U.S. patent application number 12/117599 was filed with the patent office on 2009-02-05 for apparatus for oil shale pollutant sorption/nox reburning multi-pollutant control.
Invention is credited to Richard D. Boardman, Robert A. Carrington.
Application Number | 20090031929 12/117599 |
Document ID | / |
Family ID | 36574442 |
Filed Date | 2009-02-05 |
United States Patent
Application |
20090031929 |
Kind Code |
A1 |
Boardman; Richard D. ; et
al. |
February 5, 2009 |
APPARATUS FOR OIL SHALE POLLUTANT SORPTION/NOx REBURNING
MULTI-POLLUTANT CONTROL
Abstract
A method of decreasing pollutants produced in a combustion
process. The method comprises combusting coal in a combustion
chamber to produce at least one pollutant selected from the group
consisting of a nitrogen-containing pollutant, sulfuric acid,
sulfur trioxide, carbonyl sulfide, carbon disulfide, chlorine,
hydroiodic acid, iodine, hydrofluoric acid, fluorine, hydrobromic
acid, bromine, phosphoric acid, phosphorous pentaoxide, elemental
mercury, and mercuric chloride. Oil shale particles are introduced
into the combustion chamber and are combusted to produce sorbent
particulates and a reductant. The at least one pollutant is
contacted with at least one of the sorbent particulates and the
reductant to decrease an amount of the at least one pollutant in
the combustion chamber. The reductant may chemically reduce the at
least one pollutant to a benign species. The sorbent particulates
may adsorb or absorb the at least one pollutant. A combustion
chamber that produces decreased pollutants in a combustion process
is also disclosed.
Inventors: |
Boardman; Richard D.; (Idaho
Falls, ID) ; Carrington; Robert A.; (Idaho Falls,
ID) |
Correspondence
Address: |
Stephen R. Christian;Bechtel BWXT Idaho, LLC
P. O. Box 1625
Idaho Falls
ID
83415-3899
US
|
Family ID: |
36574442 |
Appl. No.: |
12/117599 |
Filed: |
May 8, 2008 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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11004698 |
Dec 2, 2004 |
7384615 |
|
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12117599 |
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Current U.S.
Class: |
110/203 ;
110/214; 110/344; 110/345 |
Current CPC
Class: |
B01D 53/60 20130101;
B01D 2257/308 20130101; B01D 2257/602 20130101; Y02A 50/2344
20180101; B01D 2251/20 20130101; Y02A 50/20 20180101; B01D 2257/204
20130101; B01D 2253/20 20130101; F23J 15/003 20130101; B01D
2257/302 20130101; B01D 53/46 20130101; F23G 2900/7013 20130101;
F23J 7/00 20130101; B01D 2257/404 20130101 |
Class at
Publication: |
110/203 ;
110/214; 110/344; 110/345 |
International
Class: |
F23J 15/00 20060101
F23J015/00; F23J 15/02 20060101 F23J015/02 |
Goverment Interests
GOVERNMENT RIGHTS
[0002] The United States Government has certain rights in this
invention pursuant to Contract No. DE-AC07-99ID13727, and Contract
No. DE-AC07-05ID14517 between the United States Department of
Energy and Battelle Energy Alliance, LLC.
Claims
1. A combustion chamber for producing decreased pollutants in a
combustion process, comprising: a burner zone configured to combust
coal and produce at least one pollutant selected from the group
consisting of a nitrogen-containing pollutant, sulfuric acid,
sulfur trioxide, carbonyl sulfide, carbon disulfide, chlorine,
hydroiodic acid, iodine, hydrofluoric acid, fluorine, hydrobromic
acid, bromine, phosphoric acid, phosphorous pentaoxide, elemental
mercury, and mercuric chloride; at least one of a superheater zone
and a reheat zone, wherein at least one of the burner zone, the
superheater zone and the reheat zone is configured to combust oil
shale particles to produce sorbent particulates and a reductant is
configured to contact the sorbent particulates and the reductant
with the at least one pollutant; and at least one of an economizer
zone, an air preheat zone, and a gas cleaning unit configured to
contact the sorbent particulates and the reductant with the at
least one pollutant.
2. The combustion chamber of claim 1, wherein the burner zone is
configured to contact the nitrogen-containing pollutant with the
reductant to reduce the nitrogen-containing pollutant to molecular
nitrogen, carbon dioxide, and water.
3. The combustion chamber of claim 1, wherein the burner zone is
configured to maintain a temperature of greater than or equal to
about 400.degree. C. to reduce the nitrogen-containing pollutant to
molecular nitrogen, carbon dioxide, and water.
4. The combustion chamber of claim 1, wherein at least one of the
superheater zone, the reheat zone, and the economizer zone is
configured to contact at least one of sulfuric acid, sulfur
trioxide, carbonyl sulfide, and carbon disulfide with the sorbent
particulates to adsorb or absorb the at least one of sulfuric acid,
sulfur trioxide, carbonyl sulfide, and carbon disulfide onto the
sorbent particulates.
5. The combustion chamber of claim 1, wherein at least one of the
superheater zone, the reheat zone, and the economizer zone is
configured to maintain a temperature of from greater than or equal
to about 450.degree. C. to less than about 1150.degree. C.
6. The combustion chamber of claim 1, wherein at least one of the
air preheat zone and the gas cleaning unit is configured to contact
at least one of elemental mercury and mercuric chloride with the
sorbent particulates to adsorb or absorb the at least one of
elemental mercury and mercuric chloride onto the sorbent
particulates.
7. The combustion chamber of claim 1, wherein at least one of the
air preheat zone and the gas cleaning unit is configured to
maintain a temperature of less than or equal to about 200.degree.
C.
8. The combustion chamber of claim 1, wherein the combustion
chamber is configured as a pulverized coal combustor.
9. The combustion chamber of claim 1, wherein the reheat zone is
configured as a transition zone between the superheater zone and
the economizer zone.
10. The combustion chamber of claim 1, wherein at least one of the
superheater zone, the reheat zone and the economizer zone is
configured to maintain a temperature of from about 450.degree. C.
to about 1150.degree. C. in the presence of at least one of
sulfuric acid, sulfur trioxide, carbonyl sulfide, carbon disulfide,
chlorine, hydroiodic acid, iodine, hydrofluoric acid, fluorine,
hydrobromic acid, bromine, phosphoric acid, and phosphorous
pentaoxide to calcinate the sorbent particles.
