U.S. patent application number 17/173645 was filed with the patent office on 2021-07-29 for apparatus for manipulating crystal morphology to achieve stable fluidization.
This patent application is currently assigned to American Electric Power Company, Inc.. The applicant listed for this patent is American Electric Power Company, Inc.. Invention is credited to Douglas Ritzenthaler.
Application Number | 20210230771 17/173645 |
Document ID | / |
Family ID | 1000005510499 |
Filed Date | 2021-07-29 |
United States Patent
Application |
20210230771 |
Kind Code |
A1 |
Ritzenthaler; Douglas |
July 29, 2021 |
APPARATUS FOR MANIPULATING CRYSTAL MORPHOLOGY TO ACHIEVE STABLE
FLUIDIZATION
Abstract
This disclosure provides an apparatus to manipulate the crystal
morphology of a powder to improve the flow of a powder from a
vessel and/or flowability of a powder in order to achieve stable
fluidization of the powder within a vessel.
Inventors: |
Ritzenthaler; Douglas;
(Columbus, OH) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
American Electric Power Company, Inc. |
Columbus |
OH |
US |
|
|
Assignee: |
American Electric Power Company,
Inc.
Columbus
OH
|
Family ID: |
1000005510499 |
Appl. No.: |
17/173645 |
Filed: |
February 11, 2021 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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16421575 |
May 24, 2019 |
10988860 |
|
|
17173645 |
|
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62679428 |
Jun 1, 2018 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B01D 53/83 20130101;
B01D 2251/304 20130101; C30B 33/02 20130101; B01D 2251/606
20130101; C30B 29/46 20130101; B01D 2257/302 20130101 |
International
Class: |
C30B 33/02 20060101
C30B033/02; C30B 29/46 20060101 C30B029/46 |
Claims
1.-20. (canceled)
21. An apparatus for manipulating crystal structure of a powder to
improve flowability comprising: a vessel having insulation, a rigid
exterior shell, an interior space of a predetermined capacity for
storing a powder bed comprised of a powder, the powder having a
temperature and a crystal structure, the vessel further having an
inlet portal through which the powder enters the interior space,
and at least one atmospheric vent extending from the interior space
through the exterior shell of the vessel; a gas stream, provided to
the powder bed, having a temperature and pressurized to a
predetermined pressure by a gas handling system, the predetermined
pressure and temperature of the gas stream selected so as to aerate
the powder and achieve fluidization; at least one aeration device
selected from the group consisting of air slides, air pads, natural
air stones, synthetic air stones, metallic stones, and pozzolanic
stones, and installed within the interior space so as to be in
contact with the powder bed stored therein, the at least one
aeration device having at least one gas inlet connection extending
beyond the exterior shell which receives the gas stream; wherein
the aeration device, able to withstand the temperature of the gas
stream, is selected so as to evenly distribute the gas stream to
the powder bed to control the temperature of the powder, to cause
the powder to undergo a change in the crystal structure of the
powder and cause the powder bed to achieve fluidization; a
temperature control means for controlling the temperature of the
gas stream comprising at least one temperature sensing device and a
means by which to control the temperature of the gas stream,
selected so as to control the temperature of the powder; a pressure
control means to control the pressure of the gas stream comprising
at least one pressure sensing device in contact with the gas stream
and positioned upstream of the at least one gas inlet connection
and a means for varying the pressure of the gas stream prior to the
gas inlet connection; and an outlet portal positioned below the
inlet portal through which the powder exits the vessel.
22. The apparatus of claim 1, wherein the crystal structure of the
powder substantially includes twinning below a first predetermined
transition temperature and the crystal structure of the powder does
not include twinning above the first predetermined transition
temperature.
23. The apparatus of claim 1, wherein the first predetermined
transition temperature is about 100 degrees Celsius.
24. The apparatus of claim 1, wherein the atmospheric vent
comprises a bin vent filter open to the atmosphere, through which
the gas stream exits the interior space.
25. The apparatus of claim 1, wherein the gas stream is heated and
pressurized ambient air.
26. The apparatus of claim 1, further comprising a fabric covering
the aeration device.
27. The apparatus of claim 1, wherein the powder further comprises
sodium sulfate.
28. The apparatus of claim 1, wherein the temperature the aeration
device is able to withstand is at least 220 degrees F.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application claims the benefit of priority of U.S.
application Ser. No. 16/421,575, filed May 24, 2019, which claims
the benefit of U.S. Provisional Application Ser. No. 62/679,428,
filed Jun. 1, 2018. The disclosures of the prior application are
considered part of (and are incorporated by reference in) the
disclosure of this application.
