require an off-site facility. Utility costs are charged
to the project as operating
costs at a rate which covers both the investment and operating and maintenance
costs for the utility.
Operating costs are discussed in greater detail below.
[00126]
Routine operation of the control does not begin until the system has been
tested, balanced, and adjusted to work within its design parameters. Until
then, all utilities consumed,
all labor expended, and all maintenance and repairs performed are a part of
the construction phase of
the project and are included in the TC1 in the "Start-Up" component of the
Indirect Installation Costs.
[00127] In some
embodiments, total Annual Cost (TAC) 200 has three elements:
direct costs (DC) 201, indirect costs (IC) 202, and recovery credits (RC) 203,
which are related by the
following equation:
TAC = DC + IC - RC
Clearly, the basis of these costs is one year, as this period allows for
seasonal variations in production
(and emissions generation) and is directly usable in financial analyses. In a
non-limiting example, the
various annual costs and their interrelationships are displayed in Figure 2.
In some embodiments,
direct costs are those that tend to be directly proportional (variable costs)
204 or partially proportional
(semi-variable costs) 205 to some measure of productivity - generally the
company's productive output
but, in some embodiments, the proper metric may be the quantity of exhaust gas
processed by the
control system per unit time. Variable costs 204 include raw materials 206.
utilities 207 (i.e. electricity
208, fuel 209, steam 210, water 211 and compressed air 212), and waste
treatment/disposal 213. Semi-
variable costs 205 include costs for labor 214 (i.e. operating 215,
supervisory 216 and maintenance
33
CA 2952392 2019-12-23
217), maintenance materials 218, and replacement parts 219. Indirect costs 202
include costs for
overhead 220. property taxes 221. insurance 222, administrative charges 223,
capital recovery 224,
buying emissions credits 225 and regulatory 226. Finally, direct 201 and
indirect 202 annual costs
can be offset by recovery credits 203, taken for materials 227 or energy 228
recovered by the control
system, which may be sold, recycled to the process, or reused elsewhere at the
site. An example of
such credits is the by-product of controlling sulfur with an FGD. As the lime
or limestone reagent
reacts with the sulfur in the exhaust gas stream, it becomes transformed into
CaSO4, for example,
gypsum, which can be landfilled inexpensively (a direct cost) or collected and
sold to wallboard
manufacturers (a recovery credit). These credits can be calculated as net of
any associated processing,
storage, transportation, and any other costs required to make the recovered
materials or energy
reusable or resalable. Great care and judgment should be exercised in
assigning values to recovery
credits, since materials recovered may be of small quantity or of doubtful
purity, resulting in their
having less value than virgin material. Like direct annual costs, recovery
credits are variable, in that
their magnitude is directly proportional to level of production.
[00128] In some
embodiments, when alternative investment opportunities exist or, when
more than one pollution control device may be used, the selection of the most
appropriate alternative
depends on that alternative's effect on the firm's profitability.
Consequently, financial analysts have
created a set of tools that provide insight into the potential financial
consequences associated with an
investment. While no single tool works in all instances, applying several of
these tools can provide
the financial manager with sufficient insight for a meaningful decision to be
made. Most analysts use
more than one tool to make financial decisions.
[00129] The
most fundamental analysis needed is that of cash flow, which formalizes
the expected inflows of revenue and outflows of expenses associated with an
investment alternative.
Pollution control devices do not typically generate revenues, but
environmental cost accountants still
begin their evaluation of pollution control alternatives through cash flow
analysis as a precursor to the
application of other tools. The following discusses cash flow analysis and how
it applies to pollution
control equipment. Probably the most important tool in the analyst's arsenal
is net present value (NPV)
since it acts as the foundation for a number of related analyses, including
benefits/cost analysis.
Incomes and expenditures take place over the life of an investment (its
planning horizon), the amounts
and timing of which constitute the cash flows of the project. Pollution
control system costing always
includes expenditures but may not necessarily have incomes. For a control to
be income generating, it
must reduce production cost (through fewer inputs or product reformulation),
or it must capture and
recover a pollutant with recyclable characteristics, for example, saleable
flue ash.
Pay back
34
CA 2952392 2019-12-23
[00130]
Probably the simplest form of financial analysis is the payback period
analysis, which simply takes the capital cost of the investment and compares
that value to the net
annual revenues that investment would generate. If net annual revenues are the
same every year,
the revenue can simply be divided into the total capital investment to
calculate the payback
period. If the annual net revenues differ, then the values need to be summed
sequentially until
the revenue exceeds total capital investment. The payback decision rule is to
select that
investment with the shortest payback time.
