U.S. patent application number 09/915779 was filed with the patent office on 2002-02-28 for filler material mixture.
Invention is credited to Hume, John D., Mainieri, John F., Ridgeway, Russel F..
Application Number | 20020023537 09/915779 |
Document ID | / |
Family ID | 23155244 |
Filed Date | 2002-02-28 |
United States Patent
Application |
20020023537 |
Kind Code |
A1 |
Ridgeway, Russel F. ; et
al. |
February 28, 2002 |
Filler material mixture
Abstract
A low density ash particle separation and collection method and
device for separating low density particles, primarily frothy-solid
particles with internal and external porosity and thick walled
hollow particles, from the overall mixture of higher density
particles including raw fly ash as produced by coal fired power
plants. Specifically, the invention relates to a device and method
for separating and collecting the low density fly ash fraction
composed of thick walled hollow fly ash particles and frothy
generally solid particles with both internal and external porosity
and a relatively small amount of cenospheres from the overall
mixture of ash particles composing raw ash as produced by coal
fired power plants by de-energizing one or more fields of large
electrostatic precipitators during electrostatic precipitation of
the ash resulting in the dropping out of the lower density
particles in the hoppers located below the de-energized field(s) of
the electrostatic precipitator.
Inventors: |
Ridgeway, Russel F.;
(Reynoldsburg, OH) ; Mainieri, John F.;
(Granville, OH) ; Hume, John D.; (New Albany,
OH) |
Correspondence
Address: |
SAND & SEBOLT
4801 DRESSLER RD., N.W.
SUITE 194
CANTON
OH
44718
US
|
Family ID: |
23155244 |
Appl. No.: |
09/915779 |
Filed: |
July 26, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
09915779 |
Jul 26, 2001 |
|
|
|
09299538 |
Apr 26, 1999 |
|
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Current U.S.
Class: |
95/69 |
Current CPC
Class: |
C04B 18/027 20130101;
Y02W 30/92 20150501; B03C 3/88 20130101; Y02W 30/91 20150501; C04B
18/027 20130101; C04B 18/08 20130101; C04B 18/082 20130101 |
Class at
Publication: |
95/69 |
International
Class: |
B03C 003/00 |
Claims
1. A method of separating a low density fly ash fraction from an
overall group of fly ash entrained in a gas stream comprising the
steps of: passing the gas through a duct having a first area;
passing the gas stream from the duct through an expansion nozzle;
passing the gas stream through the expansion nozzle and into a
hollow body having a second area, whereby the second area is larger
than the first area; decelerating the gas stream as it enters the
expansion nozzle to separate out low density ash particles; and
collecting the low density ash particles from a hopper positioned
adjacent the expansion nozzle.
2. A method as defined in claim 1 in which the second area is in
the range of from six to twenty-five times larger than the area of
the duct.
3. A method as defined in claim 2 in which the second area is in
the range of from nine to fifteen times larger than the first
area.
4. The method as defined in claim 1 in which the expansion nozzle
is positioned adjacent an electrostatic precipitator.
5. The method as defined in claim 1, comprising the further steps
of positioning the duct adjacent an electrostatic precipitator
having at least one electrostatic field; de-energizing at least one
electrostatic field in the electrostatic precipitator; and allowing
the low density ash to fall into the hopper positioned adjacent the
expansion nozzle.
6. The method as defined in claim 5 in which the de-energized field
is the first field positioned adjacent the expansion nozzle in the
electrostatic precipitator.
7. The method as defined in claim 5 in which at least the first two
fields are de-energized in the electrostatic precipitator.
8. The method as defined in claim 1 in which the electrostatic
precipitator has a maximum capacity for a pre-determined gas stream
level, and in which the electrostatic precipitator is oversized in
capacity with respect to said pre-determined gas stream level
flowing thereby.
9. The method as defined in claim 1 in which the electrostatic
precipitator collects ash from the overall gas stream having a
first ash density, and in which the low density ash collected in
the hopper positioned adjacent the expansion nozzle is at least ten
(10) percent lower in density than the first ash density produced
by the electrostatic precipitator.