BACKGROUND OF THE INVENTION
1. Field of the Invention
[0002] The present disclosure relates to material handling, more
particularly, to improving the fluidization (flow) of a material,
providing advantages in functionality, simplicity and engineering,
operation, maintenance, and life cycle cost. The invention can be
utilized in a dry scrubber system utilizing Dry Sorbent Injection
(DSI). However, the invention is not limited to this
application.
2. Description of the Related Art
[0003] It is well known among those who work in the area of
material handling that material containing a high percentage of
solids can be difficult to remove from a storage vessel. The
foremost view in the art is that a high unconfined yield strength
is primarily responsible for flow issues in storage vessels, for
example arching, rat-holing, and bridging..sup.1 Unconfined yield
strength is the major requisite stress to cause a group of
particles to "yield," which results in shear movement of the bulk
material (this is related to resistance to flow)..sup.2 .sup.1
Johanson, Kerry, Effect of particle shape on unconfined yield
strength, Powder Technology, Vol. 194, 2009, 246-251, Elsevier
B.V..sup.2 Johanson, Kerry, Effect of particle shape on unconfined
yield strength, Powder Technology, Vol. 194, 2009, 246-251,
Elsevier B.V.
[0004] A further leading view is that any moisture in the material
will tend to congregate at the contact points between soluble
particles, causing a portion of the particles to dissolve..sup.3 If
the temperature then increases, the theory is, this moisture
between particles evaporates, leaving solid salt bridges between
adjacent particles. These salt bridges increase the adhesive force
on the particles and therefore the unconfined yield strength as
well, impeding fluidization. Therefore, the theory is, as
temperature increases, flowability deteriorates. .sup.3 Johanson,
Kerry, Powder Pointers, Summer 2018 Volume 12 No B, Material Flow
Solutions, Inc, 1-2, Gainesville, Fla.
BRIEF SUMMARY OF THE INVENTION
[0005] It is an object of this disclosure to describe the
experimentation which illuminated that the crystal structure of a
material impacts fluidization, resulting in improved flowability at
higher temperatures despite the common belief otherwise. It is an
object of the present invention to provide a system and method for
achieving stable fluidization of a powder comprising materials,
such as sodium sulfate, with crystal morphology that can be
manipulated with temperature.
BRIEF DESCRIPTION OF THE DRAWINGS
[0006] The accompanying drawings, which are included to provide a
further understanding of the disclosure and are incorporated in and
constitute a part of this specification, illustrate embodiments of
the disclosure and together with the description serve to explain
the principles of the disclosure. In the drawings:
[0007] FIG. 1 shows a typical fluidization profile used to
determine air flow (pressure) requirements for fluidizing
particles.
[0008] FIG. 2 shows experimental data, unconfined yield strength as
a function of temperature.
[0009] FIG. 3 shows moisture vs. temperature experimental data.
[0010] FIG. 4 shows additional moisture and temperature
experimental data over time.
[0011] FIG. 5 shows a solubility curve of sodium sulfate in
solution.
[0012] FIG. 6 shows an example of crystals with an orthorhombic
morphology with twinning planes.
[0013] FIG. 7 shows an example of crystals with a monoclinic
morphology, and no twinning planes.
[0014] FIG. 8 shows an example of crystals with a hexagonal
morphology, and no twinning planes.
[0015] FIG. 9 shows an example embodiment of sodium sulfate
collection and transport, representing an application of the
present disclosure in relation to the use of Dry Sorbent Injection
in a coal-fired power plant.
[0016] FIG. 10 shows a storage vessel, for example a silo, truck,
trailer, or rail car, and the accompanying system for improving
flowability and achieving stable fluidization according to an
example embodiment of the present disclosure.
[0017] FIG. 11 shows a gas stream distribution system including an
aeration device for improving flowability and achieving stable
fluidization according to an example embodiment of the present
disclosure.
DETAILED DESCRIPTION OF THE INVENTION
[0018] It is well known among those who work in the area of
material handling that material containing a high percentage of
solids can be difficult to remove from a storage vessel. The
foremost view in the art is that a high unconfined yield strength
is primarily responsible for flow issues in storage vessels..sup.4
.sup.4 Johanson, Kerry, Powder Pointers, Summer 2018 Volume 12 No
B, Material Flow Solutions, Inc, 1-2, Gainesville, Fla.
[0019] A further leading view is that any moisture in the material
will tend to congregate at the contact points between particles,
causing the portion of the soluble particles near these contact
points to dissolve..sup.5 The leading theory is that if temperature
is increased, this moisture between particles evaporates, leaving
solid salt bridges between adjacent particles. These salt bridges
increase the adhesive force on the particles and therefore the
unconfined yield strength as well, impeding powder flow. Therefore,
the theory is, as temperature increases, flowability deteriorates.