[00131] For
most pollution control devices, payback analysis may not be possible
because the device does not produce revenue. However, for a limited number of
devices the
device may produce a saleable product that produces a revenue stream. In these
cases, payback
may be a limited tool and offers only the grossest of estimates with regard to
relative
profitability, for the following reasons. First, payback ignores the magnitude
and direction of
cash flows in all of the years in the planning horizon beyond the payback
period. A project that
paid for itself in five years and produced revenues in all years after payback
would have the same
payback value as one that paid back in the same time yet incurred huge losses
in all subsequent
years. Second, payback does not take into account the time value of money.
Net Present Value
[00132] In
some embodiments, to evaluate alternative pollution control devices, the
analyst must be able to compare them in a meaningful manner. Since different
controls have
different expected useful lives and will result in different cash flows, the
first step in comparing
alternatives is to normalize their returns using the principle of the time
value of money. The
process through which future cash flows are translated into current dollars is
called present value
analysis. When the cash flows involve income and expenses, it is also commonly
referred to as
net present value analysis. In either case, the calculation is the same:
adjust the value of future
money to values based on the same (generally year zero of the project),
employing an appropriate
interest (discount) rate and then add them together. The decision rule for NPV
analysis is that
projects with negative NPVs should not be undertaken; and for projects with
positive NPVs, the
larger the net present value, the more attractive the project.
[00133] The steps for
determining .NPV are well known in the art and may include
the following:
= Identification of alternatives.
= Determination of costs and cash flows over the life of each alternative.
= Determination of an appropriate interest (discount) rate.
. For each alternative: Calculate a discounting factor for each year over the
life of
the equipment.
CA 2952392 2019-12-23
= For each year's cash flows, sum all incomes and expenses to determine the
net
cash flow for that year in nominal terms.
= Multiply each years' net cash flow by the appropriate discount factor.
= Sum the discounted net cash flows to derive the net present value.
= Compare the net present values from each alternative.
= Higher net present values indicate better investment opportunities,
relative to the
other alternatives in the decision set.
Return on Investment
[00134] Many firms make
investment decisions based upon the return on investment
(ROI) of the proposed capital purchase, rather than the magnitude of its net
present value.
However, for most pollution control investments, ROI analysis may not provide
much in the way
of useful information because, like a payback analysis, it must have positive
cash flows to work
properly. Calculated by dividing annual net income by the investment's capital
cost, results in a
percentage of the investment that is returned each year. The decision rule one
should apply for
ROI analysis is if the resulting percentage is at least as large as some
established minimum rate
of return, then the investment would be worthwhile. However, different
industries require
different rates of return on investments, and even within an industry, many
different rates can be
found. Analysts should consult with their firm's financial officers or an
industrial association to
determine what percentage would apply.
Internal Rate of Return
[00135]
Internal rate of return (IRR) is h special case of net present value analysis
used to separate "good" investment opportunities from "bad". In fact, many
trade organizations
publish standard IRR rates for their particular industry. Projects with an IRR
less than the
industry standard should be rejected as not providing sufficient income to
make them
worthwhile; and projects with IRRs greater than the industry standard should
be considered good
investment opportunities. NPV analysis is actually a series of current values,
each one associated
with a different interest rate. For each interest rate chosen, the NPV of the
same investment will
differ, increasing from a negative NPV at very low interest rates to a
positive NPV at higher
rates. For each investment analyzed, the interest rate that results in a NPV
of exactly zero is the
investment's IRR. However, the application of IRR depends on having positive
cash flows,
which may limit their use in analyzing pollution control alternatives. When
there are positive
cash flows, IRR can provide useful information.
Cost Benefit ratio
36
CA 2952392 2019-12-23
[00136] The
benefit-cost ratio of an investment is defined as the ratio of the
discounted benefits to the discounted cost, each evaluated at the same
constant dollar rate,
generally in year zero dollars. With benefits in the numerator of the ratio,
the criterion for
accepting a project on the basis of the benefit-cost ratio is whether or not
the benefit-cost ratio is
greater than or equal to one (i.e., benefits are greater than costs). However,
as with the payback
analysis and financial tools that rely on incomes, benefit cost ratios may be
limited when applied
to pollution control devices and evaluated from a strict financial standpoint.
