Document ID: EPA-HQ-RCRA-2008-0329-0214
Agency: epa
Document Type: Supporting & Related Material
Title: 
Posted Date: 2009-01-02T05:00Z

http://www.patentstorm.us/patents/6637354/fulltext.html

US Patent 6637354 - Coal combustion products recovery process

Abstract

A process for recovering the byproducts of a process that burns coal and
for reusing the byproducts is disclosed. The process includes the steps
of identifying a disposal site that contains the byproducts (typically
flyash and bottom ash), removing at least a portion of the byproducts
from the disposal site, analyzing a sample of the portion of the
byproducts to determine the loss on ignition of the portion of the
byproducts, introducing the portion of the byproducts along with
pulverized coal into a pulverized coal   HYPERLINK
"http://www.patentstorm.us/patents/6637354/fulltext.html" \t "_top" 
furnace  if the portion of byproducts have a loss on ignition greater
than or equal to a predetermined loss on ignition value (typically
greater than or equal to 1 to 5%), and burning the portion of

the byproducts in the furnace with the pulverized coal to render the
byproducts into a commercially valuable fly ash and bottom ash having
very low loss on ignition, typically lower than 3%. 

Claims

What is claimed is:

1. A process for recovering coal combustion products and reusing the
coal combustion products, the process comprising:

(a) identifying a disposal site that contains coal combustion products;

(b) removing at feast a portion of the coal combustion products from the
disposal site;

(c) introducing the portion of the coal combustion products along with
pulverized coal into a pulverized coal fired furnace; and

(d) burning the portion of the coal combustion products in the furnace
with the pulverized coal,

wherein step (a) further comprises:

identifying a location of the coal combustion products in the disposal
site by a soils investigation.

2. A process for recovering coal combustion products and reusing the
coal combustion products, the process comprising:

(a) identifying a disposal site that contains coal combustion products;

(b) removing at least a portion of the coal combustion products from the
disposal site;

(c) introducing the portion of the coal combustion products along with
pulverized coal  into a pulverized coal fired furnace; and

(d) burning the portion of the coal combustion products in the furnace
with the pulverized coal, and

separating the portion of coal combustion products from materials other
than coal combustion products after step (b) and before step (c).

3. A process for recovering coal combustion products and reusing the
coal combustion products, the process comprising:

(a) identifying a disposal site that contains coal combustion products;

(b) removing at least a portion of the coal combustion products from the
disposal site;

(c) introducing the portion of the coal combustion products along with
pulverized coal into a pulverized coal fired furnace;

(d) burning the portion of the coal combustion products in the furnace
with the pulverized coal, and analyzing a sample of the portion of the
coal combustion products to determine the loss on ignition of the
portion of the coal combustion products after step (b) and before step
(c), wherein the portion of the coal combustion products is introduced
along

with pulverized coal into the pulverized coal fired furnace if the
portion of the coal combustion products has a loss on ignition greater
than or equal to a predetermined loss on ignition value, and wherein the
predetermined loss on ignition value is 1%.

4. The process of claim 3 wherein:  the predetermined loss on ignition
value is 5%.

5. A process for recovering coal combustion products and reusing the
coal combustion products, the process comprising:

(a) identifying a disposal site that contains coal combustion products;

(b) removing at least a portion of the coal combustion products from the
disposal site;

(c) analyzing a sample of the portion of the coal combustion products to
determine the loss on ignition of the portion of the coal combustion
products;

(d) adding the portion of the coal combustion products to a supply of
coal to create a recovered coal combustion products and coal mixture if
the portion of the coal combustion products has a loss on ignition
greater than or equal to a predetermined loss on ignition value;

(e) pulverizing the recovered coal combustion products and coal mixture
to produce a pulverized mixture;

(f) introducing the pulverized mixture into a pulverized coal fired
furnace; and

(g) burning the pulverized mixture in the furnace, wherein the
predetermined loss on ignition value is 1%.