.sup.5 Johanson, Kerry, Powder Pointers, Summer 2018 Volume 12 No
B, Material Flow Solutions, Inc, 1-2, Gainesville, Fla.
[0020] Despite the view among prominent members in the art to the
contrary, both laboratory and field testing indicate that material
flow problems are not necessarily due to moles of hydration or free
water, and do not necessarily increase with temperature. Rather,
the crystalline structure of a compound influences powder
flowability.
[0021] For example, the crystal morphology (otherwise known as
crystal structure) of anhydrous sodium sulfate at ordinary
temperatures (below about 100 degrees C.) is an orthorhombic
pyramidal crystal with twinning planes..sup.6 A twin is defined as
a composite crystal built from two or more crystal specimens that
are grown together in a specific manner so that there is at least
one plane and a direction perpendicular to it that are related in
the same manner to the crystallographic axes of both parts of the
twin..sup.7 But at temperatures greater than and equal to about 100
degrees C. (212 degrees F.), the crystal shape changes to a
monoclinic crystal (without twinning) and then at about 250 degrees
C. (482 degrees F.) to hexagonal crystals (without twinning)..sup.8
The lack of twinning in the crystal morphology results in the
achievement of stable fluidization at and beyond about 100 degrees
C., versus the failure to achieve stable fluidization, or even
fluidization, below about 100 degrees C. Twinned crystals
experience a greater unconfined yield strength because of the
physical interlocking that occurs between particles due to the
shape of the twinned crystals. It has been shown that particle
shape as well as the number of contact points per adjacent particle
affect unconfined yield strength and therefore flowability..sup.9
.sup.6 The Columbia Encyclopedia, 2000, 2646, 6.sup.thh Edition,
Gale Group, U.S..sup.7 Glusker, Jenny P, Trueblood, Kenneth N.,
Crystal Structure Analysis: A Primer, 1985, 240, Oxford University
Press, New York..sup.8 The Columbia Encyclopedia, 2000, 2646,
6.sup.th Edition, Gale Group, U.S..sup.9 Johanson, Kerry, Effect of
particle shape on unconfined yield strength, Powder Technology,
Vol. 194, 2009, 246-251, Elsevier B.V.
Experimental Methods
[0022] Contrary to the popular belief that flowability deteriorates
with increasing temperature, experimental data showed that
flowability improved at higher temperatures, even to the point of
achieving stable of fluidization. Fluidization is readily
determined via a visual inspection of a column of material aerated
with air. The air flow is measured and recorded, from which air
velocities are calculated. The temperature of heated air is
measured with a thermocouple or other temperature measuring device.
If unheated, the air is assumed to be at ambient temperature, near
25 degrees C. (77 degrees F.).
[0023] If the column of material forms fissures (small, visible
tunnels through the material) that provide a multitude of visible
conduits for the air to pass through the material and relieve the
built up pressure beneath the material, then the material is said
to be experiencing fissures, or channeling, and has not reached
fluidization..sup.10 11 .sup.10 Cocco, R. et. al., Introduction to
Fluidization, Nov. 2014, 21-29, American Institute of Chemical
Engineers Journal, U.S..sup.11 Vasconcelos, P. S., Amarante
Mesquita, A. L., Minimum and Full Fluidization Velocity for Alumina
Used in the Aluminum Smelter, Nov. 2011, 8-13, Volume 3 No. 4,
International Journal of Engineering Business Management, Intech
Open Access Publisher.
[0024] Alternatively, if the column of material allows distinct
volumes of air to be relieved periodically and in an uneven manner,
the material is said to be experiencing bubbling flow, and it is
not consistently fluidized..sup.12 13 .sup.12 Cocco, R. et. al.,
Introduction to Fluidization, Nov. 2014, 21-29, American Institute
of Chemical Engineers Journal, U.S..sup.13 Vasconcelos, P. S.,
Amarante Mesquita, A. L., Minimum and Full Fluidization Velocity
for Alumina Used in the Aluminum Smelter, Nov. 2011, 8-13, Volume 3
No. 4, International Journal of Engineering Business Management,
Intech Open Access Publisher.
[0025] However, if air passes uniformly through the material
causing the material to uniformly expand and behave in a fluid-like
manner, the material is said to have achieved stable
fluidization..sup.14 15 .sup.14 Cocco, R. et. al., Introduction to
Fluidization, Nov. 2014, 21-29, American Institute of Chemical
Engineers Journal, U.S..sup.15 Vasconcelos, P. S., Amarante
Mesquita, A. L., Minimum and Full Fluidization Velocity for Alumina
Used in the Aluminum Smelter, Nov. 2011, 8-13, Volume 3 No. 4,
International Journal of Engineering Business Management, Intech
Open Access Publisher.