Accounting costs and benefits
[00137] Accounting costs are
those costs included in a financial statement, ledger, or
other accounting record. They "account for" the transfer of funds between one
entity and
another. However, economic costs are a much broader cost category. While they
include
accounting costs, other typical economic costs when assessing pollution
control devices may
include external costs such as, for example, the cost incurred by others and
not part of the
accounting system of the firm. For example, a boiler may produce large
particles of unburned or
partially burned fuels such as, for example, fly ash. While the owner of the
boiler pays for the
cost of that fuel through higher fuel costs, it does not include the cost of
cleaning that soot off of
buildings and houses upwind of the plant. The owner also does not have to pay
for the asthma
medicine for affected people who suffer respiratory problems because of that
fly ash, nor does it
compensate them for the discomfort of that asthma attack. The first of these
economic costs is
fairly straightforward and the economic literature has many examples of how to
approximate it
The second is a health issue that can also be approximated, although only
after a great deal of
study and analysis. The third cost, compensation for discomfort, is a psychic
cost and is
extremely difficult to quantify. However these and many other similar costs
should be
considered by the analysis when assessing the usefulness of a pollution
control alternative.
[00138] Similar
to economic and accounting costs, accounting benefits (revenues,
avoided production costs) are a subset of economic benefits. Pollution control
devices reduce
pollution and their installation reduces the occurrence of these economic
costs, so the analysis
may include among the benefits of the device the avoided economic costs
derived from the
pollutant. In other words, a fly ash free building does not have to pay for
cleaning - and that
avoided cost is considered a benefit of the device, Similarly, not having an
asthma attack is also
considered a benefit of the device. When making an economic assessment of a
pollution control
alternative, such as a bag house for capturing fly ash before it enters the
atmosphere, the analysis
looks at the benefit of avoiding these economic costs.
[00139] When performing an economic assessment of a pollution control
alternative,
the analysis can apply economic costs and benefits to payback, net present
value analysis (for
37
CA 2952392 2019-12-23
benefit cost analyses or to compare to the social discount rate through ROT or
IRR).
[00140] In
addition to those methods and models discussed above, one skilled in the
art might the following publication useful Whet et at. 1995 "Environmental
Cost Accounting for
Capital Budgeting" US EPA OMB#2070 0138 and Office of Air Quality and
Planning, 2002
"EPA air pollution control cost manual" 6* ed. US EPA EPA/452/5-02-001 .
[00141]
Advantageously, the costs associated with adoption of methods of the
present teachings described herein for operating coal burning utilities are
relatively low in
comparison with alternatives such as installation of chemical scrubbers, bag
houses, and other
control equipment. The low costs generally have a favorable effect on analyses
such as pay
back, NPV, IRR, ROI, and others discussed above. Importantly, methods of the
present
teachings also lead to significant cost advantages, due to costs avoided and
enhanced revenue
streams. The financial benefits are obtained whether accounting is by the
accrual method or on a
cash basis.
=
38
CA 2952392 2019-12-23
[00142] Costs avoided by virtue of use of the present teachings
include, but are not
necessarily limited to:
= Capital and other costs of installation of chemical scrubbers to remove
mercury. rn
year one of adoption, the cash outlay is 100% of the purchase price, or less
if there's
a note payable. In future years, interest is paid on the note, while
depreciation is
taken on the asset to calculate a bottom line for tax or other purposes
according to
generally accepted accounting principles. According to the size of the
generating
facility, costs of the scrubbers can range into the hundreds of millions of
dollars.
Operation of the scrubbers involves maintenance, labor, and the cost of
materials.