11. A combustion chamber for producing decreased pollutants in a
combustion process, comprising: a burner zone configured to combust
coal and produce at least one pollutant selected from the group
consisting of a nitrogen-containing pollutant, sulfuric acid,
sulfur trioxide, carbonyl sulfide, carbon disulfide, chlorine,
hydroiodic acid, iodine, hydrofluoric acid, fluorine, hydrobromic
acid, bromine, phosphoric acid, phosphorous pentaoxide, elemental
mercury, and mercuric chloride, wherein the burner zone is
configured to combust oil shale particles to produce sorbent
particulates and kerogen and wherein the burner zone is configured
to contact the sorbent particulates and the kerogen with the at
least one pollutant; at least one zone configured to convert oil
shale to sorbent particulates and kerogen and to heat the kerogen;
at least another zone configured to expose the kerogen to the at
least one nitrogen-containing pollutant; and at least one of an air
preheat zone and a gas cleaning unit configured to expose the
sorbent particles to at least one pollutant selected from the group
consisting of sulfuric acid, sulfur trioxide, carbonyl sulfide,
carbon disulfide, chlorine, hydroiodic acid, iodine, hydrofluoric
acid, fluorine, hydrobromic acid, bromine, phosphoric acid,
phosphorous pentaoxide, elemental mercury, and mercuric
chloride.
12. The combustion chamber of claim 11, wherein the burner zone is
configured to combust coal at a temperature in a range of from
about 1085.degree. C. to about 1625.degree. C. to produce the at
least one pollutant.
13. The combustion chamber of claim 11, wherein the at least one
zone comprises at least one of a superheater zone and a reheat
zone.
14. The combustion chamber of claim 11, wherein at least one of the
burner zone and the at least one zone is configured to combust oil
shale at a temperature of greater than or equal to about
200.degree. C.
15. The combustion chamber of claim 11, wherein the at least one
zone is configured to crack kerogen at a temperature of greater
than or equal to about 350.degree. C.
16. The combustion chamber of claim 11, wherein the at least
another zone is configured to calcinate the sorbent particles at a
temperature of from about 450.degree. C. to about 1150.degree. C.
in the presence of at least one of sulfuric acid, sulfur trioxide,
carbonyl sulfide, carbon disulfide, chlorine, hydroiodic acid,
iodine, hydrofluoric acid, fluorine, hydrobromic acid, bromine,
phosphoric acid, and phosphorous pentaoxide.
17. The combustion chamber of claim 11, wherein the at least
another zone comprises at least one of a superheater zone, a reheat
zone, and an economizer zone.
18. The combustion chamber of claim 17, wherein the at least one of
the economizer zone and the air preheat zone are further configured
to contact the sorbent particulates with at least one of mercury
and mercuric chloride at a temperature of less than or equal to
about 200.degree. C.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application is a divisional of application Ser. No.
11/004,698, filed Dec. 2, 2004, entitled METHODS FOR OIL SHALE
POLLUTANT SORPTION/NOx REBURNING MULTI-POLLUTANT CONTROL,
pending.
FIELD OF THE INVENTION
[0003] The present invention relates to decreasing pollutants
produced by combustion or gasification of a fuel. More
specifically, the present invention relates to using oil shale as
at least one of a sorbent and a chemical reductant to decrease the
pollutants.
BACKGROUND OF THE INVENTION
[0004] Coal, biomass residuals, and solid wastes, such as wood
waste, municipal solid waste ("MSW"), or refuse derived fuel
("RDF"), are used as fuels to generate electrical power. However,
combustion of these fuels also produces various pollutants, such as
nitrogen compounds or sulfur compounds, which are believed to be
involved in the formation of smog and acid rain. If the fuel
includes mercury, the combustion also produces mercury compounds,
which have been identified by the Environmental Protection Agency
("EPA") as a significant toxic pollutant. The pollutants include
nitrogen oxide ("NO.sub.x") compounds, such as nitric oxide ("NO")
and nitrogen dioxide ("NO.sub.2"), sulfur oxide ("SO.sub.x")
compounds, such as sulfur dioxide ("SO.sub.2") and sulfur trioxide
("SO.sub.3"), volatile elemental mercury ("Hg.degree.") and
volatile mercuric chloride ("HgCl.sub.2"). Air pollutant control
legislation, such as the Clean Air Act and the Clear Skies
Initiative, regulates emissions of many of these pollutants and is
expected to pass in the legislature and become law in United States
and other countries. The EPA is currently required to promulgate a
mercury emissions limit under the Maximum Achievable Control
Technology ("MACT") provisions of the 1990 Clean Air Act
Amendments. Therefore, many powerplants will be required to
decrease emissions of these, and other, pollutants.
[0005] If the fuel contains sulfur, the sulfur is typically
converted to reduced forms of sulfur, such as hydrogen sulfide
("H.sub.2S"), carbonyl sulfide ("COS"), and carbon disulfide
("CS.sub.2") upon gasification of fossil fuels, biomass, and waste
materials. Nitrogen contained in the fuel is converted to reduced
nitrogen compounds, including ammonia ("NH.sub.3"), hydrogen
cyanide ("HCN"), and nitrogen ("N.sub.2"). Most of the mercury
entering with the fuel is converted to volatile Hg.degree. and
HgCl.sub.2. The combustion of fossil fuels and biomass also
liberates acid gases, such as hydrochloric acid ("HCl"), sulfuric
acid ("H.sub.2SO.sub.4"), and phosphoric acid ("H.sub.3PO.sub.4").
These acid gases are corrosive to equipment used in the combustion,
such as a combustion device or boiler tubes in a combustor.
Therefore, it is desirable to limit the formation of the acid gases
or to remove the acid gases close to their point of generation in
the combustion device.
[0006] Various technologies have been developed to decrease
emissions from coal-fired powerplants. Limestone has been used as a
sorbent for SO.sub.x pollutants, as disclosed in U.S. Pat. No.
3,995,006 to Downs et al., U.S. Pat. No. 5,176,088 to Amrhein et
al. ("Amrhein"), and U.S. Pat. No. 6,143,263 to Johnson et al. This
technology is known as limestone injection multiple burner ("LIMB")
technology or limestone injection dry scrubbing ("LIDS")
technology. The limestone is injected into a region of a furnace
having a temperature of 2,000.degree. F.-2,400.degree. F.