[0026] The experiment comprised a vessel with sufficient sodium
sulfate powder to form a bed of material within the vessel. The
vessel was configured to allow air, either heated or unheated, to
be introduced below the material. The temperature of the ambient
air was recorded at 25 degrees C. (77 degrees F.). This is assumed
to be the approximate temperature of the desiccated aeration air
and thus of the sodium sulfate powder when unheated.
[0027] First, at ambient temperature, flow (pressure) was increased
until fissures were observed through the material to the surface,
relieving itself into the room. Pressure was increased gradually
until the flow rate of the desiccated air was more than twenty
times what is typically needed for fluidization. The material
gradually transitioned into bubbling flow, but fluidization was
never achieved.
[0028] The test apparatus was then modified for higher
temperatures. Desiccated air at no less than 107 degrees C. (225
degrees F.) was introduced into the now insulated apparatus to
prompt aeration. The desiccated air was permitted to run overnight
prior to visual observation to ensure that the apparatus itself, as
well as the powder in the apparatus, were sufficiently heated above
the transition temperature. The material was observed to be stably
fluidized though observation points cut into the insulation.
[0029] To confirm fluidization, the desiccated aeration air was
briefly terminated, upon which the column of material dropped
slowly to a lesser volume. Once this contraction was complete and
the desiccated aeration air again initiated, the material uniformly
increased in volume and the desiccated aeration air passed through
the material with no visible fissures, channels, or bubbling. The
material achieved stable fluidization. The test was continued by
allowing the material to cool below about 100 degrees C., and
fluidization was lost. Only the temperature of the desiccated air
was changed, meaning the fluidization that occurred above 100
degrees C. and which ceased below that temperature could not have
been due to another variable such as moisture. Likewise, upon
reheating to about 107 degrees C. (225 degrees F.), fluidization
was again achieved.
[0030] The ultimate fluidization test was conducted in the field.
The field setup was similar to that in the lab except the silo was
not insulated due to the sufficient outside temperature, and the
source of air in the field was ambient air versus desiccated air in
the lab. The temperature of the gas stream reached 225 degrees F.
(about 107 degrees C.) for a period of several days. Stable
fluidization under these conditions was achieved, as evidenced by
the silo being readily emptied.
[0031] The amount of air required for fluidization is dependent on
the material. A typical fluidization profile is depicted in FIG.
1..sup.16 Fluidization of a powder is achieved when the powder
volume increases uniformly and the resultant powder flow
characteristics approach that of a fluid. This point, fluidization,
is identified as the "Minimum Fluidization Velocity" (1). As
velocity increases further, there is a distinct reduction in the
pressure drop (.DELTA.p) across the powder (2), and then as the
velocity increases further, pressure drop (.DELTA.p) becomes stable
at the minimum operating velocity (3). Minimum operating velocity
(3), or stable fluidization, is judged to be reached where
perturbations in air flow or back pressure avoid significant
changes in pressure drops and thus do not impact the overall
fluidization of the bulk powder. The maximum operating velocity (4)
must be low enough to avoid the velocity where entrainment occurs
(5). The operating velocity range for stable fluidization must be
great enough to reach the point at which the pressure drop
decreases and becomes stable (3), and less than the velocity which
induces entrainment (5). .sup.16 Kunii, Daizo and Levenspiel,
Octave, Fludization Engineering, 1969, 74, John Wiley & Sons,
Inc., U.S.
[0032] In the experimentation completed, the minimum operating
velocity and volume for stable fluidization was calculated to be
sufficient to achieve proper fluidization. The specific values are
proprietary, but the velocity and flow rate applied were four times
the calculated value. Despite vastly exceeding the calculated
volume of air introduced to the powder bed via the aeration device
according to the above methodology, the material never achieved
fluidization at temperatures below about 100 degrees C.
[0033] During laboratory testing above the aforementioned
transition temperature of about 100 degrees C. (212 degrees F.),
stable fluidization was achieved at velocities and flow rates very
close to the calculated values, disproving the common belief in the
art that the unconfined yield strength, and therefore flow issues
as well, of soluble powders such as sodium sulfate increase with
temperature.
[0034] FIG. 2 shows a trend line of unconfined yield strength
versus temperature applied to experimental data, illustrating the
common view in the art that unconfined yield strength increases
with temperature. This indicates the expectation that unconfined
yield strength would increase beyond 100 degrees C. and therefore
flowability would continue to deteriorate.
[0035] Contrary to this common view, the lab data showed
fluidization occurred beyond about 100 degrees C., therefore
unconfined yield strength must dramatically drop. Note that no data
was collected above 100 degrees C. (212 degrees F.), yet the trend
line from the data extends beyond 100 degrees C. Those
knowledgeable in the art who created the graph assumed the
relationship was linear, and extended the trend line beyond 100
degrees C. However, as this disclosure elucidates, lower unconfined
yield strength and therefore less flow issues, not a higher
unconfined yield strength and more flow issues, are present beyond
100 degrees C., and an accurate graph would show a negative slope
beyond 100 degrees C.