Account must also be taken of down time and the costs associated with bringing
the
scrubbers back on-line. As well, there are normally costs associated with
disposal of
the mercury containing material produced by the scrubber. In some embodiments,
the avoidance of these capital. costs is a major benefit of the use of the
methods
= described herein;
= 15 = . Costs of debt on any note taken out to pay for the
equipment;
= Costs of disposal of the v./ste ash as hazardous waste. Some conventional
alternative methods of remediating mercury result in the capture of mercury in
fly
ash or bottom ash, just as in the current methods. However, in conventional
methods
the mercury is captured in the fly ash in a non-sequestered form. For example,
mercury (and other heavy metals) tend to leach from such ash under acidic
conditions such as in the TCLP- procedure as defined by the United Sates
Environmental Protection Agency. As a consequence .of the high mercury content
and the leaching characteristics, the ash is considered as hazardous waste. It
can
therefore not be used in *commerce and must be handled and disposed of as a
hazardous waste;
= Costs of non-compliance. Depending on jurisdiction, plant operators are
subject to
fines and/or other costs for exceeding regulatory limits on the release of
pollutants
= such as mercury and sulfur;
= Costs of pollution credits. In certain situations, utility operators are
allowed to avoid
fines or criminal liability from exceeding emissions of hazardous materials
such as
sulfur or mercury if they purchase so-called emission credits. These are
available on
the open market and fluctuate in price accordingly;
= Costs of ill will among the community. Utility operators that pollute the
local and
regional environment and global environment are subject to opposition from any
number of organizations and individuals in society. The costs associated with
the
opposition are sometimes intangible, but are reflected in an increased cost of
doing
39
CA 2952392 2019-12-23
business from uncooperative or unhelpful stances adopted by local governments,
unions, taxing authorities, regulatory agencies, and so on.
[00143] Moreover, adoption of methods of the present teachings leads to
advantages
that increase various revenue streams:
= The waste ash can be sold into commerce instead of buried as a hazardous
waste.
The revenue generated offsets at least partially the cost of adopting the
control
methods;
= Tax incentives for reducing pollution can be taken advantage of. As an
illustration,
section 45 of the United States tax code provides tax credits for the use of
modified
coal under certain conditions. The modified coal must be increased in value by
at
least 50%; there must be a change in a baseline chemical property of at least
20%,
and use of the modified coal must reduced NO, and either mercury or sulfur
emissions by at least 20%. By use of the current methods, financial gain is
achieved
by virtue of costs avoided and revenues realized. When the gains are
calculated on
the basis of the amount of coal being consumed to realize the gains, in some
embodiments the increased value of the coal is above 50%. The baseline
chemical
changes are above 20%. Sulfur and mercury are reduced by over 20%, while in
some embodiments reduction of NO, is seen as well. Thus the utility operator
in
some embodiments qualifies for the section 45 tax credits and applies the
credits on
its income tax return.
[00144] In addition, use of the sorbents can lead to increased output of
electricity
from a unit of coal consumed, which leads to increased revenue from the use of
the sorbents. In
some embodiments, the water temperature in the boiler tubes is increased when
the methods are
practiced. It is believed that components of the sorbents form a refractory-
like composition on
the walls of the boiler. As a result, the walls better reflect the heat
generated by combustion and
focus the heat on the boiler tubes, resulting in higher water temperatures. So
burning the same
amount of coal increases the electrical output of the boiler, or the same
level of output can be
maintained by burning less coal. The net financial gain is attributable to use
of the methods
described herein and in particular to the sorbents.
[00145] In some embodiments, improvements in operation are also seen in the
reduction of fouling and/or slagging occurring during combustion, especially
on the boiler tubes.
Fouling involves the formation of bonded deposits on the tubes, while slagging
general occurs
when the deposits are molten. Use of the sorbents tends to prevent or reduce
fouling and/or
slagging, and/or remediate or eliminate fouling and slagging in a furnace that
has been running
without use of the sorbents. In various embodiments, even one foot slag
deposits are removed
CA 2952392 2019-12-23
=
from boiler tubes while coal is burning with sorbents that remove mercury and
render the ash
non-leaching and more highly cementitious. Removal of the slag deposits leads
to better heat
transfer to the boiler tubes and a concomitant higher boiler temperature. The
higher boiler
temperature leads to increased electrical output, as more steam is generated
per unit time to spin
the turbines. Alternatively, the amount of coal being fed can be reduced until
the water
temperature is maintained at the same temperature. Either way, the amount of
electricity
generated per unit of coal burned goes up. The value of the "extra"
electricity generated by
virtue of use of the sorbents also contributes to the financial advantages of
adoption of the .
control system. Although the present teachings are not to be limited by
theory, it is believed that
the sorbent compositions described above provide additional or supplemental
sources of silica
and alumina into the coal burning process. Combustion of the coal with the
added silica and
alumina forms a geopolymeric matrix such as is known in cold ceramics.