6. The process of claim 5 wherein:  the predetermined loss on ignition
value is 5%.

7. A process for recovering coal combustion products and reusing the
coal combustion products, the process comprising:

(a) identifying a disposal site that contains coal combustion products;

(b) removing at least a portion of the coal combustion products from the
disposal site;

(c) analyzing a sample of the portion of the coal combustion products to
determine the loss on ignition of the portion of the coal combustion
products;

(d) adding the portion of the coal combustion products to a supply of
coal to create a recovered coal combustion products and coal mixture if
the portion of the coal combustion products has a loss on ignition
greater than or equal to a predetermined loss on ignition value;

(e) pulverizing the recovered coal combustion products and coal mixture
to produce a pulverized mixture;

(f) introducing the pulverized mixture into a pulverized coal fired
furnace; and

(g) burning the pulverized mixture in the furnace, wherein a fly ash
having a loss on ignition of less than about 3% is produced by the
process.

8. A process for recovering coal combustion products and reusing the
coal combustion products, the process comprising:

(a) identifying a disposal site that contains coal combustion products;

(b) removing at least a portion of the coal combustion products from the
disposal site;

(c) analyzing a sample of the portion of the coal combustion products to
determine the loss on ignition of the portion of the coal combustion
products;

(d) adding the portion of the coal combustion products to a supply of
coal to create a recovered coal combustion products and coal mixture if
the portion of the coal combustion products has a loss on ignition
greater than or equal to a predetermined loss on ignition value;

(e) pulverizing the recovered coal combustion products and coal mixture
to produce a pulverized mixture;

(f) introducing the pulverized mixture into a pulverized coal fired
furnace;

(g) burning the pulverized mixture in the furnace, and

separating the portion of coal combustion products from materials other
than coal combustion products after step (b) and before step (c).

9. A process for recovering coal combustion products and reusing the
coal combustion products, the process comprising:

(a) identifying a disposal site that contains coal combustion products;

(b) removing at least a portion of the coal combustion products from the
disposal site;

(c) analyzing a sample of the portion of the coal combustion products to
determine the loss on ignition of the portion of the coal combustion
products;

(d) if the portion of the coal combustion products has a loss on
ignition greater than 1% adding the portion of the coal combustion
products to a supply of subbituminous coal that generates an ash having
a loss on ignition less than 5% upon burning to create a recovered coal
combustion products and coal mixture;

(e) pulverizing the recovered coal combustion products and coal mixture
to produce a pulverized mixture;

(f) introducing the pulverized mixture into a pulverized coal fired
furnace; and

(g) burning the pulverized mixture in the furnace, whereby a fly ash
having a loss on ignition of less than about 3% is produced.

10. The process of claim 9 further comprising:  separating the portion
of coal combustion products from materials other than coal combustion
products after step (b) and before step (c).

11. The process of claim 10 wherein:  the portion of the coal combustion
products is added to the supply of subbituminous coal in the range of
0.5% to 3.5% by weight of the portion of recovered coal combustion
products to the subbituminous coal.

12. A process for recovering coal combustion products and reusing the
coal combustion products, the process comprising:

(a) identifying a disposal site that contains coal combustion products;

(b) removing at least a portion of the coal combustion products from the
disposal site;

(c) analyzing a sample of the portion of the coal combustion products to
determine the loss on ignition of the portion of the coal combustion
products;

(d) if the portion of the coal combustion products has a loss on
ignition greater than 1%, adding the portion of the coal combustion
products to a supply of coal that generates an ash having a loss on
ignition less than 5% upon burning to create a recovered coal combustion
products and coal mixture;

(e) pulverizing the recovered coal combustion products and coal mixture
to produce a pulverized mixture;

(f) introducing the pulverized mixture into a pulverized coal fired
furnace; and

(g) burning the pulverized mixture in the furnace, whereby a fly ash
having a loss on ignition of less than about 3% is produced.

13. A process for recovering coal combustion products and reusing the
coal combustion products, the process comprising:

(a) identifying a disposal site that contains coal combustion products;

(b) removing at least a portion of the coal combustion products from the
disposal site;

(c) introducing the portion of the coal combustion products along with
pulverized coal into a pulverized coal fired furnace; and

(d) burning the portion of the coal combustion products in the furnace
with the pulverized coal, wherein step (c) comprises:  separating the
portion of the coal combustion products into a first lot of the coal
combustion products and a second lot of the coal combustion

products, the first lot having particle sizes greater than the second
lot; adding the first lot of the coal combustion products to a supply of
coal to create a recovered coal combustion products and coal mixture;
pulverizing the recovered coal combustion products and coal mixture to
produce a pulverized mixture;

Introducing the pulverized mixture into the pulverized coal fired
furnace; and injecting the second lot of the coal combustion products
into the pulverized coal fired furnace.