[0036] Based on this trend line, the temperatures in the field were
reduced from their initial temperatures of about 93 degrees C.
(about 200 degrees F.) to about 71 degrees C. (160 degrees F.).
There were no measureable improvements to the flow of the material
out of the silo despite this reduction in temperature.
[0037] Additionally, an analysis was completed of the moisture
content of the silo powder at various temperatures to determine if
the loss in moisture at 100 degrees C. (212 degrees F.) is the
reason for its ability to fluidize. This analysis disproved the
theory that flow improved to the point of allowing stable
fluidization because of the loss of free water from the sodium
sulfate powder. In fact, moisture data indicates that most of the
free moisture is liberated at temperatures below 100 C (212 F),
pointing to an alternate cause for the dramatic change in flow
characteristics of sodium sulfate powder above 100 degrees C.
compared to below 100 degrees C.
[0038] FIG. 3 presents the released moisture from a powder sample
as a function of temperature in light of the above. Note that the
powder was tested at temperatures of up to about 215 degrees F.
(102 degrees C.). It shows no dramatic change in moisture released
at the transition temperature of 212 degrees F., meaning moisture
content is not determinative.
[0039] Similarly, FIG. 4 presents the relationship of moisture
released as a function of both powder temperature and elapsed time.
At 50 degrees C. (122 degrees F.), the moisture released is 1.2% by
weight (mass). When this temperature is raised to 100 degrees C.
(212 degrees F.), the moisture release increases from 1.2% to 1.9%,
for a net increase of 0.7%. When the transition temperature is
exceeded at the third point, 150 degrees C. (302 degrees F.), the
moisture released increases from 1.9% to 2.0% for a net increase of
0.10% moisture. It is interesting to note that when the transition
temperature of 100 degrees C. (212 degrees F.) is exceeded, the
increase in moisture release is only 0.10%. This should be
juxtaposed with the 0.7% increase from 50 to 100 degrees C. (where
no transition temperature was exceeded) or the 1.2% increase from
ambient temperature to 50 degrees C. This lack of dramatic change,
hardly any in fact, suggests that moisture content in the powder is
not the primary reason for the inability to fluidize. Desiccation
of the aeration air minimized the chances of introducing additional
moisture into the test apparatus or sodium sulfate powder. The
above results eliminate moisture in the sodium sulfate powder as a
major contributing factor to the fluidization of the powder.
[0040] Although the theoretical transition temperature is 100
degrees C. (212 degrees F.), it should be understood that due to,
for example the impurities in the mixture, the exact point of
transition may be slightly different than the published value.
Nonetheless, it is interesting to note that there is no dramatic
increase, only a net increase of 0.10%, in measured moisture
release when crossing the transition temperature of 100 degrees C.
(212 degrees F.).
[0041] Considering the crystal structure of sodium sulfate, as well
as its chemical transition temperature, sheds further light on the
lack of fluidization below the aforementioned transition
temperature. Sodium sulfate has a low-end chemical transition
temperature of about 32 degrees C. (90 degrees F.),.sup.17 as shown
in FIG. 5..sup.18 FIG. 5 shows sodium sulfate in solution,
illustrating that a chemical change occurs with temperature (the
morphology transition temperatures were approximated as they were
not yet established). .sup.17 Dickinson, H. C.; Mueller, E. F., The
transition temperature of sodium sulfate referred anew to the
international standard, 1907, 1381, 29 Journal of the American
Chemical Society..sup.18 Garrett, Donald E., Sodium Sulfate:
Handbook of Deposits, Processing, Properties, and Use, 2001, 346,
Academic Press, U.S.
[0042] At room temperature, sodium sulfate assumes an orthorhombic
crystalline structure, while above about 100 degrees C. (212
degrees F.) it assumes a monoclinic structure, and above about 250
degrees C. (482 degrees F.) it assumes a hexagonal
structure..sup.19 Other sources identify the crystalline structure
at ambient temperatures to be orthorhombic.sup.20 or orthorhombic
pyramidal..sup.21 .sup.19 The Columbia Encyclopedia, 2000, 2646,
6.sup.th Edition, Gale Group, U.S..sup.20 Wyckoff, R. W. G., The
Structure of Crystals, Second Edition, 1935, 66, Reinhold
Publishing Corporation, New York, U.S..sup.21 Garrett, Donald E.,
Sodium Sulfate: Handbook of Deposits, Processing, Properties, and
Use, 2001, 346, Academic Press, U.S.