10. The method as defined in claim 9 in which the electrostatic
precipitator collects ash from the overall gas stream having a
first ash density, and in which the low density ash collected in
the hopper positioned adjacent the expansion nozzle is at least
thirty-five (35) percent lower in density than the first ash
density produced by the electrostatic precipitator.
11. The method as defined in claim 9 in which the low density ash
that is collected has a specific gravity of 2.0 or less.
12. The method as defined in claim 11 in which the low density ash
collected in the hopper positioned adjacent the expansion nozzle
has a specific gravity in the range of from 1.6 to 1.99.
13. The method as defined in claim 1 in which the low density ash
that is collected in the hopper positioned adjacent the expansion
nozzle has a particle size distribution that is predominantly in
the range of from between 30 microns to 400 microns.
14. The method as defined in claim 13 in which the low density ash
that is collected includes a major amount of frothy, semi-solid
particles with both internal and external porosity and a minor
amount of hollow particles with thick walls containing internal and
external pores.
15. The method as defined in claim 1 in which the low density ash
that is collected includes a major amount of frothy, semi-solid
particles with both internal and external porosity and a minor
amount of hollow particles with thick walls containing internal and
external pores.
16. The method as defined in claim 15 in which the low density ash
further includes a minor amount of cenospheres.
17. An electrostatic precipitator for separating low density ash
from the overall gas stream generated from the combustion of coal
in a power generation facility comprising: a hollow body having an
inlet duct having a first area; an outlet duct; whereby the hollow
body has a second area and in which the second area is larger than
the first area; a plurality of energizable fields longitudinally
positioned next to one another within the hollow body; and a
de-energizing mechanism for de-energizing at least one of the
energizable fields resulting in the separation of the lower density
ash from the overall gas stream.
18. The electrostatic precipitator as defined in claim 17 in which
the plurality of energizable fields includes a first energizable
field nearest the inlet duct that is the field de-energized by the
de-energizing mechanism.
19. The electrostatic precipitator as defined in claim 18 in which
at least two fields are de-energized by the de-energizing
mechanism.
20. The electrostatic precipitator as defined in claim 17 further
comprising a hopper beneath each field for collecting the fallout
during the separation of the lower density ash from the overall gas
stream.
21. The electrostatic precipitator as defined in claim 17 in which
the electrostatic precipitator has a first capacity defined by the
maximum stream of overall ash flowing thereby, and in which the
electrostatic precipitator is oversized in capacity relative to the
first capacity.
22. The electrostatic precipitator as defined in claim 17 in which
the overall ash stream has a first density, and in which the low
density ash collected is at least ten (10) percent lower in density
than the first density of the ash stream.
23. The electrostatic precipitator as defined in claim 18 in which
the overall ash stream has a first density, and in which the low
density ash collected is at least thirty-five (35) percent lower in
density than the first density of the ash stream.
24. The electrostatic precipitator as defined in claim 17 in which
the low density ash that is collected has a specific gravity of 2.0
or less.
25. The electrostatic precipitator as defined in claim 24 has a
specific gravity in the range of from 1.6 to 1.99.
26. The electrostatic precipitator as defined in claim 17
comprising a low density ash derived from the ash contained in a
gas stream generated from the combustion of coal, in which the low
density ash consists of a major amount of solid particles having
internal and external porosity and a minor amount of hollow
particles having internal and external porosity.
27. The electrostatic precipitator as defined in claim 17 in which
the low density ash is sized predominantly in the range of from
between 30 microns to 400 microns.
28. A lightweight filler material consisting essentially of a body
formed primarily of fly ash generated from a coal burning power
generation facility, said body having a size predominantly in the
range of from 30 microns to 400 microns; and having a plurality of
interstitial cavities formed on and in the body.
29. A lightweight filler material as defined in claim 28 whereby
the body has a specific gravity less than 2.0.
30. A lightweight filler material as defined in claim 29 in which
the body has a specific gravity in the range of from 1.6 to
1.99.
31. A lightweight filler material as defined in claim 28 in which
the body has both internal and external porosity.
32. A lightweight filler material as defined in claim 28 in which
the overall ash stream has an average first density, and in which
the lightweight filler material has a density of at least ten (10)
percent lower than the average first density of the ash stream.