[0007] Organic and amine reducing agents, such as ammonia or urea,
are used to selectively reduce NO.sub.x pollutants, as disclosed in
U.S. Pat. Nos. 3,900,554 to Lyon. This technique is known as
selective noncatalytic reduction ("SNCR"). The reducing agent is
injected into a furnace at a temperature of from about 975K to
about 1375K so that a noncatalytic reaction selectively reduces the
NO.sub.x to molecular nitrogen ("N.sub.2"). The ammonia is injected
into a region of the furnace having a temperature of 1,600.degree.
F.-2,000.degree. F.
[0008] As disclosed in Amrhein, the LIMB and SCNR technologies have
been combined to simultaneously removing the NO.sub.x pollutants
and the SO.sub.x pollutants. The limestone is used to absorb the
SO.sub.x pollutants while the ammonia is used to absorb the
NO.sub.x pollutants. However, this combination technology is
expensive to implement and adds increased complexity to the
process.
[0009] NO.sub.x reburning has also been used to remove the NO.sub.x
pollutants, as disclosed in U.S. Pat. No. 5,139,755 to Seeker et
al. In NO.sub.x reburning, the coal is combusted in two stages. In
the first stage, a portion of the coal is combusted with a normal
amount of air (about 10% excess), producing the NO.sub.x
pollutants. In the second stage, the remaining portion of the coal
is combusted in a fuel-rich environment. Hydrocarbon radicals
formed by combustion of the coal react with the NO.sub.x pollutants
to form N.sub.2. Fuel/air staging has also been used to reduce the
NO.sub.x pollutants. Fuel and air are alternately injected into a
combustor to provide a reducing zone where the nitrogen in the fuel
is evolved, which promotes the conversion of the nitrogen to
N.sub.2. The air is injected at a separate location to combust the
fuel volatiles and char particles. By staging or alternating the
fuel and the air, the local temperature and the mixture of air and
fuel are controlled to suppress the formation of the NO.sub.x
pollutants. Fuel/air staging attempts to prevent NO.sub.x formation
while NO.sub.x reburning promotes NO.sub.x reduction and
destruction.
[0010] To absorb mercury or mercury-containing pollutants,
activated carbon is used as a sorbent, as disclosed in U.S. Pat.
Nos. 5,827,352 to Altman et al. and U.S. Pat. No. 6,712,878 to
Chang et al. The activated carbon is present as a fixed or
fluidized bed or is injected into the flue gas.
[0011] Oil shale is a sedimentary rock that includes an inorganic
matrix of carbonate, oxide, and silicate compounds impregnated with
a polymeric material called kerogen. Kerogen is an organic
substance that is insoluble in petroleum solvents. When heated, the
kerogen pyrolyzes to produce gas, oil, bitumen, and an organic
residue. Pyrolyzing the kerogen is also known as retorting. Oil
shale also includes carbonate minerals, such as calcium carbonate,
and other hydrocarbon materials, such as paraffins, cycloparaffins,
aliphatic and aromatic olefins, one- to eight-ring aromatics,
aromatic furans, aromatic thiophenes, hydroxyl-aromatics, dihydroxy
aromatics, aromatic pyrroles, and aromatic pyridines. Oil shale is
typically co-located with coal and oil and is found in various
regions of the western United States, such as in Utah, Colorado,
and Wyoming, and in the eastern United States, such as in Virginia
and Pennsylvania. Large deposits of oil shale are also found in
Canada, Europe, Russia, China, Venezuela, and Morocco. Given the
abundance of oil shale throughout the world, its value would be
significant if beneficial uses are identified and employed. Oil
shale utilization has not been presently appreciated due to the
high cost of recovering the kerogen from the shale.
[0012] When oil shale containing considerable amounts of calcium
carbonate is burned in a direct combustion process, the calcium
carbonate undergoes calcination, which is an endothermic reaction
in which the calcium carbonate is converted to lime. For each
kilogram of calcium carbonate that is calcined, as much as 1.4 MJ
to 1.6 MJ (or about 600 British Thermal Units ("BTU") to 700 BTU
per pound mass) of the available heat energy is consumed. This loss
of energy translates to a process efficiency penalty when limestone
or dolomite is used as an injected sorbent. In the case of oil
shale, the kerogen can be oxidized to offset the heat sink
associated with carbonate calcination.
[0013] To extract energy from the oil shale, the oil shale is
heated in a retorting zone of a fluidized bed combustor to a
temperature sufficient to release, but not combust, volatile
hydrocarbons from the oil shale, as disclosed in U.S. Pat. No.
4,373,454 to Pitrolo et al. The temperature used in the retorting
zone provides minimal calcination of the calcium carbonate. The
volatile hydrocarbons flow to a combustion zone of the fluidized
bed combustor, where the volatile hydrocarbons are combined with
excess air and are combusted. Calcination of the calcium carbonate
occurs in the combustion zone. During retorting, nitrogen compounds
in the oil shale are converted to NO.sub.x compounds and are
reduced to nitrogen and water or oxygen by the volatile
hydrocarbons.
[0014] Oil shale has been used to absorb SO.sub.2 and HCl in a
circulating fluidized bed, as disclosed in "Combustion of Municipal
Solid Wastes with Oil Shale in a Circulating Fluidized Bed,"
Department of Energy Grant No. DE-FG01-94CE15612, Jun . 6, 1996,
Energy-Related Inventions Program Recommendation Number 612,
Inventor R. L. Clayson, NIST Evaluator H. Robb, Consultant J. E.
Sinor and in "Niche Market Assessment for a Small-Scale Western Oil
Shale Project," J. E. Sinor, Report No. DOE/MC/11076-2759.
BRIEF SUMMARY OF THE INVENTION
[0015] The present invention relates to a method of decreasing
pollutants produced in a combustion, gasification, or stream
reforming process, which is collectively referred to herein as a
"combustion" process. The term "combustion" encompasses equivalent
derivate nouns, adjectives, and verb conjugations of this term,
such as "combusting" or "combusted." The method comprises
combusting coal in a combustion chamber to produce at least one
pollutant selected from the group consisting of a
nitrogen-containing pollutant, sulfuric acid, sulfur trioxide,
carbonyl sulfide, carbon disulfide, chlorine, hydroiodic acid,
iodine, hydrofluoric acid, fluorine, hydrobromic acid, bromine,
phosphoric acid, phosphorous pentaoxide, elemental mercury, and
mercuric chloride. Oil shale particles are introduced into the
combustion chamber and are combusted to produce sorbent
particulates and a reductant. The sorbent particulates and the
reductant may be produced by pyrolyzing the oil shale particles at
a temperature of greater than or equal to approximately 200.degree.