[0043] A 1923 USGS report further describes sodium sulfate crystals
at ambient temperature as orthorhombic crystals exhibiting
twinning..sup.22 The crystalline structure for anhydrous sodium
sulfate is an orthorhombic pyramidal crystal with twinning planes
as shown in FIG. 6..sup.23 At 100 degrees C. (212 degrees F.) the
crystal shape changes to a monoclinic crystal, shown in FIG. 7. A
comparison of FIG. 6 and FIG. 7 illustrates that the morphology
resulting from the twinning in the orthorhombic crystals makes it
more difficult for the powder to achieve stable fluidization due
the potential for the powder's twinning planes to interlock
resulting in a higher yield strength of the powder. .sup.22 Wells,
Roger C., Sodium Sulfate: Its Sources and Uses, Bulletin 717,
Department of the Interior, United States Geological Survey,
2-3..sup.23 Wells, Roger C., Sodium Sulfate: Its Sources and Uses,
Bulletin 717, Department of the Interior, United States Geological
Survey, 2-3.
[0044] The next aforementioned transition temperature is at 250
degrees C. (482 degrees F.), well above the temperature range
relevant to this discussion..sup.24 However beginning at this
transition, the morphology of sodium sulfate transforms to
hexagonal crystals as shown in FIG. 8, without twinning, and thus
fluidization can be achieved as with the monoclinic crystals.
.sup.24 Wells, Roger C., Sodium Sulfate: Its Sources and Uses,
Bulletin 717, Department of the Interior, United States Geological
Survey, 2-3.
TABLE-US-00001 TABLE 1 Table of crystalline structure of anhydrous
sodium sulfate at various transition temperatures Anhydrous Sodium
Sulfate Temperatures Crystalline Structure Room Temperature,
Orthorhombic Pyramidal 21 degrees C. (70 degrees F.) Crystal with
Twinning Planes 100 degrees C. (212 degrees F.) Monoclinic Crystal
250 degrees C. (482 degrees F.) Hexagonal Crystal
[0045] X-ray diffraction (XRD) was performed on a sample of powder
from the silo, but the results were not meaningful. Later, this
failure to obtain meaningful XRD results was attributed to the
presence of twinning crystals. XRD is unable to identify
crystalline structures when twinning is present..sup.25 26 This
limitation on one of the primary methods to identify crystalline
structures may explain why most sources fail to identify twinning
as a common structure for sodium sulfate. In fact, some even
recommend avoiding conducting an XRD on crystals exhibiting
twinning, or to modify the crystal to exclude twinning..sup.27
.sup.25 Pickworth Glusker, J., Trueblood, K. N., Crystal Structure
Analysis, A Primer, 1985, 191-194, Second Edition, Oxford
University Press..sup.26 U.S. Pat. No. 7,696,991B2, Apr. 13, 2010,
Higashi, [0004]..sup.27 Glusker, Jenny P, Trueblood, Kenneth N.,
Crystal Structure Analysis: A Primer, 1985, 194, Oxford University
Press, New York.
Invention Disclosed
[0046] Dry Sorbent Injection (DSI) is an example application of the
disclosure herein. Though not part of the claimed invention, a
discussion of DSI is included in this disclosure (FIG. 9) for
clarity. DSI is a viable option for air quality control. It
achieves mitigation of SO.sub.2 and other acid gasses at relatively
low capital costs, making it an attractive retrofit option. As this
technology is implemented on a large (e.g. power plant) scale, flow
issues can arise with the powder being collected.
[0047] In DSI as shown in FIG. 9, sodium bicarbonate (SBC) (7) is
injected in order to react with acid gasses such as SO.sub.2, for
example in a coal-fired power plant's flue gas (6), downstream or
upstream of an optional electrostatic precipitator (8) and upstream
of fabric bags in a pulse jet fabric filter (PJFF) (9) with hoppers
(12) insulated as necessary. After injection, the SBC (7) calcines
due to higher temperatures to make Na.sub.2CO.sub.3, and the
SO.sub.2 gas and Na.sub.2CO.sub.3 react to produce sodium sulfate
as expressed in Equations 1 and 2, below.
2NaHCO.sub.3+Heat.quadrature.Na.sub.2CO.sub.3+H.sub.2O(g) Eq.
1:
Na.sub.2CO.sub.3+SO.sub.2+1/2O.sub.2.fwdarw.Na.sub.2SO.sub.4+CO.sub.2(g)
Eq. 2:
[0048] A powder (11) entrained in flue gas (6) is collected by
fabric bags in PJFF (9), shed to insulated inverted pyramidal
hoppers (12), and through an airlock (13) to a pneumatic conveying
line of a heated gas stream (14), which can be of motive ambient
air (15) and which is mobilized, for example with a blower (16).