33. A lightweight filler material as defined in claim 28 in which
the overall ash stream has an average first density, and in which
the lightweight filler material has a density of at least
thirty-five (35) percent lower than the average first density of
the ash stream.
34. A mixture of filler material collected by precipitation from a
gas stream as a result of the deceleration of the gas stream
comprising: a major amount of solid particles having a size in the
range of from 30 to 400 microns; and a minor amount of hollow
particles having a size in the range of from 30 to 400 microns.
35. The mixture of filler material as defined in claim 34 in which
the overall ash stream has a first density, and in which the low
density ash collected is at least ten percent (10) lower in density
than the first density of the ash stream.
36. The mixture of filler material as defined in claim 35 in which
the overall ash stream has a first density, and in which the low
density ash collected is at least thirty-five percent (35) lower in
density than the first density of the ash stream.
37. A mixture of filler material collected by precipitation from a
gas stream as a result of deceleration of the gas stream as defined
in claim 34 in which the low density ash that is collected has a
specific gravity of less than 2.0.
38. A mixture of filler material collected by precipitation from a
gas stream as a result of deceleration of the gas stream as defined
in claim 34 in which the low density ash that is collected has a
specific gravity in the range of from 1.6 to 1.99.
39. The mixture as defined in claim 34 comprising a low density
coal ash derived from the overall ash contained in a gas stream
generated from the combustion of coal in which the major amount of
solid particles have internal and external porosity, and in which
the minor amount of hollow particles have internal and external
porosity.
40. The mixture as defined in claim 34 in which a minor amount of
cenospheres are present in the mixture.
41. The mixture as defined in claim 39 in which the mixture
contains solid particles in the range of from 10% to 70% of the
total mixture by weight; and hollow particles in the range of from
10% to 70% of the total mixture by weight.
42. The mixture as defined in claim 41 in which the mixture
contains solid particles in the range of from 20% to 60% of the
total mixture by weight; hollow particles in the range of from 10%
to 50% of the total mixture by weight.
43. The mixture as defined in claim 40 in which the cenospheres are
in the range of from 0.01% to 3% by weight in the mixture.
44. The mixture as defined in claim 41 in which the cenospheres are
in the range of from 0.75% to 1.5% by weight in the mixture.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Technical Field
[0002] The invention relates to a method and apparatus for
separating the lower density fly ash particles from the overall
mixture of various density particles contained in raw coal ash.
More particularly, the particles of fly ash separated and collected
by this method include generally solid particles with pervasive
internal and external porosity that are frothy in appearance, thick
walled hollow particles with a specific gravity in the range of
from 1.0 to 2.0 and a minor amount of thin walled hollow particles
with a specific gravity of less than 1.0 known as cenospheres.
Specifically, the method involves changing the momentum of the
exhaust gas; either by drastically changing the diameter of the
feed stream to drastically change the velocity of the gas, or by
de-energizing at least the first static electric charging field of
an electrostatic precipitator (ESP) through which the exhaust gases
pass on their way to the stack of the power plant whereby these
hollow, porous and other low density particles fall out and are
collected in a collection hopper.
[0003] 2. Background Information
[0004] Various types of filler materials have been used for decades
to improve the properties and lower costs of various industrial and
consumer products including concrete blocks; plastic composites
such as shower stalls, automobile body panels, sinks and
countertops; roofing materials; tires and other rubber products;
caulking compounds; paper; and a multitude of other applications.
For example, in plastic composites these fillers are commonly
utilized to enhance their structural and mechanical properties, to
improve the composite's fire resistance, to thicken or stiffen the
pre-formed mix prior to molding and to reduce costs.
[0005] These fillers include natural or mineral fillers such as
clay, talc and calcium carbonate, and synthetic fillers, such as
glass beads, ground polymers and ceramics. Both mineral and
synthetic fillers have proven to be useful fillers in materials
ranging from ceramics to a variety of plastics including
thermosetting plastics such as polyesters, epoxies and phenolics
and thermoplastics such as polyethylene, polypropylene, acrylic
lattices, as well as many other resin systems.