C. to devolatilize kerogen from the oil shale particles. The oil
shale particles may be introduced into at least one of a
superheater zone, a reheat zone, or an economizer zone of the
combustion chamber. The at least one pollutant is contacted with at
least one of the sorbent particulates and the reductant to decrease
an amount of the at least one pollutant in the combustion chamber.
The reductant may chemically reduce the at least one pollutant,
such as reduce the nitrogen-containing pollutant to molecular
nitrogen, water, and carbon dioxide. The sorbent particulates may
be used to adsorb or absorb the at least one pollutant, such as
adsorbing or absorbing at least one of sulfuric acid, sulfur
trioxide, carbonyl sulfide, carbon disulfide, chlorine, hydroiodic
acid, iodine, hydrofluoric acid, fluorine, hydrobromic acid,
bromine, phosphoric acid, phosphorous pentaoxide, elemental
mercury, and mercuric chloride.
[0016] The present invention also relates to a combustion chamber
for producing decreased pollutants in a combustion process. The
combustion chamber comprises a burner zone that is configured to
combust coal and to produce at least one pollutant selected from
the group consisting of a nitrogen-containing pollutant, sulfuric
acid, sulfur trioxide, carbonyl sulfide, carbon disulfide,
chlorine, hydroiodic acid, iodine, hydrofluoric acid, fluorine,
hydrobromic acid, bromine, phosphoric acid, phosphorous pentaoxide,
elemental mercury, and mercuric chloride. The burner zone is also
configured to combust oil shale particles to produce sorbent
particulates and a reductant, which are contacted with the at least
one pollutant. The burner zone may be configured to contact the
nitrogen-containing pollutant with the reductant to reduce the
nitrogen-containing pollutant to molecular nitrogen, carbon
dioxide, and water.
[0017] The combustion chamber also comprises at least one of a
superheater zone and a reheat zone that are each configured to
combust the oil shale particles to produce the sorbent particulates
and the reductant. The superheater zone and the reheat zone are
also each configured to contact the sorbent particulates and the
reductant with the at least one pollutant. The combustion chamber
also comprises at least one of an economizer zone, an air preheat
zone, and a gas cleaning unit, which are each configured to contact
the sorbent particulates and the reductant with the at least one
pollutant. Each of the superheater zone, the reheat zone, and the
economizer zone is configured to contact at least one of sulfuric
acid, sulfur trioxide, carbonyl sulfide, carbon disulfide,
chlorine, hydroiodic acid, iodine, hydrofluoric acid, fluorine,
hydrobromic acid, bromine, phosphoric acid, phosphorous pentaoxide,
elemental mercury, and mercuric chloride with the sorbent
particulates to adsorb or absorb at least one of these pollutants.
Each of the air preheat zone and the gas cleaning unit is
configured to contact at least one of the elemental mercury and
mercuric chloride with the sorbent particulates to adsorb or absorb
at least one of the elemental mercury and mercuric chloride.
[0018] In one embodiment, the combustion chamber is configured as a
pulverized coal combustor.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS
[0019] While the specification concludes with claims particularly
pointing out and distinctly claiming that which is regarded as the
present invention, the advantages of this invention may be more
readily ascertained from the following description of the invention
when read in conjunction with the accompanying drawing in
which:
[0020] FIG. 1 is a schematic illustration of an embodiment of a
pulverized coal combustor in which oil shale is used to decrease
pollutant levels.
DETAILED DESCRIPTION OF THE INVENTION
[0021] Oil shale is used to decrease or eliminate at least one
pollutant that is produced during combustion of a primary fuel. The
primary fuel may be coal, biomass, MSW, RDF, or mixtures thereof.
During combustion of the primary fuel in a combustion chamber, the
oil shale may function as a sorbent to decrease an amount of the
pollutant(s) that is released from the combustion chamber.
Alternatively, combustion of the oil shale may produce a reductant,
which reduces the pollutant(s) to a more benign chemical species,
decreasing the amount of the pollutant(s) that is released. By
adjusting or controlling a temperature in the combustion chamber,
the pollutant may be adsorbed or absorbed onto the oil shale or may
be reduced by the reductant produced by the oil shale. The
pollutant may be removed from the combustion chamber by contacting
the pollutant with the oil shale for a sufficient amount of time
for the oil shale to function as a sorbent or for the reductant to
chemically reduce the pollutant. The amount of time sufficient to
remove the pollutant is referred to herein as a residence time or a
contact time.
[0022] The pollutant may be at least one of a nitrogen-containing
pollutant, a sulfur-containing pollutant, an acid gas, and a metal.
The nitrogen-containing pollutant may be NO, NO.sub.2, N.sub.2O,
N.sub.2O.sub.5, or mixtures thereof. The sulfur-containing
pollutant may be SO.sub.2, SO.sub.3, H.sub.2SO.sub.4, H.sub.2S,
COS, CS.sub.2, or mixtures thereof. SO.sub.2 may be the major
sulfur-containing pollutant and SO.sub.3 the minor
sulfur-containing pollutant produced during combustion of primary
fuels that contain sulfur. H.sub.2S may be the major
sulfur-containing pollutant produced during gasification of
sulfur-containing primary fuels. In one embodiment, the
sulfur-containing pollutant is H.sub.2SO.sub.4, SO.sub.3, H.sub.2S,
COS, CS.sub.2, or mixtures thereof. The acid gas may be a
halide-containing volatile gas, such as HCl, chlorine ("Cl.sub.2"),
hydroiodic acid ("HI"), iodine ("I.sub.2"), hydrofluoric acid
("HF"), fluorine ("F"), hydrobromic ("HBr"), bromine ("Br"), or
mixtures thereof. The acid gas may also be a phosphate-containing
gas, such as H.sub.3PO.sub.4, phosphorus pentaoxide
("P.sub.2O.sub.5"), or mixtures thereof. The metal may be an
elemental metal or a metal compound including, but not limited to,
elemental mercury ("Hg.degree."), mercuric chloride ("HgCl.sub.2"),
mercury adsorbed on particulate matter, lead ("Pb") or compounds
thereof, arsenic ("As") or compounds thereof, chromium ("Cr") or
compounds thereof, or mixtures thereof. In one embodiment, the
metal is elemental mercury or mercuric chloride. The oil shale may
be used to remove a single pollutant or multiple pollutants from
the combustion chamber. In one embodiment, the oil shale is used to
remove nitrogen-containing pollutants, H.sub.2SO.sub.4, SO.sub.3,
H.sub.2S, COS, CS.sub.2, SO.sub.3, elemental mercury, and mercuric
chloride from the combustion chamber.