14. A process for recovering coal combustion products and reusing the
coal combustion products, the process comprising:

(a) identifying a disposal site that contains coal combustion products;

(b) removing at least a portion of the coal combustion products from the
disposal site;

(c) introducing the portion of the coal combustion products along with
pulverized coal into a pulverized coal fired furnace; and

(d) burning the portion of the coal combustion products in the furnace
with the pulverized coal,

wherein step (c) comprises:

separating the portion of the coal combustion products into a first lot
of the coal combustion products and a second lot of the coal combustion
products, the first lot being classified as a non-hazardous material
under existing environmental regulations at the site of recovery in step
(a) and the site of burning in step (d); and introducing the first lot
of the coal combustion products along with pulverized coal into the
pulverized coal fired furnace.

15. The process of claim 14 wherein:  the first lot is classified as a
non-hazardous material by way of a TCLP test.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to the recovery of coal combustion products from
landfills, and more particularly to a process for recovering coal ash
from landfills and reburning the coal ash in a coal fired boiler.

2. Description of the Related Art

Coal fired boilers are widely used to generate steam for producing
electricity. A common form of boiler uses a pulverized coal that is
injected into a furnace. Millions of tons of coal ash result each year
from such operations. The coal ash includes fly ash with a minor

proportion of bottom ash. Some of the coal ash is commercially usable in
  HYPERLINK "http://www.patentstorm.us/patents/6637354/fulltext.html" \t
"_top"  concrete , concrete products, cement production, sewage sludge
stabilization, pavement base materials, lightweight aggregate, and other
miscellaneous purposes. The remaining coal ash must generally be
disposed of by landfilling since it has no commercial value.

A principal reason for a lack of commercial value for coal ash is the
presence of unburned carbon in the ash. (When using the term "carbon
content in ash", the carbon content is as measured by loss on ignition.)
According to ASTM (American Society for Testing and Materials) C 618
"Standard Specification for Fly Ash and Raw or Calcined Natural Pozzolan
for Use as a Mineral Admixture in Portland Cement Concrete", a fly ash
must have a loss on ignition (LOI) value no higher than 6% for use in
concrete. An upper limit of 3% LOI is more realistic. Higher loss on
ignition ash cannot be used because of color problems and concerns for
durability under freezing and thawing conditions. The residual carbon
content in the coal ash depends upon a variety of factors including base
line furnace operation and boiler design. It also depends upon the
source

of the coal fuel. For example, subbituminous western coal, when burned,
will typically result in a low carbon ash with a loss on ignition of
less than 5%. However, when bituminous coal is burned, a higher carbon
ash with a loss on ignition significantly greater than 5% is generally
produced as a byproduct.

Because of the widespread use of coal fired boilers to generate steam
for producing electricity, it can be appreciated that significant
volumes of coal ash have been deposited in landfills over the years,
particularly in regions where electricity was or is still being
generated by burning bituminous coal in a coal fired boiler. In
addition, the use of greenhouse   HYPERLINK
"http://www.patentstorm.us/patents/6637354/fulltext.html" \t "_top"  gas
emission  technologies, such as low NOx burners, have a tendency to
increase the loss on ignition of a coal fired boiler's fly ash and
thereby make the fly ash unusable because of high carbon content (e.g.,
LOI>6%). As a result, a coal fired boiler using greenhouse gas emission 
 HYPERLINK "http://www.patentstorm.us/patents/6637354/fulltext.html" \t
"_top"  technologies  will also produce coal ash that must be
landfilled. It is also well known that landfill space is rapidly
dwindling in many regions

and that the construction of new landfills is very costly and, in some
regions, is not even an option because of the scarcity of available
landfill sites.

Accordingly, there is a need for a process that can recover coal
combustion products from a landfill in order to free up landfill space
for the disposal of other products, and thereby eliminate the need for
the construction of additional landfills. More particularly, there is a
need for a process that can recover coal combustion products from a
landfill in order to free up landfill space and that can cost
effectively produce commercially usable products such that the process
is economically attractive.