[0006] Generally, the selection of a filler for a specific
application is based upon its physical characteristics (e.g. color,
density, shape, thixotropic effect, reactivity, particle size
distribution and handling features) and the mechanical properties
of the filler (e.g. hardness and strength) and the resulting
properties of the filled system. One of the important properties of
a filler is its specific gravity.
[0007] When specific gravity is examined, two classes of fillers
become apparent, namely high density mineral fillers, and low
density materials, typically processed minerals or synthetic
materials.
[0008] Most of the commonly used and economically priced fillers
are high density minerals, usually having a specific gravity of 2.6
and higher. They are generally mined, are plentiful and include
calcium carbonate (limestone), clay, silica and talc.
[0009] However, when the overall weight of the filled system is a
concern, lower density fillers are much more desirable. As a
result, the demand for economically priced low density fillers is
increasing. Low density fillers are generally not plentiful in
nature and therefore are man-made or derived by processing natural
minerals. Low density fillers are generally expensive and include
glass or plastic microspheres, hollow glass beads, expanded ceramic
spheres and cenospheres.
[0010] Raw fly ash, a product created when coal is combusted in a
generation facility is plentiful, and is being generated from coal
fired power plants. More particularly, there are currently hundreds
of coal fired power plants in the U.S. alone. These plants burn
well in excess of one billion tons of coal per year, and as such,
coal combustion by-products including fly ash have become one of
the nation's most abundant resources. Growth is further expected as
nuclear power loses preference to more standard power sources such
as coal. As a result, the need to safely dispose of fly ash, and
the need to develop an economical use for fly ash is ever
increasing. Fly ash is currently used as a filler material in many
applications but has never achieved the status of a major filler.
Some of the reasons why fly ash have been unable to capture a large
portion of the filler market are its color, its difficulty to
handle due to dustiness, its wide particle size distribution, its
hardness, and the inconsistency of its composition and properties.
Most sources of fly ash have a specific gravity in the range of
2.1-2.3, which is less that than the common mineral filler, but
this apparent advantage is not enough to offset the
disadvantages.
[0011] Fly ash with a low specific gravity, whether hollow or solid
has been usually separated from raw ash using water as the
separation medium. Those particles having a specific gravity less
than 1.0 will float and the remaining portion of the ash sinks to
the bottom of the separation pond. The cenospheres must be
collected from the ponds, usually by a skimming process, cleaned of
other floating materials, dried, and often further processed.
Cenospheres, when they are present in raw fly ash, typically
represent one percent or less of the weight of the ash. However,
cenospheres have a specific gravity of less that 1.0, and are very
valuable as a low density filler, selling at a price significantly
higher than other types of ash. Similarly, all low density ash,
when cleaned and processed, is extremely valuable as a filler
material.
[0012] Functionally, fly ash is the finely divided ash material
carried in the stack gases from the furnace of power plants which
consume powdered and pulverized coal, and is collected before it
leaves the stack usually in an electrostatic precipitator or other
type of collector. The problem associated with disposal of fly ash
is large because the tonnage produced by some utility companies is
quite high. Numerous attempts have been made to utilize the
material, and the suggestion that lightweight aggregate materials
might be prepared from fly ash is the result of such an
attempt.
[0013] The present invention provides a method for economically
separating a low density fraction of ash from the entire
particulate range of fly ash created as a by-product from the
combustion of coal. The resultant low density ash has a specific
gravity of 1.6-1.99. More particularly, the resultant ash is at
least ten percent lower in density than raw fly ash and produces
very little dust when handled. Although not as light as the thin
walled cenospheres, the ash created from the present invention is
significantly more durable, and is primarily composed of a frothy,
relatively solid particles with both internal and external porosity
and larger thick walled hollow particles. In addition to its
increased durability over cenospheres, the material created by the
present invention is plentiful, comprising more than thirty percent
of the total raw fly ash produced, and is less expensive to produce
and process than cenospheres. The product created by the present
invention thus has advantages when compared to both raw fly ash and
cenospheres, making it a valuable low density filler produced in an
economical manner.