[0023] When the oil shale is heated in the combustion chamber,
shale minerals, char particles, and kerogen are produced, as shown
in Reaction 1:
oil shale+heat.fwdarw.shale minerals+char particles+kerogen
(1).
A temperature of greater than or equal to approximately 200.degree.
C. may be used to pyrolyze the oil shale. As the oil shale is
heated, the heat may cause the kerogen to depolymerize and
devolatilize while the shale minerals may be calcined. The extent
of depolymerization, devolatilization, pyrolysis, and char
formation of the oil shale may vary depending on particle heat up
rates, particle temperature, surrounding gas temperature, and an
amount of time that the oil shale is heated. When the kerogen is
devolatilized or released from the oil shale, a porous matrix of
oxides, carbonates, or silicates may remain including, but not
limited to, oxides, carbonates, or silicates of calcium ("Ca"),
magnesium ("Mg"), sodium ("Na"), potassium ("K"), iron ("Fe"), or
zinc ("Zn"). These oxides, carbonates, and silicates are
collectively referred to herein as the shale minerals. For the sake
of example only, the shale minerals may include, but are not
limited to, calcium oxide, magnesium oxide, iron oxide, calcium
carbonate, or mixtures thereof. The char particles or particles of
residual carbon may also remain after the kerogen is devolatilized
from the oil shale. The shale minerals and char particles are
collectively referred to herein as sorbent particulates. The
sorbent particulates are porous particles that have an increased
surface area. As such, the sorbent particulates have an increased
adsorption or absorption capability relative to that of the oil
shale and may be used to adsorb or absorb mercury and other
pollutants, as explained in detail below. Since the sorbent
particulates are porous, the pollutants may readily diffuse into
the sorbent particulates and react with the oxides, carbonates, and
silicates therein.
[0024] The kerogen released from the oil shale may provide a source
of the reductant used to reduce the nitrogen-containing pollutants.
As shown in Reaction 2, the kerogen may be exposed to additional
heat to crack or scission the kerogen, forming light and heavy
hydrocarbons:
kerogen+heat+radicals.fwdarw.heavy and light hydrocarbons
(C.sub.xH.sub.y) (2),
where x and y depend on the carbon and hydrogen ratio in the
kerogen and temporal conditions. For instance, x may range from 1
to 25, such as from 1 to 3 for a light hydrocarbon, from 4 to 8 for
an intermediate hydrocarbon, or from 9 to 25 for a heavy
hydrocarbon. Y may range from 1 to 50 and is typically equal to two
times "x" for a given hydrocarbon. A temperature of greater than or
equal to approximately 350.degree. C. may be used to crack and
scission the polymeric kerogen. The heavy and light hydrocarbons
may be used to reduce the nitrogen-containing pollutants to
N.sub.2, carbon dioxide ("CO.sub.2"), and water ("H.sub.2O") by
heating the heavy and light hydrocarbons to a temperature of
greater than or equal to approximately 400.degree. C. according to
the chemistries shown in Reactions 3 and 4:
C.sub.xH.sub.y+(2x+.sup.y/2)NO.fwdarw.(x+.sup.y/4)N.sub.2+xCO.sub.2+.sup-
.y/2H.sub.2O (3),
C.sub.xH.sub.y+(x+.sup.y/4)NO.sub.2.fwdarw.(.sup.x/2+.sup.y/8)N.sub.2+xC-
O.sub.2+.sup.y/2H.sub.2O (4),
where x is 1 or 2 and y is 1, 2, 3, or 4. Generally, Reactions 3
and 4 show the reduction of oxidized compounds of nitrogen to a
reduced nitrogen compound, such as N.sub.2.
[0025] The shale minerals or char particles may have an affinity
for chemical bonding with mercury or mercury compounds (adsorption)
and for physical bonding with mercury or mercury compounds
(absorption). Therefore, the shale minerals or char particles
produced by the pyrolysis of the oil shale (see Reaction 1) may be
used to adsorb or absorb mercury or mercuric chloride according to
the chemistries shown in Reactions 5, 6, 7, and 8:
char particles+Hg.degree..fwdarw.char particles-Hg.degree. (5),
char particles+HgCl.sub.2.fwdarw.char particles-HgCl.sub.2 (6),
shale minerals+Hg.degree..fwdarw.M-Hg.degree. (7),
shale minerals+HgCl.sub.2.fwdarw.M-HgCl.sub.2 (8),
where M is a metal or metal compound present in the oil shale that
has affinity for mercury or mercuric chloride. M may be Fe, Zn,
lead ("Pb"), silver ("Ag"), aluminum ("Al"), cadmium ("Cd"),
chromium ("Cr"), nickel ("Ni"), titanium ("Ti"), selenium ("Se"),
or arsenic ("As"). When the shale minerals or char particles come
into contact with these pollutants for a sufficient residence time,
the sorbent particulates may capture the elemental mercury or
mercuric chloride. The adsorption or absorption of the elemental
mercury or mercuric chloride by the shale minerals or char
particles may also depend on a temperature at which the shale
minerals or char particles contact the elemental mercury or
mercuric chloride. The temperature may be maintained so that is it
favorable for chemical or physical adsorption, such as at a
temperature of less than or equal to approximately 200.degree. C.
This temperature may be achieved in a number of locations in the
combustion chamber, such as in a process duct, in a particle cake
collected by a gas cleaning unit, such as a baghouse or
electrostatic precipitator ("ESP"), or in a packed-bed/gas
reactor.