SUMMARY OF THE INVENTION

The foregoing needs are met by a process according to the invention
wherein a disposal site that contains coal combustion products is
identified, the coal combustion products are recovered from the disposal
site, and the recovered coal combustion products are reused. In one
version of the invention, the process comprises using the coal
combustion products

removed from the disposal site as an aggregate for   HYPERLINK
"http://www.patentstorm.us/patents/6637354/fulltext.html" \t "_top" 
construction  projects. In another version of the invention, the step of
reusing the coal combustion products comprises: introducing pulverized
coal into a pulverized coal fired furnace; introducing the recovered
coal combustion products into the pulverized coal fired furnace; and
burning the recovered

coal combustion products in the furnace along with the pulverized coal
in a manner such as that described in U.S. Pat. No. 5,992,336 and PCT
International Publication Number WO 98129687, which are incorporated
herein by reference.

In yet another version of the invention, the step of reusing the coal
combustion products comprises: analyzing the recovered coal combustion
products to determine the loss on ignition of the recovered coal
combustion products; introducing pulverized coal into a pulverized coal
fired furnace, the pulverized coal typically being subbituminous coal or

other coal which generates low loss on ignition ash upon burning;
introducing the recovered coal combustion products into the pulverized
coal fired furnace if the recovered coal combustion products have a loss
on ignition greater than or equal to about 5%, and reburning any
recovered coal combustion products introduced into the furnace with the
pulverized coal (the recovered coal combustion products typically being
in the range of 0.5% to 3.5% by weight of the pulverized coal) to
produce a coal ash having a low loss on ignition. In this version of the
invention, landfilled coal combustion products which have a loss on
ignition greater than or equal to about 5% (and therefore, limited
commercial value) are reburned to produce a coal ash which has a loss on
ignition less than about 3% (and therefore commercial value in
concrete). As a result, this version of the invention provides a number
of key advantages. For instance, the invention: (1) frees up landfill
space; (2) transforms coal combustion products with no commercial value
into coal ash with significant commercial value; (3) recovers lost
energy remaining in the

coal ash; and (4) removes potential future environmental risk associated
with leaching from non-state-of-the-art landfills and ash storage ponds
and impoundments.

In still another version of the invention, the step of reusing the coal
combustion products comprises: analyzing the recovered coal combustion
products to determine the loss on ignition of the recovered coal
combustion products; introducing pulverized coal into a pulverized coal
fired furnace, the pulverized coal typically being subbituminous coal or

other coal which generates low loss on ignition ash upon burning;
introducing the recovered coal combustion products into the pulverized
coal fired furnace if the recovered coal combustion products have a loss
on ignition greater than or equal to about 1%, and reburning any
recovered coal combustion products introduced into the furnace with the
pulverized coal (the recovered coal combustion products typically being
in the range of 1% to 3.5% by weight of the pulverized coal) to produce
a coal ash having a low loss on ignition.

It is therefore an advantage of the present invention to provide a coal
combustion products recovery process that removes and recovers coal
combustion products from a landfill and characterizes the recovered coal
combustion products so that the recovered coal combustion products may
be put to beneficial use.

It is another advantage of the present invention to provide a coal
combustion products recovery process that serves to preserve licensed
landfill airspace.

It is still another advantage of the present invention to provide a coal
combustion products recovery process that reduces the need for new
gravel pits, stone quarries and landfill sites.

It is yet another advantage of the present invention to provide a coal
combustion products recovery process that allows for the recovery and
reburning of high loss on ignition landfilled coal combustion products,
such as formed from a pulverized coal furnace burning bituminous coal,
to render the coal combustion products into a commercially valuable fly
ash and bottom ash having very low loss on ignition.

It is another advantage of the present invention to provide a coal
combustion products recovery process that preserves present coal
reserves by recovering heat, as commonly measured by British thermal
units (Btu), from reclaimed coal combustion products.

It is still another advantage of the present invention to provide a coal
combustion products recovery process that produces a low loss on
ignition coal ash that may be substituted for portland cement thus
offsetting additional portland cement production and thereby reducing  
HYPERLINK "http://www.patentstorm.us/patents/6637354/fulltext.html" \t
"_top"  air emissions  from the portland cement production process.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features, aspects, objects, and advantages of the
present invention will become better understood upon consideration of
the following detailed description, appended claims and accompanying
drawings where:

FIG. 1 is a view in perspective of a portion of a typical pulverized
coal fired furnace which may be modified to carry out the method of the
present invention;

FIG. 2 is a partial view in vertical cross-section of the furnace of
FIG. 1 illustrating the location of fly ash injection nozzles;

FIG. 3 is a view in elevation of an injection pipe for injecting coal
ash into the furnace of FIG. 2; and

FIG. 4 is a schematic diagram of an installation for carrying out the
method of this invention in which coal ash is injected through separate
injection lances into the pulverized coal furnace.