Although coal
naturally contains small amounts of silica and/or alumina, it is believed that
the amount of the
materials naturally occurring in coal is normally not sufficient to provide
the geopolymeric
matrix upon combustion. Further, the silica and alumina naturally occurring in
coal is not
necessarily balanced with the natural occurring calcium in order to provide
optimum sulfur
and/or mercury capture and/or cementitious ash product upon combustion.
[00146] Although the present teachings is not to be limited by theory, it is
believed
that the sorbent compositions described above provide additional or
supplemental sources of
silica and alumina into the coal burning process. Combustion of the coal with
the added silica
and alumina forms a geopolymeric matrix such as is known in cold ceramics.
Although coal
naturally contains small amounts of silica and/or alumina, it is believed that
the amount of the
materials naturally occurring in coal is normally not sufficient to provide
the geopolymeric
matrix upon combustion. Further, the silica and alumina naturally occurring in
coal is not
necessarily balanced with the natural occurring calcium in order to provide
optimum sulfur
and/or mercury capture and/or cementitious ash product upon combustion.
[00147] Methods of operating coal burning facilities involve the application
of
technology to reduce emissions of sulfur, mercury, and/or other harmful
emissions. The
reduction in emissions results in environmental benefits and can lead to tax
credits and other
financial benefits. The methods are non-capital in that they do not require
large investments in
scrubbers or other equipment. The methods involve the addition of various
sorbent components
or sorbent compositions before or during the burning of coal to entrap
contaminants in the coal
ash rather than release the contaminants to the atmosphere. Even though the
contaminant reports
to the ash produced upon combustion of coal, the ash is still a commercially
viable product,
because it has enhanced industrial and environmental properties. Thus, in some
embodiments,
the present teachings provide both for environmental control and the gain of
value from the sale
of a waste material.
41
CA 2952392 2019-12-23
[00148] In some embodiments, the methods involve adding sorbent components,
such as calcium oxide, alumina, and silica, as well as optional 'halogens as
part of environmental
control. Use of the sorbents leads to significant reductions in sulfur and
mercury emissions that
'otherwise would result from burning coal. Use of the sorbents leads to
production of waste coal
ash that, while higher in mercury, is nevertheless usable as a commercial
product because the
mercury in the ash is non-leaching and because the coal ash has a higher
cementitious nature by
virtue of the increased content of the sorbent components in the ash. Thus, in
some
embodiments, the methods involve adding powders having qualities that lead to
the production of
a cementitious coal ash while at the same time reducing emissions from a coal
burning facility.
[00149] Use of the methods provides a wide range of benefits to the coal
burning
utility:
I) emissions of mercury (both oxidized and elemental mercury) and/or sulfur
are significantly decreased, allowing compliance with sulfur and mercury
emission
regulations and protecting the local environment. In some embodiments,
nitrogen oxides
are also reduced;
2) no scrubbers are needed to comply with environmental and health concerns,
resulting in the avoidance of high capital investment costs;
3) the ash resulting from the burning of coal has an increased cementitious
nature and can be used in various industrial applications;
4) the value of the coal is increased as much as 50% or greater;
5) the disposal costs of the fly ash are avoided because the ash has
commercial
value;
6) costs of non-compliance with environmental regulations such as fines and
costs of emission credits are avoided;
7) the costs avoided and revenue realized contribute favorably to the balance
sheet of the utility operator; and
8) the costs avoided and the revenue realized increase the return on
investment
from adoption of the control systems described herein.
[00150] In some embodiments, the present teachings provide methods for
improving
the leaching quality of heavy metals such as mercury from coal. The methods
involve adding
sufficient silica and/or alumina to the coal to cause a geopolymer to form
upon combustion.
Preferably, the silica and alumina are added along with sufficient alkali
powders to reduce sulfur
pitting. The alkali powders tend to neutralize the silica and alumina, with
formation of
geopolymeric ash along with coupling silica and/or alumina to form a ceramic
like matrix that
reports as a stabilized ash. It may also be that the alumina and silica
burning with the coal forms
a refractory like mixture compound with mercury, lead, arsenic, cadmium,
antimony, cobalt,
42
CA 2952392 2019-12-23
copper, manganese, zinc, and/or other heavy metals. As a result, the resulting
coal ash or fly ash
containing heavy metals is resistant to leaching under standard conditions. As
noted above, the
non-leaching quality of the coal ash leads to commercial advantages because
the product would
no longer be considered as a hazardous material.