[0026] Carbonate or oxide compounds produced by the combustion of
the oil shale may be used to remove sulfur-containing pollutants,
such as H.sub.2SO.sub.4, SO.sub.3, SO.sub.2, H.sub.2S, COS,
CS.sub.2, or mixtures thereof, according to the chemistries shown
in Reactions 9-15:
M.sub.x-(CO.sub.3).sub.y+heat.fwdarw.M.sub.x-O.sub.y+yCO.sub.2
(9),
CaCO.sub.3+SO.sub.2+1/2O.sub.2.fwdarw.CaSO.sub.4+CO.sub.2 (10),
CaCO.sub.3+SO.sub.3.fwdarw.CaSO.sub.4+CO.sub.2 (11),
CaCO.sub.3+H.sub.2S.fwdarw.CaS+H.sub.2O+CO.sub.2 (12),
CaO+SO.sub.2+1/2O.sub.2.fwdarw.CaSO.sub.4 (13),
CaO+SO.sub.3.fwdarw.CaSO.sub.4 (14),
CaO+H.sub.2S.fwdarw.CaS+H.sub.2O (15),
where M is a metal, such as Ca, Mg, Na, K, Fe, or Zn, and where x
and y vary depending on the metal carbonates present in the oil
shale. For instance, x may be 1 or 2 and y may be 1, 2, or 3. While
the reactions shown above are between SO.sub.2, SO.sub.3, or
H.sub.2S and calcium carbonate or calcium oxide, similar reactions
may occur between SO.sub.2, SO.sub.3, or H.sub.2S and carbonates or
oxides of Mg, Na, K, Fe, or Zn and between H.sub.2SO.sub.4, COS, or
CS.sub.2 and carbonates or oxides of Ca, Mg, Na, K, Fe, or Zn. The
shale minerals, such as the carbonate compounds, may be calcined by
heating the oil shale to a temperature greater than or equal to
approximately 450.degree. C. The adsorption of the
sulfur-containing pollutant may occur in a location of the
combustion chamber where the temperature is relatively hot. The
temperature may be sufficiently high to achieve favorable reaction
of the sulfur-containing pollutant with the alkali compounds,
alkaline-earth compounds, or other metal oxides present in the oil
shale to produce sulfate or sulfide compounds. However, the
temperature may be less than the dissociation temperatures of the
compounds. To achieve reaction between the shale minerals and the
H.sub.2SO.sub.4, SO.sub.2, SO.sub.3, H.sub.2S, COS, or CS.sub.2, a
temperature ranging from greater than or equal to approximately
450.degree. C. to less than approximately 1150.degree. C. may be
used.
[0027] The shale minerals, such as the carbonate or oxide
compounds, may also be used to remove HCl and Cl.sub.2 according to
the chemistries shown in Reactions 16 and 17:
CaO+2HCl.fwdarw.CaCl.sub.2+H.sub.2O (16),
CaO+Cl.sub.2.fwdarw.CaCl.sub.2+1/2O.sub.2 (17).
While the reactions shown above are between calcium oxide and
chlorine-containing compounds, similar reactions may occur between
HCl or Cl.sub.2 and Mg, Na, K, Fe, or Zn. Similar reactions may
also occur with iodine, iodine-containing compounds, fluorine,
fluorine-containing compounds, bromine, and bromine-containing
compounds. The adsorption of the HCl, Cl.sub.2, HI, I.sub.2, HF, F,
HBr, or Br may occur in a location of the combustion chamber where
the temperature is relatively hot. The temperature may be
sufficiently high to achieve favorable reaction of the HCl,
Cl.sub.2, HI, I.sub.2, HF, F, HBr, and Br with the alkali
compounds, alkaline-earth compounds, or other metal oxides present
in the oil shale to produce chloride compounds. However, the
temperature may be less than the dissociation temperatures of the
compounds. To react the HCl with the shale minerals, the
temperature of the reaction may be maintained from greater than or
equal to approximately 500.degree. C. to less than approximately
1150.degree. C.
[0028] The oil shale used in the combustion chamber may be ore that
is obtained from a conventional oil shale mine and pulverized into
particles. The oil shale may be obtained from mines in Utah,
Colorado, or Wyoming that yield approximately 10 gallons of oil per
ton of ore to approximately 80 gallons of oil per ton of ore. The
oil shale may initially be ground or milled to a desired coarse
particle size of less than or equal to approximately 5 cm
(approximately 2 inches). The oil shale may be ground using
conventional techniques, similar to the crushing and grinding
techniques used in coal mining. The oil shale particles may be
further pulverized into microsize particles having a particle size
ranging from approximately 50 .mu.m to approximately 150 .mu.m,
which are introduced into the combustion chamber. The microsize
particles may be pulverized, classified, and entrained in an air
stream using conventional techniques, similar to the techniques for
pulverizing, classifying, and entraining coal in an air stream. As
such, existing coal pulverizers, classifiers, and injectors may be
used to produce and inject the oil shale particles into the
combustion chamber. The oil shale particles may be unreacted, in
that the oil shale particles have not been pyrolyzed or
devolatilized. However, oil shale retort (devolatilized oil shale
particles) may also be used in the combustion chamber.
[0029] To decrease the amount of the pollutants produced by
combustion of the primary fuel, the oil shale particles may be
introduced into the combustion chamber, which may be a pulverized
coal combustor ("PCC"), a furnace, a boiler, fluidized bed
combustor or gasifier, a circulating bed combustor or gasifier, a
staged reactor combustor or gasifier, an entrained-flow combustor
or gasifier, an offgas duct, an offgas cleanup transport reactor,
or a cement kiln. The oil shale particles may also be used in a
metallurgical process, such as during the production of iron ore.
The combustion chamber may be configured to combust coal or other
fossil fuels, biomass, MSW, or RDF. While the embodiments herein
describe using the oil shale particles in the PCC, the oil shale
particles may be used in other types of combustion chambers as long
as the combustion chamber is capable of producing the temperatures
at which the reactions with the oil shale particles occur. In
addition, while the embodiments herein describe using coal as the
primary fuel, other fuels, such as biomass, MSW, or RDF, may be
used.
[0030] PCCs are designed to burn coal as the primary fuel and to
convert the chemical energy (enthalpy) of the burning coal into
heat, which is transferred to steam tubes to produce super-heated,
high pressure steam. The PCC may produce from approximately 200
MW.sub.e to approximately 1000 MW.sub.e of energy. The PCC may be a
long, vertical burner box that is lined with the steam tubes or has
pendant arrangements of the steam tubes. PCCs are known in the art
and, therefore, are not discussed in detail herein. A schematic
illustration of a PCC 2 into which the oil shale particles 4 may be
introduced is shown in FIG. 1. The PCC 2 includes a burner zone 6,
a superheater zone 8, a reheat zone 10, an economizer zone 12, an
air preheat zone 14, and a gas cleaning unit 16. To decrease the
pollutants produced by combusting the coal in the PCC 2, the
temperature in each of these zones may be controlled to achieve the
desired reactions between the pollutants and the kerogen and
between the pollutants and the sorbent particulates.