FIG. 5 is a flow chart illustrating the steps in the process according
to the invention.

It should be understood that the drawings are not necessarily to scale
and that the embodiments are sometimes illustrated by graphic symbols,
phantom lines, diagrammatic representations and fragmentary views. In
certain instances, details which are not necessary for an understanding
of the present invention or which render other details difficult to
perceive may have been omitted. It should be understood, of course, that
the invention is not necessarily limited to the particular embodiments
illustrated

herein.

DETAILED DESCRIPTION OF THE INVENTION

The invention provides a process for reclaiming and reusing coal
combustion products that have been previously placed in a licensed or
unlicensed landfill or disposal area. As used herein, a disposal area
also includes ponded coal combustion products. While numerous uses of
the reclaimed coal combustion products are contemplated, the reclaimed
coal combustion products are particularly useful as: (1) an alternative
sand, gravel or crushed stone material for various applications such as
road base and

sub-base, structural fill, backfill, drainage media, aggregate for
concrete, asphalt and   HYPERLINK
"http://www.patentstorm.us/patents/6637354/fulltext.html" \t "_top" 
masonry , abrasives/traction, and manufactured soil products; and (2) a
supplementary fuel and feedstock for production of low carbon (less than
about 3%) coal combustion products for various uses. As used herein,
"coal combustion products" means any byproduct of a process that burns
coal.

One version of a coal combustion products recovery, reclamation and
reuse process according to the invention includes the following steps.
First, the location of previously landfilled or disposed coal combustion
products is identified. After location of a landfill or disposal area
containing coal combustion products, the quantity and location of coal
combustion products in the landfill or disposal area is determined from
prior records

and/or from a conventional soils investigation.

Samples of the coal combustion products are then obtained using
conventional landfill boring and sampling techniques. This step is
particularly important as the coal combustion products placed in
existing landfills may include high-volume coal combustion products such
as fly ash, bottom ash, and boiler slag, and low-volume coal combustion
products such as   HYPERLINK
"http://www.patentstorm.us/patents/6637354/fulltext.html" \t "_top" 
cooling tower  sludge and sludge from coal pile runoff. In the most
preferred version of the invention detailed below, it is preferred that
the reclaimed coal combustion products only contain coal combustion
by-products and that the coal ash not be commingled with other municipal
waste, demolition debris, or hazardous waste.

After obtaining samples, the samples are then characterized for
potential consistency and categorization to environmental regulatory
parameters. For example, the samples may be tested using total elemental
analysis techniques and leach parameters analysis techniques to
determine the chemical nature of the coal combustion products in the
landfill. In

certain situations, a TCLP test may be run on the coal combustion
products to verify that the coal combustion products have not been
commingled with other materials that may be classified under
environmental regulations as a hazardous material. Accordingly, the TCLP
test can verify that the coal combustion products are a non-hazardous
material under existing environmental regulations at the site of
recovery and subsequent burning.

Preferably, an ASTM D 3987 Water Leach Test is used on the samples to
characterize potential recovered coal combustion product leachate
characteristics for soil and structural fill type applications. Physical
data on consistency and grain size distribution for the coal combustion
products may also be obtained from the samples. For example, an ASTM D
4749 Sieve Analysis may be used on the samples. Preferably, an elemental

and physical characteristic analysis of the recovered coal combustion
products can be compared to an elemental and physical characteristic
analysis of bottom ash and fly ash recovered directly from a coal fired
boiler.

After the samples of the coal combustion products obtained using the
boring techniques have been analyzed, an end use for the coal combustion
products can be determined based on this data. For instance, if the
original coal combustion products contained cementitious properties,
they may be suitable for use as an alternative material for sand,
gravel, or crushed stone; or if the original coal combustion products
were high in residual

energy content, i.e., the original coal combustion products have a high
loss on ignition (e.g., greater than 5%), they may be suitable for use
as a supplementary fuel as will be described in further detail below.