[00151] Although the above
discussion of the present teachings used coal burning
power plants as an example, those skilled in the art will appreciate that the
teaching are
applicable to any coal burning facilities including cement manufacture, paper
production, steam
generation, residential or commercial heating, and the like. The major use of
coal world wide is
for the generation of electricity and as such, the present teachings are
applicable to coal burning
facilities that generate electricity. Those skilled in the art will appreciate
that slight variations or
modifications to the business analysis may be necessary depending on which
type of coal
burning facility is being analyzed.
[00152] On March 15, 2005. EPA issued the final Clean Air Mercury Rule (CAMR)
for coal-based power plants. There are two essential elements of the rule. The
first are
performance standards limiting mercury emissions from coal-fired power plants
built after
January 30, 2004. The second applies to coal-fired power plants regardless of
when they were
built and is a market-based "cap-and-trade" program, which will allow
utilities to trade mercury
emissions. The program establishes a two-phase "cap," or national limit, on
mercury emissions.
The CAMR utilizes a market-based cap-and-trade approach under section 111 of
the Clean Air
Act (CAA) that requires emission reductions in two phases: a cap of 38 tons in
2010, and 15 tons
after 2018, for a total reduction of 70 percent from current levels.
Facilities demonstrate
compliance with the standard by holding one "allowance" for each ounce of
mercury emitted in
any given year. In the final rule, EPA has stated that regulation of nickel
emissions from oil-fired
plants is not "appropriate and necessary." Emissions trading is a system of
establishing a cap on
emissions and allowing sources (e.g., power plants) the flexibility to choose
the emissions
reduction plan that works best for their situation. Trading allows a source
that can over-control
its emissions to sell extra reduction credits to another source for which
controls would be
prohibitively expensive or technologically difficult to install.
[00153] Those
familiar with the art acknowledge that emissions trading markets for
sulfur dioxide (SO2) and nitrogen oxides (N0x) have proven relatively
successful to date. For
example, under the US Acid Rain Program, created under the 1990 Clean Air Act
Amendments,
SO2 sources were allowed to determine which emission reduction solutions, for
example, fuel
switching, control technology, or emissions trading, were most economical for
each facility. This
flexibility can result in greater environmental benefit at lower cost. The
newer, evolving, NOx
market has also reduced emissions, although prices have been morc volatile.
[00154] A cap-
and-trade program could provide several benefits in terms of
43
CA 2952392 2019-12-23
controlling emissions. Trading programs generally provide regulated units with
more flexibility
to meet overall emissions reductions than do conventional command-and-control
approaches
because a unit may apply whichever control method it finds to be most
appropriate and cost-
effective to meet emission limits. This flexibility serves to minimize overall
control costs in the
market. Furthermore, cap-and-trade programs can provide greater environmental
certainty by
establishing fixed national emissions caps that cannot be exceeded. However, a
cap-and-trade
program's environmental benefits will depend on the adequacy of the cap.
[00155] Under
EPA's proposed mercury emissions trading program, units that cannot
cost-effectively reduce emissions through controls may buy allowances from
units that were able
to reduce emissions beyond their established allowance limits and are willing
to sell their extra
allowances. Each unit is required to possess one emissions allowance per each
ounce of mercury
it emits. Units would be allowed to buy and sell credits among one another in
a national
emissions market. EPA's proposed cap-and-trade alternative proposes that the
interim mercury
emissions cap for 2010 be based on the amount of mercury reductions achieved
solely as a co-
benefit through implementation of SO2 and NOx controls under the proposed
Clean Air Interstate
Rule (CAIR).
[00156] In some embodiments, the present teachings provide methods for
lowering
mercury emissions from a coal burning facility as described above. In some
embodiments, the
present teachings provide methods for meeting emission limits for mercury as
determined by a
regulatory body or governmental agency. In some embodiments, the present
teaching provide
methods for trading emission credits created by use of at least of sorbent
discussed above. In
some embodiments, the emission trading credits can appear on a financial
statement and such
financial statements are discussed above. In some embodiments, an emission
credit can be used
as an asset or provide profit to an operator with a profit.
[00157] In some embodiments,
the present teachings provides methods for improving
the leaching quality of heavy metals such as mercury from coal. The methods
involve adding
sufficient silica and/or alumina to the coal to cause a geopolyrner to form
upon combustion.