[0031] Pulverized coal 18 may be introduced into the burner zone 6
of the PCC 2 and combusted with air 20. An amount of pulverized
coal 18 added to the PCC 2 may depend on an efficiency of the PCC 2
and its desired power output. A feed rate at which the pulverized
coal 18 is introduced into the PCC 2 may be calculated based on the
efficiency of the PCC 2 and desired power output, as known in the
art. The pulverized coal 18 may be entrained with the air 20 and
injected into the PCC 2 through multiple burners (not shown), which
are also referred to in the art as burner registers or burner
boxes. Alternatively, the pulverized coal 18 may be injected into
the burner zone 6 through primary ports (not shown). The air 20 may
be injected with the pulverized coal 18 or may be injected through
secondary or tertiary ports (not shown). To combust the pulverized
coal 18, the burner zone 6 may be maintained at a temperature
ranging from approximately 1085.degree. C. to approximately
1625.degree. C. (approximately 2000.degree. F. to approximately
3000.degree. F.). Upon combustion, nitrogen that is present in the
pulverized coal 18 and the air 20 may be converted to the
nitrogen-containing pollutants. Sulfur in the pulverized coal 18,
such as organically bound sulfur or inorganic or pyrite-phase
sulfur, may be released and oxidized to the sulfur-containing
pollutants, such as H.sub.2SO.sub.4, SO.sub.2, SO.sub.3, H.sub.2S,
COS, CS.sub.2, or mixtures thereof. Chlorine in the pulverized coal
18 may be converted to HCl, Cl.sub.2, or other volatile chlorine
compounds. Iodine in the pulverized coal 18 may be converted to HI,
I.sub.2, or other volatile iodine compounds while fluorine in the
pulverized coal 18 may be converted to HF, F, or other volatile
fluoride compounds. Bromine in the pulverized coal 18 may be
converted to HBr, Br, or other volatile bromide compounds. Mercury
present in the pulverized coal 18 may be released as Hg.degree. or
HgCl.sub.2.
[0032] The oil shale particles 4 may be entrained and injected into
the PCC 2 in at least one of the burner zone 6, the superheater
zone 8, and the reheat zone 10, depending on the temperature
profile of the PCC 2 and the properties of the oil shale. For the
sake of clarity and simplicity, the oil shale particles 4 are shown
in FIG. 1 as being injected into the superheater zone 8. The oil
shale particles 4 may be injected into the PCC 2 through multiple
burners (not shown), primary ports (not shown), or secondary or
tertiary ports (not shown). The oil shale particles 4 are not
injected into a zone of the PCC 2 where the oil shale particles 4
would fuse and slag since this may affect the ability of the oil
shale particles 4 to capture the pollutant in later stages of the
gas exit path. A feed rate at which the oil shale particles 4 are
introduced into the PCC 2 may depend on the efficiency of the
sorbent reactions. This feed rate may be determined as known in the
art. In one embodiment, the oil shale particles 4 are injected into
an upper region of the burner zone 6 or a lower region of the
superheater zone 8. Oil shale retort (devolatilized oil shale
particles) may also be injected into the reheat zone 10. After
being injected into the PCC 2, the oil shale particles 4 may begin
to devolatilize and release the kerogen, which reacts with the
nitrogen-containing pollutant as described in Reactions 1-4. The
temperature in at least one of the burner zone 6, the superheater
zone 8, and the reheat zone 10 may be maintained so that it is
favorable to chemical reduction of the nitrogen-containing
pollutants to N.sub.2, CO.sub.2, and H.sub.2O, significantly
decreasing the amount of the nitrogen-containing pollutants that
exit the PCC 2.
[0033] The shale minerals produced after the kerogen is released
may react with gaseous H.sub.2SO.sub.4, SO.sub.3, SO.sub.2, HCl,
H.sub.2S, COS, CS.sub.2, or mixtures thereof as described in
Reactions 9-17. Calcium oxide, magnesium oxide, iron oxide, and
other metal oxides from the oil shale may react and capture the
H.sub.2SO.sub.4, SO.sub.3, SO.sub.2, HCl, H.sub.2S, COS, CS.sub.2,
or mixtures thereof when the reaction kinetics and thermodynamics
are favorable for the formation of CaSO.sub.4 or CaS. Generally,
favorable reactions may occur at a temperature ranging from
approximately 451.degree. C. to approximately 1125.degree. C.
Temperatures within this range may occur in at least one of the
superheater zone 8, the reheat zone 10, and the economizer zone 12.
Therefore, the capture of the HCl, H.sub.2SO.sub.4, SO.sub.3,
SO.sub.2, H.sub.2S, COS, CS.sub.2, or mixtures thereof may occur as
the oil shale particles 4 pass out of the superheater zone 8 and
into the reheat zone 10 and the economizer zone 12. The capture of
the HCl, H.sub.2SO.sub.4, SO.sub.3, SO.sub.2, H.sub.2S, COS,
CS.sub.2, or mixtures thereof may also continue into a lower
portion of the air preheat zone 14. A residence time or contact
time between the shale minerals and the pollutants may be greater
than or equal to approximately 5 seconds to capture these
pollutants.
[0034] The mercury or mercuric chloride may react with the shale
minerals or char particles by two mechanisms: physical absorption
or chemical adsorption. As the shale minerals or char particles
pass into portions of the PCC 2 having cooler temperatures, the
mercury or mercuric chloride may be adsorbed or absorbed, as
described in Reactions 5-8. For instance, the mercury or mercuric
chloride may be adsorbed or absorbed by the sorbent particulates in
the air preheat zone 14 or the gas cleaning unit 16. These
reactions may occur when the temperature drops below approximately
200.degree. C. (approximately 392.degree. F.). Since temperatures
within this range may occur in the air preheat zone 14 or the gas
cleaning unit 16, these portions of the PCC 2 may be the most
effective in removing the mercury or mercuric chloride. To
effectively capture these pollutants, the contact time between the
sorbent particulates and the mercury or mercuric chloride may be
greater than approximately 30 seconds. Such long contact times may
be achieved in the gas cleaning unit 16.
[0035] The hot gases and entrained flyash particles produced by
combusting the pulverized coal 18 may exit the burner zone 6 and
pass into the superheater zone 8, where the hot gases contact the
steam tubes 22. The steam tubes 22 extract heat from the hot gases
and increase the steam temperature. In the superheater zone 8, the
temperature of the hot gases ranges from approximately 975.degree.