After an end use for the coal combustion products has been determined,
an engineered and staged approach for removal of coal combustion
products in a nuisance free manner is identified. For example, in one
version of the invention, this involves the staged and planned removal
of cover materials such as topsoil, clay or synthetic liners, fill, and
rooting zone cover materials if these cover materials are placed over
the coal combustion

products being reclaimed. Alternatively, the coal combustion products
may not be covered in the landfill and therefore, it will not be
necessary to remove cover materials. Dust is minimized by using known
techniques (such as watering) especially when excavated materials dry
out, and surface water runoff is redirected to avoid erosion and loss of
the coal combustion products being reclaimed. Sedimentation controls are
also used, and leachate collection and treatment techniques are used to
address potential nuisance situations, in one version of the invention,
engineering plans for the final use and restoration of the property are
developed. In addition, it may be necessary to obtain local and state
approvals as required to reclaim and recover the subject coal combustion

products.

After development of a coal combustion products recovery plan,
excavation and processing of the coal combustion products begins. In one
version of the invention, excavation is performed using standard
earthmoving equipment such as backhoes, excavators, and scrapers.
Preferably, dust control is performed by use of water or commercial dust
abatement compounds that are compatible with coal combustion products,
the environment and the ultimate end use of the coal combustion
products. The

excavated coal combustion products are then run through crushing and/or
screening equipment to remove lumps and chunks as well as any foreign
materials. Often, the need for crushing will be dependent on the
cementitious qualities of previously placed materials. Some coal
combustion products contain large amounts of calcium oxide (CaO) which
can hydrate and form hardened masses. These materials when crushed can
form

alternative materials for sand, gravel, and crushed stone based on their
gradations and hardness. In addition, screening may not be necessary in
certain cases where the end use does not require specific particle size
distributions.

In one version of the invention, the coal combustion products are stored
in a pile in a designated area of the landfill, and a representative
sample is obtained from the pile for testing using testing guidelines
such as those presented in ASTM D 75, "Standard Practice for Sampling
Aggregates". In another version of the invention, ASTM D 2234 "Standard
Practice for Collection of Gross Sample of Coal" is used to collect
samples from a transfer point where the coal combustion products fall
onto a conveyor during the reclamation operation. Testing is preferably
performed on the samples to measure the following parameters: (1)
Leachable--Antimony, Arsenic, Beryllium, Cadmium, Lead, Iron, Thallium
and pH; (2) Total--Arsenic, Beryllium and Sulfur; and (3)
Dissolved--Aluminum, Antimony and Barium. Of course, additional tests
can be performed to

determine the concentration of additional elements and organic
compounds. Preferably, the samples are also evaluated for homogeneity as
homogeneous coal combustion products are preferred. Material that is not
suitable for beneficial use (e.g. debris or soil) can be separated from
reusable materials. The reclaimed and processed coal combustion products
are then stockpiled, and loaded into trucks for hauling in accordance
with all

applicable regulations.

In another version of the invention, the recovered coal combustion
products are analyzed for loss on ignition values, and in the event that
the loss on ignition values are greater than or equal to about 5%, the
recovered coal combustion products are reburned as described below to
render the recovered coal combustion products into a usable fly ash
having a low loss on ignition (less than about 3%). While recovered coal
combustion products having loss on ignition values greater than or equal
to about 5% provide

for optimum burning, recovered coal combustion products having loss on
ignition values greater than or equal to about 1% can be reburned as
described below to render the recovered coal combustion products into a
usable fly ash having an even lower loss on ignition, typically less
than about %%. As detailed above, low loss on ignition fly ash can then
be used in concrete. In this most preferred version of the invention,
the

recovered coal combustion products are burned as a supplementary fuel in
a pulverized coal furnace. However, the results of the analyses of the
recovered coal combustion products are first used to perform
calculations for air emissions expected upon burning of the recovered
coal combustion as a supplementary fuel in the pulverized coal furnace,
and all required air permits are obtained.