[0014] The need thus exists for an ash that which is relatively
inexpensive to produce, which may be separated from the existing
raw fly ash with limited cost, and which provides for a low
specific gravity for use as a filler material. The need also exists
for an apparatus and system for separating the above described ash
for collection and use as a filler material.
SUMMARY OF THE INVENTION
[0015] Objectives of the invention include providing an improved
device, system and method of separating and collecting the lower
density fly ash particles including semi-solid frothy particles
with internal and external porosity, thick walled hollow particles
and a smaller amount of thin walled hollow particles (cenospheres)
from the other higher density solid particles contained in raw fly
ash.
[0016] A further objective is to provide a low density ash particle
separation and collection method and device that effectively
separates the particles by size and density, without the use of
water and subsequent de-watering and drying processes.
[0017] A further objective is to provide such a low density ash
particle separation and collection method and device that lessens
the amount of ash disposed in land fills.
[0018] A further objective is to provide such a low density ash
particle which has both internal and external porosity.
[0019] A still further objective is to provide a mixture of low
density ash particles having a size in the range of from 30 microns
to 400 microns.
[0020] A further objective is to provide such a low density ash
particle separation and collection method and device that produces
an inexpensive source of low density mineral filler.
[0021] A further objective is to provide such a low density ash
particle separation and collection method and device that produces
large quantities of low density ash particles.
[0022] A further objective is to provide such a low density ash
particle separation and collection method and device that produces
a low density filler that is useful in plastics, ceramics, concrete
and other materials.
[0023] A further objective is to provide such a low density ash
particle separation and collection method and device that is
inexpensive to operate and uses existing equipment such as
electrostatic precipitators.
[0024] A further objective is to provide such a low density ash
particle separation and collection method and device that
incorporates one or more or all of the above objectives and
advantages.
[0025] A further objective is to provide such a low density ash
particle separation and collection method and device which
accomplishes its objective in a dry environment.
[0026] A further objective is to provide such a low density ash
particle separation collection method and device which
substantially decreases the momentum of the gas stream in order to
remove low density fly ash from the gas stream.
[0027] These and other objectives and advantages of the invention
are obtained by the invention which includes a method of separating
lower density ash from the exhaust gas stream which contain the
entrained fly ash, and then collecting the low density ash that
drops out below the de-energized fields of the electrostatic
precipitator. The invention further includes an electrostatic
precipitator or similar device that is designed in such a manner to
cause the gas or air stream to rapidly decelerate causing the
entrained particles to slow down and fall out suspension. The low
density fly ash particles having less momentum (relative to their
size and therefore subject to greater deceleration due to drag
forces) tend to fall out sooner (i.e. in the inlet portion, first
hoppers, of the precipitator or similar device). The denser ash
particles, with greater momentum and affected to a lesser extent by
drag forces, are carried further into the precipitator. The
precipitator or other device is, in effect, a hollow body with a
larger cross sectional area than the inlet and outlet ducts. The
electrostatic precipitator further includes a plurality of
energizable fields associated with one or more collecting plates
longitudinally positioned next to one another within the hollow
body where the plurality of energizable fields includes a first
energizable field nearest the inlet. The electrostatic precipitator
further includes a de-energizing mechanism for de-energizing the
first energizable field(s) resulting in the separation of the lower
density ash from the overall ash stream. The ESP is equipped with
collection hoppers below the plurality of energizable fields. The
ash falls out of the precipitator body, due to gravity, and is
collected in the hoppers. Typically a hopper would span one
collecting plate having one or more electrostatic fields associated
therewith. The ash can be removed from individual hoppers or from
rows of hoppers by modifying the existing transport system or by
installing a separate system to extract the collected low density
ash.
BRIEF DESCRIPTION OF THE DRAWINGS
[0028] Preferred embodiment of the invention, illustrative of the
best mode in which applicant has contemplated applying the
principles, is set forth in the following description and is shown
in the drawings and is particularly and distinctly pointed out and
set forth in the appended claims.
[0029] FIG. 1 is a sectional view of the electrostatic precipitator
of the present invention;
[0030] FIG. 2 is a photograph of the low density ash of the present
invention;
[0031] FIG. 3 is a photograph showing thick wall hollow particles
having internal and external pores;
[0032] FIG. 4 is a photograph depicting cenospheres; and
[0033] FIG. 5 is a photograph depicting solid low density
particles.