C. to approximately 1320.degree. C. (from approximately
1800.degree. F. to approximately 2400.degree. F.). The hot gases
and entrained flyash particles may pass into the reheat zone 10,
which is a transition zone between the superheater zone 8 and the
economizer zone 12. Steam tubes 22 may also be present in the
reheat zone 10. The temperature in the reheat zone 10 may vary from
approximately 650.degree. C. to approximately 980.degree. C. (from
approximately 1200.degree. F. to approximately 1800.degree. F.).
The hot gases may be cooled in the economizer zone 12 by additional
steam tubes 22. The temperature of the hot gases in the economizer
zone 12 may range from approximately 535.degree. C. to
approximately 650.degree. C. (from approximately 1000.degree. F. to
approximately 1200.degree. F.).
[0036] The gases that exit the economizer zone 12 are referred to
in the art as flue gas. At this point, the flue gas may include
air, combustion products, such as water vapor, carbon dioxide,
mercury, and particulate matter. The flue gas may be substantially
free of the nitrogen-containing pollutants, the sulfur-containing
pollutants, and the HCl because these pollutants are removed in the
burner zone 6, the superheater zone 8, or the reheat zone 10. The
flue gas may be further cooled by gas-to-gas heat exchangers (not
shown) in the air preheat zone 14 to preheat the incoming
combustion air. The temperature of the flue gas in the air preheat
zone 14 may range from approximately 120.degree. C. to
approximately 230.degree. C. (from approximately 250.degree. F. to
approximately 450.degree. F.). The flue gas 24 may flow into the
gas cleaning unit 16, such as the baghouse or ESP, to remove the
particulate matter, such as the flyash 26. The flyash 26 may be
collected on a filter in the gas cleaning unit 16.
[0037] Since introducing the oil shale particles 4 into the PCC 2
utilizes many existing coal handling and processing technologies,
this method of decreasing levels of pollutants in the flue gas 24
may be readily implemented in existing PCCs because it does not
require the installation of new equipment. The use of the oil shale
particles 4 may also be incorporated into future PCC designs
without significant costs.
[0038] As described above, the oil shale particles 4 may be used to
decrease the amount of a single type of pollutant, such as a
nitrogen-containing pollutant, H.sub.2SO.sub.4, SO.sub.3, SO.sub.2,
H.sub.2S, COS, CS.sub.2, mercury, or mercury chloride, in the flue
gas 24. The oil shale particles 4 may also be used to decrease the
amount of different types of pollutants in the flue gas 24.
Therefore, the oil shale particles 4 may provide multi-pollutant
control. In addition, since pyrolization of the oil shale particles
4 produces porous sorbent particulates, higher pollutant loadings
may be achieved. As such, lower injection rates of the oil shale
particles 4 may be used, which decreases the amount of solid
material for disposal. While the oil shale particles 4 effectively
decrease the pollutant levels in the flue gas 24, the oil shale
particles 4 may also be used in combination with other technologies
to further decrease the amounts of the pollutants, such as the
LIMB, LIDS, SNCR, and NO.sub.x reburning technologies.
[0039] In addition to removing the pollutants, the oil shale
particles 4 may add enthalpy (i.e., heating value) since the oil
shale particles 4 are combusted along with the primary fuel. The
char particles and the heavy and light hydrocarbons, which are
produced during the combustion of the oil shale, may be fully or
partially combusted to provide additional heat, as shown by
Reactions 18-25:
C.sub.xH.sub.y+(x+.sup.y/4)O.sub.2.fwdarw.xCO.sub.2+.sup.y/2H.sub.2O
(18),
CO+1/2O.sub.2.fwdarw.CO.sub.2 (19),
C.sub.xH.sub.y+.sup.x/2O.sub.2.fwdarw.xCO+.sup.y/2H.sub.2 (20),
C.sub.xH.sub.y+xH.sub.2O.fwdarw.xCO+(x+.sup.y/2)H.sub.2 (21),
Char carbon+O.sub.2.fwdarw.CO.sub.2 (22),
Char carbon+1/2O.sub.2.fwdarw.CO (23),
Char carbon+CO.sub.2.fwdarw.2CO (24),
Char carbon+H.sub.2O.fwdarw.CO+H.sub.2 (25).
Reactions 18-20 may occur at a temperature greater than or equal to
approximately 200.degree. C. and reactions 19-25 may occur at a
temperature greater than or equal to approximately 400.degree. C.
While not all of Reactions 18-25 are exothermic, the reactions
either produce heat or produce reactive gases that may be used to
produce heat. The oil shale may provide a net positive heat of
combustion that ranges from approximately 4.7 MJ/kg (or
approximately 2,000 BTU/lb) to approximately 9.3 MJ/kg (or
approximately 4,000 BTU/lb). The energy provided by the combustion
of the oil shale may offset the heat lost due to the pollutant
sorption reactions.
[0040] The unreacted heavy and light hydrocarbons may be
substantially completely reacted in the superheater zone 8 or the
reheat zone 10 with excess oxygen (not shown) that is introduced.
In addition, supplementary oxygen (not shown) may be added to the
superheater zone 8 or the reheat zone 10 as needed to combust the
heavy and light hydrocarbons. Most combustion chambers are equipped
with soot blowing air injectors or air lances, which may be used to
adjust the oxygen concentration to achieve complete combustion of
the heavy and light hydrocarbons.
[0041] Using the oil shale particles 4 in the combustion process
may also improve the disposal of flyash produced during the
combustion of the primary fuel. The combustion of the oil shale may
also produce flyash 26 and slag 28 (coal and oil shale byproduct
mineral matter). The oil shale particles 4 may be used to make the
flyash 26 or the slag 28 suitable for disposal in a landfill.
During combustion, the oil shale particles 4 are calcined and
converted to a pozzolanic material that includes oxide compounds.
The pozzolanic material may encapsulate and immobilize the metals,
slag 28, and flyash 26 produced during the combustion. The flyash
26 may also be used as a road bed material or a construction
material.
[0042] While the invention may be susceptible to various
modifications and alternative forms, specific embodiments have been
shown by way of example in the drawings and have been described in
detail herein. However, it should be understood that the invention
is not intended to be limited to the particular forms disclosed.
Rather, the invention is to cover all modifications, equivalents,
and alternatives falling within the spirit and scope of the
invention as defined by the following appended claims.
* * * * *