The recovered coal combustion products to be reburned can be added to
loaded coal cars using a front end loader. The recovered coal combustion
products can also be added to the coal prior to unloading in a rotary
car unloader. The coal cars can then be unloaded in a normal manner and
the coal can be transported by a conveyor system to the power plant's
coal silos. The recovered coal combustion products will typically have a
larger

particle size and may require grinding to reduce the particle size of
the recovered coal combustion products to the size of the pulverized
coal stream. The preferred approach for handling of the recovered coal
combustion products is to add it to the supply of coal prior to the coal
being ground. However, the recovered coal combustion products may be

introduced directly into a boiler along with the other fuel.

Therefore, it can be seen that tests for the particle size of the
recovered coal combustion products may be particularly valuable. For
instance, recovered ash with a larger particle size may require grinding
to reduce it to the size of a pulverized coal stream in a typical
pulverized coal furnace. In this case, the preferred approach for
handling of the recovered ash is to add it to the store of coal prior to
the coal being ground. Ideally, the recovered ash and coal mixture has a
grindability index on the Hardgrove scale which is acceptable. Smaller
particle size recovered ash typically cannot be introduced into the coal
upstream of the mills or other pulverizers because of dusting and mixing
problems. However, smaller particle size recovered ash can be introduced
with the pulverized coal stream entering the pulverizer classifiers.
This has the advantage of thorough mixing upstream of the burners and
would require only a slight additional volume of air to transport the
recovered ash. Smaller particle size recovered ash can be introduced
with the pulverized

coal stream at each burner location. Since each classifier typically
feeds several burners, the number of feed points for the smaller
particle size recovered ash would be greater. Smaller particle size
recovered ash can also be introduced with the secondary air flow stream
as it enters the pulverized coal furnace. The secondary air flow with
the smaller particle size recovered ash provides sufficient mixing. The
smaller particle size recovered ash can be introduced through
heat-resistant or stainless pipes. The smaller particle size recovered
ash can also be introduced into the furnace either above or adjacent to
the existing burner level through separate pipes. Injection points
through a waterwall could be used, although this may require
modifications of the waterwalls in the boilers. The classification of
recovered ash into higher and smaller particle sizes will depend on the
operating characteristics of the pulverized coal furnace being used.

FIG. 1 illustrates a portion of a typical pulverized coal furnace 20
that may be used to carry out the most preferred version of the
invention. The pulverized fuel system includes coal hoppers 21 which
connect through a coal spout 22 to a gravimetric feeder 23 which leads
to a crusher   HYPERLINK
"http://www.patentstorm.us/patents/6637354/fulltext.html" \t "_top" 
dryer  24. The crusher dryer 24 extends to a bypass damper 25 which
connects to a ball mill 26. The pulverized coal from the ball mill 26
and coal dust from

the bypass damper 25 are discharged through coal discharge ducts 27
which lead to a centrifugal classifier 28. In the classifier 28,
oversized particles are returned to the ball mill 26 for further
processing while proper size particles are fed through coal pipes 29 to
flame burners 30 that extend into the side of the furnace 20. Stop
valves 31 are inserted

in the coal pipe lines 29. A primary air fan 35 forces air through an
air heater 36 to a primary air duct 37. A tempering air duct 38 also
extends from the fan 35 to the furnace 20. Hot air from the primary air
duct 37 is ducted through a hot air damper 39 to the crusher dryers 24
and tempering air is ducted through a damper 40 also to the crusher
dryer 24. The air is used to transport the pulverized coal through the
coal pipes 29 to the

burners 30.

Recovered ash having larger particle sizes may be introduced into the
coal hoppers 21 to be processed along with the coal being pulverized.
Recovered ash having smaller particle sizes may be added to the
pulverized coal stream at the classifiers 28 or at the coal pipes 29.
(The classification of recovered ash into higher and smaller particle
sizes will depend on the operating characteristics of the pulverized
coal furnace being used.) In certain circumstances, the recovered ash
having smaller particle sizes is separately dried and pulverized before
being added to the pulverized coal stream at the classifiers 28 or at
the coal pipes 29. The smaller particle size recovered ash (which may
have been separately dried and pulverized) can be injected separately
into the furnace 20. Such an arrangement is shown in FIGS. 2 and 4. FIG.
2 shows the typical entry point of the burners 30 into the furnace 20.
Injection pipes 10 or lances like that shown in FIG. 3 are disposed
slightly above the location of the coal burners 30. FIG. 4 shows a
schematic arrangement for injecting the smaller particle size recovered
ash through separate injector pipes or lances into a furnace. Referring
to FIG. 4, a smaller particle size recovered ash storage silo 45
receives ash through an inlet 46. A bag filter 47 is attached to the top
of the silo 45. A coal spout 48 including a cut-off gate 49 feeds a
gearmotor-type feeder blower 50 which leads to an intake tee 51. An air
blower 52 also connects to the intake tee 51. Air from the