DESCRIPTION OF THE PREFERRED EMBODIMENT
[0034] The invention is a device and method of separating and
collecting low density fly ash particles from the overall and
unprocessed raw fly ash stream produced by coal burning in a coal
fired, steam generating, electric power plant by setting out such
low density fly ash particles from the raw coal ash stream using
the de-energized inlet portion of an electrostatic precipitator as
a separating device. This is specifically accomplished using a
method and device that utilizes velocity deceleration to separate
and collect the low density fly ash from the raw coal fly ash which
will be collected by energized fields of the electrostatic
precipitator.
[0035] The invention includes an electrostatic precipitator 10 as
shown in one embodiment in FIG. 1. The electrostatic precipitator
10 generally includes an inlet or expansion nozzle 11, an outlet or
outlet nozzle 12, and an enlarged hollow body 13 therebetween which
is divided into multiple fields 14A, 14B, 14C, etc. that are
energizable as described below. Many different varieties and
constructions of electrostatic precipitators have been or are
available on the market, all of which may incorporate this
invention as described herein. The variety of precipitators
available is large and includes, for example, models such as those
described in the following U.S. Patents: 1,298,409, 1,381,660,
3,898,060, 4,308,036, 4,374,652, and 5,160,510, as well as any
other commercially available electrostatic precipitator.
[0036] In more detail, the electrostatic precipitator 10 is fluidly
connected within an exhaust duct on a coal fired power plant that
is between a combustor 21, or other combustion chamber, and a stack
23 which releases exhaust to the atmosphere 22. The exhaust duct is
thus broken into an inlet duct 20, the precipitator 10, and an
outlet duct 25. This is typically accomplished by cutting the
exhaust duct into two pieces, namely a first section or inlet duct
20 and a second section or outlet duct 25, with the electrostatic
precipitator 10 attached therebetween whereby the inlet duct 20
separates the combustor 21 from the electrostatic precipitator 10
while the outlet duct 25 separates the electrostatic precipitator
10 from the stack 23 and subsequently the atmosphere 22. An exhaust
gas-to-air heat exchanger is typically used to preheat the air for
combustion, and can be either on the inlet or outlet side of the
precipitator, such as within the inlet duct 20 or the outlet duct
25.
[0037] The inlet and outlet ducts 20 and 25 are generally of a
similar diameter and cross sectional area, while the diameter and
cross-sectional area of the hollow body 13 is larger so as to
substantially slow down the fluid flow therein due to an overall
increase in volume. More particularly, the cross sectional area of
hollow body 13 is in the range of from six to twenty-five times
larger than the duct. More particularly, the large diameter of
expansion nozzle 11 and hollow body 13 has an area at least ten
times larger than the area associated with inlet duct 20.
Basically, the flow or velocity of fluid, in the form of gas with
particulate suspended therein, must be sufficiently slowed for the
electrostatic precipitator to properly charge the particles, and
this is accomplished by a significant increase in volume in the
expansion nozzle 11 to the body 13. Thereafter, the flow is
increased in the outlet nozzle 12 by decreasing the exhaust cross
section. In one embodiment, the gas flow in the inlet duct 20 is
approximately 60 ft./sec. while it falls to 2.5 to 5 ft./sec. in
the precipitator body 13.
[0038] The electrostatic precipitator 10 is longitudinally
subdivided into the fields between expansion nozzle 11 and outlet
nozzle 12. As is standard for electrostatic precipitator, each
field 14A, 14B, 14C, etc. includes one or more power supplies and
each power supply is connected to one or more independently
energizable portions known as bus sections. The number of fields is
not important as the precipitator may only have a few or may have
in excess of a dozen, while most standard precipitators have six or
eight.
[0039] Per this longitudinal subdivision, the fields are aligned
one after another from the expansion nozzle 11 to the outlet nozzle
12 with the first field 14A being adjacent or nearest the expansion
nozzle 11, the second field 14B being next to the first field, and
so on across the hollow body 13 to the outlet nozzle 12. Each field
14A, 14B, 14C, etc. is an arrangement of collecting surfaces and
discharge electrodes as is well known in the art.