Preferably, the silica and alumina are added along with sufficient alkali
powders to reduce sulfur
pitting. The alkali powders tend to neutralize the silica and alumina, with
formation of
geopolymeric ash along with coupling silica and/or alumina to form a ceramic
like matrix that
reports as a stabilized ash. It may also be that the alumina and silica
burning with the coal forms
a refractory like mixture compound with mercury, lead, arsenic, cadmium,
antimony, cobalt,
copper, manganese, zinc, and/or other heavy metals. As a result, the resulting
coal ash or fly ash
containing heavy metals is resistant to leaching under standard conditions. As
noted above, the
non-leaching quality of the coal ash leads to commercial advantages because
the product would
no longer be considered as a hazardous material.
44
CA 2952392 2019-12-23
EXAMPLES
Example 1
[00158] Coal is burned in a
positive draft tangentially fired boiler to generate
electricity for consumer use. Powdered coal (75% passing 200 mesh) is fed to
the boiler. Before
introduction of the powdered coal into the boiler, a powder sorbent is added
to the coal at a rate
of 6% by weight, based on the rate of coal being consumed by combustion. The
powder sorbent
contains 93% by weight of a 50150 mixture of cement kiln dust and lime kiln
dust, and 7% by
weight of calcium montmorillonite. At the same time, a 50% by weight solution
of calcium
bromide in water is dripped onto the coal at a rate of 0.1 to 2% by weight
based on the rate of
consumption of coal by combustion. Fly ash samples are collected before
addition of sorbents
(baseline), and after addition of the powder and liquid sorbents. The levels
of chlorine and heavy
metals are determined according to standard methods. Results are in Table 1.
Table 1
Fly Ash Composition with and without sorbents
Element Test - After Baseline - Prior to
sorbent addition sorbent addition
(ppb except for (ppb except for
chlorine) chlorine)
Arsenic 59.3 26.5
Barium 1.3 1.4
Cadmium 2.3 1.1
Cobalt 44.8 38.5
Chromium 52.0 34.3
Copper 61.0 48.8
Manganese 455.7 395.5
Molybdenum 26.0 31.5
Nickel 208.5 325.5
Lead 45.8 31.3
Antimony 23.0 7.3
Vanadium 473.0 874.5
Zino 3954.0 974.7
Mercury 0.246 0.128
CA 2952392 2019-12-23
Chlorine 0.940% 0.56%
Example 2
[00159] Next,
the ash samples are tested according to the TCLP procedure of the
EPA, as described above, to determine the acid leaching thresholds of key
elements. Results are
in Table 2.
Table 2
Fly Ash TCLP Test Results
Element EPA Baseline ¨ Test ¨ with
Threshold prior to sorbent addition
Limit sorbent (PPb)
(PPb) addition
(PPb)
Arsenic 5.00 <0.04 <0.04
Barium 100.00 0.814 0.313
Cadmium 1.00 <0.04 <0.04
Chromium 5.00 0.030 <0.007
Lead 5.00 0.513 0.096
Mercury 0.20 0.095 0.078
Selenium 1.00 <0.07 <0.07
Silver 5.00 3.835 3.291
[00160] It is
seen in these non-limiting Examples that use of the sorbents increases
the level of several heavy metals found in the fly ash. For example, arsenic,
cadmium,
chromium, lead, mercury, and chlorine are present at higher levels in the test
ash than in the
baseline. This is believed to represent increased capture of these exemplary
elements in the ash.
The increased level of zinc in the test ash is unexplained. However, it could
be due to the fact
that a great deal of de-slagging is observed from the boiler tubes upon use of
sorbents of the
present teachings. It could be that the increased levels of zinc are
attributable to material
removed from the boiler tubes during combustion with the sorbents.
[00161] Table 2 shows that,
while the fly ash is higher in absolute levels of elements
such as arsenic, lead, and mercury, nevertheless the amount of leachable
arsenic, lead, and
mercury is actually lower in the test fly ash than in the baseline.
46
CA 2952392 2019-12-23
[00162] Some embodiments and the examples described herein are exemplary and
not intended to be limiting in describing the full scope of compositions and
methods of these
teachings. Equivalent changes, modifications and variations of some
embodiments, materials,
compositions and methods can be made within the scope of the present
teachings, with
substantially similar results.
47
CA 2952392 2019-12-23