blower 52 and smaller particle size recovered ash from the feeder blower
50 are carried through a steel pipe 53 to a splitter 54 which divides
the flow in half and feeds two additional splitters 55 where the flow is
again divided to four splitters 56 each of which feeds an injection
lance 57 which enters the furnace 20. An air cylinder-operated valve 58
is disposed in each of the lines leading to an injection lance 57. A
second ash spout

60 extends from the ash silo 45 to feed a similar injection system for
the other side of the furnace 20.

The following Example is presented to illustrate the invention and is
not intended to limit the invention in any way.

EXAMPLE

Approximately 7,000 cubic yards of coal combustion products were
recovered as part of a remediation project at a closed landfill site in
Waukesha, Wis., USA. It was determined from records that the coal
combustion products comprised fly ash and bottom ash from a Wisconsin  
HYPERLINK "http://www.patentstorm.us/patents/6637354/fulltext.html" \t
"_top"  Electric Power  Plant, and were disposed in the landfill from
1969 to 1978. A sample of the ash was analyzed using ASTM Specifications
D 3173, D 3174, D 3175, D

3172, D 3286, and D 4239, and had the following proximate analysis shown
in Table 1:

 TABLE 1

 Recovered Coal Combustion Products Proximate Analysis %

 As Received Dry Basis

 % Moisture 24.66 xxxxx

 % Ash 69.67 92.47

 % Volatile 4.74 6.29

 % Fixed Carbon 0.93 1.24

 Total 100.00% 100.00%

 Btu/lb. 382 507

 Loss on Ignition 5.67% 7.53%

 % Sulfur 0.28 0.37

 Type of Ash: Bituminous

Upon review of the chemical and physical characteristics of the sample
of recovered ash of Table 1, it was determined that the recovered coal
combustion products could be introduced along with pulverized coal into
a pulverized coal fired furnace and burned to produce a commercially
marketable coal ash. Accordingly, the recovered coal combustion products
were processed as follows. The coal combustion products excavated from
the Waukesha, Wis., USA landfill were first screened to remove large
chunks and any foreign materials. The screened recovered coal combustion
products were then transported to a receiving hopper which then conveyed
the wet/moist recovered coal combustion products (comprising a mixture
of bottom ash and fly ash because they were commingled in this landfill)
to a 125 ton capacity storage silo where the recovered coal combustion
products were then conveyed onto a coal belt at a set addition rate of
1%. The point of entry onto the coal belt was after the coal car dumper
but before the primary coal crushers. After being crushed with the coal,
the recovered coal combustion products were then transported into the
plant coal silos where the recovered coal combustion products were fed
to ball mills. The coal and wet/moist recovered coal combustion products
mixture was further pulverized in the coal ball mills and then
transported into

the furnace as fuel.

Thus, there has been provided a coal combustion products recovery
process that allows for the recovery and reburning of high loss on
ignition landfilled coal combustion products to render the coal
combustion products into a commercially valuable fly ash and bottom ash
having very low loss on ignition. This process frees up landfill space,
transforms coal combustion products with no commercial value into coal
ash with

significant commercial value, recovers lost energy remaining in the coal
ash, and removes potential future environmental risk associated with
leaching from non-state-of-the-art landfills.

Although the present invention has been described with reference to
certain versions, the invention can be practiced by other than the
described versions, which have been presented for purposes of
illustration and not of limitation. Therefore, the scope of the appended
claims should not be limited to the description of the preferred
embodiments contained herein.

* * * * *

Other References

Bruce W. Ramme et al., "Use of Wisconsin Electric Bottom Ash Sand and
Gravel as Sub-Base and Base Material for Rigid and Flexible Pavements
and Floors", ASCE Materials Engineering Division, May 10, 1999, pp. 1-16

American Society for Testing and Materials, "Standard Specification for
Fly Ash and Raw or Calcined Natural Pozzolan for Use as a Mineral
Admixture in Portland Cement Concrete", Designation: C 618-99, Jul. 1999