[0040] In use, the fields 14A, 14B, 14C, etc. are energized with
high voltage by a transformer-rectifier combination that is
electrically attached to a variety of controls and other electrical
components. The energizing of the fields as the products of coal
combustion in the form of exhaust gases with suspended particles
pass through electrostatic precipitator 10 basically imparts a
charge on the particles within the gas stream to separate out
particles. This is well known in the industry as it has been in use
for years, and ash separation from exhaust gas is required by
environmental regulations. For these reasons, a large percentage of
coal fired power plants have electrostatic precipitators on each
exhaust duct after the combustor.
[0041] The electrostatic precipitator is positioned in a horizontal
manner such that the gases must travel horizontally or
approximately horizontally through it. This allows for particle
fallout. Below or at the bottom of each field, or a collection of
fields, is a hopper or collection chamber, namely hopper 30A for
field 14A, hopper 30B for field 14B, etc. These hoppers are
separated by walls 31. Each hopper basically collects any fall out
that occurs above it as gases and particles pass through the
precipitator and the specific field above it.
[0042] Electrostatic fields are created when the precipitator's
charging wires are energized. Particles passing these charged wires
are imparted with electrostatic charge. As a result, the charged
particles are collected and later dislodged from grounded plates
and the particles fall into the hoppers while the gaseous
components of the flue gas pass through and are exhausted to the
atmosphere 22. Basically, only non-particulate matter passes all
the way through the precipitator 10 to the outlet 12 and thus is
exhausted to the atmosphere 22.
[0043] In accordance with one of the features of the invention, the
electrostatic precipitator 10 is oversized. Oversized being defined
as having excess capacity in that either lesser capacity or lesser
number of fields are needed to fully remove the particles from the
exhaust gases of the coal combustion process in order to meet
environmental regulations. An oversized electrostatic precipitator
10 has fields that may be de-energized while still performing all
of its particulate removal objectives.
[0044] In accordance with yet another feature of the invention, the
first field 14A is de-energized by turning off the electric power
to section 14A by operating breaker A or other similar device. As a
result, a first area is provided in the precipitator body 13 that
does not impart charges on the particles but is of a significantly
increased cross sectional dimension, thus decelerating the exhaust
gases containing the particles. In this first field when
de-energized, a large portion of the low density ash 40 falls out
into hopper 30A and accumulates as captured low density ash 45
while almost all of the higher density ash particles 41, due to
greater momentum and less drag, pass into the next fields where
they are charged and fall out into the hoppers 30B, 30C, etc. as
captured higher density ash 46. The first hopper 30A may then be
evacuated using a conveying system and the contents packaged as low
density mineral material.
[0045] Referring specifically to the fly ash, it is, as stated, the
dust-like material collected from the gas stream to be passed out
of the stack, leaving the furnace of power plants which consume
coal, and specifically powdered and pulverized coal. Chemically,
fly ash is essentially a mixture of silica, aluminum oxide and
other metal oxides containing minor proportions of alkalis and
carbon. The carbon content of the fly ash represents that portion
of the carbon of the original total that did not burn during the
combustion in the furnace due to the short time of exposure of the
coal to combustion temperatures and to inconsistencies in
operation. Hence, depending on these and other factors, the fly ash
may contain from as little as less than 1% to as high as even 40%
by weigh of carbon in isolated instances. A typical fly ash
analysis is as follows:
1 Silica, SiO.sub.2 54.6 Aluminum Oxide, Al2O.sub.3 23.3 Iron
Oxide, Fe2O.sub.3 2.1 Titanium Oxide, TiO.sub.2 1.4 Calcium Oxide,
CaO 0.4 Magnesium Oxide, MgO 0.5 Sodium Oxide, NA2O 0.2 Potassium
Oxide, K2O 1.8 Sulfur Trioxide, SO.sub.3 0.3 Phosphorous Pentoxide,
P2O.sub.5 <0.1 Barium Oxide, BaO <0.1 Magnesium Oxide,
Mn2O.sub.3 <0.1 Strontium Oxide, SrO <0.1 Total Carbon, C
12.4 Net Ignition Loss (+)/Gain (-) +4.4 Total 101.4
[0046] Additionally, this mixture contains an available alkali
equivalent Na2O of 0.33, and an Iron Oxide of Fe3O.sub.4 of 2.0.