Pneumatic conveying line of heated gas stream (14) has a pressure
relief valve (17) to eliminate any excess pressure, and is conveyed
for example by a conduit (18), and heated with a temperature
control means such as an electric heater (19). The temperature of
the ambient air (15) is measured by a temperature sensor, for
example a thermocouple (21), which is sent to a temperature control
means (20), and this temperature is compared to a first set point
temperature. If the temperature is lower than the first set point
temperature, the temperature control means (20) sends a signal to
energize heater (19), to heat the ambient air (15) to at least the
first set point temperature.
[0049] Pneumatic conveying line of a heated gas stream (14)
pneumatically transports powder (11) to a vessel (34) as shown in
FIG. 10. Flue gas (6) is exhausted at location (10), eventually to
the environment.
[0050] Powder (11), used to illustrate the preferred embodiment is
mainly sodium sulfate (greater than about 98%) combined with
impurities, which are in the present disclosure as a small amount
of fly ash (less than about 1%) and activated carbon (less than
about 1%) depending on the amount of mercury in the fuel, but can
be these materials in other amounts or other materials. An issue
occurs when the silo will not discharge the powder effectively into
a disposal container, for example, in the application of DSI. The
present invention comprises an apparatus and method for
manipulating crystal structure of a powder in order to achieve
stable fluidization. Embodiments of the present invention will now
be described in detail with reference to the drawings.
[0051] A preferred embodiment of the invention is shown in FIG. 10.
FIG. 10 shows a storage vessel (34) such as a truck, trailer, rail
car, or as in the present embodiment, a silo, and the accompanying
system for achieving stable fluidization according to an example
embodiment of the present disclosure.
[0052] Vessel (34) has a rigid exterior shell (30), and collects
powder (11) for disposal, forming powder bed (24). The silo of the
preferred embodiment has a flat bottom but the vessel is not
limited to having a flat bottom. The disclosure herein allows for
the achievement of stable fluidization in silos with flat bottoms,
thereby avoiding the additional costs associated with silos with
conical bottoms.
[0053] As shown in FIG. 10, vessel (34) has a rigid exterior shell
(30) which can have insulation (31), has an inlet portal (22)
through which powder (11) enters into an interior space (23) in the
silo forming powder bed (24). Vessel (34) also comprises at least
one atmospheric vent (33) which can be a bin vent filter with an
optional exhaust fan, extending from interior space (23) through
exterior shell of the vessel (30).
[0054] A gas stream (43) is introduced to interior space (23) of
vessel (34) and powder bed (24) therein via at least one gas inlet
connection (25) and an aeration device (29). Aeration device (29)
can be, but is not limited to, air slides, pads, or pozzolanic
stones. Aeration device (29) can further comprise a mesh, cloth,
felt, or other fabric (woven or unwoven) that covers the air
slides, pads, or other pozzolanic stones, and provides a medium to
evenly distribute the heated air across the area of the air slides,
pads, or stones and is designed for a uniform gas velocity
determined to be sufficient for fluidization. Once fluidized, the
powder exits the silo via an outlet portal (32).
[0055] Gas stream (43) heats powder bed (24). The temperature of
powder bed (24) is measured by a temperature sensor (26), for
example a thermocouple that in the preferred embodiment extends
from the exterior of the vessel (30) to interior space (23). Powder
bed (24) is heated to at least a first predetermined transition
temperature, which in the present embodiment is about 100 degrees
C. for sodium sulfate. This controls the crystal structure such
that twinning is eliminated, and combined with the motive force
imparted by gas stream (43) via aeration device (29), powder bed
(24) achieves stable fluidization. Gas stream (43) exits via
atmospheric vent (33) and powder (11), now fluidized, exits the
vessel via an outlet portal (32).
[0056] Gas stream (43) is also pressurized and controlled by a
pressure control device such as a control or throttling valve (28)
to establish a gas stream flow rate sufficient to achieve initial
fluidization of powder bed (24). A pressure indicator (27) (for
example, a pressure gauge) may be used to determine when to adjust
the air pressure to establish stable fluidization which is defined
further in FIG. 1.
[0057] The preferred embodiment shown in FIG. 11 utilizes gas
stream distribution system (100). Gas stream (43) is controlled to
maintain at least a first predetermined transition temperature
selected so that the powder (11) lacks twinning.
[0058] A temperature sensor (26), for example a thermocouple,
measures the temperature of powder bed (24). The temperature of
powder bed (24) is sent to a temperature control means (42), and
this temperature is compared to the first predetermined transition
temperature. If the temperature of powder bed (24) is lower than
the first predetermined transition temperature, temperature control
means (42) sends a signal to energize a heating device (39) to heat
gas stream (43) to at least the first predetermined transition
temperature. Temperature sensor (26) can be located elsewhere in
gas stream (43) as long as it is downstream of heating device
(39).