The low density ash of the present invention includes a major
amount of frothy, solid particles with both internal and external
porosity or interstitial cavities such as those shown on attached
FIG. 2, and a minor amount of thick wall hollow particles as shown
in FIG. 3 having both internal and external pores. Still further, a
minor amount of cenospheres, such as those shown in FIG. 4 are also
collected in the low density ash of the present invention. More
particularly, the present invention includes from 10% to 70% of the
total mixture by weight of frothy, solid particles such as those
shown in FIG. 2, from 10% to 70% of thick walled hollow particles
such as those shown in FIG. 3, and less than 1% of cenospheres such
as those shown in FIG. 4. More particularly, and in one embodiment
of the invention, the mixture of low density fly ash includes from
20% to 60% of frothy, solid particles and from 10% to 50% of thick
walled hollow particles such as those shown in FIG. 3.
[0047] It has been found that the low density ash particles from
the first hopper are of a significantly lower density than the
other ash particles which tend to fall out in hoppers 30B, 30C,
etc. The accumulation of material in the first hopper 30A is of a
good quality and is of a high percentage, if not all, low density
ash. The density of this accumulation in hopper 30A is at least 10%
lower in density than raw fly ash normally produced by
electrostatic precipitation, and it has been found to be 35% or
more lower in density.
[0048] In experiments, the accumulation of material had a specific
gravity of less than 2 and often is in the range of 1.6 to 1.99,
which is a very good grade low density filler material. The vast
majority of particles collected in hopper 30A were also about
between 30 microns to 400 microns in size. It is also noted that
the cost of collection of such low density ash from the first
hoppers 30A is very low, far less than the costs associated with
other processes to separate ash by particle size or density.
Chemically, the composition of the low density ash particles is
similar to the composition of the overall ash population passing in
the gas stream, and is lower in density as a result of its frothy
form and structure which has both internal and external porosity,
which ensures that there is a relatively low density associated
with the product.
[0049] In an alternative embodiment, the first and second fields
14A and 14B, or first three fields 14A-14C may be de-energized. In
this case, low density fly ash is deposited in all three respective
hoppers although a gradual increase in the density generally occurs
in each successive field. Still further, the present invention may
be operated by ensuring that expansion nozzle 11 has a cross
sectional configuration large enough to decelerate the gas stream
efficiently to ensure that lower density particles will fall out of
the gas stream and into hopper 30A. In this manner, de-energizing
the electrostatic precipitator is not necessary as the large
diameter expansion nozzle 11 is sufficient to slow the gas stream
and allow low density air entrained particles to fall out as a
result of the drastic reduction in momentum. Expansion nozzle 11
may not be positioned adjacent an electrostatic precipitator, and
simply decelerate the gas stream to allow low density particles to
fall out of the stream. However, if expansion nozzle 11 is
positioned adjacent a precipitator, then the collector plates must
be de-energized to allow low density particles to fall.
[0050] Accordingly, the improved low density ash separation and
collection method and device achieves all the enumerated
objectives, does so with great cost efficiency and generates an
entirely new low density fly ash material with unique properties
and characteristics as a result of this new art.
[0051] In the foregoing description, certain terms have been used
for brevity, clearness and understanding; but no unnecessary
limitations are to be implied therefrom beyond the requirement of
the prior art, because such terms are used for descriptive purposes
and are intended to be broadly construed.
[0052] Moreover, the description and illustration of the invention
is by way of example, and the scope of the invention is not limited
to the exact details shown or described.
[0053] Having now described the features, discoveries and
principles of the invention, the manner in which the improved low
density ash separation and collection method and device is
constructed and used, the characteristics of the construction, and
the advantageous, new and useful results obtained; the new and
useful structures, devices, elements, arrangements, parts and
combinations, are set forth in the appended claims.
* * * * *