[0059] As described above, gas stream (43) is also pressurized and
controlled by pressure control device such as a control or
throttling valve (28) to establish a gas stream flow rate
sufficient to achieve initial fluidization of the powder bed.
Pressure indicator (27) (for example, a pressure gauge) may be used
to determine when to adjust the air pressure to establish stable
fluidization, which is defined further in FIG. 1. A pressure relief
valve (37) allows excess pressure to be released from the
system.
[0060] The gas stream (43) must overcome a first resistance to the
gas stream flow inherent in gas stream distribution system (100).
It must also overcome a second resistance to gas flow resulting
from the structure of powder bed (24), wherein after achieving
initial fluidization of the powder bed, the flow rate of gas stream
(43) is further adjusted to achieve stable fluidization of powder
bed (24) without causing powder (11) to become entrained in gas
stream (43).
[0061] Gas stream distribution system (100) further comprises
heater (39) and mobilization means (36) such as a compressor or
blower to mobilize ambient air (35), forming gas stream (43). Gas
stream (43) is transported via a conduit such as a pipe, tube, or
hose (38) to heater (39) and then to a manifold (40), where gas
stream (43) is delivered via a pipe, tubing, hose, or other conduit
(41), to at least one aeration device (29) and then introduced into
powder bed (24).
[0062] The relative locations of the optional manifold (40) and
heater (39) are insignificant, but the gas stream at the exit of
aeration device (29) must be heated to at least the first
predetermined transition temperature. The pressure control device
(28) can be manual or automated. In this embodiment, the pressure
control device (28) is manually adjusted to attain the desired
pressure as indicated on the pressure indicator (27).
[0063] The following embodiments are provided as specific support
and/or enablement for the appended claims. Accordingly, the present
disclosure provides:
[0064] E1. A method for manipulating crystal structure to fluidize
a powder comprising: collecting a powder comprising a crystal
structure in a vessel wherein the vessel comprises an exterior wall
and an interior volume and wherein the powder forms a powder bed
within the interior volume; injecting a heated compressed gas into
the vessel by way of one or more gas inlet ports; and agitating and
heating the powder with the heated compressed gas to bring an
average temperature of the powder to least a predetermined
transition temperature, so as to transform the crystal structure of
substantially all of the powder so that the crystal structure is
transmuted to facilitate an improvement in flowability relative to
the former crystal shape.
[0065] E2. The method of E1, wherein the injecting a heated
compressed gas step further comprises providing the heated
compressed gas stream to at least one aeration device in contact
with the powder bed, wherein the at least one aeration device is
selected so as to evenly distribute the heated compressed gas
stream throughout the powder bed.
[0066] E3. The method of E1, wherein the injecting a heated
compressed gas step further comprises pressurizing the heated
compressed gas to a predetermined pressure by a gas handling
system, the predetermined pressure selected so as to facilitate the
fluidization of the powder bed.
[0067] E4. The method of E1, further comprising controlling the
temperature of the heated pressurized gas via a temperature control
means comprising at least one temperature sensing device and having
a means by which to control the temperature of the heated
pressurized gas.
[0068] E5. The method of E1, further comprising controlling the
pressure of the gas stream via a pressure control means comprising
at least one pressure sensing device located in contact with the
heated pressurized gas and positioned upstream of the at least one
gas inlet connection and having a means for varying the pressure of
the heated pressurized gas stream prior to the gas inlet
connection.
[0069] E6. The method of E1, wherein the injecting a heated
compressed gas step further comprises establishing a heated
pressurized gas stream flow rate sufficient to achieve initial
fluidization of the powder bed by overcoming a first resistance to
the heated pressurized gas stream flow inherent in the gas handling
system and a second resistance to gas flow resulting from the
structure of the powder bed wherein after achieving initial
fluidization of the powder bed, the heated pressurized gas stream
flow rate is further adjusted to achieve stable fluidization of the
powder bed without causing the powder to become entrained in the
gas stream.
[0070] E7. The method of E1, wherein the agitating and heating the
powder step further comprises achieving stable fluidization of the
powder by altering the crystal structure of the powder.
[0071] E8. The method of E1, further comprising removing the heated
pressurized gas stream from the vessel via vessel at least one
atmospheric vent.
[0072] E9. The method of E1, further comprising removing the
agitated and heated powder from the vessel via an outlet
portal.
[0073] Several variations in the implementation of the present
invention have been described. The specific arrangements and
methods described here are illustrative of the principles of this
invention. Those skilled in the art may make numerous modifications
in form and detail without departing from the true spirit and scope
of the invention. Although this invention has been shown in
relation to a particular embodiment, it should not be considered so
limited. Rather it is limited only by the appended claims.
* * * * *